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

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Date:	Mon, 25 Nov 2013 12:16:10 +0000
From:	David Woodhouse <dwmw2@...radead.org>
To:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
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

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.

-- 
dwmw2

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