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

[Boris Brezillon]

On Tue, 23 Jan 2018 09:00:46 +0100
Miquel Raynal <miquel.raynal at free-electrons.com> wrote:

> 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?

This sounds reasonable.

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

Thanks.

Boris

> 
> 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