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
