It’s the end of the working week, the weekend is calling, and it’s time for another weekly GNOME Foundation update. As always, there’s plenty going on at the GNOME Foundation, and this post just covers the highlights that are easy to share. Let’s get started.

Board meeting

The Board of Directors had a regular meeting on Tuesday this week (the meeting was regular in the sense that it is regularly scheduled for the 2nd Tuesday of the month).

We were extremely pleased to approve the addition of two new members to the Circle Committee : welcome to Alireza and Ignacy, who will be helping out with the fantastic Circle initiative !

For those who don’t know, the Circle Committee is the team that is responsible for reviewing app submissions, as well as doing regular maintenance on the list of member apps. It’s valuable work.

The main item on the agenda for this week’s Board meeting was the 2025-26 budget, which we finalized and approved. Our financial year runs from October to September, so the budget approval was slightly late, but a delay this small doesn’t have any practical consequence for our operations. We’ll provide a separate post on the budget itself, to provide more details on our plans and financial position.

GIMP grants

Some news which I can share now, even though it isn’t technically from this week: last week the Foundation finished the long process of awarding the GIMP project’s first two development grants. I’m really excited for the GIMP project now that we have reached this milestone, and I’m sure that the grants will give their development efforts a major boost.

More specifics about the grants are coming in a dedicated announcement, so I won’t go into too many details now. However, I will say that a fair amount of work was required on the Foundation side to implement the grants in a compliant manner, including the creation and roll out of a new conflict of interest policy. The nice thing about this is that, with the necessary frameworks in place, it will be relatively easy to award additional grants in the future.

Fundraising Committee

The new Fundraising Committee had its first meeting this week, and I hear that its members have started working through a list of tasks, which is great news. I’m very appreciative of this effort, and especial thanks has to go to Maria Majadas who has pushed it forward.

The committee isn’t an official committee just yet – this is something that the Board will hopefully look at during its next meeting.

Message ends

That’s it for this week! Thanks for reading, and see you next week.

Greetings readers. I’m writing to you from a hotel room in Manchester which I’m currently sharing with a variant of COVID 19. We are listening to disco funk music.

This virus prevents me from working or socializing, but I at least I have time to do some cyber-janitorial tasks like updating my “dotfiles” (which configuration for all the programs i use on Linux, stored in Git… for those who aren’t yet converts).

I also caught up with some big upcoming changes in the GNOME 50 release cycle — more on that below.

nvim

I picked up Vim as my text editor ten years ago while working on a very boring project. This article by Jon Beltran de Heredia, “Why, oh WHY, do those #?@! nutheads use vi?” sold me on the key ideas: you use “normal mode” for everything, which gives you powerful and composable edit operations. I printed out this Vim quick reference card by Michael Goerz and resolved to learn one new operation every day.

It worked and I’ve been a convert ever since. Doing consultancy work makes you a nomad: often working via SSH or WSL on other people’s computers. So I never had the luxury of setting up an IDE like GNOME Builder, or using something that isn’t packaged in 99% of distros. Luckily Vim is everywhere.

Over the years, I read a newletter named Vimtricks and I picked up various Vim plugins like ALE , ctrlp , and sideways . But there’s a problem: some of these depend on extra Vim features like Python support. If a required feature is missing, you get an error message that appears on like… every keystroke :

In this case, on a Debian 12 build machine, I could work around by installing the vim-gtk3 package. But it’s frustrating enough that I decided it was time to try Neovim.

The Neovim project began around the time I was switching to Vim, and is based on the premise that “Vim is, without question, the worst C codebase I have seen.” .

So far its been painless to switch and everything works a little better. The :terminal feels better integrated. I didn’t need to immediately disable mouse mode . I can link to online documentation! The ALE plugin (which provides language server integration) is even ready packaged in Fedora .

I’d send a screenshot but my editor looks… exactly the same as before. Boring!

I also briefly tried out Helix , which appears to take the good bits of Vim (modal editing) and run in a different direction (visible selection and multiple cursors). I need a more boring project before I’ll be able to learn a completely new editor. Give me 10 years.

Endless OS 7

I’ve been working flat out on Endless OS 7 , as last month. Now that the basics work and the system boots, we were mainly looking at integrating Endless-specific Pay as you Go functionality that they use for affordable laptop programs .

I learned more than I wanted to about Linux early boot process, particularly the dracut-ng initramfs generator (one of many Linux components that seems to be named after a town in Massachusetts).

GNOME OS actually dropped Dracut altogether, in “vm-secure: Get rid of dracut and use systemd’s ukify” by Valentin David, and now uses a simple Python script. A lot of Dracut’s features aren’t necessary for building atomic, image-based distros. For EOS we decided to stick with Dracut, at least for now.

So we get to deal with fun changes such as the initramfs growing from 90MB to 390MB after we updated to latest Dracut. Something which is affecting Fedora too (LWN: “Last-minute /boot boost for Fedora 43” ).

I requested time after the contract finishes to write up a technical article on the work we did, so I won’t go into more details yet. Watch this space!

GNOME 50

I haven’t had a minute to look at upstream GNOME this month, but there are some interesting things cooking there.

Jordan merged the GNOME OS openQA tests into the main gnome-build-meta repo . This is a simple solution to a number of basic questions we had around testing, such as, “how do we target tests to specific versions of GNOME?”.

We separated the tests out of gnome-build-meta because, at the time, each new CI pipeline would track new versions of each GNOME module. This meant, firstly that pipelines could take anywhere from 10 minutes to 4 hours rebuilding a disk image before the tests even started, and secondly that the system under test would change every time you ran the pipeline.

While that sounds dumb, it worked this way for historical reasons: GNOME OS has been an under-resourced ad-hoc project ongoing since 2011, whose original goal was simply to continuously build: already a huge challenge if you remember GNOME in the early 2010s. Of course, such as CI pipeline is highly counterproductive if you’re trying to develop and review changes to the tests , and not the system: so the separate openqa-tests repo was a necessary step.

Thanks to Abderrahim’s work in 2022 ( “Commit refs to the repository” and “Add script to update refs” ), plus my work on a tool to run the openQA tests locally before pushing to CI ( ssam_openqa ), I hope we’re not going to have those kinds of problems any more. We enter a brave new world of testing!

The next thing the openQA tests need, in my opinion, is dedicated test infrastructure. The shared Gitlab CI runners we have are in high demand. The openQA tests have timeouts, as they ultimately are doing this in a loop:

• Send an input event
• Wait for the system under test to react

If a VM is running on a test runner with overloaded CPU or IO then tests will start to time out in unhelpful ways. So, if you want to have better testing for GNOME, finding some dedicated hardware to run tests would be a significant help.

There are also some changes cooking in Localsearch thanks to Carlos Garnacho:

• Per removeable device databases
• Index homedir recursively

The first of these is a nicely engineered way to allow searching files on removable disks like external HDs. This should be opt-in: so you can opt in to indexing your external hard drive full of music, but your machine wouldn’t be vulnerable to an attack where someone connects a malicious USB stick while your back is turned. (The sandboxing in localsearch makes it non-trivial to construct such an attack, but it would require a significantly greater level of security auditing before I’d make any guarantees about that).

The second of these changes is pretty big: in GNOME 50, localsearch will now consider everything in your homedir for indexing.

As Carlos notes in the commit message, he has spent years working on performance optimisations and bug fixes in localsearch to get to a point where he considers it reasonable to enable by default. From a design point of view, discussed in the issue “ Be more encompassing about what get indexed “, it’s hard to justify a search feature that only surfaces a subset of your files.

I don’t know if it’s a great time to do this, but nothing is perfect and sometimes you have to take a few risks to move forwards.

There’s a design, testing and user support element to all of this, and it’s going to require help from the GNOME community and our various downstream distributors, particularly around:

• Widely testing the new feature before the GNOME 50 release.
• Making sure users are aware of the change and how to manage the search config.
• Handling an expected increase in bug reports and support requests.
• Highlighting how privacy-focused localsearch is.

I never got time to extend the openQA tests to cover media indexing ; it’s not a trivial job. We will rely on volunteers and downstream testers to try out the config change as widely as possible over the next 6 months.

One thing that makes me support this change is that the indexer in Android devices already works like this: everything is scanned into a local cache, unless there’s a .nomedia file. Unfortunately Google don’t document how the Android media scanner works. But it’s not like this is GNOME treading a radical new path.

The localsearch index lives in the same filesystem as the data, and never leaves your PC. In a world where Microsoft Windows can now send your boss screenshots of everything you looked at , GNOME is still very much on your side. Let’s see if we can tell that story.

Building code for Android with Meson has long been possible, but a bit hacky and not particularly well documented. Recently some new features have landed in Meson main, which make the experience quite a bit nicer. To demonstrate, I have updated the Platypus sample project to build and run on Android. The project itself aims demonstrate how you'd build a GUI application with shared native code on multiple platforms using native widget toolkits on each of them. Currently it supports GTK, Win32, Cocoa, WASM and Android. In addition to building the code it also generates native packages and installers.

It would be nice if you could build full Android applications with just a toolchain directly from the command line. As you start looking into how Android builds work you realize that this is not really the way to go if you want to preserve your sanity. Google has tied app building very tightly into Android Studio. Thus the simple way is to build the native code with Meson, Java/Kotlin code with Android Studio and then merge the two together.

The Platypus repo has a script called build_android.py , which does exactly this. The steps needed to get a working build are the following:

1. Use Meson's env2mfile to introspect the current Android Studio installation and create cross files for all discovered Android toolchains
2. Set up a build directory for the toolchain version/ABI/CPU combination given, defaulting to the newest toolchain and arm64-v8a
3. Compile the code.
4. Install the generated shared library in the source tree under <app source dir>/jniLibs/<cpu> .
5. Android Studio will then automatically install the built libs when deploying the project.

Here is a picture of the end result. The same application is running both in an emulator (x86_64) and a physical device (arm64-v8a).

The main downside is that you have to run the native build step by hand. It should be possible to make this a custom build step in Gradle but I've never actually written Gradle code so I don't know how to do it.

Misc news about the gedit text editor , mid-October edition! (Some sections are a bit technical).

Rework of the file loading and saving (continued)

The refactoring continues in the libgedit-gtksourceview module, this time to tackle a big class that takes too much responsibilities. A utility is in development which will permit to delegate a part of the work.

The utility is about character encoding conversion, with support of invalid bytes. It takes as input a single GBytes (the file content), and transforms it into a list of chunks. A chunk contains either valid (successfully converted) bytes, or invalid bytes. The output format - the "list of chunks" - is subject to change to improve memory consumption and performances.

Note that invalid bytes are allowed, to be able to open really any kind of files with gedit.

I must also note that this is quite sensitive work, at the heart of document loading for gedit. Normally all these refactorings and improvements will be worth it!

Progress in other modules

There has been some progress on other modules:

• gedit: version 48.1.1 has been released with a few minor updates.
• The Flatpak on Flathub: update to gedit 48.1.1 and the GNOME 49 runtime.
• gspell: version 1.14.1 has been released, mainly to pick up the updated translations.

GitHub Sponsors

In addition to Liberapay, you can now support the work that I do on GitHub Sponsors. See the gedit donations page.

Thank you ❤️

Over the past few weeks, I’ve been working on improving some test code that I had written.

Refactoring time!

My first order of business was to refactor the test code. There was a lot of boilerplate, which made it difficult to add new tests, and also created visual clutter.

For example, have a look at this test case:

static void
test_egg_ipuz (void)
{
 g_autoptr (WordList) word_list = NULL;
 IpuzGrid *grid;
 g_autofree IpuzClue *clue = NULL;
 g_autoptr (WordArray) clue_matches = NULL;

 word_list = get_broda_word_list ();
 grid = create_grid (EGG_IPUZ_FILE_PATH);
 clue = get_clue (grid, IPUZ_CLUE_DIRECTION_ACROSS, 2);
 clue_matches = word_list_find_clue_matches (word_list, clue, grid);

 g_assert_cmpint (word_array_len (clue_matches), ==, 3);
 g_assert_cmpstr (word_list_get_indexed_word (word_list,
 word_array_index (clue_matches, 0)),
 ==,
 "EGGS");
 g_assert_cmpstr (
 word_list_get_indexed_word (word_list,
 word_array_index (clue_matches, 1)),
 ==,
 "EGGO");
 g_assert_cmpstr (
 word_list_get_indexed_word (word_list,
 word_array_index (clue_matches, 2)),
 ==,
 "EGGY");
}

That’s an awful lot of code just to say:

1. Use the EGG_IPUZ_FILE_PATH file.
2. Run the word_list_find_clue_matches() function on the 2-Across clue.
3. Assert that the results are ["EGGS", "EGGO", "EGGY"] .

And this was repeated in every test case, and needed to be repeated in every new test case I added. So, I knew that I had to refactor my code.

Fixtures and functions

My first step was to extract all of this setup code:

g_autoptr (WordList) word_list = NULL;
IpuzGrid *grid;
g_autofree IpuzClue *clue = NULL;
g_autoptr (WordArray) clue_matches = NULL;

word_list = get_broda_word_list ();
grid = create_grid (EGG_IPUZ_FILE_PATH);
clue = get_clue (grid, IPUZ_CLUE_DIRECTION_ACROSS, 2);
clue_matches = word_list_find_clue_matches (word_list, clue, grid);

To do this, I used a fixture:

typedef struct {
 WordList *word_list;
 IpuzGrid *grid;
} Fixture;

static void fixture_set_up (Fixture *fixture, gconstpointer user_data)
{
 const gchar *ipuz_file_path = (const gchar *) user_data;

 fixture->word_list = get_broda_word_list ();
 fixture->grid = create_grid (ipuz_file_path);
}

static void fixture_tear_down (Fixture *fixture, gconstpointer user_data)
{
 g_object_unref (fixture->word_list);
}

My next step was to extract all of this assertion code:

g_assert_cmpint (word_array_len (clue_matches), ==, 3);
g_assert_cmpstr (word_list_get_indexed_word (word_list,
 word_array_index (clue_matches, 0)),
 ==,
 "EGGS");
g_assert_cmpstr (
 word_list_get_indexed_word (word_list,
 word_array_index (clue_matches, 1)),
 ==,
 "EGGO");
g_assert_cmpstr (
 word_list_get_indexed_word (word_list,
 word_array_index (clue_matches, 2)),
 ==,
 "EGGY");

To do this, I created a new function that runs word_list_find_clue_matches() and asserts that the result equals an expected_words parameter.

static void
test_clue_matches (WordList *word_list,
 IpuzGrid *grid,
 IpuzClueDirection clue_direction,
 guint clue_index,
 const gchar *expected_words[])
{
 const IpuzClue *clue = NULL;
 g_autoptr (WordArray) clue_matches = NULL;
 g_autoptr (WordArray) expected_word_array = NULL;

 clue = get_clue (grid, clue_direction, clue_index);
 clue_matches = word_list_find_clue_matches (word_list, clue, grid);
 expected_word_array = str_array_to_word_array (expected_words, word_list);

 g_assert_true (word_array_equals (clue_matches, expected_word_array));
}

After all that, here’s what my test case looked like:

static void
test_egg_ipuz (Fixture *fixture, gconstpointer user_data)
{
 test_clue_matches (fixture->word_list,
 fixture->grid,
 IPUZ_CLUE_DIRECTION_ACROSS,
 2,
 (const gchar*[]){"EGGS", "EGGO", "EGGY", NULL});
}

Much better!

Macro functions

But as great as that was, I knew that I could take it even further, with macro functions.

I created a macro function to simplify test case definitions:

#define ASSERT_CLUE_MATCHES(DIRECTION, INDEX, ...) \
 test_clue_matches (fixture->word_list, \
 fixture->grid, \
 DIRECTION, \
 INDEX, \
 (const gchar*[]){__VA_ARGS__, NULL})

Now, test_egg_ipuz() looked like this:

static void
test_egg_ipuz (Fixture *fixture, gconstpointer user_data)
{
 ASSERT_CLUE_MATCHES (IPUZ_CLUE_DIRECTION_ACROSS, 2, "EGGS", "EGGO", "EGGY");
}

I also made a macro function for the test case declarations:

#define ADD_IPUZ_TEST(test_name, file_name) \
 g_test_add ("/clue_matches/" #test_name, \
 Fixture, \
 "tests/clue-matches/" #file_name, \
 fixture_set_up, \
 test_name, \
 fixture_tear_down)

Which turned this:

g_test_add ("/clue_matches/test_egg_ipuz",
 Fixture,
 EGG_IPUZ,
 fixture_set_up,
 test_egg_ipuz,
 fixture_tear_down);

Into this:

ADD_IPUZ_TEST (test_egg_ipuz, egg.ipuz);

An unfortunate bug

So, picture this: You’ve just finished refactoring your test code. You add some finishing touches, do a final test run, look over the diff one last time…and everything seems good. So, you open up an MR and start working on other things.

But then, the unthinkable happens—the CI pipeline fails! And apparently, it’s due to a test failure? But you ran your tests locally, and everything worked just fine. (You run them again just to be sure, and yup, they still pass.) And what’s more, it’s only the Flatpak CI tests that failed. The native CI tests succeeded.

So…what, then? What could be the cause of this? I mean, how do you even begin debugging a test failure that only happens in a particular CI job and nowhere else? Well, let’s just try running the CI pipeline again and see what happens. Maybe the problem will go away. Hopefully, the problem goes away.

…

Nope. Still fails.

…

Rats.

Well, I’ll spare you the gory details that it took for me to finally figure this one out. But the cause of the bug was me accidentally freeing an object that I should never have freed.

This meant that the corresponding memory segment could be —but, importantly, did not necessarily have to be —filled with garbage data. And this is why only the Flatpak job’s test run failed…well, at first, anyway. By changing around some of the test cases, I was able to get the native CI tests and local tests to fail. And this is what eventually clued me into the true nature of this bug.

So, after spending the better part of two weeks, here is the fix I ended up with:

@@ -94,7 +94,7 @@ test_clue_matches (WordList *word_list,
 guint clue_index,
 const gchar *expected_words[])
 {
- g_autofree IpuzClue *clue = NULL;
+ const IpuzClue *clue = NULL;
 g_autoptr (WordArray) clue_matches = NULL;
 g_autoptr (WordArray) expected_word_array = NULL;

Recently I got around tackling a long standing issue for good. There were multiple attempts in the past 6 years to cache flatpak-builder artifacts with Gitlab but none had worked so far.

On the technical side of things, flatpak-builder relies heavily on extended attributes (xattrs) on files to do cache validation. Using gitlab’s built-in cache or artifacts mechanisms results in a plain zip archive which strips all the attributes from the files, causing the cache to always be invalid once restored. Additionally the hardlinks/symlinks in the cache break. One workaround for this is to always tar the directories and then manually extract them after they are restored.

On the infrastructure of things we stumble once again into Gitlab. When a cache or artifact is created, it’s uploaded into the Gitlab’s instance storage so it can later be reused/redownloaded into any runner. While this is great, it also quickly ramps up the network egress bill we have to pay along with storage.
 And since its a public gitlab instance that anyone can make request against repositories, it gets out of hand fast.

Couple weeks ago Bart pointed me out to Flathub ’s workaround for this same problem. It comes down to making it someone else problem, and ideally one someone who is willing to fund FOSS infrastructure. We can use ORAS to wrap files and directories into an OCI wrapper and publish it to public registries. And it worked. Quite handy! OCI images are the new tarballs.

Now when a pipeline run against your default branch (and assuming it’s protected) it will create a cache artifact and upload to the currently configured OCI registry. Afterwards, any build, including Merge Request pipelines, will download the image, extract the artifacts and check how much of it is still valid.

From some quick tests and numbers, GNOME Builder went from a ~16 minute build to 6 minutes for our x86_64 runners. While on the AArch64 runner the impact was even bigger, going from 50 minutes to 16 minutes. Not bad. The more modules you are building in your manifest, the more noticeable it is.

Unlike Buildstream , there is no Content Addressable Server and flatpak-builder itself isn’t aware of the artifacts we publish or can associate them with the cache keys. The OCI/ORAS cache artifacts are manual and a bit hacky of a solution but works well in practice and until we have better tooling. To optimize a bit better for less cache-misses consider building modules from pinned commits/tags/tarballs and building modules from moving branches as late as possible.

If you are curious in the details, take a look at the related Merge Request in the templates repository and the follow up commits.

Free Palestine

Last month GNOME 49 was released , very smooth overall, especially given the amount of changes across the entire stack that we shipped.

One thing that is missing and that flew under the radar however, is that 32 bit Compatibility extension (org.gnome.Platform.i386.Compat) of the GNOME Flatpak Runtime is now gone. We were planning on making an announcement earlier but life got in the way.

That extension is a 32-bit version of the Runtime that applications could request to use. This is mostly helpful so Wine can use a 32 bit environment to run against. However your wine or legacy applications most likely don’t require a 32 bit build of GTK 4, libadwaita or WebkitGTK.

We rebuild all of GNOME from the latest commits in git in each module, at least twice a day. This includes 2 builds of WebkitGTK, a build of mozjs and a couple of rust libraries and applications. Multiplied for each architecture we support. This is no small task for our CI machines to handle. There were also a couple of updates that were blocked on 32-bit specific build failures, as projects rarely test for that before merging the code. Suffice to say that supporting builds that almost nobody used or needed was a universal annoyance across developers and projects.

When we lost our main pool of donated CI machines and builders, the first thing in the chopping block was the 32-bit build of the runtime. It affected no applications, as none are relying on the Nightly version of the extension but it would affect some applications on Flathub once released.

In order to keep the applications working, and to avoid having to overload our runners again, we thought about another approach. In theory it would be possible to make the runtime compatible with the org.Freedesktop.i386.Compat extension point instead. We already use freedesktop-sdk as the base for the runtime so we did not expect many issues.

There were exactly 4 applications that made use of the gnome specific extension, 2 in Flathub, 1 in Flathub Beta and 1 archived.

Abderrahim and I worked on porting all the application to the GNOME 49 runtime and have Pull Requests open. The developers of Bottles were great help in our testing and the subsequent PR is almost ready to be merged. Lutris and Minigalaxy need some extra work to upgrade the runtime but its for unrelated reasons.

Since everything was working we never re-published the i386 GNOME compatibility extension again in Nightly, and thus we also didn’t for GNOME 49. As a result, the GNOME Runtime is only available for x86_64 and AArch64.

Couple years ago we dropped the normal armv7 and i386 build as of the Runtime. With the i386 compatibility extension also gone, it means that we no longer have any 32 bit targets we QA before releasing GNOME as a whole. Previously, all modules we released would be guaranteed to at least compile for i386/x86 but going forward that will not be the case.

Some projects, for example glib, have their own CI specifically for 32 bit architectures. What was a project-wide guarantee before, is now a per-project opt-in. While many maintainers will no longer go out of their way to fix 32 bit specific issues anymore, they will most likely still review and merge any patches sent their way.

If you are a distributor, relying on 32 bit builds of GNOME, you will now be expected to debug and fix issues on your own for the majority of the projects. Alternatively you could also get involved upstream and help avoid further bit rot of 32 bit builds.

Free Palestine

Not as much as I wanted to do was done in September.

libopenraw

Extracting more of the calibration values for colour correction on DNG. Currently work on fixing the purple colour cast.

Added Nikon ZR and EOS C50.

ExifTool

Submitted some metadata updates to ExifTool. Because it nice to have, and also because libopenraw uses some of these autogenerated: I have a Perl script to generate Rust code from it (it used to do C++).

Niepce

Finally merged the develop branch with all the import dialog work after having requested that it be removed from Damned Lies to not strain the translator is there is a long way to go before we can freeze the strings.

Supporting cast

Among the number of packages I maintain / update on flathub, LightZone is a digital photo editing application written in Java ¹ . Updating to the latest runtime 25.08 cause it to ignore the HiDPI setting. It will honour GDK_SCALE environment but this isn't set. So I wrote the small command line too gdk-scale to output the value. See gdk-scale on gitlab . And another patch in the wrapper script.

HiDPI support remains a mess across the board. Fltk just recently gained support for it (it's used by a few audio plugins).

A while ago I wrote about the limited usefulness of SO_PEERPIDFD . for authenticating sandboxed applications. The core problem was simple: while pidfds gave us a race-free way to identify a process, we still had no standardized way to figure out what that process actually was - which sandbox it ran in, what application it represented, or what permissions it should have.

The situation has improved considerably since then.

cgroup xattrs

Cgroups now support user extended attributes. This feature allows arbitrary metadata to be attached to cgroup inodes using standard xattr calls.

We can change flatpak (or snap, or any other container engine) to create a cgroup for application instances it launches, and attach metadata to it using xattrs. This metadata can include the sandboxing engine, application ID, instance ID, and any other information the compositor or D-Bus service might need.

Every process belongs to a cgroup, and you can query which cgroup a process belongs to through its pidfd - completely race-free.

Standardized Authentication

Remember the complexity from the original post? Services had to implement different lookup mechanisms for different sandbox technologies:

• For flatpak: look in /proc/$PID/root/.flatpak-info
• For snap: shell out to snap routine portal-info
• For firejail: no solution
• …

All of this goes away. Now there’s a single path:

1. Accept a connection on a socket
2. Use SO_PEERPIDFD to get a pidfd for the client
3. Query the client’s cgroup using the pidfd
4. Read the cgroup’s user xattrs to get the sandbox metadata

This works the same way regardless of which sandbox engine launched the application.

A Kernel Feature, Not a systemd One

It’s worth emphasizing: cgroups are a Linux kernel feature. They have no dependency on systemd or any other userspace component. Any process can manage cgroups and attach xattrs to them. The process only needs appropriate permissions and is restricted to a subtree determined by the cgroup namespace it is in. This makes the approach universally applicable across different init systems and distributions.

To support non-Linux systems, we might even be able to abstract away the cgroup details, by providing a varlink service to register and query running applications. On Linux, this service would use cgroups and xattrs internally.

Replacing Socket-Per-App

The old approach - creating dedicated wayland, D-Bus, etc. sockets for each app instance and attaching metadata to the service which gets mapped to connections on that socket - can now be retired. The pidfd + cgroup xattr approach is simpler: one standardized lookup path instead of mounting special sockets. It works everywhere: any service can authenticate any client without special socket setup. And it’s more flexible: metadata can be updated after process creation if needed.

For compositor and D-Bus service developers, this means you can finally implement proper sandboxed client authentication without needing to understand the internals of every container engine. For sandbox developers, it means you have a standardized way to communicate application identity without implementing custom socket mounting schemes.