[PATCH v3] mtd: super: don't rely on mtdblock device minor

[Daniel Golle]

On Mon, May 10, 2021 at 12:18:37PM +0200, Miquel Raynal wrote:
> Hi Daniel,
> 
> Daniel Golle <daniel at makrotopia.org> wrote on Mon, 12 Apr 2021 16:14:44
> +0100:
> 
> > For blktrans devices with partitions (ie. part_bits != 0) the
> > assumption that the minor number of the mtdblock device matches
> > the mtdnum doesn't hold true.
> > Properly resolve mtd device from blktrans layer instead.
> 
> Unfortunately I cannot apply your patch anymore, would you mind
> rebasing it on top of v5.13-rc1?

I will send a rebased and improved version.

Thank you!


> 
> Thanks,
> Miquèl
> 
> > 
> > Signed-off-by: Daniel Golle <daniel at makrotopia.org>
> > ---
> > v3: fix typo in patch description
> > v2: remove BUG() calls as requested by Miquel Raynal
> > 
> >  drivers/mtd/mtdsuper.c | 31 ++++++++++++++++++++++++-------
> >  1 file changed, 24 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/mtd/mtdsuper.c b/drivers/mtd/mtdsuper.c
> > index c3e2098372f2e..d3af80a7ce86e 100644
> > --- a/drivers/mtd/mtdsuper.c
> > +++ b/drivers/mtd/mtdsuper.c
> > @@ -9,6 +9,7 @@
> >   */
> >  
> >  #include <linux/mtd/super.h>
> > +#include <linux/mtd/blktrans.h>
> >  #include <linux/namei.h>
> >  #include <linux/export.h>
> >  #include <linux/ctype.h>
> > @@ -121,7 +122,8 @@ int get_tree_mtd(struct fs_context *fc,
> >  {
> >  #ifdef CONFIG_BLOCK
> >  	struct block_device *bdev;
> > -	int ret, major;
> > +	struct mtd_blktrans_dev *blktrans_dev;
> > +	int ret, major, part_bits;
> >  #endif
> >  	int mtdnr;
> >  
> > @@ -169,21 +171,36 @@ int get_tree_mtd(struct fs_context *fc,
> >  	/* try the old way - the hack where we allowed users to mount
> >  	 * /dev/mtdblock$(n) but didn't actually _use_ the blockdev
> >  	 */
> > -	bdev = lookup_bdev(fc->source);
> > +	bdev = blkdev_get_by_path(fc->source, FMODE_READ, NULL);
> >  	if (IS_ERR(bdev)) {
> >  		ret = PTR_ERR(bdev);
> >  		errorf(fc, "MTD: Couldn't look up '%s': %d", fc->source, ret);
> >  		return ret;
> >  	}
> > -	pr_debug("MTDSB: lookup_bdev() returned 0\n");
> > +	pr_debug("MTDSB: blkdev_get_by_path() returned 0\n");
> >  
> >  	major = MAJOR(bdev->bd_dev);
> > -	mtdnr = MINOR(bdev->bd_dev);
> > -	bdput(bdev);
> >  
> > -	if (major == MTD_BLOCK_MAJOR)
> > -		return mtd_get_sb_by_nr(fc, mtdnr, fill_super);
> > +	if (major == MTD_BLOCK_MAJOR) {
> > +		if (!bdev->bd_disk) {
> > +			blkdev_put(bdev, FMODE_READ);
> > +			return -EINVAL;
> > +		}
> > +
> > +		blktrans_dev = (struct mtd_blktrans_dev *)(bdev->bd_disk->private_data);
> > +		if (!blktrans_dev || !blktrans_dev->tr) {
> > +			blkdev_put(bdev, FMODE_READ);
> > +			return -EINVAL;
> > +		}
> > +		mtdnr = blktrans_dev->devnum;
> > +		part_bits = blktrans_dev->tr->part_bits;
> > +		blkdev_put(bdev, FMODE_READ);
> > +		if (MINOR(bdev->bd_dev) != (mtdnr << part_bits))
> > +			return -EINVAL;
> >  
> > +		return mtd_get_sb_by_nr(fc, mtdnr, fill_super);
> > +	}
> > +	blkdev_put(bdev, FMODE_READ);
> >  #endif /* CONFIG_BLOCK */
> >  
> >  	if (!(fc->sb_flags & SB_SILENT))
>