linux-kernel - Re: [PATCH v3] Documentation: sysrq: Rewrite /proc/sysrq-trigger usage

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Message-ID: <87jz06bsjj.fsf@trenco.lwn.net>
Date: Mon, 03 Nov 2025 16:33:20 -0700
From: Jonathan Corbet <corbet@....net>
To: Bagas Sanjaya <bagasdotme@...il.com>, 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>, Bagas Sanjaya <bagasdotme@...il.com>,
 Tomas Mudrunka <tomas.mudrunka@...il.com>, Jiri Slaby
 <jirislaby@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Anselm Schüler <mail@...elmschueler.com>, Randy Dunlap
 <rdunlap@...radead.org>
Subject: Re: [PATCH v3] Documentation: sysrq: Rewrite /proc/sysrq-trigger usage

Bagas Sanjaya <bagasdotme@...il.com> writes:

> /proc/sysrq-trigger usage documentation (in "On all" section) states
> that it is not recommended to write extra characters to it. The sentence
> may imply a contradiction to previous sentence which writes that such
> characters are ignored.
>
> Rewrite the description.
>
> Link: https://lore.kernel.org/lkml/7ca05672-dc20-413f-a923-f77ce0a9d307@anselmschueler.com/
> Signed-off-by: Bagas Sanjaya <bagasdotme@...il.com>
> ---
> Changes since v2 [1]:
>
>   - Keep /proc/sysrq-trigger future API change note (Tomas)
>
> Anselm: Do you object to the rewrite?

It still seems confusing...

> [1]: https://lore.kernel.org/linux-doc/20251016103609.33897-2-bagasdotme@gmail.com/
>
>  Documentation/admin-guide/sysrq.rst | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/admin-guide/sysrq.rst b/Documentation/admin-guide/sysrq.rst
> index 9c7aa817adc72d..a88266b171aa17 100644
> --- a/Documentation/admin-guide/sysrq.rst
> +++ b/Documentation/admin-guide/sysrq.rst
> @@ -75,16 +75,15 @@ On other
>  	submit a patch to be included in this section.
>  
>  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.::
> +	Write a single character to /proc/sysrq-trigger. E.g.::
>  
>  		echo t > /proc/sysrq-trigger
>  
> -	Alternatively, write multiple characters prepended by underscore.
> -	This way, all characters will be processed. E.g.::
> +	Only the first character is processed; any following characters are
> +	ignored for now, which might change in the future.
> +
> +	Alternatively, to write multiple characters, prepend them with an
> +	underscore so that these all will be processed. E.g.::

You're still saying that following characters are ignored, then give an
example where they are not:

>  		echo _reisub > /proc/sysrq-trigger

So, for me, this still isn't really right.

This, I think, is a holdover from before, but I have to point out that:

>  		echo t > /proc/sysrq-trigger

Does *not* write a single character: it writes "t\n".

jon