Re: [PATCH v6] /proc/sysrq-trigger: accept multiple keys at once

Jiri Slaby
2023-11-14T18:04:59Z

On 14. 11. 23, 16:12, Tomas Mudrunka wrote:
> Just for convenience.
> This way we can do:
> `echo _reisub > /proc/sysrq-trigger`
> Instead of:
> `for i in r e i s u b; do echo "$i" > /proc/sysrq-trigger; done;`
>
> This can be very useful when trying to execute sysrq combo remotely
> or from userspace. When sending keys in multiple separate writes,
> userspace can be killed before whole combo is completed.
> Therefore putting all keys in single write is more robust approach.
>
> Signed-off-by: Tomas Mudrunka <tomas.mudrunka@gmail.com>
> ---
> V5 -> V6: Documentation now has notice about undefined behavior
> V4 -> V5: Added this list of changes
> V3 -> V4: Bulk is now bool instead of char (and fixed typo)
> V2 -> V3: Fixed code styling (and introduced typo)
> V1 -> V2: Bulk mode only activated by underscore now, added docs
>
> Documentation/admin-guide/sysrq.rst | 11 ++++++++++-
> drivers/tty/sysrq.c | 17 ++++++++++++++---
> 2 files changed, 24 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/admin-guide/sysrq.rst b/Documentation/admin-guide/sysrq.rst
> index 51906e473..e7a82cba7 100644
> --- a/Documentation/admin-guide/sysrq.rst
> +++ b/Documentation/admin-guide/sysrq.rst
> @@ -75,10 +75,19 @@ On other
> submit a patch to be included in this section.
>
> On all
> - Write a character to /proc/sysrq-trigger. e.g.::
> + Write single character to /proc/sysrq-trigger.

a single

> + Only first character is interpreted, rest of string is ignored.

the first; the rest of the string

> + However it is not reccomended to write any extra characters

However, <- comma
recommended

> + as the behavior is undefined and might change in the future versions.
> + e.g.::

Even the original was lowercase. But it should be "E.g.::", right --
Greg/Jon?

>
> echo t > /proc/sysrq-trigger
>
> + Alternatively write multiple keys combo prepended by underscore.

Alternatively, <- comma
s/keys/characters/
an underscore

> + All characters are interpreted this way. e.g.::

This way, all characters are interpreted. (IMO this has a different
meaning, but natives would have to tell us.)

> +
> + echo _reisub > /proc/sysrq-trigger
> +
> The :kbd:`<command key>` is case sensitive.
>
> What are the 'command' keys?
> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> index 6b4a28bcf..ad07bc812 100644
> --- a/drivers/tty/sysrq.c
> +++ b/drivers/tty/sysrq.c
> @@ -1150,16 +1150,27 @@ EXPORT_SYMBOL(unregister_sysrq_key);
> #ifdef CONFIG_PROC_FS
> /*
> * writing 'C' to /proc/sysrq-trigger is like sysrq-C
> + * If first character in write is underscore, all characters are interpreted.

If the first character written is

thanks,
--
js
suse labs