xfs: enable the rmap btree functionality

Originally-From: Dave Chinner <dchinner@redhat.com>

Add the feature flag to the supported matrix so that the kernel can
mount and use rmap btree enabled filesystems

Signed-off-by: Dave Chinner <dchinner@redhat.com>
[darrick.wong@oracle.com: move the experimental tag]
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/libxfs/xfs_format.h

@@ -457,7 +457,8 @@ xfs_sb_has_compat_feature(
 #define XFS_SB_FEAT_RO_COMPAT_FINOBT   (1 << 0)		/* free inode btree */
 #define XFS_SB_FEAT_RO_COMPAT_RMAPBT   (1 << 1)		/* reverse map btree */
 #define XFS_SB_FEAT_RO_COMPAT_ALL \
-		(XFS_SB_FEAT_RO_COMPAT_FINOBT)
+		(XFS_SB_FEAT_RO_COMPAT_FINOBT | \
+		 XFS_SB_FEAT_RO_COMPAT_RMAPBT)
 #define XFS_SB_FEAT_RO_COMPAT_UNKNOWN	~XFS_SB_FEAT_RO_COMPAT_ALL
 static inline bool
 xfs_sb_has_ro_compat_feature(

fs/xfs/xfs_super.c

@@ -1574,6 +1574,10 @@ xfs_fs_fill_super(
 		}
 	}
 
+	if (xfs_sb_version_hasrmapbt(&mp->m_sb))
+		xfs_alert(mp,
+	"EXPERIMENTAL reverse mapping btree feature enabled. Use at your own risk!");
+
 	error = xfs_mountfs(mp);
 	if (error)
 		goto out_filestream_unmount;