linux-kernel - Re: [PATCH v1 2/2] jffs2: make cleanmarker support option

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Date:   Mon, 23 Oct 2023 18:55:57 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Martin Kurbanov <mmkurbanov@...utedevices.com>,
        Richard Weinberger <richard@....at>
Cc:     Christian Brauner <brauner@...nel.org>,
        Dave Chinner <dchinner@...hat.com>,
        Yu Zhe <yuzhe@...china.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-mtd <linux-mtd@...ts.infradead.org>, kernel@...rdevices.ru
Subject: Re: [PATCH v1 2/2] jffs2: make cleanmarker support option

On Mon, 2023-10-23 at 17:54 +0300, Martin Kurbanov wrote:
> Hello Richard,
> 
> On 19.10.2023 11:12, Richard Weinberger wrote:
> > > This patch support for disable cleanmarker option. This is useful on
> > > some NAND devices which entire OOB area is protected by ECC. Problem
> > > fires when JFFS2 driver writes cleanmarker to some page and later it
> > > tries to write to this page - write will be done successfully, but after
> > > that such page becomes unreadable due to invalid ECC codes. This occurs
> > > because the second write necessitates an update to ECC, but it is
> > > impossible to do it correctly without block erase.
> > Hmm, I miss an explanation why this change is correct and safe.
> > You explain why the OOB area can't be used, okay. But you need to
> > add more details on why you change is safe in terms of filesystem
> > consistency.
>  
> If you disable the cleanmarker, the found clean block (filled with 0xff)
> will be erased again (see fs/jffs2/scan.c#L162).
> In my opinion, it is better to perform the block erasure again than to
> not work with such a nand flash at all.

Erasing all unused blocks over and over again on every reboot/remount
is going to destroy your flash quite quickly, surely?

I think you need to come up with a way to log the clean blocks (or
erase requests) in the JFFS2 log itself.

Perhaps a 'block erase log' node type, which just contains a version#
and a list of blocks which are currently being erased. You write it out
before doing any erase operation. And then at *some* point after the
erase completes (it doesn't need to be immediate) you write out a new
one (which may be empty, or may list new blocks which are about to be
erased).

On mount, we just need to re-erase any blocks which are indicated as
being erased in the latest erase log node.

> > Beside of that, I don't think this should be kernel config option.
> > Why not a mount option?
> 
> Agreed

Why even a mount option? Shouldn't it be automatic, depending on the
type of flash chip?

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