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

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Date:   Fri, 5 Nov 2021 15:06:23 +0100
From:   Andrzej Pietrasiewicz <andrzej.p@...labora.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "Maciej W. Rozycki" <macro@...am.me.uk>,
        Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org,
        linux-input@...r.kernel.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 Greg,

W dniu 05.11.2021 o 14:27, Greg Kroah-Hartman pisze:
> On Fri, Nov 05, 2021 at 02:01:23PM +0100, Andrzej Pietrasiewicz wrote:
>> 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?
> 
> The fact that this patch adds a "new" sysrq key no matter what is a
> non-starter, please think through the consequences of such a change...
> 

I wouldn't say this RFC adds a "new" sysrq no matter what. It does so only
when the input device (keyboard) does _not_ have SysRq key at all. So I would
say that this patch adds a replacement SysRq key if the SysRq key proper is
_physically_ absent. Which seems not such a bad thing to me. The problem I'm
trying to solve is exactly this: what to use as SysRq if there's no SysRq?

Andrzej