[patch v2] manual: Update signal descriptions

[Stefan Liebler]

On 2/3/25 11:52, Florian Weimer wrote:
> * Stefan Liebler:
> 
>> On 1/21/25 11:14, Andreas Schwab wrote:
>>> On Jan 21 2025, Florian Weimer wrote:
>>>
>>>> Stefan, does s390x call these notifications “ctrl-alt-del
>>>> notifications”, or this there some other name for them?  Is this kernel
>>>> code path really active on current systems?
>>>
>>> It is also available as function key 0x020c (Boot) in the vt keyboard
>>> driver, and used by various other drivers in the kernel (look for
>>> kill_cad_pid and ctrl_alt_del).
>>>
>>
>> FYI: I've asked around in our kernel-team and the answer:
>> Yes, the kernel sends SIGPWR on a machine check warning.
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/s390/kernel/nmi.c#n177
>>
>> Thus the description is fine.
> 
> Thanks.  Does this include the ctrl-alt-del reference?  I thought this
> was about a different IBM thing. 8-)
> 
> Florian
> 
We don't exactly know what you mean, but we have:
- kernel/reboot.c:822:void ctrl_alt_del(void)
=> The ctrl_alt_del implementation itself uses "kill_cad_pid(SIGINT,
1);" to send SIGINT to the init process.

- arch/s390/kernel/nmi.c:192:			kill_cad_pid(SIGPWR, 1);
=> In case of a machine check warning, "kill_cad_pid(SIGPWR, 1);" is
used to send SIGPWR to the init process (from the SIGPWR-description in
the patch: "to the process designated to receive ctrl-alt-del
notifications").

- drivers/s390/char/sclp_quiesce.c:39:	ctrl_alt_del();
=> The signal quiesce is an s390x specific mechanism where HMC or
zVM-hypervisor informs the running kernel that it shall shut down.
Therefore "ctrl_alt_del();" is used which sends SIGINT to the init process.

Thus from my perspective nmi.c is the one for the description of SIGPWR
and the description is fine.

If those information is not the desired one, please ask again with a few
more hints about which ctrl-alt-del reference you mean.

Thanks,
Stefan