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

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Message-ID: <CA+CK2bDSvtuwrrXGOC07Rj42yGFHWR4Sse7Q5z1z8f1ZFHWQ2Q@mail.gmail.com>
Date: Fri, 7 Nov 2025 07:00:27 -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

> 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