NFSv4: Follow a referral

Respond to a moved error on NFS lookup by setting up the referral.
Note: We don't actually follow the referral during lookup/getattr, but
later when we detect fsid mismatch in inode revalidation (similar to the
processing done for cloning submounts). Referrals will have fake attributes
until they are actually followed or traversed.

Signed-off-by: Manoj Naik <manoj@almaden.ibm.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 0d8302e..ee13cb0 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -888,7 +888,10 @@
 				set_bit(NFS_INO_ADVISE_RDPLUS, &NFS_FLAGS(inode));
 			/* Deal with crossing mountpoints */
 			if (!nfs_fsid_equal(&NFS_SB(sb)->fsid, &fattr->fsid)) {
-				inode->i_op = &nfs_mountpoint_inode_operations;
+				if (fattr->valid & NFS_ATTR_FATTR_V4_REFERRAL)
+					inode->i_op = &nfs_referral_inode_operations;
+				else
+					inode->i_op = &nfs_mountpoint_inode_operations;
 				inode->i_fop = NULL;
 			}
 		} else if (S_ISLNK(inode->i_mode))