On Thu, Jul 17, 2014 at 01:03:01AM -0700, Christoph Hellwig wrote:
> On Wed, Jul 16, 2014 at 02:37:56PM -0700, Luis R. Rodriguez wrote:
> > From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx>
> >
> > This makes the implementation simpler by stuffing the struct on
> > the driver and just letting the driver iinsert it and remove it
> > onto the sb list. This avoids the kzalloc() completely.
>
> Again, NAK. Make btrfs report the proper anon dev_t in stat and
> everything will just work.
Let's consider this userspace case:
struct stat buf;
struct ustat ubuf;
/* Find a valid device number */
if (stat("/", &buf)) {
fprintf(stderr, "Stat failed: %s\n", strerror(errno));
return 1;
}
/* Call ustat on it */
if (ustat(buf.st_dev, &ubuf)) {
fprintf(stderr, "Ustat failed: %s\n", strerror(errno));
return 1;
}
In the btrfs case it has an inode op for getattr, that is used and we set
the dev to anonymous dev_t. Later ustat will use user_get_super() which
will only be able to work with a userblock if the super block's only
dev_t is assigned to it. Since we have many anonymous to dev_t mapping
to super block though we can't complete the search for btfs and ustat()
fails with -EINVAL. The series expands the number of dev_t's that a super
block can have and allows this search to complete.
Luis
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