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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 <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
This commit is contained in:
Brian Foster 2014-04-24 16:00:52 +10:00 committed by Dave Chinner
parent 57bd3dbe40
commit 8e2c84df20
1 changed files with 7 additions and 0 deletions
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7
fs/xfs/xfs_sb.h
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@ -587,6 +587,7 @@ xfs_sb_has_compat_feature(
return (sbp->sb_features_compat & feature) != 0;
}
#define XFS_SB_FEAT_RO_COMPAT_FINOBT (1 << 0) /* free inode btree */
#define XFS_SB_FEAT_RO_COMPAT_ALL 0
#define XFS_SB_FEAT_RO_COMPAT_UNKNOWN ~XFS_SB_FEAT_RO_COMPAT_ALL
static inline bool
@ -641,6 +642,12 @@ static inline int xfs_sb_version_hasftype(struct xfs_sb *sbp)
(sbp->sb_features2 & XFS_SB_VERSION2_FTYPE));
}
static inline int xfs_sb_version_hasfinobt(xfs_sb_t *sbp)
{
return (XFS_SB_VERSION_NUM(sbp) == XFS_SB_VERSION_5) &&
(sbp->sb_features_ro_compat & XFS_SB_FEAT_RO_COMPAT_FINOBT);
}
/*
* end of superblock version macros
*/