shl: dlist: fix *_but_one() loops to allow "start == head"

If we iterate over a non-empty list and pass the same pointer for start
and head, then we will never leave that loop.

It might be unclear why this is supported at all as we can simply use the
shl_dlist_for_each() for that. However, it makes code a lot easier to read
if the user can simply use shl_dlist_for_each_but_one() without checking
whether they passed the same for start and head.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
seat: implement delayed session switching

If we want to allow external programs to control sessions inside of
kmscon, we need to give them some time for session
activation/deactivation. Therefore, the whole session-management is
asynchronous now and allows the session code to return EINPROGRESS or
similar if they need more time.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
seat: allow sessions to notify seat when deactivating

If a session is deactivated asynchronously, it can now notify the seat
when it is done. This will then cause a re-schedule of the session list.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: do not modify TTY settings

We do not use the TTY for anything except VT functions. Hence, there is no
need to modify the TTY settings before using it.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: fix not overwriting 'ret' in error paths

We cannot use 'ret' in error paths, otherwise, we might return 0. This
might then cause instabilities as the objects weren't initialized
correctly.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
test_vt: use a dummy input-object

We cannot allocate VT objects without an associated input object.
Therefore, allocate a dummy device with no input devices assigned to it
and use it for the test-vt object.

Note that this makes switching from/to this VT via command-line
impossible.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
test_vt: remove trailing newline in log-message

The log-subsystem adds these automatically so we shouldn't use them.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
test_vt: add --vt=<path> option

This new option allows specifying a path to the VT that should be used.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
test_vt: add --switchvt option

This has the same effect as for kmscon but is disabled by default.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
seat: remove bogus debug statements

These shouldn't be pushed into the public repository. Sorry.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
build: fix wlterm wayland-dependency check

The logic behind this two-layer check is bogus and doesn't work. Merge
both layers so we have a proper dependency-check again. This will make the
error messages less verbose but at least it works again.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: do not check SIGUSR1/2 for SI_KERNEL

If we want to run as client under user-space fake-VT implementations like
kmscon-cdev, we need to be able to catch those signals from
userspace-daemons. Therefore, do not check whether the signals were
generated by the kernel.

This doesn't affect security in any way as non-priviledged processes
aren't allowed to send signals, anyway. Moreover, this increases
debugability of VT layers a lot as we can fake these signals now.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
seat: allow calling go_foreground if already in foreground

If we are asleep and in foreground, go_foreground() should return success
so we can safely unload asynchronous sessions. Otherwise, we wouldn't be
able to handle them properly while being inactive or we would need a whole
bunch of other checks.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
seat: fix forwarding errors in seat_pause()

If we force a pause we need to forward the error code. Otherwise, we
cannot properly react on it and print warnings.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: do nothing if target-VT is already active during deactivation

If we deactivate our VT and the target-VT is already active (probably
because we opened the _current_ VT during uterm-vt creation), we shouldn't
do anything but simply close the VT.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: do nothing if VT-switch targets our VT

If the user presses some keys to switch VTs and the target VT is our VT
(which is already active in this case), we shouldn't do anything. Calling
VT_ACTIVATE doesn't particularly hurt, but it doesn't get us anything
here so skip it.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: implement delayed VT-switches

If we cannot immediately perform a VT switch away from our application, we
might want to retry this shortly after. Therefore, we can now call
uterm_vt_retry() which then performs any outstanding VT-switches.

To avoid unexpected behavior, we limit this to a 2-3 second delay.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
seat: allow sessions to control VT-switches

A new helper allows sessions to manually handly input events so the core
does no longer perform session/VT switches on their behalf.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
seat: allow sessions to switch between background/foreground

Two new helpers allow sessions to mark them as background and foreground
sessions. This will immediately switch them into the new state.

The internal infrastructure was already available, but we currently always
used foreground sessions.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
seat: fix calling parent-callbacks on forced sleeping

If we force a seat to go asleep, we should _always_ notify the parent
about this. Otherwise, we might get unexpected results.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>