nfsd41: CREATE_EXCLUSIVE4_1

Implement the CREATE_EXCLUSIVE4_1 open mode conforming to
http://tools.ietf.org/html/draft-ietf-nfsv4-minorversion1-26

This mode allows the client to atomically create a file
if it doesn't exist while setting some of its attributes.

It must be implemented if the server supports persistent
reply cache and/or pnfs.

Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index e206053..b2883e9 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -93,6 +93,21 @@
 	open->op_truncate = 0;
 
 	if (open->op_create) {
+		/* FIXME: check session persistence and pnfs flags.
+		 * The nfsv4.1 spec requires the following semantics:
+		 *
+		 * Persistent   | pNFS   | Server REQUIRED | Client Allowed
+		 * Reply Cache  | server |                 |
+		 * -------------+--------+-----------------+--------------------
+		 * no           | no     | EXCLUSIVE4_1    | EXCLUSIVE4_1
+		 *              |        |                 | (SHOULD)
+		 *              |        | and EXCLUSIVE4  | or EXCLUSIVE4
+		 *              |        |                 | (SHOULD NOT)
+		 * no           | yes    | EXCLUSIVE4_1    | EXCLUSIVE4_1
+		 * yes          | no     | GUARDED4        | GUARDED4
+		 * yes          | yes    | GUARDED4        | GUARDED4
+		 */
+
 		/*
 		 * Note: create modes (UNCHECKED,GUARDED...) are the same
 		 * in NFSv4 as in v3.