linux-kernel - Re: [PATCH v3 1/2] kho: history: track previous kernel version

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Message-ID: <2vxzy0m0gfyo.fsf@kernel.org>
Date: Wed, 14 Jan 2026 19:19:11 +0000
From: Pratyush Yadav <pratyush@...nel.org>
To: Breno Leitao <leitao@...ian.org>
Cc: Alexander Graf <graf@...zon.com>,  Mike Rapoport <rppt@...nel.org>,
  Pasha Tatashin <pasha.tatashin@...een.com>,  Pratyush Yadav
 <pratyush@...nel.org>,  linux-kernel@...r.kernel.org,
  kexec@...ts.infradead.org,  linux-mm@...ck.org,  usamaarif642@...il.com,
  rmikey@...a.com,  clm@...com,  riel@...riel.com,  kernel-team@...a.com
Subject: Re: [PATCH v3 1/2] kho: history: track previous kernel version

Hi Breno,

On Thu, Jan 08 2026, Breno Leitao wrote:

> Store and display the kernel version from the previous kexec boot.
>
> The current kernel's release string is saved to the "previous-release"
> property in the KHO FDT before kexec. On the next boot, if this property
> exists, the previous kernel version is retrieved and printed during
> early boot.
>
> This helps diagnose bugs that only manifest when kexecing from specific
> kernel versions, making it easier to correlate crashes with the kernel
> that initiated the kexec.

The KHO FDT is ABI. So you should be bumping the version number when you
make changes to it.

But honestly, adding this "optional" stuff to the core KHO ABI makes me
uneasy. I say optional since it is not needed for the main functionality
of KHO. Making this a part of the ABI increases the surface area we
have. The more things we stuff in the ABI, the more inflexible it gets
over time.

Any changes to the KHO ABI means all consumers also need a version bump.
This includes LUO and all its users for example. So I would really like
to avoid adding optional things in core KHO FDT.

The easy fix is to add a separate subtree for the optional metadata. You
would still need to create an ABI for the data format, but being
independent of core KHO, it will make it more flexible and easier to
change in the future. You can keep the code in kexec_handover.c.

>
> Signed-off-by: Breno Leitao <leitao@...ian.org>
[...]

-- 
Regards,
Pratyush Yadav