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

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

[Bagas Sanjaya]

/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@gmail.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.::
 
 		echo t > /proc/sysrq-trigger
 

base-commit: c746c3b5169831d7fb032a1051d8b45592ae8d78
-- 
An old man doll... just what I always wanted! - Clara

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

[Randy Dunlap]

On 10/8/25 4:24 AM, Bagas Sanjaya wrote:
> /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@gmail.com>

Reviewed-by: Randy Dunlap <rdunlap@infradead.org>

Thanks.

> ---
>  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.::
>  
>  		echo t > /proc/sysrq-trigger
>  
> 
> base-commit: c746c3b5169831d7fb032a1051d8b45592ae8d78

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

[Jonathan Corbet]

Bagas Sanjaya <bagasdotme@gmail.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@gmail.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?

jon

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

[Randy Dunlap]

On 10/14/25 7:55 AM, Jonathan Corbet wrote:
> Bagas Sanjaya <bagasdotme@gmail.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@gmail.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

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

[Bagas Sanjaya]

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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@gmail.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@gmail.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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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@gmail.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@gmail.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>...

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

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

[Bagas Sanjaya]

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On Wed, Oct 15, 2025 at 08:18:44AM +0200, Jiri Slaby wrote:
> On 15. 10. 25, 2:11, Bagas Sanjaya wrote:
> > 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.
> 

OK, thanks!

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

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

[Tomas Mudrunka]

Hi. I am author of that sentence and this is NACK from me.

> 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.

As you've said... I don't see anything confusing about that.
The warning was added for a reason, because there was discussion
about some people writing extra characters in there, which might
cause issues down the line if we refactor the code in future.

> After all these years, I think
> the chances of fundamental sysrq changes are pretty small,

Actualy it is not that long since the underscore mode was added...

> but I still don't see why we would take the warning out?

Exactly. Thank you.

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

[Bagas Sanjaya]

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On Thu, Oct 16, 2025 at 12:17:58PM +0200, Tomas Mudrunka wrote:
> Hi. I am author of that sentence and this is NACK from me.

Oops, I didn't see your review when I send v2 [1].

[1]: https://lore.kernel.org/linux-doc/20251016103609.33897-2-bagasdotme@gmail.com/

> 
> > 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.
> 
> As you've said... I don't see anything confusing about that.
> The warning was added for a reason, because there was discussion
> about some people writing extra characters in there, which might
> cause issues down the line if we refactor the code in future.

Any pointers to these discussions? Or do you have any idea on better
description on /proc/sysrq-trigger itself?

Confused...

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

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

[Randy Dunlap]

Hi,

On 10/16/25 3:17 AM, Tomas Mudrunka wrote:
> Hi. I am author of that sentence and this is NACK from me.
> 
>> 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.
> 
> As you've said... I don't see anything confusing about that.
> The warning was added for a reason, because there was discussion
> about some people writing extra characters in there, which might
> cause issues down the line if we refactor the code in future.

You have already provided a way to write (enter) multiple characters
to /proc/sysrq-trigger. Are you suggesting that someone may come
along and add yet another way to write multiple characters and that
this paragraph is present in case that happens?


>> After all these years, I think
>> the chances of fundamental sysrq changes are pretty small,
> 
> Actualy it is not that long since the underscore mode was added...
> 
>> but I still don't see why we would take the warning out?
> 
> Exactly. Thank you.
> 

-- 
~Randy