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

Jiri, Greg,


W dniu 05.11.2021 o 15:06, Andrzej Pietrasiewicz pisze:

Hi Greg,

W dniu 05.11.2021 o 14:27, Greg Kroah-Hartman pisze:

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On Fri, Nov 05, 2021 at 02:01:23PM +0100, Andrzej Pietrasiewicz wrote:

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Hi,

W dniu 04.11.2021 o 15:17, Andrzej Pietrasiewicz pisze:

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Hi Maciej,

W dniu 04.11.2021 o 14:13, Maciej W. Rozycki pisze:

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On Thu, 4 Nov 2021, Maciej W. Rozycki wrote:

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   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?

What approach is acceptable then? Any criteria other than "go guess"?
Is "connect an external keyboard" the _only_ choice Linux wants to offer
to its users in case of devices such as e.g. Chromebooks?

Regards,

Andrzej