linux-kernel - Re: [RFC] tty/sysrq: Add alternative SysRq key

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Date:   Thu, 4 Nov 2021 15:17:22 +0100
From:   Andrzej Pietrasiewicz <andrzej.p@...labora.com>
To:     "Maciej W. Rozycki" <macro@...am.me.uk>
Cc:     Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org,
        linux-input@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Jiri Slaby <jirislaby@...nel.org>, kernel@...labora.com
Subject: Re: [RFC] tty/sysrq: Add alternative SysRq key

Hi Maciej,

W dniu 04.11.2021 o 14:13, Maciej W. Rozycki pisze:
> On Thu, 4 Nov 2021, Maciej W. Rozycki wrote:
> 
>>   The reason for this is with their more recent laptops Lenovo in their
>> infinite wisdom have placed the <PrintScreen> key (which in a traditional
>> PS/2-keyboard manner produces <SysRq> when combined with <Alt>) in their
>> keyboards between the right <Alt> and <Ctrl> keys.  With thumbs not being
>> as accurate as other fingers (and the overall misdesign of the keyboard
>> and touchpad interface) you can imagine how often I have inadvertently hit
>> <SysRq> combined with a letter key, wreaking havoc to my system (and of
>> course I want to keep the key enabled for times when I do need it).
> 
>   On second thoughts this can be disabled with `setkeycodes 54 0' once we
> do have an alternative combination available.
> 

Doesn't `setkeycodes` affect only one keyboard? What if there are more
keyboards connected to a machine?

 From drivers/tty/vt/keyboard.c:

/*
  * Translation of scancodes to keycodes. We set them on only the first
  * keyboard in the list that accepts the scancode and keycode.
  * Explanation for not choosing the first attached keyboard anymore:
  *  USB keyboards for example have two event devices: one for all "normal"
  *  keys and one for extra function keys (like "volume up", "make coffee",
  *  etc.). So this means that scancodes for the extra function keys won't
  *  be valid for the first event device, but will be for the second.
  */

Regards,

Andrzej