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

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Message-ID: <a3b15524-8e50-4e50-b3d3-95fd2092ec8d@infradead.org>
Date: Fri, 22 Dec 2023 11:43:28 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Sreenath Vijayan <sreenath.vijayan@...y.com>
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,
 taichi.shimoyashiki@...y.com
Subject: Re: [PATCH] tty/sysrq: Dump kernel ring buffer messages via sysrq



On 12/22/23 03:44, Sreenath Vijayan wrote:
> 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.

You are correct. Sorry for the confusion. It can be messy trying to
read/review a diff when there is alignment involved.

>>
>> 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.

Documentation/admin-guide/kernel-parameters.txt refers to:
	ftrace ring buffer
	printk ring buffer
	tracing ring buffer
so saying "kernel ring buffer" is not very specific.

I expect that you are referring to the printk ring buffer, although
I would prefer to call it something like the console log buffer (FWIW).

thanks.
-- 
#Randy
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