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

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Message-ID: <CA+CK2bC_+repP-q183hjAuYYB2-Yx7fr_U3zr2cxysAWx5hzpg@mail.gmail.com>
Date: Fri, 7 Nov 2025 07:02:53 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Zhu Yanjun <yanjun.zhu@...ux.dev>
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 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