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

[Andrzej Pietrasiewicz]

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