linux-kernel - Re: [PATCH v5 2/2] tty/sysrq: Replay kernel log messages on consoles via sysrq

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Date: Thu, 07 Mar 2024 15:06:17 +0106
From: John Ogness <john.ogness@...utronix.de>
To: Sreenath Vijayan <sreenath.vijayan@...y.com>, pmladek@...e.com,
 corbet@....net, gregkh@...uxfoundation.org, jirislaby@...nel.org
Cc: rdunlap@...radead.org, rostedt@...dmis.org, senozhatsky@...omium.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-serial@...r.kernel.org, taichi.shimoyashiki@...y.com,
 daniel.palmer@...y.com, anandakumar.balasubramaniam@...y.com,
 sreenath.vijayan@...y.com
Subject: Re: [PATCH v5 2/2] tty/sysrq: Replay kernel log messages on
 consoles via sysrq

On 2024-03-07, Sreenath Vijayan <sreenath.vijayan@...y.com> wrote:
> diff --git a/Documentation/admin-guide/sysrq.rst b/Documentation/admin-guide/sysrq.rst
> index 2f2e5bd440f9..8098a1b4908d 100644
> --- a/Documentation/admin-guide/sysrq.rst
> +++ b/Documentation/admin-guide/sysrq.rst
> @@ -161,6 +161,8 @@ Command	    Function
>              will be printed to your console. (``0``, for example would make
>              it so that only emergency messages like PANICs or OOPSes would
>              make it to your console.)
> +
> +``R``	    Replay the kernel log messages on consoles.
>  =========== ===================================================================
>  
>  Okay, so what can I use them for?
> @@ -211,6 +213,12 @@ processes.
>  "just thaw ``it(j)``" is useful if your system becomes unresponsive due to a
>  frozen (probably root) filesystem via the FIFREEZE ioctl.
>  
> +``Replay logs(R)`` is useful to view the kernel log messages when system is hung
> +or you are not able to use dmesg command to view the messages in printk buffer.
> +User may have to press the key combination multiple times if console system is
> +busy. If it is completely locked up, then messages won't be printed. Output
> +messages depend on current console loglevel.
> +

I recommend including a reference to SysRq [0-9] about changing the
loglevel.

>  Sometimes SysRq seems to get 'stuck' after using it, what can I do?
>  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  
> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> index 02217e3c916b..c4deea41a8b5 100644
> --- a/drivers/tty/sysrq.c
> +++ b/drivers/tty/sysrq.c
> @@ -450,6 +450,17 @@ static const struct sysrq_key_op sysrq_unrt_op = {
>  	.enable_mask	= SYSRQ_ENABLE_RTNICE,
>  };
>  
> +static void sysrq_handle_replay_logs(u8 key)
> +{
> +	console_replay_all();
> +}
> +static struct sysrq_key_op sysrq_replay_logs_op = {
> +	.handler        = sysrq_handle_replay_logs,
> +	.help_msg       = "replay-kernel-logs(R)",
> +	.action_msg     = "replay kernel logs on consoles",

If I do:

$ grep '\.action_msg' drivers/tty/sysrq.c

This is the only action message that begins lowercase. Please start with
a capital letter for consistency.

With the change to the action message:

Reviewed-by: John Ogness <john.ogness@...utronix.de>