xfs: add parent pointer support to attribute code

Add the new parent attribute type. XFS_ATTR_PARENT is used only for parent pointer
entries; it uses reserved blocks like XFS_ATTR_ROOT.

[dchinner: forward ported and cleaned up]
[achender: rebased]

Signed-off-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Allison Henderson <allison.henderson@oracle.com>

fs/xfs/libxfs/xfs_attr.c

@@ -649,11 +649,13 @@ xfs_attr_set(
 	struct xfs_inode	*dp = args->dp;
 	struct xfs_mount	*mp = dp->i_mount;
 	struct xfs_trans_res	tres;
-	bool			rsvd = (args->attr_filter & XFS_ATTR_ROOT);
+	bool			rsvd;
 	int			error, local;
 	int			rmt_blks = 0;
 	unsigned int		total;
 
+	rsvd = ((args->attr_filter & XFS_ATTR_ROOT) | XFS_ATTR_PARENT) != 0;
+
 	if (XFS_FORCED_SHUTDOWN(dp->i_mount))
 		return -EIO;
 

fs/xfs/libxfs/xfs_da_format.h

@@ -687,12 +687,15 @@ struct xfs_attr3_leafblock {
 #define	XFS_ATTR_LOCAL_BIT	0	/* attr is stored locally */
 #define	XFS_ATTR_ROOT_BIT	1	/* limit access to trusted attrs */
 #define	XFS_ATTR_SECURE_BIT	2	/* limit access to secure attrs */
+#define 	XFS_ATTR_PARENT_BIT	3	/* parent pointer secure attrs */
 #define	XFS_ATTR_INCOMPLETE_BIT	7	/* attr in middle of create/delete */
 #define XFS_ATTR_LOCAL		(1 << XFS_ATTR_LOCAL_BIT)
 #define XFS_ATTR_ROOT		(1 << XFS_ATTR_ROOT_BIT)
 #define XFS_ATTR_SECURE		(1 << XFS_ATTR_SECURE_BIT)
+#define XFS_ATTR_PARENT		(1 << XFS_ATTR_PARENT_BIT)
 #define XFS_ATTR_INCOMPLETE	(1 << XFS_ATTR_INCOMPLETE_BIT)
-#define XFS_ATTR_NSP_ONDISK_MASK	(XFS_ATTR_ROOT | XFS_ATTR_SECURE)
+#define XFS_ATTR_NSP_ONDISK_MASK \
+			(XFS_ATTR_ROOT | XFS_ATTR_SECURE | XFS_ATTR_PARENT)
 
 /*
  * Alignment for namelist and valuelist entries (since they are mixed