linux-kernel - Re: [PATCH] tty/sysrq: Dump kernel ring buffer messages via sysrq

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Date: Fri, 22 Dec 2023 17:14:51 +0530
From: Sreenath Vijayan <sreenath.vijayan@...y.com>
To: rdunlap@...radead.org
Cc: anandakumar.balasubramaniam@...y.com, corbet@....net,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org, sreenath.vijayan@...y.com,
        taichi.shimoyashiki@...y.com
Subject: Re: [PATCH] tty/sysrq: Dump kernel ring buffer messages via sysrq

On Thu, Dec 21, 2023 at 03:12:46PM -0800, Randy Dunlap wrote:
> 
> 
> On 12/21/23 08:52, Greg KH wrote:
> > On Thu, Dec 21, 2023 at 07:09:53PM +0530, Sreenath Vijayan wrote:
> >> When terminal is unresponsive, one cannot use dmesg to view kernel
> >> ring buffer messages. Also, syslog services may be disabled,
> >> to check them after a reboot, especially on embedded systems.
> >> In this scenario, dump the kernel ring buffer messages via sysrq
> >> by pressing sysrq+D.
> >>
> >> Signed-off-by: Sreenath Vijayan <sreenath.vijayan@...y.com>
> >> Signed-off-by: Shimoyashiki Taichi <taichi.shimoyashiki@...y.com>
> >> ---
> >>  Documentation/admin-guide/sysrq.rst |  2 ++
> >>  drivers/tty/sysrq.c                 | 43 ++++++++++++++++++++++++++++-
> >>  2 files changed, 44 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/Documentation/admin-guide/sysrq.rst b/Documentation/admin-guide/sysrq.rst
> >> index 2f2e5bd440f9..464c4e138b9d 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.)
> >> +
> >> +``D``	    Dump the kernel ring buffer
> >>  =========== ===================================================================
> > 
> > Nit, this doesn't line up anymore :(
> 
> Yes, that will cause a docs build warning.

Thank you for the review comments. When I apply the patch, I don't
notice any alignment issues in the document. I tried with multiple
editors(vim,emacs) and the combination of tabs and spaces looks to
be the same as in the existing lines above the newly added line.
Tried "make htmldocs" and no warnings were observed and the html
page looks ok. Please suggest the modifications to be done.

> 
> Also, can you be more explicit about which ring buffer this patch
> is referring to, please.
> 

We see the term "kernel ring buffer" used throughout the documents
and commit messages, and thought it is the right term. Even dmesg
manual page uses it. Would "kernel log buffer" be a more appropriate
term? Please share your suggestion.

Thanks,
Sreenath