After seven years of service as member and secretary on the GHC Steering Committee, I have resigned from that role. So this is a good time to look back and retrace the formation of the GHC proposal process and committee. In my memory, I helped define and shape the proposal process, optimizing it for effectiveness and throughput, but memory can be misleading, and judging from the paper trail in my email archives, this was indeed mostly Ben Gamari s and Richard Eisenberg s achievement: Already in Summer of 2016, Ben Gamari set up the ghc-proposals Github repository with a sketch of a process and sent out a call for nominations on the GHC user s mailing list, which I replied to. The Simons picked the first set of members, and in the fall of 2016 we discussed the committee s by-laws and procedures. As so often, Richard was an influential shaping force here.

Three ingredients For example, it was him that suggested that for each proposal we have one committee member be the Shepherd , overseeing the discussion. I believe this was one ingredient for the process effectiveness: There is always one person in charge, and thus we avoid the delays incurred when any one of a non-singleton set of volunteers have to do the next step (and everyone hopes someone else does it). The next ingredient was that we do not usually require a vote among all members (again, not easy with volunteers with limited bandwidth and occasional phases of absence). Instead, the shepherd makes a recommendation (accept/reject), and if the other committee members do not complain, this silence is taken as consent, and we come to a decision. It seems this idea can also be traced back on Richard, who suggested that once a decision is requested, the shepherd [generates] consensus. If consensus is elusive, then we vote. At the end of the year we agreed and wrote down these rules, created the mailing list for our internal, but publicly archived committee discussions, and began accepting proposals, starting with Adam Gundry s OverloadedRecordFields. At that point, there was no secretary role yet, so how I did become one? It seems that in February 2017 I started to clean-up and refine the process documentation, fixing bugs in the process (like requiring authors to set Github labels when they don t even have permissions to do that). This in particular meant that someone from the committee had to manually handle submissions and so on, and by the aforementioned principle that at every step there ought to be exactly one person in change, the role of a secretary followed naturally. In the email in which I described that role I wrote:

Simon already shoved me towards picking up the secretary hat, to reduce load on Ben.

So when I merged the updated process documentation, I already listed myself secretary . It wasn t just Simon s shoving that put my into the role, though. I dug out my original self-nomination email to Ben, and among other things I wrote:

I also hope that there is going to be clear responsibilities and a clear workflow among the committee. E.g. someone (possibly rotating), maybe called the secretary, who is in charge of having an initial look at proposals and then assigning it to a member who shepherds the proposal.

So it is hardly a surprise that I became secretary, when it was dear to my heart to have a smooth continuous process here. I am rather content with the result: These three ingredients single secretary, per-proposal shepherds, silence-is-consent helped the committee to be effective throughout its existence, even as every once in a while individual members dropped out.

Ulterior motivation I must admit, however, there was an ulterior motivation behind me grabbing the secretary role: Yes, I did want the committee to succeed, and I did want that authors receive timely, good and decisive feedback on their proposals but I did not really want to have to do that part. I am, in fact, a lousy proposal reviewer. I am too generous when reading proposals, and more likely mentally fill gaps in a specification rather than spotting them. Always optimistically assuming that the authors surely know what they are doing, rather than critically assessing the impact, the implementation cost and the interaction with other language features. And, maybe more importantly: why should I know which changes are good and which are not so good in the long run? Clearly, the authors cared enough about a proposal to put it forward, so there is some need and I do believe that Haskell should stay an evolving and innovating language but how does this help me decide about this or that particular feature. I even, during the formation of the committee, explicitly asked that we write down some guidance on Vision and Guideline ; do we want to foster change or innovation, or be selective gatekeepers? Should we accept features that are proven to be useful, or should we accept features so that they can prove to be useful? This discussion, however, did not lead to a concrete result, and the assessment of proposals relied on the sum of each member s personal preference, expertise and gut feeling. I am not saying that this was a mistake: It is hard to come up with a general guideline here, and even harder to find one that does justice to each individual proposal. So the secret motivation for me to grab the secretary post was that I could contribute without having to judge proposals. Being secretary allowed me to assign most proposals to others to shepherd, and only once in a while myself took care of a proposal, when it seemed to be very straight-forward. Sneaky, ain t it?

7 Years later For years to come I happily played secretary: When an author finished their proposal and public discussion ebbed down they would ping me on GitHub, I would pick a suitable shepherd among the committee and ask them to judge the proposal. Eventually, the committee would come to a conclusion, usually by implicit consent, sometimes by voting, and I d merge the pull request and update the metadata thereon. Every few months I d summarize the current state of affairs to the committee (what happened since the last update, which proposals are currently on our plate), and once per year gathered the data for Simon Peyton Jones annually GHC Status Report. Sometimes some members needed a nudge or two to act. Some would eventually step down, and I d sent around a call for nominations and when the nominations came in, distributed them off-list among the committee and tallied the votes. Initially, that was exciting. For a long while it was a pleasant and rewarding routine. Eventually, it became a mere chore. I noticed that I didn t quite care so much anymore about some of the discussion, and there was a decent amount of naval-gazing, meta-discussions and some wrangling about claims of authority that was probably useful and necessary, but wasn t particularly fun. I also began to notice weaknesses in the processes that I helped shape: We could really use some more automation for showing proposal statuses, notifying people when they have to act, and nudging them when they don t. The whole silence-is-assent approach is good for throughput, but not necessary great for quality, and maybe the committee members need to be pushed more firmly to engage with each proposal. Like GHC itself, the committee processes deserve continuous refinement and refactoring, and since I could not muster the motivation to change my now well-trod secretarial ways, it was time for me to step down. Luckily, Adam Gundry volunteered to take over, and that makes me feel much less bad for quitting. Thanks for that! And although I am for my day job now enjoying a language that has many of the things out of the box that for Haskell are still only language extensions or even just future proposals (dependent types, BlockArguments, do notation with ( foo) expressions and Unicode), I m still around, hosting the Haskell Interlude Podcast, writing on this blog and hanging out at ZuriHac etc.

For the fifth year in a row, I've asked Soci t de Transport de Montr al, Montreal's transit agency, for the foot traffic data of Montreal's subway. By clicking on a subway station, you'll be redirected to a graph of the station's foot traffic.

• Orange line (top10)
• Green line (top10)
• Blue line
• Yellow line
• Global Top 10

Licences

• The subway map displayed on this page, the original dataset and my modified dataset are licenced under CCO 1.0: they are in the public domain.
• The R code I wrote is licensed under the GPLv3+. It's pretty much the same code as last year. I tweaked last's year converter script and although I had to clean some of the data by hand, it worked pretty well.

Review: Making Money, by Terry Pratchett

Series:	Discworld #36
Publisher:	Harper
Copyright:	October 2007
Printing:	November 2014
ISBN:	0-06-233499-9
Format:	Mass market
Pages:	473

Making Money is the 36th Discworld novel, the second Moist von Lipwig book, and a direct sequel to Going Postal. You could start the series with Going Postal, but I would not start here. The post office is running like a well-oiled machine, Adora Belle is out of town, and Moist von Lipwig is getting bored. It's the sort of boredom that has him picking his own locks, taking up Extreme Sneezing, and climbing buildings at night. He may not realize it, but he needs something more dangerous to do. Vetinari has just the thing. The Royal Bank of Ankh-Morpork, unlike the post office before Moist got to it, is still working. It is a stolid, boring institution doing stolid, boring things for rich people. It is also the battleground for the Lavish family past-time: suing each other and fighting over money. The Lavishes are old money, the kind of money carefully entangled in trusts and investments designed to ensure the family will always have money regardless of how stupid their children are. Control of the bank is temporarily in the grasp of Joshua Lavish's widow Topsy, who is not a true Lavish, but the vultures are circling. Meanwhile, Vetinari has grand city infrastructure plans, and to carry them out he needs financing. That means he needs a functional bank, and preferably one that is much less conservative. Moist is dubious about running a bank, and even more reluctant when Topsy Lavish sees him for exactly the con artist he is. His hand is forced when she dies, and Moist discovers he has inherited her dog, Mr. Fusspot. A dog that now owns 51% of the Royal Bank and therefore is the chairman of the bank's board of directors. A dog whose safety is tied to Moist's own by way of an expensive assassination contract. Pratchett knew he had a good story with Going Postal, so here he runs the same formula again. And yes, I was happy to read it again. Moist knows very little about banking but quite a lot about pretending something will work until it does, which has more to do with banking than it does with running a post office. The bank employs an expert, Mr. Bent, who is fanatically devoted to the gold standard and the correctness of the books and has very little patience for Moist. There are golem-related hijinks. The best part of this book is Vetinari, who is masterfully manipulating everyone in the story and who gets in some great lines about politics.

"We are not going to have another wretched empire while I am Patrician. We've only just got over the last one."

Also, Vetinari processing dead letters in the post office was an absolute delight. Making Money does have the recurring Pratchett problem of having a fairly thin plot surrounded by random... stuff. Moist's attempts to reform the city currency while staying ahead of the Lavishes is only vaguely related to Mr. Bent's plot arc. The golems are unrelated to the rest of the plot other than providing a convenient deus ex machina. There is an economist making water models in the bank basement with an Igor, which is a great gag but has essentially nothing to do with the rest of the book. One of the golems has been subjected to well-meaning older ladies and 1950s etiquette manuals, which I thought was considerably less funny (and somewhat creepier) than Pratchett did. There are (sigh) clowns, which continue to be my least favorite Ankh-Morpork world-building element. At least the dog was considerably less annoying than I was afraid it was going to be. This grab-bag randomness is a shame, since I think there was room here for a more substantial plot that engaged fully with the high weirdness of finance. Unfortunately, this was a bit like the post office in Going Postal: Pratchett dives into the subject just enough to make a few wry observations and a few funny quips, and then resolves the deeper issues off-camera. Moist tries to invent fiat currency, because of course he does, and Pratchett almost takes on the gold standard, only to veer away at the last minute into vigorous hand-waving. I suspect part of the problem is that I know a little bit too much about finance, so I kept expecting Pratchett to take the humorous social commentary a couple of levels deeper. On a similar note, the villains have great potential that Pratchett undermines by adding too much over-the-top weirdness. I wish Cosmo Lavish had been closer to what he appears to be at the start of the book: a very wealthy and vindictive man (and a reference to Cosimo de Medici) who doesn't have Moist's ability to come up with wildly risky gambits but who knows considerably more than he does about how banking works. Instead, Pratchett gives him a weird obsession that slowly makes him less sinister and more pathetic, which robs the book of a competent antagonist for Moist. The net result is still a fun book, and a solid Discworld entry, but it lacks the core of the best series entries. It felt more like a skit comedy show than a novel, but it's an excellent skit comedy show with the normal assortment of memorable Pratchettisms. Certainly if you've read this far, or even if you've only read Going Postal, you'll want to read Making Money as well. Followed by Unseen Academicals. The next Moist von Lipwig book is Raising Steam. Rating: 8 out of 10

As well as the collection and distribution of compromised keys, the pwnedkeys project also matches those pwned keys against issued SSL certificates. I m excited to announce that, as of the beginning of 2024, all matched certificates are now being published on the Fediverse, thanks to the botsin.space Mastodon server. Want to know which sites are susceptible to interception and interference, in (near-)real time? Do you have a burning desire to know who is issuing certificates to people that post their private keys in public? Now you can.

How It Works The process for publishing pwned certs is, roughly, as follows:

1. All the certificates in Certificate Transparency (CT) logs are hoovered up (using my scrape-ct-log tool, the fastest log scraper in the west!), and the fingerprint of the public key of each certificate is stored in an LMDB datafile.
2. As new private keys are identified as having been compromised, the fingerprint of that key is checked against all the LMDB files, which map key fingerprints to certificates (actually to CT log entry IDs, from which the certificates themselves are retrieved).
3. If one or more matches are found, then the certificates using the compromised key are forwarded to the tooter , which publishes them for the world to marvel at.

This makes it sound all very straightforward, and it is in theory. The trick comes in optimising the pipeline so that the five million or so new certificates every day can get indexed on the one slightly middle-aged server I ve got, without getting backlogged.

Why Don t You Just Have the Certificates Revoked? Funny story about that I used to notify CAs of certificates they d issued using compromised keys, which had the effect of requiring them to revoke the associated certificates. However, several CAs disliked having to revoke all those certificates, because it cost them staff time (and hence money) to do so. They went so far as to change their procedures from the standard way of accepting problem reports (emailing a generic attestation of compromise), and instead required CA-specific hoop-jumping to notify them of compromised keys. Since the effectiveness of revocation in the WebPKI is, shall we say, homeopathic at best, I decided I couldn t be bothered to play whack-a-mole with CAs that just wanted to be difficult, and I stopped sending compromised key notifications to CAs. Instead, now I m publishing the details of compromised certificates to everyone, so that users can protect themselves directly should they choose to.

Further Work The astute amongst you may have noticed, in the above How It Works description, a bit of a gap in my scanning coverage. CAs can (and do!) issue certificates for keys that are already compromised, including weak keys that have been known about for a decade or more (1, 2, 3). However, as currently implemented, the pwnedkeys certificate checker does not automatically find such certificates. My plan is to augment the CT scraping / cert processing pipeline to check all incoming certificates against the existing (2M+) set of pwned keys. Though, with over five million new certificates to check every day, it s not necessarily as simple as just hit the pwnedkeys API for every new cert . The poor old API server might not like that very much.

Support My Work If you d like to see this extra matching happen a bit quicker, I ve setup a ko-fi supporters page, where you can support my work on pwnedkeys and the other open source software and projects I work on by buying me a refreshing beverage. I would be very appreciative, and your support lets me know I should do more interesting things with the giant database of compromised keys I ve accumulated.

Like each month, have a look at the work funded by Freexian s Debian LTS offering.

Debian LTS contributors In December, 18 contributors have been paid to work on Debian LTS, their reports are available:

• Abhijith PA did 7.0h (out of 7.0h assigned and 7.0h from previous period), thus carrying over 7.0h to the next month.
• Adrian Bunk did 16.0h (out of 26.25h assigned and 8.75h from previous period), thus carrying over 19.0h to the next month.
• Bastien Roucari s did 16.0h (out of 16.0h assigned and 4.0h from previous period), thus carrying over 4.0h to the next month.
• Ben Hutchings did 8.0h (out of 7.25h assigned and 16.75h from previous period), thus carrying over 16.0h to the next month.
• Chris Lamb did 18.0h (out of 18.0h assigned).
• Emilio Pozuelo Monfort did 8.0h (out of 26.75h assigned and 8.25h from previous period), thus carrying over 27.0h to the next month.
• Guilhem Moulin did 25.0h (out of 18.0h assigned and 7.0h from previous period).
• Holger Levsen did 5.5h (out of 5.5h assigned).
• Jochen Sprickerhof did 0.0h (out of 0h assigned and 10.0h from previous period), thus carrying over 10.0h to the next month.
• Lee Garrett did 0.0h (out of 25.75h assigned and 9.25h from previous period), thus carrying over 35.0h to the next month.
• Markus Koschany did 35.0h (out of 35.0h assigned).
• Roberto C. S nchez did 9.5h (out of 5.5h assigned and 6.5h from previous period), thus carrying over 2.5h to the next month.
• Santiago Ruano Rinc n did 8.255h (out of 3.26h assigned and 12.745h from previous period), thus carrying over 7.75h to the next month.
• Sean Whitton did 4.25h (out of 3.25h assigned and 6.75h from previous period), thus carrying over 5.75h to the next month.
• Sylvain Beucler did 16.5h (out of 21.25h assigned and 13.75h from previous period), thus carrying over 18.5h to the next month.
• Thorsten Alteholz did 14.0h (out of 14.0h assigned).
• Tobias Frost did 10.25h (out of 12.0h assigned), thus carrying over 1.75h to the next month.
• Utkarsh Gupta did 18.75h (out of 11.25h assigned and 13.5h from previous period), thus carrying over 6.0h to the next month.

Evolution of the situation In December, we have released 29 DLAs. A particularly notable update in December was prepared by LTS contributor Santiago Ruano Rinc n for the openssh package. The updated produced DLA-3694-1 and included a fix for the Terrapin Attack (CVE-2023-48795), which was a rather serious flaw in the SSH protocol itself. The package bluez was the subject of another notable update by LTS contributor Chris Lamb, which resulted in DLA-3689-1 to address an insecure default configuration which allowed attackers to inject keyboard commands over Bluetooth without first authenticating. The LTS team continues its efforts to have a positive impact beyond the boundaries of LTS. Several contributors worked on packages, preparing LTS updates, but also preparing patches or full updates which were uploaded to the unstable, stable, and oldstable distributions, including: Guilhem Moulin s update of tinyxml (uploads to LTS and unstable and patches submitted to the security team for stable and oldstable); Guilhem Moulin s update of xerces-c (uploads to LTS and unstable and patches submitted to the security team for oldstable); Thorsten Alteholz s update of libde265 (uploads to LTS and stable and additional patches submitted to the maintainer for stable and oldstable); Thorsten Alteholz s update of cjson (upload to LTS and patches submitted to the maintainer for stable and oldstable); and Tobias Frost s update of opendkim (sponsor maintainer-prepared upload to LTS and additionally prepared updates for stable and oldstable). Going beyond Debian and looking to the broader community, LTS contributor Bastien Roucari s was contacted by SUSE concerning an update he had prepared for zbar. He was able to assist by coordinating with the former organization of the original zbar author to secure for SUSE access to information concerning the exploits. This has enabled another distribution to benefit from the work done in support of LTS and from the assistance of Bastien in coordinating the access to information. Finally, LTS contributor Santiago Ruano Rinc n continued work relating to how updates for packages in statically-linked language ecosystems (e.g., Go, Rust, and others) are handled. The work is presently focused on more accurately and reliably identifying which packages are impacted in a given update scenario to enable notifications to be published so that users will be made aware of these situations as they occur. As the work continues, it will eventually result in improvements to Debian infrustructure so that the LTS team and Security team are able to manage updates of this nature in a more consistent way.

Thanks to our sponsors Sponsors that joined recently are in bold.

• Platinum sponsors:
  • TOSHIBA (for 100 months)
  • Civil Infrastructure Platform (CIP) (for 68 months)
• Gold sponsors:
  • Roche Diagnostics International AG (for 111 months)
  • Linode (for 105 months)
  • Babiel GmbH (for 94 months)
  • Plat Home (for 94 months)
  • University of Oxford (for 50 months)
  • Deveryware (for 37 months)
  • VyOS Inc (for 32 months)
  • EDF SA (for 21 months)
• Silver sponsors:
  • Domeneshop AS (for 115 months)
  • Nantes M tropole (for 109 months)
  • Univention GmbH (for 101 months)
  • Universit Jean Monnet de St Etienne (for 101 months)
  • Ribbon Communications, Inc. (for 95 months)
  • Exonet B.V. (for 85 months)
  • Leibniz Rechenzentrum (for 79 months)
  • CINECA (for 68 months)
  • Minist re de l Europe et des Affaires trang res (for 62 months)
  • Cloudways by DigitalOcean (for 52 months)
  • Dinahosting SL (for 50 months)
  • Bauer Xcel Media Deutschland KG (for 44 months)
  • Platform.sh SAS (for 44 months)
  • Moxa Inc. (for 38 months)
  • sipgate GmbH (for 35 months)
  • OVH US LLC (for 33 months)
  • Tilburg University (for 33 months)
  • GSI Helmholtzzentrum f r Schwerionenforschung GmbH (for 25 months)
  • Soliton Systems K.K. (for 22 months)
• Bronze sponsors:
  • Evolix (for 116 months)
  • Seznam.cz, a.s. (for 116 months)
  • Intevation GmbH (for 113 months)
  • Linuxhotel GmbH (for 113 months)
  • Daevel SARL (for 111 months)
  • Bitfolk LTD (for 110 months)
  • Megaspace Internet Services GmbH (for 110 months)
  • Greenbone AG (for 109 months)
  • NUMLOG (for 109 months)
  • WinGo AG (for 109 months)
  • Ecole Centrale de Nantes - LHEEA (for 105 months)
  • Entr ouvert (for 100 months)
  • Adfinis AG (for 97 months)
  • GNI MEDIA (for 92 months)
  • Laboratoire LEGI - UMR 5519 / CNRS (for 92 months)
  • Tesorion (for 92 months)
  • Bearstech (for 83 months)
  • LiHAS (for 83 months)
  • Catalyst IT Ltd (for 78 months)
  • Supagro (for 73 months)
  • Demarcq SAS (for 72 months)
  • Universit Grenoble Alpes (for 58 months)
  • TouchWeb SAS (for 50 months)
  • SPiN AG (for 47 months)
  • CoreFiling (for 42 months)
  • Institut des sciences cognitives Marc Jeannerod (for 37 months)
  • Observatoire des Sciences de l Univers de Grenoble (for 34 months)
  • Tem Innovations GmbH (for 29 months)
  • WordFinder.pro (for 28 months)
  • CNRS DT INSU R sif (for 27 months)
  • Alter Way (for 20 months)
  • Institut Camille Jordan (for 9 months)

This year was hard from a personal and work point of view, which impacted the amount of Free Software bits I ended up doing - even when I had the time I often wasn t in the right head space to make progress on things. However writing this annual recap up has been a useful exercise, as I achieved more than I realised. For previous years see 2019, 2020, 2021 + 2022.

Conferences The only Free Software related conference I made it to this year was DebConf23 in Kochi, India. Changes with projects at work meant I couldn t justify anything work related. This year I m planning to make it to FOSDEM, and haven t made a decision on DebConf24 yet.

Debian Most of my contributions to Free software continue to happen within Debian. I started the year working on retrogaming with Kodi on Debian. I got this to a much better state for bookworm, with it being possible to run the bsnes-mercury emulator under Kodi using RetroArch. There are a few other libretro backends available for RetroArch, but Kodi needs some extra controller mappings packaged up first. Plenty of uploads were involved, though some of this was aligning all the dependencies and generally cleaning things up in iterations.

• retroarch: 1.13.0-dfsg+3, 1.14.0+dfsg-1, 1.15.0+dfsg-1, 1.16.0.3+dfgs-1
• libretro-core-info uploads: 1.14.0-1, 1.15.0-1.
• libretro-bsnes-mercury: 094+git20220807-2, 094+git20220807-3, 094+git20220807-4, 094+git20220807-5, 094+git20220807-6, 094+git20220807-7, 094+git20220807-8.
• kodi-game-libretro: 20.2.0-2, 20.2.2-1, 20.2.2-2, 20.2.4-1, 20.2.4-2
• rcheevos: 10.5.0-2, 10.6.0-1, 10.7.0-1, 10.7.1-1.

I continued to work on a few packages within the Debian Electronics Packaging Team. OpenOCD produced a new release in time for the bookworm release, so I uploaded 0.12.0-1. There were a few minor sigrok cleanups - sigrok 0.3, libsigrokdecode 0.5.3-4 + libsigrok 0.5.2-4 / 0.5.2-5. While I didn t manage to get the work completed I did some renaming of the ESP8266 related packages - gcc-xtensa-lx106 (which saw a 13 upload pre-bookworm) has become gcc-xtensa (with 14) and binutils-xtensa-lx106 has become binutils-xtensa (with 6). Binary packages remain the same, but this is intended to allow for the generation of ESP32 compiler toolchains from the same source. onak saw 0.6.3-1 uploaded to match the upstream release. I also uploaded libgpg-error 1.47-1 (though I can claim no credit for any of the work in preparing the package) to help move things forward on updating gnupg2 in Debian. I NMUed tpm2-pkcs11 1.9.0-0.1 to fix some minor issues pre-bookworm release; I use this package myself to store my SSH key within my laptop TPM, so I care about it being in a decent state. sg3-utils also saw a bit of love with 1.46-2 + 1.46-3 - I don t work in the storage space these days, but I m still listed as an uploaded and there was an RC bug around the library package naming that I was qualified to fix and test pre-bookworm. Related to my retroarch work I sponsored uploads of mgba for Ryan Tandy: 0.10.0+dfsg-1, 0.10.0+dfsg-2, 0.10.1+dfsg-1, 0.10.2+dfsg-1, mgba 0.10.1+dfsg-1+deb12u1. As part of the Data Protection Team I responded to various inbound queries to that team, both from project members and those external to the project. I continue to keep an eye on Debian New Members, even though I m mostly inactive as an application manager - we generally seem to have enough available recently. Mostly my involvement is via Front Desk activities, helping out with queries to the team alias, and contributing to internal discussions as well as our panel at DebConf23. Finally the 3 month rotation for Debian Keyring continues to operate smoothly. I dealt with 2023.03.24, 2023.06.26, 2023.06.29, 2023.09.10, 2023.09.24 + 2023.12.24.

Linux I had a few minor patches accepted to the kernel this year. A pair of safexcel cleanups (improved error logging for firmware load fail and cleanup on load failure) came out of upgrading the kernel running on my RB5009. The rest were related to my work on repurposing my C.H.I.P.. The AXP209 driver needed extended to support GPIO3 (with associated DT schema update). That allowed Bluetooth to be enabled. Adding the AXP209 internal temperature ADC as an iio-hwmon node means it can be tracked using the normal sensor monitoring framework. And finally I added the pinmux settings for mmc2, which I use to support an external microSD slot on my C.H.I.P.

Personal projects 2023 saw another minor release of onak, 0.6.3, which resulted in a corresponding Debian upload (0.6.3-1). It has a couple of bug fixes (including a particularly annoying, if minor, one around systemd socket activation that felt very satisfying to get to the bottom of), but I still lack the time to do any of the major changes I would like to. I wrote listadmin3 to allow easy manipulation of moderation queues for Mailman3. It s basic, but it s drastically improved my timeliness on dealing with held messages.

Work related This year only involved a single upstream related submission; a fix for tpm_tis interrupts with the Lenovo P620 that then got dropped when the change that caused the issue was reverted. That wraps up 2023. I ve got no particular goals for this year; looking around my desk I ve a few ARM based devices I d like to get running a mainline kernel. I need to play about a bit more with the retroarch bits (if I really had time I d do the migration for Kodi to PCRE2, as that s currently causing testing migration issues), perhaps getting some more controller mappings packaged. But no promises.

In 2023, I finished and reviewed 53 books, continuing a trend of year-over-year increases and of reading the most books since 2012 (the last year I averaged five books a month). Reviewing continued to be uneven, with a significant slump in the summer and smaller slumps in February and November, and a big clump of reviews finished in October in addition to my normal year-end reading and reviewing vacation. The unevenness this year was mostly due to finishing books and not writing reviews immediately. Reviews are much harder to write when the finished books are piling up, so one goal for 2024 is to not let that happen again. I enter the new year with one book finished and not yet reviewed, after reading a book about every day and a half during my December vacation. I read two all-time favorite books this year. The first was Emily Tesh's debut novel Some Desperate Glory, which is one of the best space opera novels I have ever read. I cannot improve on Shelley Parker-Chan's blurb for this book: "Fierce and heartbreakingly humane, this book is for everyone who loved Ender's Game, but Ender's Game didn't love them back." This is not hard science fiction but it is fantastic character fiction. It was exactly what I needed in the middle of a year in which I was fighting a "burn everything down" mood. The second was Night Watch by Terry Pratchett, the 29th Discworld and 6th Watch novel. Throughout my Discworld read-through, Pratchett felt like he was on the cusp of a truly stand-out novel, one where all the pieces fit and the book becomes something more than the sum of its parts. This was that book. It's a book about ethics and revolutions and governance, but also about how your perception of yourself changes as you get older. It does all of the normal Pratchett things, just... better. While I would love to point new Discworld readers at it, I think you do have to read at least the Watch novels that came before it for it to carry its proper emotional heft. This was overall a solid year for fiction reading. I read another 15 novels I rated 8 out of 10, and 12 that I rated 7 out of 10. The largest contributor to that was my Discworld read-through, which was reliably entertaining throughout the year. The run of Discworld books between The Fifth Elephant (read late last year) and Wintersmith (my last of this year) was the best run of Discworld novels so far. One additional book I'll call out as particularly worth reading is Thud!, the Watch novel after Night Watch and another excellent entry. I read two stand-out non-fiction books this year. The first was Oliver Darkshire's delightful memoir about life as a rare book seller, Once Upon a Tome. One of the things I will miss about Twitter is the regularity with which I stumbled across fascinating people and then got to read their books. I'm off Twitter permanently now because the platform is designed to make me incoherently angry and I need less of that in my life, but it was very good at finding delightfully quirky books like this one. My other favorite non-fiction book of the year was Michael Lewis's Going Infinite, a profile of Sam Bankman-Fried. I'm still bemused at the negative reviews that this got from people who were upset that Lewis didn't turn the story into a black-and-white morality play. Bankman-Fried's actions were clearly criminal; that's not in dispute. Human motivations can be complex in ways that are irrelevant to the law, and I thought this attempt to understand that complexity by a top-notch storyteller was worthy of attention. Also worth a mention is Tony Judt's Postwar, the first book I reviewed in 2023. A sprawling history of post-World-War-II Europe will never have the sheer readability of shorter, punchier books, but this was the most informative book that I read in 2023. 2024 should see the conclusion of my Discworld read-through, after which I may return to re-reading Mercedes Lackey or David Eddings, both of which I paused to make time for Terry Pratchett. I also have another re-read similar to my Chronicles of Narnia reviews that I've been thinking about for a while. Perhaps I will start that next year; perhaps it will wait for 2025. Apart from that, my intention as always is to read steadily, write reviews as close to when I finished the book as possible, and make reading time for my huge existing backlog despite the constant allure of new releases. Here's to a new year full of more new-to-me books and occasional old favorites. The full analysis includes some additional personal reading statistics, probably only of interest to me.

It can be incredibly easy for a frontend developer to accidentally write a client-side cross-site-scripting (DOM-XSS) security issue, and yet these are hard for security teams to detect. Vulnerability scanners are slow, and suffer from false positives. Can smarter collaboration between development, operations and security teams provide a way to eliminate these problems altogether? Google claims that Trusted Types has all but eliminated DOM-XSS exploits on those of their sites which have implemented it. Let s find out how this can work!

DOM-XSS vulnerabilities are easy to write, but hard for security teams to catch It is very easy to accidentally introduce a client-side XSS problem. As an example of what not to do, suppose you are setting an element s text to the current URL, on the client side:

// Don't do this
para.innerHTML = location.href;

Unfortunately, an attacker can now manipulate the URL (and e.g. send this link in a phishing email), and any HTML tags they add will be interpreted by the user s browser. This could potentially be used by the attacker to send private data to a different server. Detecting DOM-XSS using vulnerability scanning tools is challenging - typically this requires crawling each page of the website and attempting to detect problems such as the one above, but there is a significant risk of false positives, especially as the complexity of the logic increases. There are already ways to avoid these exploits developers should validate untrusted input before making use of it. There are libraries such as DOMPurify which can help with sanitization.¹ However, if you are part of a security team with responsibility for preventing these issues, it can be complex to understand whether you are at risk. Different developer teams may be using different techniques and tools. It may be impossible for you to work closely with every developer so how can you know that the frontend team have used these libraries correctly?

Trusted Types closes the DevSecOps feedback loop for DOM-XSS, by allowing Ops and Security to verify good Developer practices Trusted Types enforces sanitization in the browser², by requiring the web developer to assign a particular kind of JavaScript object rather than a native string to .innerHTML and other dangerous properties. Provided these special types are created in an appropriate way, then they can be trusted not to expose XSS problems. This approach will work with whichever tools the frontend developers have chosen to use, and detection of issues can be rolled out by infrastructure engineers without requiring frontend code changes.

Content Security Policy allows enforcement of security policies in the browser itself Because enforcing this safer approach in the browser for all websites would break backwards-compatibility, each website must opt-in through Content Security Policy headers. Content Security Policy (CSP) is a mechanism that allows web pages to restrict what actions a browser should execute on their page, and a way for the site to receive reports if the policy is violated. Figure 1: Content-Security-Policy browser communication This is revolutionary, because it allows servers to receive feedback in real time on errors that may be appearing in the browser s console.

Trusted Types can be rolled out incrementally, with continuous feedback Web.dev s article on Trusted Types explains how to safely roll out the feature using the features of CSP itself:

• Deploy a CSP collector if you haven t already
• Switch on CSP reports without enforcement (via Content-Security-Policy-Report-Only headers)
• Iteratively review and fix the violations
• Switch to enforcing mode when there are a low enough rate of reports

Static analysis in a continuous integration pipeline is also sensible you want to prevent regressions shipping in new releases before they trigger a flood of CSP reports. This will also give you a chance of finding any low-traffic vulnerable pages.

Smart security teams will use techniques like Trusted Types to eliminate entire classes of bugs at a time Rather than playing whack-a-mole with unreliable vulnerability scanning or bug bounties, techniques such as Trusted Types are truly in the spirit of Secure by Design build high quality in from the start of the engineering process, and do this in a way which closes the DevSecOps feedback loop between your Developer, Operations and Security teams.

---

1. Sanitization libraries are especially needed when the examples become more complex, e.g. if the application must manipulate the input. DOMPurify version 1.0.9 also added Trusted Types support, so can still be used to help developers adopt this feature.
2. Trusted Types has existed in Chrome and Edge since 2020, and should soon be coming to Firefox as well. However, it s not necessary to wait for Firefox or Safari to add support, because the large market share of Chrome and Edge will let you identify and fix your site s DOM-XSS issues, even if you do not set enforcing mode, and users of all browsers will benefit. Even so, it is great that Mozilla is now on board.

It was 2013, and I was on a break from work between Christmas and New Year of 2013. I had been working at Linaro for well over a year, on the LAVA project. I was living and breathing automated testing infrastructure, mostly for testing low-level components such as kernels and bootloaders, on real hardware. At this point I was also a Debian contributor for quite some years, and had become an official project members two years prior. Most of my involvement was in the Ruby team, where we were already consistently running upstream test suites during package builds. During that break, I put these two contexts together, and came to the conclusion that Debian needed a dedicated service that would test the contents of the Debian archive. I was aware of the existance of autopkgtest, and started working on a very simple service that would later become Debian CI. In January 2014, debci was initially announced on that month's Misc Developer News, and later uploaded to Debian. It's been continuously developed for the last 10 years, evolved from a single shell script running tests in a loop into a distributed system with 47 geographically-distributed machines as of writing this piece, became part of the official Debian release process gating migrations to testing, had 5 Summer of Code and Outrechy interns working on it, and processed beyond 40 million test runs. In there years, Debian CI has received contributions from a lot of people, but I would like to give special credits to the following:

• Ian Jackson - created autopkgtest.
• Martin Pitt - was the maintainer of autopkgtest when Debian CI launched and helped a lot for some time.
• Paul Gevers - decided that he wanted Debian CI test runs to control testing migration. While at it, became a member of the Debian Release Team and the other half of the permanent Debian CI team together with me.
• Lucas Kanashiro - Google Summer of Code intern, 2014.
• Brandon Fairchild - Google Summer of Code intern, 2014.
• Candy Tsai - Outreachy intern, 2019.
• Pavit Kaur - Google Summer of Code intern, 2021
• Abiola Ajadi - Outreachy intern, December 2021-2022.

Review: A Study in Scarlet, by Arthur Conan Doyle

Series:	Sherlock Holmes #1
Publisher:	AmazonClassics
Copyright:	1887
Printing:	February 2018
ISBN:	1-5039-5525-7
Format:	Kindle
Pages:	159

A Study in Scarlet is the short mystery novel (probably a novella, although I didn't count words) that introduced the world to Sherlock Holmes. I'm going to invoke the 100-year-rule and discuss the plot of this book rather freely on the grounds that even someone who (like me prior to a few days ago) has not yet read it is probably not that invested in avoiding all spoilers. If you do want to remain entirely unspoiled, exercise caution before reading on. I had somehow managed to avoid ever reading anything by Arthur Conan Doyle, not even a short story. I therefore couldn't be sure that some of the assertions I was making in my review of A Study in Honor were correct. Since A Study in Scarlet would be quick to read, I decided on a whim to do a bit of research and grab a free copy of the first Holmes novel. Holmes is such a part of English-speaking culture that I thought I had a pretty good idea of what to expect. This was largely true, but cultural osmosis had somehow not prepared me for the surprise Mormons. A Study in Scarlet establishes the basic parameters of a Holmes story: Dr. James Watson as narrator, the apartment he shares with Holmes at 221B Baker Street, the Baker Street Irregulars, Holmes's competition with police detectives, and his penchant for making leaps of logical deduction from subtle clues. The story opens with Watson meeting Holmes, agreeing to split the rent of a flat, and being baffled by the apparent randomness of Holmes's fields of study before Holmes reveals he's a consulting detective. The first case is a murder: a man is found dead in an abandoned house, without a mark on him although there are blood splatters on the walls and the word "RACHE" written in blood. Since my only prior exposure to Holmes was from cultural references and a few TV adaptations, there were a few things that surprised me. One is that Holmes is voluble and animated rather than aloof. Doyle is clearly going for passionate eccentric rather than calculating mastermind. Another is that he is intentionally and unabashedly ignorant on any topic not related to solving mysteries.

My surprise reached a climax, however, when I found incidentally that he was ignorant of the Copernican Theory and of the composition of the Solar System. That any civilized human being in this nineteenth century should not be aware that the earth travelled round the sun appeared to be to me such an extraordinary fact that I could hardly realize it. "You appear to be astonished," he said, smiling at my expression of surprise. "Now that I do know it I shall do my best to forget it." "To forget it!" "You see," he explained, "I consider that a man's brain originally is like a little empty attic, and you have to stock it with such furniture as you chose. A fool takes in all the lumber of every sort that he comes across, so that the knowledge which might be useful to him gets crowded out, or at best is jumbled up with a lot of other things so that he has a difficulty in laying his hands upon it. Now the skilful workman is very careful indeed as to what he takes into his brain-attic. He will have nothing but the tools which may help him in doing his work, but of these he has a large assortment, and all in the most perfect order. It is a mistake to think that that little room has elastic walls and can distend to any extent. Depend upon it there comes a time when for every addition of knowledge you forget something that you knew before. It is of the highest importance, therefore, not to have useless facts elbowing out the useful ones."

This is directly contrary to my expectation that the best way to make leaps of deduction is to know something about a huge range of topics so that one can draw unexpected connections, particularly given the puzzle-box construction and odd details so beloved in classic mysteries. I'm now curious if Doyle stuck with this conception, and if there were any later mysteries that involved astronomy. Speaking of classic mysteries, A Study in Scarlet isn't quite one, although one can see the shape of the genre to come. Doyle does not "play fair" by the rules that have not yet been invented. Holmes at most points knows considerably more than the reader, including bits of evidence that are not described until Holmes describes them and research that Holmes does off-camera and only reveals when he wants to be dramatic. This is not the sort of story where the reader is encouraged to try to figure out the mystery before the detective. Rather, what Doyle seems to be aiming for, and what Watson attempts (unsuccessfully) as the reader surrogate, is slightly different: once Holmes makes one of his grand assertions, the reader is encouraged to guess what Holmes might have done to arrive at that conclusion. Doyle seems to want the reader to guess technique rather than outcome, while providing only vague clues in general descriptions of Holmes's behavior at a crime scene. The structure of this story is quite odd. The first part is roughly what you would expect: first-person narration from Watson, supposedly taken from his journals but not at all in the style of a journal and explicitly written for an audience. Part one concludes with Holmes capturing and dramatically announcing the name of the killer, who the reader has never heard of before. Part two then opens with... a western?

In the central portion of the great North American Continent there lies an arid and repulsive desert, which for many a long year served as a barrier against the advance of civilization. From the Sierra Nevada to Nebraska, and from the Yellowstone River in the north to the Colorado upon the south, is a region of desolation and silence. Nor is Nature always in one mood throughout the grim district. It comprises snow-capped and lofty mountains, and dark and gloomy valleys. There are swift-flowing rivers which dash through jagged ca ons; and there are enormous plains, which in winter are white with snow, and in summer are grey with the saline alkali dust. They all preserve, however, the common characteristics of barrenness, inhospitality, and misery.

First, I have issues with the geography. That region contains some of the most beautiful areas on earth, and while a lot of that region is arid, describing it primarily as a repulsive desert is a bit much. Doyle's boundaries and distances are also confusing: the Yellowstone is a northeast-flowing river with its source in Wyoming, so the area between it and the Colorado does not extend to the Sierra Nevadas (or even to Utah), and it's not entirely clear to me that he realizes Nevada exists. This is probably what it's like for people who live anywhere else in the world when US authors write about their country. But second, there's no Holmes, no Watson, and not even the pretense of a transition from the detective novel that we were just reading. Doyle just launches into a random western with an omniscient narrator. It features a lean, grizzled man and an adorable child that he adopts and raises into a beautiful free spirit, who then falls in love with a wild gold-rush adventurer. This was written about 15 years before the first critically recognized western novel, so I can't blame Doyle for all the cliches here, but to a modern reader all of these characters are straight from central casting. Well, except for the villains, who are the Mormons. By that, I don't mean that the villains are Mormon. I mean Brigham Young is the on-page villain, plotting against the hero to force his adopted daughter into a Mormon harem (to use the word that Doyle uses repeatedly) and ruling Salt Lake City with an iron hand, border guards with passwords (?!), and secret police. This part of the book was wild. I was laughing out-loud at the sheer malevolent absurdity of the thirty-day countdown to marriage, which I doubt was the intended effect. We do eventually learn that this is the backstory of the murder, but we don't return to Watson and Holmes for multiple chapters. Which leads me to the other thing that surprised me: Doyle lays out this backstory, but then never has his characters comment directly on the morality of it, only the spectacle. Holmes cares only for the intellectual challenge (and for who gets credit), and Doyle sets things up so that the reader need not concern themselves with aftermath, punishment, or anything of that sort. I probably shouldn't have been surprised this does fit with the Holmes stereotype but I'm used to modern fiction where there is usually at least some effort to pass judgment on the events of the story. Doyle draws very clear villains, but is utterly silent on whether the murder is justified. Given its status in the history of literature, I'm not sorry to have read this book, but I didn't particularly enjoy it. It is very much of its time: everyone's moral character is linked directly to their physical appearance, and Doyle uses the occasional racial stereotype without a second thought. Prevailing writing styles have changed, so the prose feels long-winded and breathless. The rivalry between Holmes and the police detectives is tedious and annoying. I also find it hard to read novels from before the general absorption of techniques of emotional realism and interiority into all genres. The characters in A Study in Scarlet felt more like cartoon characters than fully-realized human beings. I have no strong opinion about the objective merits of this book in the context of its time other than to note that the sudden inserted western felt very weird. My understanding is that this is not considered one of the better Holmes stories, and Holmes gets some deeper characterization later on. Maybe I'll try another of Doyle's works someday, but for now my curiosity has been sated. Followed by The Sign of the Four. Rating: 4 out of 10

Review: Wintersmith, by Terry Pratchett

Series:	Discworld #35
Publisher:	Clarion Books
Copyright:	2006
Printing:	2007
ISBN:	0-06-089033-9
Format:	Mass market
Pages:	450

Wintersmith is the 35th Discworld novel and the 3rd Tiffany Aching novel. You could probably start here, since understanding the backstory isn't vital for following the plot, but I'm not sure why you would. Tiffany is now training with Miss Treason, a 113-year-old witch who is quite different in her approach from Miss Level, Tiffany's mentor in A Hat Full of Sky. Miss Level was the unassuming and constantly helpful glue that held the neighborhood together. Miss Treason is the judge; her neighbors are scared of her and proud of being scared of her, since that means they have a proper witch who can see into their heads and sort out their problems. On the surface, they're quite different; part of the story of this book is Tiffany learning to see the similarities. First, though, Miss Treason rushes Tiffany to a strange midnight Morris Dance, without any explanation. The Morris Dance usually celebrates the coming of spring and is at the center of a village party, so Tiffany is quite confused by seeing it danced on a dark and windy night in late autumn. But there is a hole in the dance where the Fool normally is, and Tiffany can't keep herself from joining it. This proves to be a mistake. That space was left for someone very different from Tiffany, and now she's entangled herself in deep magic that she doesn't understand. This is another Pratchett novel where the main storyline didn't do much for me. All the trouble stems from Miss Treason being maddeningly opaque, and while she did warn Tiffany, she did so in that way that guarantees a protagonist of a middle-grade novel will ignore. The Wintersmith is a boring, one-note quasi-villain, and the plot mainly revolves around elemental powers being dumber than a sack of hammers. The one thing I will say about the main plot is that the magic Tiffany danced into is entangled with courtship and romance, Tiffany turns thirteen over the course of this book, and yet this is not weird and uncomfortable reading the way it would be in the hands of many other authors. Pratchett has a keen eye for the age range that he's targeting. The first awareness that there is such a thing as romance that might be relevant to oneself pairs nicely with the Wintersmith's utter confusion at how Tiffany's intrusion unbalanced his dance. This is a very specific age and experience that I think a lot of authors would shy away from, particularly with a female protagonist, and I thought Pratchett handled it adroitly. I personally found the Wintersmith's awkward courting tedious and annoying, but that's more about me than about the book. As with A Hat Full of Sky, though, everything other than the main plot was great. It is becoming obvious how much Tiffany and Granny Weatherwax have in common, and that Granny Weatherwax recognizes this and is training Tiffany herself. This is high-quality coming-of-age material, not in the traditional fantasy sense of chosen ones and map explorations, but in the sense of slowly-developing empathy and understanding of people who think differently than you do. Tiffany, like Granny Weatherwax, has very little patience with nonsense, and her irritation with stupidity is one of her best characteristics. But she's learning how to blunt it long enough to pay attention, and to understand how people she doesn't like can still be the right people for specific situations. I particularly loved how Granny carries on with a feud at the same time that Tiffany is learning to let go of one. It's not a contradiction or hypocrisy; it's a sign that Tiffany is entitled to her judgments and feelings, but has to learn how to keep them in their place and not let them take over. One of the great things about the Tiffany Aching books is that the villages are also characters. We don't see that much of the individual people, but one of the things Tiffany is learning is how to see the interpersonal dynamics and patterns of village life. Somehow the feelings of irritation and exasperation fade once you understand people's motives and see more sides to their character. There is a lot more Nanny Ogg in this book than there has been in the last few, and that reminded me of how much I love her character. She has a completely different approach than Granny Weatherwax, but it's just as effective in different ways. She's also the perfect witch to have around when you've stumbled into a stylized love story that you don't want to be a part of, and yet find oddly fascinating. It says something about the skill of Pratchett's characterization that I could enjoy a book this much while having no interest in the main plot. The Witches have always been great characters, but somehow they're even better when seen through Tiffany's perspective. Good stuff; if you liked any of the other Tiffany Aching books, you will like this as well. Followed by Making Money in publication order. The next Tiffany Aching novel is I Shall Wear Midnight. Rating: 8 out of 10

Earlier this year, after Github accidentally committed their private RSA SSH host key to a public repository, I wrote about how better support for SSH host certificates would allow this sort of situation to be handled in a user-transparent way without any negative impact on security. I was hoping that someone would read this and be inspired to fix the problem but sadly that didn't happen so I've actually written some code myself.

The core part of this is straightforward - if a server presents you with a certificate associated with a host key, then make the trust in that host be whoever signed the certificate rather than just trusting the host key. This means that if someone needs to replace the host key for any reason (such as, for example, them having published the private half), you can replace the host key with a new key and a new certificate, and as long as the new certificate is signed by the same key that the previous certificate was, you'll trust the new key and key rotation can be carried out without any user errors. Hurrah!

So obviously I wrote that bit and then thought about the failure modes and it turns out there's an obvious one - if an attacker obtained both the private key and the certificate, what stops them from continuing to use it? The certificate isn't a secret, so we basically have to assume that anyone who possesses the private key has access to it. We may have silently transitioned to a new host key on the legitimate servers, but a hostile actor able to MITM a user can keep on presenting the old key and the old certificate until it expires.

There's two ways to deal with this - either have short-lived certificates (ie, issue a new certificate every 24 hours or so even if you haven't changed the key, and specify that the certificate is invalid after those 24 hours), or have a mechanism to revoke the certificates. The former is viable if you have a very well-engineered certificate issuing operation, but still leaves a window for an attacker to make use of the certificate before it expires. The latter is something SSH has support for, but the spec doesn't define any mechanism for distributing revocation data.

So, I've implemented a new SSH protocol extension that allows a host to send a key revocation list to a client. The idea is that the client authenticates to the server, receives a key revocation list, and will no longer trust any certificates that are contained within that list. This seems simple enough, but a naive implementation opens the client to various DoS attacks. For instance, if you simply revoke any key contained within the received KRL, a hostile server could revoke any certificates that were otherwise trusted by the client. The easy way around this is for the client to ensure that any revoked keys are associated with the same CA that signed the host certificate - that way a compromised host can only revoke certificates associated with that CA, and can't interfere with anyone else.

Unfortunately that still means that a single compromised host can still trigger revocation of certificates inside that trust domain (ie, a compromised host a.test.com could push a KRL that invalidated the certificate for b.test.com), because there's no way in the KRL format to indicate that a given revocation is associated with a specific hostname. This means we need a mechanism to verify that the KRL update is legitimate, and the easiest way to handle that is to sign it. The KRL format specifies an in-band signature but this was deprecated earlier this year - instead KRLs are supposed to be signed with the sshsig format. But we control both the server and the client, which means it's easy enough to send a detached signature as part of the extension data.

Putting this all together: you ssh to a server you've never contacted before, and it presents you with a host certificate. Instead of the host key being added to known_hosts, the CA key associated with the certificate is added. From now on, if you ssh to that host and it presents a certificate signed by that CA, it'll be trusted. Optionally, the host can also send you a KRL and a signature. If the signature is generated by the CA key that you already trust, any certificates in that KRL associated with that CA key will be incorporated into local storage. The expected flow if a key is compromised is that the owner of the host generates a new keypair, obtains a new certificate for the new key, and adds the old certificate to a KRL that is signed with the CA key. The next time the user connects to that host, they receive the new key and new certificate, trust it because it's signed by the same CA key, and also receive a KRL signed with the same CA that revokes trust in the old certificate.

Obviously this breaks down if a user is MITMed with a compromised key and certificate immediately after the host is compromised - they'll see a legitimate certificate and won't receive any revocation list, so will trust the host. But this is the same failure mode that would occur in the absence of keys, where the attacker simply presents the compromised key to the client before trust in the new key has been created. This seems no worse than the status quo, but means that most users will seamlessly transition to a new key and revoke trust in the old key with no effort on their part.

The work in progress tree for this is here - at the point of writing I've merely implemented this and made sure it builds, not verified that it actually works or anything. Cleanup should happen over the next few days, and I'll propose this to upstream if it doesn't look like there's any showstopper design issues.

comments

I know that people rave about GMail's spam filtering, but it didn't work for me: I was seeing too many false positives. I personally prefer to see some false negatives (i.e. letting some spam through), but to reduce false positives as much as possible (and ideally have a way to tune this). Here's the local SpamAssassin setup I have put together over many years. In addition to the parts I describe here, I also turn off greylisting on my email provider (KolabNow) because I don't want to have to wait for up to 10 minutes for a "2FA" email to go through. This setup assumes that you download all of your emails to your local machine. I use fetchmail for this, though similar tools should work too.

Three tiers of emails The main reason my setup works for me, despite my receiving hundreds of spam messages every day, is that I split incoming emails into three tiers via procmail:

1. not spam: delivered to inbox
2. likely spam: quarantined in a soft_spam/ folder
3. definitely spam: silently deleted

I only ever have to review the likely spam tier for false positives, which is on the order of 10-30 spam emails a day. I never even see the the hundreds that are silently deleted due to a very high score. This is implemented based on a threshold in my .procmailrc:

# Use spamassassin to check for spam
:0fw: .spamassassin.lock
  /usr/bin/spamassassin
# Throw away messages with a score of > 12.0
:0
* ^X-Spam-Level: \*\*\*\*\*\*\*\*\*\*\*\*
/dev/null
:0:
* ^X-Spam-Status: Yes
$HOME/Mail/soft_spam/
# Deliver all other messages
:0:
$ DEFAULT 

I also use the following ~/.muttrc configuration to easily report false negatives/positives and examine my likely spam folder via a shortcut in mutt:

unignore X-Spam-Level
unignore X-Spam-Status
macro index S "c=soft_spam/\n" "Switch to soft_spam"
# Tell mutt about SpamAssassin headers so that I can sort by spam score
spam "X-Spam-Status: (Yes No), (hits score)=(-?[0-9]+\.[0-9])" "%3"
folder-hook =soft_spam 'push ol'
folder-hook =spam 'push ou'
# <Esc>d = de-register as non-spam, register as spam, move to spam folder.
macro index \ed "<enter-command>unset wait_key\n<pipe-entry>spamassassin -r\n<enter-command>set wait_key\n<save-message>=spam\n" "report the message as spam"
# <Esc>u = unregister as spam, register as non-spam, move to inbox folder.
macro index \eu "<enter-command>unset wait_key\n<pipe-entry>spamassassin -k\n<enter-command>set wait_key\n<save-message>=inbox\n" "correct the false positive (this is not spam)"

Custom SpamAssassin rules In addition to the default ruleset that comes with SpamAssassin, I've also accrued a number of custom rules over the years. The first set comes from the (now defunct) SpamAssassin Rules Emporium. The second set is the one that backs bugs.debian.org and lists.debian.org. Note this second one includes archived copies of some of the SARE rules and so I only use some of the rules in the common/ directory. Finally, I wrote a few custom rules of my own based on specific kinds of emails I have seen slip through the cracks. I haven't written any of those in a long time and I suspect some of my rules are now obsolete. You may want to do your own testing before you copy these outright. In addition to rules to match more spam, I've also written a ruleset to remove false positives in French emails coming from many of the above custom rules. I also wrote a rule to get a bonus to any email that comes with a patch:

describe FM_PATCH   Includes a patch
body FM_PATCH   /\bdiff -pruN\b/
score FM_PATCH  -1.0

since it's not very common in spam emails

SpamAssassin settings When it comes to my system-wide SpamAssassin configuration in /etc/spamassassin/, I enable the following plugins:

loadplugin Mail::SpamAssassin::Plugin::AntiVirus
loadplugin Mail::SpamAssassin::Plugin::AskDNS
loadplugin Mail::SpamAssassin::Plugin::ASN
loadplugin Mail::SpamAssassin::Plugin::AutoLearnThreshold
loadplugin Mail::SpamAssassin::Plugin::Bayes
loadplugin Mail::SpamAssassin::Plugin::BodyEval
loadplugin Mail::SpamAssassin::Plugin::Check
loadplugin Mail::SpamAssassin::Plugin::DKIM
loadplugin Mail::SpamAssassin::Plugin::DNSEval
loadplugin Mail::SpamAssassin::Plugin::FreeMail
loadplugin Mail::SpamAssassin::Plugin::FromNameSpoof
loadplugin Mail::SpamAssassin::Plugin::HashBL
loadplugin Mail::SpamAssassin::Plugin::HeaderEval
loadplugin Mail::SpamAssassin::Plugin::HTMLEval
loadplugin Mail::SpamAssassin::Plugin::HTTPSMismatch
loadplugin Mail::SpamAssassin::Plugin::ImageInfo
loadplugin Mail::SpamAssassin::Plugin::MIMEEval
loadplugin Mail::SpamAssassin::Plugin::MIMEHeader
loadplugin Mail::SpamAssassin::Plugin::OLEVBMacro
loadplugin Mail::SpamAssassin::Plugin::PDFInfo
loadplugin Mail::SpamAssassin::Plugin::Phishing
loadplugin Mail::SpamAssassin::Plugin::Pyzor
loadplugin Mail::SpamAssassin::Plugin::Razor2
loadplugin Mail::SpamAssassin::Plugin::RelayEval
loadplugin Mail::SpamAssassin::Plugin::ReplaceTags
loadplugin Mail::SpamAssassin::Plugin::Rule2XSBody
loadplugin Mail::SpamAssassin::Plugin::SpamCop
loadplugin Mail::SpamAssassin::Plugin::TextCat
loadplugin Mail::SpamAssassin::Plugin::TxRep
loadplugin Mail::SpamAssassin::Plugin::URIDetail
loadplugin Mail::SpamAssassin::Plugin::URIEval
loadplugin Mail::SpamAssassin::Plugin::VBounce
loadplugin Mail::SpamAssassin::Plugin::WelcomeListSubject
loadplugin Mail::SpamAssassin::Plugin::WLBLEval

Some of these require extra helper packages or Perl libraries to be installed. See the comments in the relevant *.pre files. My ~/.spamassassin/user_prefs file contains the following configuration:

required_hits   5
ok_locales en fr
# Bayes options
score BAYES_00 -4.0
score BAYES_40 -0.5
score BAYES_60 1.0
score BAYES_80 2.7
score BAYES_95 4.0
score BAYES_99 6.0
bayes_auto_learn 1
bayes_ignore_header X-Miltered
bayes_ignore_header X-MIME-Autoconverted
bayes_ignore_header X-Evolution
bayes_ignore_header X-Virus-Scanned
bayes_ignore_header X-Forwarded-For
bayes_ignore_header X-Forwarded-By
bayes_ignore_header X-Scanned-By
bayes_ignore_header X-Spam-Level
bayes_ignore_header X-Spam-Status

as well as manual score reductions due to false positives, and manual score increases to help push certain types of spam emails over the 12.0 definitely spam threshold. Finally, I have the FuzzyOCR package installed since it has occasionally flagged some spam that other tools had missed. It is a little resource intensive though and so you may want to avoid this one if you are filtering spam for other people. As always, feel free to leave a comment if you do something else that works well and that's not included in my setup. This is a work-in-progress.

Like each month, have a look at the work funded by Freexian s Debian LTS offering. Some notable fixes which were made in LTS during the month of November include the gnutls28 cryptographic library and the freerdp2 Remote Desktop Protocol client/server implementation. The gnutls28 update was prepared by LTS contributor Markus Koschany and dealt with a timing attack which could be used to compromise a cryptographic system, while the freerdp2 update was prepared by LTS contributor Tobias Frost and is the result of work spanning 3 months to deal with dozens of vulnerabilities. In addition to the many ordinary LTS tasks which were completed (CVE triage, patch backports, package updates, etc), there were several contributions by LTS contributors for the benefit of Debian stable and old-stable releases, as well as for the benefit of upstream projects. LTS contributor Abhijith PA uploaded an update of the puma package to unstable in order to fix a vulnerability in that package while LTS contributor Thosten Alteholz sponsored an upload to unstable of libde265 and himself made corresponding uploads of libde265 to Debian stable and old-stable. LTS contributor Bastien Roucari s developed patches for vulnerabilities in zbar and audiofile which were then provided to the respective upstream projects. Updates to packages in Debian stable were made by Markus Koschany to deal with security vulnerabilities and by Chris Lamb to deal with some non-security bugs. As always, the LTS strives to provide high quality updates to packages under the direct purview of the LTS team while also rendering assistance to maintainers, the stable security team, and upstream developers whenever practical.

Debian LTS contributors In November, 18 contributors have been paid to work on Debian LTS, their reports are available:

• Abhijith PA did 7.0h (out of 0h assigned and 14.0h from previous period), thus carrying over 7.0h to the next month.
• Adrian Bunk did 15.0h (out of 14.0h assigned and 9.75h from previous period), thus carrying over 8.75h to the next month.
• Anton Gladky did 10.0h (out of 9.5h assigned and 5.5h from previous period), thus carrying over 5.0h to the next month.
• Bastien Roucari s did 16.0h (out of 18.25h assigned and 1.75h from previous period), thus carrying over 4.0h to the next month.
• Ben Hutchings did 12.0h (out of 16.5h assigned and 12.25h from previous period), thus carrying over 16.75h to the next month.
• Chris Lamb did 18.0h (out of 17.25h assigned and 0.75h from previous period).
• Emilio Pozuelo Monfort did 15.5h (out of 23.5h assigned and 0.25h from previous period), thus carrying over 8.25h to the next month.
• Guilhem Moulin did 13.0h (out of 12.0h assigned and 8.0h from previous period), thus carrying over 7.0h to the next month.
• Lee Garrett did 14.5h (out of 16.75h assigned and 7.0h from previous period), thus carrying over 9.25h to the next month.
• Markus Koschany did 30.0h (out of 30.0h assigned).
• Ola Lundqvist did 6.5h (out of 8.25h assigned and 15.5h from previous period), thus carrying over 17.25h to the next month.
• Roberto C. S nchez did 5.5h (out of 12.0h assigned), thus carrying over 6.5h to the next month.
• Santiago Ruano Rinc n did 3.25h (out of 13.62h assigned and 2.375h from previous period), thus carrying over 12.745h to the next month.
• Sean Whitton did 3.25h (out of 10.0h assigned), thus carrying over 6.75h to the next month.
• Sylvain Beucler did 10.0h (out of 13.5h assigned and 10.25h from previous period), thus carrying over 13.75h to the next month.
• Thorsten Alteholz did 14.0h (out of 14.0h assigned).
• Tobias Frost did 12.0h (out of 12.0h assigned).
• Utkarsh Gupta did 0.0h (out of 6.0h assigned and 17.75h from previous period), thus carrying over 23.75h to the next month.

Evolution of the situation In November, we have released 35 DLAs.

Thanks to our sponsors Sponsors that joined recently are in bold.

• Platinum sponsors:
  • TOSHIBA (for 99 months)
  • Civil Infrastructure Platform (CIP) (for 67 months)
• Gold sponsors:
  • Roche Diagnostics International AG (for 110 months)
  • Linode (for 104 months)
  • Babiel GmbH (for 93 months)
  • Plat Home (for 93 months)
  • University of Oxford (for 49 months)
  • Deveryware (for 36 months)
  • VyOS Inc (for 31 months)
  • EDF SA (for 20 months)
• Silver sponsors:
  • Domeneshop AS (for 114 months)
  • Nantes M tropole (for 108 months)
  • Univention GmbH (for 100 months)
  • Universit Jean Monnet de St Etienne (for 100 months)
  • Ribbon Communications, Inc. (for 94 months)
  • Exonet B.V. (for 84 months)
  • Leibniz Rechenzentrum (for 78 months)
  • CINECA (for 67 months)
  • Minist re de l Europe et des Affaires trang res (for 61 months)
  • Cloudways Ltd (for 51 months)
  • Dinahosting SL (for 49 months)
  • Bauer Xcel Media Deutschland KG (for 43 months)
  • Platform.sh SAS (for 43 months)
  • Moxa Inc. (for 37 months)
  • sipgate GmbH (for 34 months)
  • OVH US LLC (for 32 months)
  • Tilburg University (for 32 months)
  • GSI Helmholtzzentrum f r Schwerionenforschung GmbH (for 23 months)
  • Soliton Systems K.K. (for 21 months)
• Bronze sponsors:
  • Evolix (for 115 months)
  • Seznam.cz, a.s. (for 115 months)
  • Intevation GmbH (for 112 months)
  • Linuxhotel GmbH (for 112 months)
  • Daevel SARL (for 110 months)
  • Bitfolk LTD (for 109 months)
  • Megaspace Internet Services GmbH (for 109 months)
  • Greenbone AG (for 108 months)
  • NUMLOG (for 108 months)
  • WinGo AG (for 108 months)
  • Ecole Centrale de Nantes - LHEEA (for 104 months)
  • Entr ouvert (for 99 months)
  • Adfinis AG (for 96 months)
  • GNI MEDIA (for 91 months)
  • Laboratoire LEGI - UMR 5519 / CNRS (for 91 months)
  • Tesorion (for 91 months)
  • Bearstech (for 82 months)
  • LiHAS (for 82 months)
  • Catalyst IT Ltd (for 77 months)
  • Supagro (for 72 months)
  • Demarcq SAS (for 71 months)
  • Universit Grenoble Alpes (for 57 months)
  • TouchWeb SAS (for 49 months)
  • SPiN AG (for 46 months)
  • CoreFiling (for 41 months)
  • Institut des sciences cognitives Marc Jeannerod (for 36 months)
  • Observatoire des Sciences de l Univers de Grenoble (for 33 months)
  • Tem Innovations GmbH (for 27 months)
  • WordFinder.pro (for 27 months)
  • CNRS DT INSU R sif (for 26 months)
  • Alter Way (for 19 months)
  • Institut Camille Jordan (for 8 months)

Focus This month I didn't have any particular focus. I just worked on issues in my info bubble.

Changes

• tracer: mention needrestart
• duck: add inactive project indicator
• Debian wiki pages: AutoGeneratedFiles, CopyrightReviewTools, CornerCase, CrossGrading, DeveloperNews, Hardware/Wanted, InstallingDebianOn/SiFive/HiFiveUnmatched
• FOSSjobs wiki pages: Resources
• vcs-home wiki: add more dotfile repos/tools

Issues

• Files in wrong dir in git-cola
• Conffile removal needed in dkms
• New SWH listers needed for HGKeeper, Smithy, humungus, git-arr, gitile, gotweb, ABF, Bonobo Git Server, darcsden

Review

• Debian packages: sponsored purple-discord x2
• Debian wiki: RecentChanges for the month
• Debian BTS usertags: changes for the month
• Debian screenshots:
  • approved c-evo-dh-gtk2 fim fish foliate mpc123 nfoview qpwgraph scite viewnior
  • rejected hw-probe (photos), wine64 (desktop logo), phasex (artwork), qpwgraph (about dialog), fim/fish (help output), python-lunch (full desktop), ruby-full (website), ausweisapp2 (PII), pngtools (movie poster), x11vnc (web page,) mount (systemd), blastem (photo), ca-certificates (tiny, Windows)

Administration

• Debian servers: extract user data from recent wiki backups
• Debian wiki: fix broken user account, approve accounts

Communication

• Respond to queries from Debian users and contributors on the mailing lists and IRC.

Sponsors The SWH work was sponsored. All other work was done on a volunteer basis.

Did you hear the news? Firefox development is moving from Mercurial to Git. While the decision is far from being mine, and I was barely involved in the small incremental changes that ultimately led to this decision, I feel I have to take at least some responsibility. And if you are one of those who would rather use Mercurial than Git, you may direct all your ire at me. But let's take a step back and review the past 25 years leading to this decision. You'll forgive me for skipping some details and any possible inaccuracies. This is already a long post, while I could have been more thorough, even I think that would have been too much. This is also not an official Mozilla position, only my personal perception and recollection as someone who was involved at times, but mostly an observer from a distance. From CVS to DVCS From its release in 1998, the Mozilla source code was kept in a CVS repository. If you're too young to know what CVS is, let's just say it's an old school version control system, with its set of problems. Back then, it was mostly ubiquitous in the Open Source world, as far as I remember. In the early 2000s, the Subversion version control system gained some traction, solving some of the problems that came with CVS. Incidentally, Subversion was created by Jim Blandy, who now works at Mozilla on completely unrelated matters. In the same period, the Linux kernel development moved from CVS to Bitkeeper, which was more suitable to the distributed nature of the Linux community. BitKeeper had its own problem, though: it was the opposite of Open Source, but for most pragmatic people, it wasn't a real concern because free access was provided. Until it became a problem: someone at OSDL developed an alternative client to BitKeeper, and licenses of BitKeeper were rescinded for OSDL members, including Linus Torvalds (they were even prohibited from purchasing one). Following this fiasco, in April 2005, two weeks from each other, both Git and Mercurial were born. The former was created by Linus Torvalds himself, while the latter was developed by Olivia Mackall, who was a Linux kernel developer back then. And because they both came out of the same community for the same needs, and the same shared experience with BitKeeper, they both were similar distributed version control systems. Interestingly enough, several other DVCSes existed:

• SVK, a DVCS built on top of Subversion, allowing users to create local (offline) branches of remote Subversion repositories. It was also known for its powerful merging capabilities. I picked it at some point for my Debian work, mainly because I needed to interact with Subversion repositories.
• Arch (tla), later known as GNU arch. From what I remember, it was awful to use. You think Git is complex or confusing? Arch was way worse. It was forked as "Bazaar", but the fork was abandoned in favor of "Bazaar-NG", now known as "Bazaar" or "bzr", a much more user-friendly DVCS. The first release of Bzr actually precedes Git's by two weeks. I guess it was too new to be considered by Linus Torvalds for the Linux kernel needs.
• Monotone, which I don't know much about, but it was mentioned by Linus Torvalds two days before the initial Git commit of Git. As far as I know, it was too slow for the Linux kernel's needs. I'll note in passing that Monotone is the creation of Graydon Hoare, who also created Rust.
• Darcs, with its patch-based model, rather than the common snapshot-based model, allowed more flexible management of changes. This approach came, however, at the expense of performance.

In this landscape, the major difference Git was making at the time was that it was blazing fast. Almost incredibly so, at least on Linux systems. That was less true on other platforms (especially Windows). It was a game-changer for handling large codebases in a smooth manner. Anyways, two years later, in 2007, Mozilla decided to move its source code not to Bzr, not to Git, not to Subversion (which, yes, was a contender), but to Mercurial. The decision "process" was laid down in two rather colorful blog posts. My memory is a bit fuzzy, but I don't recall that it was a particularly controversial choice. All of those DVCSes were still young, and there was no definite "winner" yet (GitHub hadn't even been founded). It made the most sense for Mozilla back then, mainly because the Git experience on Windows still wasn't there, and that mattered a lot for Mozilla, with its diverse platform support. As a contributor, I didn't think much of it, although to be fair, at the time, I was mostly consuming the source tarballs. Personal preferences Digging through my archives, I've unearthed a forgotten chapter: I did end up setting up both a Mercurial and a Git mirror of the Firefox source repository on alioth.debian.org. Alioth.debian.org was a FusionForge-based collaboration system for Debian developers, similar to SourceForge. It was the ancestor of salsa.debian.org. I used those mirrors for the Debian packaging of Firefox (cough cough Iceweasel). The Git mirror was created with hg-fast-export, and the Mercurial mirror was only a necessary step in the process. By that time, I had converted my Subversion repositories to Git, and switched off SVK. Incidentally, I started contributing to Git around that time as well. I apparently did this not too long after Mozilla switched to Mercurial. As a Linux user, I think I just wanted the speed that Mercurial was not providing. Not that Mercurial was that slow, but the difference between a couple seconds and a couple hundred milliseconds was a significant enough difference in user experience for me to prefer Git (and Firefox was not the only thing I was using version control for) Other people had also similarly created their own mirror, or with other tools. But none of them were "compatible": their commit hashes were different. Hg-git, used by the latter, was putting extra information in commit messages that would make the conversion differ, and hg-fast-export would just not be consistent with itself! My mirror is long gone, and those have not been updated in more than a decade. I did end up using Mercurial, when I got commit access to the Firefox source repository in April 2010. I still kept using Git for my Debian activities, but I now was also using Mercurial to push to the Mozilla servers. I joined Mozilla as a contractor a few months after that, and kept using Mercurial for a while, but as a, by then, long time Git user, it never really clicked for me. It turns out, the sentiment was shared by several at Mozilla. Git incursion In the early 2010s, GitHub was becoming ubiquitous, and the Git mindshare was getting large. Multiple projects at Mozilla were already entirely hosted on GitHub. As for the Firefox source code base, Mozilla back then was kind of a Wild West, and engineers being engineers, multiple people had been using Git, with their own inconvenient workflows involving a local Mercurial clone. The most popular set of scripts was moz-git-tools, to incorporate changes in a local Git repository into the local Mercurial copy, to then send to Mozilla servers. In terms of the number of people doing that, though, I don't think it was a lot of people, probably a few handfuls. On my end, I was still keeping up with Mercurial. I think at that time several engineers had their own unofficial Git mirrors on GitHub, and later on Ehsan Akhgari provided another mirror, with a twist: it also contained the full CVS history, which the canonical Mercurial repository didn't have. This was particularly interesting for engineers who needed to do some code archeology and couldn't get past the 2007 cutoff of the Mercurial repository. I think that mirror ultimately became the official-looking, but really unofficial, mozilla-central repository on GitHub. On a side note, a Mercurial repository containing the CVS history was also later set up, but that didn't lead to something officially supported on the Mercurial side. Some time around 2011~2012, I started to more seriously consider using Git for work myself, but wasn't satisfied with the workflows others had set up for themselves. I really didn't like the idea of wasting extra disk space keeping a Mercurial clone around while using a Git mirror. I wrote a Python script that would use Mercurial as a library to access a remote repository and produce a git-fast-import stream. That would allow the creation of a git repository without a local Mercurial clone. It worked quite well, but it was not able to incrementally update. Other, more complete tools existed already, some of which I mentioned above. But as time was passing and the size and depth of the Mercurial repository was growing, these tools were showing their limits and were too slow for my taste, especially for the initial clone. Boot to Git In the same time frame, Mozilla ventured in the Mobile OS sphere with Boot to Gecko, later known as Firefox OS. What does that have to do with version control? The needs of third party collaborators in the mobile space led to the creation of what is now the gecko-dev repository on GitHub. As I remember it, it was challenging to create, but once it was there, Git users could just clone it and have a working, up-to-date local copy of the Firefox source code and its history... which they could already have, but this was the first officially supported way of doing so. Coincidentally, Ehsan's unofficial mirror was having trouble (to the point of GitHub closing the repository) and was ultimately shut down in December 2013. You'll often find comments on the interwebs about how GitHub has become unreliable since the Microsoft acquisition. I can't really comment on that, but if you think GitHub is unreliable now, rest assured that it was worse in its beginning. And its sustainability as a platform also wasn't a given, being a rather new player. So on top of having this official mirror on GitHub, Mozilla also ventured in setting up its own Git server for greater control and reliability. But the canonical repository was still the Mercurial one, and while Git users now had a supported mirror to pull from, they still had to somehow interact with Mercurial repositories, most notably for the Try server. Git slowly creeping in Firefox build tooling Still in the same time frame, tooling around building Firefox was improving drastically. For obvious reasons, when version control integration was needed in the tooling, Mercurial support was always a no-brainer. The first explicit acknowledgement of a Git repository for the Firefox source code, other than the addition of the .gitignore file, was bug 774109. It added a script to install the prerequisites to build Firefox on macOS (still called OSX back then), and that would print a message inviting people to obtain a copy of the source code with either Mercurial or Git. That was a precursor to current bootstrap.py, from September 2012. Following that, as far as I can tell, the first real incursion of Git in the Firefox source tree tooling happened in bug 965120. A few days earlier, bug 952379 had added a mach clang-format command that would apply clang-format-diff to the output from hg diff. Obviously, running hg diff on a Git working tree didn't work, and bug 965120 was filed, and support for Git was added there. That was in January 2014. A year later, when the initial implementation of mach artifact was added (which ultimately led to artifact builds), Git users were an immediate thought. But while they were considered, it was not to support them, but to avoid actively breaking their workflows. Git support for mach artifact was eventually added 14 months later, in March 2016. From gecko-dev to git-cinnabar Let's step back a little here, back to the end of 2014. My user experience with Mercurial had reached a level of dissatisfaction that was enough for me to decide to take that script from a couple years prior and make it work for incremental updates. That meant finding a way to store enough information locally to be able to reconstruct whatever the incremental updates would be relying on (guess why other tools hid a local Mercurial clone under hood). I got something working rather quickly, and after talking to a few people about this side project at the Mozilla Portland All Hands and seeing their excitement, I published a git-remote-hg initial prototype on the last day of the All Hands. Within weeks, the prototype gained the ability to directly push to Mercurial repositories, and a couple months later, was renamed to git-cinnabar. At that point, as a Git user, instead of cloning the gecko-dev repository from GitHub and switching to a local Mercurial repository whenever you needed to push to a Mercurial repository (i.e. the aforementioned Try server, or, at the time, for reviews), you could just clone and push directly from/to Mercurial, all within Git. And it was fast too. You could get a full clone of mozilla-central in less than half an hour, when at the time, other similar tools would take more than 10 hours (needless to say, it's even worse now). Another couple months later (we're now at the end of April 2015), git-cinnabar became able to start off a local clone of the gecko-dev repository, rather than clone from scratch, which could be time consuming. But because git-cinnabar and the tool that was updating gecko-dev weren't producing the same commits, this setup was cumbersome and not really recommended. For instance, if you pushed something to mozilla-central with git-cinnabar from a gecko-dev clone, it would come back with a different commit hash in gecko-dev, and you'd have to deal with the divergence. Eventually, in April 2020, the scripts updating gecko-dev were switched to git-cinnabar, making the use of gecko-dev alongside git-cinnabar a more viable option. Ironically(?), the switch occurred to ease collaboration with KaiOS (you know, the mobile OS born from the ashes of Firefox OS). Well, okay, in all honesty, when the need of syncing in both directions between Git and Mercurial (we only had ever synced from Mercurial to Git) came up, I nudged Mozilla in the direction of git-cinnabar, which, in my (biased but still honest) opinion, was the more reliable option for two-way synchronization (we did have regular conversion problems with hg-git, nothing of the sort has happened since the switch). One Firefox repository to rule them all For reasons I don't know, Mozilla decided to use separate Mercurial repositories as "branches". With the switch to the rapid release process in 2011, that meant one repository for nightly (mozilla-central), one for aurora, one for beta, and one for release. And with the addition of Extended Support Releases in 2012, we now add a new ESR repository every year. Boot to Gecko also had its own branches, and so did Fennec (Firefox for Mobile, before Android). There are a lot of them. And then there are also integration branches, where developer's work lands before being merged in mozilla-central (or backed out if it breaks things), always leaving mozilla-central in a (hopefully) good state. Only one of them remains in use today, though. I can only suppose that the way Mercurial branches work was not deemed practical. It is worth noting, though, that Mercurial branches are used in some cases, to branch off a dot-release when the next major release process has already started, so it's not a matter of not knowing the feature exists or some such. In 2016, Gregory Szorc set up a new repository that would contain them all (or at least most of them), which eventually became what is now the mozilla-unified repository. This would e.g. simplify switching between branches when necessary. 7 years later, for some reason, the other "branches" still exist, but most developers are expected to be using mozilla-unified. Mozilla's CI also switched to using mozilla-unified as base repository. Honestly, I'm not sure why the separate repositories are still the main entry point for pushes, rather than going directly to mozilla-unified, but it probably comes down to switching being work, and not being a top priority. Also, it probably doesn't help that working with multiple heads in Mercurial, even (especially?) with bookmarks, can be a source of confusion. To give an example, if you aren't careful, and do a plain clone of the mozilla-unified repository, you may not end up on the latest mozilla-central changeset, but rather, e.g. one from beta, or some other branch, depending which one was last updated. Hosting is simple, right? Put your repository on a server, install hgweb or gitweb, and that's it? Maybe that works for... Mercurial itself, but that repository "only" has slightly over 50k changesets and less than 4k files. Mozilla-central has more than an order of magnitude more changesets (close to 700k) and two orders of magnitude more files (more than 700k if you count the deleted or moved files, 350k if you count the currently existing ones). And remember, there are a lot of "duplicates" of this repository. And I didn't even mention user repositories and project branches. Sure, it's a self-inflicted pain, and you'd think it could probably(?) be mitigated with shared repositories. But consider the simple case of two repositories: mozilla-central and autoland. You make autoland use mozilla-central as a shared repository. Now, you push something new to autoland, it's stored in the autoland datastore. Eventually, you merge to mozilla-central. Congratulations, it's now in both datastores, and you'd need to clean-up autoland if you wanted to avoid the duplication. Now, you'd think mozilla-unified would solve these issues, and it would... to some extent. Because that wouldn't cover user repositories and project branches briefly mentioned above, which in GitHub parlance would be considered as Forks. So you'd want a mega global datastore shared by all repositories, and repositories would need to only expose what they really contain. Does Mercurial support that? I don't think so (okay, I'll give you that: even if it doesn't, it could, but that's extra work). And since we're talking about a transition to Git, does Git support that? You may have read about how you can link to a commit from a fork and make-pretend that it comes from the main repository on GitHub? At least, it shows a warning, now. That's essentially the architectural reason why. So the actual answer is that Git doesn't support it out of the box, but GitHub has some backend magic to handle it somehow (and hopefully, other things like Gitea, Girocco, Gitlab, etc. have something similar). Now, to come back to the size of the repository. A repository is not a static file. It's a server with which you negotiate what you have against what it has that you want. Then the server bundles what you asked for based on what you said you have. Or in the opposite direction, you negotiate what you have that it doesn't, you send it, and the server incorporates what you sent it. Fortunately the latter is less frequent and requires authentication. But the former is more frequent and CPU intensive. Especially when pulling a large number of changesets, which, incidentally, cloning is. "But there is a solution for clones" you might say, which is true. That's clonebundles, which offload the CPU intensive part of cloning to a single job scheduled regularly. Guess who implemented it? Mozilla. But that only covers the cloning part. We actually had laid the ground to support offloading large incremental updates and split clones, but that never materialized. Even with all that, that still leaves you with a server that can display file contents, diffs, blames, provide zip archives of a revision, and more, all of which are CPU intensive in their own way. And these endpoints are regularly abused, and cause extra load to your servers, yes plural, because of course a single server won't handle the load for the number of users of your big repositories. And because your endpoints are abused, you have to close some of them. And I'm not mentioning the Try repository with its tens of thousands of heads, which brings its own sets of problems (and it would have even more heads if we didn't fake-merge them once in a while). Of course, all the above applies to Git (and it only gained support for something akin to clonebundles last year). So, when the Firefox OS project was stopped, there wasn't much motivation to continue supporting our own Git server, Mercurial still being the official point of entry, and git.mozilla.org was shut down in 2016. The growing difficulty of maintaining the status quo Slowly, but steadily in more recent years, as new tooling was added that needed some input from the source code manager, support for Git was more and more consistently added. But at the same time, as people left for other endeavors and weren't necessarily replaced, or more recently with layoffs, resources allocated to such tooling have been spread thin. Meanwhile, the repository growth didn't take a break, and the Try repository was becoming an increasing pain, with push times quite often exceeding 10 minutes. The ongoing work to move Try pushes to Lando will hide the problem under the rug, but the underlying problem will still exist (although the last version of Mercurial seems to have improved things). On the flip side, more and more people have been relying on Git for Firefox development, to my own surprise, as I didn't really push for that to happen. It just happened organically, by ways of git-cinnabar existing, providing a compelling experience to those who prefer Git, and, I guess, word of mouth. I was genuinely surprised when I recently heard the use of Git among moz-phab users had surpassed a third. I did, however, occasionally orient people who struggled with Mercurial and said they were more familiar with Git, towards git-cinnabar. I suspect there's a somewhat large number of people who never realized Git was a viable option. But that, on its own, can come with its own challenges: if you use git-cinnabar without being backed by gecko-dev, you'll have a hard time sharing your branches on GitHub, because you can't push to a fork of gecko-dev without pushing your entire local repository, as they have different commit histories. And switching to gecko-dev when you weren't already using it requires some extra work to rebase all your local branches from the old commit history to the new one. Clone times with git-cinnabar have also started to go a little out of hand in the past few years, but this was mitigated in a similar manner as with the Mercurial cloning problem: with static files that are refreshed regularly. Ironically, that made cloning with git-cinnabar faster than cloning with Mercurial. But generating those static files is increasingly time-consuming. As of writing, generating those for mozilla-unified takes close to 7 hours. I was predicting clone times over 10 hours "in 5 years" in a post from 4 years ago, I wasn't too far off. With exponential growth, it could still happen, although to be fair, CPUs have improved since. I will explore the performance aspect in a subsequent blog post, alongside the upcoming release of git-cinnabar 0.7.0-b1. I don't even want to check how long it now takes with hg-git or git-remote-hg (they were already taking more than a day when git-cinnabar was taking a couple hours). I suppose it's about time that I clarify that git-cinnabar has always been a side-project. It hasn't been part of my duties at Mozilla, and the extent to which Mozilla supports git-cinnabar is in the form of taskcluster workers on the community instance for both git-cinnabar CI and generating those clone bundles. Consequently, that makes the above git-cinnabar specific issues a Me problem, rather than a Mozilla problem. Taking the leap I can't talk for the people who made the proposal to move to Git, nor for the people who put a green light on it. But I can at least give my perspective. Developers have regularly asked why Mozilla was still using Mercurial, but I think it was the first time that a formal proposal was laid out. And it came from the Engineering Workflow team, responsible for issue tracking, code reviews, source control, build and more. It's easy to say "Mozilla should have chosen Git in the first place", but back in 2007, GitHub wasn't there, Bitbucket wasn't there, and all the available options were rather new (especially compared to the then 21 years-old CVS). I think Mozilla made the right choice, all things considered. Had they waited a couple years, the story might have been different. You might say that Mozilla stayed with Mercurial for so long because of the sunk cost fallacy. I don't think that's true either. But after the biggest Mercurial repository hosting service turned off Mercurial support, and the main contributor to Mercurial going their own way, it's hard to ignore that the landscape has evolved. And the problems that we regularly encounter with the Mercurial servers are not going to get any better as the repository continues to grow. As far as I know, all the Mercurial repositories bigger than Mozilla's are... not using Mercurial. Google has its own closed-source server, and Facebook has another of its own, and it's not really public either. With resources spread thin, I don't expect Mozilla to be able to continue supporting a Mercurial server indefinitely (although I guess Octobus could be contracted to give a hand, but is that sustainable?). Mozilla, being a champion of Open Source, also doesn't live in a silo. At some point, you have to meet your contributors where they are. And the Open Source world is now majoritarily using Git. I'm sure the vast majority of new hires at Mozilla in the past, say, 5 years, know Git and have had to learn Mercurial (although they arguably didn't need to). Even within Mozilla, with thousands(!) of repositories on GitHub, Firefox is now actually the exception rather than the norm. I should even actually say Desktop Firefox, because even Mobile Firefox lives on GitHub (although Fenix is moving back in together with Desktop Firefox, and the timing is such that that will probably happen before Firefox moves to Git). Heck, even Microsoft moved to Git! With a significant developer base already using Git thanks to git-cinnabar, and all the constraints and problems I mentioned previously, it actually seems natural that a transition (finally) happens. However, had git-cinnabar or something similarly viable not existed, I don't think Mozilla would be in a position to take this decision. On one hand, it probably wouldn't be in the current situation of having to support both Git and Mercurial in the tooling around Firefox, nor the resource constraints related to that. But on the other hand, it would be farther from supporting Git and being able to make the switch in order to address all the other problems. But... GitHub? I hope I made a compelling case that hosting is not as simple as it can seem, at the scale of the Firefox repository. It's also not Mozilla's main focus. Mozilla has enough on its plate with the migration of existing infrastructure that does rely on Mercurial to understandably not want to figure out the hosting part, especially with limited resources, and with the mixed experience hosting both Mercurial and git has been so far. After all, GitHub couldn't even display things like the contributors' graph on gecko-dev until recently, and hosting is literally their job! They still drop the ball on large blames (thankfully we have searchfox for those). Where does that leave us? Gitlab? For those criticizing GitHub for being proprietary, that's probably not open enough. Cloud Source Repositories? "But GitHub is Microsoft" is a complaint I've read a lot after the announcement. Do you think Google hosting would have appealed to these people? Bitbucket? I'm kind of surprised it wasn't in the list of providers that were considered, but I'm also kind of glad it wasn't (and I'll leave it at that). I think the only relatively big hosting provider that could have made the people criticizing the choice of GitHub happy is Codeberg, but I hadn't even heard of it before it was mentioned in response to Mozilla's announcement. But really, with literal thousands of Mozilla repositories already on GitHub, with literal tens of millions repositories on the platform overall, the pragmatic in me can't deny that it's an attractive option (and I can't stress enough that I wasn't remotely close to the room where the discussion about what choice to make happened). "But it's a slippery slope". I can see that being a real concern. LLVM also moved its repository to GitHub (from a (I think) self-hosted Subversion server), and ended up moving off Bugzilla and Phabricator to GitHub issues and PRs four years later. As an occasional contributor to LLVM, I hate this move. I hate the GitHub review UI with a passion. At least, right now, GitHub PRs are not a viable option for Mozilla, for their lack of support for security related PRs, and the more general shortcomings in the review UI. That doesn't mean things won't change in the future, but let's not get too far ahead of ourselves. The move to Git has just been announced, and the migration has not even begun yet. Just because Mozilla is moving the Firefox repository to GitHub doesn't mean it's locked in forever or that all the eggs are going to be thrown into one basket. If bridges need to be crossed in the future, we'll see then. So, what's next? The official announcement said we're not expecting the migration to really begin until six months from now. I'll swim against the current here, and say this: the earlier you can switch to git, the earlier you'll find out what works and what doesn't work for you, whether you already know Git or not. While there is not one unique workflow, here's what I would recommend anyone who wants to take the leap off Mercurial right now:

• Make sure git is installed. Chances are you already have it.
• Install git-cinnabar where mach bootstrap would install it.

  $ mkdir -p ~/.mozbuild/git-cinnabar
  $ cd ~/.mozbuild/git-cinnabar
  $ curl -sOL https://raw.githubusercontent.com/glandium/git-cinnabar/master/download.py
  $ python3 download.py && rm download.py

• Add git-cinnabar to your PATH. Make sure to also set that wherever you keep your PATH up-to-date (.bashrc or wherever else).

  $ PATH=$PATH:$HOME/.mozbuild/git-cinnabar

• Enter your mozilla-central or mozilla-unified Mercurial working copy, we'll do an in-place conversion, so that you don't need to move your mozconfigs, objdirs and what not.
• Initialize the git repository from GitHub.

  $ git init
  $ git remote add origin https://github.com/mozilla/gecko-dev
  $ git remote update origin

• Switch to a Mercurial remote.

  $ git remote set-url origin hg::https://hg.mozilla.org/mozilla-unified
  $ git config --local remote.origin.cinnabar-refs bookmarks
  $ git remote update origin --prune

• Fetch your local Mercurial heads.

  $ git -c cinnabar.refs=heads fetch hg::$PWD refs/heads/default/*:refs/heads/hg/*

  This will create a bunch of hg/<sha1> local branches, not all relevant to you (some come from old branches on mozilla-central). Note that if you're using Mercurial MQ, this will not pull your queues, as they don't exist as heads in the Mercurial repo. You'd need to apply your queues one by one and run the command above for each of them.
  Or, if you have bookmarks for your local Mercurial work, you can use this instead:

  $ git -c cinnabar.refs=bookmarks fetch hg::$PWD refs/heads/*:refs/heads/hg/*

  This will create hg/<bookmark_name> branches.
• Now, make git know what commit your working tree is on.

  $ git reset $(git cinnabar hg2git $(hg log -r . -T ' node '))

  This will take a little moment because Git is going to scan all the files in the tree for the first time. On the other hand, it won't touch their content or timestamps, so if you had a build around, it will still be valid, and mach build won't rebuild anything it doesn't have to.

As there is no one-size-fits-all workflow, I won't tell you how to organize yourself from there. I'll just say this: if you know the Mercurial sha1s of your previous local work, you can create branches for them with:

$ git branch <branch_name> $(git cinnabar hg2git <hg_sha1>)

At this point, you should have everything available on the Git side, and you can remove the .hg directory. Or move it into some empty directory somewhere else, just in case. But don't leave it here, it will only confuse the tooling. Artifact builds WILL be confused, though, and you'll have to ./mach configure before being able to do anything. You may also hit bug 1865299 if your working tree is older than this post. If you have any problem or question, you can ping me on #git-cinnabar or #git on Matrix. I'll put the instructions above somewhere on wiki.mozilla.org, and we can collaboratively iterate on them. Now, what the announcement didn't say is that the Git repository WILL NOT be gecko-dev, doesn't exist yet, and WON'T BE COMPATIBLE (trust me, it'll be for the better). Why did I make you do all the above, you ask? Because that won't be a problem. I'll have you covered, I promise. The upcoming release of git-cinnabar 0.7.0-b1 will have a way to smoothly switch between gecko-dev and the future repository (incidentally, that will also allow to switch from a pure git-cinnabar clone to a gecko-dev one, for the git-cinnabar users who have kept reading this far). What about git-cinnabar? With Mercurial going the way of the dodo at Mozilla, my own need for git-cinnabar will vanish. Legitimately, this begs the question whether it will still be maintained. I can't answer for sure. I don't have a crystal ball. However, the needs of the transition itself will motivate me to finish some long-standing things (like finalizing the support for pushing merges, which is currently behind an experimental flag) or implement some missing features (support for creating Mercurial branches). Git-cinnabar started as a Python script, it grew a sidekick implemented in C, which then incorporated some Rust, which then cannibalized the Python script and took its place. It is now close to 90% Rust, and 10% C (if you don't count the code from Git that is statically linked to it), and has sort of become my Rust playground (it's also, I must admit, a mess, because of its history, but it's getting better). So the day to day use with Mercurial is not my sole motivation to keep developing it. If it were, it would stay stagnant, because all the features I need are there, and the speed is not all that bad, although I know it could be better. Arguably, though, git-cinnabar has been relatively stagnant feature-wise, because all the features I need are there. So, no, I don't expect git-cinnabar to die along Mercurial use at Mozilla, but I can't really promise anything either. Final words That was a long post. But there was a lot of ground to cover. And I still skipped over a bunch of things. I hope I didn't bore you to death. If I did and you're still reading... what's wrong with you? ;) So this is the end of Mercurial at Mozilla. So long, and thanks for all the fish. But this is also the beginning of a transition that is not easy, and that will not be without hiccups, I'm sure. So fasten your seatbelts (plural), and welcome the change. To circle back to the clickbait title, did I really kill Mercurial at Mozilla? Of course not. But it's like I stumbled upon a few sparks and tossed a can of gasoline on them. I didn't start the fire, but I sure made it into a proper bonfire... and now it has turned into a wildfire. And who knows? 15 years from now, someone else might be looking back at how Mozilla picked Git at the wrong time, and that, had we waited a little longer, we would have picked some yet to come new horse. But hey, that's the tech cycle for you.

Like each month, have a look at the work funded by Freexian s Debian LTS offering.

Debian LTS contributors In October, 18 contributors have been paid to work on Debian LTS, their reports are available:

• Adrian Bunk did 8.0h (out of 7.75h assigned and 10.0h from previous period), thus carrying over 9.75h to the next month.
• Anton Gladky did 9.5h (out of 9.5h assigned and 5.5h from previous period), thus carrying over 5.5h to the next month.
• Bastien Roucari s did 16.0h (out of 16.75h assigned and 1.0h from previous period), thus carrying over 1.75h to the next month.
• Ben Hutchings did 8.0h (out of 17.75h assigned), thus carrying over 9.75h to the next month.
• Chris Lamb did 17.0h (out of 17.75h assigned), thus carrying over 0.75h to the next month.
• Emilio Pozuelo Monfort did 17.5h (out of 17.75h assigned), thus carrying over 0.25h to the next month.
• Guilhem Moulin did 9.75h (out of 17.75h assigned), thus carrying over 8.0h to the next month.
• Helmut Grohne did 1.5h (out of 10.0h assigned), thus carrying over 8.5h to the next month.
• Lee Garrett did 10.75h (out of 17.75h assigned), thus carrying over 7.0h to the next month.
• Markus Koschany did 30.0h (out of 30.0h assigned).
• Ola Lundqvist did 4.0h (out of 0h assigned and 19.5h from previous period), thus carrying over 15.5h to the next month.
• Roberto C. S nchez did 12.0h (out of 5.0h assigned and 7.0h from previous period).
• Santiago Ruano Rinc n did 13.625h (out of 7.75h assigned and 8.25h from previous period), thus carrying over 2.375h to the next month.
• Sean Whitton did 13.0h (out of 6.0h assigned and 7.0h from previous period).
• Sylvain Beucler did 7.5h (out of 11.25h assigned and 6.5h from previous period), thus carrying over 10.25h to the next month.
• Thorsten Alteholz did 14.0h (out of 14.0h assigned).
• Tobias Frost did 16.0h (out of 9.25h assigned and 6.75h from previous period).
• Utkarsh Gupta did 0.0h (out of 0.75h assigned and 17.0h from previous period), thus carrying over 17.75h to the next month.

Evolution of the situation In October, we have released 49 DLAs. Of particular note in the month of October, LTS contributor Chris Lamb issued DLA 3627-1 pertaining to Redis, the popular key-value database similar to Memcached, which was vulnerable to an authentication bypass vulnerability. Fixing this vulnerability involved dealing with a race condition that could allow another process an opportunity to establish an otherwise unauthorized connection. LTS contributor Markus Koschany was involved in the mitigation of CVE-2023-44487, which is a protocol-level vulnerability in the HTTP/2 protocol. The impacts within Debian involved multiple packages, across multiple releases, with multiple advisories being released (both DSA for stable and old-stable, and DLA for LTS). Markus reviewed patches and security updates prepared by other Debian developers, investigated reported regressions, provided patches for the aforementioned regressions, and issued several security updates as part of this. Additionally, as MariaDB 10.3 (the version originally included with Debian buster) passed end-of-life earlier this year, LTS contributor Emilio Pozuelo Monfort has begun investigating the feasibility of backporting MariaDB 10.11. The work is in early stages, with much testing and analysis remaining before a final decision can be made, as this only one of several available potential courses of action concerning MariaDB. Finally, LTS contributor Lee Garrett has invested considerable effort into the development the Functional Test Framework here. While so far only an initial version has been published, it already has several features which we intend to begin leveraging for testing of LTS packages. In particular, the FTF supports provisioning multiple VMs for the purposes of performing functional tests of network-facing services (e.g., file services, authentication, etc.). These tests are in addition to the various unit-level tests which are executed during package build time. Development work will continue on FTF and as it matures and begins to see wider use within LTS we expect to improve the quality of the updates we publish.

Thanks to our sponsors Sponsors that joined recently are in bold.

• Platinum sponsors:
  • TOSHIBA (for 98 months)
  • Civil Infrastructure Platform (CIP) (for 66 months)
• Gold sponsors:
  • Roche Diagnostics International AG (for 109 months)
  • Linode (for 103 months)
  • Babiel GmbH (for 92 months)
  • Plat Home (for 92 months)
  • University of Oxford (for 48 months)
  • Deveryware (for 35 months)
  • VyOS Inc (for 30 months)
  • EDF SA (for 19 months)
• Silver sponsors:
  • Domeneshop AS (for 113 months)
  • Nantes M tropole (for 107 months)
  • Univention GmbH (for 99 months)
  • Universit Jean Monnet de St Etienne (for 99 months)
  • Ribbon Communications, Inc. (for 93 months)
  • Exonet B.V. (for 83 months)
  • Leibniz Rechenzentrum (for 77 months)
  • CINECA (for 66 months)
  • Minist re de l Europe et des Affaires trang res (for 60 months)
  • Cloudways Ltd (for 50 months)
  • Dinahosting SL (for 48 months)
  • Bauer Xcel Media Deutschland KG (for 42 months)
  • Platform.sh (for 42 months)
  • Moxa Inc. (for 36 months)
  • sipgate GmbH (for 33 months)
  • OVH US LLC (for 31 months)
  • Tilburg University (for 31 months)
  • GSI Helmholtzzentrum f r Schwerionenforschung GmbH (for 23 months)
  • Soliton Systems K.K. (for 20 months)
• Bronze sponsors:
  • Evolix (for 114 months)
  • Seznam.cz, a.s. (for 114 months)
  • Intevation GmbH (for 111 months)
  • Linuxhotel GmbH (for 111 months)
  • Daevel SARL (for 109 months)
  • Bitfolk LTD (for 108 months)
  • Megaspace Internet Services GmbH (for 108 months)
  • Greenbone AG (for 107 months)
  • NUMLOG (for 107 months)
  • WinGo AG (for 107 months)
  • Ecole Centrale de Nantes - LHEEA (for 103 months)
  • Entr ouvert (for 98 months)
  • Adfinis AG (for 95 months)
  • GNI MEDIA (for 90 months)
  • Laboratoire LEGI - UMR 5519 / CNRS (for 90 months)
  • Tesorion (for 90 months)
  • Bearstech (for 81 months)
  • LiHAS (for 81 months)
  • Catalyst IT Ltd (for 76 months)
  • Supagro (for 71 months)
  • Demarcq SAS (for 70 months)
  • Universit Grenoble Alpes (for 56 months)
  • TouchWeb SAS (for 48 months)
  • SPiN AG (for 45 months)
  • CoreFiling (for 40 months)
  • Institut des sciences cognitives Marc Jeannerod (for 35 months)
  • Observatoire des Sciences de l Univers de Grenoble (for 32 months)
  • Tem Innovations GmbH (for 27 months)
  • WordFinder.pro (for 26 months)
  • CNRS DT INSU R sif (for 25 months)
  • Alter Way (for 18 months)
  • Institut Camille Jordan (for 7 months)

Meeting Debian people for having a good time together, for some good hacking, for learning, for teaching Is always fun and welcome. It brings energy, life and joy. And this year, due to the six-months-long relocation my family and me decided to have to Argentina, I was unable to attend the real deal, DebConf23 at India. And while I know DebConf is an experience like no other, this year I took part in two miniDebConfs. One I have already shared in this same blog: I was in MiniDebConf Tamil Nadu in India, followed by some days of pre-DebConf preparation and scouting in Kochi proper, where I got to interact with the absolutely great and loving team that prepared DebConf. The other one is still ongoing (but close to finishing). Some months ago, I talked with Santiago Ruano, jokin as we were Spanish-speaking DDs announcing to the debian-private mailing list we d be relocating to around R o de la Plata. And things worked out normally: He has been for several months in Uruguay already, so he decided to rent a house for some days, and invite Debian people to do what we do best. I left Paran Tuesday night (and missed my online class at UNAM! Well, you cannot have everything, right?). I arrived early on Wednesday, and around noon came to the house of the keysigning (well, the place is properly called Casa Key , it s a publicity agency that is also rented as a guesthouse in a very nice area of Montevideo, close to Nuevo Pocitos beach). In case you don t know it, Montevideo is on the Northern (or Eastern) shore of R o de la Plata, the widest river in the world (up to 300Km wide, with current and non-salty water). But most important for some Debian contributors: You can even come here by boat! That first evening, we received Ilu, who was in Uruguay by chance for other issues (and we were very happy about it!) and a young and enthusiastic Uruguayan, Felipe, interested in getting involved in Debian. We spent the evening talking about life, the universe and everything Which was a bit tiring, as I had to interface between Spanish and English, talking with two friends that didn t share a common language On Thursday morning, I went out for an early walk at the beach. And lets say, if only just for the narrative, that I found a lost penguin emerging from R o de la Plata! For those that don t know (who d be most of you, as he has not been seen at Debian events for 15 years), that s Lisandro Dami n Nicanor P rez Meyer (or just lisandro), long-time maintainer of the Qt ecosystem, and one of our embedded world extraordinaires. So, after we got him dry and fed him fresh river fishes, he gave us a great impromptu talk about understanding and finding our way around the Device Tree Source files for development boards and similar machines, mostly in the ARM world. From Argentina, we also had Emanuel (eamanu) crossing all the way from La Rioja. I spent most of our first workday getting my laptop in shape to be useful as the driver for my online class on Thursday (which is no small feat people that know the particularities of my much loved ARM-based laptop will understand), and running a set of tests again on my Raspberry Pi labortory, which I had not updated in several months. I am happy to say we are also finally also building Raspberry images for Trixie (Debian 13, Testing)! Sadly, I managed to burn my USB-to-serial-console (UART) adaptor, and could neither test those, nor the oldstable ones we are still building (and will probably soon be dropped, if not for anything else, to save disk space). We enjoyed a lot of socialization time. An important highlight of the conference for me was that we reconnected with a long-lost DD, Eduardo Tr pani, and got him interested in getting involved in the project again! This second day, another local Uruguayan, Mauricio, joined us together with his girlfriend, Alicia, and Felipe came again to hang out with us. Sadly, we didn t get photographic evidence of them (nor the permission to post it). The nice house Santiago got for us was very well equipped for a miniDebConf. There were a couple of rounds of pool played by those that enjoyed it (I was very happy just to stand around, take some photos and enjoy the atmosphere and the conversation). Today (Saturday) is the last full-house day of miniDebConf; tomorrow we will be leaving the house by noon. It was also a very productive day! We had a long, important conversation about an important discussion that we are about to present on debian-vote@lists.debian.org. It has been a great couple of days! Sadly, it s coming to an end But this at least gives me the opportunity (and moral obligation!) to write a long blog post. And to thank Santiago for organizing this, and Debian, for sponsoring our trip, stay, foods and healthy enjoyment!

TL;DR: This blog post explores the color capabilities of AMD hardware and how they are exposed to userspace through driver-specific properties. It discusses the different color blocks in the AMD Display Core Next (DCN) pipeline and their capabilities, such as predefined transfer functions, 1D and 3D lookup tables (LUTs), and color transformation matrices (CTMs). It also highlights the differences in AMD HW blocks for pre and post-blending adjustments, and how these differences are reflected in the available driver-specific properties. Overall, this blog post provides a comprehensive overview of the color capabilities of AMD hardware and how they can be controlled by userspace applications through driver-specific properties. This information is valuable for anyone who wants to develop applications that can take advantage of the AMD color management pipeline. Get a closer look at each hardware block s capabilities, unlock a wealth of knowledge about AMD display hardware, and enhance your understanding of graphics and visual computing. Stay tuned for future developments as we embark on a quest for GPU color capabilities in the ever-evolving realm of rainbow treasures.

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Operating Systems can use the power of GPUs to ensure consistent color reproduction across graphics devices. We can use GPU-accelerated color management to manage the diversity of color profiles, do color transformations to convert between High-Dynamic-Range (HDR) and Standard-Dynamic-Range (SDR) content and color enhacements for wide color gamut (WCG). However, to make use of GPU display capabilities, we need an interface between userspace and the kernel display drivers that is currently absent in the Linux/DRM KMS API. In the previous blog post I presented how we are expanding the Linux/DRM color management API to expose specific properties of AMD hardware. Now, I ll guide you to the color features for the Linux/AMD display driver. We embark on a journey through DRM/KMS, AMD Display Manager, and AMD Display Core and delve into the color blocks to uncover the secrets of color manipulation within AMD hardware. Here we ll talk less about the color tools and more about where to find them in the hardware. We resort to driver-specific properties to reach AMD hardware blocks with color capabilities. These blocks display features like predefined transfer functions, color transformation matrices, and 1-dimensional (1D LUT) and 3-dimensional lookup tables (3D LUT). Here, we will understand how these color features are strategically placed into color blocks both before and after blending in Display Pipe and Plane (DPP) and Multiple Pipe/Plane Combined (MPC) blocks. That said, welcome back to the second part of our thrilling journey through AMD s color management realm!

AMD Display Driver in the Linux/DRM Subsystem: The Journey In my 2022 XDC talk I m not an AMD expert, but , I briefly explained the organizational structure of the Linux/AMD display driver where the driver code is bifurcated into a Linux-specific section and a shared-code portion. To reveal AMD s color secrets through the Linux kernel DRM API, our journey led us through these layers of the Linux/AMD display driver s software stack. It includes traversing the DRM/KMS framework, the AMD Display Manager (DM), and the AMD Display Core (DC) [1]. The DRM/KMS framework provides the atomic API for color management through KMS properties represented by struct drm_property. We extended the color management interface exposed to userspace by leveraging existing resources and connecting them with driver-specific functions for managing modeset properties. On the AMD DC layer, the interface with hardware color blocks is established. The AMD DC layer contains OS-agnostic components that are shared across different platforms, making it an invaluable resource. This layer already implements hardware programming and resource management, simplifying the external developer s task. While examining the DC code, we gain insights into the color pipeline and capabilities, even without direct access to specifications. Additionally, AMD developers provide essential support by answering queries and reviewing our work upstream. The primary challenge involved identifying and understanding relevant AMD DC code to configure each color block in the color pipeline. However, the ultimate goal was to bridge the DC color capabilities with the DRM API. For this, we changed the AMD DM, the OS-dependent layer connecting the DC interface to the DRM/KMS framework. We defined and managed driver-specific color properties, facilitated the transport of user space data to the DC, and translated DRM features and settings to the DC interface. Considerations were also made for differences in the color pipeline based on hardware capabilities.

Exploring Color Capabilities of the AMD display hardware Now, let s dive into the exciting realm of AMD color capabilities, where a abundance of techniques and tools await to make your colors look extraordinary across diverse devices. First, we need to know a little about the color transformation and calibration tools and techniques that you can find in different blocks of the AMD hardware. I borrowed some images from [2] [3] [4] to help you understand the information.

Predefined Transfer Functions (Named Fixed Curves): Transfer functions serve as the bridge between the digital and visual worlds, defining the mathematical relationship between digital color values and linear scene/display values and ensuring consistent color reproduction across different devices and media. You can learn more about curves in the chapter GPU Gems 3 - The Importance of Being Linear by Larry Gritz and Eugene d Eon. ITU-R 2100 introduces three main types of transfer functions:

• OETF: the opto-electronic transfer function, which converts linear scene light into the video signal, typically within a camera.
• EOTF: electro-optical transfer function, which converts the video signal into the linear light output of the display.
• OOTF: opto-optical transfer function, which has the role of applying the rendering intent .

AMD s display driver supports the following pre-defined transfer functions (aka named fixed curves):

• Linear/Unity: linear/identity relationship between pixel value and luminance value;
• Gamma 2.2, Gamma 2.4, Gamma 2.6: pure power functions;
• sRGB: 2.4: The piece-wise transfer function from IEC 61966-2-1:1999;
• BT.709: has a linear segment in the bottom part and then a power function with a 0.45 (~1/2.22) gamma for the rest of the range; standardized by ITU-R BT.709-6;
• PQ (Perceptual Quantizer): used for HDR display, allows luminance range capability of 0 to 10,000 nits; standardized by SMPTE ST 2084.

These capabilities vary depending on the hardware block, with some utilizing hardcoded curves and others relying on AMD s color module to construct curves from standardized coefficients. It also supports user/custom curves built from a lookup table.

1D LUTs (1-dimensional Lookup Table): A 1D LUT is a versatile tool, defining a one-dimensional color transformation based on a single parameter. It s very well explained by Jeremy Selan at GPU Gems 2 - Chapter 24 Using Lookup Tables to Accelerate Color Transformations It enables adjustments to color, brightness, and contrast, making it ideal for fine-tuning. In the Linux AMD display driver, the atomic API offers a 1D LUT with 4096 entries and 8-bit depth, while legacy gamma uses a size of 256.

3D LUTs (3-dimensional Lookup Table): These tables work in three dimensions red, green, and blue. They re perfect for complex color transformations and adjustments between color channels. It s also more complex to manage and require more computational resources. Jeremy also explains 3D LUT at GPU Gems 2 - Chapter 24 Using Lookup Tables to Accelerate Color Transformations

CTM (Color Transformation Matrices): Color transformation matrices facilitate the transition between different color spaces, playing a crucial role in color space conversion.

HDR Multiplier: HDR multiplier is a factor applied to the color values of an image to increase their overall brightness.

AMD Color Capabilities in the Hardware Pipeline First, let s take a closer look at the AMD Display Core Next hardware pipeline in the Linux kernel documentation for AMDGPU driver - Display Core Next In the AMD Display Core Next hardware pipeline, we encounter two hardware blocks with color capabilities: the Display Pipe and Plane (DPP) and the Multiple Pipe/Plane Combined (MPC). The DPP handles color adjustments per plane before blending, while the MPC engages in post-blending color adjustments. In short, we expect DPP color capabilities to match up with DRM plane properties, and MPC color capabilities to play nice with DRM CRTC properties. Note: here s the catch there are some DRM CRTC color transformations that don t have a corresponding AMD MPC color block, and vice versa. It s like a puzzle, and we re here to solve it!

AMD Color Blocks and Capabilities We can finally talk about the color capabilities of each AMD color block. As it varies based on the generation of hardware, let s take the DCN3+ family as reference. What s possible to do before and after blending depends on hardware capabilities describe in the kernel driver by struct dpp_color_caps and struct mpc_color_caps. The AMD Steam Deck hardware provides a tangible example of these capabilities. Therefore, we take SteamDeck/DCN301 driver as an example and look at the Color pipeline capabilities described in the file: driver/gpu/drm/amd/display/dcn301/dcn301_resources.c

/* Color pipeline capabilities */
dc->caps.color.dpp.dcn_arch = 1; // If it is a Display Core Next (DCN): yes. Zero means DCE.
dc->caps.color.dpp.input_lut_shared = 0;
dc->caps.color.dpp.icsc = 1; // Intput Color Space Conversion  (CSC) matrix.
dc->caps.color.dpp.dgam_ram = 0; // The old degamma block for degamma curve (hardcoded and LUT).  Gamma correction  is the new one.
dc->caps.color.dpp.dgam_rom_caps.srgb = 1; // sRGB hardcoded curve support
dc->caps.color.dpp.dgam_rom_caps.bt2020 = 1; // BT2020 hardcoded curve support (seems not actually in use)
dc->caps.color.dpp.dgam_rom_caps.gamma2_2 = 1; // Gamma 2.2 hardcoded curve support
dc->caps.color.dpp.dgam_rom_caps.pq = 1; // PQ hardcoded curve support
dc->caps.color.dpp.dgam_rom_caps.hlg = 1; // HLG hardcoded curve support
dc->caps.color.dpp.post_csc = 1; // CSC matrix
dc->caps.color.dpp.gamma_corr = 1; // New  Gamma Correction  block for degamma user LUT;
dc->caps.color.dpp.dgam_rom_for_yuv = 0;
dc->caps.color.dpp.hw_3d_lut = 1; // 3D LUT support. If so, it's always preceded by a shaper curve. 
dc->caps.color.dpp.ogam_ram = 1; //  Blend Gamma  block for custom curve just after blending
// no OGAM ROM on DCN301
dc->caps.color.dpp.ogam_rom_caps.srgb = 0;
dc->caps.color.dpp.ogam_rom_caps.bt2020 = 0;
dc->caps.color.dpp.ogam_rom_caps.gamma2_2 = 0;
dc->caps.color.dpp.ogam_rom_caps.pq = 0;
dc->caps.color.dpp.ogam_rom_caps.hlg = 0;
dc->caps.color.dpp.ocsc = 0;
dc->caps.color.mpc.gamut_remap = 1; // Post-blending CTM (pre-blending CTM is always supported)
dc->caps.color.mpc.num_3dluts = pool->base.res_cap->num_mpc_3dlut; // Post-blending 3D LUT (preceded by shaper curve)
dc->caps.color.mpc.ogam_ram = 1; // Post-blending regamma.
// No pre-defined TF supported for regamma.
dc->caps.color.mpc.ogam_rom_caps.srgb = 0;
dc->caps.color.mpc.ogam_rom_caps.bt2020 = 0;
dc->caps.color.mpc.ogam_rom_caps.gamma2_2 = 0;
dc->caps.color.mpc.ogam_rom_caps.pq = 0;
dc->caps.color.mpc.ogam_rom_caps.hlg = 0;
dc->caps.color.mpc.ocsc = 1; // Output CSC matrix.

I included some inline comments in each element of the color caps to quickly describe them, but you can find the same information in the Linux kernel documentation. See more in struct dpp_color_caps, struct mpc_color_caps and struct rom_curve_caps. Now, using this guideline, we go through color capabilities of DPP and MPC blocks and talk more about mapping driver-specific properties to corresponding color blocks.

DPP Color Pipeline: Before Blending (Per Plane) Let s explore the capabilities of DPP blocks and what you can achieve with a color block. The very first thing to pay attention is the display architecture of the display hardware: previously AMD uses a display architecture called DCE

• Display and Compositing Engine, but newer hardware follows DCN - Display Core Next.

The architectute is described by: dc->caps.color.dpp.dcn_arch

AMD Plane Degamma: TF and 1D LUT Described by: dc->caps.color.dpp.dgam_ram, dc->caps.color.dpp.dgam_rom_caps,dc->caps.color.dpp.gamma_corr AMD Plane Degamma data is mapped to the initial stage of the DPP pipeline. It is utilized to transition from scanout/encoded values to linear values for arithmetic operations. Plane Degamma supports both pre-defined transfer functions and 1D LUTs, depending on the hardware generation. DCN2 and older families handle both types of curve in the Degamma RAM block (dc->caps.color.dpp.dgam_ram); DCN3+ separate hardcoded curves and 1D LUT into two block: Degamma ROM (dc->caps.color.dpp.dgam_rom_caps) and Gamma correction block (dc->caps.color.dpp.gamma_corr), respectively. Pre-defined transfer functions:

• they are hardcoded curves (read-only memory - ROM);
• supported curves: sRGB EOTF, BT.709 inverse OETF, PQ EOTF and HLG OETF, Gamma 2.2, Gamma 2.4 and Gamma 2.6 EOTF.

The 1D LUT currently accepts 4096 entries of 8-bit. The data is interpreted as an array of struct drm_color_lut elements. Setting TF = Identity/Default and LUT as NULL means bypass. References:

• [PATCH v3 04/32] drm/amd/display: add driver-specific property for plane degamma LUT
• [PATCH v3 05/32] drm/amd/display: add plane degamma TF driver-specific property
• [PATCH v3 19/32] drm/amd/display: add plane degamma TF and LUT support

AMD Plane 3x4 CTM (Color Transformation Matrix) AMD Plane CTM data goes to the DPP Gamut Remap block, supporting a 3x4 fixed point (s31.32) matrix for color space conversions. The data is interpreted as a struct drm_color_ctm_3x4. Setting NULL means bypass. References:

• [PATCH v3 30/32] drm/amd/display: add plane CTM driver-specific property
• [PATCH v3 31/32] drm/amd/display: add plane CTM support
• [PATCH v3 32/32] drm/amd/display: Add 3x4 CTM support for plane CTM

AMD Plane Shaper: TF + 1D LUT Described by: dc->caps.color.dpp.hw_3d_lut The Shaper block fine-tunes color adjustments before applying the 3D LUT, optimizing the use of the limited entries in each dimension of the 3D LUT. On AMD hardware, a 3D LUT always means a preceding shaper 1D LUT used for delinearizing and/or normalizing the color space before applying a 3D LUT, so this entry on DPP color caps dc->caps.color.dpp.hw_3d_lut means support for both shaper 1D LUT and 3D LUT. Pre-defined transfer function enables delinearizing content with or without shaper LUT, where AMD color module calculates the resulted shaper curve. Shaper curves go from linear values to encoded values. If we are already in a non-linear space and/or don t need to normalize values, we can set a Identity TF for shaper that works similar to bypass and is also the default TF value. Pre-defined transfer functions:

• there is no DPP Shaper ROM. Curves are calculated by AMD color modules. Check calculate_curve() function in the file amd/display/modules/color/color_gamma.c.
• supported curves: Identity, sRGB inverse EOTF, BT.709 OETF, PQ inverse EOTF, HLG OETF, and Gamma 2.2, Gamma 2.4, Gamma 2.6 inverse EOTF.

The 1D LUT currently accepts 4096 entries of 8-bit. The data is interpreted as an array of struct drm_color_lut elements. When setting Plane Shaper TF (!= Identity) and LUT at the same time, the color module will combine the pre-defined TF and the custom LUT values into the LUT that s actually programmed. Setting TF = Identity/Default and LUT as NULL works as bypass. References:

• [PATCH v3 10/32] drm/amd/display: add plane shaper LUT and TF
• [PATCH v3 23/32] drm/amd/display: add plane shaper LUT support
• [PATCH v3 24/32] drm/amd/display: add plane shaper TF support

AMD Plane 3D LUT Described by: dc->caps.color.dpp.hw_3d_lut The 3D LUT in the DPP block facilitates complex color transformations and adjustments. 3D LUT is a three-dimensional array where each element is an RGB triplet. As mentioned before, the dc->caps.color.dpp.hw_3d_lut describe if DPP 3D LUT is supported. The AMD driver-specific property advertise the size of a single dimension via LUT3D_SIZE property. Plane 3D LUT is a blog property where the data is interpreted as an array of struct drm_color_lut elements and the number of entries is LUT3D_SIZE cubic. The array contains samples from the approximated function. Values between samples are estimated by tetrahedral interpolation The array is accessed with three indices, one for each input dimension (color channel), blue being the outermost dimension, red the innermost. This distribution is better visualized when examining the code in [RFC PATCH 5/5] drm/amd/display: Fill 3D LUT from userspace by Alex Hung:

+	for (nib = 0; nib < 17; nib++)  
+		for (nig = 0; nig < 17; nig++)  
+			for (nir = 0; nir < 17; nir++)  
+				ind_lut = 3 * (nib + 17*nig + 289*nir);
+
+				rgb_area[ind].red = rgb_lib[ind_lut + 0];
+				rgb_area[ind].green = rgb_lib[ind_lut + 1];
+				rgb_area[ind].blue = rgb_lib[ind_lut + 2];
+				ind++;
+			 
+		 
+	 

In our driver-specific approach we opted to advertise it s behavior to the userspace instead of implicitly dealing with it in the kernel driver. AMD s hardware supports 3D LUTs with 17-size or 9-size (4913 and 729 entries respectively), and you can choose between 10-bit or 12-bit. In the current driver-specific work we focus on enabling only 17-size 12-bit 3D LUT, as in [PATCH v3 25/32] drm/amd/display: add plane 3D LUT support:

+		/* Stride and bit depth are not programmable by API yet.
+		 * Therefore, only supports 17x17x17 3D LUT (12-bit).
+		 */
+		lut->lut_3d.use_tetrahedral_9 = false;
+		lut->lut_3d.use_12bits = true;
+		lut->state.bits.initialized = 1;
+		__drm_3dlut_to_dc_3dlut(drm_lut, drm_lut3d_size, &lut->lut_3d,
+					lut->lut_3d.use_tetrahedral_9,
+					MAX_COLOR_3DLUT_BITDEPTH);

A refined control of 3D LUT parameters should go through a follow-up version or generic API. Setting 3D LUT to NULL means bypass. References:

• [PATCH v3 09/32] drm/amd/display: add plane 3D LUT driver-specific properties
• [PATCH v3 25/32] drm/amd/display: add plane 3D LUT support

AMD Plane Blend/Out Gamma: TF + 1D LUT Described by: dc->caps.color.dpp.ogam_ram The Blend/Out Gamma block applies the final touch-up before blending, allowing users to linearize content after 3D LUT and just before the blending. It supports both 1D LUT and pre-defined TF. We can see Shaper and Blend LUTs as 1D LUTs that are sandwich the 3D LUT. So, if we don t need 3D LUT transformations, we may want to only use Degamma block to linearize and skip Shaper, 3D LUT and Blend. Pre-defined transfer function:

• there is no DPP Blend ROM. Curves are calculated by AMD color modules;
• supported curves: Identity, sRGB EOTF, BT.709 inverse OETF, PQ EOTF, HLG inverse OETF, and Gamma 2.2, Gamma 2.4, Gamma 2.6 EOTF.

The 1D LUT currently accepts 4096 entries of 8-bit. The data is interpreted as an array of struct drm_color_lut elements. If plane_blend_tf_property != Identity TF, AMD color module will combine the user LUT values with pre-defined TF into the LUT parameters to be programmed. Setting TF = Identity/Default and LUT to NULL means bypass. References:

• [PATCH v3 11/32] drm/amd/display: add plane blend
• [PATCH v3 27/32] drm/amd/display: add plane blend LUT and TF support

MPC Color Pipeline: After Blending (Per CRTC)

DRM CRTC Degamma 1D LUT The degamma lookup table (LUT) for converting framebuffer pixel data before apply the color conversion matrix. The data is interpreted as an array of struct drm_color_lut elements. Setting NULL means bypass. Not really supported. The driver is currently reusing the DPP degamma LUT block (dc->caps.color.dpp.dgam_ram and dc->caps.color.dpp.gamma_corr) for supporting DRM CRTC Degamma LUT, as explaning by [PATCH v3 20/32] drm/amd/display: reject atomic commit if setting both plane and CRTC degamma.

DRM CRTC 3x3 CTM Described by: dc->caps.color.mpc.gamut_remap It sets the current transformation matrix (CTM) apply to pixel data after the lookup through the degamma LUT and before the lookup through the gamma LUT. The data is interpreted as a struct drm_color_ctm. Setting NULL means bypass.

DRM CRTC Gamma 1D LUT + AMD CRTC Gamma TF Described by: dc->caps.color.mpc.ogam_ram After all that, you might still want to convert the content to wire encoding. No worries, in addition to DRM CRTC 1D LUT, we ve got a AMD CRTC gamma transfer function (TF) to make it happen. Possible TF values are defined by enum amdgpu_transfer_function. Pre-defined transfer functions:

• there is no MPC Gamma ROM. Curves are calculated by AMD color modules.
• supported curves: Identity, sRGB inverse EOTF, BT.709 OETF, PQ inverse EOTF, HLG OETF, and Gamma 2.2, Gamma 2.4, Gamma 2.6 inverse EOTF.

The 1D LUT currently accepts 4096 entries of 8-bit. The data is interpreted as an array of struct drm_color_lut elements. When setting CRTC Gamma TF (!= Identity) and LUT at the same time, the color module will combine the pre-defined TF and the custom LUT values into the LUT that s actually programmed. Setting TF = Identity/Default and LUT to NULL means bypass. References:

• [PATCH v3 12/32] drm/amd/display: add CRTC gamma TF driver-specific property
• [PATCH v3 15/32] drm/amd/display: add CRTC gamma TF support

Others

AMD CRTC Shaper and 3D LUT We have previously worked on exposing CRTC shaper and CRTC 3D LUT, but they were removed from the AMD driver-specific color series because they lack userspace case. CRTC shaper and 3D LUT works similar to plane shaper and 3D LUT but after blending (MPC block). The difference here is that setting (not bypass) Shaper and Gamma blocks together are not expected, since both blocks are used to delinearize the input space. In summary, we either set Shaper + 3D LUT or Gamma.

Input and Output Color Space Conversion There are two other color capabilities of AMD display hardware that were integrated to DRM by previous works and worth a brief explanation here. The DC Input CSC sets pre-defined coefficients from the values of DRM plane color_range and color_encoding properties. It is used for color space conversion of the input content. On the other hand, we have de DC Output CSC (OCSC) sets pre-defined coefficients from DRM connector colorspace properties. It is uses for color space conversion of the composed image to the one supported by the sink. References:

• [PATCH] amd/display/dc: Fix COLOR_ENCODING and COLOR_RANGE doing nothing for DCN20+
• [PATCH v6 00/13] Enable Colorspace connector property in amdgpu

The search for rainbow treasures is not over yet If you want to understand a little more about this work, be sure to watch Joshua and I presented two talks at XDC 2023 about AMD/Steam Deck colors on Gamescope:

• The rainbow treasure map: advanced color management on Linux with AMD/Steam Deck
• Rainbow Frogs: HDR + Color Management in Gamescope/SteamOS

In the time between the first and second part of this blog post, Uma Shashank and Chaitanya Kumar Borah published the plane color pipeline for Intel and Harry Wentland implemented a generic API for DRM based on VKMS support. We discussed these two proposals and the next steps for Color on Linux during the Color Management workshop at XDC 2023 and I briefly shared workshop results in the 2023 XDC lightning talk session. The search for rainbow treasures is not over yet! We plan to meet again next year in the 2024 Display Hackfest in Coru a-Spain (Igalia s HQ) to keep up the pace and continue advancing today s display needs on Linux. Finally, a HUGE thank you to everyone who worked with me on exploring AMD s color capabilities and making them available in userspace.

Tomorrow is going to be a new first day in a new job for me: I am joining the Lean FRO, and I m excited.

What is Lean? Lean is the new kid on the block of theorem provers. It s a pure functional programming language (like Haskell, with and on which I have worked a lot), but it s dependently typed (which Haskell may be evolving to be as well, but rather slowly and carefully). It has a refreshing syntax, built on top of a rather good (I have been told, not an expert here) macro system. As a dependently typed programming language, it is also a theorem prover, or proof assistant, and there exists already a lively community of mathematicians who started to formalize mathematics in a coherent library, creatively called mathlib.

What is a FRO? A Focused Research Organization has the organizational form of a small start up (small team, little overhead, a few years of runway), but its goals and measure for success are not commercial, as funding is provided by donors (in the case of the Lean FRO, the Simons Foundation International, the Alfred P. Sloan Foundation, and Richard Merkin). This allows us to build something that we believe is a contribution for the greater good, even though it s not (or not yet) commercially interesting enough and does not fit other forms of funding (such as research grants) well. This is a very comfortable situation to be in.

Why am I excited? To me, working on Lean seems to be the perfect mix: I have been working on language implementation for about a decade now, and always with a preference for functional languages. Add to that my interest in theorem proving, where I have used Isabelle and Coq so far, and played with Agda and others. So technically, clearly up my alley. Furthermore, the language isn t too old, and plenty of interesting things are simply still to do, rather than tried before. The ecosystem is still evolving, so there is a good chance to have some impact. On the other hand, the language isn t too young either. It is no longer an open question whether we will have users: we have them already, they hang out on zulip, so if I improve something, there is likely someone going to be happy about it, which is great. And the community seems to be welcoming and full of nice people. Finally, this library of mathematics that these users are building is itself an amazing artifact: Lots of math in a consistent, machine-readable, maintained, documented, checked form! With a little bit of optimism I can imagine this changing how math research and education will be done in the future. It could be for math what Wikipedia is for encyclopedic knowledge and OpenStreetMap for maps and the thought of facilitating that excites me. With this new job I find that when I am telling friends and colleagues about it, I do not hesitate or hedge when asked why I am doing this. This is a good sign.

What will I be doing? We ll see what main tasks I ll get to tackle initially, but knowing myself, I expect I ll get broadly involved. To get up to speed I started playing around with a few things already, and for example created Loogle, a Mathlib search engine inspired by Haskell s Hoogle, including a Zulip bot integration. This seems to be useful and quite well received, so I ll continue maintaining that. Expect more about this and other contributions here in the future.