The kernel Secure Attention Key killer, triggered by SysRq+k, kills all
processes that hold an fd referencing the tty.
To avoid its attention, we stop storing the fd for the currently active
VT in seat state. This has the added benefit of simplifying state a bit.
If a client closed while it was disabled, the VT would not be torn down.
If the user navigated back to the VT it belonged to, they would be
stuck.
When a client is disabled, open the fd for the VT it belonged to and
perform regular teardown on it.
Linux only requires acking release and ignores ack of acquire, but
FreeBSD is more stringent and will patiently wait for both to be acked.
Implement proper acking for both events.
The seat activation logic did not correctly handle VT switching and
switching between multiple sessions.
Session switching on VT-bound seats is now performed using a VT switch,
taking advantage of VT signals to perform the actual switch. This
simplifies switching logic and makes it more robust.
Previously, seatd would not deactivate devices until the client had
acked the disable. In once instance, this lead to libinput spending
significant time checking and closing each input device.
As a workaround, mimick logind's behavior of deactivating devices first.
The original behavior can be reintroduced if the client-side problem is
fixed.
Closes: https://todo.sr.ht/~kennylevinsen/seatd/5
The VT and KD ioctl's are picky about the tty fd used. In order to
satisfy these, and to improve state cleanup, we now only and store the
current tty when opening a client, and use this fd to perform teardown
later. The presence of the fd is also used to signal that teardown is
needed.
FreeBSD device numbers cannot be used to check the type of a device, as
they are merely unique filesystem IDs.
As the paths we use have been sanitized with realpath, we can simply use
the path to check if a requested file is an evdev or drm device. This
also allows us to make the check before the file is opened.
