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/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index 09271b1..1527989 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -409,6 +409,7 @@
  */
 extern struct list_head nfs_automount_list;
 extern struct inode_operations nfs_mountpoint_inode_operations;
+extern struct inode_operations nfs_referral_inode_operations;
 extern int nfs_mountpoint_expiry_timeout;
 extern void nfs_release_automount_timer(void);