linux-kernel - Re: [PATCH] Make the mtdblock read/write skip the bad nand sector

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Message-ID: <20131125123012.GE2408@localhost>
Date:	Mon, 25 Nov 2013 09:30:13 -0300
From:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Hans Zhang <zhanghonghui@...ofidei.com>,
	Richard Genoud <richard.genoud@...il.com>,
	linux-mtd <linux-mtd@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	zhouguangming@...ofidei.com
Subject: Re: [PATCH] Make the mtdblock read/write skip the bad nand sector

David,

On Mon, Nov 25, 2013 at 12:16:10PM +0000, David Woodhouse wrote:
> On Mon, 2013-11-25 at 08:52 -0300, Ezequiel Garcia wrote:
> > 
> > Your understanding is correct: NAND *must* be erased explictly in
> > userspace
> > before writing. However, keep in mind the following additional
> > constraints:
> > 
> > * Writing should be always performed using 'nandwrite',
> >   not tools such as 'cat' or 'dd'.
> > 
> > * An mtdblock shouldn't be used to access directly the NAND from
> >   userspace. AFAICS, the primarily usage of mtdblock is to be able to
> >   mount JFFS2.
> 
> No. You don't need mtdblock to mount JFFS2 at all.
> 
> The mtdblock driver was used in the *very* early days of the MTD system,
> on NOR flash with a "traditional" file system. Either in read-only mode
> for something like cramfs, or in a very unsafe writeable mode. We
> actually put ext2 on it for the Compaq iPaq for a while, before we had
> JFFS.
> 
> It was used as a shortcut for mounting JFFS2, and still is by a lot of
> people, but it's certainly not necessary. You can turn off CONFIG_BLOCK
> entirely and still use JFFS2.
> 
> You should consider mtdblock to be the most basic, primitive, "flash
> translation layer" that can possibly exist. And thus, should basically
> never use it. I certainly don't approve of trying to extend it.
> 

Thanks a lot for the insight. After reading this, I'm wondering what's
preventing us from killing MTD block support altogether. Artem, already
suggested it a while back...
-- 
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com
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