NFSv4: Track the number of referring calls in struct cb_process_state

When the server gives us a set of referring calls, to tell us that the
NFSv4.1 callback needs to be ordered with respect to those calls, then
we may want to make that information available to the operations. In
certain cases, it may allow them to optimise their behaviour due to the
extra knowledge.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/callback.h

@@ -40,11 +40,12 @@ enum nfs4_callback_opnum {
 
 struct nfs4_slot;
 struct cb_process_state {
-	__be32			drc_status;
 	struct nfs_client	*clp;
 	struct nfs4_slot	*slot;
-	u32			minorversion;
 	struct net		*net;
+	u32			minorversion;
+	__be32			drc_status;
+	unsigned int		referring_calls;
 };
 
 struct cb_compound_hdr_arg {

fs/nfs/callback_proc.c

@@ -450,6 +450,7 @@ static int referring_call_exists(struct nfs_client *clp,
 	__acquires(lock)
 {
 	int status = 0;
+	int found = 0;
 	int i, j;
 	struct nfs4_session *session;
 	struct nfs4_slot_table *tbl;
@@ -478,11 +479,12 @@ static int referring_call_exists(struct nfs_client *clp,
 			spin_lock(lock);
 			if (status)
 				goto out;
+			found++;
 		}
 	}
 
 out:
-	return status;
+	return status < 0 ? status : found;
 }
 
 __be32 nfs4_callback_sequence(void *argp, void *resp,
@@ -493,6 +495,7 @@ __be32 nfs4_callback_sequence(void *argp, void *resp,
 	struct nfs4_slot_table *tbl;
 	struct nfs4_slot *slot;
 	struct nfs_client *clp;
+	int ret;
 	int i;
 	__be32 status = htonl(NFS4ERR_BADSESSION);
 
@@ -552,11 +555,13 @@ __be32 nfs4_callback_sequence(void *argp, void *resp,
 	 * related callback was received before the response to the original
 	 * call.
 	 */
-	if (referring_call_exists(clp, args->csa_nrclists, args->csa_rclists,
-				&tbl->slot_tbl_lock) < 0) {
+	ret = referring_call_exists(clp, args->csa_nrclists, args->csa_rclists,
+				    &tbl->slot_tbl_lock);
+	if (ret < 0) {
 		status = htonl(NFS4ERR_DELAY);
 		goto out_unlock;
 	}
+	cps->referring_calls = ret;
 
 	/*
 	 * RFC5661 20.9.3