Re: [PATCH] Documentation: sysrq: Remove contradicting sentence on extra /proc/sysrq-trigger characters

[Jiri Slaby]

On 15. 10. 25, 2:11, Bagas Sanjaya wrote:
> On Tue, Oct 14, 2025 at 10:57:45AM -0700, Randy Dunlap wrote:
> > On 10/14/25 7:55 AM, Jonathan Corbet wrote:
> > > Bagas Sanjaya <bagasdotme@xxxxxxxxx> writes:
> > >
> > > > /proc/sysrq-trigger documentation states that only first character is
> > > > processed and the rest is ignored, yet it is not recommended to write
> > > > any extra characters to it. The latter statement is contradictive as
> > > > these characters are also ignored as implied by preceding sentence.
> > > >
> > > > Remove it.
> > > >
> > > > Link: https://lore.kernel.org/lkml/7ca05672-dc20-413f-a923-f77ce0a9d307@xxxxxxxxxxxxxxxxxx/
> > > > Signed-off-by: Bagas Sanjaya <bagasdotme@xxxxxxxxx>
> > > > ---
> > > >   Documentation/admin-guide/sysrq.rst | 4 +---
> > > >   1 file changed, 1 insertion(+), 3 deletions(-)
> > > >
> > > > diff --git a/Documentation/admin-guide/sysrq.rst b/Documentation/admin-guide/sysrq.rst
> > > > index 9c7aa817adc72d..63ff415ce85d66 100644
> > > > --- a/Documentation/admin-guide/sysrq.rst
> > > > +++ b/Documentation/admin-guide/sysrq.rst
> > > > @@ -77,9 +77,7 @@ On other
> > > >   On all
> > > >   	Write a single character to /proc/sysrq-trigger.
> > > >   	Only the first character is processed, the rest of the string is
> > > > -	ignored. However, it is not recommended to write any extra characters
> > > > -	as the behavior is undefined and might change in the future versions.
> > > > -	E.g.::
> > > > +	ignored. E.g.::
> > >
> > > I'm not sure this is right - there is a warning here that additional
> > > characters may acquire a meaning in the future, so one should not
> > > develop the habit of writing them now.  After all these years, I think
> > > the chances of fundamental sysrq changes are pretty small, but I still
> > > don't see why we would take the warning out?
> >
> > but the following paragraph says:
> >
> > 	Alternatively, write multiple characters prepended by underscore.
> > 	This way, all characters will be processed. E.g.::
> >
> > 		echo _reisub > /proc/sysrq-trigger
> >
> > so it is confuzing.
>
> I guess the whole "On all" description can be rewritten like:
>
> Write a single character to /proc/sysrq-trigger, e.g.::
>
> <snipped>...
>
> If a string (multiple characters) is written instead, only the first character
> is processed unless the string is prepended by an underscore, like::
>
> <snipped>...

Some kind of, yes. So Either:
* you write no underscore and a character -- the rest is ignored and you 
should not write more than one.
* you prepend underscore and write more of them -- all are processed.

thanks,
--
js
suse labs