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

[Miquel Raynal <miquel.raynal@bootlin.com>]

On 12/11/2025 at 10:43:17 +01, Christian Marangi <ansuelsmth@gmail.com> wrote:

> 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@gmail.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

Thanks for the digging. I will apply this to -next and not -fixes. It
will be slightly longer to get it backported, but this gives a bit more
time for this patch to be thought about as I plan on sending my fixes PR
in the next days.

Miquèl

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