[systemd-devel] logind: support of shared devices

[Oleg Samarin]

Hello!

The default systemd behavior is to grant/revoke access on devices
attached to a seat when the user activates/deactivates a session on the
seat.

But sometimes it needs the user has an access to some device when he/she
activates a session with ANY seat. 

For example, I have two seats:
seat0 with ordinary monitor/keyboard/mouse/usb hub/usb sound card and
seat1 that is using as a music workstation: it has some midi keyboards
and sound cards connected. Usually I run midi applications on seat1, but
sometimes I run them on seat1. All midi applications require the access
to /dev/snd/seq kernel device. So it should be granted when a user
activates a session on any seat.

My approach to make this is to introduce a special UDEV tag 'shared'
that tells logind that this device is attached to all seats and logind
has to grant access to all sessions on all seats

I've made a patch to systemd/logind that processes the 'shared' tag.

After adding the simple udev rule:

----------------------------------------------
KERNEL=="seq", SUBSYSTEM=="sound", TAG+="shared"
----------------------------------------------

/dev/snd/seq becomes accessible from all seats.

Could you resolve this patch upstream or propose another way of granting
access to /dev/snd/seq on activating sessions?

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