NFS: Add options for finer control of the lookup cache

Add the flag NFS_MOUNT_LOOKUP_CACHE_NONEG to turn off the caching of
negative dentries. In reality what we do is to force
nfs_lookup_revalidate() to always discard negative dentries.

Add the flag NFS_MOUNT_LOOKUP_CACHE_NONE for enforcing stricter
revalidation of dentries. It forces the revalidate code to always do a
lookup instead of just checking the cached mtime of the parent directory.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/nfs_mount.h

@@ -65,4 +65,8 @@ struct nfs_mount_data {
 #define NFS_MOUNT_UNSHARED	0x8000	/* 5 */
 #define NFS_MOUNT_FLAGMASK	0xFFFF
 
+/* The following are for internal use only */
+#define NFS_MOUNT_LOOKUP_CACHE_NONEG	0x10000
+#define NFS_MOUNT_LOOKUP_CACHE_NONE	0x20000
+
 #endif