+/*
+ * Write a character on the metadata poll pipe to wake the metadata thread.
+ * Returns 0 on success, -1 on error.
+ */
+int consumer_metadata_wakeup_pipe(const struct lttng_consumer_channel *channel)
+{
+ int ret = 0;
+
+ DBG("Waking up metadata poll thread (writing to pipe): channel name = '%s'",
+ channel->name);
+ if (channel->monitor && channel->metadata_stream) {
+ const char dummy = 'c';
+ const ssize_t write_ret = lttng_write(
+ channel->metadata_stream->ust_metadata_poll_pipe[1],
+ &dummy, 1);
+
+ if (write_ret < 1) {
+ if (errno == EWOULDBLOCK) {
+ /*
+ * This is fine, the metadata poll thread
+ * is having a hard time keeping-up, but
+ * it will eventually wake-up and consume
+ * the available data.
+ */
+ ret = 0;
+ } else {
+ PERROR("Failed to write to UST metadata pipe while attempting to wake-up the metadata poll thread");
+ ret = -1;
+ goto end;
+ }
+ }
+ }
+
+end:
+ return ret;
+}
+
+/*
+ * Trigger a dump of the metadata content. Following/during the succesful
+ * completion of this call, the metadata poll thread will start receiving
+ * metadata packets to consume.
+ *
+ * The caller must hold the channel and stream locks.
+ */
+static
+int consumer_metadata_stream_dump(struct lttng_consumer_stream *stream)
+{
+ int ret;
+
+ ASSERT_LOCKED(stream->chan->lock);
+ ASSERT_LOCKED(stream->lock);
+ assert(stream->metadata_flag);
+ assert(stream->chan->trace_chunk);
+
+ switch (consumer_data.type) {
+ case LTTNG_CONSUMER_KERNEL:
+ /*
+ * Reset the position of what has been read from the
+ * metadata cache to 0 so we can dump it again.
+ */
+ ret = kernctl_metadata_cache_dump(stream->wait_fd);
+ break;
+ case LTTNG_CONSUMER32_UST:
+ case LTTNG_CONSUMER64_UST:
+ /*
+ * Reset the position pushed from the metadata cache so it
+ * will write from the beginning on the next push.
+ */
+ stream->ust_metadata_pushed = 0;
+ ret = consumer_metadata_wakeup_pipe(stream->chan);
+ break;
+ default:
+ ERR("Unknown consumer_data type");
+ abort();
+ }
+ if (ret < 0) {
+ ERR("Failed to dump the metadata cache");
+ }
+ return ret;
+}
+
+static
+int lttng_consumer_channel_set_trace_chunk(
+ struct lttng_consumer_channel *channel,
+ struct lttng_trace_chunk *new_trace_chunk)
+{
+ pthread_mutex_lock(&channel->lock);
+ if (channel->is_deleted) {
+ /*
+ * The channel has been logically deleted and should no longer
+ * be used. It has released its reference to its current trace
+ * chunk and should not acquire a new one.
+ *
+ * Return success as there is nothing for the caller to do.
+ */
+ goto end;
+ }
+
+ /*
+ * The acquisition of the reference cannot fail (barring
+ * a severe internal error) since a reference to the published
+ * chunk is already held by the caller.
+ */
+ if (new_trace_chunk) {
+ const bool acquired_reference = lttng_trace_chunk_get(
+ new_trace_chunk);
+
+ assert(acquired_reference);
+ }
+
+ lttng_trace_chunk_put(channel->trace_chunk);
+ channel->trace_chunk = new_trace_chunk;
+end:
+ pthread_mutex_unlock(&channel->lock);
+ return 0;
+}
+