nfsd: implement OPEN_ARGS_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION

Allow clients to request getting a delegation xor an open stateid if a
delegation isn't available. This allows the client to avoid sending a
final CLOSE for the (useless) open stateid, when it is granted a
delegation.

If this flag is requested by the client and there isn't already a new
open stateid, discard the new open stateid before replying.

Signed-off-by: Jeff Layton <[email protected]>
Signed-off-by: Chuck Lever <[email protected]>

Author: jtlayton

fs/nfsd/nfs4state.c

@@ -6242,6 +6242,17 @@ static void nfsd4_deleg_xgrade_none_ext(struct nfsd4_open *open,
 	 */
 }
 
+/* Are we returning only a delegation stateid? */
+static bool open_xor_delegation(struct nfsd4_open *open)
+{
+	if (!(open->op_deleg_want & OPEN4_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION))
+		return false;
+	/* Did we actually get a delegation? */
+	if (!deleg_is_read(open->op_delegate_type) && !deleg_is_write(open->op_delegate_type))
+		return false;
+	return true;
+}
+
 /**
  * nfsd4_process_open2 - finish open processing
  * @rqstp: the RPC transaction being executed
@@ -6339,6 +6350,17 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
 	* OPEN succeeds even if we fail.
 	*/
 	nfs4_open_delegation(open, stp, &resp->cstate.current_fh);
+
+	/*
+	 * If there is an existing open stateid, it must be updated and
+	 * returned. Only respect WANT_OPEN_XOR_DELEGATION when a new
+	 * open stateid would have to be created.
+	 */
+	if (new_stp && open_xor_delegation(open)) {
+		memcpy(&open->op_stateid, &zero_stateid, sizeof(open->op_stateid));
+		open->op_rflags |= OPEN4_RESULT_NO_OPEN_STATEID;
+		release_open_stateid(stp);
+	}
 nodeleg:
 	status = nfs_ok;
 	trace_nfsd_open(&stp->st_stid.sc_stateid);
@@ -6355,7 +6377,7 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
 	/*
 	* To finish the open response, we just need to set the rflags.
 	*/
-	open->op_rflags = NFS4_OPEN_RESULT_LOCKTYPE_POSIX;
+	open->op_rflags |= NFS4_OPEN_RESULT_LOCKTYPE_POSIX;
 	if (nfsd4_has_session(&resp->cstate))
 		open->op_rflags |= NFS4_OPEN_RESULT_MAY_NOTIFY_LOCK;
 	else if (!(open->op_openowner->oo_flags & NFS4_OO_CONFIRMED))

fs/nfsd/nfs4xdr.c

@@ -3421,7 +3421,8 @@ static __be32 nfsd4_encode_fattr4_xattr_support(struct xdr_stream *xdr,
 #define NFSD_OA_SHARE_ACCESS_WANT	(BIT(OPEN_ARGS_SHARE_ACCESS_WANT_ANY_DELEG)		| \
 					 BIT(OPEN_ARGS_SHARE_ACCESS_WANT_NO_DELEG)		| \
 					 BIT(OPEN_ARGS_SHARE_ACCESS_WANT_CANCEL)		| \
-					 BIT(OPEN_ARGS_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS))
+					 BIT(OPEN_ARGS_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS)	| \
+					 BIT(OPEN_ARGS_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION))
 
 #define NFSD_OA_OPEN_CLAIM	(BIT(OPEN_ARGS_OPEN_CLAIM_NULL)		| \
 				 BIT(OPEN_ARGS_OPEN_CLAIM_PREVIOUS)	| \