On Mon, Nov 25, 2024 at 4:50 AM Lennart Poettering <lenn...@poettering.net> wrote:
> On So, 24.11.24 12:35, Michael Kilburn (crusader.m...@gmail.com) wrote: > > > Hi, > > > > OS: Pop!_OS 22.04 LTS (Debian-based distro). User service (fluidsynth) > > fails to start on user login: > > > > ALSA lib seq_hw.c:466:(snd_seq_hw_open) open /dev/snd/seq failed: > > Permission denied > > > > because at that moment that device's ACL was not updated yet (to grant > > access to the user being logged in). > > > > When an active user logs in udev executes rules stored in > > /lib/udev/rules.d/70-uaccess.rules (via 73-seat-late.rules) to grant that > > user access to local devices (like soundcard, etc). > > > > Is there a way to express this dependency between user service and > > completion of execution of udev rules? > > > > Or (if this is a wrong approach) -- what is the correct way to deal with > > this? > > "uaccess" ḿeans access to devices can come and go any time, as the > user switches sessions, as sessions come and go. This means programs > which want access to such devices need to be written with this in > mind: watch udev events, and try to reopen the devices whenever you > receive an event for the relevant audio device and access is > permitted. (logind will re-retrigger relevant devices whenever the fg > session changes, so that the udev rules are rerun and apps are > notified about the new situation via udev events) > Turns out, related udev rule(s) only mark /dev/snd devices with "uaccess" tags, actual ACL update happens in logind. And (to my knowledge) there is no event/condition/target you could use to wait for this ACL update to happen. This is the main problem. Waiting in a loop doesn't look like a proper solution at all. Which means user services that need access to these devices are kind of in limbo... You can't configure them to auto-run, have to use hacks. If the device "goes away" (because of a user switch) -- it is not a problem in this case... fluid synth needs to open /de/snd/seq only once (and keeps it open, afaik). Regards, Michael.
