+ stream->rotate_position = stream->last_sequence_number + 1 +
+ ((produced_pos - consumed_pos) / stream->max_sb_size);
+ DBG("Set rotation position for stream %" PRIu64 " at position %" PRIu64,
+ stream->key, stream->rotate_position);
+
+ if (!is_local_trace) {
+ /*
+ * The relay daemon control protocol expects a rotation
+ * position as "the sequence number of the first packet
+ * _after_ the current trace chunk".
+ */
+ const struct relayd_stream_rotation_position position = {
+ .stream_id = stream->relayd_stream_id,
+ .rotate_at_seq_num = stream->rotate_position,
+ };
+
+ ret = lttng_dynamic_array_add_element(
+ &stream_rotation_positions,
+ &position);
+ if (ret) {
+ ERR("Failed to allocate stream rotation position");
+ goto end_unlock_stream;
+ }
+ stream_count++;
+ }
+
+ stream->opened_packet_in_current_trace_chunk = false;
+
+ if (rotating_to_new_chunk && !stream->metadata_flag) {
+ /*
+ * Attempt to flush an empty packet as close to the
+ * rotation point as possible. In the event where a
+ * stream remains inactive after the rotation point,
+ * this ensures that the new trace chunk has a
+ * beginning timestamp set at the begining of the
+ * trace chunk instead of only creating an empty
+ * packet when the trace chunk is stopped.
+ *
+ * This indicates to the viewers that the stream
+ * was being recorded, but more importantly it
+ * allows viewers to determine a useable trace
+ * intersection.
+ *
+ * This presents a problem in the case where the
+ * ring-buffer is completely full.
+ *
+ * Consider the following scenario:
+ * - The consumption of data is slow (slow network,
+ * for instance),
+ * - The ring buffer is full,
+ * - A rotation is initiated,
+ * - The flush below does nothing (no space left to
+ * open a new packet),
+ * - The other streams rotate very soon, and new
+ * data is produced in the new chunk,
+ * - This stream completes its rotation long after the
+ * rotation was initiated
+ * - The session is stopped before any event can be
+ * produced in this stream's buffers.
+ *
+ * The resulting trace chunk will have a single packet
+ * temporaly at the end of the trace chunk for this
+ * stream making the stream intersection more narrow
+ * than it should be.
+ *
+ * To work-around this, an empty flush is performed
+ * after the first consumption of a packet during a
+ * rotation if open_packet fails. The idea is that
+ * consuming a packet frees enough space to switch
+ * packets in this scenario and allows the tracer to
+ * "stamp" the beginning of the new trace chunk at the
+ * earliest possible point.
+ */
+ const enum open_packet_status status =
+ open_packet(stream);
+
+ switch (status) {
+ case OPEN_PACKET_STATUS_OPENED:
+ DBG("Opened a packet after a rotation: stream id = %" PRIu64
+ ", channel name = %s, session id = %" PRIu64,
+ stream->key, stream->chan->name,
+ stream->chan->session_id);
+ break;
+ case OPEN_PACKET_STATUS_NO_SPACE:
+ /*
+ * Can't open a packet as there is no space left
+ * in the buffer. A new packet will be opened
+ * once one has been consumed.
+ */
+ DBG("No space left to open a packet after a rotation: stream id = %" PRIu64
+ ", channel name = %s, session id = %" PRIu64,
+ stream->key, stream->chan->name,
+ stream->chan->session_id);
+ break;
+ case OPEN_PACKET_STATUS_ERROR:
+ /* Logged by callee. */
+ ret = -1;
+ goto end_unlock_stream;
+ default:
+ abort();
+ }
+ }
+
+ pthread_mutex_unlock(&stream->lock);
+ }
+ stream = NULL;
+ pthread_mutex_unlock(&channel->lock);
+
+ if (is_local_trace) {
+ ret = 0;
+ goto end;
+ }
+
+ relayd = consumer_find_relayd(relayd_id);
+ if (!relayd) {
+ ERR("Failed to find relayd %" PRIu64, relayd_id);
+ ret = -1;
+ goto end;
+ }
+
+ pthread_mutex_lock(&relayd->ctrl_sock_mutex);
+ ret = relayd_rotate_streams(&relayd->control_sock, stream_count,
+ rotating_to_new_chunk ? &next_chunk_id : NULL,
+ (const struct relayd_stream_rotation_position *)
+ stream_rotation_positions.buffer.data);
+ pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
+ if (ret < 0) {
+ ERR("Relayd rotate stream failed. Cleaning up relayd %" PRIu64,
+ relayd->net_seq_idx);
+ lttng_consumer_cleanup_relayd(relayd);
+ goto end;
+ }
+
+ ret = 0;
+ goto end;
+
+end_unlock_stream:
+ pthread_mutex_unlock(&stream->lock);
+end_unlock_channel:
+ pthread_mutex_unlock(&channel->lock);
+end:
+ rcu_read_unlock();
+ lttng_dynamic_array_reset(&stream_rotation_positions);
+ return ret;
+}
+
+static
+int consumer_clear_buffer(struct lttng_consumer_stream *stream)
+{
+ int ret = 0;
+ unsigned long consumed_pos_before, consumed_pos_after;
+
+ ret = lttng_consumer_sample_snapshot_positions(stream);
+ if (ret < 0) {
+ ERR("Taking snapshot positions");
+ goto end;
+ }
+
+ ret = lttng_consumer_get_consumed_snapshot(stream, &consumed_pos_before);
+ if (ret < 0) {
+ ERR("Consumed snapshot position");
+ goto end;
+ }
+
+ switch (consumer_data.type) {
+ case LTTNG_CONSUMER_KERNEL:
+ ret = kernctl_buffer_clear(stream->wait_fd);
+ if (ret < 0) {
+ ERR("Failed to clear kernel stream (ret = %d)", ret);
+ goto end;
+ }
+ break;
+ case LTTNG_CONSUMER32_UST:
+ case LTTNG_CONSUMER64_UST:
+ lttng_ustconsumer_clear_buffer(stream);
+ break;
+ default:
+ ERR("Unknown consumer_data type");
+ abort();
+ }
+
+ ret = lttng_consumer_sample_snapshot_positions(stream);
+ if (ret < 0) {
+ ERR("Taking snapshot positions");
+ goto end;
+ }
+ ret = lttng_consumer_get_consumed_snapshot(stream, &consumed_pos_after);
+ if (ret < 0) {
+ ERR("Consumed snapshot position");
+ goto end;
+ }
+ DBG("clear: before: %lu after: %lu", consumed_pos_before, consumed_pos_after);
+end:
+ return ret;
+}
+
+static
+int consumer_clear_stream(struct lttng_consumer_stream *stream)
+{
+ int ret;
+
+ ret = consumer_flush_buffer(stream, 1);
+ if (ret < 0) {
+ ERR("Failed to flush stream %" PRIu64 " during channel clear",
+ stream->key);
+ ret = LTTCOMM_CONSUMERD_FATAL;
+ goto error;
+ }
+
+ ret = consumer_clear_buffer(stream);
+ if (ret < 0) {
+ ERR("Failed to clear stream %" PRIu64 " during channel clear",
+ stream->key);
+ ret = LTTCOMM_CONSUMERD_FATAL;
+ goto error;
+ }
+
+ ret = LTTCOMM_CONSUMERD_SUCCESS;
+error:
+ return ret;
+}