linux-kernel - Re: [PATCH] mtd: mtdpart: ignore error -ENOENT from parsers on subpartitions

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Message-ID: <691456b8.050a0220.3c21b3.5c4c@mx.google.com>
Date: Wed, 12 Nov 2025 10:43:17 +0100
From: Christian Marangi <ansuelsmth@...il.com>
To: Miquel Raynal <miquel.raynal@...tlin.com>
Cc: Richard Weinberger <richard@....at>,
	Vignesh Raghavendra <vigneshr@...com>,
	Rafał Miłecki <rafal@...ecki.pl>,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] mtd: mtdpart: ignore error -ENOENT from parsers on
 subpartitions

On Wed, Nov 12, 2025 at 10:33:25AM +0100, Miquel Raynal wrote:
> Hi Christian,
> 
> On 09/11/2025 at 12:52:44 +01, Christian Marangi <ansuelsmth@...il.com> wrote:
> 
> > Commit 5c2f7727d437 ("mtd: mtdpart: check for subpartitions parsing
> > result") introduced some kind of regression with parser on subpartitions
> > where if a parser emits an error then the entire parsing process from the
> > upper parser fails and partitions are deleted.
> >
> > Not checking for error in subpartitions was originally intended as
> > special parser can emit error also in the case of the partition not
> > correctly init (for example a wiped partition) or special case where the
> > partition should be skipped due to some ENV variables externally
> > provided (from bootloader for example)
> >
> > One example case is the TRX partition where, in the context of a wiped
> > partition, returns a -ENOENT as the trx_magic is not found in the
> > expected TRX header (as the partition is wiped)
> 
> I didn't had in mind this was a valid case. I am a bit puzzled because
> it opens the breach to other special cases, but at the same time I have
> no strong arguments to refuse this situation so let's go for it.
> 

Thanks a lot for accepting this. I checked all the parser both upstream
and downstream and I found this ""undocumented"" pattern of returning
-ENOENT. [1] [2] [3]

For sure it's a regression, we had various device on OpenWrt that broke
from migrating from 6.6 to 6.12. I agree there is the risk you are
pointing out but I feel this is a good compromise to restore original
functionality of the upstream parsers.

(the other error condition are -ENOMEM or sometimes -EINVAL for parser
header present but very wrong)

[1] https://elixir.bootlin.com/linux/v6.17.7/source/drivers/mtd/parsers/tplink_safeloader.c#L93
[2] https://elixir.bootlin.com/linux/v6.17.7/source/drivers/mtd/parsers/scpart.c#L170
[3] https://elixir.bootlin.com/linux/v6.17.7/source/drivers/mtd/parsers/ofpart_bcm4908.c#L47

-- 
	Ansuel