linux-kernel - [RFC PATCH 0/4] Add specific vt input's key map

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Date:   Wed, 22 Aug 2018 23:50:31 +0200
From:   Remi Pommarel <repk@...plefau.lt>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Kees Cook <keescook@...omium.org>,
        Elie Roudninski <xademax@...il.com>,
        Remi Pommarel <repk@...plefau.lt>
Subject: [RFC PATCH 0/4] Add specific vt input's key map

This patchset adds a way to have a specific keyboard config (i.e.
keycode to keysym map) for a vt attached input.

Because one can have different keyboards with different layouts on the
same VT, it can be useful to be able to associate a different keymap
with a different input. In order to do so this patchset introduces
three new ioctls:

1) KDGKBIENT
	Get an input key map's entry. If the input does not have a
	specific key map the requested entry is fetched from global
	key map.

2) KDSKBIENT
	Set an input key map's entry. If the input does not yet have a
	specific key map, a new one is created with the current global
	key map content copied in.

3) KDSKBIRST
	Reset an input key map. The input does not use a specific key
	map anymore and keycode translations are done with global key
	map.

In order to keep old behavior compatibility and not waste memory, an
input uses the global key_maps[] array by default and KDGKBENT/KDSKBENT
ioctls still get/set entries in this global key map. The specific key
map is only allocated on the first call to KDSKBIENT.

A patch for loadkeys is ready to be sent to the ML if this patchset
seems sane to you.

Here are some questions I had while doing this patchset:

- Maybe there is a way, I am not aware of, that can allow one to use
  different keyboard layout on same VT ?

- Is it ok to add new ioctl to old legacy code ? I added those ioctl
  the old way in order to match the header style. Maybe it is better to
  use the __IO* macros ?

- Should key_down bitmap be really input specific (i.e. PATCH 3/4) ?

- I am not quite sure about the meaning of keymap_count. IIUC, it is a
  counter of used keymap function arrays statically or dynamically
  allocated. If it is not the case, the modificiation in kc_setent() that
  decrements keymap_count even if a statically keymap function is removed
  with "K_NOSUCHMAP" (in PATCH 2/4) may be wrong ?

- kbd_detach_conf is a bit clumsy because it tries to copy a shared sparse
  pointer array without using GFP_ATOMIC.

- Is this patchset even a sensible idea ?

Remi Pommarel (4):
  drivers/tty/vt/keyboard.c: refactor getting/setting a keymap entry
  drivers/tty/vt/keyboard.c: add keyboard config for each vt's input
  drivers/tty/vt/keyboard.c: Make key_down[] bitmap input dependent
  drivers/tty/vt: add ioctl to manage input specific keyboard configs

 drivers/tty/vt/keyboard.c | 531 ++++++++++++++++++++++++++++++--------
 drivers/tty/vt/vt_ioctl.c |   9 +
 fs/compat_ioctl.c         |   3 +
 include/linux/vt_kern.h   |   4 +
 include/uapi/linux/kd.h   |   9 +
 5 files changed, 452 insertions(+), 104 deletions(-)

-- 
2.18.0