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logind: implement generic multi-session

System Internals / systemd - David Herrmann [gmail.com] - 17 September 2013 17:15 UTC

This enables the multi-session capability for seats that don't have VTs. For legacy seats with VTs, everything stays the same. However, all other seats now also get the multi-session capability.

The only feature that was missing was session-switching. As logind can force a session-switch and signal that via the "Active" property, we only need a way to allow synchronized/delayed session switches. Compositors need to cleanup some devices before acknowledging the session switch. Therefore, we use the session-devices to give compositors a chance to block a session-switch until they cleaned everything up.

If you activate a session on a seat without VTs, we send a PauseDevice signal to the active session for every active device. Only once the session acknowledged all these with a PauseDeviceComplete() call, we perform the final session switch.

One important note is that delayed session-switching is meant for backwards compatibility. New compositors or other sessions should really try to deal correctly with forced session switches! They only need to handle EACCES/EPERM from syscalls and treat them as "PauseDevice" signal.

Following logind patches will add a timeout to session-switches which forces the switch if the active session does not react in a timely fashion. Moreover, explicit ForceActivate() calls might also be supported. Hence, sessions must not crash if their devices get paused.

d7bd01b logind: implement generic multi-session
src/login/logind-seat.c | 15 +++++++++++++++
src/login/logind-seat.h | 2 ++
src/login/logind-session-device.c | 28 ++++++++++++++++++++++++++++
src/login/logind-session-device.h | 1 +
src/login/logind-session.c | 31 ++++++++++++++++++++++++++-----
5 files changed, 72 insertions(+), 5 deletions(-)

Upstream: github.com