[lttng-dev] [PATCH lttng-tools 1/2] Fix: handle backward compatibility with lttng-modules 2.7

[mathieu.desnoyers@efficios.com (Mathieu Desnoyers)]

There is no major version bump between lttng-module 2.7 and 2.8 ABI.
Even though we do not guarantee compatibility, do a best effort to
maintain it when possible.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
---
 src/common/kernel-consumer/kernel-consumer.c | 38 +++++++++++++++++++++++-----
 1 file changed, 32 insertions(+), 6 deletions(-)

diff --git a/src/common/kernel-consumer/kernel-consumer.c b/src/common/kernel-consumer/kernel-consumer.c
index 65dcce4..a8abcd7 100644
--- a/src/common/kernel-consumer/kernel-consumer.c
+++ b/src/common/kernel-consumer/kernel-consumer.c
@@ -1085,15 +1085,27 @@ static int get_index_values(struct ctf_packet_index *index, int infd)
 
 	ret = kernctl_get_instance_id(infd, &index->stream_instance_id);
 	if (ret < 0) {
-		PERROR("kernctl_get_instance_id");
-		goto error;
+		if (ret == -ENOTTY) {
+			/* Command not implemented by lttng-modules. */
+			index->stream_instance_id = -1ULL;
+			ret = 0;
+		} else {
+			PERROR("kernctl_get_instance_id");
+			goto error;
+		}
 	}
 	index->stream_instance_id = htobe64(index->stream_instance_id);
 
 	ret = kernctl_get_sequence_number(infd, &index->packet_seq_num);
 	if (ret < 0) {
-		PERROR("kernctl_get_sequence_number");
-		goto error;
+		if (ret == -ENOTTY) {
+			/* Command not implemented by lttng-modules. */
+			index->packet_seq_num = -1ULL;
+			ret = 0;
+		} else {
+			PERROR("kernctl_get_sequence_number");
+			goto error;
+		}
 	}
 	index->packet_seq_num = htobe64(index->packet_seq_num);
 
@@ -1145,8 +1157,14 @@ int update_stream_stats(struct lttng_consumer_stream *stream)
 
 	ret = kernctl_get_sequence_number(stream->wait_fd, &seq);
 	if (ret < 0) {
-		PERROR("kernctl_get_sequence_number");
-		goto end;
+		if (ret == -ENOTTY) {
+			/* Command not implemented by lttng-modules. */
+			seq = -1ULL;
+			ret = 0;
+		} else {
+			PERROR("kernctl_get_sequence_number");
+			goto end;
+		}
 	}
 
 	/*
@@ -1205,6 +1223,14 @@ int metadata_stream_check_version(int infd, struct lttng_consumer_stream *stream
 
 	ret = kernctl_get_metadata_version(infd, &cur_version);
 	if (ret < 0) {
+		if (ret == -ENOTTY) {
+			/*
+			 * LTTng-modules does not implement this
+			 * command.
+			 */
+			ret = 0;
+			goto end;
+		}
 		ERR("Failed to get the metadata version");
 		goto end;
 	}
-- 
2.1.4