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authorDavid Herrmann <dh.herrmann@gmail.com>2013-11-28 14:58:57 +0100
committerDavid Herrmann <dh.herrmann@gmail.com>2013-11-28 15:16:49 +0100
commit6d33772f9ae6769c557e2267d16b7d31f67db914 (patch)
tree96c49df6aa556b07b8d9e51cbf8db8833ab9c96f /src/login/test-inhibit.c
parentd1107170f9e0fa2cb6e8d18586a003f0d96abfc3 (diff)
logind: restore session-controller after crash
We now save the unique bus-name of a session-controller as CONTROLLER=%s in the session files. This allows us to restore the controller after a crash or restart. Note that we test whether the name is still valid (dbus guarantees that the name is unique as long as the machine is up and running). If it is, we know that the controller still exists and can safely restore it. Our dbus-name-tracking guarantees that we're notified once it exits. Also note that session-devices are *not* restored. We have no way to know which devices where used before the crash. We could store all these on disk, too, or mark them via udev. However, this seems to be rather cumbersome. Instead, we expect controllers to listen for NewSession signals for their own session. This is sent on session_load() and they can then re-request all devices. The only race I could find is if logind crashes, then the session controller tries calling ReleaseControl() (which will fail as logind is down) but keeps the bus-connection valid for other independent requests. If logind is restarted, it will restore the old controller and thus block the session. However, this seems unlikely for several reasons: - The ReleaseControl() call must occur exactly in the timespan where logind is dead. - A process which calls ReleaseControl() usually closes the bus-connection afterwards. Especially if ReleaseControl() fails, the process should notice that something is wrong and close the bus. - A process calling ReleaseControl() usually exits afterwards. There may be any cleanup pending, but other than that, usual compositors exit. - If a session-controller calls ReleaseControl(), a session is usually considered closing. There is no known use-case where we hand-over session-control in a single session. So we don't care whether the controller is locked afterwards. So this seems negligible.
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