+void lttng_channel_destroy(struct lttng_channel *channel)
+{
+ if (!channel) {
+ return;
+ }
+
+ if (channel->attr.extended.ptr) {
+ free(channel->attr.extended.ptr);
+ }
+ free(channel);
+}
+
+/*
+ * Enable channel per domain
+ * Returns size of returned session payload data or a negative error code.
+ */
+int lttng_enable_channel(struct lttng_handle *handle,
+ struct lttng_channel *in_chan)
+{
+ int ret;
+ struct lttcomm_session_msg lsm;
+ size_t total_buffer_size_needed_per_cpu = 0;
+
+ /* NULL arguments are forbidden. No default values. */
+ if (handle == NULL || in_chan == NULL) {
+ return -LTTNG_ERR_INVALID;
+ }
+
+ memset(&lsm, 0, sizeof(lsm));
+ memcpy(&lsm.u.channel.chan, in_chan, sizeof(lsm.u.channel.chan));
+ lsm.u.channel.chan.attr.extended.ptr = NULL;
+
+ if (!in_chan->attr.extended.ptr) {
+ struct lttng_channel *channel;
+ struct lttng_channel_extended *extended;
+
+ channel = lttng_channel_create(&handle->domain);
+ if (!channel) {
+ return -LTTNG_ERR_NOMEM;
+ }
+
+ /*
+ * Create a new channel in order to use default extended
+ * attribute values.
+ */
+ extended = (struct lttng_channel_extended *)
+ channel->attr.extended.ptr;
+ memcpy(&lsm.u.channel.extended, extended, sizeof(*extended));
+ lttng_channel_destroy(channel);
+ } else {
+ struct lttng_channel_extended *extended;
+
+ extended = (struct lttng_channel_extended *)
+ in_chan->attr.extended.ptr;
+ memcpy(&lsm.u.channel.extended, extended, sizeof(*extended));
+ }
+
+ /*
+ * Verify that the amount of memory required to create the requested
+ * buffer is available on the system at the moment.
+ */
+ total_buffer_size_needed_per_cpu = lsm.u.channel.chan.attr.num_subbuf *
+ lsm.u.channel.chan.attr.subbuf_size;
+ if (!check_enough_available_memory(total_buffer_size_needed_per_cpu)) {
+ return -LTTNG_ERR_NOMEM;
+ }
+
+ lsm.cmd_type = LTTNG_ENABLE_CHANNEL;
+ COPY_DOMAIN_PACKED(lsm.domain, handle->domain);
+
+ ret = lttng_strncpy(lsm.session.name, handle->session_name,
+ sizeof(lsm.session.name));
+ if (ret) {
+ ret = -LTTNG_ERR_INVALID;
+ goto end;
+ }
+
+ ret = lttng_ctl_ask_sessiond(&lsm, NULL);
+end:
+ return ret;
+}
+
+/*
+ * All tracing will be stopped for registered events of the channel.