xfs: reserve v5 superblock read-only compat. feature bit for finobt
xfs: reserve v5 superblock read-only compat. feature bit for finobt

Reserve a v5 read-only compatibility feature bit for the finobt and
create the xfs_sb_version_hasfinobt() helper to determine whether
an fs has the feature enabled.

The finobt does not change existing on-disk structures, but must
remain consistent with the ialloc btree. Modifications from older
kernels would violate that constrant. Therefore, we restrict older
kernels to read-only mounts of finobt-enabled filesystems.

Note that this does not yet enable the ability to rw mount a finobt
fs (by setting the feature bit in the XFS_SB_FEAT_RO_COMPAT_ALL
mask).

Signed-off-by: Brian Foster <335646b5e374a776a6a2caca10969d6e3ec1cd2b@redhat.com>
Reviewed-by: Dave Chinner <4d9e23a041ac966f5316a7481300d4ae12e806fe@redhat.com>
Signed-off-by: Dave Chinner <aa743a0aaec8f7d7a1f01442503957f4d7a2d634@fromorbit.com>


KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs