NFS: client needs to maintain list of inodes with active layouts

In particular, server reboot will invalidate all layouts.

Note that in order to have an active layout, we must get a successful response
from the server.  To avoid adding that machinery, this patch just includes a
stub that fakes up a successful return.  Since the layout is never referenced
for io, this is not a problem.

Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Dean Hildebrand <dhildebz@umich.edu>
Signed-off-by: Fred Isaman <iisaman@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index eba0bcc..e55ad21 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -156,7 +156,9 @@
 	cred = rpc_lookup_machine_cred();
 	if (!IS_ERR(cred))
 		clp->cl_machine_cred = cred;
-
+#if defined(CONFIG_NFS_V4_1)
+	INIT_LIST_HEAD(&clp->cl_layouts);
+#endif
 	nfs_fscache_get_client_cookie(clp);
 
 	return clp;