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

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Message-ID: <aW_QOpA1ocySNLAF@kernel.org>
Date: Tue, 20 Jan 2026 20:58:02 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Pratyush Yadav <pratyush@...nel.org>
Cc: Breno Leitao <leitao@...ian.org>, Alexander Graf <graf@...zon.com>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	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,

On Tue, Jan 20, 2026 at 03:40:12PM +0000, Pratyush Yadav wrote:
> On Fri, Jan 16 2026, Breno Leitao wrote:
> >     
> >     On cold boot, kexec-count starts at 0 and increments with each kexec.
> >     The count helps identify issues that only manifest after multiple
> >     consecutive kexec reboots.
> 
> Very well written changelog!

@Breno, the submission would be perfect if you'd start a new thread rather
than reply to v1 ;-)
 
> > +/*
> > + * The "history" subtree stores optional metadata about the kexec chain.
> > + * It is registered as a separate FDT via kho_add_subtree(), keeping it
> > + * independent from the core KHO ABI. This allows the history format to
> > + * evolve without affecting other KHO consumers.
> > + *
> > + * The history FDT structure:
> 
> I don't have a strong preference here, but you don't _have_ to use FDT.
> For example, with memfd, we moved from FDT to plain C structs during the
> evolution of the patchset. Main reason is that FDT programming is a bit
> annoying. C structs make many things much easier. For example, you can
> always assume a certain property always exists and is of a given size,
> and you don't have to validate every single property you read.
> 
> Anyway, I don't mind either way.

Yeah, I agree that a plain C structure with an array of chars and u64 will
make things simpler.

> > + *
> > + *   / {
> > + *       compatible = "kho-history-v1";
> > + *       previous-release = "6.x.y-...";
> > + *       kexec-count = <N>;
> > + *   };
> > + */
> > +#define KHO_HISTORY_NODE_NAME "history"
> 
> Do we want to call it history? Perhaps "kexec-metadata" instead? So we
> could use it for other misc information if needed later.
> 
> Mike/Pasha, any thoughts?

I like kexec-metadata.

-- 
Sincerely yours,
Mike.