snapd udev rules are incompatible with unified cgroup hierarchy

[Neal Gompa]

snapd / snap-confine currently assume that the legacy CGroup hierarchy is used, however the new unified CGroup hierarchy is coming and is incompatible with the udev hooks currently distributed with the snap-confine aspect of Snappy.

[Zbigniew (zbigniew-redhat-bugs)]

Description of problem:
It's not something that matters much right now, but as people will be moving to unified cgroup hierarchy, this will matter more.
/usr/lib/udev/snappy-app-dev hardcodes paths which are specific to legacy hierarchy (and assumes that devices controller is mounted...).

Version-Release number of selected component (if applicable):
snapd-2.23.6-1.fc27

Expected results:
All code which touches cgroups is ready for legacy and unified hierarchies.

[Zbigniew (zbigniew-redhat-bugs)]

The udev rules are in snap-confine-2.23.6-1.fc26.x86_64.rpm actually.

[Zbigniew (zbigniew-redhat-bugs)]

So there's snap-confine in dist git, but snap-confine is now built from snapd. Confusing!

[Zygmunt Krynicki (zyga)]

Thanks for reporting this issue. As you seem to know more about this than I do, can you tell me how the new cgroup hierarchy works? Snapd has very modest requirements wrt control groups, it merely wants to create a new device control group in specific conditions. We don't care (particularly) about much else, apart from the fact that a process is placed there and that we can put certain devices there.

[Neal Gompa (ngompa13)]

@Zygmunt, I have no idea. I just forwarded the bug on from Red Hat Bugzilla. You'll want to ask Zbigniew Jędrzejewski-Szmek in the linked bug.

[Zygmunt (zygmunt-redhat-bugs)]

Thank you for the bug report. We will look at solving this!