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

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Message-ID: <d6cd375c-dad6-4047-9574-bac7dfc24315@infradead.org>
Date: Tue, 14 Oct 2025 10:57:45 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Jonathan Corbet <corbet@....net>, 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>, 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 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.


-- 
~Randy