uterm: vt: move kmscon_vt_supported() to uterm-vt

Instead of having a global symbol, we simply move the check to uterm-vt
and can remove it from global namespace. Furthermore, we cache the result
so we can reuse it on the VT-master if required.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: move all vt.h/c code into uterm_vt.c

This merges both files so we can reduce the code overhead here. This is
still some very old code that was never correctly merged into new
uterm_vt.c subsystem. This should help doing it now.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: remove duplicate kmscon_vt_action

This enum is not needed as the uterm-vt code already has enums for
vt-actions. Replace it with UTERM_VT_ACTIVATE/DEACTIVATE.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: remove obsolete kmscon_vt_id

We always open a new VT as there is no need for us to open an existing VT.
Hard-code this behavior but keep the open_tty() backend accepting
VT-numbers just in case we want this some time in the future.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: merge uterm_vt and kmscon_vt

There is no need to use separate structures so merge both into a unified
uterm_vt.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: remove connect_eloop/disconnect_eloop functions

This removes both functions and merges them into the callers. They're
small enough to be directly included.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: rename real VTs internally to real_*

Instead of using the old kmscon_vt_* names we now prefix everything that
implements real linux VTs with real_*. An internal flag specifies which
mode the VT is in so we can check whether we are a real VT or a fake one.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: always register signal handlers

This register the SIGUSR1/2 signal handlers even though we are no real VT.
This is needed to implement other fake-VT helpers for systems were real
VTs are not available.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: mark vts as dead during deallocation

To avoid useless checks wether a vt is valid we simply mark it as dead and
centralize the checks in the API entry point.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: ignore non-kernel signals in real-mode

If using real linux VTs, we must ignore all signals that are not sent from
the kernel. Otherwise, we might get problems if we reuse SIGUSR for other
functionality.
Note that we already check that we are the active VT before handling
SIGUSR. However, this hardens this check to be more sure that this is
really the signal we want.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
uterm: vt: add fake-vt logic for debugging

This adds a very limited non-multi-seat-capable fake-VT logic. If you use
this in production it will break your multi-seat systems so do not use it
except for debugging.

On SIGUSR1 we activate fake VTs and on SIGUSR2 we deactivate them. The
signals must be sent from a priviledged process. Kernel signals are
ignored.

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