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.

This is done by moving the increment of the open stateid and unlocking
of the st_mutex until after we acquire a delegation. If we get a
delegation, we zero out the op_stateid field and set the NO_OPEN_STATEID
flag. If the open stateid was brand new, then unhash it too in this case
since it won't be needed.

If we can't get a delegation or the new flag wasn't requested, then just
increment and copy the open stateid as usual.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfsd/nfs4state.c       | 33 +++++++++++++++++++++++++++++----
 fs/nfsd/nfs4xdr.c         |  5 +++--
 include/uapi/linux/nfs4.h |  7 +++++--
 3 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index ecf02badf598d147feb5133cb43225e3611d6d8e..a9eb7cf9fd7e74a648170c60bf031fdc32533dd3 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -6054,6 +6054,17 @@ static void nfsd4_deleg_xgrade_none_ext(struct nfsd4_open *open,
 	 */
 }
 
+/* Are we only returning 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;
+	if (open->op_delegate_type != NFS4_OPEN_DELEGATE_READ &&
+	    open->op_delegate_type != NFS4_OPEN_DELEGATE_WRITE)
+		return false;
+	return true;
+}
+
 /**
  * nfsd4_process_open2 - finish open processing
  * @rqstp: the RPC transaction being executed
@@ -6076,6 +6087,7 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
 	struct nfs4_delegation *dp = NULL;
 	__be32 status;
 	bool new_stp = false;
+	bool deleg_only = false;
 
 	/*
 	 * Lookup file; if found, lookup stateid and check open request,
@@ -6130,9 +6142,6 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
 			open->op_odstate = NULL;
 	}
 
-	nfs4_inc_and_copy_stateid(&open->op_stateid, &stp->st_stid);
-	mutex_unlock(&stp->st_mutex);
-
 	if (nfsd4_has_session(&resp->cstate)) {
 		if (open->op_deleg_want & NFS4_SHARE_WANT_NO_DELEG) {
 			open->op_delegate_type = NFS4_OPEN_DELEGATE_NONE_EXT;
@@ -6146,7 +6155,23 @@ 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.
+	 */
+	deleg_only = new_stp && open_xor_delegation(open);
 nodeleg:
+	if (deleg_only) {
+		memcpy(&open->op_stateid, &zero_stateid, sizeof(open->op_stateid));
+		open->op_rflags |= OPEN4_RESULT_NO_OPEN_STATEID;
+		release_open_stateid(stp);
+	} else {
+		nfs4_inc_and_copy_stateid(&open->op_stateid, &stp->st_stid);
+	}
+	mutex_unlock(&stp->st_mutex);
+
 	status = nfs_ok;
 	trace_nfsd_open(&stp->st_stid.sc_stateid);
 out:
@@ -6162,7 +6187,7 @@ 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))
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 9fb7764924240a8c584517bcdf682fea1b417180..dad6875aa17eb99759cdbacb814b7988848a961b 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -1067,7 +1067,7 @@ static __be32 nfsd4_decode_share_access(struct nfsd4_compoundargs *argp, u32 *sh
 		return nfs_ok;
 	if (!argp->minorversion)
 		return nfserr_bad_xdr;
-	switch (w & NFS4_SHARE_WANT_MASK) {
+	switch (w & NFS4_SHARE_WANT_TYPE_MASK) {
 	case NFS4_SHARE_WANT_NO_PREFERENCE:
 	case NFS4_SHARE_WANT_READ_DELEG:
 	case NFS4_SHARE_WANT_WRITE_DELEG:
@@ -3408,7 +3408,8 @@ 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_CANCEL)		| \
+					 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)	| \
diff --git a/include/uapi/linux/nfs4.h b/include/uapi/linux/nfs4.h
index caf4db2fcbb94686631ec2232a8ff189c97c8617..4273e0249fcbb54996f5642f9920826b9d68b7b9 100644
--- a/include/uapi/linux/nfs4.h
+++ b/include/uapi/linux/nfs4.h
@@ -58,7 +58,7 @@
 #define NFS4_SHARE_DENY_BOTH	0x0003
 
 /* nfs41 */
-#define NFS4_SHARE_WANT_MASK		0xFF00
+#define NFS4_SHARE_WANT_TYPE_MASK	0xFF00
 #define NFS4_SHARE_WANT_NO_PREFERENCE	0x0000
 #define NFS4_SHARE_WANT_READ_DELEG	0x0100
 #define NFS4_SHARE_WANT_WRITE_DELEG	0x0200
@@ -66,13 +66,16 @@
 #define NFS4_SHARE_WANT_NO_DELEG	0x0400
 #define NFS4_SHARE_WANT_CANCEL		0x0500
 
-#define NFS4_SHARE_WHEN_MASK		0xF0000
+#define NFS4_SHARE_WHEN_MASK				0xF0000
 #define NFS4_SHARE_SIGNAL_DELEG_WHEN_RESRC_AVAIL	0x10000
 #define NFS4_SHARE_PUSH_DELEG_WHEN_UNCONTENDED		0x20000
 
+#define NFS4_SHARE_WANT_MOD_MASK			0xF00000
 #define NFS4_SHARE_WANT_DELEG_TIMESTAMPS		0x100000
 #define NFS4_SHARE_WANT_OPEN_XOR_DELEGATION		0x200000
 
+#define NFS4_SHARE_WANT_MASK	(NFS4_SHARE_WANT_TYPE_MASK | NFS4_SHARE_WANT_MOD_MASK)
+
 #define NFS4_CDFC4_FORE	0x1
 #define NFS4_CDFC4_BACK 0x2
 #define NFS4_CDFC4_BOTH 0x3

-- 
2.46.2