From: David Goulet <dgoulet@efficios.com>
Date: Wed, 19 Dec 2012 20:36:59 +0000 (-0500)
Subject: Fix: Off by one in seq num for data pending command
X-Git-Tag: v2.1.0~15
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=39df6d9f42d8644d9ee25c8c02517b2cef6f5941;p=lttng-tools.git

Fix: Off by one in seq num for data pending command

Like the close stream command, the next sequence number of the stream
needs to be used minus 1 for the data pending or else we are off by one
on the relayd during the check since 4 data packets for instance means a
prev_seq value of 4 but a last_next_seq_num of 5 hence creating an off
by one for the data pending check.

Furthermore, the check was actually wrong on the relayd side. Having a
previous sequence number lower than the last one seen does NOT mean that
the data is not pending so the check needed was actually equal or
greater.

Signed-off-by: David Goulet <dgoulet@efficios.com>
---

diff --git a/src/bin/lttng-relayd/main.c b/src/bin/lttng-relayd/main.c
index 47780e266..d0cf15a30 100644
--- a/src/bin/lttng-relayd/main.c
+++ b/src/bin/lttng-relayd/main.c
@@ -1427,7 +1427,7 @@ int relay_data_pending(struct lttcomm_relayd_hdr *recv_hdr,
 			last_net_seq_num);
 
 	/* Avoid wrapping issue */
-	if (((int64_t) (stream->prev_seq - last_net_seq_num)) <= 0) {
+	if (((int64_t) (stream->prev_seq - last_net_seq_num)) >= 0) {
 		/* Data has in fact been written and is NOT pending */
 		ret = 0;
 	} else {
diff --git a/src/common/consumer.c b/src/common/consumer.c
index be984a492..61d6f2e79 100644
--- a/src/common/consumer.c
+++ b/src/common/consumer.c
@@ -782,6 +782,13 @@ static int write_relayd_stream_header(struct lttng_consumer_stream *stream,
 		data_hdr.stream_id = htobe64(stream->relayd_stream_id);
 		data_hdr.data_size = htobe32(data_size);
 		data_hdr.padding_size = htobe32(padding);
+		/*
+		 * Note that net_seq_num below is assigned with the *current* value of
+		 * next_net_seq_num and only after that the next_net_seq_num will be
+		 * increment. This is why when issuing a command on the relayd using
+		 * this next value, 1 should always be substracted in order to compare
+		 * the last seen sequence number on the relayd side to the last sent.
+		 */
 		data_hdr.net_seq_num = htobe64(stream->next_net_seq_num++);
 		/* Other fields are zeroed previously */
 
@@ -3021,7 +3028,8 @@ int consumer_data_pending(uint64_t id)
 						stream->relayd_stream_id);
 			} else {
 				ret = relayd_data_pending(&relayd->control_sock,
-						stream->relayd_stream_id, stream->next_net_seq_num);
+						stream->relayd_stream_id,
+						stream->next_net_seq_num - 1);
 			}
 			pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
 			if (ret == 1) {