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

[Hans Zhang <zhanghonghui@innofidei.com>]

On 2013/11/21 18:59, Richard Genoud wrote:
> I don't think it's a good idea to skip bad blocks at mtd level.
> That will definitely break the userspace.
> The nanddump mtd-tool for instance has a bad block handling argument:
> --bb=METHOD, where METHOD can be `padbad', `dumpbad', or `skipbad':
>     padbad:  dump flash data, substituting 0xFF for any bad blocks
>     dumpbad: dump flash data, including any bad blocks
>     skipbad: dump good data, completely skipping any bad blocks (default)
>
> The bad block handling is done by the upper layer (UBI/jffs2...) not by mtd.

AFAIK the nanddump mtd-tool dump the nand through mtdchar driver. So this patch
will not break the userspace for this scenario.

>
> So, if you really need to read/write the mtd layer from userspace and
> jump bad block, you'll have to use the MEMGETBADBLOCK ioctl to check
> if the block is bad before reading/writing.
>
> But using UBI is usually a better option.

The ioctl handling is just for mtdchar device, not mtdblock. Definitely we can
get the badblock info before reading/writing. But if we just want to read/write
the mtdblock device, mtdchar device need to be checked first, that is not
convenience.

Here's my scenario, I want to write nand through mtdblock by dd command, it will
abort writing when there's a bad block, but will continually reading ingore(or
even don't know about) the bad block info. That break the consistency of the data.

To make the dd command work, I think we need this patch.

thanks.

>
> Richard.
>
>


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