Living in California, I’ve (sadly) grown accustomed to needing to keep track of our local air quality index (AQI) ratings, particularly as we live close to places where large wildfires happen every other year.

Last year, Josh and I bought a PurpleAir outdoor air quality meter, which has been great. We contribute our data to a collection of very local air quality meters, which is important, since the hilly nature of the North Bay means that the nearest government air quality ratings can be significantly different to what we experience here in Petaluma.

I recently went looking to pull my PurpleAir sensor data into my Home Assistant setup. Unfortunately, the PurpleAir API does not return the AQI metric for air quality, only the raw PM2.5/PM5/PM10 numbers. After some searching, I found a nice template sensor solution on the Home Assistant forums, which I’ve modernised by adding the AQI as a sub-sensor, and adding unique ID fields to each useful sensor, so that you can assign them to a location.

You’ll end up with sensors for raw PM2.5, the PM2.5 AQI value, the US EPA air quality category, air pressure, relative humidity and air pressure.

How to use this

First up, visit the PurpleAir Map, find the sensor you care about, click “get this widgetâ€�, and then “JSONâ€�. That will give you the URL to set as the resource key in purpleair.yaml.

Adding the configuration

In HomeAssistant, add the following line to your configuration.yaml:

sensor: !include purpleair.yaml

and then add the following contents to purpleair.yaml

 - platform: rest
   name: 'PurpleAir'

   # Substitute in the URL of the sensor you care about.  To find the URL, go
   # to purpleair.com/map, find your sensor, click on it, click on "Get This
   # Widget" then click on "JSON".
   resource: https://www.purpleair.com/json?key={KEY_GOES_HERE}&show={SENSOR_ID}

   # Only query once a minute to avoid rate limits:
   scan_interval: 60

   # Set this sensor to be the AQI value.
   #
   # Code translated from JavaScript found at:
   # https://docs.google.com/document/d/15ijz94dXJ-YAZLi9iZ_RaBwrZ4KtYeCy08goGBwnbCU/edit#
   value_template: >
     {{ value_json["results"][0]["Label"] }}
   unit_of_measurement: ""
   # The value of the sensor can't be longer than 255 characters, but the
   # attributes can.  Store away all the data for use by the templates below.
   json_attributes:
     - results

 - platform: template
   sensors:
     purpleair_aqi:
       unique_id: 'purpleair_SENSORID_aqi_pm25'
       friendly_name: 'PurpleAir PM2.5 AQI'
       value_template: >
         {% macro calcAQI(Cp, Ih, Il, BPh, BPl) -%}
           {{ (((Ih - Il)/(BPh - BPl)) * (Cp - BPl) + Il)|round|float }}
         {%- endmacro %}
         {% if (states('sensor.purpleair_pm25')|float) > 1000 %}
           invalid
         {% elif (states('sensor.purpleair_pm25')|float) > 350.5 %}
           {{ calcAQI((states('sensor.purpleair_pm25')|float), 500.0, 401.0, 500.0, 350.5) }}
         {% elif (states('sensor.purpleair_pm25')|float) > 250.5 %}
           {{ calcAQI((states('sensor.purpleair_pm25')|float), 400.0, 301.0, 350.4, 250.5) }}
         {% elif (states('sensor.purpleair_pm25')|float) > 150.5 %}
           {{ calcAQI((states('sensor.purpleair_pm25')|float), 300.0, 201.0, 250.4, 150.5) }}
         {% elif (states('sensor.purpleair_pm25')|float) > 55.5 %}
           {{ calcAQI((states('sensor.purpleair_pm25')|float), 200.0, 151.0, 150.4, 55.5) }}
         {% elif (states('sensor.purpleair_pm25')|float) > 35.5 %}
           {{ calcAQI((states('sensor.purpleair_pm25')|float), 150.0, 101.0, 55.4, 35.5) }}
         {% elif (states('sensor.purpleair_pm25')|float) > 12.1 %}
           {{ calcAQI((states('sensor.purpleair_pm25')|float), 100.0, 51.0, 35.4, 12.1) }}
         {% elif (states('sensor.purpleair_pm25')|float) >= 0.0 %}
           {{ calcAQI((states('sensor.purpleair_pm25')|float), 50.0, 0.0, 12.0, 0.0) }}
         {% else %}
           invalid
         {% endif %}
       unit_of_measurement: "bit"
     purpleair_description:
       unique_id: 'purpleair_SENSORID_description'
       friendly_name: 'PurpleAir AQI Description'
       value_template: >
         {% if (states('sensor.purpleair_aqi')|float) >= 401.0 %}
           Hazardous
         {% elif (states('sensor.purpleair_aqi')|float) >= 301.0 %}
           Hazardous
         {% elif (states('sensor.purpleair_aqi')|float) >= 201.0 %}
           Very Unhealthy
         {% elif (states('sensor.purpleair_aqi')|float) >= 151.0 %}
           Unhealthy
         {% elif (states('sensor.purpleair_aqi')|float) >= 101.0 %}
           Unhealthy for Sensitive Groups
         {% elif (states('sensor.purpleair_aqi')|float) >= 51.0 %}
           Moderate
         {% elif (states('sensor.purpleair_aqi')|float) >= 0.0 %}
           Good
         {% else %}
           undefined
         {% endif %}
       entity_id: sensor.purpleair
     purpleair_pm25:
       unique_id: 'purpleair_SENSORID_pm25'
       friendly_name: 'PurpleAir PM 2.5'
       value_template: "{{ state_attr('sensor.purpleair','results')[0]['PM2_5Value'] }}"
       unit_of_measurement: "μg/m3"
       entity_id: sensor.purpleair
     purpleair_temp:
       unique_id: 'purpleair_SENSORID_temperature'
       friendly_name: 'PurpleAir Temperature'
       value_template: "{{ state_attr('sensor.purpleair','results')[0]['temp_f'] }}"
       unit_of_measurement: "°F"
       entity_id: sensor.purpleair
     purpleair_humidity:
       unique_id: 'purpleair_SENSORID_humidity'
       friendly_name: 'PurpleAir Humidity'
       value_template: "{{ state_attr('sensor.purpleair','results')[0]['humidity'] }}"
       unit_of_measurement: "%"
       entity_id: sensor.purpleair
     purpleair_pressure:
       unique_id: 'purpleair_SENSORID_pressure'
       friendly_name: 'PurpleAir Pressure'
       value_template: "{{ state_attr('sensor.purpleair','results')[0]['pressure'] }}"
       unit_of_measurement: "hPa"
       entity_id: sensor.purpleair

Quirks

I had difficulty getting the AQI to display as a numeric graph when I didn’t set a unit. I went with bit, and that worked just fine. 🤷â€�♂ï¸�

So, this idea has been brewing for a while now… try and watch all of Doctor Who. All of it. All 38 seasons. Today(ish), we started. First up, from 1963 (first aired not quite when intended due to the Kennedy assassination): An Unearthly Child. The first episode of the first serial.

A lot of iconic things are there from the start: the music, the Police Box, embarrassing moments of not quite remembering what time one is in, and normal humans accidentally finding their way into the TARDIS.

I first saw this way back when a child, where they were repeated on ABC TV in Australia for some anniversary of Doctor Who (I forget which one). Well, I saw all but the first episode as the train home was delayed and stopped outside Caulfield for no reason for ages. Some things never change.

Of course, being a show from the early 1960s, there’s some rougher spots. We’re not about to have the picture of diversity, and there’s going to be casual racism and sexism. What will be interesting is noticing these things today, and contrasting with my memory of them at the time (at least for episodes I’ve seen before), and what I know of the attitudes of the time.

“This year-ometer is not calculating properly” is a very 2020 line though (technically from the second episode).

It’s been a while since my last post about tracking support for the Oculus Rift in February. There’s been big improvements since then – working really well a lot of the time. It’s gone from “If I don’t make any sudden moves, I can finish an easy Beat Saber level” to “You can’t hide from me!” quality.

Equally, there are still enough glitches and corner cases that I think I’ll still be at this a while.

Here’s a video from 3 weeks ago of (not me) playing Beat Saber on Expert+ setting showing just how good things can be now:

Strap in. Here’s what I’ve worked on in the last 6 weeks:

Pose Matching improvements

Most of the biggest improvements have come from improving the computer vision algorithm that’s matching the observed LEDs (blobs) in the camera frames to the 3D models of the devices.

I split the brute-force search algorithm into 2 phases. It now does a first pass looking for ‘obvious’ matches. In that pass, it does a shallow graph search of blobs and their nearest few neighbours against LEDs and their nearest neighbours, looking for a match using a “Strong” match metric. A match is considered strong if expected LEDs match observed blobs to within 1.5 pixels.

Coupled with checks on the expected orientation (matching the Gravity vector detected by the IMU) and the pose prior (expected position and orientation are within predicted error bounds) this short-circuit on the search is hit a lot of the time, and often completes within 1 frame duration.

In the remaining tricky cases, where a deeper graph search is required in order to recover the pose, the initial search reduces the number of LEDs and blobs under consideration, speeding up the remaining search.

I also added an LED size model to the mix – for a candidate pose, it tries to work out how large (in pixels) each LED should appear, and use that as a bound on matching blobs to LEDs. This helps reduce mismatches as devices move further from the camera.

LED labelling

When a brute-force search for pose recovery completes, the system now knows the identity of various blobs in the camera image. One way it avoids a search next time is to transfer the labels into future camera observations using optical-flow tracking on the visible blobs.

The problem is that even sped-up the search can still take a few frame-durations to complete. Previously LED labels would be transferred from frame to frame as they arrived, but there’s now a unique ID associated with each blob that allows the labels to be transferred even several frames later once their identity is known.

IMU Gyro scale

One of the problems with reverse engineering is the guesswork around exactly what different values mean. I was looking into why the controller movement felt “swimmy” under fast motions, and one thing I found was that the interpretation of the gyroscope readings from the IMU was incorrect.

The touch controllers report IMU angular velocity readings directly as a 16-bit signed integer. Previously the code would take the reading and divide by 1024 and use the value as radians/second.

From teardowns of the controller, I know the IMU is an Invensense MPU-6500. From the datasheet, the reported value is actually in degrees per second and appears to be configured for the +/- 2000 °/s range. That yields a calculation of Gyro-rad/s = Gyro-°/s * (2000 / 32768) * (?/180) – or a divisor of 938.734.

The 1024 divisor was under-estimating rotation speed by about 10% – close enough to work until you start moving quickly.

Limited interpolation

If we don’t find a device in the camera views, the fusion filter predicts motion using the IMU readings – but that quickly becomes inaccurate. In the worst case, the controllers fly off into the distance. To avoid that, I added a limit of 500ms for ‘coasting’. If we haven’t recovered the device pose by then, the position is frozen in place and only rotation is updated until the cameras find it again.

Exponential filtering

I implemented a 1-Euro exponential smoothing filter on the output poses for each device. This is an idea from the Project Esky driver for Project North Star/Deck-X AR headsets, and almost completely eliminates jitter in the headset view and hand controllers shown to the user. The tradeoff is against introducing lag when the user moves quickly – but there are some tunables in the exponential filter to play with for minimising that. For now I’ve picked some values that seem to work reasonably.

Non-blocking radio

Communications with the touch controllers happens through USB radio command packets sent to the headset. The main use of radio commands in OpenHMD is to read the JSON configuration block for each controller that is programmed in at the factory. The configuration block provides the 3D model of LED positions as well as initial IMU bias values.

Unfortunately, reading the configuration block takes a couple of seconds on startup, and blocks everything while it’s happening. Oculus saw that problem and added a checksum in the controller firmware. You can read the checksum first and if it hasn’t changed use a local cache of the configuration block. Eventually, I’ll implement that caching mechanism for OpenHMD but in the meantime it still reads the configuration blocks on each startup.

As an interim improvement I rewrote the radio communication logic to use a state machine that is checked in the update loop – allowing radio communications to be interleaved without blocking the regularly processing of events. It still interferes a bit, but no longer causes a full multi-second stall as each hand controller turns on.

Haptic feedback

The hand controllers have haptic feedback ‘rumble’ motors that really add to the immersiveness of VR by letting you sense collisions with objects. Until now, OpenHMD hasn’t had any support for applications to trigger haptic events. I spent a bit of time looking at USB packet traces with Philipp Zabel and we figured out the radio commands to turn the rumble motors on and off.

In the Rift CV1, the haptic motors have a mode where you schedule feedback events into a ringbuffer – effectively they operate like a low frequency audio device. However, that mode was removed for the Rift S (and presumably in the Quest devices) – and deprecated for the CV1.

With that in mind, I aimed for implementing the unbuffered mode, with explicit ‘motor on + frequency + amplitude’ and ‘motor off’ commands sent as needed. Thanks to already having rewritten the radio communications to use a state machine, adding haptic commands was fairly easy.

The big question mark is around what API OpenHMD should provide for haptic feedback. I’ve implemented something simple for now, to get some discussion going. It works really well and adds hugely to the experience. That code is in the https://github.com/thaytan/OpenHMD/tree/rift-haptics branch, with a SteamVR-OpenHMD branch that uses it in https://github.com/thaytan/SteamVR-OpenHMD/tree/controller-haptics-wip

Problem areas

Unexpected tracking losses

I’d say the biggest problem right now is unexpected tracking loss and incorrect pose extractions when I’m not expecting them. Especially my right controller will suddenly glitch and start jumping around. Looking at a video of the debug feed, it’s not obvious why that’s happening:

To fix cases like those, I plan to add code to log the raw video feed and the IMU information together so that I can replay the video analysis frame-by-frame and investigate glitches systematically. Those recordings will also work as a regression suite to test future changes.

Sensor fusion efficiency

The Kalman filter I have implemented works really nicely – it does the latency compensation, predicts motion and extracts sensor biases all in one place… but it has a big downside of being quite expensive in CPU. The Unscented Kalman Filter CPU cost grows at O(n^3) with the size of the state, and the state in this case is 43 dimensional – 22 base dimensions, and 7 per latency-compensation slot. Running 1000 updates per second for the HMD and 500 for each of the hand controllers adds up quickly.

At some point, I want to find a better / cheaper approach to the problem that still provides low-latency motion predictions for the user while still providing the same benefits around latency compensation and bias extraction.

Lens Distortion

To generate a convincing illusion of objects at a distance in a headset that’s only a few centimetres deep, VR headsets use some interesting optics. The LCD/OLED panels displaying the output get distorted heavily before they hit the users eyes. What the software generates needs to compensate by applying the right inverse distortion to the output video.

Everyone that tests the CV1 notices that the distortion is not quite correct. As you look around, the world warps and shifts annoyingly. Sooner or later that needs fixing. That’s done by taking photos of calibration patterns through the headset lenses and generating a distortion model.

Camera / USB failures

The camera feeds are captured using a custom user-space UVC driver implementation that knows how to set up the special synchronisation settings of the CV1 and DK2 cameras, and then repeatedly schedules isochronous USB packet transfers to receive the video.

Occasionally, some people experience failure to re-schedule those transfers. The kernel rejects them with an out-of-memory error failing to set aside DMA memory (even though it may have been running fine for quite some time). It’s not clear why that happens – but the end result at the moment is that the USB traffic for that camera dies completely and there’ll be no more tracking from that camera until the application is restarted.

Often once it starts happening, it will keep happening until the PC is rebooted and the kernel memory state is reset.

Occluded cases

Tracking generally works well when the cameras get a clear shot of each device, but there are cases like sighting down the barrel of a gun where we expect that the user will line up the controllers in front of one another, and in front of the headset. In that case, even though we probably have a good idea where each device is, it can be hard to figure out which LEDs belong to which device.

If we already have a good tracking lock on the devices, I think it should be possible to keep tracking even down to 1 or 2 LEDs being visible – but the pose assessment code will have to be aware that’s what is happening.

Upstreaming

April 14th marks 2 years since I first branched off OpenHMD master to start working on CV1 tracking. How hard can it be, I thought? I’ll knock this over in a few months.

Since then I’ve accumulated over 300 commits on top of OpenHMD master that eventually all need upstreaming in some way.

One thing people have expressed as a prerequisite for upstreaming is to try and remove the OpenCV dependency. The tracking relies on OpenCV to do camera distortion calculations, and for their PnP implementation. It should be possible to reimplement both of those directly in OpenHMD with a bit of work – possibly using the fast LambdaTwist P3P algorithm that Philipp Zabel wrote, that I’m already using for pose extraction in the brute-force search.

Others

I’ve picked the top issues to highlight here. https://github.com/thaytan/OpenHMD/issues has a list of all the other things that are still on the radar for fixing eventually.

Other Headsets

At some point soon, I plan to put a pin in the CV1 tracking and look at adapting it to more recent inside-out headsets like the Rift S and WMR headsets. I implemented 3DOF support for the Rift S last year, but getting to full positional tracking for that and other inside-out headsets means implementing a SLAM/VIO tracking algorithm to track the headset position.

Once the headset is tracking, the code I’m developing here for CV1 to find and track controllers will hopefully transfer across – the difference with inside-out tracking is that the cameras move around with the headset. Finding the controllers in the actual video feed should work much the same.

Sponsorship

This development happens mostly in my spare time and partly as open source contribution time at work at Centricular. I am accepting funding through Github Sponsorships to help me spend more time on it – I’d really like to keep helping Linux have top-notch support for VR/AR applications. Big thanks to the people that have helped get this far.

Every so often, I release a new libeatmydata. This has not happened for a long time. This is just some bug fixes, most of which have been in the Debian package for some time, I’ve just been lazy and not sat down and merged them.

git clone https://github.com/stewartsmith/libeatmydata.git

Download the source tarball from here: libeatmydata-129.tar.gz and GPG signature: libeatmydata-129.tar.gz.asc from my GPG key.

Or, feel free to grab some Fedora RPMs:

• libeatmydata-129-1.fc33.src.rpm
• libeatmydata-129-1.fc33.x86_64.rpm
• libeatmydata-129-1.fc33.ppc64le.rpm
• libeatmydata-debuginfo-129-1.fc33.ppc64le.rpm
• libeatmydata-debuginfo-129-1.fc33.x86_64.rpm
• libeatmydata-debugsource-129-1.fc33.ppc64le.rpm
• libeatmydata-debugsource-129-1.fc33.x86_64.rpm

Releases published also in the usual places:

• https://www.flamingspork.com/projects/libeatmydata/
• https://github.com/stewartsmith/libeatmydata/releases/tag/v129

Today, 30 March, is World Bipolar Day.

Why that particular date? It’s Vincent van Gogh’s birthday (1853), and there is a fairly strong argument that the Dutch painter suffered from bipolar (among other things).

The image on the side is Vincent’s drawing “Worn Out” (from 1882), and it seems to capture the feeling rather well – whether (hypo)manic, depressed, or mixed. It’s exhausting.

Bipolar is complicated, often undiagnosed or misdiagnosed, and when only treated with anti-depressants, it can trigger the (hypo)mania – essentially dragging that person into that state near-permanently.

Have you heard of Bipolar II?

Hypo-mania is the “lesser” form of mania that distinguishes Bipolar I (the classic “manic depressive” syndrome) from Bipolar II. It’s “lesser” only in the sense that rather than someone going so hyper they may think they can fly (Bipolar I is often identified when someone in manic state gets admitted to hospital – good catch!) while with Bipolar II the hypo-mania may actually exhibit as anger. Anger in general, against nothing in particular but potentially everyone and everything around them. Or, if it’s a mixed episode, anger combined with strong negative thoughts. Either way, it does not look like classic mania. It is, however, exhausting and can be very debilitating.

Bipolar II people often present to a doctor while in depressed state, and GPs (not being psychiatrists) may not do a full diagnosis. Note that D.A.S. and similar test sheets are screening tools, they are not diagnostic. A proper diagnosis is more complex than filling in a form some questions (who would have thought!)

Call to action

If you have a diagnosis of depression, only from a GP, and are on medication for this, I would strongly recommend you also get a referral to a psychiatrist to confirm that diagnosis.

Our friends at the awesome Black Dog Institute have excellent information on bipolar, as well as a quick self-test – if that shows some likelihood of bipolar, go get that referral and follow up ASAP.

I will be writing more about the topic in the coming time.

Recently I’ve been playing a bit more with Docker images and Docker image repositories. I had in the past written a quick hack to let me extract files from a Docker image, but I wanted to do something a little more mature than that.

For example, sometimes you want to download an image from a Docker image repository without using Docker. Naively if you had Docker, you’d do something like this:

docker pull busybox
docker save busybox

However, that assumes that you have Docker installed on the machine downloading the images, and that’s sometimes not possible for security reasons. The most obvious example I can think of is airgapped secure environments where you need to walk the data between two networks, and the unclassified network machine doesn’t allow administrator access to install Docker.

So I wrote a little tool to do image manipulation for me. The tool is called Occy Strap, is written in python, and is available on pypi. That means installing it is relatively simple:

python3 -m venv ~/virtualenvs/occystrap
. ~/virtualenvs/occystrap/bin/activate
pip install occystrap

Which doesn’t require administrator permissions. There are then a few things we can do with Occy Strap.

Downloading an image from a repository and storing as a tarball

Let’s say we want to download an image from a repository and store it as a local tarball. This is a common thing to want to do in airgapped environments for example. You could do this with docker with a docker pull; docker save. The Occy Strap equivalent is:

occystrap fetch-to-tarfile registry-1.docker.io library/busybox \
    latest busybox.tar

In this example we’re pulling from the Docker Hub (registry-1.docker.io), and are downloading busybox’s latest version into a tarball named busybox-occy.tar. This tarball can be loaded with docker load -i busybox.tar on an airgapped Docker environment.

Downloading an image from a repository and storing as an extracted tarball

occystrap fetch-to-extracted registry-1.docker.io library/centos 7 \
    centos7

cd centos7; tar -cf ../centos7.tar *

Downloading an image from a repository and storing it in a merged directory

occystrap fetch-to-extracted --use-unique-names registry-1.docker.io \ 
    homeassistant/home-assistant latest merged_images
occystrap fetch-to-extracted --use-unique-names registry-1.docker.io \ 
    homeassistant/home-assistant stable merged_images
occystrap fetch-to-extracted --use-unique-names registry-1.docker.io \ 
    homeassistant/home-assistant 2021.3.0.dev20210219 merged_images

0465ae924726adc52c0216e78eda5ce2a68c42bf688da3f540b16f541fd3018c
10556f40181a651a72148d6c643ac9b176501d4947190a8732ec48f2bf1ac4fb
...
catalog.json 
cd8d37c8075e8a0195ae12f1b5c96fe4e8fe378664fc8943f2748336a7d2f2f3 
d1862a2c28ec9e23d88c8703096d106e0fe89bc01eae4c461acde9519d97b062 
d1ac3982d662e038e06cc7e1136c6a84c295465c9f5fd382112a6d199c364d20.json 
... 
d81f69adf6d8aeddbaa1421cff10ba47869b19cdc721a2ebe16ede57679850f0.json 
...
manifest-homeassistant_home-assistant-2021.3.0.dev20210219.json 
manifest-homeassistant_home-assistant-latest.json manifest-
homeassistant_home-assistant-stable.json

occystrap recreate-image merged_images homeassistant/home-assistant \
    latest ha-latest.tar

Exploring the contents of layers and overwritten files

occystrap fetch-to-extracted --expand quay.io \ 
    ukhomeofficedigital/centos-base latest ukhomeoffice-centos

This is the second business paper I’ve read this week while reading along with my son’s university studies. The first is discussed here if you’re interested. This paper is better written, but more academic in its style. This ironically makes it harder to read, because its grammar style is more complicated and harder to parse.

The take aways for me from this paper is that 3M is good at encouraging serendipity and opportune moments that create innovation. This is similar to Google’s attempts to build internal peer networks and deliberate lack of structure. In 3M’s case its partially expressed as 15% time, which is similar to Google’s 20% time. Specifically, “eureka moments” cannot be planned or scheduled, but require prior engagement.

chance favors only the prepared mind — Pasteur

3M has a variety of methods for encouraging peer networks, including technology fairs, “bootlegging” (borrowing idle resources from other teams), innovation grants, and so on.

At the same time, 3M tries to keep at least a partial focus on events driving by schedules. The concept of time is important here — there is a “time to wait” (we are ahead of the market); “a time in between” (15% time); and “a time across” (several parallel efforts around related innovations to speed up the process).

The idea of “a time to wait” is quite interesting. 3M has a history of discovering things where there is no current application, but somehow corporately remembering those things so that when there are applications years later they can jump in with a solution. They embrace story telling as part of their corporate memory, as well as a way of ensuring they learn from past success and failure.

Finally, 3M is similar to Google in their deliberate flexibility with the rules. 15% time isn’t rigidly counted for example — it might be 15% a week, or 15% of a year, or more or less than that. As long as it can be justified as a good use of resources its ok.

This was a good read and I enjoyed it.

So, one of my kids is studying some business units at university and was assigned this paper to read. I thought it looked interesting, so I gave it a read as well.

While not being particularly well written in terms of style, this is an approachable introduction to the culture and values of Google and how they play into Google’s continued ability to innovate. The paper identifies seven important attributes of the company’s culture that promote innovation, as ranked by the interviewed employees:

• The culture is innovation oriented.
• They put a lot of effort into selecting individuals who will fit well with the culture at hiring time.
• Leaders are seen as performing a facilitiation role, not a directive one.
• The organizational structure is loosely defined.
• OKRs and aligned performance incentives.
• A culture of organizational learning through postmortems and building internal social networks. Learning is considered a peer to peer activity that is not heavily structured.
• External interaction — especially in the form of aggressive acquisition of skills and technologies in areas Google feels they are struggling in.

Additionally, they identify eight habits of a good leader:

• A good coach.
• Empoyer your team and don’t micro-manage.
• Express interest in employees’ success and well-being.
• Be productive and results oriented.
• Be a good communicator and listen to your team.
• Help employees with career development.
• Have a clear vision and strategy for the team.
• Have key technical skills, so you can help advise the team.

Overall, this paper is well worth the time to read. I enjoyed it and found it insightful.

So, I learned something recently: if you pick up your iPhone with eBay open on an auction bid screen in just the right way, you may accidentally click the bid button and end up buying an old computer. Totally not the worst thing ever, and certainly a creative way to make a decision.

So, not too long later, a box arrives!

In the 1990s, Apple created some pretty “interesting” computers and product line. One thing you could get is a DOS Compatibility (or PC Compatibility) card. This was a card that went into one of the expansion slots on a Mac and had something really curious on it: most of the guts of a PC.

Others have written on these cards too: https://www.engadget.com/2009-12-10-before-there-was-boot-camp-there-were-dos-compatibility-cards.html and http://www.edibleapple.com/2009/12/09/blast-from-the-past-a-look-back-at-apples-dos-compatibility-cards/. There’s also the Service Manual https://tim.id.au/laptops/apple/misc/pc_compatibility_card.pdf with some interesting details.

The machine I’d bought was an Apple Power Macintosh 7200/120 with the PC Compatible card added afterwards (so it doesn’t have the PC Compatible label on the front like some models ended up getting).

Wikipedia has a good article on the line, noting that it was first released in August 1995, and fitting for the era, was sold as about 14 million other model numbers (okay not quite that bad, it was only a total of four model numbers for essentially the same machine). This specific model, the 7200/120 was introduced on April 22nd, 1996, and the original web page describing it from Apple is on the wayback machine.

For older Macs, Low End Mac is a good resource, and there’s a page on the 7200, and amazingly Apple still has the tech specs on their web site!

The 7200 series replaced the 7100, which was one of the original PowerPC based Macs. The big changes are using the industry standard PCI bus for its three expansion slots rather than NuBus. Rather surprisingly, NuBus was not Apple specific, but you could not call it widely adopted by successful manufacturers. Apple first used NuBus in the 1987 Macintosh II.

The PCI bus was standardized in 1992, and it’s almost certain that a successor to it is in the computer you’re using to read this. It really quite caught on as an industry standard.

The processor of the machine is a PowerPC 601. The PowerPC was an effort of IBM, Apple, and Motorola (the AIM Alliance) to create a class of processors for personal computers based on IBM’s POWER Architecture. The PowerPC 601 was the first of these processors, initially used by Apple in its Power Macintosh range. The machine I have has one running at a whopping 120Mhz. There continued to be PowerPC chips for a number of years, and IBM continued making POWER processors even after that. However, you are almost certainly not using a PowerPC derived processor in the computer you’re using to read this.

The PC Compatibility card has on it a full on legit Pentium 100 processor, and hardware for doing VGA graphics, a Sound Blaster 16 and the other things you’d usually expect of a PC from 1996. Since it’s on a PCI card though, it’s a bit different than a PC of the era. It doesn’t have any expansion slots of its own, and in fact uses up one of the three PCI slots in the Mac. It also doesn’t have its own floppy drive, or hard drive. There’s software on the Mac that will let the PC card use the Mac’s floppy drive, and part of the Mac’s hard drive for the PC!

The Pentium 100 was the first mass produced superscalar processor. You are quite likely to be using a computer with a processor related to the Pentium to read this, unless you’re using a phone or tablet, or one of the very latest Macs; in which case you’re using an ARM based processor. You likely have more ARM processors in your life than you have socks.

Basically, this computer is a bit of a hodge-podge of historical technology, some of which ended up being successful, and other things less so.

Let’s have a look inside!

So, one of the PCI slots has a Vertex Twin Turbo 128M8A video card in it. There is not much about this card on the internet. There’s a photo of one on Wikimedia Commons though. I’ll have to investigate more.

Does it work though? Yes! Here it is on my desk:

Even with Microsoft Internet Explorer 4.0 that came with MacOS 8.6, you can find some places on the internet you can fetch files from, at a not too bad speed even!

More fun times with this machine to come!

TL;DR: There should be an option, taproot=lockintrue, which allows users to set lockin-on-timeout to true. It should not be the default, though.

As stated in my previous post, we need actual consensus, not simply the appearance of consensus. I’m pretty sure we have that for taproot, but I would like a template we can use in future without endless debate each time.

• Giving every group a chance to openly signal for (or against!) gives us the most robust assurance that we actually have consensus. Being able to signal opposition is vital, since everyone can lie anyway; making opposition difficult just reduces the reliability of the signal.
• Developers should not activate. They’ve tried to assure themselves that there’s broad approval of the change, but that’s not really a transferable proof. We should be concerned about about future corruption, insanity, or groupthink. Moreover, even the perception that developers can set the rules will lead to attempts to influence them as Bitcoin becomes more important. As a (non-Bitcoin-core) developer I can’t think of a worse hell myself, nor do we want to attract developers who want to be influenced!
• Miner activation is actually brilliant. It’s easy for everyone to count, and majority miner enforcement is sufficient to rely on the new rules. But its real genius is that miners are most directly vulnerable to the economic majority of users: in a fork they have to pick sides continuously knowing that if they are wrong, they will immediately suffer economically through missed opportunity cost.
• Of course, economic users are ultimately in control. Any system which doesn’t explicitly encode that is fragile; nobody would argue that fair elections are unnecessary because if people were really dissatisfied they could always overthrow the government themselves! We should make it as easy for them to exercise this power as possible: this means not requiring them to run unvetted or home-brew modifications which will place them at more risk, so developers need to supply this option (setting it should also change the default User-Agent string, for signalling purposes). It shouldn’t be an upgrade either (which inevitably comes with other changes). Such a default-off option provides both a simple method, and a Schelling point for the lockinontimeout parameters. It also means much less chance of this power being required: “Si vis pacem, para bellum“.

This triumverate model may seem familiar, being widely used in various different governance systems. It seems the most robust to me, and is very close to what we have evolved into already. Formalizing it reduces uncertainty for any future changes, as well.

Bitcoin’s consensus rules define what is valid, but this isn’t helpful when we’re looking at changing the rules themselves. The trend in Bitcoin has been to make such changes in an increasingly inclusive and conservative manner, but we are still feeling our way through this, and appreciating more nuance each time we do so.

To use Bitcoin, you need to remain in the supermajority of consensus on what the rules are. But you can never truly know if you are. Everyone can signal, but everyone can lie. You can’t know what software other nodes or miners are running: even expensive testing of miners by creating an invalid block only tests one possible difference, may still give a false negative, and doesn’t mean they can’t change a moment later.

This risk of being left out is heightened greatly when the rules change. This is why we need to rely on multiple mechanisms to reassure ourselves that consensus will be maintained:

1. Developers assure themselves that the change is technically valid, positive and has broad support. The main tools for this are open communication, and time. Developers signal support by implementing the change.
2. Users signal their support by upgrading their nodes.
3. Miners signal their support by actually tagging their blocks.

We need actual consensus, not simply the appearance of consensus. Thus it is vital that all groups know they can express their approval or rejection, in a way they know will be heard by others. In the end, the economic supermajority of Bitcoin users can set the rules, but no other group or subgroup should have inordinate influence, nor should they appear to have such control.

The Goodwill Dividend

A Bitcoin community which has consensus and knows it is not only safest from a technical perspective: the goodwill and confidence gives us all assurance that we can make (or resist!) changes in future.

It will also help us defend against the inevitable attacks and challenges we are going to face, which may be a more important effect than any particular soft-fork feature.

Shaken Fist v0.4.2 snuck out yesterday as part of shooting this tutorial video. That’s because I really wanted to demonstrate floating IPs, which I only recently got working nicely. Overall in v0.4.2 we:

• Improved CI for image API calls.
• Improved upgrade CI testing.
• Improved network state tracking.
• Floating IPs now work, and have covering CI. shakenfist#257
• Resolve leaks of floating IPs from both direct use and NAT gateways. shakenfist#256
• Resolve leaks of IPManagers on network delete. shakenfist#675
• Use system packages for ansible during install.

As a bit of an experiment, I’ve made this quick and dirty “vlog” style tutorial video to show you how to install Shaken Fist on a single machine and boot your first instance. I demonstrate how to install, setup your first virtual network, start the instance, inspect events that the instance has experienced, and then log in.

Let me know if you think its useful.

Update:

This post documented an older method of building SteamVR-OpenHMD. I moved them to a page here. That version will be kept up to date for any future changes, so go there.

I’ve had a few people ask how to test my OpenHMD development branch of Rift CV1 positional tracking in SteamVR. Here’s what I do:

• Make sure Steam + SteamVR are already installed.
• Clone the SteamVR-OpenHMD repository:

git clone --recursive https://github.com/ChristophHaag/SteamVR-OpenHMD.git

• Switch the internal copy of OpenHMD to the right branch:

cd subprojects/openhmd
git remote add thaytan-github https://github.com/thaytan/OpenHMD.git
git fetch thaytan-github
git checkout -b rift-kalman-filter thaytan-github/rift-kalman-filter
cd ../../

• Use meson to build and register the SteamVR-OpenHMD binaries. You may need to install meson first (see below):

meson -Dbuildtype=release build
ninja -C build
./install_files_to_build.sh
./register.sh

• It is important to configure in release mode, as the kalman filtering code is generally too slow for real-time in debug mode (it has to run 2000 times per second)
• Make sure your USB devices are accessible to your user account by configuring udev. See the OpenHMD guide here: https://github.com/OpenHMD/OpenHMD/wiki/Udev-rules-list
• Please note – only Rift sensors on USB 3.0 ports will work right now. Supporting cameras on USB 2.0 requires someone implementing JPEG format streaming and decoding.
• It can be helpful to test OpenHMD is working by running the simple example. Check that it’s finding camera sensors at startup, and that the position seems to change when you move the headset:

./build/subprojects/openhmd/openhmd_simple_example

• Calibrate your expectations for how well tracking is working right now! Hint: It’s very experimental
• Start SteamVR. Hopefully it should detect your headset and the light(s) on your Rift Sensor(s) should power on.

Meson

I prefer the Meson build system here. There’s also a cmake build for SteamVR-OpenHMD you can use instead, but I haven’t tested it in a while and it sometimes breaks as I work on my development branch.

If you need to install meson, there are instructions here – https://mesonbuild.com/Getting-meson.html summarising the various methods.

I use a copy in my home directory, but you need to make sure ~/.local/bin is in your PATH

pip3 install --user meson

I spent some time this weekend implementing a couple of my ideas for improving the way the tracking code in OpenHMD filters and rejects (or accepts) possible poses when trying to match visible LEDs to the 3D models for each device.

In general, the tracking proceeds in several steps (in parallel for each of the 3 devices being tracked):

1. Do a brute-force search to match LEDs to 3D models, then (if matched)
   1. Assign labels to each LED blob in the video frame saying what LED they are.
   2. Send an update to the fusion filter about the position / orientation of the device
2. Then, as each video frame arrives:
   1. Use motion flow between video frames to track the movement of each visible LED
   2. Use the IMU + vision fusion filter to predict the position/orientation (pose) of each device, and calculate which LEDs are expected to be visible and where.
3. Try and match up and refine the poses using the predicted pose prior and labelled LEDs. In the best case, the LEDs are exactly where the fusion predicts they’ll be. More often, the orientation is mostly correct, but the position has drifted and needs correcting. In the worst case, we send the frame back to step 1 and do a brute-force search to reacquire an object.

The goal is to always assign the correct LEDs to the correct device (so you don’t end up with the right controller in your left hand), and to avoid going back to the expensive brute-force search to re-acquire devices as much as possible

What I’ve been working on this week is steps 1 and 3 – initial acquisition of correct poses, and fast validation / refinement of the pose in each video frame, and I’ve implemented two new strategies for that.

Gravity Vector matching

The first new strategy is to reject candidate poses that don’t closely match the known direction of gravity for each device. I had a previous implementation of that idea which turned out to be wrong, so I’ve re-worked it and it helps a lot with device acquisition.

The IMU accelerometer and gyro can usually tell us which way up the device is (roll and pitch) but not which way they are facing (yaw). The measure for ‘known gravity’ comes from the fusion Kalman filter covariance matrix – how certain the filter is about the orientation of the device. If that variance is small this new strategy is used to reject possible poses that don’t have the same idea of gravity (while permitting rotations around the Y axis), with the filter variance as a tolerance.

Partial tracking matches

The 2nd strategy is based around tracking with fewer LED correspondences once a tracking lock is acquired. Initial acquisition of the device pose relies on some heuristics for how many LEDs must match the 3D model. The general heuristic threshold I settled on for now is that 2/3rds of the expected LEDs must be visible to acquire a cold lock.

With the new strategy, if the pose prior has a good idea where the device is and which way it’s facing, it allows matching on far fewer LED correspondences. The idea is to keep tracking a device even down to just a couple of LEDs, and hope that more become visible soon.

While this definitely seems to help, I think the approach can use more work.

Status

With these two new approaches, tracking is improved but still quite erratic. Tracking of the headset itself is quite good now and for me rarely loses tracking lock. The controllers are better, but have a tendency to “fly off my hands” unexpectedly, especially after fast motions.

I have ideas for more tracking heuristics to implement, and I expect a continuous cycle of refinement on the existing strategies and new ones for some time to come.

For now, here’s a video of me playing Beat Saber using tonight’s code. The video shows the debug stream that OpenHMD can generate via Pipewire, showing the camera feed plus overlays of device predictions, LED device assignments and tracked device positions. Red is the headset, Green is the right controller, Blue is the left controller.

Initial tracking is completely wrong – I see some things to fix there. When the controllers go offline due to inactivity, the code keeps trying to match LEDs to them for example, and then there are some things wrong with how it’s relabelling LEDs when they get incorrect assignments.

After that, there are periods of good tracking with random tracking losses on the controllers – those show the problem cases to concentrate on.

Its been 10 years since I’ve read enough to write one of these summary posts… Which I guess means something. This month I’ve been thinking a lot about systems design and how to avoid Second Systems effect while growing a product, which guided my reading choices a fair bit. A fair bit of that reading has been in the form of blog posts and twitter threads, so I am going to start including those in these listings of things I’ve read.

Social media posts of note:

• A better Kubernetes from the ground up
• Systems Design Explains the World, Volume 1
• This twitter thread about why Google Cloud isn’t winning in the cloud platform wars
• Stevey’s Google Platforms Rant
• OKRs — Secrets to Success
• Goals Gone Wild

Books:

• The Mythical Man-Month
• Bolos 1: Honor of the Regiment (re-read, in the hope that learning about artificially intelligent super tanks killing aliens would help me with motivational techniques for my team).
• Bolos 2: The Unconquerable (another re-read).

I hit an important OpenHMD milestone tonight – I completed a Beat Saber level using my Oculus Rift CV1!

I’ve been continuing to work on integrating Kalman filtering into OpenHMD, and on improving the computer vision that matches and tracks device LEDs. While I suspect noone will be completing Expert levels just yet, it’s working well enough that I was able to play through a complete level of Beat Saber. For a long time this has been my mental benchmark for tracking performance, and I’m really happy

Check it out:

I should admit at this point that completing this level took me multiple attempts. The tracking still has quite a tendency to lose track of controllers, or to get them confused and swap hands suddenly.

I have a list of more things to work on. See you at the next update!

I don’t blog about every Shaken Fist release here, but I do feel like the 0.4 release (and the subsequent minor bug fix release 0.4.1) are a pretty big deal in the life of the project.

The focus of the v0.4 series is reliability — we’ve used behaviour in the continuous integration pipeline as a proxy for that, but it should be a significant improvement in the real world as well. This has included:

• much more extensive continuous integration coverage, including several new jobs.
• checksumming image downloads, and retrying images where the checksum fails.
• reworked locking.
• etcd reliability improvements.
• refactoring instances and networks to a new “non-volatile” object model where only immutable values are cached.
• images now track a state much like instances and networks.
• a reworked state model for instances, where its clearer why an instance ended up in an error state. This is documented in our developer docs.

In terms of new features, we also added:

• a network ping API, which will emit ICMP ping packets on the network node onto your virtual network. We use this in testing to ensure instances booted and ended up online.
• networks are now checked to ensure that they have a reasonable minimum size.
• addition of a simple etcd backup and restore tool (sf-backup).
• improved data upgrade of previous installations.
• VXLAN ids are now randomized, and this has forced a new naming scheme for network interfaces and bridges.
• we are smarter about what networks we restore on startup, and don’t restore dead networks.

We also now require python 3.8.

Overall, Shaken Fist v0.4 is a place that makes me much more comfortable to run workloads I care about on that previous releases. Its far from perfect, but we’re definitely moving in the right direction.

In my experience, the C programming language is still hard to beat, even 50 years after it was first developed (and I feel the same way about UNIX). When it comes to general-purpose utility, low-level systems programming, performance, and portability (even to tiny embedded systems), I would choose C over most modern or fashionable alternatives. In some cases, it is almost the only choice.

Many developers believe that it is difficult to write secure and reliable software in C, due to its free pointers, the lack of enforced memory integrity, and the lack of automatic memory management; however in my opinion it is possible to overcome these risks with discipline and a more secure system of libraries constructed on top of C and libc. Daniel J. Bernstein and Wietse Venema are two developers who have been able to write highly secure, stable, reliable software in C.

My other favourite language is Python. Although Python has numerous desirable features, my favourite is the light-weight syntax: in Python, block structure is indicated by indentation, and braces and semicolons are not required. Apart from the pleasure and relief of reading and writing such light and clear code, which almost appears to be executable pseudo-code, there are many other benefits. In C or JavaScript, if you omit a trailing brace somewhere in the code, or insert an extra brace somewhere, the compiler may tell you that there is a syntax error at the end of the file. These errors can be annoying to track down, and cannot occur in Python. Python not only looks better, the clear syntax helps to avoid errors.

The obvious disadvantage of Python, and other dynamic interpreted languages, is that most programs run extremely slower than C programs. This limits the scope and generality of Python. No AAA or performance-oriented video game engines are programmed in Python. The language is not suitable for low-level systems programming, such as operating system development, device drivers, filesystems, performance-critical networking servers, or real-time systems.

C is a great all-purpose language, but the code is uglier than Python code. Once upon a time, when I was experimenting with the Plan 9 operating system (which is built on C, but lacks Python), I missed Python’s syntax, so I decided to do something about it and write a little preprocessor for C. This converts from a “Pythonesque” indented syntax to regular C with the braces and semicolons. Having forked a little dialect of my own, I continued from there adding other modules and features (which might have been a mistake, but it has been fun and rewarding).

At first I called this translator Brace, because it added in the braces for me. I now call the language CZ. It sounds like “C-easy”. Ease-of-use for developers (DX) is the primary goal. CZ has all of the features of C, and translates cleanly into C, which is then compiled to machine code as normal (using any C compiler; I didn’t write one); and so CZ has the same features and performance as C, but enjoys a more pleasing syntax.

CZ is now self-hosted, in that the translator is written in the language CZ. I confess that originally I wrote most of it in Perl; I’m proficient at Perl, but I consider it to be a fairly ugly language, and overly complicated.

I intend for CZ’s new syntax to be “optional”, ideally a developer will be able to choose to use the normal C syntax when editing CZ, if they prefer it. For this, I need a tool to convert C back to CZ, which I have not fully implemented yet. I am aware that, in addition to traditionalists, some vision-impaired developers prefer to use braces and semicolons, as screen readers might not clearly indicate indentation. A C to CZ translator would of course also be valuable when porting an existing C program to CZ.

CZ has a number of useful features that are not found in standard C, but I did not go so far as C++, which language has been described as “an octopus made by nailing extra legs onto a dog”. I do not consider C to be a dog, at least not in a negative sense; but I think that C++ is not an improvement over plain C. I am creating CZ because I think that it is possible to improve on C, without losing any of its advantages or making it too complex.

One of the most interesting features I added is a simple syntax for fast, light coroutines. I based this on Simon Tatham’s approach to Coroutines in C, which may seem hacky at first glance, but is very efficient and can work very well in practice. I implemented a very fast web server with very clean code using these coroutines. The cost of switching coroutines with this method is little more than the cost of a function call.

CZ has hygienic macros. The regular cpp (C preprocessor) macros are not hygenic and many people consider them hacky and unsafe to use. My CZ macros are safe, and somewhat more powerful than standard C macros. They can be used to neatly add new program control structures. I have plans to further develop the macro system in interesting ways.

I added automatic prototype and header generation, as I do not like having to repeat myself when copying prototypes to separate header files. I added support for the UNIX #! scripting syntax, and for cached executables, which means that CZ can be used like a scripting language without having to use a separate compile or make command, but the programs are only recompiled when something has been changed.

For CZ, I invented a neat approach to portability without conditional compilation directives. Platform-specific library fragments are automatically included from directories having the name of that platform or platform-category. This can work very well in practice, and helps to avoid the nightmare of conditional compilation, feature detection, and Autotools. Using this method, I was able easily to implement portable interfaces to features such as asynchronous IO multiplexing (aka select / poll).

The CZ library includes flexible error handling wrappers, inspired by W. Richard Stevens’ wrappers in his books on Unix Network Programming. If these wrappers are used, there is no need to check return values for error codes, and this makes the code much safer, as an error cannot accidentally be ignored.

CZ has several major faults, which I intend to correct at some point. Some of the syntax is poorly thought out, and I need to revisit it. I developed a fairly rich library to go with the language, including safer data structures, IO, networking, graphics, and sound. There are many nice features, but my CZ library is more prototype than a finished product, there are major omissions, and some features are misconceived or poorly implemented. The misfeatures should be weeded out for the time-being, or moved to an experimental section of the library.

I think that a good software library should come in two parts, the essential low-level APIs with the minimum necessary functionality, and a rich set of high-level convenience functions built on top of the minimal API. I need to clearly separate these two parts in order to avoid polluting the namespaces with all sorts of nonsense!

CZ is lacking a good modern system of symbol namespaces. I can look to Python for a great example. I need to maintain compatibility with C, and avoid ugly symbol encodings. I think I can come up with something that will alleviate the need to type anything like gtk_window_set_default_size, and yet maintain compatibility with the library in question. I want all the power of C, but it should be easy to use, even for children. It should be as easy as BASIC or Processing, a child should be able to write short graphical demos and the like, without stumbling over tricky syntax or obscure compile errors.

Here is an example of a simple CZ program which plots the Mandelbrot set fractal. I think that the program is fairly clear and easy to understand, although there is still some potential to improve and clarify the code.

#!/usr/local/bin/cz --
use b
use ccomplex

Main:
	num outside = 16, ox = -0.5, oy = 0, r = 1.5
	long i, max_i = 50, rb_i = 30
	space()
	uint32_t *px = pixel()  # CONFIGURE!
	num d = 2*r/h, x0 = ox-d*w_2, y0 = oy+d*h_2
	for(y, 0, h):
		cmplx c = x0 + (y0-d*y)*I
		repeat(w):
			cmplx w = c
			for i=0; i < max_i && cabs(w) < outside; ++i
				w = w*w + c
			*px++ = i < max_i ? rainbow(i*359 / rb_i % 360) : black
			c += d

I wrote a more elaborate variant of this program, which generates images like the one shown below. There are a few tricks used: continuous colouring, rainbow colours, and plotting the logarithm of the iteration count, which makes the plot appear less busy close to the black fractal proper. I sell some T-shirts and other products with these fractal designs online.

I am interested in graph programming, and have been for three decades since I was a teenager. By graph programming, I mean programming and modelling based on mathematical graphs or diagrams. I avoid the term visual programming, because there is no necessary reason that vision impaired folks could not use a graph programming language; a graph or diagram may be perceived, understood, and manipulated without having to see it.

Mathematics is something that naturally exists, outside time and independent of our universe. We humans discover mathematics, we do not invent or create it. One of my main ideas for graph programming is to represent a mathematical (or software) model in the simplest and most natural way, using relational operators. Elementary mathematics can be reduced to just a few such operators:

I think that a language and notation based on these few operators (and similar) can be considerably simpler and more expressive than conventional math or programming languages.

CZ is for me a stepping-stone toward this goal of an expressive relational graph language. It is more pleasant for me to develop software tools in CZ than in C or another language.

Thanks for reading. I wrote this article during the process of applying to join Toptal, which appears to be a freelancing portal for top developers; and in response to this article on toptal: After All These Years, the World is Still Powered by C Programming.

My CZ project has been stalled for quite some time. I foolishly became discouraged after receiving some negative feedback. I now know that honest negative feedback should be valued as an opportunity to improve, and I intend to continue the project until it lacks glaring faults, and is useful for other people. If this project or this article interests you, please contact me and let me know. It is much more enjoyable to work on a project when other people are actively interested in it!

The uBITX uses an Arduino internally. This article describes how to update its software.

Required hardware

The connector on the back is a Mini-B USB connector, so you'll need a "Mini-B to A" USB cable. This is not the same cable as used with older Android smartphones. The Mini-B connector was used with a lot of cameras a decade ago.

You'll also need a computer. I use a laptop with Fedora Linux installed.

Required software for software development

In Fedora all the required software is installed with sudo dnf install arduino git. Add yourself to the users and lock groups with sudo usermod -a -G users,lock $USER (on Debian-style systems use sudo usermod -a -G dialout,lock $USER). You'll need to log out and log in again for that to have an effect (if you want to see which groups you are already in, then use the id command).

Run arduino as your ordinary non-root user to create the directories used by the Arduino IDE. You can quit the IDE once it starts.

Obtain the uBITX software

$ cd ~/Arduino
$ git clone https://github.com/afarhan/ubitxv6.git ubitx_v6.1_code

Connect the uBITX to your computer

Plug in the USB cable and turn on the radio. Running dmesg will show the Arduino appearing as a "USB serial" device:

usb 1-1: new full-speed USB device number 6 using xhci_hcd
usb 1-1: New USB device found, idVendor=1a86, idProduct=7523, bcdDevice= 2.64
usb 1-1: New USB device strings: Mfr=0, Product=2, SerialNumber=0
usb 1-1: Product: USB Serial
usbcore: registered new interface driver ch341
usbserial: USB Serial support registered for ch341-uart
ch341 1-1:1.0: ch341-uart converter detected
usb 1-1: ch341-uart converter now attached to ttyUSB1

If you want more information about the USB device then use:

$ lsusb -d 1a86:7523
Bus 001 Device 006: ID 1a86:7523 QinHeng Electronics CH340 serial converter

In the last post I had started implementing an Unscented Kalman Filter for position and orientation tracking in OpenHMD. Over the Christmas break, I continued that work.

A Quick Recap

When reading below, keep in mind that the goal of the filtering code I’m writing is to combine 2 sources of information for tracking the headset and controllers.

The first piece of information is acceleration and rotation data from the IMU on each device, and the second is observations of the device position and orientation from 1 or more camera sensors.

The IMU motion data drifts quickly (at least for position tracking) and can’t tell which way the device is facing (yaw, but can detect gravity and get pitch/roll).

The camera observations can tell exactly where each device is, but arrive at a much lower rate (52Hz vs 500/1000Hz) and can take a long time to process (hundreds of milliseconds) to analyse to acquire or re-acquire a lock on the tracked device(s).

The goal is to acquire tracking lock, then use the motion data to predict the motion closely enough that we always hit the ‘fast path’ of vision analysis. The key here is closely enough – the more closely the filter can track and predict the motion of devices between camera frames, the better.

Integration in OpenHMD

When I wrote the last post, I had the filter running as a standalone application, processing motion trace data collected by instrumenting a running OpenHMD app and moving my headset and controllers around. That’s a really good way to work, because it lets me run modifications on the same data set and see what changed.

However, the motion traces were captured using the current fusion/prediction code, which frequently loses tracking lock when the devices move – leading to big gaps in the camera observations and more interpolation for the filter.

By integrating the Kalman filter into OpenHMD, the predictions are improved leading to generally much better results. Here’s one trace of me moving the headset around reasonably vigourously with no tracking loss at all.

If it worked this well all the time, I’d be ecstatic! The predicted position matched the observed position closely enough for every frame for the computer vision to match poses and track perfectly. Unfortunately, this doesn’t happen every time yet, and definitely not with the controllers – although I think the latter largely comes down to the current computer vision having more troubler matching controller poses. They have fewer LEDs to match against compared to the headset, and the LEDs are generally more side-on to a front-facing camera.

Taking a closer look at a portion of that trace, the drift between camera frames when the position is interpolated using the IMU readings is clear.

This is really good. Most of the time, the drift between frames is within 1-2mm. The computer vision can only match the pose of the devices to within a pixel or two – so the observed jitter can also come from the pose extraction, not the filtering.

The worst tracking is again on the Z axis – distance from the camera in this case. Again, that makes sense – with a single camera matching LED blobs, distance is the most uncertain part of the extracted pose.

Losing Track

The trace above is good – the computer vision spots the headset and then the filtering + computer vision track it at all times. That isn’t always the case – the prediction goes wrong, or the computer vision fails to match (it’s definitely still far from perfect). When that happens, it needs to do a full pose search to reacquire the device, and there’s a big gap until the next pose report is available.

That looks more like this

This trace has 2 kinds of errors – gaps in the observed position timeline during full pose searches and erroneous position reports where the computer vision matched things incorrectly.

Fixing the errors in position reports will require improving the computer vision algorithm and would fix most of the plot above. Outlier rejection is one approach to investigate on that front.

Latency Compensation

There is inherent delay involved in processing of the camera observations. Every 19.2ms, the headset emits a radio signal that triggers each camera to capture a frame. At the same time, the headset and controller IR LEDS light up brightly to create the light constellation being tracked. After the frame is captured, it is delivered over USB over the next 18ms or so and then submitted for vision analysis. In the fast case where we’re already tracking the device the computer vision is complete in a millisecond or so. In the slow case, it’s much longer.

Overall, that means that there’s at least a 20ms offset between when the devices are observed and when the position information is available for use. In the plot above, this delay is ignored and position reports are fed into the filter when they are available. In the worst case, that means the filter is being told where the headset was hundreds of milliseconds earlier.

To compensate for that delay, I implemented a mechanism in the filter where it keeps extra position and orientation entries in the state that can be used to retroactively apply the position observations.

The way that works is to make a prediction of the position and orientation of the device at the moment the camera frame is captured and copy that prediction into the extra state variable. After that, it continues integrating IMU data as it becomes available while keeping the auxilliary state constant.

When a the camera frame analysis is complete, that delayed measurement is matched against the stored position and orientation prediction in the state and the error used to correct the overall filter. The cool thing is that in the intervening time, the filter covariance matrix has been building up the right correction terms to adjust the current position and orientation.

Here’s a good example of the difference:

Notice how most of the disconnected segments have now slotted back into position in the timeline. The ones that haven’t can either be attributed to incorrect pose extraction in the compute vision, or to not having enough auxilliary state slots for all the concurrent frames.

At any given moment, there can be a camera frame being analysed, one arriving over USB, and one awaiting “long term” analysis. The filter needs to track an auxilliary state variable for each frame that we expect to get pose information from later, so I implemented a slot allocation system and multiple slots.

The downside is that each slot adds 6 variables (3 position and 3 orientation) to the covariance matrix on top of the 18 base variables. Because the covariance matrix is square, the size grows quadratically with new variables. 5 new slots means 30 new variables – leading to a 48 x 48 covariance matrix instead of 18 x 18. That is a 7-fold increase in the size of the matrix (48 x 48 = 2304 vs 18 x 18 = 324) and unfortunately about a 10x slow-down in the filter run-time.

At that point, even after some optimisation and vectorisation on the matrix operations, the filter can only run about 3x real-time, which is too slow. Using fewer slots is quicker, but allows for fewer outstanding frames. With 3 slots, the slow-down is only about 2x.

There are some other possible approaches to this problem:

• Running the filtering delayed, only integrating IMU reports once the camera report is available. This has the disadvantage of not reporting the most up-to-date estimate of the user pose, which isn’t great for an interactive VR system.

• Keeping around IMU reports and rewinding / replaying the filter for late camera observations. This limits the overall increase in filter CPU usage to double (since we at most replay every observation twice), but potentially with large bursts when hundreds of IMU readings need replaying.
• It might be possible to only keep 2 “full” delayed measurement slots with both position and orientation, and to keep some position-only slots for others. The orientation of the headset tends to drift much more slowly than position does, so when there’s a big gap in the tracking it would be more important to be able to correct the position estimate. Orientation is likely to still be close to correct.
• Further optimisation in the filter implementation. I was hoping to keep everything dependency-free, so the filter implementation uses my own naive 2D matrix code, which only implements the features needed for the filter. A more sophisticated matrix library might perform better – but it’s hard to say without doing some testing on that front.

Controllers

So far in this post, I’ve only talked about the headset tracking and not mentioned controllers. The controllers are considerably harder to track right now, but most of the blame for that is in the computer vision part. Each controller has fewer LEDs than the headset, fewer are visible at any given moment, and they often aren’t pointing at the camera front-on.

This screenshot is a prime example. The controller is the cluster of lights at the top of the image, and the headset is lower left. The computer vision has gotten confused and thinks the controller is the ring of random blue crosses near the headset. It corrected itself a moment later, but those false readings make life very hard for the filtering.

Here’s a typical example of the controller tracking right now. There are some very promising portions of good tracking, but they are interspersed with bursts of tracking losses, and wild drifting from the computer vision giving wrong poses – leading to the filter predicting incorrect acceleration and hence cascaded tracking losses. Particularly (again) on the Z axis.

Timing Improvements

One of the problems I was looking at in my last post is variability in the arrival timing of the various USB streams (Headset reports, Controller reports, camera frames). I improved things in OpenHMD on that front, to use timestamps from the devices everywhere (removing USB timing jitter from the inter-sample time).

There are still potential problems in when IMU reports from controllers get updated in the filters vs the camera frames. That can be on the order of 2-4ms jitter. Time will tell how big a problem that will be – after the other bigger tracking problems are resolved.

Sponsorships

All the work that I’m doing implementing this positional tracking is a combination of my free time, hours contributed by my employer Centricular and contributions from people via Github Sponsorships. If you’d like to help me spend more hours on this and fewer on other paying work, I appreciate any contributions immensely!

Next Steps

The next things on my todo list are:

• Integrate the delayed-observation processing into OpenHMD (at the moment it is only in my standalone simulator).
• Improve the filter code structure – this is my first kalman filter and there are some implementation decisions I’d like to revisit.
• Publish the UKF branch for other people to try.
• Circle back to the computer vision and look at ways to improve the pose extraction and better reject outlying / erroneous poses, especially for the controllers.
• Think more about how to best handle / schedule analysis of frames from multiple cameras. At the moment each camera operates as a separate entity, capturing frames and analysing them in threads without considering what is happening in other cameras. That means any camera that can’t see a particular device starts doing full pose searches – which might be unnecessary if another camera still has a good view of the device. Coordinating those analyses across cameras could yield better CPU consumption, and let the filter retain fewer delayed observation slots.

On December 22, I decided to brew an oatmeal stout (5kg Gladfield ale malt, 250g dark chocolate malt, 250g light chocolate malt, 250g dark crystal malt, 500g rolled oats, 150g rice hulls to stop the mash sticking, 25g Pride of Ringwood hops, Safale US-05 yeast). This all takes a good few hours to do the mash and the boil and everything, so while that was underway I thought it’d be a good opportunity to remove a crappy old cupboard from the laundry, so I could put our nice Miele upright freezer in there, where it’d be closer to the kitchen (the freezer is presently in a room at the other end of the house).

The cupboard was reasonably easy to rip out, but behind it was a mouldy and unexpectedly bright yellow wall with an ugly gap at the top where whoever installed it had removed the existing cornice.

Underneath the bottom half of the cupboard, I discovered not the cork tiles which cover the rest of the floor, but a layer of horrific faux-tile linoleum. Plus, more mould. No way was I going to put the freezer on top of that.

So, up came the floor covering, back to nice hardwood boards.

Of course, the sink had to come out too, to remove the flooring from under its cabinet, and that meant pulling the splashback tiles (they had ugly screw holes in them anyway from a shelf that had been bracketed up on top of them previously).

Removing the tiles meant replacing a couple of sections of wall.

Also, we still needed to be able to use the washing machine through all this, so I knocked up a temporary sink support.

New cornice went in.

The rest of the plastering was completed and a ceiling fan installed.

Waterproofing membrane was applied where new tiles will go around a new sink.

I removed the hideous old aluminium backed weather stripping from around the exterior door and plastered up the exposed groove.

We still need to paint everything, get the new sink installed, do the tiling work and install new taps.

As for the oatmeal stout, I bottled that on January 2. From a sample taken at the time, it should be excellent, but right now still needs to carbonate and mature.

A few years ago we went to Taiwan. I managed to capture some random bits of the city on film (and also some shots on my then phone, a Google Pixel). I find the different style of art on the streets around the world to be fascinating, and Taiwan had some good examples.

I’ve really enjoyed shooting Kodak E100VS film over the years, and some of my last rolls were shot in Taiwan. It’s a film that unfortunately is not made anymore, but at least we have a new Ektachrome to have fun with now.

This is, of course, only a small number of the total photos I took there. I’d really recommend a trip to Taiwan, and I look forward to going back there some day.

In my last post I wrote about changes in my OpenHMD positional tracking branch to split analysis of the tracking frames from the camera sensors across multiple threads. In the 2 months since then, the only real change in the repository was to add some filtering to the pose search that rejects bad poses by checking if they align with the gravity vector observed by the IMU. That is in itself a nice improvement, but there is other work I’ve been doing that isn’t published yet.

The remaining big challenge (I think) to a usable positional tracking solution is fusing together the motion information that comes from the inertial tracking sensors (IMU) in the devices (headset, controllers) with the observations that come from the camera sensors (video frames). There are some high level goals for that fusion, and lots of fiddly details about why it’s hard.

At the high level, the IMUs provide partial information about the motion of each device at a high rate, while the cameras provide observations about the actual position in the room – but at a lower rate, and with sometimes large delays.

In the Oculus CV1, the IMU provides Accelerometer and Gyroscope readings at 1000Hz (500Hz for controllers), and from those it’s possible to compute the orientation of the device relative to the Earth (but not the compass direction it’s facing), and also to integrate acceleration readings to get velocity and position – but the position tracking from an IMU is only useful in the short term (a few seconds) as it drifts rapidly due to that double integration.

The accelerometers measure (surprise) the acceleration of the device, but are always also sensing the Earth’s gravity field. If a device is at rest, it will ideally report 9.81 m/s², give or take noise and bias errors. When the device is in motion, the acceleration measured is the sum of the gravity field, bias errors and actual linear acceleration. To interpolate the position with any accuracy at all, you need to separate those 3 components with tight tolerance.

That’s about the point where the position observations from the cameras come into play. You can use those snapshots of the device position to determine the real direction that the devices are facing, and to correct for any errors in the tracked position and device orientation from the IMU integration – by teasing out the bias errors and gravity offset.

The current code uses some simple hacks to do the positional tracking – using the existing OpenHMD 3DOF complementary filter to compute the orientation, and some hacks to update the position when a camera finds the pose of a device.

The simple hacks work surprisingly well when devices don’t move too fast. The reason is (as previously discussed) that the video analysis takes a variable amount of time – if we can predict where a device is with a high accuracy and maintain “tracking lock”, then the video analysis is fast and runs in a few milliseconds. If tracking lock is lost, then a full search is needed to recover the tracking, and that can take hundreds of milliseconds to complete… by which time the device has likely moved a long way and requires another full pose search, which takes hundreds of milliseconds..

So, the goal of my current development is to write a single unified fusion filter that combines IMU and camera observations to better track and predict the motion of devices between camera frames. Better motion prediction means hitting the ‘fast analysis’ path more often, which leads to more frequent corrections of the unknowns in the IMU data, and (circularly) better motion predictions.

To do that, I am working on an Unscented Kalman Filter that tracks the position, velocity, acceleration, orientation and IMU accelerometer and gyroscope biases – with promising initial results.

In the above graphs, the filter is predicting the position of the headset at each camera frame to within 1cm most of the time and the pose to within a few degrees, but with some significant spikes that still need fixing. The explanation for the spikes lies in the data sets that I’m testing against, and points to the next work that needs doing.

To develop the filter, I’ve modifed OpenHMD to record traces as I move devices around. It saves out a JSON file for each device with a log of each IMU reading and each camera frame. The idea is to have a baseline data set that can be used to test each change in the filter – but there is a catch. The current data was captured using the upstream positional tracking code – complete with tracking losses and long analysis delays.

The spikes in the filter graph correspond with when the OpenHMD traces have big delays between when a camera frame was captured and when the analysis completes.

What this means is that when the filter makes bad predictions, it’s because it’s trying to predict the position of the device at the time the sensor result became available, instead of when the camera frame was captured – hundreds of milliseconds earlier.

So, my next step is to integrate the Kalman filter code into OpenHMD itself, and hopefully capture a new set of motion data with fewer tracking losses to prove the filter’s accuracy more clearly.

Second – I need to extend the filter to compensate for that delay between when a camera frame is captured and when the results are available for use, by using an augmented state matrix and lagged covariances. More on that next time.

To finish up, here’s a taste of another challenge hidden in the data – variability in the arrival time of IMU updates. The IMU updates at 1000Hz – ideally we’d receive those IMU updates 1 per millisecond, but transfer across the USB and variability in scheduling on the host computer make that much noisier. Sometimes further apart, sometimes bunched together – and in one part there’s a 1.2 second gap.

On my desktop system, I’m running XFCE on openSUSE Tumbleweed. When I leave my desk, I hit the “lock screen” button, the screen goes black, and the monitors go into standby. So far so good. When I come back and mash the keyboard, everything lights up again, the screens go white, and it says:

blank: Shows nothing but a black screen
Name: tserong@HOSTNAME
Password:
Enter password to unlock; select icon to lock

So I type my password, hit ENTER, and I’m back in action. So far so good again. Except… Several times recently, when I’ve come back and mashed the keyboard, the white overlay is gone. I can see all my open windows, my mail client, web browser, terminals, everything, but the screen is still locked. If I type my password and hit ENTER, it unlocks and I can interact again, but this is where it gets really weird. All the windows have moved down a bit on the screen. For example, a terminal that was previously neatly positioned towards the bottom of the screen is now partially off the screen. So “something” crashed – whatever overlay the lock thingy put there is gone? And somehow this affected the position of all my application windows? What in the name of all that is good and holy is going on here?

Update 2020-12-21: I’ve opened boo#1180241 to track this.

If you’re near Melbourne, you should go to Healseville Sanctuary and enjoy the Australian native animals. I’ve been a number of times over the years, and here’s a couple of photos from a (relatively, as in, the last couple of years) trip.

Some shots on Kodak Portra 400 from Adelaide. These would have been shot with my Nikon F80 35mm body, I think all with the 50mm lens. These are all pre-pandemic, and I haven’t gone and looked up when exactly. I’m just catching up on scanning some negatives.

There’s something really quite subtle about how the nproc utility from GNU coreutils works. If you look at the man page, it’s even the very first sentence:

Print the number of processing units available to the current process, which may be less than the number of online processors.

So, what does that actually mean? Well, just because the computer some code is running on has a certain number of CPUs (and here I mean “number of hardware threads”) doesn’t necessarily mean that you can spawn a process that uses that many. What’s a simple example? Containers! Did you know that when you invoke docker to run a container, you can easily limit how much CPU the container can use? In this case, we’re looking at the --cpuset-cpus parameter, as the --cpus one works differently.

$ nproc
8

$ docker run --cpuset-cpus=0-1 --rm=true -it  amazonlinux:2
bash-4.2# nproc
2
bash-4.2# exit

$ docker run --cpuset-cpus=0-2 --rm=true -it  amazonlinux:2
bash-4.2# nproc
3

As you can see, nproc here gets the right bit of information, so if you’re wanting to do a calculation such as “Please use up to the maximum available CPUs” as a parameter to the configuration of a piece of software (such as how many threads to run), you get the right number.

But what if you use some of the other common methods?

$ /usr/bin/lscpu -p | grep -c "^[0-9]"
8
$ grep -c 'processor' /proc/cpuinfo 
8

$ docker run --cpuset-cpus=0-1 --rm=true -it  amazonlinux:2
bash-4.2# yum install -y /usr/bin/lscpu
......
bash-4.2# /usr/bin/lscpu -p | grep -c "^[0-9]"
8
bash-4.2# grep -c 'processor' /proc/cpuinfo 
8
bash-4.2# nproc
2

In this case, if you base your number of threads off grepping lscpu you take another dependency (on the util-linux package), which isn’t needed. You also get the wrong answer, as you do by grepping /proc/cpuinfo. So, what this will end up doing is just increase the number of context switches, possibly also adding a performance degradation. It’s not just in docker containers where this could be an issue of course, you can use the same mechanism that docker uses anywhere you want to control resources of a process.

Another subtle thing to watch out for is differences in /proc/cpuinfo content depending on CPU architecture. You may not think it’s an issue today, but who wants to needlessly debug something?

tl;dr: for determining “how many processes to run”: use nproc, don’t grep lscpu or /proc/cpuinfo

On the random old photos train, there’s some from spending time in Tasmania post linux.conf.au 2017 in Hobart.

All of these are Kodak E100VS film, which was no doubt a bit out of date by the time I shot it (and when they stopped making Ektachrome for a while). It was a nice surprise to be reminded of a truly wonderful Tassie trip, taken with friends, and after the excellent linux.conf.au.

udev can be used to block a USB device (or even an entire class of devices, such as USB storage). Add a file /etc/udev/rules.d/99-local-blacklist.rules containing:

SUBSYSTEM=="usb", ATTRS{idVendor}=="0123", ATTRS{idProduct}=="4567", ATTR{authorized}="0"

Digital TV uses MPEG Transport Stream, which is a container for video designed for lossy transmission, such as radio. To save CPU cycles, Personal Video Records often save the MPEG-TS stream directly to disk. The more usual MPEG is technically MPEG Program Stream, which is designed for lossless transmission, such as storage on a disk.

Since these are a container formats, it should be possible to losslessly and quickly re-code from MPEG-TS to MPEG-PS.

ffmpeg -ss "${STARTTIME}" -to "${DURATION}" -i "${FILENAME}" -ignore_unknown -map 0 -map -0:2 -c copy "${FILENAME}.mpeg"

I gave the talk Practicality Beats Purity: The Zen of Python’s Escape Hatch as part of PyConline AU 2020, the very online replacement for PyCon AU this year. In that talk, I included a few interesting links code samples which you may be interested in:

Links and code samples

• 20 Pythonic Fec^WTheses by Tim Peters, from comp.lang.python The Way of Python
• Fantastic Blocks and Where to Hide Them, from PyCon AU 2019
• PEP 8
• PEP 318 which introduce decorators

@apply

def apply(transform):

    def __decorator__(using_this):
        return transform(using_this)

    return __decorator__


numbers = [1, 2, 3, 4, 5]

@apply(lambda f: list(map(f, numbers)))
def squares(i):
  return i * i

print(list(squares))

# prints: [1, 4, 9, 16, 25]

Init.java

public class Init {
  public static void main(String[] args) {
    System.out.println("Hello, World!")
  }
}

@switch and @case

__NOT_A_MATCHER__ = object()
__MATCHER_SORT_KEY__ = 0

def switch(cls):

    inst = cls()
    methods = []

    for attr in dir(inst):
        method = getattr(inst, attr)
        matcher = getattr(method, "__matcher__", __NOT_A_MATCHER__)

        if matcher == __NOT_A_MATCHER__:
            continue

        methods.append(method)

    methods.sort(key = lambda i: i.__matcher_sort_key__)

    for method in methods:
        matches = method.__matcher__()
        if matches:
            return method()

    raise ValueError(f"No matcher matches value {test_value}")

def case(matcher):

    def __decorator__(f):
        global __MATCHER_SORT_KEY__

        f.__matcher__ = matcher
        f.__matcher_sort_key__ = __MATCHER_SORT_KEY__
        __MATCHER_SORT_KEY__ += 1
        return f

    return __decorator__



if __name__ == "__main__":
    for i in range(100):

        @switch
        class FizzBuzz:

            @case(lambda: i % 15 == 0)
            def fizzbuzz(self):
                return "fizzbuzz"

            @case(lambda: i % 3 == 0)
            def fizz(self):
                return "fizz"

            @case(lambda: i % 5 == 0)
            def buzz(self):
                return "buzz"

            @case(lambda: True)
            def default(self):
                return "-"

        print(f"{i} {FizzBuzz}")

fuck grey text on white backgrounds
fuck grey text on black backgrounds
fuck thin, spindly fonts
fuck 10px text
fuck any size of anything in px
fuck font-weight 300
fuck unreadable web pages
fuck themes that implement this unreadable idiocy
fuck sites that don’t work without javascript
fuck reactjs and everything like it

thank fuck for Stylus. and uBlock Origin. and uMatrix.

Fuck Grey Text is a post from: Errata

TL;DR: exchanges are casinos and don’t want to onboard anyone into bitcoin. Avoid.

There’s a classic scam in the “crypto” space: advertize Bitcoin to get people in, then sell suckers something else entirely. Over the last few years, this bait-and-switch has become the core competency of “bitcoin” exchanges.

I recently visited the homepage of Australian exchange btcmarkets.net: what a mess. There was a list of dozens of identical-looking “cryptos”, with bitcoin second after something called “XRP”; seems like it was sorted by volume?

Incentives have driven exchanges to become casinos, and they’re doing exactly what you’d expect unregulated casinos to do. This is no place you ever want to send anyone.

Incentives For Exchanges

Exchanges make money on trading, not on buying and holding. Despite the fact that bitcoin is the only real attempt to create an open source money, scams with no future are given false equivalence, because more assets means more trading. Worse than that, they are paid directly to list new scams (the crappier, the more money they can charge!) and have recently taken the logical step of introducing and promoting their own crapcoins directly.

It’s like a gold dealer who also sells 57 varieties of pyrite, which give more margin than selling actual gold.

For a long time, I thought exchanges were merely incompetent. Most can’t even give out fresh addresses for deposits, batch their outgoing transactions, pay competent fee rates, perform RBF or use segwit.

But I misunderstood: they don’t want to sell bitcoin. They use bitcoin to get you in the door, but they want you to gamble. This matters: you’ll find subtle and not-so-subtle blockers to simply buying bitcoin on an exchange. If you send a friend off to buy their first bitcoin, they’re likely to come back with something else. That’s no accident.

Looking Deeper, It Gets Worse.

Regrettably, looking harder at specific exchanges makes the picture even bleaker.

Consider Binance: this mainland China backed exchange pretending to be a Hong Kong exchange appeared out of nowhere with fake volume and demonstrated the gullibility of the entire industry by being treated as if it were a respected member. They lost at least 40,000 bitcoin in a known hack, and they also lost all the personal information people sent them to KYC. They aggressively market their own coin. But basically, they’re just MtGox without Mark Karpales’ PHP skills or moral scruples and much better marketing.

Coinbase is more interesting: an MBA-run “bitcoin” company which really dislikes bitcoin. They got where they are by spending big on regulations compliance in the US so they could operate in (almost?) every US state. (They don’t do much to dispel the wide belief that this regulation protects their users, when in practice it seems only USD deposits have any guarantee). Their natural interest is in increasing regulation to maintain that moat, and their biggest problem is Bitcoin.

They have much more affinity for the centralized coins (Ethereum) where they can have influence and control. The anarchic nature of a genuine open source community (not to mention the developers’ oft-stated aim to improve privacy over time) is not culturally compatible with a top-down company run by the Big Dog. It’s a running joke that their CEO can’t say the word “Bitcoin”, but their recent “what will happen to cryptocurrencies in the 2020s” article is breathtaking in its boldness: innovation is mainly happening on altcoins, and they’re going to overtake bitcoin any day now. Those scaling problems which the Bitcoin developers say they don’t know how to solve? This non-technical CEO knows better.

So, don’t send anyone to an exchange, especially not a “market leading” one. Find some service that actually wants to sell them bitcoin, like CashApp or Swan Bitcoin.

Because posting private keys on the Internet is a bad idea, some people like to “redact” their private keys, so that it looks kinda-sorta like a private key, but it isn’t actually giving away anything secret. Unfortunately, due to the way that private keys are represented, it is easy to “redact” a key in such a way that it doesn’t actually redact anything at all. RSA private keys are particularly bad at this, but the problem can (potentially) apply to other keys as well.

I’ll show you a bit of “Inside Baseball” with key formats, and then demonstrate the practical implications. Finally, we’ll go through a practical worked example from an actual not-really-redacted key I recently stumbled across in my travels.

The Private Lives of Private Keys

Here is what a typical private key looks like, when you come across it:

-----BEGIN RSA PRIVATE KEY-----
MGICAQACEQCxjdTmecltJEz2PLMpS4BXAgMBAAECEDKtuwD17gpagnASq1zQTYEC
CQDVTYVsjjF7IQIJANUYZsIjRsR3AgkAkahDUXL0RSECCB78r2SnsJC9AghaOK3F
sKoELg==
-----END RSA PRIVATE KEY-----

Obviously, there’s some hidden meaning in there – computers don’t encrypt things by shouting “BEGIN RSA PRIVATE KEY!”, after all. What is between the BEGIN/END lines above is, in fact, a base64-encoded DER format ASN.1 structure representing a PKCS#1 private key.

In simple terms, it’s a list of numbers – very important numbers. The list of numbers is, in order:

• A version number (0);
• The “public modulus”, commonly referred to as “n”;
• The “public exponent”, or “e” (which is almost always 65,537, for various unimportant reasons);
• The “private exponent”, or “d”;
• The two “private primes”, or “p” and “q”;
• Two exponents, which are known as “dmp1” and “dmq1”; and
• A coefficient, known as “iqmp”.

Why Is This a Problem?

The thing is, only three of those numbers are actually required in a private key. The rest, whilst useful to allow the RSA encryption and decryption to be more efficient, aren’t necessary. The three absolutely required values are e, p, and q.

Of the other numbers, most of them are at least about the same size as each of p and q. So of the total data in an RSA key, less than a quarter of the data is required. Let me show you with the above “toy” key, by breaking it down piece by piece¹:

• MGI – DER for “this is a sequence”
• CAQ – version (0)
• CxjdTmecltJEz2PLMpS4BX – n
• AgMBAA – e
• ECEDKtuwD17gpagnASq1zQTY – d
• ECCQDVTYVsjjF7IQ – p
• IJANUYZsIjRsR3 – q
• AgkAkahDUXL0RS – dmp1
• ECCB78r2SnsJC9 – dmq1
• AghaOK3FsKoELg== – iqmp

Remember that in order to reconstruct all of these values, all I need are e, p, and q – and e is pretty much always 65,537. So I could “redact” almost all of this key, and still give all the important, private bits of this key. Let me show you:

-----BEGIN RSA PRIVATE KEY-----
..............................................................EC
CQDVTYVsjjF7IQIJANUYZsIjRsR3....................................
........
-----END RSA PRIVATE KEY-----

Now, I doubt that anyone is going to redact a key precisely like this… but then again, this isn’t a “typical” RSA key. They usually look a lot more like this:

-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----

People typically redact keys by deleting whole lines, and usually replacing them with [...] and the like. But only about 345 of those 1588 characters (excluding the header and footer) are required to construct the entire key. You can redact about 4/5ths of that giant blob of stuff, and your private parts (or at least, those of your key) are still left uncomfortably exposed.

But Wait! There’s More!

Remember how I said that everything in the key other than e, p, and q could be derived from those three numbers? Let’s talk about one of those numbers: n.

This is known as the “public modulus” (because, along with e, it is also present in the public key). It is very easy to calculate: n = p * q. It is also very early in the key (the second number, in fact).

Since n = p * q, it follows that q = n / p. Thus, as long as the key is intact up to p, you can derive q by simple division.

Real World Redaction

At this point, I’d like to introduce an acquaintance of mine: Mr. Johan Finn. He is the proud owner of the GitHub repo johanfinn/scripts. For a while, his repo contained a script that contained a poorly-redacted private key. He since deleted it, by making a new commit, but of course because git never really deletes anything, it’s still available.

Of course, Mr. Finn may delete the repo, or force-push a new history without that commit, so here is the redacted private key, with a bit of the surrounding shell script, for our illustrative pleasure:

#Add private key to .ssh folder
cd /home/johan/.ssh/
echo  "-----BEGIN RSA PRIVATE KEY-----
MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK
ÄÄÄÄÄÄÄÄÄÄÄÄÄÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅ
MIIJKgIBAAKCAgEAxEVih1JGb8gu/Fm4AZh+ZwJw/pjzzliWrg4mICFt1g7SmIE2
TCQMKABdwd11wOFKCPc/UzRH/fHuQcvWrpbOSdqev/zKff9iedKw/YygkMeIRaXB
fYELqvUAOJ8PPfDm70st9GJRhjGgo5+L3cJB2gfgeiDNHzaFvapRSU0oMGQX+kI9
ezsjDAn+0Pp+r3h/u1QpLSH4moRFGF4omNydI+3iTGB98/EzuNhRBHRNq4oBV5SG
Pq/A1bem2ninnoEaQ+OPESxYzDz3Jy9jV0W/6LvtJ844m+XX69H5fqq5dy55z6DW
sGKn78ULPVZPsYH5Y7C+CM6GAn4nYCpau0t52sqsY5epXdeYx4Dc+Wm0CjXrUDEe
Egl4loPKDxJkQqQ/MQiz6Le/UK9vEmnWn1TRXK3ekzNV4NgDfJANBQobOpwt8WVB
rbsC0ON7n680RQnl7PltK9P1AQW5vHsahkoixk/BhcwhkrkZGyDIl9g8Q/Euyoq3
eivKPLz7/rhDE7C1BzFy7v8AjC3w7i9QeHcWOZFAXo5hiDasIAkljDOsdfD4tP5/
wSO6E6pjL3kJ+RH2FCHd7ciQb+IcuXbku64ln8gab4p8jLa/mcMI+V3eWYnZ82Yu
axsa85hAe4wb60cp/rCJo7ihhDTTvGooqtTisOv2nSvCYpcW9qbL6cGjAXECAwEA
AQKCAgEAjz6wnWDP5Y9ts2FrqUZ5ooamnzpUXlpLhrbu3m5ncl4ZF5LfH+QDN0Kl
KvONmHsUhJynC/vROybSJBU4Fu4bms1DJY3C39h/L7g00qhLG7901pgWMpn3QQtU
4P49qpBii20MGhuTsmQQALtV4kB/vTgYfinoawpo67cdYmk8lqzGzzB/HKxZdNTq
s+zOfxRr7PWMo9LyVRuKLjGyYXZJ/coFaobWBi8Y96Rw5NZZRYQQXLIalC/Dhndm
AHckpstEtx2i8f6yxEUOgPvV/gD7Akn92RpqOGW0g/kYpXjGqZQy9PVHGy61sInY
HSkcOspIkJiS6WyJY9JcvJPM6ns4b84GE9qoUlWVF3RWJk1dqYCw5hz4U8LFyxsF
R6WhYiImvjxBLpab55rSqbGkzjI2z+ucDZyl1gqIv9U6qceVsgRyuqdfVN4deU22
LzO5IEDhnGdFqg9KQY7u8zm686Ejs64T1sh0y4GOmGsSg+P6nsqkdlXH8C+Cf03F
lqPFg8WQC7ojl/S8dPmkT5tcJh3BPwIWuvbtVjFOGQc8x0lb+NwK8h2Nsn6LNazS
0H90adh/IyYX4sBMokrpxAi+gMAWiyJHIHLeH2itNKtAQd3qQowbrWNswJSgJzsT
JuJ7uqRKAFkE6nCeAkuj/6KHHMPsfCAffVdyGaWqhoxmPOrnVgECggEBAOrCCwiC
XxwUgjOfOKx68siFJLfHf4vPo42LZOkAQq5aUmcWHbJVXmoxLYSczyAROopY0wd6
Dx8rqnpO7OtZsdJMeBSHbMVKoBZ77hiCQlrljcj12moFaEAButLCdZFsZW4zF/sx
kWIAaPH9vc4MvHHyvyNoB3yQRdevu57X7xGf9UxWuPil/jvdbt9toaraUT6rUBWU
GYPNKaLFsQzKsFWAzp5RGpASkhuiBJ0Qx3cfLyirjrKqTipe3o3gh/5RSHQ6VAhz
gdUG7WszNWk8FDCL6RTWzPOrbUyJo/wz1kblsL3vhV7ldEKFHeEjsDGroW2VUFlS
asAHNvM4/uYcOSECggEBANYH0427qZtLVuL97htXW9kCAT75xbMwgRskAH4nJDlZ
IggDErmzBhtrHgR+9X09iL47jr7dUcrVNPHzK/WXALFSKzXhkG/yAgmt3r14WgJ6
5y7010LlPFrzaNEyO/S4ISuBLt4cinjJsrFpoo0WI8jXeM5ddG6ncxdurKXMymY7
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::.::
:::::::::::::::::::::::::::.::::::::::::::::::::::::::::::::::::
LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLlL
ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ
ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
ÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅ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-----END RSA PRIVATE KEY-----" >> id_rsa

Now, if you try to reconstruct this key by removing the “obvious” garbage lines (the ones that are all repeated characters, some of which aren’t even valid base64 characters), it still isn’t a key – at least, openssl pkey doesn’t want anything to do with it. The key is very much still in there, though, as we shall soon see.

Using a gem I wrote and a quick bit of Ruby, we can extract a complete private key. The irb session looks something like this:

>> require "derparse"
>> b64 = <<EOF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>> b64 += <<EOF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>> der = b64.unpack("m").first
>> c = DerParse.new(der).first_node.first_child
>> version = c.value
=> 0
>> c = c.next_node
>> n = c.value
=> 80071596234464993385068908004931... # (etc)
>> c = c.next_node
>> e = c.value
=> 65537
>> c = c.next_node
>> d = c.value
=> 58438813486895877116761996105770... # (etc)
>> c = c.next_node
>> p = c.value
=> 29635449580247160226960937109864... # (etc)
>> c = c.next_node
>> q = c.value
=> 27018856595256414771163410576410... # (etc)

What I’ve done, in case you don’t speak Ruby, is take the two “chunks” of plausible-looking base64 data, chuck them together into a variable named b64, unbase64 it into a variable named der, pass that into a new DerParse instance, and then walk the DER value tree until I got all the values I need.

Interestingly, the q value actually traverses the “split” in the two chunks, which means that there’s always the possibility that there are lines missing from the key. However, since p and q are supposed to be prime, we can “sanity check” them to see if corruption is likely to have occurred:

>> require "openssl"
>> OpenSSL::BN.new(p).prime?
=> true
>> OpenSSL::BN.new(q).prime?
=> true

Excellent! The chances of a corrupted file producing valid-but-incorrect prime numbers isn’t huge, so we can be fairly confident that we’ve got the “real” p and q. Now, with the help of another one of my creations we can use e, p, and q to create a fully-operational battle key:

>> require "openssl/pkey/rsa"
>> k = OpenSSL::PKey::RSA.from_factors(p, q, e)
=> #<OpenSSL::PKey::RSA:0x0000559d5903cd38>
>> k.valid?
=> true
>> k.verify(OpenSSL::Digest::SHA256.new, k.sign(OpenSSL::Digest::SHA256.new, "bob"), "bob")
=> true

… and there you have it. One fairly redacted-looking private key brought back to life by maths and far too much free time.

Sorry Mr. Finn, I hope you’re not still using that key on anything Internet-facing.

What About Other Key Types?

EC keys are very different beasts, but they have much the same problems as RSA keys. A typical EC key contains both private and public data, and the public portion is twice the size – so only about 1/3 of the data in the key is private material. It is quite plausible that you can “redact” an EC key and leave all the actually private bits exposed.

What Do We Do About It?

In short: don’t ever try and redact real private keys. For documentation purposes, just put “KEY GOES HERE” in the appropriate spot, or something like that. Store your secrets somewhere that isn’t a public (or even private!) git repo.

Generating a “dummy” private key and sticking it in there isn’t a great idea, for different reasons: people have this odd habit of reusing “demo” keys in real life. There’s no need to encourage that sort of thing.

Some time ago, I wrote “floats, bits, and constant expressions” about converting floating point number into its representative ones and zeros as a C++ constant expression – constructing the IEEE 754 representation without being able to examine the bits directly.

I’ve been playing around with Rust recently, and rewrote that conversion code as a bit of a learning exercise for myself, with a thoroughly contrived set of constraints: using integer and single-precision floating point math, at compile time, without unsafe blocks, while using as few unstable features as possible.

I’ve included the listing below, for your bemusement and/or head-shaking, and you can play with the code in the Rust Playground and rust.godbolt.org

// Jonathan Adamczewski 2020-05-12
//
// Constructing the bit-representation of an IEEE 754 single precision floating 
// point number, using integer and single-precision floating point math, at 
// compile time, in rust, without unsafe blocks, while using as few unstable 
// features as I can.
//
// or "What if this silly C++ thing https://brnz.org/hbr/?p=1518 but in Rust?"


// Q. Why? What is this good for?
// A. To the best of my knowledge, this code serves no useful purpose. 
//    But I did learn a thing or two while writing it :)


// This is needed to be able to perform floating point operations in a const 
// function:
#![feature(const_fn)]


// bits_transmute(): Returns the bits representing a floating point value, by
//                   way of std::mem::transmute()
//
// For completeness (and validation), and to make it clear the fundamentally 
// unnecessary nature of the exercise :D - here's a short, straightforward, 
// library-based version. But it needs the const_transmute flag and an unsafe 
// block.
#![feature(const_transmute)]
const fn bits_transmute(f: f32) -> u32 {
  unsafe { std::mem::transmute::<f32, u32>(f) }
}



// get_if_u32(predicate:bool, if_true: u32, if_false: u32):
//   Returns if_true if predicate is true, else if_false
//
// If and match are not able to be used in const functions (at least, not 
// without #![feature(const_if_match)] - so here's a branch-free select function
// for u32s
const fn get_if_u32(predicate: bool, if_true: u32, if_false: u32) -> u32 {
  let pred_mask = (-1 * (predicate as i32)) as u32;
  let true_val = if_true & pred_mask;
  let false_val = if_false & !pred_mask;
  true_val | false_val
}

// get_if_f32(predicate, if_true, if_false):
//   Returns if_true if predicate is true, else if_false
//
// A branch-free select function for f32s.
// 
// If either is_true or is_false is NaN or an infinity, the result will be NaN,
// which is not ideal. I don't know of a better way to implement this function
// within the arbitrary limitations of this silly little side quest.
const fn get_if_f32(predicate: bool, if_true: f32, if_false: f32) -> f32 {
  // can't convert bool to f32 - but can convert bool to i32 to f32
  let pred_sel = (predicate as i32) as f32;
  let pred_not_sel = ((!predicate) as i32) as f32;
  let true_val = if_true * pred_sel;
  let false_val = if_false * pred_not_sel;
  true_val + false_val
}


// bits(): Returns the bits representing a floating point value.
const fn bits(f: f32) -> u32 {
  // the result value, initialized to a NaN value that will otherwise not be
  // produced by this function.
  let mut r = 0xffff_ffff;

  // These floation point operations (and others) cause the following error:
  //     only int, `bool` and `char` operations are stable in const fn
  // hence #![feature(const_fn)] at the top of the file
  
  // Identify special cases
  let is_zero    = f == 0_f32;
  let is_inf     = f == f32::INFINITY;
  let is_neg_inf = f == f32::NEG_INFINITY;
  let is_nan     = f != f;

  // Writing this as !(is_zero || is_inf || ...) cause the following error:
  //     Loops and conditional expressions are not stable in const fn
  // so instead write this as type coversions, and bitwise operations
  //
  // "normalish" here means that f is a normal or subnormal value
  let is_normalish = 0 == ((is_zero as u32) | (is_inf as u32) | 
                        (is_neg_inf as u32) | (is_nan as u32));

  // set the result value for each of the special cases
  r = get_if_u32(is_zero,    0,           r); // if (iz_zero)    { r = 0; }
  r = get_if_u32(is_inf,     0x7f80_0000, r); // if (is_inf)     { r = 0x7f80_0000; }
  r = get_if_u32(is_neg_inf, 0xff80_0000, r); // if (is_neg_inf) { r = 0xff80_0000; }
  r = get_if_u32(is_nan,     0x7fc0_0000, r); // if (is_nan)     { r = 0x7fc0_0000; }
 
  // It was tempting at this point to try setting f to a "normalish" placeholder 
  // value so that special cases do not have to be handled in the code that 
  // follows, like so:
  // f = get_if_f32(is_normal, f, 1_f32);
  //
  // Unfortunately, get_if_f32() returns NaN if either input is NaN or infinite.
  // Instead of switching the value, we work around the non-normalish cases 
  // later.
  //
  // (This whole function is branch-free, so all of it is executed regardless of 
  // the input value)

  // extract the sign bit
  let sign_bit  = get_if_u32(f < 0_f32,  1, 0);

  // compute the absolute value of f
  let mut abs_f = get_if_f32(f < 0_f32, -f, f);

  
  // This part is a little complicated. The algorithm is functionally the same 
  // as the C++ version linked from the top of the file.
  // 
  // Because of the various contrived constraints on thie problem, we compute 
  // the exponent and significand, rather than extract the bits directly.
  //
  // The idea is this:
  // Every finite single precision float point number can be represented as a
  // series of (at most) 24 significant digits as a 128.149 fixed point number 
  // (128: 126 exponent values >= 0, plus one for the implicit leading 1, plus 
  // one more so that the decimal point falls on a power-of-two boundary :)
  // 149: 126 negative exponent values, plus 23 for the bits of precision in the 
  // significand.)
  //
  // If we are able to scale the number such that all of the precision bits fall 
  // in the upper-most 64 bits of that fixed-point representation (while 
  // tracking our effective manipulation of the exponent), we can then 
  // predictably and simply scale that computed value back to a range than can 
  // be converted safely to a u64, count the leading zeros to determine the 
  // exact exponent, and then shift the result into position for the final u32 
  // representation.
  
  // Start with the largest possible exponent - subsequent steps will reduce 
  // this number as appropriate
  let mut exponent: u32 = 254;
  {
    // Hex float literals are really nice. I miss them.

    // The threshold is 2^87 (think: 64+23 bits) to ensure that the number will 
    // be large enough that, when scaled down by 2^64, all the precision will 
    // fit nicely in a u64
    const THRESHOLD: f32 = 154742504910672534362390528_f32; // 0x1p87f == 2^87

    // The scaling factor is 2^41 (think: 64-23 bits) to ensure that a number 
    // between 2^87 and 2^64 will not overflow in a single scaling step.
    const SCALE_UP: f32 = 2199023255552_f32; // 0x1p41f == 2^41

    // Because loops are not available (no #![feature(const_loops)], and 'if' is
    // not available (no #![feature(const_if_match)]), perform repeated branch-
    // free conditional multiplication of abs_f.

    // use a macro, because why not :D It's the most compact, simplest option I 
    // could find.
    macro_rules! maybe_scale {
      () => {{
        // care is needed: if abs_f is above the threshold, multiplying by 2^41 
        // will cause it to overflow (INFINITY) which will cause get_if_f32() to
        // return NaN, which will destroy the value in abs_f. So compute a safe 
        // scaling factor for each iteration.
        //
        // Roughly equivalent to :
        // if (abs_f < THRESHOLD) {
        //   exponent -= 41;
        //   abs_f += SCALE_UP;
        // }
        let scale = get_if_f32(abs_f < THRESHOLD, SCALE_UP,      1_f32);    
        exponent  = get_if_u32(abs_f < THRESHOLD, exponent - 41, exponent); 
        abs_f     = get_if_f32(abs_f < THRESHOLD, abs_f * scale, abs_f);
      }}
    }
    // 41 bits per iteration means up to 246 bits shifted.
    // Even the smallest subnormal value will end up in the desired range.
    maybe_scale!();  maybe_scale!();  maybe_scale!();
    maybe_scale!();  maybe_scale!();  maybe_scale!();
  }

  // Now that we know that abs_f is in the desired range (2^87 <= abs_f < 2^128)
  // scale it down to be in the range (2^23 <= _ < 2^64), and convert without 
  // loss of precision to u64.
  const INV_2_64: f32 = 5.42101086242752217003726400434970855712890625e-20_f32; // 0x1p-64f == 2^64
  let a = (abs_f * INV_2_64) as u64;

  // Count the leading zeros.
  // (C++ doesn't provide a compile-time constant function for this. It's nice 
  // that rust does :)
  let mut lz = a.leading_zeros();

  // if the number isn't normalish, lz is meaningless: we stomp it with 
  // something that will not cause problems in the computation that follows - 
  // the result of which is meaningless, and will be ignored in the end for 
  // non-normalish values.
  lz = get_if_u32(!is_normalish, 0, lz); // if (!is_normalish) { lz = 0; }

  {
    // This step accounts for subnormal numbers, where there are more leading 
    // zeros than can be accounted for in a valid exponent value, and leading 
    // zeros that must remain in the final significand.
    //
    // If lz < exponent, reduce exponent to its final correct value - lz will be
    // used to remove all of the leading zeros.
    //
    // Otherwise, clamp exponent to zero, and adjust lz to ensure that the 
    // correct number of bits will remain (after multiplying by 2^41 six times - 
    // 2^246 - there are 7 leading zeros ahead of the original subnormal's
    // computed significand of 0.sss...)
    // 
    // The following is roughly equivalent to:
    // if (lz < exponent) {
    //   exponent = exponent - lz;
    // } else {
    //   exponent = 0;
    //   lz = 7;
    // }

    // we're about to mess with lz and exponent - compute and store the relative 
    // value of the two
    let lz_is_less_than_exponent = lz < exponent;

    lz       = get_if_u32(!lz_is_less_than_exponent, 7,             lz);
    exponent = get_if_u32( lz_is_less_than_exponent, exponent - lz, 0);
  }

  // compute the final significand.
  // + 1 shifts away a leading 1-bit for normal, and 0-bit for subnormal values
  // Shifts are done in u64 (that leading bit is shifted into the void), then
  // the resulting bits are shifted back to their final resting place.
  let significand = ((a << (lz + 1)) >> (64 - 23)) as u32;

  // combine the bits
  let computed_bits = (sign_bit << 31) | (exponent << 23) | significand;

  // return the normalish result, or the non-normalish result, as appopriate
  get_if_u32(is_normalish, computed_bits, r)
}


// Compile-time validation - able to be examined in rust.godbolt.org output
pub static BITS_BIGNUM: u32 = bits(std::f32::MAX);
pub static TBITS_BIGNUM: u32 = bits_transmute(std::f32::MAX);
pub static BITS_LOWER_THAN_MIN: u32 = bits(7.0064923217e-46_f32);
pub static TBITS_LOWER_THAN_MIN: u32 = bits_transmute(7.0064923217e-46_f32);
pub static BITS_ZERO: u32 = bits(0.0f32);
pub static TBITS_ZERO: u32 = bits_transmute(0.0f32);
pub static BITS_ONE: u32 = bits(1.0f32);
pub static TBITS_ONE: u32 = bits_transmute(1.0f32);
pub static BITS_NEG_ONE: u32 = bits(-1.0f32);
pub static TBITS_NEG_ONE: u32 = bits_transmute(-1.0f32);
pub static BITS_INF: u32 = bits(std::f32::INFINITY);
pub static TBITS_INF: u32 = bits_transmute(std::f32::INFINITY);
pub static BITS_NEG_INF: u32 = bits(std::f32::NEG_INFINITY);
pub static TBITS_NEG_INF: u32 = bits_transmute(std::f32::NEG_INFINITY);
pub static BITS_NAN: u32 = bits(std::f32::NAN);
pub static TBITS_NAN: u32 = bits_transmute(std::f32::NAN);
pub static BITS_COMPUTED_NAN: u32 = bits(std::f32::INFINITY/std::f32::INFINITY);
pub static TBITS_COMPUTED_NAN: u32 = bits_transmute(std::f32::INFINITY/std::f32::INFINITY);


// Run-time validation of many more values
fn main() {
  let end: usize = 0xffff_ffff;
  let count = 9_876_543; // number of values to test
  let step = end / count;
  for u in (0..=end).step_by(step) {
      let v = u as u32;
      
      // reference
      let f = unsafe { std::mem::transmute::<u32, f32>(v) };
      
      // compute
      let c = bits(f);

      // validation
      if c != v && 
         !(f.is_nan() && c == 0x7fc0_0000) && // nans
         !(v == 0x8000_0000 && c == 0) { // negative 0
          println!("{:x?} {:x?}", v, c); 
      }
  }
}

Over the weekend, the boredom of COVID-19 isolation motivated me to move my personal website from WordPress on a self-managed 10-year-old virtual private server to a generated static site on a static site hosting platform with a content delivery network.

This decision was overdue. WordPress never fit my brain particularly well, and it was definitely getting to a point where I wasn’t updating my website at all (my last post was two weeks before I moved from Hobart; I’ve been living in Petaluma for more than three years now).

Settling on which website framework wasn’t a terribly difficult choice (I chose Jekyll, everyone else seems to be using it), and I’ve had friends who’ve had success moving their blogs over. The difficulty I ended up facing was that the standard exporter that everyone to move from WordPress to Jekyll uses does not expect Debian’s package layout.

Backing up a bit: I made a choice, 10 years ago, to deploy WordPress on a machine that I ran myself, using the Debian system wordpress package, a simple aptitude install wordpress away. That decision was not particularly consequential then, but it chewed up 3 hours of my time on Saturday.

Why? The exporter plugin assumes that it will be able to find all of the standard WordPress files in the usual WordPress places, and when it didn’t find that, it broke in unexpected ways. And why couldn’t it find it?

Debian makes packaging choices that prioritise all the software on a system living side-by-side with minimal difficulty. It sets strict permissions. It separates application code from configuration from user data (which in the case of WordPress, includes plugins), in a way that is consistent between applications. This choice makes it easy for Debian admins to understand how to find bits of an application. It also minimises the chance of one PHP application from clobbering another.

10 years later, the install that I had set up was still working, having survived 3-4 Debian versions, and so 3-4 new WordPress versions. I don’t recall the last time I had to think about keeping my WordPress instance secure and updated. That’s quite a good run. I’ve had a working website despite not caring about keeping it updated for at least three years.

The same decisions that meant I spent 3 hours on Saturday doing a simple WordPress export saved me a bunch of time that I didn’t incrementally spend over the course a decade. Am I even? I have no idea.

Anyway, the least I can do is provide some help to people who might run into this same problem, so here’s a 5-step howto.

How to migrate a Debian WordPress site to Jekyll

Should you find the Jekyll exporter not working on your Debian WordPress install:

1. Use the standard WordPress export to export an XML feel of your site.
2. Spin up a new instance of WordPress (using WordPress.com, or on a new Virtual Private Server, whatever, really).
3. Import the exported XML feed.
4. Install the Jekyll exporter plugin.
5. Follow the documentation and receive a Jekyll export of your site.

Basically, the plugin works with a stock WordPress install. If you don’t have one of those, it’s easy to move it over.

I've spent the last couple of days trying to deploy Fedora CoreOS to some physical hardware/bare metal for a colleague using the official PXE installer from Fedora CoreOS. It wasn't very pleasant, and just wouldn't work reliably.

Maybe my expectations were to high, in that I thought I could use Ignition to prepare more of the system for me, as my colleague has been able to bare metal installs correctly. I just tried to use Ignition as documented.

A few interesting aspects I encountered:

1. The PXE installer for it has a 618MB initrd file. This takes quite a while to transfer via tftp!
2. It can't build software RAID for the main install device (and the developers have no intention of adding this), and it seems very finicky to build other RAID sets for other partitions.
3. And, well, I just kept having problems where the built systems would hang during boot for no obvious reason.
4. The time to do an installation was incredibly long.
5. The initrd image is really just running coreos-installer against the nominated device.

During the night I got feed up with that process and wrote a Fully Automatic Installer (FAI) profile that'd install CoreOS instead. I can now use setup-storage from FAI using it's standard disk_config files. This allows me to build complicated disk configurations with software RAID and LVM easily.

A big bonus is that a rebuild is a lot faster, timed from typing reboot to a fresh login prompt is 10 minutes - and this is on physical hardware so includes BIOS POST and RAID controller set up, twice each.

I thought this might be of interest to other people, so the FAI profile I developed for this is located here: https://github.com/catalyst-cloud/fai-profile-fedora-coreos

FAI was initially developed to deploy Debian systems, it has since been extended to be able to install a number of other operating systems, however I think this is a good example of how easy it is to deploy non-Debian derived operating systems using FAI without having to modify FAI itself.

For the last year I’ve been incrementally moving away from lifting static weights and towards body weight based exercises, or callisthenics. I’ve been doing this for a number of reasons, including better avoidance of injury (if I collapse, the entire stack is dynamic, if a bar held above my head drops on me, most of the weight is just dead weight – ouch), accessibility during travel – most hotel gyms are very poor, and functional relevance – I literally never need to put 100 kg on my back, but I do climb stairs, for instance.

Covid-19 shutting down the gym where I train is a mild inconvenience for me as a result, because even though I don’t do it, I am able to do nearly all my workouts entirely from home. And I thought a post about this approach might be of interest to other folk newly separated from their training facilities.

I’ve gotten most of my information from a few different youtube channels:

• FitnessFAQs
• Calimove
• Minus the gym
• Jerry Teixeira
• Saturno Movement

There are many more channels out there, and I encourage you to go and look and read and find out what works for you. Those 5 are my greatest hits, if you will. I’ve bought the FitnessFAQs exercise programs to help me with my my training, and they are indeed very effective.

While you don’t need a gymnasium, you do need some equipment, particularly if you can’t go and use a local park. Exactly what you need will depend on what you choose to do – for instance, doing dips on the edge of a chair can avoid needing any equipment, but doing them with some portable parallel bars can be much easier. Similarly, doing pull ups on the edge of a door frame is doable, but doing them with a pull-up bar is much nicer on your fingers.

Depending on your existing strength you may not need bands, but I certainly did. Buying rings is optional – I love them, but they aren’t needed to have a good solid workout.

I bought parallettes for working on the planche. Parallel bars for dips and rows. A pull-up bar for pull-ups and chin-ups, though with the rings you can add flys, rows, face-pulls, unstable push-ups and more. The rings. And a set of 3 bands that combine for 7 different support amounts.

In terms of routine, I do a upper/lower split, with 3 days on upper body, one day off, one day on lower, and the weekends off entirely. I was doing 2 days on lower body, but found I was over-training with Aikido later that same day.

On upper body days I’ll do (roughly) chin ups or pull ups, push ups, rows, dips, hollow body and arch body holds, handstands and some grip work. Today, as I write this on Sunday evening, 2 days after my last training day on Friday, I can still feel my lats and biceps from training Friday afternoon. Zero issue keeping the intensity up.

For lower body, I’ll do pistol squats, nordic drops, quad extensions, wall sits, single leg calf raises, bent leg calf raises. Again, zero issues hitting enough intensity to achieve growth / strength increases. The only issue at home is having a stable enough step to get a good heel drop for the calf raises.

If you haven’t done bodyweight training at all before, when starting, don’t assume it will be easy – even if you’re a gym junkie, our bodies are surprisingly heavy, and there’s a lot of resistance just moving them around.

Good luck, train well!

The OpenSTEM® materials are ideally suited to online teaching. In these times of new challenges and requirements, there are a lot of technological possibilities. Schools and teachers are increasingly being asked to deliver material online to students. Our materials can assist with that process, especially for Humanities and Science subjects from Prep/Kindy/Foundation to Year 6. […]

Recording some thoughts about Covid 19 numbers.

Today’s figures

The Government says:

“As at 6.30am on 22 March 2020, there have been 1,098 confirmed cases of COVID-19 in Australia”.

The reference is https://www.health.gov.au/news/health-alerts/novel-coronavirus-2019-ncov-health-alert/coronavirus-covid-19-current-situation-and-case-numbers. However, that page is updated daily (ish), so don’t expect it to be the same if you check the reference.

Estimating Lag

If a person tests positive to the virus today, that means they were infected at some time in the past. So, what is the lag between infection and a positive test result?

Incubation Lag – about 5 days

When you are infected you don’t show symptoms immediately. Rather, there’s an incubation period before symptoms become apparent.  The time between being infected and developing symptoms varies from person to person, but most of the time a person shows symptoms after about 5 days (I recall seeing somewhere that 1 in a 1000 cases will develop symptoms after 14 days).

Presentation Lag – about 2 days

I think it’s fair to also assume that people are not presenting at testing immediately they become ill. It is probably taking them a couple of days from developing symptoms to actually get to the doctor – I read a story somewhere (have since lost the reference) about a young man who went to a party, then felt bad for days but didn’t go for a test until someone else from the party had returned a positive test.  Let’s assume there’s a mix of worried well and stoic types and call it 2 days from becoming symptomatic to seeking a test.

Referral Lag – about a day

Assuming that a GP is available straight away and recommends a test immediately, logistically there will still be most of a day taken up between deciding to see a doctor and having a test carried out.

Testing lag – about 2 days

The graph of infections “epi graph” today looks like this:

One thing you notice about the graph is that the new cases bars seem to increase for a couple of days, then decrease – so about 100 new cases in the last 24 hours, but almost 200 in the 24 hours before that. From the graph, the last 3 “dips” have been today (Sunday), last Thursday and last Sunday.  This seems to be happening every 3 to 4 days. I initially thought that the dips might mean fewer (or more) people presenting over weekends, but the period is inconsistent with that. I suspect, instead, that this actually means that testing is being batched.

That would mean that neither the peaks nor troughs is representative of infection surges/retreats, but is simply reflecting when tests are being processed. This seems to be a 4 day cycle, so, on average it seems that it would be about 2 days between having the test conducted and receiving a result. So a confirmed case count published today is actually showing confirmed cases as at about 2 days earlier.

Total lag

From the date someone is infected to the time that they receive a positive confirmation is about:

lag = time for symptoms to show+time to seek a test+referral time + time for the test to return a result

So, the published figures on confirmed infections are probably lagging actual infections in the community by about 10 days (5+2+1+2).

If there’s about a 10 day lag between infection and confirmation, then what a figure published today says is that about a week and a half ago there were about this many cases in the community.  So, the 22 March figure of 1098 infections is actually really a 12 March figure.

What the lag means for Physical (ie Social) Distancing

The main thing that the lag means is that if we were able to wave a magic wand today and stop all further infections, we would continue to record new infections for about 10 days (and the tail for longer). In practical terms, implementing physical distancing measures will not show any effect on new cases for about a week and a half. That’s because today there are infected people who are yet to be tested.

The silver lining to that is that the physical distancing measures that have been gaining prominence since 15 March should start to show up in the daily case numbers from the middle of the coming week, possibly offset by overseas entrants rushing to make the 20 March entry deadline.

Estimating Actual Infections as at Today

How many people are infected, but unconfirmed as at today? To estimate actual infections you’d need to have some idea of the rate at which infections are increasing. For example, if infections increased by 10% per day for 10 days, then you’d multiply the most recent figure by 1.1 raised to the power of 10 (ie about 2.5).  Unfortunately, the daily rate of increase (see table on the wiki page) has varied a fair bit (from 20% to 27%) over the most recent 10 days of data (that is, over the 10 days prior to 12 March, since the 22 March figures roughly correspond to 12 March infections) and there’s no guarantee that since that time the daily increase in infections will have remained stable, particularly in light of the implementation of physical distancing measures. At 23.5% per day, the factor is about 8.

There aren’t any reliable figures we can use to estimate the rate of infection during the current lag period (ie from 12 March to 22 March). This is because the vast majority of cases have not been from unexplained community transmission. Most of the cases are from people who have been overseas in the previous fortnight and they’re the cohort that has been most significantly impacted by recent physical distancing measures. From 15 March, they have been required to self isolate and from 20 March most of their entry into the country has stopped.  So I’d expect a surge in numbers up to about 30 March – ie reflecting infections in the cohort of people rushing to get into the country before the borders closed followed by a flattening. With the lag factor above, you’ll need to wait until 1 April or thereabouts to know for sure.

Note:

This post is just about accounting for the time lag between becoming infected and receiving a positive test result. It assumes, for example, that everyone who is infected seeks a test, and that everyone who is infected and seeks a test is, in fact, tested. As at today, neither of these things is true.

We thought it timely to review a few facts and observations, relying on published medical papers (or those submitted for peer review) and reliable sources.

As I was an organiser of the conference this year, I didn’t get to see many talks, fortunately many of the talks were recorded, so i get to watch the conference well after the fact.

Conference Opening

That white balance on the lectern slides is indeed bad, I really should get around to adding this as a suggestion on the logos documentation. (With some help, I put up all the lectern covers, it was therapeutic and rush free).

I actually think there was a lot of information in this introduction. Perhaps too much?

OpenZFS and Linux

A nice update on where zfs is these days.

Dev/Ops relationships, status: It’s Complicated

A bit of  a war story about production systems, leading to a moment of empathy.

Samba 2020: Why are we still in the 1980s for authentication?

There are a lot of old security standards that are showing there age, there are a lot of modern security standards, but which to choose?

Tyranny of the Clock

A very interesting problem solving adventure, with a few nuggets of interesting information about tools and techniques.

Configuration Is (riskier than?) Code

Because configuration files are parsed by a program, and the program changes how it runs depending on the contents of that configuration file, every program that parses configuration files is basically an interpreter, and thus every configuration file is basically a program. So, configuation is code, and we should be treating configuration like we do code, e.g. revision control, commenting, testing, review.

Easy Geo-Redundant Handover + Failover with MARS + systemd

Using a local process organiser to handle a cluster, interesting, not something I’d really promote. Not the best video cutting in this video, lots of time with the speaker pointing to his slides offscreen.

2019 was a very busy year for us. I hadn’t realised how busy it was until I sat down to write this post. There’s also some moderately heavy stuff in here – if you have topics that trigger you, perhaps make sure you have spoons before reading.

We had all the usual stuff. Movies – my top two were Alita and Abominable though the Laundromat and Ford v Ferrari were both excellent and moving pieces. I introduced Cynthia to Teppanyaki and she fell in love with having egg roll thrown at her face hole.

When Cynthia started school we dropped gymnastics due to the time overload – we wanted some downtime for her to process after school, and with violin having started that year she was just looking so tired after a full day of school we felt it was best not to have anything on. Then last year we added in a specific learning tutor to help with the things that she approaches differently to the other kids in her class, giving 2 days a week of extra curricular activity after we moved swimming to the weekends.

At the end of last year she was finally chipper and with it most days after school, and she had been begging to get into more stuff, so we all got together and negotiated drama class and Aikido.

The drama school we picked, HSPA, is pretty amazing. Cynthia adored her first teacher there, and while upset at a change when they rearranged classes slightly, is again fully engaged and thrilled with her time there. Part of the class is putting on a full scale production – they did a version of the Happy Prince near the end of term 3 – and every student gets a part, with the ability for the older students to audition for more parts. On the other hand she tells me tonight that she wants to quit. So shrug, who knows :).

I last did martial arts when I took Aikido with sensei Darren Friend at Aikido Yoshinkai NSW back in Sydney, in the late 2000’s. And there was quite a bit less of me then. Cynthia had been begging to take a martial art for about 4 years, and we’d said that when she was old enough, we’d sign her up, so this year we both signed up for Aikido at the Rangiora Aikido Dojo. The Rangiora dojo is part of the NZ organisation Aikido Shinryukan which is part of the larger Aikikai style, which is quite different, yet the same, as the Yoshinkai Aikido that I had been learning. There have been quite a few moments where I have had to go back to something core – such as my stance – and unlearn it, to learn the Aikikai technique. Cynthia has found the group learning dynamic a bit challenging – she finds the explanations – needed when there are twenty kids of a range of ages and a range of experience – from new intakes each term through to ones that have been doing it for 5 or so years – get boring, and I can see her just switch off. Then she misses the actual new bit of information she didn’t have previously :(. Which then frustrates her. But she absolutely loves doing it, and she’s made a couple of friends there (everyone is positive and friendly, but there are some girls that like to play with her after the kids lesson). I have gotten over the body disconnect and awkwardness and things are starting to flow, I’m starting to be able to reason about things without just freezing in overload all the time, so that’s not bad after a year. However, the extra weight is making my forward rolls super super awkward. I can backward roll easily, with moderately good form; forward rolls though my upper body strength is far from what’s needed to support my weight through the start of the roll – my arm just collapses – so I’m in a sort of limbo – if I get the moment just right I can just start the contact on the shoulder; but if I get the moment slightly wrong, it hurts quite badly. And since I don’t want large scale injuries, doing the higher rolls is very unnerving for me. I suspect its 90% psychological, but am not sure how to get from where I am to having confidence in my technique, other than rinse-and-repeat. My hip isn’t affecting training much, and sensei Chris seems to genuinely like training with Cynthia and I, which is very nice: we feel welcomed and included in the community.

Speaking of my hip – earlier this year something ripped cartilage in my right hip – ended up having to have an MRI scan – and those machines sound exactly like a dot matrix printer – to diagnose it. Interestingly, having the MRI improved my symptoms, but we are sadly in hurry-up-and-wait mode. Before the MRI, I’d wake up at night with some soreness, and my right knee bent, foot on the bed, then sleepily let my leg collapse sideways to the right – and suddenly be awake in screaming agony as the joint opened up with every nerve at its disposal. When the MRI was done, they pumped the joint full of local anaesthetic for two purposes – one is to get a clean read on the joint, and the second is so that they can distinguish between referred surrounding pain, vs pain from the joint itself. It is to be expected with a joint issue that the local will make things feel better (duh), for up to a day or so while the local dissipates. The expression on the specialists face when I told him that I had had a permanent improvement trackable to the MRI date was priceless. Now, when I wake up with joint pain, and my leg sleepily falls back to the side, its only mildly uncomfortable, and I readjust without being brought to screaming awakeness. Similarly, early in Aikido training many activities would trigger pain, and now there’s only a couple of things that do. In another 12 or so months if the joint hasn’t fully healed, I’ll need to investigate options such as stem cells (which the specialist was negative about) or steroids (which he was more negative about) or surgery (which he was even more negative about). My theory about the improvement is that the cartilage that was ripped was sitting badly and the inflation for the MRI allowed it to settle back into the appropriate place (and perhaps start healing better). I’m told that reducing inflammation systematically is a good option. Turmeric time.

Sadly Cynthia has had some issues at school – she doesn’t fit the average mould and while wide spread bullying doesn’t seem to be a thing, there is enough of it, and she receives enough of it that its impacted her happiness more than a little – this blows up in school and at home as well. We’ve been trying a few things to improve this – helping her understand why folk behave badly, what to do in the moment (e.g. this video), but also that anything that goes beyond speech is assault and she needs to report that to us or teachers no matter what.

We’ve also had some remarkably awful interactions with another family at the school. We thought we had a friendly relationship, but I managed to trigger a complete meltdown of the relationship – not by doing anything objectively wrong, but because we had (unknown to me) different folkways, and some perfectly routine and normal behaviour turned out to be stressful and upsetting to them, and then they didn’t discuss it with us at all until it had brewed up in their heads into a big mess… and its still not resolved (and may not ever be: they are avoiding us both).

I weighed in at 110kg this morning. Jan the 4th 2019 I was 130.7kg. Feb 1 2018 I was 115.2kg. This year I peaked at 135.4kg, and got down to 108.7kg before Christmas food set in. That’s pretty happy making all things considered. Last year I was diagnosed with Coitus headaches and though I didn’t know it the medicine I was put on has a known side effect of weight gain. And it did – I had put it down to ongoing failure to manage my diet properly, but once my weight loss doctor gave me an alternative prescription for the headaches, I was able to start losing weight immediately. Sadly, though the weight gain through 2018 was effortless, losing the weight through 2019 was not. Doable, but not effortless. I saw a neurologist for the headaches when they recurred in 2019, and got a much more informative readout on them, how to treat and so on – basically the headaches can be thought of as an instability in the system, and the medicines goal is to stabilise things, and once stable for a decent period, we can attempt to remove the crutch. Often that’s successful, sometimes not, sometimes its successful on a second or third time. Sometimes you’re stuck with it forever. I’ve been eating a keto / LCHF diet – not super strict keto, though Jonie would like me to be on that, I don’t have the will power most of the time – there’s a local truck stop that sells killer hotdogs. And I simply adore them.

I started this year working for one of the largest companies on the planet – VMware. I left there in February and wrote a separate post about that. I followed that job with nearly the polar opposite – a startup working on a blockchain content distribution system. I wrote about that too. Changing jobs is hard in lots of ways – for instance I usually make friendships at my jobs, and those suffer some when you disappear to a new context – not everyone makes connections with you outside of the job context. Then there’s the somewhat non-rational emotional impact of not being in paid employment. The puritans have a lot to answer for. I’m there again, looking for work (and hey, if you’re going to be at Linux.conf.au (Gold Coast Australia January 13-17) I’ll be giving a presentation about some of the interesting things I got up to in the last job interregnum I had.

My feet have been giving me trouble for a couple of years now. My podiatrist is reasonably happy with my progress – and I can certainly walk further than I could – I even did some running earlier in the year, until I got shin splints. However, I seem to have hyper sensitive soles, so she can’t correct my pro-nation until we fix that, which at least for now means a 5 minute session where I touch my feet, someone else does, then something smooth then something rough – called “sensory massage”.

In 2017 and 2018 I injured myself at the gym, and in 2019 I wanted to avoid that, so I sought out ways to reduce injury. Moving away from machines was a big part of that; more focus on technique another part. But perhaps the largest part was moving from lifting dead weight to focusing on body weight exercises – callisthenics. This shifts from a dead weight to control when things go wrong, to an active weight, which can help deal with whatever has happened. So far at least, this has been pretty successful – although I’ve had minor issues – I managed to inflame the fatty pad the olecranon displaces when your elbow locks out – I’m nearly entirely transitioned to a weights-free program – hand stands, pistol squats, push ups, dead hangs and so on. My upper body strength needs to come along some before we can really go places though… and we’re probably going to max out the hamstring curl machine (at least for regular two-leg curls) before my core is strong enough to do a Nordic drop.

Lynne has been worried about injuring herself with weight lifting at the gym for some time now, but recently saw my physio – Ben Cameron at Pegasus PhysioSouth – who is excellent, and he suggested that she could have less chronic back pain if she took weights back up again. She’s recently told me that I’m allowed one ‘told you so’ about this, since she found herself in a spot where previously she would have put herself in a poor lifting position, but the weight training gave her a better option and she intuitively used it, avoiding pain. So that’s a good thing – complicated because of her bodies complicated history, but an excellent trainer and physio team are making progress.

Earlier this year she had a hell of a fright, with a regular eye checkup getting referred into a ‘you are going blind; maybe tomorrow, maybe within 10 years’ nightmare scenario. Fortunately a second opinion got a specialist who probably knows the same amount but was willing to communicate it with actual words… Lynne has a condition which diabetes (type I or II) can affect, and she has a vein that can alter state somewhat arbitrarily but will probably only degrade slowly, particularly if Lynne’s diet is managed as she has been doing.

Diet wise, Lynne also has been losing some weight but this is complicated by her chronic idiopathic pancreatitis. That’s code for ‘it keeps happening and we don’t know why’ pancreatitis. We’ve consulted a specialist in the North Island who comes highly recommended by Lynne’s GP, who said that rapid weight loss is a little known but possible cause of pancreatitis – and that fits the timelines involved. So Lynne needs to lose weight to manage the onset of type II diabetes. But not to fast, to avoid pancreatitis, which will hasten the onset of type II diabetes. Aiee. Slow but steady – she’s working with the same doctor I am for that, and a similar diet, though lower on the fats as she has no gall… bladder.

In April our kitchen waste pipe started chronically blocking, and investigation with a drain robot revealed a slump in the pipe. Ground penetrating radar reveal an anomaly under the garage… and this escalated. We’re going to have to move out of the house for a week while half the house’s carpets are lifted, grout is pumped into the foundations to tighten it all back up again – and hopefully they don’t over pump it – and then it all gets replaced. Oh, and it looks like the drive will be replaced again, to fix the slumped pipe permanently. It will be lovely when done but right now we’re facing a wall of disruption and argh.

Around September I think, we managed to have a gas poisoning scare – our gas hob was left on and triggered a fireball which fortunately only scared Lynne rather than flambéing her face. We did however not know how much exposure we’d had to the LPG, nor to partially combusted gas – which produces toxic CO as a by-product, so there was a trip into the hospital for observation with Cynthia, with Lynne opting out. Lynne and Cynthia had had plenty of the basic symptoms – headaches, dizziness and so on at the the time, but after waiting for 2 hours in the ER queue that had faded. Le sigh. The hospital, bless their cotton socks don’t have the necessary equipment to diagnose CO poisoning without a pretty invasive blood test, but still took Cynthia’s vitals using methods (manual observation and a infra-red reader) that are confounded by the carboxyhemoglobin that forms from the CO that has been inhaled. Pretty unimpressed – our GP was livid. (This is one recommended protocol). Oh, and our gas hob when we got checked out – as we were not sure if we had left it on, or it had been misbehaving, turned out to have never been safe, got decertified and the pipe cut at the regulator. So we’re cooking on a portable induction hob for now.

When we moved to Rangiora I was travelling a lot more, Christchurch itself had poorer air quality than Rangiora, and our financial base was a lot smaller. Now, Rangiora’s population has gone up nearly double (13k to 19k conservatively – and that’s ignoring the surrounds that use Rangiora as a base), we have more to work with, the air situation in Christchurch has improved massively, and even a busy years travel is less than I was doing before Cynthia came along. We’re looking at moving – we’re not sure where yet; maybe more country, maybe more city.

One lovely bright spot over the last few years has been reconnecting with friends from school, largely on Facebook – some of whom I had forgotten that I knew back at school – I had a little clique but was not very aware of the wider school population in hindsight (this was more than a little embarrassing to me, as I didn’t want to blurt out “who are you?!”) – and others whom I had not :). Some of these reconnections are just light touch person-X exists and cares somewhat – and that’s cool. One in particular has grown into a deeper friendship than we had back as schoolkids, and I am happy and grateful that that has happened.

Our cats are fat and happy. Well mostly. Baggy is fat and stressed and spraying his displeasure everywhere whenever the stress gets too much :(. Cynthia calls him Mr Widdlepants. The rest of the time he cuddles and purrs and is generally happy with life. Dibbler and Kitten-of-the-wild are relatively fine with everything.

Cynthia’s violin is coming along well. She did a small performance for her classroom (with her teacher) and wowed them. I’ve been inspired to start practising trumpet again. After 27 years of decay my skills are decidedly rusty, but they are coming along. Finding arrangements for violin + trumpet is a bit challenging, and my sight-reading-with-transposition struggles to cope, but we make do. Lynne is muttering about getting a clarinet or drum-kit and joining in.

So, 2019. Whew. I hope yours was less stressful and had as many or more bright points than ours. Onwards to 2020.

BlueHackers has in the past arranged for a free counsellor/psychologist at several conferences (LCA, OSDC). Given the popularity and great reception of this service, we want to make this a regular thing and try to get this service available at every conference possible – well, at least Australian open source and related events.

Right now we’re trying to arrange for the service to be available at LCA2020 at the Gold Coast, we have excellent local psychologists already, and the LCA organisers are working on some of the logistical aspects.

Meanwhile, we need to get the funds organised. Fortunately this has never been a problem with BlueHackers, people know this is important stuff. We can make a real difference.

Unfortunately BlueHackers hasn’t yet completed its transition from OSDClub project to Linux Australia subcommittee, so this fundraiser is running in my personal name. Well, you know who I (Arjen) am, so I hope you’re ok all with that.

We have a little over a week until LCA2020 starts, let’s make this happen! Thanks. You can donate via MyCause.

In June 2019 I started a new role as a software engineer at a startup called Cachecash. Today is probably the last day of payroll there, and as is my usual practice, I’m going to reflect back on my time there. Less commonly, I’m going to do so in public, as we’re about to open the code (yay), and its not a mega-corporation with everything shuttered up (also yay).

Framing

This is intended to be a blameless reflection on what has transpired. Blameless doesn’t mean inaccurate; but it means placing the focus on the process and system, not on the particular actor that happened to be wearing the hat at the time a particular event happened. Sometimes the system is defined by the actors, and in that case – well, I’ll let you draw your own conclusions if you encounter that case.

A retrospective that we can’t learn from is useless. Worse than useless, because it takes time to write and time to read and that time is lost to us forever. So if a thing is a particular way, it is going to get said. Not to be mean, but because false niceness will waste everyone’s time. Mine and my ex-colleagues whose time I respect. And yours, if you are still reading this.

What was Cachecash

Cachecash was a startup – still is in a very technical sense, corporation law being what it is. But it is still a couple of code bases – and a nascent open source project (which will hopefully continue) – built to operationalise and productise this research paper that the Cachecash founders wrote.

What it isn’t anymore is a company investing significant amounts of time and money in the form of engineering in making code, to make those code bases better.

Cachecash was also a team of people. That obviously changed over time, but at the time I write this it is:

• Ghada
• Justin
• Kevin
• Marcus
• Petar
• Robert
• Scott

And we’re all pretty fantastic, if you ask me :).

Technical overview

The CAPNet paper that I linked above doesn’t describe a product. What it describes is a system that permits paying caches (think squid/varnish etc) for transmitting content to clients, while also detecting attempts by such caches to claim payment when they haven’t transmitted, or attempting to collude with a client to pretend to overtransmit and get paid that way. A classic incentives-aligned scheme.

Note that there is no blockchain involved at this layer.

The blockchain was added into this core system as a way to build a federated marketplace – the idea was that the blockchain provided a suitable substrate for negotiating the purchase and sale of contracts that would be audited using the CAPNet accounting system, the payments could be micropayments back onto the blockchain, and so on – we’d avoid the regular financial system, and we wouldn’t be building a fragile central system that would prevent other companies also participating.

Miners would mine coins, publishers would buy coins then place them in escrow as a promise to pay caches to deliver content to clients, and a client would deliver proof of delivery back to the cache which would then claim payment from the publisher.

Technical Challenges

There were a few things that turned up as significant issues. In no particular order:

The protocol

The protocol itself adds additional round trips to multiple peers – in its ‘normal’ configuration the client ends up running (web- for browers) GRPC connections to 5 endpoints (with all the normal windowing concerns, but potentially over QUIC), and then gets chunks of content in batches (concurrently) from 4 of the peers, runs a small crypto brute force operation on the combined result, and then moves onto the next group of content. This should be sounding suspiciously like TCP – it is basically a window management problem, and it has exactly the same performance management problems – fast start, maximum window size, how far to reduce it when problems are suffered. But accentuated: those 4 cache peers can all suffer their own independent noise problems, or be hostile. But also, they can also suffer correlated problems: they might all be in the same datacentre, or be all run by a hostile actor, or the client might be on a hostile WiFi link, or the client’s OS/browser might be hostile. Lets just say that there is a long, rich road for optimising this new protocol to make it fast, robust, reliable. Much as we have taken many years to make HTTP into QUIC, drawing upon techniques like forward error correction rather than retries – similar techniques will need to be applied to give this protocol similar performance characteristics. And evolving the protocol while maintaining the security properties is a complicated task, with three actors involved, who may collude in various ways.

An early performance analysis I did on the go code implementation showed that the brute forcing work was a bottleneck because while the time (once optimise) per second was entirely modest for any small amount of data, the delay added per window element acts as a brake on performance for high capacity low latency links. For a 1Gbps 25ms RTT link I estimated a need for 8 cores doing crypto brute forcing on the client.

JS

Cachecash is essentially implementing a new network protocol. There are some great hooks these days in browsers, and one can hook in and provide streams to things like video players to let them get one segment of video. However, for downloading an entire file – for instance, if one is downloading a full video, it is not so easy. This bug, open for 2 years now, is the standards based way to do it. Even so non-standards based way to do it involves buffering the entire content in memory, oh and reflecting everything through a static github service worker. (You of course host such a static page yourself, but then the whole idea of this federated distributed system breaks down a little).

Our initial JS implementation was getting under 512KBps with all-local servers – part of that was the bandwidth delay product issue mentioned above. Moving to getting chunks of content from each cache concurrently using futures improved that up to 512KBps, but thats still shocking for a system we want to be able to compete with the likes of Youtube, Cloudflare and Akamai.

One of the hot spots turned out to be calculating SHA-256 values – the CAPNet algorithm calculates thousands (it’s tunable, but 8k in the set I was analysing) of independent SHA’s per chunk of received data. This is a problem – in browser SHA routines, even the recent native hosted ones – are slow per SHA. They are not slow per byte. Most folk want to make a small number of SHA calculations. Maybe thousands in total. Not tens of thousands per MB of data received….. So we wrote an implementation of the core crypto routines in Rust WASM, which took our performance locally up to 2MBps in Firefox and 6MBps in Chromium.

It is also possible we’d show up as crypto-JS at that point and be blacklisted as malware!

Blockchain

Having chosen to involve a block chain in the stack we had to deal with that complexity. We chose to take bitcoin’s good bits and run with those rather than either running a sidechain, trying to fit new transaction types into bitcoin itself, or trying to shoehorn our particular model into e.g. Ethereum. This turned out to be a fairly large amount of work : not the core chain itself – cloning the parts of bitcoin that we wanted was very quick. But then layering on the changes that we needed, to start dealing with escrows and negotiating parameters between components and so forth. And some of the operational challenges below turned up here as well even just in developer test setups (in particular endpoint discovery).

Operational Challenges

The operational model was pretty interesting. The basic idea was that eventually there would be this big distributed system, a bit-coin like set of miners etc, and we’d be one actor in that ecosystem running some subset of the components, but that until then we’d be running:

• A centralised ledger
• Centralised random number generation for the micropayment system
• Centralised deployment and operations for the cache fleet
• Software update / vetting for the publisher fleet
• Software update / publishing for the JS library
• Some number of seed caches
• Demo publishers to show things worked
• Metrics, traces, chain explorer, centralised logging

We had most of this live and running in some fashion for most of the time I was there – we evolved it and improved it a number of times as we iterated on things. Where appropriate we chose open source components like Jaeger, Prometheus and Elasticsearch. We also added policy layers on top of them to provide rate limiting and anti-spoofing facilities. We deployed stuff in AWS, with EKS, and there were glitches and things to workaround but generally only a tiny amount of time went into that part of it. I think I spent a day on actual operations a month, or thereabouts.

Other parties were then expected to bring along additional caches to expand the network, additional publishers to expand the content accessible via the network, and clients to use the network.

Ensuring a process run by a third party is network reachable by a browser over HTTPS is a surprisingly non-simple problem. We partly simplified it by mandating that they run a docker container that we supplied, but there’s still the chance that they are running behind a firewall with asymmetric ingress. And after that we still need a domain name for their endpoint. You can give every cache a CNAME in a dedicated subdomain – say using their public key as the subdomain, so that only that cache can issue requests to update their endpoint information in DNS. It is all solvable, but doing it so that the amount of customer interaction and handholding is reduced to the bare minimum is important: a user with a fleet of 1000 machines doesn’t want to talk to us 1000 times, and we don’t want to talk to them either. But this was a another bit of this-isn’t-really-distributed-is-it grit in the distributed-ointment.

Adoption Challenges

ISPs with large fleets of machines are in principle happy to sell capacity on them in return for money – yay. But we have no revenue stream at the moment, so they aren’t really incentivised to put effort in, it becomes a matter of principle, not a fiscal “this is 10x better for my business” imperative. And right now, its 10x slower than HTTP. Or more.

Content owners with large amounts of content being delivered without a CDN would like a radically cheaper CDN. Except – we’re not actually radically cheaper on a cost structure basis. Current CDN’s are expensive for their expensive 2nd and third generation products because no-one offers what they offer – seamless in-request edge computing. But that ISP that is contributing a cache to the fleet is going to want the cache paid for, and thats the same cost structure as existing CDNs – who often have a free entry tier. We might have been able to make our network cheaper eventually, but I’m just not sure about the radically cheaper bit.

Content owners who would like a CDN marketplace where the CDN caches are competing with each other – driving costs down – rather than than the CDN operators competing – would absolutely love us. But I rather suspect that those owners want more sophisticated offerings. To be clear, I wasn’t on the customer development team, and didn’t get much in the way of customer development briefings. But things like edge computing workers, where completely custom code can run in the CDN network, adjacent to ones user, are much more powerful offerings than simple static content shipping offerings, and offered by all major CDN’s. These are trusted services – the CAPNet paper doesn’t solve the problem of running edge code and providing proof that it was run. Enarx might go some, or even a long way way to running such code in an untrusted context, but providing a proof that it was run – so that running it can become a mining or mining-like operation is a whole other question. Without such an answer, an edge computing network starts to depend on trusting the caches behaviour a lot more all over again – the network has no proof of execution to depend on.

Rapid adjustment – load spikes – is another possible use case, but the use of the blockchain to negotiate escrows actually seemed to work against our ability to offer that. Akami define load spike in a time frame faster than many block chains can decide that a transaction has actually been accepted. Offchain transactions are of course a known thing in the block chain space but again that becomes additional engineering.

Our use of a new network protocol – for all that it was layered on standard web technology – made it harder for potential content owners to adopt our technology. Rather than “we have 200 local proxies that will deliver content to your users, just generate a url of the form X.Y.Z”, our solution is “we do not trust the 200 local proxies that we have, so you need to run complicated JS in your browser/phone app etc” to verify that the proxies are actually doing their job. This is better in some ways – precisely because we don’t trust those proxies, but it also increases both the runtime cost of using the service, the integration cost adopting the service, and complexity of debugging issues receiving content via the service.

What did we learn?

It is said that “A startup is an organization formed to search for a repeatable and scalable business model.” What did we uncover in our search? What can we take away going forward?

In principle we have a classic two sided market – people with excess capacity close to users want to sell it, and people with excess demand for their content want to buy delivery capacity.

The baseline market is saturated. The market as a whole is on its third or perhaps fourth (depending on how you define things) major iteration of functionality.

Content delivery purchasers are ok with trusting their suppliers : any supply chain fraud happening in this space at the moment is so small no-one is talking about it that I heard about.

Some of the things we were doing don’t seem to have been important to the customers we talked to – I don’t have a great read on this, but in particular, the blockchain aspect seems to have been more important to our long term vision than to the 2-sided market place that we perceived. It would be fascinating to me to validate that somehow – would cache capacity suppliers be willing to trust us enough to sell capacity to us with just the auditing mechanism, without the blockchain? Would content providers be happy buying credit from us rather than from a neutral exchange?

What did I learn?

I think in hindsight my startup muscles were atrophied – it had been some years since Canonical and it took a few months to start really thinking lean-startup again on a personal basis. That’s ok, because I was hired to build systems. But its not great, because I can do better. So number one: think lean-startup and really step up to help with learning and validation.

I levelled up my Go lang skills. That was really nice – Kevin has deep knowledge there, and though I’ve written Go before I didn’t have a good appreciation for style or aesthetics, or why. I do now. Where before I’d say ‘I’m happy to dive in but its not a language I feel I really know’, I am now happy to say that I know Go. More to learn – there always is – but in a good place.

I did a similar thing to my JS skills, but not to the same degree. Having climbed fairly deeply into the JS client – which is written in Typescript, converted its bundling system to webpack to work better with Rust-WASM, and so on. Its still not my go-to place, but I’m much more comfortable there now.

And of course playing with Rust-WASM was pure delight. Markus and I are both Rust afficionados, and having a genuine reason to write some Rust code for work was just delightful. Finding this bug was just a bonus :).

It was also really really nice being back in a truely individual contributor role for a while. I really enjoyed being able to just fix bugs and get on with things while I got my bearings. I’ve ended up doing a bit more leadership – refining of requirements, translating between idea-and-specification and the like recently, but still about 80% of time has been able to be sit-down-and-code, and that really is a pleasant holiday.

What am I going to change?

I’m certainly going to get a new job :). If you’re hiring, hit me up. (If you don’t have my details already, linkedin is probably best).

I’m think there the core thing I need to do is more alignment of the day to day work I’m doing with needs of customer development : I don’t want to take on or take over the customer development role – that will often be done best in person with a customer for startups, and I’m happy remote – but the more I can connect what I’m trying to achieve with what will get the customers to pay us, the more successful any business I’m working in will be. This may be a case for non-vanity metrics, or talking more with the customer-development team, or – well, I don’t know exactly what it will look like until I see the context I end up in, but I think more connection will be important.

And I think the second major thing is to find a better balance between individual contribution and leadership. I love individual contribution, it is perhaps the least stressful and most Zen place to be. But it is also the least effective unless the project has exactly one team member. My most impactful and successful roles have been leadership roles, but the pure leadership role with no individual contribution slowly killed me inside. Pure individual contribution has been like I imagine crack to be, and perhaps just as toxic in the long term.

Daniel wrote a lovely blog post about Rust’s ability to be included in distributions, both as a language that you can get via the distribution, and as the language that components of the distribution are being written in.

I think this is a great goal to raise and I have just a few thoughts and quibbles. First I want to acknowledge and agree with him on the Rust community, its so very nice, and he is doing a great thing as rustup lead; I wish I had more time to put in, I have more things I want to contribute to rustup. I’ll try to get back to the meetings soon.

On trust

I completely agree about the need for the crates index improvement : without those we cannot have a mirror network, and thats a significant issue for offline users and slow-region users.

On curlsh though

It isn’t the worst possible thing, for all that its “untrusted bootstrapping”, the actual thing downloaded is https secured etc, and so is the rustup binary itself. Put another way, I think the horror is more perceptual than analyzed risk. Someone that trusts Verisign etc enough to download the Debian installer enough over it, has exactly the same risk as someone trusting Verisign enough to download rustup at that point in time.

Cross signing curlsh that with per-distro keys or something seems pretty ridiculous to me, since the root of trust is still that first download; unless you’re wandering up to someone who has bootstrapped their compiler by hand (to avoid reflections-on-trust attacks), to get an installer, to build a system, to then do reproducible builds, to check that other systems are actually safe… aieeee.

I think its easier to package the curl|sh shell script in Debian itself perhaps? apt install get-rustup; then if / when rustup becomes packaged the user instructions don’t change but the root of trust would, as get-rustup would be updated to not download rustup, but to trigger a different package install, and so forth.

I don’t think its desirable though, to have distribution forks of the contents that rustup manages – Debian+Redhat+Suse+… builds of nightly rust with all the things failing or not, and so on – I don’t see who that would help. And if we don’t have that then the root of trust would still not be shifted under the GPG keychain – it would still be the HTTPS infrastructure for downloading rust toolchains + the integrity of the rustup toolchain builds themselves. Making rustup, which currently shares that trust, have a different trust root, seems pointless.

On duplication of dependencies

I think Debian needs to become more inclusive here, not Rustup. Debian has spent; pauses, counts, yes, DECADES, rejecting multiple entire ecosystems because of a prejuidiced view about what the Right Way to manage dependencies is. And they are not right in a universal sense. They were right in an engineering sense: given constraints (builds are expensive, bandwidth is expensive, disk is expensive), they are right. But those are not universal constraints, and seeking to impose those constraints on Java and Node – its been an unmitigated disaster. It hasn’t made those upstreams better, or more secure, or systematically fixed problems for users. I have another post on this so rather than repeating I’m going to stop here :).

I think Rust has – like those languages – made the crucial, maintainer and engineering efficiency important choice to embrace enabling incremental change across libraries, with the consequence that dependencies don’t shift atomically, and sure, this is basically incompatible with Debian packaging world view which says that point and patch releases of libraries are not distinct packages, and thus the shared libs for these things all coexist in the same file on disk. Boom! Crash!

I assert that it is entirely possible to come up with a reasonable design for managing a respository of software that doesn’t make this conflation, would allow actual point and patch releases of exist as they are for the languages that have this characteristic, and be amenable to automation, auditing and reporting for security issues. E.g. Modernise Debian to cope with this fundamentally different language design decision… which would make Java and Node and Rust work so very much better.

Alternatively, if Debian doesn’t want to make it possible to natively support languages that have made this choice, Debian could:

• ship static-but-for-system-libs builds
• not include things written in rust
• ask things written in rust to converge their dependencies again and again and again (and only update them when the transitive dependencies across the entire distro have converged)

I have a horrible suspicion about which Debian will choose to do :(. The blinkers / echo chamber are so very strong in that community.

For Windows

We got to parity with Linux for IO for non-McAfee users, but I guess there are a lot of them out there; we probably need to keep pushing on tweaking it until it work better for them too; perhaps autodetect McAfee and switch to minimal? I agree that making Windows users – like I am these days – feel tier one, would be nice :). Maybe a survey of user experience would be a good starting point.

Shared libraries

Perhaps generating versioned symbols automatically and building many versions of the crate and then munging them together? But I’d also like to point here again that the whole focus on shared libraries is a bit of a distribution blind spot, and looking at the vast amount of distribution of software occuring in app stores and their model, suggests different ways of dealing with these things. See also the fairly specific suggestion I make about the packaging system in Debian that is the root of the problem in my entirely humble view.

Bonus

John Goerzen posted an entirely different thing recently, but in it he discusses programs that don’t properly honour terminfo. Sadly I happen to know that large chunks of the Rust ecosystem assume that everything is ANSI these days, and it certainly sounds like, at least for John, that isn’t true. So thats another way in which Rust could be more inclusive – use these things that have been built, rather than being modern and new age and reinventing the 95% match.

To my intense amazement, it seems that NBN Co have finally done sufficient capacity expansion on our local fixed wireless tower to actually resolve the evening congestion issues we’ve been having for the past couple of years. Where previously we’d been getting 22-23Mbps during the day and more like 2-3Mbps (or worse) during the evenings, we’re now back to 22-23Mbps all the time, and the status lights on the NTD remain a pleasing green, rather than alternating between green and amber. This is how things were way back at the start, six years ago.

We received an email from iiNet in early July advising us of the pending improvements. It said:

Your NBN Wireless service offers maximum internet speeds of 25Mbps downland and 5Mbps upload.

NBN Co have identified that your service is connected to a Wireless cell that is currently experiencing congestion, with estimated typical evening speeds of 3~6 Mbps. This congestion means that activities like browsing, streaming or gaming might have been and could continue to be slower than promised, especially when multiple people or devices are using the internet at the same time.

NBN Co estimates that capacity upgrades to improve the speed congestion will be completed by Dec-19.

At the time we were given the option of moving to a lower speed plan with a $10 refund because we weren’t getting the advertised speed, or to wait it out on our current plan. We chose the latter, because if we’d downgraded, that would have reduced our speed during the day, when everything was otherwise fine.

We did not receive any notification from iiNet of exactly when works would commence, nor was I ever able to find any indication of planned maintenance on iiNet’s status page. Instead, I’ve come to rely on notifications from my neighbour, who’s with activ8me. He receives helpful emails like this:

This is a courtesy email from Activ8me, Letting you know NBN will be performing Fixed Wireless Network capacity work in your area that might affect your connectivity to the internet. This activity is critical to the maintenance and optimisation of the network. The approximate dates of this maintenance/upgrade work will be:

Impacted location: Neika, TAS & Downstream Sites & Upstream Sites
NBN estimates interruption 1 (Listed Below) will occur between:
Start: 24/09/19 7:00AM End: 24/09/19 8:00PM
NBN estimates interruption 2 (Listed Below) will occur between:
Start: 25/09/19 7:00AM End: 25/09/19 8:00PM
NBN estimates interruption 3 (Listed Below) will occur between:
Start: 01/10/19 7:00AM End: 01/10/19 8:00PM
NBN estimates interruption 4 (Listed Below) will occur between:
Start: 02/10/19 7:00AM End: 02/10/19 8:00PM
NBN estimates interruption 5 (Listed Below) will occur between:
Start: 03/10/19 7:00AM End: 03/10/19 8:00PM
NBN estimates interruption 6 (Listed Below) will occur between:
Start: 04/10/19 7:00AM End: 04/10/19 8:00PM
NBN estimates interruption 7 (Listed Below) will occur between:
Start: 05/10/19 7:00AM End: 05/10/19 8:00PM
NBN estimates interruption 8 (Listed Below) will occur between:
Start: 06/10/19 7:00AM End: 06/10/19 8:00PM

Change start
24/09/2019 07:00 Australian Eastern Standard Time

Change end
06/10/2019 20:00 Australian Eastern Daylight Time

This is expected to improve your service with us however, occasional loss of internet connectivity may be experienced during the maintenance/upgrade work.
Please note that the upgrades are performed by NBN Co and Activ8me has no control over them.
Thank you for your understanding in this matter, and your patience for if it does affect your service. We appreciate it.

The astute observer will note that this is pretty close to two weeks of scheduled maintenance. Sure enough, my neighbour and I (and presumably everyone else in the area) enjoyed major outages almost every weekday during that period, which is not ideal when you work from home. But, like I said at the start, they did finally get the job done.

Interestingly, according to activ8me, there is yet more NBN maintenance scheduled from 21 October 07:00 ’til 27 October 21:00, then again from 28 October 07:00 ’til 3 November 21:00 (i.e. another two whole weeks). The only scheduled upgrade I could find listed on iiNet’s status page is CM-177373, starting “in 13 days” with a duration of 6 hours, so possibly not the same thing.

Based on the above, I am convinced that there is some problem with iiNet’s status page not correctly reporting NBN incidents, but of course I have no idea whether this is NBN Co not telling iiNet, iiNet not listening to NBN Co, or if it’s just that the status web page is busted.

Reach out to me – I’m currently looking for something interesting to do. https://www.linkedin.com/in/rbtcollins/ and https://twitter.com/rbtcollins are good ways to grab me if you don’t already have my details.

Should you reach out to me? Maybe :). First, a little retrospective.

Three years ago, I wrote the following when reflecting on what I wanted to be doing:

Priorities (roughly ordered most to least important):

• Keep living in Rangiora (family)
• Up to moderate travel requirements – 4 trips a year + LCA/PyCon
• Significant autonomy (not at the expense of doing the right thing for the company, just I work best with the illusion of free will )
• Be doing something that matters
  • -> Being open source is one way to this, but not the only one
• Something cutting edge would be awesome
  • -> Rust / Haskell / High performance requirements / scale / ….
• Salary

How well did that work for me? Pretty good. I had a good satisfying job at VMware for 3 years, met some wonderful people, achieved some very cool things. And those priorities above were broadly achieved.
The one niggle that stands out was this – Did the things we were doing matter? Certainly there was no social impact – VMware isn’t a non-profit, being right at the core of capitalism as it is. There was direct connection and impact with the team, the staff we worked with and the users of the products… but it is just a bit hard to feel really connected through that though: VMware is a very large company and there are many layers between users and developers.

We were quite early adopters of Kubernetes, which allowed me to deepen my Go knowledge and experience some more fun with AWS scale operations. I had many interesting discussions about the relative strengths of Python Go and Rust and Java with colleagues there. (Hi Geoffrey).

Company culture is very important to me, and VMware has a fantastically supportive culture. One of the most supportive companies I’ve been in, bar none. It isn’t a truely remote-organised company though: rather its a bunch of offices that talk to each other, which I think is sad. True remote-first offers so much more engagement.

I enjoy building things to solve problems. I’ve either directly built, or shaped what is built, in all my most impactful and successful roles. Solving a problem once by hand is fine; solving it for years to come by creating a tool is far more powerful.

I seem to veer into toolmaking very often: giving other people the ability to solve their problems takes the power of a tool and multiplies it even further.

It should be no surprise then that I very much enjoy reading white papers like the original Dapper and Map-reduce ones, LinkedIn’s Kafka or for more recent fodder the Facebook Akkio paper. Excellent synthesis and toolmaking applied at industrial scale. I read those things and I want to be a part of the creation of those sorts of systems.

I was fortunate enough to take some time to go back to university part-time, which though logistically challenging is something I want to see through.

Thus I think my new roughly ordered (descending) list of priorities needs to be something like this:

• Keep living in Rangiora (family)
• Up to moderate travel requirements – 4 team-meeting trips a year + 2 conferences
• Significant autonomy (not at the expense of doing the right thing for the company, just I work best with the illusion of free will )
• Be doing something that matters
  • Be working directly on a problem / system that has problems
• Something cutting edge would be awesome
  • Rust / Haskell / High performance requirements / scale / ….
• A generative (Westrum definition) + supportive company culture
• Remote-first or at least very remote familiar environment
• Support my part time study / self improvement initiative
• Salary

Since moving down to Melbourne my poor sleep has started up again. It’s really hard to say what the main factor driving this is. My doctor down here has put me onto a drug free way of trying to improve my sleep, and I think I kind of like it, while it’s no silver bullet, it is something I can go back to if I’m having trouble with my sleep, without having to get a prescription.

The basic idea is to maximise sleep efficiency. If you’re only getting n hours sleep a night, only spend n hours  a night in bed. This forces you to stay up and go to bed rather late for a few nights. Hopefully, being tired will help you sleep through the night in one large segment. Once you’ve successfully slept through the night a few times, relax your bed time by say fifteen minutes, and get used to that. Slowly over time, you increase the amount of sleep you’re getting, while keeping your efficiency high.

With the upcoming federal election, many teachers want to do some related activities in class – and we have the materials ready for you! To make selecting suitable resources a bit easier, we have an Election Activity Bundle containing everything you need, available for just $9.90. Did you know that the secret ballot is an Australian […]

Navigation mesh encodes where in the game world an agent can stand, and where it can go. (here “agent” means bot, actor, enemy, NPC, etc)

At runtime, the main thing navigation mesh is used for is to find paths between points using an algorithm like A*: https://en.wikipedia.org/wiki/A*_search_algorithm

In Insomniac’s engine, navigation mesh is made of triangles. Triangle edge midpoints define a connected graph for pathfinding purposes.

In addition to triangles, we have off-mesh links (“Custom Nav Clues” in Insomniac parlance) that describe movement that isn’t across the ground. These are used to represent any kind of off-mesh connection – could be jumping over a car or railing, climbing up to a rooftop, climbing down a ladder, etc. Exactly what it means for a particular type of bot is handled by clue markup and game code.

These links are placed by artists and designers in the game environment, and included in prefabs for commonly used bot-traversable objects in the world, like railings and cars.

Navigation mesh makes a certain operations much, much simpler than it would be if done by trying to reason about render or physics geometry.

Our game work is made up of a lot of small objects, which are each typically made from many triangles.

Using render or physics geometry to answer the question “can this bot stand here” hundreds of times every frame is not scalable. (Sunset Overdrive had 33ms frames. That’s not a lot of time.)

It’s much faster to ask: is there navigation mesh where this bot is

Navigation mesh is relatively sparse and simple, so the question can be answered quickly. We pre-compute bounding volumes for navmesh, to make answering that question even faster, and if a bot was standing on navmesh last frame, it’s even less work to reason about where they are this frame.

In addition to path-finding, navmesh can be useful to quickly and safely limit movement in a single direction. We sweep lines across navmesh to find boundaries to clamp bot movement. For example, a bot animating through a somersault will have its movement through the world clamped to the edge of navmesh, rather than rolling off into who-knows-what.

(If you’re making a game where you want bots to be able to freely somersault in any direction, you can ignore the navmesh )

Building navmesh requires a complete view of the static world. The generated mesh is only correct when it accounts for all objects: interactions between objects affect the generated mesh in ways that are not easy (or fast) to reason about independently.

Intersecting objects can become obstructions to movement. Or they can form new surfaces that an agent can stand upon. You can’t really tell what it means to an agent until you mash it all together.

To do as little work as possible at runtime, we required *all* of the static objects to be loaded at one time to pre-build mesh for Sunset City.

We keep that pre-built navmesh loading during the game at all times. For the final version of the game (with both of the areas added via DLC) this required ~55MB memory.

We use Recast https://github.com/recastnavigation/recastnavigation to generate the triangle mesh, and (mostly for historical reasons) repack this into our own custom format.

Sunset Overdrive had two meshes: one for “normal” humanoid-sized bots (2m tall, 0.5m radius)

and one for “large” bots (4.5m tall, 1.35m radius)

Both meshes are generated as 16x16m tiles, and use a cell size of 0.125m when rasterizing collision geometry.

There were a few tools used in Sunset Overdrive to add some sense of dynamism to the static environment:

For pathfinding and bot-steering, we have runtime systems to control bot movement around dynamic obstacles.

For custom nav clues, we keep track of whether they are in use, to make it less likely that multiple bots are jumping over the same thing at the same time. This can help fan-out groups of bots, forcing them to take distinctly different paths.

Since Sunset Overdrive, we’ve added a dynamic obstruction system based on Detour https://github.com/recastnavigation/recastnavigation to temporarily cut holes in navmesh for larger impermanent obstacles like stopped cars or temporary structures.

We also have a way to mark-up areas of navmesh so that they can be toggled in a controlled fashion from script. It’s less flexible than the dyanamic obstruction system – but it is very fast: toggling flags for tris rather than retriangulation.

I spoke about Sunset Overdrive at the AI Summit a few years back – my slide deck is here:
Sunset City Express: Improving the NavMesh Pipeline in Sunset Overdrive

I can also highly recommend @AdamNoonchester‘s talk from GDC 2015:
AI in the Awesomepocalypse – Creating the Enemies of Sunset Overdrive

Here’s some navigation mesh, using the default in-engine debug draw (click for larger version)

What are we looking at? This is a top-down orthographic view of a location in the middle of Sunset City.

The different colors indicate different islands of navigation mesh – groups of triangles that are reachable from other islands via custom nav clues.
Bright sections are where sections of navmesh overlap in the X-Z plane.

There are multiple visualization modes for navmesh.

Usually, this is displayed over some in-game geometry – it exists to debug/understand the data in game and editor. Depending on what the world looks like, some colors are easier to read than others. (click for larger versions)

The second image shows the individual triangles – adjacent triangles do not reliably have different colors. And there is stable color selection as the camera moves, almost

Also, if you squint, you can make out the 16x16m tile boundaries, so you can get a sense of scale.

Here’s a map of the entirety of Sunset City:

“The Mystery of the Mooil Rig” DLC area:

“Dawn of the Rise of the Fallen Machine” DLC area:

Referencing the comments from up-thread, these maps represent the places where agents can be. Additionally, there is connectivity information – we have visualization for that as well.

This image has a few extra in-engine annotations, and some that I added:

The purple lines represent custom nav clues – one line in each direction that is connected.

Also marked are some railings with clues placed at regular intervals, a car with clues crisscrossing it, and moored boats with clues that allow enemies to chase the player.

Also in this image are very faint lines on the mesh that show connectivity between triangles. When a bot is failing to navigate, it can be useful to visualize the connectivity that the mesh thinks it has :)

The radio tower where the fight with Fizzie takes place:

The roller coaster:

The roller coaster tracks are one single, continuous and complete island of navmesh.

Navigation mesh doesn’t line up neatly with collision geometry, or render geometry. To make it easier to see, we draw it offset +0.5m up in world-space, so that it’s likely to be above the geometry it has been generated for. (A while ago, I wrote a full-screen post effect that drew onto rendered geometry based on proximity to navmesh. I thought it was pretty cool, and it was nicely unambiguous & imho easier to read – but I never finished it, it bitrot, and I never got back to it alas.)

Since shipping Sunset Overdrive, we added support for keeping smaller pieces of navmesh in memory – they’re now loaded in 128x128m parts, along with the rest of the open world.

@despair‘s recent technical postmortem has a little more on how this works:
‘Marvel’s Spider-Man’: A Technical Postmortem

Even so, we still load it all of an open world region to build the navmesh: the asset pipeline doesn’t provide information that is needed to generate navmesh for sub-regions efficiently & correctly, so it’s all-or-nothing. (I have ideas on how to improve this. One day…)

Let me know if you have any questions – preferably via twitter @twoscomplement

This post was originally a twitter thread:

It occurs to me that I never wrote up the end result of the support ticket I opened with iiNet after discovering significant evening packet loss on our fixed wireless NBN connection in August 2017.

The whole saga took about a month. I was asked to run a battery of tests (ping, traceroute, file download and speedtest, from a laptop plugged directly into the NTD) three times a day for three days, then send all the results in so that a fault could be lodged. I did this, but somehow there was a delay in the results being communicated, so that by the time someone actually looked at them, they were considered stale, and I had to run the whole set of tests all over again. It’s a good thing I work from home, because otherwise there’s no way it would be possible to spend half an hour three times a day running tests like this. Having finally demonstrated significant evening slowdowns, a fault was lodged, and eventually NBN Co admitted that there was congestion in the evenings.

We have investigated and the cell which this user is connected to experiences high utilisation during busy periods. This means that the speed of this service is likely to be reduced, particularly in the evening when more people are using the internet.

nbn constantly monitors the fixed wireless network for sites which require capacity expansion and we aim to upgrade site capacity before congestion occurs, however sometimes demand exceeds expectations, resulting in a site becoming congested.

This site is scheduled for capacity expansion in Quarter 4, 2017 which should result in improved performance for users on the site. While we endeavour to upgrade sites on their scheduled date, it is possible for the date to change.

I wasn’t especially happy with that reply after a support experience that lasted for a month, but some time in October that year, the evening packet loss became less, and the window of time where we experienced congestion shrank. So I guess they did do some sort of capacity expansion.

It’s been mostly the same since then, i.e. slower in the evenings than during the day, but, well, it could be worse than it is. There was one glitch in November or December 2018 (poor speed / connection issues again, but this time during the day) which resulted in iiNet sending out a new router, but I don’t have a record of this, because it was a couple of hours of phone support that for some reason never appeared in the list of tickets in the iiNet toolbox, and even if it had, once a ticket is closed, it’s impossible to click it to view the details of what actually happened. It’s just a subject line, status and last modified date.

Fast forward to Monday March 25 2019 – a day with a severe weather warning for damaging winds – and I woke up to 34% packet loss, ping times all over the place (32-494ms), continual disconnections from IRC and a complete inability to use a VPN connection I need for work. I did the power-cycle-everything dance to no avail. I contemplated a phone call to support, then tethered my laptop to my phone instead in order to get a decent connection, and decided to wait it out, confident that the issue had already been reported by someone else after chatting to my neighbour.

Tuesday morning it was still horribly broken, so I unplugged the router from the NTD, plugged a laptop straight in, and started running ping, traceroute and speed tests. Having done that I called support and went through the whole story (massive packet loss, unusable connection). They asked me to run speed tests again, almost all of which failed immediately with a latency error. The one that did complete showed about 8Mbps down, compared to the usual ~20Mbps during the day. So iiNet lodged a fault, and said there was an appointment available on Thursday for someone to come out. I said fine, thank you, and plugged the router back in to the NTD.

Curiously, very shortly after this, everything suddenly went back to normal. If I was a deeply suspicious person, I’d imagine that because I’d just given the MAC address of my router to support, this enabled someone to reset something that was broken at the other end, and fix my connection. But nobody ever told me that anything like this happened; instead I received a phone call the next day to say that the “speed issue” I had reported was just regular congestion and that the tower was scheduled for an upgrade later in the year. I thanked them for the call, then pointed out that the symptoms of this particular issue were completely different to regular congestion and that I was sure that something had actually been broken, but I was left with the impression that this particular feedback would be summarily ignored.

I’m still convinced something was broken, and got fixed. I’d be utterly unsurprised if there had been some problem with the tower on the Sunday night, given the strong winds, and it took ’til mid-Tuesday to get it sorted. But we’ll never know, because NBN Co don’t publish information about congestion, scheduled upgrades, faults and outages anywhere the general public can see it. I’m not even sure they make this information consistently available to retail ISPs. My neighbour, who’s with a different ISP, sent me a notice that says there’ll be maintenance/upgrades occurring on April 18, then again from April 23-25. There’s nothing about this on iiNet’s status page when I enter my address.

There was one time in the past few years though, when there was an outage that impacted me, and it was listed on iiNet’s status page. It said “customers in the area of Herringback may be affected”. I initially didn’t realise that meant me, as I’d never heard for a suburb, region, or area called Herringback. Turns out it’s the name of the mountain our NBN tower is on.

Back in 2010 the continuous delivery meme was just grabbing traction. Today its extremely well established… except in F/LOSS projects.

I want that to change, so I’m going to try and really bring together a technical view on how that could work – which may require multiple blog posts – and if it gets traction I’ll put my fingers where my thoughts are and get into specifics with any project that wants to do this.

This is however merely a worked model today: it may be possible to do things quite differently, and I welcome all discussion about the topic!

tl;dr

Pick a service discovery mechanism (e.g. environment variables), write two small APIs – one for flag delivery, with streaming updates, and one for telemetry, with an optional aggressive data hiding proxy, then use those to feed enough data to drive a true CI/CD cycle back to upstream open source projects.

Who is in?

Background

(This assumes you know what C/D is – if you don’t, go read the link above, maybe wikipedia etc, then come back.)

Consider a typical SaaS C/D pipeline:

Here all stages are owned by the one organisation. Once deployed, the build is usable by users – its basically the simplest pipeline around.

Now consider a typical on-premise C/D pipeline:

Here the last stage, the install stage, takes place in the users context, but it may be under the control of the create, or it may be under the control of the user. For instance, Google play updates on an Android phone: when one selects ‘Update Now’, the install phase is triggered. Leaving the phone running with power and Wi-Fi will trigger it automatically, and security updates can be pushed anytime. Continuing the use of Google Play as an example, the expose step here is an API call to upload precompiled packages, so while there are three parties, the distributor – Google – isn’t performing any software development activities (they do gatekeep, but not develop).

Where it gets awkward is when there are multiple parties doing development in the pipeline.

Distributing and C/D

Lets consider an OpenStack cloud underlay circa 2015: an operating system, OpenStack itself, some configuration management tool (or tools), a log egress tool, a metrics egress handler, hardware mgmt vendor binaries. And lets say we’re working on something reasonably standalone. Say horizon.

OpenStack for most users is something obtained from a vendor. E.g. Cisco or Canonical or RedHat. And the model here is that the vendor is responsible for what the user receives; so security fixes – in particular embargoed security fixes – cannot be published publically and the slowly propogate. They must reach users very quickly. Often, ideally, before the public publication.

Now we have something like this:

Can we not just say ‘the end of the C/D pipeline is a .tar.gz of horizon at the distribute step? Then every organisation can make their own decisions?

Maybe…

Why C/D?

• Lower risk upgrades (smaller changes that can be reasoned about better; incremental enablement of new implementations to limit blast radius, decoupling shipping and enablement of new features)
• Faster delivery of new features (less time dealing with failed upgrades == more time available to work on new features; finished features spend less time in inventory before benefiting users).
• Better code hygiene (the same disciplines needed to make C/D safe also make more aggressive refactoring and tidiness changes safer to do, so it gets done more often).

1. If the upstream C/D pipeline stops at a tar.gz file, the lower-risk upgrade benefit is reduced or lost: the pipeline isn’t able to actually push all the to installation, and thus we cannot tell when a particular upgrade workaround is no longer needed.

But Robert, that is the vendors problem!

I wish it was: in OpenStack so many vendors had the same problem they created shared branches to work on it, then asked for shared time from the project to perform C/I on those branches. The benefit is only realise when the developer who is responsible for creating the issue can fix it, and can be sure that the fix has been delivered; this means either knowing that every install will install transiently every intermediary version, or that they will keep every workaround for every issue for some minimum time period; or that there will be a pipeline that can actually deliver the software.

2. .tar.gz files are not installed and running systems. A key characteristic of a C/D pipeline is that is exercises the installation and execution of software; the ability to run a component up is quite tightly coupled to the component itself, for all the the ‘this is a process’ interface is very general, the specific ‘this is server X’ or ‘this is CLI utility Y’ interfaces are very concrete. Perhaps a container based approach, where a much narrower interface in many ways can be defined, could be used to mitigate this aspect. Then even if different vendors use different config tools to do last mile config, the dev cycle knows that configuration and execution works. We need to make sure that we don’t separate the teams and their products though: the pipeline upstream must only test code that is relevant to upstream – and downstream likewise. We may be able to find a balance here, but I think more work articulating what that looks like it needed.

3. it will break the feedback cycle if the running metrics are not receive upstream; yes we need to be careful of privacy aspects, but basic telemetry: the upgrade worked, the upgrade failed, here is a crash dump – these are the tools for sifting through failure at scale, and a number of open source projects like firefox, Ubuntu and chromium have adopted them, with great success. Notably all three have direct delivery models: their preference is to own the relationship with the user and gather such telemetry directly.

C/D and technical debt

Sidebar: ignoring public APIs and external dependencies, because they form the contract that installations and end users interact with, which we can reasonably expect to be quite sticky, the rest of a system should be entirely up to the maintainers right? Refactor the DB; Switch frameworks, switch languages. Cleanup classes and so on. With microservices there is a grey area: APIs that other microservices use which are not publically supported.

The grey area is crucial, because it is where development drag comes in: anything internal to the system can be refactored in a single commit, or in a series of small commits that is rolled up into one, or variations on this theme.

But some aspect that another discrete component depends upon, with its own delivery cycle: that cannot be fixed, and unless it was built with the same care public APIs were, it may well have poor scaling or performance characteristics that making fixing it very important.

Given two C/D’d components A and B, where A wants to remove some private API B uses, A cannot delete that API from its git repo until all B’s everywhere that receive A via C/D have been deployed with a version that does not use the private API.

That is, old versions of B place technical debt on A across the interfaces of A that they use. And this actually applies to public interfaces too – even if they are more sticky, we can expect the components of an ecosystem to update to newer APIs that are cheaper to serve, and laggards hold performance back, keep stale code alive in the codebase for longer and so on.

This places a secondary requirement on the telemetry: we need to be able to tell whether the fleet is upgraded or not.

So what does a working model look like?

I think we need a different diagram than the pipeline; the pipeline talks about the things most folk doing an API or some such project will have directly in hand, but its not actually the full story. The full story is rounded out with two additional features. Feature flags and telemetry. And since we want to protect our users, and distributors probably will simply refuse to provide insights onto actual users, lets assume a near-zero-trust model around both.

Feature flags

As I discussed in my previous blog post, feature flags can be used for fairly arbitrary purposes, but in this situation, where trust is limited, I think we need to identify the crucial C/D enabling use cases, and design for them.

I think that those can be reduce to soft launches – decoupling activating new code paths from getting them shipped out onto machines, and kill switches – killing off flawed / faulty code paths when they start failing in advance of a massive cascade failure; which we can implement with essentially the same thing: some identifier for a code path and then a percentage of the deployed base to enable it on. If we define this API with efficient streaming updates and a consistent service discovery mechanism for the flag API, then this could be replicated by vendors and other distributors or even each user, and pull the feature API data downstream in near real time.

Telemetry

The difficulty with telemetry APIs is that they can egress anything. OTOH this is open source code, so malicious telemetry would be visible. But we can structure it to make it harder to violate privacy.

What does the C/D cycle need from telemetry, and what privacy do we need to preserve?

This very much needs discussion with stakeholders, but at a first approximation: the C/D cycle depends on knowing what versions are out there and whether they are working. It depends on known what feature flags have actually activated in the running versions. It doesn’t depend on absolute numbers of either feature flags or versions

Using Google Play again as an example, there is prior art – https://support.google.com/firebase/answer/6317485 – but I want to think truely minimally, because the goal I have is to enable C/D in situations with vastly different trust levels than Google play has. However, perhaps this isn’t enough, perhaps we do need generic events and the ability to get deeper telemetry to enable confidence.

That said, let us sketch what an API document for that might look like:

project:
version:
health:
flags:
- name:
  value:

If that was reported by every deployed instance of a project, once per hour, maybe with a dependencies version list added to deal with variation in builds, it would trivially reveal the cardinality of reporters. Many reporters won’t care (for instance QA testbeds). Many will.

If we aggregate through a cardinality hiding proxy, then that vector is addressed – something like this:

- project:
  version:
  weight:
  health:
  flags:
  - name:
    value:
- project: ...

Because this data is really only best effort, such a proxy could be backed by memcache or even just an in-memory store, depending on what degree of ‘cloud-nativeness’ we want to offer. It would receive accurate data, then deduplicate to get relative weights, round those to (say) 5% as a minimum to avoid disclosing too much about long tail situations (and yes, the sum of 100 1% reports would exceed 100 :)), and then push that up.

Open Questions

• Should library projects report, or are they only used in the context of an application/service?
  • How can we help library projects answer questions like ‘has every user stopped using feature Y so that we can finally remove it’ ?
• Would this be enough to get rid of the fixation on using stable branches everyone seems to have?
  • If not why not?
• What have I forgotten?

Feature toggles, feature flags – they’ve been written about a lot already (use a search engine :)), yet I feel like writing a post about them. Why? I’ve been personally involved in two from-scratch implementations, and it may be interesting for folk to read about that.

I say that lots has been written; http://featureflags.io/ (which appears to be a bit of an astroturf site for LaunchDarkly ) nevertheless has gathered a bunch of links to literature as well as a number of SDKs and the like; there are *other* FFaaS offerings than LaunchDarkly; I have no idea which I would use for my next project at this point – but hopefully you’ll have some tools to reason about that at the end of this piece.

I’m going to entirely skip over the motivation (go read those other pieces), other than to say that the evidence is in, trunk based development is better.

A feature flag is a very simple thing: it is a value controlled outside of your development cycle that in turn controls the behaviour of your code. There are dozens of ways to implement that. hash-defines and compile time flags have been used for a very long time, so long that we don’t even think of them as feature flags, but they are are. So are configuration options in configuration files in the broadest possible sense. The difference is largely in focus, and where the same system meets all parties needs, I think its entirely fine to use just the one system – that is what we did for Launchpad, and it worked quite well I think – as far as I know it hasn’t been changed. Specifically in Launchpad the Zope runtime config is regular ZCML files on disk, and feature flags are complementary to that (but see the profiling example below).

Configuration tends to be thought of as “choosing behaviour after the system is compiled and before the process is started” – e.g. creating files on disk. But this is not always the case – some enterprise systems are notoriously flexible with database managed configuration rulesets which no-one can figure out – and we don’t want to create that situation.

Lets generalise things a little – a flag could be configured over the lifetime of the binary (compile flag), execution (runtime flag/config file or one-time evaluation of some dynamic system), time(dynamically reconfigured from changed config files or some dynamic system), or configured based on user/team/organisation, URL path (of a web request naturally :P), and generally any other thing that could be utilised in making a decision about whether to conditionally perform some code. It can also be useful to be able to randomly bucket some fraction of checks (e.g. 1/3 of all requests will go down this code path).. but do it consistently for the same browser.

Depending on what sort of system you are building, some of those sorts of scopes will be more or less important to you – for instance, if you are shipping on-premise software, you may well want to be turning unreleased features entirely off in the binary. If you are shipping a web API, doing soft launches with population rollouts and feature kill switches may be your priority.

Similarly, if you have an existing microservices architecture, having a feature flags aaS API is probably much more important (so that your different microservices can collaborate on in-progress features!) than if you have a monolithic DB where you put all your data today.

Ultimately you will end up with something that looks roughly like a key-value store: get_flag_value(flagname, context) -> value. Somewhere separate to your code base you will have a configuration store where you put rules that define how that key-value interface comes to a given value.

There are a few key properties that I consider beneficial in a feature flag systems:

• Graceful degradation
• Permissionless / (or alternatively namespaced)
• Loosely typed
• Observable
• Centralised
• Dynamic

Graceful Degradation

Feature flags will be consulted from all over the place – browser code, templates, DB mapper, data exporters, test harnesses etc. If the flag system itself is degraded, you need the systems behaviour to remain graceful, rather than stopping catastrophically. This often requires multiple different considerations; for instance, having sensible defaults for your flags (choose a default that is ok, change the meaning of defaults as what is ‘ok’ changes over time), having caching layers to deal with internet flakiness or API blips back to your flag store, making sure you have memory limits on local caches to prevent leaks and so forth. Different sorts of flag implementations have different failure modes : an API based flag system will be quite different to one stored in the same DB the rest of your code is using, which will be different to a process-startup command line option flag system.

A second dimension where things can go wrong is dealing with missing or unexpected flags. Remember that your system changes over time: a new flag in the code base won’t exist in the database until after the rollout, and when a flag is deleted from the codebase, it may still be in your database. Worse, if you have multiple instances running of a service, you may have different code all examining the same flag at the same time, so operations like ‘we are changing the meaning of a flag’ won’t take place atomically.

Permissions

Flags have dual audiences; one part is pure dev: make it possible to keep integration costs and risks low by merging fully integrated code on a continual basis without activating not-yet-ready (or released!) codepaths. The second part is pure operations: use flags to control access to dark launches, demo new features, killswitch parts of the site during attack mitigation, target debug features to staff and so forth.

Your developers need some way to add and remove the flags needed in their inner loop of development. Lifetimes of a few days for some flags.

Whoever is doing operations on prod though, may need some stronger guarantees – particularly they may need some controls over who can enable what flags. e.g. if you have a high control environment then team A shouldn’t be able to influence team B’s flags. One way is to namespace the flags and only permit configuration for the namespace a developer’s team(s) owns. Another way is to only have trusted individuals be able to set flags – but this obviously adds friction to processes.

Loose Typing

Some systems model the type of each flag: is it boolean, numeric, string etc. I think this is a poor idea mainly because it tends to interact poorly with the ephemeral nature of each deployment of a code base. If build X defines flag Y as boolean, and build X+1 defines it as string, the configuration store has to interact with both at the same time during rollouts, and do so gracefully. One way is to treat everything as a string and cast it to the desired type just in time, with failures being treated as default.

Observable

Make sure that when a user reports crazy weird behaviour, that you can figure out what value they had for what flags. For instance, in Launchpad we put them in the HTML.

Centralised

Having all your flags in one system lets you write generic tooling – such as ‘what flags are enabled in QA but not production’, or ‘what flags are set but have not been queried in the last month’. It is well worth the effort to build a single centralised system (or consume one such thing) and then use it everywhere. Writing adapters to different runtimes is relatively low overhead compared to rummaging through N different config systems because you can’t remember which one is running which platform.

Scope things in the system with a top level tenant / project style construct (any FFaaS will have this I’m sure :)).

Dynamic

There may be some parts of the system that cannot apply some flags rapidly, but generally speaking the less poking around that needs to be done to make something take effect the better. So build or buy a dynamic system, and if you want a ‘only on process restart’ model for some bits of it, just consult the dynamic system at the relevant time (e.g. during k8s Deployment object creation, or process startup, or …). But then everywhere else, you can react just-in-time; and even make the system itself be script driven.

The Launchpad feature flag system

I was the architect for Launchpad when the flag system was added. Martin Pool wanted to help accelerate feature development on Launchpad, and we’d all become aware of the feature flag style things hip groups like YouTube were doing; so he wrote a LEP: https://dev.launchpad.net/LEP/FeatureFlags , pushed that through our process and then turned it into code and docs (and once the first bits landed folk started using and contributing to it). Here’s a patch I wrote using the system to allow me to turn on Python profiling remotely. Here’s one added by William Grant to allow working around a crash in a packaging tool.

Launchpad has a monolithic data store, with bulk data federated out to various disk stores, but all relational data in one schema; we didn’t see much benefit in pushing for a dedicated API per se at that time – it can always be added later, as the design was deliberately minimal. The flags implementation is all in-process as a result, though there may be a JS thunk at this point – I haven’t gone looking. Permissions are done through trusted staff members, it is loosely typed and has an audit log for tracking changes.

The other one

The other one I was involved in was at VMware a couple years ago now; its in-house, but some interesting anecdotes I can share. The thinking on feature flags when I started the discussion was that they were strictly configuration file settings – I was still finding my feet with the in-house Xenon framework at the time (I think this was week 3 ? so I whipped up an API specification and a colleague (Tyler Curtis) turned that into a draft engine; it wasn’t the most beautiful thing but it was still going strong and being enhanced by the team when I left earlier this year. The initial implementation had a REST API and a very basic set of scopes. That lasted about 18 months before tenant based scopes were needed and added. I had designed it with the intent of adding multi-arm bandit selection down the track, but we didn’t make the time to develop that capability, which is a bit sad.

Comparing that API with LaunchDarkly I see that they do support A/B trials but don’t have multivariate tests live yet, which suggests that they are still very limited in that space. I think there is room for some very simple home grown work in this area to pay off nicely for Symphony (the project codename the flags system was written for).

Should you run your own?

It would be very unusual to have PII or customer data in the flag configuration store; and you shouldn’t have access control lists in there either (in LP we did allow turning on code by group, which is somewhat similar). Point is, that the very worst thing that can happen if someone else controls your feature flags and is malicious is actually not very bad. So as far as aaS vendor trust goes, not a lot of trust is needed to be pretty comfortable using one.

But, if you’re in a particularly high-trust environment, or you have no internet access, running your own may be super important, and then yeah, do it :). They aren’t big complex systems, even with multi-arm bandit logic added in (the difficulty there is the logic, not the processing).

Or if you think the prices being charged by the incumbents are ridiculous. Actually, perhaps hit me up and we’ll make a startup and do this right…

Should you build your own?

A trivial flag system + persistence could be as little as a few days work. Less if you grab an existing bolt-on for your framework. If you have multiple services, or teams, or languages.. expect that to become the gift that keeps on giving as you have to consolidate and converge across your organisation indefinitely. If you have the resources – great, not a problem.

I think most people will be better off taking one of the existing open source flag systems – perhaps https://unleash.github.io/ – and using it; even if it is more complex than a system tightly fitted to your needs, the benefit of having one that is a true API from the start will pay for itself the very first time you split a project, or want to report what features are on in dev and off in prod, not to mention multiple existing language bindings etc.

This has become substantially simpler in Fedora 29:

sudo dnf install notebook R-IRKernel R-IRdisplay

It might be tempting to use MP3's variable bit rate for encoding ripped foreign languages CDs. With the large periods of silence that would seem to make a lot of sense. But you lose the ability to rewind to an exact millisecond, which turns out to be essential as you want to hear a particular phrase a handful of times. So use CBR -- constant bit rate -- encoding, and at a high bit rate like 160kbps.

In case you want to choose a different security compromise, the update has a nice summary:

wpasupplicant (2:2.6-19) unstable; urgency=medium

  With this release, wpasupplicant no longer respects the system
  default minimum TLS version, defaulting to TLSv1.0, not TLSv1.2. If
  you're sure you will never connect to EAP networks requiring anything less
  than 1.2, add this to your wpasupplicant configuration:

    tls_disable_tlsv1_0=1
    tls_disable_tlsv1_1=1

  wpasupplicant also defaults to a security level 1, instead of the system
  default 2. Should you need to change that, change this setting in your
  wpasupplicant configuration:

    openssl_ciphers=DEFAULT@SECLEVEL=2

  Unlike wpasupplicant, hostapd still respects system defaults.

 -- Andrej Shadura <…@debian.org>  Sat, 15 Dec 2018 14:22:18 +0100

To find passwords in libsecret you need to know what attributes to search for. These are often set by some shim but not documented. The attributes tend to vary by shim.

For git's libsecret shim the attributes are: protocol, server, user.

A worked example, the account gdt on git.example.org:

$ secret-tool search --all 'protocol' 'https' 'server' 'git.example.org' 'user' 'gdt'
[/org/freedesktop/secrets/collection/login/123]
label = Git: https://git.example.org/
secret = CvKxlezMsSDuR7piMBTzREJ7l8WL1T
created = 2019-02-01 10:20:34
modified = 2019-02-01 10:20:34
schema = org.gnome.keyring.NetworkPassword
attribute.protocol = https
attribute.server = git.example.org
attribute.user = gdt

Note that the "label" is mere documentation, it's the "attribute" entries which matter.

On January 21, 2019 I presented Distributed Storage is Easier Now: Usability from Ceph Luminous to Nautilus at the linux.conf.au 2019 Systems Administration Miniconf. Thanks to the incredible Next Day Video crew, the video was online the next day, and you can watch it here:

If you’d rather read than watch, the meat of the talk follows, but before we get to that I have two important announcements:

1. Cephalocon 2019 is coming up on May 19-20, in Barcelona, Spain. The CFP is open until Friday February 1, so time is rapidly running out for submissions. Get onto it.
2. If you’re able to make it to FOSDEM on February 2-3, there’s a whole Software Defined Storage Developer Room thing going on, with loads of excellent content including What’s new in Ceph Nautilus – project status update and preview of the coming release and Managing and Monitoring Ceph with the Ceph Manager Dashboard, which will cover rather more than I was able to here.

Back to the talk. At linux.conf.au 2018, Sage Weil presented “Making distributed storage easy: usability in Ceph Luminous and beyond”. What follows is somewhat of a sequel to that talk, covering the changes we’ve made in the meantime, and what’s still coming down the track. If you’re not familiar with Ceph, you should probably check out A Gentle Introduction to Ceph before proceeding. In brief though, Ceph provides object, block and file storage in a single, horizontally scalable cluster, with no single points of failure. It’s Free and Open Source software, it runs on commodity hardware, and it tries to be self-managing wherever possible, so it notices when disks fail, and replicates data elsewhere. It does background scrubbing, and it tries to balance data evenly across the cluster. But you do still need to actually administer it.

This leads to one of the first points Sage made this time last year: Ceph is Hard. Status display and logs were traditionally difficult to parse visually, there were (and still are) lots of configuration options, tricky authentication setup, and it was difficult to figure out the number of placement groups to use (which is really an internal detail of how Ceph shards data across the cluster, and ideally nobody should need to worry about it). Also, you had to do everything with a CLI, unless you had a third-party GUI.

I’d like to be able to flip this point to the past tense, because a bunch of those things were already fixed in the Luminous release in August 2017; status display and logs were cleaned up, a balancer module was added to help ensure data is spread more evenly, crush device classes were added to differentiate between HDDs and SSDs, a new in-tree web dashboard was added (although it was read-only, so just cluster status display, no admin tasks), plus a bunch of other stuff.

But we can’t go all the way to saying “Ceph was hard”, because that might imply that everything is now easy. So until we reach that frabjous day, I’m just going to say that Ceph is easier now, and it will continue to get easier in future.

At linux.conf.au in January 2018, we were half way through the Mimic development cycle, and at the time the major usability enhancements planned included:

• Centralised configuration management
• Slick deployment in Kubernetes with Rook
• A vastly improved dashboard based on ceph-mgr and openATTIC
• Placement Group merging

We got some of that stuff done for Mimic, which was released in June 2018, and more of it is coming in the Nautilus release, which is due out very soon.

In terms of usability improvements, Mimic gave us a new dashboard, inspired by and derived from openATTIC. This dashboard includes all the features of the Luminous dashboard, plus username/password authentication, SSL/TLS support, RBD and RGW management, and a configuration settings browser. Mimic also brought the ability to store and manage configuration options centrally on the MONs, which means we no longer need to set options in /etc/ceph/ceph.conf, replicate that across the cluster, and restart whatever daemons were affected. Instead, you can run `ceph config set ...` to make configuration changes. For initial cluster bootstrap, you can even use DNS SRV records rather than specifying MON hosts in the ceph.conf file.

As I mentioned, the Nautilus release is due out really soon, and will include a bunch more good stuff:

• PG autoscaling:
  • Because we now have PG merging (as well as PG splitting) we can now decrease or increase the number of PGs at will. So you can do this by hand, or you can turn on PG autoscaling, and Ceph will try to take care of this for you, based on certain storage size targets that you can set (see http://docs.ceph.com/docs/master/rados/operations/placement-groups/#autoscaling-placement-groups)
• More dashboard enhancements, including:
  • Multiple users/roles, also single sign on via SAML
  • Internationalisation and localisation
  • iSCSI and NFS Ganesha management
  • Embedded Grafana dashboards
  • The ability to mark OSDs up/down/in/out, and trigger scrubs/deep scrubs
  • Storage pool management
  • A configuration settings editor which actually tells you what the configuration settings mean, and do
  • Embedded Grafana dashboards
  • To see what this all looks like, check out Ceph Manager Dashboard Screenshots as of 2019-01-17
• Blinky lights, that being the ability to turn on or off the ident and fault LEDs for the disk(s) backing a given OSD, so you can find the damn things in your DC.
• Orchestrator module(s)

Blinky lights, and some of the dashboard functionality (notably configuring iSCSI gateways and NFS Ganesha) means that Ceph needs to be able to talk to whatever tool it was that deployed the cluster, which leads to the final big thing I want to talk about for the Nautilus release, which is the Orchestrator modules.

There’s a bunch of ways to deploy Ceph, and your deployment tool will always know more about your environment, and have more power to do things than Ceph itself will, but if you’re managing Ceph, through the inbuilt dashboard and CLI tools, there’s things you want to be able to do as a Ceph admin, that Ceph itself can’t do. Ceph can’t deploy a new MDS, or RGW, or NFS Ganesha host. Ceph can’t deploy new OSDs by itself. Ceph can’t blink the lights on a disk on some host if Ceph itself has somehow failed, but the host is still up. For these things, you rely on your deployment tool, whatever it is. So Nautilus will include Orchestrator modules for Ansible, DeepSea/Salt, and Rook/Kubernetes, which allow the Ceph management tools to call out to your deployment tool as necessary to have it perform those tasks. This is the bit I’m working on at the moment.

Beyond Nautilus, Octopus is the next release, due in a bit more than nine months, and on the usability front I know we can expect more dashboard and more orchestrator functionality, but before that, we have the Software Defined Storage Developer Room at FOSDEM on February 2-3 and Cephalocon 2019 on May 19-20. Hopefully some of you reading this will be able to attend

Update 2019-02-04: Check out Sage’s What’s new in Ceph Nautilus FOSDEM talk for much more detail on what’s coming up in Nautilus and beyond.

• Implementable - BGP implementations must be able to implement it, and do so correctly, ideally with a minimum of effort.
• Deployable - Networks need to be able to deploy it, when authentication issues occur error messages should be no worse than with standard BGP (this is an area most TCP-MD5 implementations fail at, of those I've used JunOS is a notable exception, Linux required kernel changes for it to even be *possible* to debug)

• Two BGP implementations, not derived from the same source.
• Using two TLS implementations, not derived from the same source.
• Running on two kernels (at the very least, Linux & FreeBSD)

• Using a zero-length BGP capability in the BGP OPEN message implementations advertise their support for TLS
  • TLS version MUST be at least 1.3
  • If TLS is required, the AS field in the OPEN MAY be set to a well-known value to prevent information leakage, and other capabilities MAY be removed, however implementations MUST NOT require the TLS capability be the first, last or only capability in the OPEN
  • If TLS is optional, which MUST NOT be default behaviour), the OPEN MUST be (other than the capability) be the same as a session configured for no encryption
• After the TCP client receives a conformation of TLS support from the TCP server's OPEN message, a TLS handshake begins
  • To make this deployable TLS-PSK MUST be supported, although exact configuration is TBD.
  • Authentication-only variants of TLS (ex RFC4785) REALLY SHOULD NOT be supported.
  • Standard certificate-based verification MAY be supported, and if supported MUST validate use client certificates, validating both. However, how roots of trust would work for this has not been investigated.
• Once the TCP handshake completes the BGP state starts over with the client sending a new OPEN
  • Signalling the TLS capability in this OPEN is invalid and MUST be rejected
• (From here, everything is unchanged from normal BGP)

• Capability: (to be referred to as EXPERIMENTAL-STARTTLS) 219
• ASN (for avoiding data leaks in OPEN messages): 123456
  • Yes this means also sending 4-byte capability. Every implementation that might possibly implement this already supports 4-byte ASNs.

I am extremely pleased to announce the public release of pwnedkeys.com – a database of compromised asymmetric encryption keys. I hope this will become the go-to resource for anyone interested in avoiding the re-use of known-insecure keys. If you have a need, or a desire, to check whether a key you’re using, or being asked to accept, is potentially in the hands of an adversary, I would encourage you to take a look.

Pwnage... EVERYWHERE

By now, most people in the IT industry are aware of the potential weaknesses of passwords, especially short or re-used passwords. Using a password which is too short (or, more technically, with “insufficient entropy”) leaves us open to brute force attacks, while re-using the same password on multiple sites invites a credential stuffing attack.

It is rare, however, that anyone thinks about the “quality” of RSA or ECC keys that we use with the same degree of caution. There are so many possible keys, all of which are “high quality” (and thus not subject to “brute force”), that we don’t imagine that anyone could ever compromise a private key except by actually taking a copy of it off our hard drives.

There is a unique risk with the use of asymmetric cryptography, though. Every time you want someone to encrypt something to you, or verify a signature you’ve created, you need to tell them your public key. While someone can’t calculate your private key from your public key, the public key does have enough information in it to be able to identify your private key, if someone ever comes across it.

So what?

The risk here is that, in many cases, a public key truly is public. Every time your browser connects to a HTTPS-protected website, the web server sends a copy of the site’s public key (embedded in the SSL certificate). Similarly, when you connect to an SSH server, you get the server’s public key as part of the connection process. Some services provide a way for anyone to query a user’s public keys.

Once someone has your public key, it can act like an “index” into a database of private keys that they might already have. This is only a problem, of course, if someone happens to have your private key in their stash. The bad news is that there are a lot of private keys already out there, that have either been compromised by various means (accident or malice), or perhaps generated by a weak RNG.

When you’re generating keys, you usually don’t have to worry. The chances of accidentally generating a key that someone else already has is as close to zero as makes no difference. Where you need to be worried is when you’re accepting public keys from other people. Unlike a “weak” password, you can’t tell a known-compromised key just by looking at it. Even if you saw the private key, it would look just as secure as any other key. You cannot know whether a public key you’re being asked to accept is associated with a known-compromised private key. Or you couldn’t, until pwnedkeys.com came along.

The solution!

The purpose of pwnedkeys.com is to try and collect every private key that’s ever gotten “out there” into the public, and warn people off using them ever again. Don’t think that people don’t re-use these compromised keys, either. One of the “Debian weak keys” was used in an SSL certificate that was issued in 2016, some eight years after the vulnerability was made public!

My hope is that pwnedkeys.com will come to be seen as a worthwhile resource for anyone who accepts public keys, and wants to know that they’re not signing themselves up for a security breach in the future.

The world needs it, so I may as well write it.

• The number of items on a page is fixed for all time.
• The number of items on a page is fixed for one user.
• The number of items on a page is fixed for one result set.
• The pages are only browsed in one direction.
• No item will be added to the result set during retrieval.
• No item will be removed from the result set during retrieval.
• Item sort order is stable.
• Only one page of results will be retrieved at one time.
• Pages will be retrieved in order.
• Pages will be retrieved in a timely manner.
• No problem will result from two different users seeing different pagination of the same items at about the same time. (From @ronburk)

Are you considering implementing our integrated HASS+Science program, but getting a tad confused by the pricing?  Our subscription model didn’t not provide a So nowstraightforward calculation for a whole school or year-level.  However, it generally works out to $4.40 (inc.GST) per student.  So now we’re providing this as an option directly: implement our integrated HASS+Science program […]

Jamie Pride has partnered with Swinburne University and Dr Bronwyn Eager to conduct the largest mental health and well-being survey of Australian entrepreneurs and founders. This survey will take approx 5 minutes to complete. Can you also please spread the word and share this via your networks!

Getting current and relevant Australian data is extremely important! The findings of this study will contribute to the literature on mental health and well-being in entrepreneurs, and that this will potentially lead to future improvements in the prevention and treatment of psychological distress.

Jamie is extremely passionate about this cause! Your help is greatly appreciated.

https://www.weforum.org/agenda/2018/10/singapore-has-abolished-school-exam-rankings-here-s-why The island nation is changing its educational focus to encourage school children to develop the life skills they will need when they enter the world of work.

The end of the school year is fast approaching with the third term either over or about to end and the start of the fourth term looming ahead. There never seems to be enough time in the last term with making sure students have met all their learning outcomes for the year and with final […]

In 2008 a new group of human ancestors – the Denisovans, were defined on the basis of a single finger knuckle (phalanx) bone discovered in Denisova cave in the Altai mountains of Siberia. A molar tooth, found at Denisova cave earlier (in 2000) was determined to be of the same group. Since then extensive work […]

Now that the paperwork has finally all been dealt with, I can announce that I’ll be moving down to Melbourne to take up a position with the Australian Synchrotron, basically a super duper x-ray machine used for research of all types. My official position is a >in< Senior Scientific Software Engineer <out> I’ll be moving down to Melbourne shortly, staying with friends (you remember that offer you made, months ago?) until I find a rental near Monash Uni, Clayton.

I will be leaving behind Humbug, the computer group that basically opened up my entire career, and The Edge, SLQ, my home-away-from-home study. I do hope to be able to find replacements for these down south.

The end of August and beginning of September is traditionally linked to the beginning of Spring in Australia, although the change in seasons is experienced in different ways in different parts of the country and was marked in locally appropriate ways by Aboriginal people. As a uniquely Australian celebration of Spring, National Wattle Day, celebrated […]

Janet Hawtin Reid (@lucychili) sadly passed away last week.

A mutual friend called me a earlier in the week to tell me, for which I’m very grateful.  We both appreciate that BlueHackers doesn’t ever want to be a news channel, so I waited writing about it here until other friends, just like me, would have also had a chance to hear via more direct and personal channels. I think that’s the way these things should flow.

I knew Janet as a thoughtful person, with strong opinions particularly on openness and inclusion.  And as an artist and generally creative individual,  a lover of nature.  In recent years I’ve also seen her produce the most awesome knitted Moomins.

Short diversion as I have an extra connection with the Moomin stories by Tove Jansson: they have a character called My, after whom Monty Widenius’ eldest daughter is named, which in turn is how MySQL got named.  I used to work for MySQL AB, and I’ve known that My since she was a little smurf (she’s an adult now).

I’m not sure exactly when I met Janet, but it must have been around 2004 when I first visited Adelaide for Linux.conf.au.  It was then also that Open Source Industry Australia (OSIA) was founded, for which Janet designed the logo.  She may well have been present at the founding meeting in Adelaide’s CBD, too.  Anyhow, Janet offered to do the logo in a conversation with David Lloyd, and things progressed from there. On the OSIA logo design, Janet wrote:

I’ve used a star as the current one does [an earlier doodle incorporated the Southern Cross]. The 7 points for 7 states [counting NT as a state]. The feet are half facing in for collaboration and half facing out for being expansive and progressive.

You may not have realised this as the feet are quite stylised, but you’ll definitely have noticed the pattern-of-7, and the logo as a whole works really well. It’s a good looking and distinctive logo that has lasted almost a decade and a half now.

As Linux Australia’s president Kathy Reid wrote, Janet also helped design the ‘penguin feet’ logo that you see on Linux.org.au.  Just reading the above (which I just retrieved from a 2004 email thread) there does seem to be a bit of a feet-pattern there… of course the explicit penguin feet belong with the Linux penguin.

So, Linux Australia and OSIA actually share aspects of their identity (feet with a purpose), through their respective logo designs by Janet!  Mind you, I only realised all this when looking through old stuff while writing this post, as the logos were done at different times and only a handful of people have ever read the rationale behind the OSIA logo until now.  I think it’s cool, and a fabulous visual legacy.

Which brings me to a related issue that’s close to my heart, and I’ve written and spoken about this before.  We’re losing too many people in our community – where, in case you were wondering, too many is defined as >0.  Just like in a conversation on the road toll, any number greater than zero has to be regarded as unacceptable. Zero must be the target, as every individual life is important.

There are many possible analogies with trees as depicted in the above artwork, including the fact that we’re all best enabled to grow further.

Please connect with the people around you.  Remember that connecting does not necessarily mean talking per-se, as sometimes people just need to not talk, too.  Connecting, just like the phrase “I see you” from Avatar, is about being thoughtful and aware of other people.  It can just be a simple hello passing by (I say hi to “strangers” on my walks), a short email or phone call, a hug, or even just quietly being present in the same room.

We all know that you can just be in the same room as someone, without explicitly interacting, and yet feel either connected or disconnected.  That’s what I’m talking about.  Aim to be connected, in that real, non-electronic, meaning of the word.

If you or someone you know needs help or talk right now, please call 1300 659 467 (in Australia – they can call you back, and you can also use the service online).  There are many more resources and links on the BlueHackers.org website.  Take care.

At the start of July, the LCA2019 team announced that the Call for Proposals for linux.conf.au 2019 were open! This Call for Proposals will close on July 30. If you want to submit a proposal, you don't have much time!

linux.conf.au is one of the best-known community driven Free and Open Source Software conferences in the world. In 2019 we welcome you to join us in Christchurch, New Zealand on Monday 21 January through to Friday 25 January.

For full details including those not covered by this announcement visit https://linux.conf.au/call-for-papers/, and the full announcement is here.

IMPORTANT DATES

• Call for Proposals Opens: 2 July 2018
• Call for Proposals Closes: 30 July 2018 (no extensions)
• Notifications from the programme committee: early-September 2018
• Conference Opens: 21st January 2019

• I ended up buying the wrong USB connectors for the footprint I chose (the same thing happened with the first run of USB-C modules I did in 2016), and while I could bodge them into use easily enough there wasn't enough mechanical retention so I ended up ripping one connector off the board. I ordered some correct ones, but because I wasn't able to wick all solder off the pads they don't attach as strongly as they should, and whilst less fragile, are hardly what I'd call solid.
• The surface mount GPS antenna (Taoglas AP.10H.01 visible in this tweet) I used was 11dB higher gain than the antenna I'd tested with the devkit, I never managed to get it to lock while connected to the board, although once on a cable it did work ok. To allow easier testing, in the end I removed the antenna and bodged on an SMA connector for easy testing.
• When selecting the buffer I accidentally chose one with an open-drain output, I'd meant to use one with a push-pull output. This took quite a silly long time for me to realise what mistake I'd made. Compounding this, the buffer is on the 1PPS line, which only strobes while locked to GPS, however my apartment is a concrete box, with what GPS signal I can get inside only available in my bedroom, and my oscilloscope is in my lab, so I couldn't demonstrate the issue live, and had to inject test signals. Luckily a push-pull is available in the same footprint, and a quick hot-air aided swap later (once parts arrived from Digikey) it was fixed.

• Yes I can solder down to ~0.5mm pitch, but not reliably.
• More test points on dev boards, particularly all voltage rails, and notable signals not otherwise exposed.
• Flux is magic, you probably aren't using enough.

This thread happened…

Choose:

— Elan Ruskin (@despair) May 24, 2018

What is the type of x?

— Jonathan Adamczewski (@twoscomplement) May 24, 2018

std::optional<std::any>

— Andreas Fredriksson (@deplinenoise) May 24, 2018

I’ll see your C++17, and raise you C89:#define x rand()

— Jonathan Adamczewski (@twoscomplement) May 24, 2018

auto x = []() { return rand(); }

— Andreas Fredriksson (@deplinenoise) May 24, 2018

tsk tsk… that’s not mordern enough: auto x = []() { std::random_device rd; std::mt19937 gen(rd()); std::uniform_int_distribution<> dis(0, 32767); return dis(gen); } <— FIXED IT FOR YOU!

— Bobby Anguelov (@BobbyAnguelov) May 24, 2018

So, rand() assembles to ‘jmp rand’. That abomination on the other hand.. My eyes! https://t.co/ujNkLrzavs

— Andreas Fredriksson (@deplinenoise) May 24, 2018

So I did a little digging to satisfy my own curiosity about the “modern C++” version, and have learned a few things that I didn’t know previously…

(this is a manual unrolled twitter thread that starts here, with slight modifications)

Nearly all of this I gleaned from the invaluable http://cppreference.com  and http://godbolt.org . Comments about implementation refer specifically to the gcc-8.1 C++ standard library, examined using Compiler Explorer and the -E command line option.

std::random_device is a platform-specific source of entropy.

std: mt19937 is a parameterized typedef of std::mersenne_twister_engine

specifically:
std::mersenne_twister_engine<uint_fast32_t, 32, 624, 397, 31, 0x9908b0df, 11, 0xffffffff, 7, 0x9d2c5680, 15, 0xefc60000, 18, 1812433253>
(What do those number mean? I don’t know.)

And std::uniform_int_distribution produces uniformly distributed random numbers over a specified range, from a provided generator.

The default constructor for std::random_device takes an implementation-defined argument, with a default value.

The meaning of the argument is implementation-defined – but the type is not: std::string. (I’m not sure why a dynamically modifiable string object was the right choice to be the configuration parameter for an entropy generator.)

There are out-of-line private functions for much of this implementation of std::random_device. The constructor that calls the out-of-line init function is itself inline – so the construction and destruction of the default std::string param is also generated inline.

Also, peeking inside std::random_generator, there is a union with two members:

void* _M_file, which I guess would be used to store a file handle for /dev/urandom or similar.

std::mt19937 _M_mt, which is a … parameterized std::mersenne_twister_engine object.

So it seems reasonable to me that if you can’t get entropy* from outside your program, generate your own approximation. It looks like it is possible that the entropy for the std::mersenne_twister_engine will be provided by a std::mersenne_twister_engine.

Unlike std::random_device, which has its implementation out of line, std::mersenne_twister_engine‘s implementation seems to be all inline. It is unclear what benefits this brings, but it results in a few hundred additional instructions generated.

And then there’s std::uniform_int_distribution, which seems mostly unsurprising. It is again fully inline, which (from a cursory eyeballing) may allow a sufficiently insightful compiler to avoid a couple of branches and function calls.

The code that got me started on this was presented in jest – but (std::random_device + std::mt19937 + std::uniform_int_distribution) is a commonly recommended pattern for generating random numbers using these modern C++ library features.

My takeaways:
std::random_device is potentially very expensive to use – and doesn’t provide strong cross-platform guarantees about the randomness it provides. It is configured with an std::string – the meaning of which is platform dependent. I am not compelled to use this type.

std::mt19937 adds a sizeable chunk of codegen via its inline implementation – and there are better options than Mersenne Twister.

Bottom line: I’m probably going to stick with rand(), and if I need something a little fancier, http://www.pcg-random.org/ or one of the other suggestions provided as replies to the twitter thread.

Addition: the code I was able to gather, representing some relevant parts

I am now actively looking for work, ideally something with Unix/C/Python in the research/open source/not-for-proft space. My long out of date resume has been updated.

So Australia’s long-term accepted refugee detainees on Manus and Nauru will not be able to migrate to the US, if they come from a country that’s on Trump’s list.  So anyone from a particular set of countries is classified as bad.  Because Muslim.

Fundamentally of course, these fellow humans should not be detained at all. They have been accepted as genuine refugees by the Australian immigration department.  Their only “crime”, which is not actually a crime by either Australian or International law, was to arrive by boat.  They are now, as a group, abused as deterrent marketing material.  Anyone coming by boat to Australia is classified as bad.  Because boat (although stats actually indicate that it might correlate better with skin colour).

My grandfather, a surgeon at a Berlin hospital, lost his job on the same day that Hitler was elected.  Since not even decrees move that quickly and the exclusion of jews from  particular professions happened gradually over the 1930s, we can only assume that the hospital management contained some overzealous individuals, who took initiatives that they thought would be looked on favourably by their new superiors. Because Jew.

The Berlin events are a neat example of how a hostile atmosphere enables certain behaviour – of course, if you’d asked the superiors, they didn’t order any such thing and it had nothing to do with them. Sound familiar?

Via jiggly paths, my family came to the UK.  Initially interned.  Because German.

My grandfather, whom as I mentioned was an accomplished surgeon, had to re-do all his medical education in Britain – during that period he was separated from his wife and two young daughters (Scotland vs the south of England – a long way in the 1930s).  Because [the qualifications and experience] not British.  Possibly also Because German.

Hassles with running a practice, and being allowed a car.  Because German.

Then allowed those things.  Because Useful.  He was still a German Jew though….

I mentioned this, because other refugees at the time would have had the same rules applied, but my grandfather had the advantage of his profession and thus being regarded as useful.  Others would not have had that benefit.  This means that people were being judged “worthy” merely based on their immediate usefulness to the local politics of the day, not for being a fellow human being in need, or any other such consideration.

Group Labels and Value Judgements

Any time we classify some group as more or less worthy than another group or set of groups, trouble will follow – both directly, and indirectly.  Every single time.  And the trouble will affect everybody, it’s not selective to some group(s).  Also every time.  Historically verifiable.

Populists simplify, for political gain.  Weak leaders pander to extreme elements, in the hope that it will keep them in power.

The method of defining groups doesn’t matter, nor does one need to add specific “instructions”. The “Blue Eye experiment” proved this. The nasties are initiated merely through a “simple” value judgement of one group vs another.  That’s all that’s required, and the bad consequences are all implied and in a way predetermined.  Trouble will follow, and it’s not going to end well.

Identity

It’s fine to identify as a member of a particular group, or more  likely multiple groups as many factors overlap.  That is part of our identity.  But that’s is not the same as passing a judgement on the relative value of one of those groups vs another group.

• Brown vs blue eyes
• Muslim vs Christian vs Jew
• White vs black “race”
• One football club vs another

It really doesn’t matter.  Many of these groupings are entirely arbitrary.  The concept of “race” has no scientific basis, we humans are verifiably a single species.

You can make up any arbitrary classification.  It won’t make a difference.  It doesn’t matter.  The outcomes will be the same.

Given what we know about these dynamics, anyone making such value judgements is culpable.  If they’re in a leadership position, I’d suggest that any utterances in that realm indicate either incompetence or criminal intent. Don’t do that.

Don’t accept it.  Don’t ignore it.  Don’t pander to it.  Don’t vote for it.

Speak up and out against it.  For everybody’s sake.  Because I assure you, every single example in history shows that it comes back to bite everyone.  So even if you don’t really feel a connection with people you don’t know, it’ll come and bite you and yours, too.

It’s rearing its ugly head, again, and if we ignore it it will bite us. Badly. Just like any previous time in history.  Guaranteed.

• I failed to add any test pins, given this was the first try I really should have, being able to inject power just before the switching convertor was helpful while debugging, but I had to solder wires to the input cap to do that.
• Similarly, I should have had a 5v output pin, for now I've just been shorting the two diodes I had near the output which were intended to let me switch input power between two feeds.
• The last, and the only actual problem with the circuit was that when selecting which exact parts to use I optimised by choosing the same diode for both input protection & switching, however this was a mistake, as the switcher needed a Schottky diode, and one with better ratings in other ways than the input diode. With the incorrect diode the board actually worked fine under low loads, but would quickly go into thermal shutdown if asked to supply more than about 1W. With the diode swapped to a correctly rated one it now supplies 10W just fine.
• While debugging the previous I also noticed that the thermal pads on both main chips weren't well connected through. It seems the combination of via-in-thermal-pad (even tented), along with Kicad's normal reduction in paste in those large pads, plus my manufacturer's use of a fairly thin application of paste all contributed to this. Next time I'll probably avoid via-in-pad.