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

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Date:   Fri, 5 Nov 2021 14:01:23 +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,

W dniu 04.11.2021 o 15:17, Andrzej Pietrasiewicz pisze:
> 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.
>   */
> 

My second thoughts: if we run `setkeycodes` to map, say, F10 as SysRq,
don't we lose F10?

Andrzej