xfs: remove shared supberlock feature checking

We reject any filesystem that is mounted with this feature bit set,
so we don't need to check for it anywhere else. Remove the function
for checking if the feature bit is set and any code that uses it.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jie Liu <jeff.liu@oracle.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_fsops.c

@@ -84,8 +84,6 @@ xfs_fs_geometry(
 				XFS_FSOP_GEOM_FLAGS_IALIGN : 0) |
 			(xfs_sb_version_hasdalign(&mp->m_sb) ?
 				XFS_FSOP_GEOM_FLAGS_DALIGN : 0) |
-			(xfs_sb_version_hasshared(&mp->m_sb) ?
-				XFS_FSOP_GEOM_FLAGS_SHARED : 0) |
 			(xfs_sb_version_hasextflgbit(&mp->m_sb) ?
 				XFS_FSOP_GEOM_FLAGS_EXTFLG : 0) |
 			(xfs_sb_version_hassector(&mp->m_sb) ?

fs/xfs/xfs_sb.c

@@ -291,7 +291,8 @@ xfs_mount_validate_sb(
 	    (sbp->sb_imax_pct > 100 /* zero sb_imax_pct is valid */)	||
 	    sbp->sb_dblocks == 0					||
 	    sbp->sb_dblocks > XFS_MAX_DBLOCKS(sbp)			||
-	    sbp->sb_dblocks < XFS_MIN_DBLOCKS(sbp))) {
+	    sbp->sb_dblocks < XFS_MIN_DBLOCKS(sbp)			||
+	    sbp->sb_shared_vn != 0)) {
 		xfs_notice(mp, "SB sanity check failed");
 		return XFS_ERROR(EFSCORRUPTED);
 	}

fs/xfs/xfs_sb.h

@@ -51,11 +51,12 @@ struct xfs_trans;
 
 /*
  * Supported feature bit list is just all bits in the versionnum field because
- * we've used them all up and understand them all.
+ * we've used them all up and understand them all. Except, of course, for the
+ * shared superblock bit, which nobody knows what it does and so is unsupported.
  */
 #define	XFS_SB_VERSION_OKBITS		\
-	(XFS_SB_VERSION_NUMBITS		| \
-	 XFS_SB_VERSION_ALLFBITS)
+	((XFS_SB_VERSION_NUMBITS | XFS_SB_VERSION_ALLFBITS) & \
+		~XFS_SB_VERSION_SHAREDBIT)
 
 /*
  * There are two words to hold XFS "feature" bits: the original
@@ -341,10 +342,6 @@ static inline bool xfs_sb_good_v4_features(struct xfs_sb *sbp)
 	     (sbp->sb_features2 & ~XFS_SB_VERSION2_OKBITS)))
 		return false;
 
-	/* We don't support shared superblocks - nobody knows what it is */
-	if (sbp->sb_versionnum & XFS_SB_VERSION_SHAREDBIT)
-		return false;
-
 	return true;
 }
 
@@ -397,12 +394,6 @@ static inline bool xfs_sb_version_hasdalign(struct xfs_sb *sbp)
 	return (sbp->sb_versionnum & XFS_SB_VERSION_DALIGNBIT);
 }
 
-static inline bool xfs_sb_version_hasshared(struct xfs_sb *sbp)
-{
-	return XFS_SB_VERSION_NUM(sbp) == XFS_SB_VERSION_4 &&
-		(sbp->sb_versionnum & XFS_SB_VERSION_SHAREDBIT);
-}
-
 static inline bool xfs_sb_version_haslogv2(struct xfs_sb *sbp)
 {
 	return XFS_SB_VERSION_NUM(sbp) == XFS_SB_VERSION_5 ||