Re: [PATCH 3/6] tty/sysrq: Allow configurable SysRq key

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

Hi Andrzej,

On Mon, May 11, 2020 at 03:59:15PM +0200, Andrzej Pietrasiewicz wrote:
> There are existing machines which don't have SysRq key, e.g. chromebooks.
> This patch allows configuring which key acts as SysRq. The value is passed
> with sysrq's module parameter.
> 
> Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
> ---
>  drivers/tty/sysrq.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> index 93202fc24308..ebad9799fdc0 100644
> --- a/drivers/tty/sysrq.c
> +++ b/drivers/tty/sysrq.c
> @@ -604,6 +604,7 @@ EXPORT_SYMBOL(handle_sysrq);
>  
>  #ifdef CONFIG_INPUT
>  static int sysrq_reset_downtime_ms;
> +static unsigned short sysrq_key = KEY_SYSRQ;
>  
>  /* Simple translation table for the SysRq keys */
>  static const unsigned char sysrq_xlate[KEY_CNT] =
> @@ -735,10 +736,10 @@ static void sysrq_reinject_alt_sysrq(struct work_struct *work)
>  
>  		/* Simulate press and release of Alt + SysRq */
>  		input_inject_event(handle, EV_KEY, alt_code, 1);
> -		input_inject_event(handle, EV_KEY, KEY_SYSRQ, 1);
> +		input_inject_event(handle, EV_KEY, sysrq_key, 1);
>  		input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
>  
> -		input_inject_event(handle, EV_KEY, KEY_SYSRQ, 0);
> +		input_inject_event(handle, EV_KEY, sysrq_key, 0);
>  		input_inject_event(handle, EV_KEY, alt_code, 0);
>  		input_inject_event(handle, EV_SYN, SYN_REPORT, 1);

Unfortunately this means that if I connect my external keyboard to
chromebook SysRq there will stop working, which is not great. If we want
to support this we need to figure out how to make this handling
per-device.

FWIW Chrome OS cheats and simply adds more keys to be handled as SysRq
without removing "classic" SysRq. But that hack is obviously not
suitable for the mainline.

Thanks.

-- 
Dmitry