[PATCH] mtd: Make sure the device supports erase operations in mtd_erase()

[Miquel Raynal]

Hello Boris,

On Mon, 22 Jan 2018 10:38:01 +0100
Boris Brezillon <boris.brezillon at free-electrons.com> wrote:

> Some devices do not implement ->_erase() or have an invalid ->erasesize
> value. In this case, mtd_erase() should return -ENOTSUPP.
> 
> Note that the test is not done on the MTD_NO_ERASE flag because this
> flag means 'erasing a block before writing to it is unnecessary',
> not 'the erase operation is not supported'. Actually, some drivers are
> setting the MTD_NO_ERASE flag but still implementing the ->_erase()
> hook and setting a valid ->erasesize value.
> 
> Signed-off-by: Boris Brezillon <boris.brezillon at free-electrons.com>
> ---
>  drivers/mtd/mtdcore.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> index d7ab091b36b2..f24144cbc99c 100644
> --- a/drivers/mtd/mtdcore.c
> +++ b/drivers/mtd/mtdcore.c
> @@ -971,10 +971,14 @@ EXPORT_SYMBOL_GPL(__put_mtd_device);
>   */
>  int mtd_erase(struct mtd_info *mtd, struct erase_info *instr)
>  {
> +	if (!mtd->erasesize || !mtd->_erase)
> +		return -ENOTSUPP;
> +
>  	if (instr->addr >= mtd->size || instr->len > mtd->size - instr->addr)
>  		return -EINVAL;
>  	if (!(mtd->flags & MTD_WRITEABLE))
>  		return -EROFS;

This remark is not inherent to this patch in particular but as we are
adding a new error path, I thought it might be interesting to also
patch:
- INFTL_formatblock() from inftlmount.c [1] (mtd_erase called twice)
- NFTL_formatblock() from nftlmount.c [2]

They both call mtd_erase() without checking the return code and then
error out only if instr->state == MTD_ERASE_FAILED, which has not been
set before quitting mtd_erase() in the conditions above. I guess the
right thing to do is to add another condition in both functions on the
return code of mtd_erase(). What do you think?

Otherwise:
Reviewed-by: Miquel Raynal <miquel.raynal at free-electrons.com>

Have a good day,
Miquèl

[1]
http://elixir.free-electrons.com/linux/latest/source/drivers/mtd/inftlmount.c#L396
[2]
http://elixir.free-electrons.com/linux/latest/source/drivers/mtd/nftlmount.c#L334