nbd: add tracepoints for send/receive timing

This adds four tracepoints to nbd, enabling separate tracing of payload
and header sending/receipt.

In the send path for headers that have already been sent, we also
explicitly initialize the handle so it can be referenced by the later
tracepoint.

Signed-off-by: Andrew Hall <[e-mail]>
Signed-off-by: Matt Mullins <[e-mail]>
Reviewed-by: Josef Bacik <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>

drivers/block/nbd.c

···
 	if (sent) {
 		if (sent >= sizeof(request)) {
 			skip = sent - sizeof(request);
+
+			/* initialize handle for tracing purposes */
+			handle = nbd_cmd_handle(cmd);
+
 			goto send_pages;
 		}
 		iov_iter_advance(&from, sent);
···
 		(unsigned long long)blk_rq_pos(req) << 9, blk_rq_bytes(req));
 	result = sock_xmit(nbd, index, 1, &from,
 			(type == NBD_CMD_WRITE) ? MSG_MORE : 0, &sent);
+	trace_nbd_header_sent(req, handle);
 	if (result <= 0) {
 		if (was_interrupted(result)) {
 			/* If we havne't sent anything we can just return BUSY,
···
 		bio = next;
 	}
 out:
+	trace_nbd_payload_sent(req, handle);
 	nsock->pending = NULL;
 	nsock->sent = 0;
 	return 0;
···
 			tag, req);
 		return ERR_PTR(-ENOENT);
 	}
+	trace_nbd_header_received(req, handle);
 	cmd = blk_mq_rq_to_pdu(req);
 
 	mutex_lock(&cmd->lock);
···
 		}
 	}
 out:
+	trace_nbd_payload_received(req, handle);
 	mutex_unlock(&cmd->lock);
 	return ret ? ERR_PTR(ret) : cmd;
 }

include/trace/events/nbd.h

···
 
 #include <linux/tracepoint.h>
 
+DECLARE_EVENT_CLASS(nbd_transport_event,
+
+	TP_PROTO(struct request *req, u64 handle),
+
+	TP_ARGS(req, handle),
+
+	TP_STRUCT__entry(
+		__field(struct request *, req)
+		__field(u64, handle)
+	),
+
+	TP_fast_assign(
+		__entry->req = req;
+		__entry->handle = handle;
+	),
+
+	TP_printk(
+		"nbd transport event: request %p, handle 0x%016llx",
+		__entry->req,
+		__entry->handle
+	)
+);
+
+DEFINE_EVENT(nbd_transport_event, nbd_header_sent,
+
+	TP_PROTO(struct request *req, u64 handle),
+
+	TP_ARGS(req, handle)
+);
+
+DEFINE_EVENT(nbd_transport_event, nbd_payload_sent,
+
+	TP_PROTO(struct request *req, u64 handle),
+
+	TP_ARGS(req, handle)
+);
+
+DEFINE_EVENT(nbd_transport_event, nbd_header_received,
+
+	TP_PROTO(struct request *req, u64 handle),
+
+	TP_ARGS(req, handle)
+);
+
+DEFINE_EVENT(nbd_transport_event, nbd_payload_received,
+
+	TP_PROTO(struct request *req, u64 handle),
+
+	TP_ARGS(req, handle)
+);
+
 DECLARE_EVENT_CLASS(nbd_send_request,
 
 	TP_PROTO(struct nbd_request *nbd_request, int index,