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

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Message-ID: <aO7mnXCajeIdUYON@archie.me>
Date: Wed, 15 Oct 2025 07:11:09 +0700
From: Bagas Sanjaya <bagasdotme@...il.com>
To: Randy Dunlap <rdunlap@...radead.org>, Jonathan Corbet <corbet@....net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Documentation <linux-doc@...r.kernel.org>,
	Linux Serial <linux-serial@...r.kernel.org>
Cc: Cengiz Can <cengiz@...nel.wtf>,
	Tomas Mudrunka <tomas.mudrunka@...il.com>,
	Jiri Slaby <jirislaby@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Anselm Schüler <mail@...elmschueler.com>
Subject: Re: [PATCH] Documentation: sysrq: Remove contradicting sentence on
 extra /proc/sysrq-trigger characters

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@...il.com> 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@anselmschueler.com/
> >> Signed-off-by: Bagas Sanjaya <bagasdotme@...il.com>
> >> ---
> >>  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>...

Thanks.

-- 
An old man doll... just what I always wanted! - Clara

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