linux-kernel - Re: [PATCH v9 1/9] kho: make debugfs interface optional

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Message-ID: <029090cf-9a4d-4f79-b857-04c3ada83323@linux.dev>
Date: Fri, 7 Nov 2025 15:35:55 -0800
From: "Yanjun.Zhu" <yanjun.zhu@...ux.dev>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: akpm@...ux-foundation.org, brauner@...nel.org, corbet@....net,
 graf@...zon.com, jgg@...pe.ca, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org, linux-mm@...ck.org, masahiroy@...nel.org,
 ojeda@...nel.org, pratyush@...nel.org, rdunlap@...radead.org,
 rppt@...nel.org, tj@...nel.org
Subject: Re: [PATCH v9 1/9] kho: make debugfs interface optional


On 11/7/25 4:02 AM, Pasha Tatashin wrote:
> On Fri, Nov 7, 2025 at 7:00 AM Pasha Tatashin <pasha.tatashin@...een.com> wrote:
>>> Hi, Pasha
>>>
>>> In our previous discussion, we talked about counting the number of times
>>> the kernel is rebooted via kexec. At that time, you suggested adding a
>>> variable in debugfs to keep track of this count.
>>> However, since debugfs is now optional, where would be an appropriate
>>> place to store this variable?
>> It is an optional config and can still be enabled if the live update
>> reboot number value needs to be accessed through debugfs. However,
>> given that debugfs does not guarantee a stable interface, tooling
>> should not be built to require these interfaces.
>>
>> In the WIP LUO [1] I have, I pr_info() the live update number during
>> boot and also store it in the incoming LUO FDT tree, which can also be
>> accessed through this optional debugfs interface.
>>
>> The pr_info message appears like this during boot:
>> [    0.000000] luo: Retrieved live update data, liveupdate number: 17
>>
>> Pasha
> Forgot to add link to WIP LUOv5:
> [1] https://github.com/soleen/linux/tree/luo/v5rc04


Thanks a lot. I’ve carefully read this commit: 
https://github.com/soleen/linux/commit/60205b9a95c319dc9965f119303a1d83f0ff08fa.

To be honest, I’d like to run some tests with who/luo, including the 
selftest for kho/luo. Could you please share the steps with me?

If the testing steps have already been documented somewhere, could you 
please share the link?

Best Regards,

Yanjun.Zhu