+end:
+ return ret;
+}
+
+/*
+ * Check the status of the index for the given stream. This function
+ * updates the index structure if needed and can put (close) the vstream
+ * in the HUP situation.
+ *
+ * Return 0 means that we can proceed with the index. A value of 1 means
+ * that the index has been updated and is ready to be sent to the
+ * client. A negative value indicates an error that can't be handled.
+ *
+ * Called with rstream lock held.
+ */
+static int check_index_status(struct relay_viewer_stream *vstream,
+ struct relay_stream *rstream, struct ctf_trace *trace,
+ struct lttng_viewer_index *index)
+{
+ int ret;
+
+ DBG("Check index status: index_received_seqcount %" PRIu64 " "
+ "index_sent_seqcount %" PRIu64 " "
+ "for stream %" PRIu64,
+ rstream->index_received_seqcount,
+ vstream->index_sent_seqcount,
+ vstream->stream->stream_handle);
+ if ((trace->session->connection_closed || rstream->closed)
+ && rstream->index_received_seqcount
+ == vstream->index_sent_seqcount) {
+ /*
+ * Last index sent and session connection or relay
+ * stream are closed.
+ */
+ index->status = htobe32(LTTNG_VIEWER_INDEX_HUP);
+ goto hup;
+ } else if (rstream->beacon_ts_end != -1ULL &&
+ (rstream->index_received_seqcount == 0 ||
+ (vstream->index_sent_seqcount != 0 &&
+ rstream->index_received_seqcount
+ <= vstream->index_sent_seqcount))) {
+ /*
+ * We've received a synchronization beacon and the last index
+ * available has been sent, the index for now is inactive.
+ *
+ * In this case, we have received a beacon which allows us to
+ * inform the client of a time interval during which we can
+ * guarantee that there are no events to read (and never will
+ * be).
+ *
+ * The sent seqcount can grow higher than receive seqcount on
+ * clear because the rotation performed by clear will push
+ * the index_sent_seqcount ahead (see
+ * viewer_stream_sync_tracefile_array_tail) and skip over
+ * packet sequence numbers.
+ */
+ index->status = htobe32(LTTNG_VIEWER_INDEX_INACTIVE);
+ index->timestamp_end = htobe64(rstream->beacon_ts_end);
+ index->stream_id = htobe64(rstream->ctf_stream_id);
+ DBG("Check index status: inactive with beacon, for stream %" PRIu64,
+ vstream->stream->stream_handle);
+ goto index_ready;
+ } else if (rstream->index_received_seqcount == 0 ||
+ (vstream->index_sent_seqcount != 0 &&
+ rstream->index_received_seqcount
+ <= vstream->index_sent_seqcount)) {
+ /*
+ * This checks whether received <= sent seqcount. In
+ * this case, we have not received a beacon. Therefore,
+ * we can only ask the client to retry later.
+ *
+ * The sent seqcount can grow higher than receive seqcount on
+ * clear because the rotation performed by clear will push
+ * the index_sent_seqcount ahead (see
+ * viewer_stream_sync_tracefile_array_tail) and skip over
+ * packet sequence numbers.
+ */
+ index->status = htobe32(LTTNG_VIEWER_INDEX_RETRY);
+ DBG("Check index status: retry for stream %" PRIu64,
+ vstream->stream->stream_handle);
+ goto index_ready;
+ } else if (!tracefile_array_seq_in_file(rstream->tfa,
+ vstream->current_tracefile_id,
+ vstream->index_sent_seqcount)) {
+ /*
+ * The next index we want to send cannot be read either
+ * because we need to perform a rotation, or due to
+ * the producer having overwritten its trace file.
+ */
+ DBG("Viewer stream %" PRIu64 " rotation",
+ vstream->stream->stream_handle);
+ ret = viewer_stream_rotate(vstream);
+ if (ret == 1) {
+ /* EOF across entire stream. */
+ index->status = htobe32(LTTNG_VIEWER_INDEX_HUP);
+ goto hup;
+ }
+ /*
+ * If we have been pushed due to overwrite, it
+ * necessarily means there is data that can be read in
+ * the stream. If we rotated because we reached the end
+ * of a tracefile, it means the following tracefile
+ * needs to contain at least one index, else we would
+ * have already returned LTTNG_VIEWER_INDEX_RETRY to the
+ * viewer. The updated index_sent_seqcount needs to
+ * point to a readable index entry now.
+ *
+ * In the case where we "rotate" on a single file, we
+ * can end up in a case where the requested index is
+ * still unavailable.
+ */
+ if (rstream->tracefile_count == 1 &&
+ !tracefile_array_seq_in_file(
+ rstream->tfa,
+ vstream->current_tracefile_id,
+ vstream->index_sent_seqcount)) {
+ index->status = htobe32(LTTNG_VIEWER_INDEX_RETRY);
+ DBG("Check index status: retry: "
+ "tracefile array sequence number %" PRIu64
+ " not in file for stream %" PRIu64,
+ vstream->index_sent_seqcount,
+ vstream->stream->stream_handle);
+ goto index_ready;