NFSv4: Defer inode revalidation when setting up a delegation

Currently we force a synchronous call to __nfs_revalidate_inode() in
nfs_inode_set_delegation(). This not only ensures that we cannot call
nfs_inode_set_delegation from an asynchronous context, but it also slows
down any call to open().

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index cf39535..e949710 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -184,6 +184,7 @@
 #define NFS_INO_INVALID_ACCESS	0x0008		/* cached access cred invalid */
 #define NFS_INO_INVALID_ACL	0x0010		/* cached acls are invalid */
 #define NFS_INO_REVAL_PAGECACHE	0x0020		/* must revalidate pagecache */
+#define NFS_INO_REVAL_FORCED	0x0040		/* force revalidation ignoring a delegation */
 
 /*
  * Bit offsets in flags field