[lttng-dev] [PATCH lttng-tools 1/1] Fix: consumer snapshot: handle unsigned long overflow

[Mathieu Desnoyers]

Comparing the consumed iterator and the produced position without
using a difference generates an empty snapshot when the iterator is
before unsigned long overflow and the produced position is after
unsigned long overflow.

This applies to both UST and kernel consumers.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
---
 src/common/kernel-consumer/kernel-consumer.c | 2 +-
 src/common/ust-consumer/ust-consumer.c       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/common/kernel-consumer/kernel-consumer.c b/src/common/kernel-consumer/kernel-consumer.c
index 9bed7b55..1533e9ef 100644
--- a/src/common/kernel-consumer/kernel-consumer.c
+++ b/src/common/kernel-consumer/kernel-consumer.c
@@ -234,7 +234,7 @@ int lttng_kconsumer_snapshot_channel(struct lttng_consumer_channel *channel,
 				produced_pos, nb_packets_per_stream,
 				stream->max_sb_size);
 
-		while (consumed_pos < produced_pos) {
+		while ((long) (consumed_pos - produced_pos) < 0) {
 			ssize_t read_len;
 			unsigned long len, padded_len;
 
diff --git a/src/common/ust-consumer/ust-consumer.c b/src/common/ust-consumer/ust-consumer.c
index 46f33005..94b761cb 100644
--- a/src/common/ust-consumer/ust-consumer.c
+++ b/src/common/ust-consumer/ust-consumer.c
@@ -1168,7 +1168,7 @@ static int snapshot_channel(struct lttng_consumer_channel *channel,
 				produced_pos, nb_packets_per_stream,
 				stream->max_sb_size);
 
-		while (consumed_pos < produced_pos) {
+		while ((long) (consumed_pos - produced_pos) < 0) {
 			ssize_t read_len;
 			unsigned long len, padded_len;
 
-- 
2.11.0