xfs: allow sunit mount option to repair bad primary sb stripe values

xfs: allow sunit mount option to repair bad primary sb stripe values

Source kernel commit: 15922f5dbf51dad334cde888ce6835d377678dc9

If a filesystem has a busted stripe alignment configuration on disk
(e.g. because broken RAID firmware told mkfs that swidth was smaller
than sunit), then the filesystem will refuse to mount due to the
stripe validation failing. This failure is triggering during distro
upgrades from old kernels lacking this check to newer kernels with
this check, and currently the only way to fix it is with offline
xfs_db surgery.

This runtime validity checking occurs when we read the superblock
for the first time and causes the mount to fail immediately. This
prevents the rewrite of stripe unit/width via
mount options that occurs later in the mount process. Hence there is
no way to recover this situation without resorting to offline xfs_db
rewrite of the values.

However, we parse the mount options long before we read the
superblock, and we know if the mount has been asked to re-write the
stripe alignment configuration when we are reading the superblock
and verifying it for the first time. Hence we can conditionally
ignore stripe verification failures if the mount options specified
will correct the issue.

We validate that the new stripe unit/width are valid before we
overwrite the superblock values, so we can ignore the invalid config
at verification and fail the mount later if the new values are not
valid. This, at least, gives users the chance of correcting the
issue after a kernel upgrade without having to resort to xfs-db
hacks.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>