9P: Add cancelled() to the transport functions.

RDMA needs to post a buffer for each incoming reply.
Hence it needs to keep count of these and needs to be
aware of whether a flushed request has received a reply
or not.

This patch adds the cancelled() callback to the transport modules.
It is called when RFLUSH has been received and that the corresponding
request will never receive a reply.
Signed-off-by: Simon Derr <simon.derr@bull.net>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

include/net/9p/transport.h

@@ -40,6 +40,8 @@
  * @close: member function to discard a connection on this transport
  * @request: member function to issue a request to the transport
  * @cancel: member function to cancel a request (if it hasn't been sent)
+ * @cancelled: member function to notify that a cancelled request will not
+ *             not receive a reply
  *
  * This is the basic API for a transport module which is registered by the
  * transport module with the 9P core network module and used by the client
@@ -58,6 +60,7 @@ struct p9_trans_module {
 	void (*close) (struct p9_client *);
 	int (*request) (struct p9_client *, struct p9_req_t *req);
 	int (*cancel) (struct p9_client *, struct p9_req_t *req);
+	int (*cancelled)(struct p9_client *, struct p9_req_t *req);
 	int (*zc_request)(struct p9_client *, struct p9_req_t *,
 			  char *, char *, int , int, int, int);
 };

net/9p/client.c

@@ -658,12 +658,18 @@ static int p9_client_flush(struct p9_client *c, struct p9_req_t *oldreq)
 
 	/*
 	 * if we haven't received a response for oldreq,
-	 * remove it from the list.
+	 * remove it from the list, and notify the transport
+	 * layer that the reply will never arrive.
 	 */
 	spin_lock(&c->lock);
-	if (oldreq->status == REQ_STATUS_FLSH)
+	if (oldreq->status == REQ_STATUS_FLSH) {
 		list_del(&oldreq->req_list);
 		spin_unlock(&c->lock);
+		if (c->trans_mod->cancelled)
+			c->trans_mod->cancelled(c, req);
+	} else {
+		spin_unlock(&c->lock);
+	}
 
 	p9_free_req(c, req);
 	return 0;

net/9p/trans_rdma.c

@@ -588,6 +588,17 @@ static int rdma_cancel(struct p9_client *client, struct p9_req_t *req)
 	return 1;
 }
 
+/* A request has been fully flushed without a reply.
+ * That means we have posted one buffer in excess.
+ */
+static int rdma_cancelled(struct p9_client *client, struct p9_req_t *req)
+{
+	struct p9_trans_rdma *rdma = client->trans;
+
+	atomic_inc(&rdma->excess_rc);
+	return 0;
+}
+
 /**
  * trans_create_rdma - Transport method for creating atransport instance
  * @client: client instance