NFS: Introduce NFS_ATTR_FATTR_V4_LOCATIONS

The Linux NFS client must distinguish between referral events (which
it currently supports) and migration events (which it does not yet
support).

In both types of events, an fs_locations array is returned.  But upper
layers, not the XDR layer, should make the distinction between a
referral and a migration.  There really isn't a way for an XDR decoder
function to distinguish the two, in general.

Slightly adjust the FATTR flags returned by decode_fs_locations()
to set NFS_ATTR_FATTR_V4_LOCATIONS only if a non-empty locations
array was returned from the server.  Then have logic in nfs4proc.c
distinguish whether the locations array is for a referral or
something else.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
index 046c1bf..210da5d 100644
--- a/include/linux/nfs_xdr.h
+++ b/include/linux/nfs_xdr.h
@@ -88,11 +88,12 @@
 #define NFS_ATTR_FATTR_PRECTIME		(1U << 16)
 #define NFS_ATTR_FATTR_CHANGE		(1U << 17)
 #define NFS_ATTR_FATTR_PRECHANGE	(1U << 18)
-#define NFS_ATTR_FATTR_V4_REFERRAL	(1U << 19)	/* NFSv4 referral */
-#define NFS_ATTR_FATTR_MOUNTPOINT	(1U << 20)	/* Treat as mountpoint */
-#define NFS_ATTR_FATTR_MOUNTED_ON_FILEID		(1U << 21)
-#define NFS_ATTR_FATTR_OWNER_NAME	(1U << 22)
-#define NFS_ATTR_FATTR_GROUP_NAME	(1U << 23)
+#define NFS_ATTR_FATTR_V4_LOCATIONS	(1U << 19)
+#define NFS_ATTR_FATTR_V4_REFERRAL	(1U << 20)
+#define NFS_ATTR_FATTR_MOUNTPOINT	(1U << 21)
+#define NFS_ATTR_FATTR_MOUNTED_ON_FILEID (1U << 22)
+#define NFS_ATTR_FATTR_OWNER_NAME	(1U << 23)
+#define NFS_ATTR_FATTR_GROUP_NAME	(1U << 24)
 
 #define NFS_ATTR_FATTR (NFS_ATTR_FATTR_TYPE \
 		| NFS_ATTR_FATTR_MODE \