Re: Some feature requests for guest consoles

[Jan Beulich <jbeulich@xxxxxxxx>]

On 14.03.2022 17:36, Andy Smith wrote:
> - Ability to remap the "magic sysrq" key combination which is
>   ctrl-o, and possibly disable it while leaving "xl sysrq" and
>   /proc/sysrq-trigger in the guest generally working.
> 
>   Reason: guest administrators are often inexperienced with the
>   details of Xen. ctrl-o is a bad choice because it's actually the
>   "save buffer" shortcut in the popular editor nano. On more than
>   one occasion I have had guest administrators be editing a file
>   with nano on their console, they go to save it with ctrl-o which
>   appears to do nothing (because Xen is waiting for the sysrq
>   command that follows), so they do ctrl-o again which is taken as
>   being command 'o' - immediate power off! I have had an emergency
>   support ticket about this because "my guest randomly crashed while
>   I was editing a file".
> 
>   I would therefore like to remap "magic sysrq" to something more
>   obscure, or failing that disable it in guests as we/they will use
>   "xl sysrq" instead.

Without meaning to turn down the request, I'd like to point out that
- as of Linux commit 368c1e3249af (over 13 years ago) pressing ^O
  twice does not have the described effect, but actually means an
  individual ^O to be sent to the application,
- independent of that commit ^O followed by another ^O would not
  trigger the 'o' sysrq handler, but do nothing; said sysrq handler
  would be triggered when ^O is followed by O or o (without Ctrl),
- this sysrq triggering model isn't specific to Xen (and hence
  sending the request here may not reach the necessary audience) -
  besides being implemented in code common to all hvc drivers, it
  is additionally handled by some non-hvc tty drivers as well.

Jan