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[Launchpad Bug Tracker <2107340@xxxxxxxxxxxxxxxxxx>]

Status changed to 'Confirmed' because the bug affects multiple users.

** Changed in: pipewire (Ubuntu Plucky)
       Status: New => Confirmed

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https://bugs.launchpad.net/bugs/2107340

Title:
  [SRU] Pipewire fails to reacquire a realtime priority when restarted

Status in pipewire package in Ubuntu:
  Triaged
Status in xdg-desktop-portal package in Ubuntu:
  Triaged
Status in pipewire source package in Plucky:
  Confirmed
Status in xdg-desktop-portal source package in Plucky:
  Confirmed

Bug description:
  [Impact]
  Restarting the pipewire user daemon causes it to lose realtime privileges, potentially resulting in hard-to-diagnose choppy audio.

  [Test plan]
  1. Fresh boot machine
  2. See expected realtime parameters
  ps -e -o pri,ni,comm | grep wire
   30 -11 pipewire
   19 0 pipewire
   30 -11 wireplumber
   30 -11 pipewire-pulse
  3. Restart the services
   systemctl --user restart pipewire wireplumber pipewire-pulse
  4. Ensure the realtime parameters are unchanged from before the restart,
  ps -e -o pri,ni,comm | grep wire
   30 -11 pipewire
   19 0 pipewire
   30 -11 wireplumber
   30 -11 pipewire-pulse

  [Regression potential]
  Backporting both commit dd08d451e3019f4ec6285ecb14d4c746b6e1d420 and 522236e41043a558a825da4cee70ee31ce607147 has a very low regression potential. The first change is purely refactoring commit, which enhances code clarity by renaming functions and variables to better differentiate between pidfds and /proc/$PID directory file descriptors without altering any underlying logic or behavior. The second fixes a specific bug where a function was incorrectly called with a pidfd instead of a /proc/$PID directory file descriptor, introducing a new, correct pidfd-aware function. The PIDFD_GET_PID_NAMESPACE ioctl is a standard Linux kernel interface for interacting with PID file descriptors. Its usage here is straightforward and unlikely to cause unexpected side effects if the underlying kernel support is present.

  [Original report]
  Pipewire tries to acquire a realtime priority when it starts via the libpipewire-module-rt plugin. By default, it prefers to use the org.freedesktop.portal.Realtime interface if xdg-desktop-portal is running (it checks if org.freedesktop.portal.Desktop exists on the session bus). If xdg-desktop-portal isn't running, it uses rtkit directly - see https://gitlab.freedesktop.org/pipewire/pipewire/-/tree/1.2.7/src/modules?ref_type=tags#L932.

  I started looking at this because I have an annoying issue with my
  audio which results in my speakers making popping noises frequently
  when they're outputting anything. I have another issue where my USB
  speakers are frequently not detected by pipewire without restarting
  it.

  When pipewire starts with a new session, it acquires a realtime
  priority by using rtkit directly because xdg-desktop-portal isn't
  running at this stage. However, if you restart pipewire manually later
  on when xdg-desktop-portal is running, pipewire uses the portal
  interface to request a realtime priority, and this fails with xdg-
  desktop-portal outputting the following error to the journal:

  Apr 13 02:58:01 farnsworth xdg-desktop-por[7283]: Realtime error:
  Could not get pidns: Could not fstatat ns/pid: Not a directory

  The libpipewire-module-rt plugin does have an option to disable usage
  of the portal interface for requesting a realtime priority
  (rtportal.enabled=false).

  This is tested with pipewire 1.2.7 in plucky.

  [Additional information]
  See the xdg-desktop-portal package rebuild here:
  https://launchpad.net/~charles05/+archive/ubuntu/ppa/+packages

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