From: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Date: Wed, 12 Jan 2022 23:18:08 +0000 (-0500)
Subject: Fix: liblttng-ctl comm: lttng_channel is not packed
X-Git-Url: http://git.efficios.com/?p=lttng-tools.git;a=commitdiff_plain;h=33b9609d08bf77e0afcb34d8d14b6fee44ffa0aa

Fix: liblttng-ctl comm: lttng_channel is not packed

Observed issue
==============

The size of the struct differs between bitness for x86-64 and x86
leading to serialization/deserialization problem across client
(liblttng-ctl) and lttng-sessiond.

sizeof(struct lttng_channel):

  x86: 608
  x86-64: 624

The struct cannot be marked as LTTNG_PACKED since it is part of the API.

Solution
========

Adopt a similar pattern to the new API with a "serialize" &
"create_from_buffer" approach. The only particularity is that we need to
flatten the channels on listing.

Most of the complexity is moved to `src/common/channel.c`

Known drawbacks
=========

None.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I59b0e92286e36c4f183d2950417cb180d4efc200
---

diff --git a/include/lttng/channel-internal.h b/include/lttng/channel-internal.h
index 04b19322f..2e9590836 100644
--- a/include/lttng/channel-internal.h
+++ b/include/lttng/channel-internal.h
@@ -9,6 +9,10 @@
 #define LTTNG_CHANNEL_INTERNAL_H
 
 #include <common/macros.h>
+#include <lttng/channel.h>
+
+struct lttng_dynamic_buffer;
+struct lttng_buffer_view;
 
 struct lttng_channel_extended {
 	uint64_t discarded_events;
@@ -17,4 +21,51 @@ struct lttng_channel_extended {
 	int64_t blocking_timeout;
 } LTTNG_PACKED;
 
+struct lttng_channel_comm {
+	/* Includes terminator `\0`. */
+	uint32_t name_len;
+	uint8_t enabled;
+
+	/* attr */
+	int8_t overwrite;
+	uint64_t subbuf_size;
+	uint64_t num_subbuf;
+	uint32_t switch_timer_interval;
+	uint32_t read_timer_interval;
+	uint8_t output;
+	uint64_t tracefile_size;
+	uint64_t tracefile_count;
+	uint32_t live_timer_interval;
+
+	/* Extended struct */
+	uint64_t discarded_events;
+	uint64_t lost_packets;
+	uint64_t monitor_timer_interval;
+	int64_t blocking_timeout;
+} LTTNG_PACKED;
+
+LTTNG_HIDDEN
+struct lttng_channel *lttng_channel_create_internal(void);
+
+LTTNG_HIDDEN
+struct lttng_channel *lttng_channel_copy(const struct lttng_channel *src);
+
+LTTNG_HIDDEN
+ssize_t lttng_channel_create_from_buffer(const struct lttng_buffer_view *view,
+		struct lttng_channel **event);
+
+LTTNG_HIDDEN
+int lttng_channel_serialize(struct lttng_channel *channel,
+		struct lttng_dynamic_buffer *buf);
+
+LTTNG_HIDDEN
+void lttng_channel_set_default_extended_attr(struct lttng_domain *domain,
+		struct lttng_channel_extended *extended_attr);
+
+LTTNG_HIDDEN
+enum lttng_error_code lttng_channels_create_and_flatten_from_buffer(
+		const struct lttng_buffer_view *view,
+		unsigned int count,
+		struct lttng_channel **channels);
+
 #endif /* LTTNG_CHANNEL_INTERNAL_H */
diff --git a/src/bin/lttng-sessiond/channel.c b/src/bin/lttng-sessiond/channel.c
index e2596ce58..365b24a59 100644
--- a/src/bin/lttng-sessiond/channel.c
+++ b/src/bin/lttng-sessiond/channel.c
@@ -544,3 +544,56 @@ end:
 error:
 	return ret;
 }
+
+struct lttng_channel *trace_ust_channel_to_lttng_channel(
+		const struct ltt_ust_channel *uchan)
+{
+	struct lttng_channel *channel = NULL, *ret = NULL;
+
+	channel = lttng_channel_create_internal();
+	if (!channel) {
+		goto end;
+	}
+
+	if (lttng_strncpy(channel->name, uchan->name, LTTNG_SYMBOL_NAME_LEN)) {
+		goto end;
+	}
+
+	channel->attr.overwrite = uchan->attr.overwrite;
+	channel->attr.subbuf_size = uchan->attr.subbuf_size;
+	channel->attr.num_subbuf = uchan->attr.num_subbuf;
+	channel->attr.switch_timer_interval = uchan->attr.switch_timer_interval;
+	channel->attr.read_timer_interval = uchan->attr.read_timer_interval;
+	channel->enabled = uchan->enabled;
+	channel->attr.tracefile_size = uchan->tracefile_size;
+	channel->attr.tracefile_count = uchan->tracefile_count;
+
+	/*
+	 * Map enum lttng_ust_output to enum lttng_event_output.
+	 */
+	switch (uchan->attr.output) {
+	case LTTNG_UST_MMAP:
+		channel->attr.output = LTTNG_EVENT_MMAP;
+		break;
+	default:
+		/*
+		 * LTTNG_UST_MMAP is the only supported UST
+		 * output mode.
+		 */
+		abort();
+		break;
+	}
+
+	lttng_channel_set_blocking_timeout(
+			channel, uchan->attr.u.s.blocking_timeout);
+	lttng_channel_set_monitor_timer_interval(
+			channel, uchan->monitor_timer_interval);
+
+	ret = channel;
+	channel = NULL;
+
+end:
+	lttng_channel_destroy(channel);
+
+	return ret;
+}
diff --git a/src/bin/lttng-sessiond/channel.h b/src/bin/lttng-sessiond/channel.h
index b4ff9f4fd..1b6e29bd7 100644
--- a/src/bin/lttng-sessiond/channel.h
+++ b/src/bin/lttng-sessiond/channel.h
@@ -31,4 +31,7 @@ int channel_ust_enable(struct ltt_ust_session *usess,
 int channel_ust_disable(struct ltt_ust_session *usess,
 		struct ltt_ust_channel *uchan);
 
+struct lttng_channel *trace_ust_channel_to_lttng_channel(
+		const struct ltt_ust_channel *uchan);
+
 #endif /* _LTT_CHANNEL_H */
diff --git a/src/bin/lttng-sessiond/client.c b/src/bin/lttng-sessiond/client.c
index be907ebe3..5e95a59f0 100644
--- a/src/bin/lttng-sessiond/client.c
+++ b/src/bin/lttng-sessiond/client.c
@@ -23,6 +23,7 @@
 #include <pthread.h>
 #include <signal.h>
 #include <stddef.h>
+#include <stdint.h>
 #include <sys/stat.h>
 
 #include "client.h"
@@ -716,6 +717,9 @@ static int process_client_msg(struct command_ctx *cmd_ctx, int *sock,
 	int ret = LTTNG_OK;
 	int need_tracing_session = 1;
 	int need_domain;
+	struct lttng_dynamic_buffer payload;
+
+	lttng_dynamic_buffer_init(&payload);
 
 	DBG("Processing client command %d", cmd_ctx->lsm->cmd_type);
 
@@ -1195,12 +1199,7 @@ error_add_context:
 	}
 	case LTTNG_ENABLE_CHANNEL:
 	{
-		cmd_ctx->lsm->u.channel.chan.attr.extended.ptr =
-				(struct lttng_channel_extended *) &cmd_ctx->lsm->u.channel.extended;
-		ret = cmd_enable_channel(cmd_ctx->session,
-				ALIGNED_CONST_PTR(cmd_ctx->lsm->domain),
-				ALIGNED_CONST_PTR(cmd_ctx->lsm->u.channel.chan),
-				kernel_poll_pipe[1]);
+		ret = cmd_enable_channel(cmd_ctx, *sock, kernel_poll_pipe[1]);
 		break;
 	}
 	case LTTNG_PROCESS_ATTR_TRACKER_ADD_INCLUDE_VALUE:
@@ -1706,20 +1705,20 @@ error_add_context:
 	}
 	case LTTNG_LIST_CHANNELS:
 	{
-		ssize_t payload_size;
-		struct lttng_channel *channels = NULL;
+		uint32_t nb_channel;
+		enum lttng_error_code ret_code;
+		struct lttcomm_list_command_header cmd_header = { 0 };
 
-		payload_size = cmd_list_channels(cmd_ctx->lsm->domain.type,
-				cmd_ctx->session, &channels);
-		if (payload_size < 0) {
-			/* Return value is a negative lttng_error_code. */
-			ret = -payload_size;
+		ret_code = cmd_list_channels(cmd_ctx->lsm->domain.type,
+				cmd_ctx->session, &payload, &nb_channel);
+		if (ret_code != LTTNG_OK) {
+			ret = (int) ret_code;
 			goto error;
 		}
 
-		ret = setup_lttng_msg_no_cmd_header(cmd_ctx, channels,
-			payload_size);
-		free(channels);
+		cmd_header.count = nb_channel;
+		ret = setup_lttng_msg(cmd_ctx, payload.data, payload.size,
+				&cmd_header, sizeof(cmd_header));
 
 		if (ret < 0) {
 			goto setup_error;
@@ -2108,6 +2107,7 @@ setup_error:
 	}
 init_setup_error:
 	assert(!rcu_read_ongoing());
+	lttng_dynamic_buffer_reset(&payload);
 	return ret;
 }
 
diff --git a/src/bin/lttng-sessiond/cmd.c b/src/bin/lttng-sessiond/cmd.c
index 655e4727d..01dc3bb74 100644
--- a/src/bin/lttng-sessiond/cmd.c
+++ b/src/bin/lttng-sessiond/cmd.c
@@ -111,6 +111,10 @@ static int cmd_enable_event_internal(struct ltt_session *session,
 		struct lttng_filter_bytecode *filter,
 		struct lttng_event_exclusion *exclusion,
 		int wpipe);
+static int cmd_enable_channel_internal(struct ltt_session *session,
+		const struct lttng_domain *domain,
+		const struct lttng_channel *_attr,
+		int wpipe);
 
 /*
  * Create a session path used by list_lttng_sessions for the case that the
@@ -281,118 +285,6 @@ end:
 	return ret;
 }
 
-/*
- * Fill lttng_channel array of all channels.
- */
-static ssize_t list_lttng_channels(enum lttng_domain_type domain,
-		struct ltt_session *session, struct lttng_channel *channels,
-		struct lttng_channel_extended *chan_exts)
-{
-	int i = 0, ret = 0;
-	struct ltt_kernel_channel *kchan;
-
-	DBG("Listing channels for session %s", session->name);
-
-	switch (domain) {
-	case LTTNG_DOMAIN_KERNEL:
-		/* Kernel channels */
-		if (session->kernel_session != NULL) {
-			cds_list_for_each_entry(kchan,
-					&session->kernel_session->channel_list.head, list) {
-				uint64_t discarded_events, lost_packets;
-				struct lttng_channel_extended *extended;
-
-				extended = (struct lttng_channel_extended *)
-						kchan->channel->attr.extended.ptr;
-
-				ret = get_kernel_runtime_stats(session, kchan,
-						&discarded_events, &lost_packets);
-				if (ret < 0) {
-					goto end;
-				}
-				/* Copy lttng_channel struct to array */
-				memcpy(&channels[i], kchan->channel, sizeof(struct lttng_channel));
-				channels[i].enabled = kchan->enabled;
-				chan_exts[i].discarded_events =
-						discarded_events;
-				chan_exts[i].lost_packets = lost_packets;
-				chan_exts[i].monitor_timer_interval =
-						extended->monitor_timer_interval;
-				chan_exts[i].blocking_timeout = 0;
-				i++;
-			}
-		}
-		break;
-	case LTTNG_DOMAIN_UST:
-	{
-		struct lttng_ht_iter iter;
-		struct ltt_ust_channel *uchan;
-
-		rcu_read_lock();
-		cds_lfht_for_each_entry(session->ust_session->domain_global.channels->ht,
-				&iter.iter, uchan, node.node) {
-			uint64_t discarded_events = 0, lost_packets = 0;
-
-			if (lttng_strncpy(channels[i].name, uchan->name,
-					LTTNG_SYMBOL_NAME_LEN)) {
-				break;
-			}
-			channels[i].attr.overwrite = uchan->attr.overwrite;
-			channels[i].attr.subbuf_size = uchan->attr.subbuf_size;
-			channels[i].attr.num_subbuf = uchan->attr.num_subbuf;
-			channels[i].attr.switch_timer_interval =
-				uchan->attr.switch_timer_interval;
-			channels[i].attr.read_timer_interval =
-				uchan->attr.read_timer_interval;
-			channels[i].enabled = uchan->enabled;
-			channels[i].attr.tracefile_size = uchan->tracefile_size;
-			channels[i].attr.tracefile_count = uchan->tracefile_count;
-
-			/*
-			 * Map enum lttng_ust_output to enum lttng_event_output.
-			 */
-			switch (uchan->attr.output) {
-			case LTTNG_UST_MMAP:
-				channels[i].attr.output = LTTNG_EVENT_MMAP;
-				break;
-			default:
-				/*
-				 * LTTNG_UST_MMAP is the only supported UST
-				 * output mode.
-				 */
-				assert(0);
-				break;
-			}
-
-			chan_exts[i].monitor_timer_interval =
-					uchan->monitor_timer_interval;
-			chan_exts[i].blocking_timeout =
-				uchan->attr.u.s.blocking_timeout;
-
-			ret = get_ust_runtime_stats(session, uchan,
-					&discarded_events, &lost_packets);
-			if (ret < 0) {
-				break;
-			}
-			chan_exts[i].discarded_events = discarded_events;
-			chan_exts[i].lost_packets = lost_packets;
-			i++;
-		}
-		rcu_read_unlock();
-		break;
-	}
-	default:
-		break;
-	}
-
-end:
-	if (ret < 0) {
-		return -LTTNG_ERR_FATAL;
-	} else {
-		return LTTNG_OK;
-	}
-}
-
 static int increment_extended_len(const char *filter_expression,
 		struct lttng_event_exclusion *exclusion,
 		const struct lttng_userspace_probe_location *probe_location,
@@ -1434,30 +1326,84 @@ error:
  *
  * The wpipe arguments is used as a notifier for the kernel thread.
  */
-int cmd_enable_channel(struct ltt_session *session,
-		const struct lttng_domain *domain, const struct lttng_channel *_attr, int wpipe)
+int cmd_enable_channel(struct command_ctx *cmd_ctx, int sock, int wpipe)
+{
+	int ret;
+	size_t channel_len;
+	ssize_t sock_recv_len;
+	struct lttng_channel *channel = NULL;
+	struct lttng_buffer_view view;
+	struct lttng_dynamic_buffer channel_buffer;
+
+	lttng_dynamic_buffer_init(&channel_buffer);
+	channel_len = (size_t) cmd_ctx->lsm->u.channel.length;
+	ret = lttng_dynamic_buffer_set_size(&channel_buffer, channel_len);
+	if (ret) {
+		ret = LTTNG_ERR_NOMEM;
+		goto end;
+	}
+
+	sock_recv_len = lttcomm_recv_unix_sock(sock, channel_buffer.data,
+			channel_len);
+	if (sock_recv_len < 0 || sock_recv_len != channel_len) {
+		ERR("Failed to receive \"enable channel\" command payload");
+		ret = LTTNG_ERR_INVALID;
+		goto end;
+	}
+
+	view = lttng_buffer_view_from_dynamic_buffer(&channel_buffer, 0, channel_len);
+	if (!lttng_buffer_view_is_valid(&view)) {
+		ret = LTTNG_ERR_INVALID;
+		goto end;
+	}
+
+	if (lttng_channel_create_from_buffer(&view, &channel) != channel_len) {
+		ERR("Invalid channel payload received in \"enable channel\" command");
+		ret = LTTNG_ERR_INVALID;
+		goto end;
+	}
+
+	ret = cmd_enable_channel_internal(cmd_ctx->session,
+			ALIGNED_CONST_PTR(cmd_ctx->lsm->domain), channel,
+			wpipe);
+
+end:
+	lttng_dynamic_buffer_reset(&channel_buffer);
+	lttng_channel_destroy(channel);
+	return ret;
+}
+
+static int cmd_enable_channel_internal(struct ltt_session *session,
+		const struct lttng_domain *domain,
+		const struct lttng_channel *_attr,
+		int wpipe)
 {
 	int ret;
 	struct ltt_ust_session *usess = session->ust_session;
 	struct lttng_ht *chan_ht;
 	size_t len;
-	struct lttng_channel attr;
+	struct lttng_channel *attr = NULL;
 
 	assert(session);
 	assert(_attr);
 	assert(domain);
 
-	attr = *_attr;
-	len = lttng_strnlen(attr.name, sizeof(attr.name));
+	attr = lttng_channel_copy(_attr);
+	if (!attr) {
+		ret = -LTTNG_ERR_NOMEM;
+		goto end;
+	}
+
+	len = lttng_strnlen(attr->name, sizeof(attr->name));
 
 	/* Validate channel name */
-	if (attr.name[0] == '.' ||
-		memchr(attr.name, '/', len) != NULL) {
+	if (attr->name[0] == '.' ||
+		memchr(attr->name, '/', len) != NULL) {
 		ret = LTTNG_ERR_INVALID_CHANNEL_NAME;
 		goto end;
 	}
 
-	DBG("Enabling channel %s for session %s", attr.name, session->name);
+	DBG("Enabling channel %s for session %s", attr->name, session->name);
 
 	rcu_read_lock();
 
@@ -1467,8 +1413,8 @@ int cmd_enable_channel(struct ltt_session *session,
 	 * beacons for inactive streams.
 	 */
 	if (session->live_timer > 0) {
-		attr.attr.live_timer_interval = session->live_timer;
-		attr.attr.switch_timer_interval = 0;
+		attr->attr.live_timer_interval = session->live_timer;
+		attr->attr.switch_timer_interval = 0;
 	}
 
 	/* Check for feature support */
@@ -1480,8 +1426,8 @@ int cmd_enable_channel(struct ltt_session *session,
 			WARN("Kernel tracer does not support buffer monitoring. "
 					"Setting the monitor interval timer to 0 "
 					"(disabled) for channel '%s' of session '%s'",
-					attr.name, session->name);
-			lttng_channel_set_monitor_timer_interval(&attr, 0);
+					attr->name, session->name);
+			lttng_channel_set_monitor_timer_interval(attr, 0);
 		}
 		break;
 	}
@@ -1506,8 +1452,8 @@ int cmd_enable_channel(struct ltt_session *session,
 	{
 		struct ltt_kernel_channel *kchan;
 
-		kchan = trace_kernel_get_channel_by_name(attr.name,
-				session->kernel_session);
+		kchan = trace_kernel_get_channel_by_name(
+				attr->name, session->kernel_session);
 		if (kchan == NULL) {
 			/*
 			 * Don't try to create a channel if the session has been started at
@@ -1521,10 +1467,11 @@ int cmd_enable_channel(struct ltt_session *session,
 			if (session->snapshot.nb_output > 0 ||
 					session->snapshot_mode) {
 				/* Enforce mmap output for snapshot sessions. */
-				attr.attr.output = LTTNG_EVENT_MMAP;
+				attr->attr.output = LTTNG_EVENT_MMAP;
 			}
-			ret = channel_kernel_create(session->kernel_session, &attr, wpipe);
-			if (attr.name[0] != '\0') {
+			ret = channel_kernel_create(
+					session->kernel_session, attr, wpipe);
+			if (attr->name[0] != '\0') {
 				session->kernel_session->has_non_default_channel = 1;
 			}
 		} else {
@@ -1554,19 +1501,19 @@ int cmd_enable_channel(struct ltt_session *session,
 		 * adhered to.
 		 */
 		if (domain->type == LTTNG_DOMAIN_JUL) {
-			if (strncmp(attr.name, DEFAULT_JUL_CHANNEL_NAME,
+			if (strncmp(attr->name, DEFAULT_JUL_CHANNEL_NAME,
 					LTTNG_SYMBOL_NAME_LEN)) {
 				ret = LTTNG_ERR_INVALID_CHANNEL_NAME;
 				goto error;
 			}
 		} else if (domain->type == LTTNG_DOMAIN_LOG4J) {
-			if (strncmp(attr.name, DEFAULT_LOG4J_CHANNEL_NAME,
+			if (strncmp(attr->name, DEFAULT_LOG4J_CHANNEL_NAME,
 					LTTNG_SYMBOL_NAME_LEN)) {
 				ret = LTTNG_ERR_INVALID_CHANNEL_NAME;
 				goto error;
 			}
 		} else if (domain->type == LTTNG_DOMAIN_PYTHON) {
-			if (strncmp(attr.name, DEFAULT_PYTHON_CHANNEL_NAME,
+			if (strncmp(attr->name, DEFAULT_PYTHON_CHANNEL_NAME,
 					LTTNG_SYMBOL_NAME_LEN)) {
 				ret = LTTNG_ERR_INVALID_CHANNEL_NAME;
 				goto error;
@@ -1575,7 +1522,7 @@ int cmd_enable_channel(struct ltt_session *session,
 
 		chan_ht = usess->domain_global.channels;
 
-		uchan = trace_ust_find_channel_by_name(chan_ht, attr.name);
+		uchan = trace_ust_find_channel_by_name(chan_ht, attr->name);
 		if (uchan == NULL) {
 			/*
 			 * Don't try to create a channel if the session has been started at
@@ -1586,8 +1533,8 @@ int cmd_enable_channel(struct ltt_session *session,
 				goto error;
 			}
 
-			ret = channel_ust_create(usess, &attr, domain->buf_type);
-			if (attr.name[0] != '\0') {
+			ret = channel_ust_create(usess, attr, domain->buf_type);
+			if (attr->name[0] != '\0') {
 				usess->has_non_default_channel = 1;
 			}
 		} else {
@@ -1600,12 +1547,13 @@ int cmd_enable_channel(struct ltt_session *session,
 		goto error;
 	}
 
-	if (ret == LTTNG_OK && attr.attr.output != LTTNG_EVENT_MMAP) {
+	if (ret == LTTNG_OK && attr->attr.output != LTTNG_EVENT_MMAP) {
 		session->has_non_mmap_channel = true;
 	}
 error:
 	rcu_read_unlock();
 end:
+	lttng_channel_destroy(attr);
 	return ret;
 }
 
@@ -2232,7 +2180,8 @@ static int _cmd_enable_event(struct ltt_session *session,
 				goto error;
 			}
 
-			ret = cmd_enable_channel(session, domain, attr, wpipe);
+			ret = cmd_enable_channel_internal(
+					session, domain, attr, wpipe);
 			if (ret != LTTNG_OK) {
 				goto error;
 			}
@@ -2371,7 +2320,8 @@ static int _cmd_enable_event(struct ltt_session *session,
 				goto error;
 			}
 
-			ret = cmd_enable_channel(session, domain, attr, wpipe);
+			ret = cmd_enable_channel_internal(
+					session, domain, attr, wpipe);
 			if (ret != LTTNG_OK) {
 				goto error;
 			}
@@ -3665,67 +3615,113 @@ error:
 /*
  * Command LTTNG_LIST_CHANNELS processed by the client thread.
  */
-ssize_t cmd_list_channels(enum lttng_domain_type domain,
-		struct ltt_session *session, struct lttng_channel **channels)
+enum lttng_error_code cmd_list_channels(enum lttng_domain_type domain,
+		struct ltt_session *session,
+		struct lttng_dynamic_buffer *buffer,
+		uint32_t *nb_channel)
 {
-	ssize_t nb_chan = 0, payload_size = 0, ret;
+	int ret = 0;
+	uint32_t i = 0;
+
+	assert(session);
+	assert(buffer);
+	assert(nb_channel);
+
+	DBG("Listing channels for session %s", session->name);
 
 	switch (domain) {
 	case LTTNG_DOMAIN_KERNEL:
+	{
+		/* Kernel channels */
+		struct ltt_kernel_channel *kchan;
 		if (session->kernel_session != NULL) {
-			nb_chan = session->kernel_session->channel_count;
-		}
-		DBG3("Number of kernel channels %zd", nb_chan);
-		if (nb_chan <= 0) {
-			ret = -LTTNG_ERR_KERN_CHAN_NOT_FOUND;
-			goto end;
-		}
-		break;
-	case LTTNG_DOMAIN_UST:
-		if (session->ust_session != NULL) {
-			rcu_read_lock();
-			nb_chan = lttng_ht_get_count(
-				session->ust_session->domain_global.channels);
-			rcu_read_unlock();
-		}
-		DBG3("Number of UST global channels %zd", nb_chan);
-		if (nb_chan < 0) {
-			ret = -LTTNG_ERR_UST_CHAN_NOT_FOUND;
-			goto end;
+			cds_list_for_each_entry(kchan,
+					&session->kernel_session->channel_list.head, list) {
+				uint64_t discarded_events, lost_packets;
+				struct lttng_channel_extended *extended;
+
+				extended = (struct lttng_channel_extended *)
+						kchan->channel->attr.extended.ptr;
+
+				ret = get_kernel_runtime_stats(session, kchan,
+						&discarded_events, &lost_packets);
+				if (ret < 0) {
+					goto end;
+				}
+
+				/*
+				 * Update the discarded_events and lost_packets
+				 * count for the channel
+				 */
+				extended->discarded_events = discarded_events;
+				extended->lost_packets = lost_packets;
+
+				ret = lttng_channel_serialize(
+						kchan->channel, buffer);
+				if (ret) {
+					ret = -1;
+					goto end;
+				}
+
+				i++;
+			}
 		}
 		break;
-	default:
-		ret = -LTTNG_ERR_UND;
-		goto end;
 	}
+	case LTTNG_DOMAIN_UST:
+	{
+		struct lttng_ht_iter iter;
+		struct ltt_ust_channel *uchan;
 
-	if (nb_chan > 0) {
-		const size_t channel_size = sizeof(struct lttng_channel) +
-			sizeof(struct lttng_channel_extended);
-		struct lttng_channel_extended *channel_exts;
+		rcu_read_lock();
+		cds_lfht_for_each_entry(session->ust_session->domain_global.channels->ht,
+				&iter.iter, uchan, node.node) {
+			uint64_t discarded_events = 0, lost_packets = 0;
+			struct lttng_channel *channel = NULL;
+			struct lttng_channel_extended *extended;
 
-		payload_size = nb_chan * channel_size;
-		*channels = zmalloc(payload_size);
-		if (*channels == NULL) {
-			ret = -LTTNG_ERR_FATAL;
-			goto end;
-		}
+			channel = trace_ust_channel_to_lttng_channel(uchan);
+			if (!channel) {
+				ret = -1;
+				break;
+			}
 
-		channel_exts = ((void *) *channels) +
-				(nb_chan * sizeof(struct lttng_channel));
-		ret = list_lttng_channels(domain, session, *channels, channel_exts);
-		if (ret != LTTNG_OK) {
-			free(*channels);
-			*channels = NULL;
-			goto end;
+			extended = (struct lttng_channel_extended *)
+						   channel->attr.extended.ptr;
+
+			ret = get_ust_runtime_stats(session, uchan,
+					&discarded_events, &lost_packets);
+			if (ret < 0) {
+				lttng_channel_destroy(channel);
+				break;
+			}
+
+			extended->discarded_events = discarded_events;
+			extended->lost_packets = lost_packets;
+
+			ret = lttng_channel_serialize(channel, buffer);
+			if (ret) {
+				ret = -1;
+				break;
+			}
+
+			i++;
 		}
-	} else {
-		*channels = NULL;
+		rcu_read_unlock();
+		break;
+	}
+	default:
+		break;
 	}
 
-	ret = payload_size;
 end:
-	return ret;
+	if (ret < 0) {
+		*nb_channel = 0;
+		return LTTNG_ERR_FATAL;
+	} else {
+		*nb_channel = i;
+		return LTTNG_OK;
+	}
 }
 
 /*
diff --git a/src/bin/lttng-sessiond/cmd.h b/src/bin/lttng-sessiond/cmd.h
index 1be746031..65e3846c8 100644
--- a/src/bin/lttng-sessiond/cmd.h
+++ b/src/bin/lttng-sessiond/cmd.h
@@ -15,6 +15,7 @@
 #include <common/tracker.h>
 
 struct notification_thread_handle;
+struct lttng_dynamic_buffer;
 
 /*
  * A callback (and associated user data) that should be run after a command
@@ -46,9 +47,7 @@ int cmd_destroy_session(struct ltt_session *session,
 /* Channel commands */
 int cmd_disable_channel(struct ltt_session *session,
 		enum lttng_domain_type domain, char *channel_name);
-int cmd_enable_channel(struct ltt_session *session,
-		const struct lttng_domain *domain, const struct lttng_channel *attr,
-		int wpipe);
+int cmd_enable_channel(struct command_ctx *cmd_ctx, int sock, int wpipe);
 
 /* Process attribute tracker commands */
 enum lttng_error_code cmd_process_attr_tracker_get_tracking_policy(
@@ -112,8 +111,10 @@ ssize_t cmd_list_domains(struct ltt_session *session,
 ssize_t cmd_list_events(enum lttng_domain_type domain,
 		struct ltt_session *session, char *channel_name,
 		struct lttng_event **events, size_t *total_size);
-ssize_t cmd_list_channels(enum lttng_domain_type domain,
-		struct ltt_session *session, struct lttng_channel **channels);
+enum lttng_error_code cmd_list_channels(enum lttng_domain_type domain,
+		struct ltt_session *session,
+		struct lttng_dynamic_buffer *buffer,
+		uint32_t *nb_channel);
 ssize_t cmd_list_domains(struct ltt_session *session,
 		struct lttng_domain **domains);
 void cmd_list_lttng_sessions(struct lttng_session *sessions,
diff --git a/src/bin/lttng-sessiond/trace-ust.h b/src/bin/lttng-sessiond/trace-ust.h
index 960ba57d5..f0e35b8bd 100644
--- a/src/bin/lttng-sessiond/trace-ust.h
+++ b/src/bin/lttng-sessiond/trace-ust.h
@@ -196,6 +196,7 @@ struct agent *trace_ust_find_agent(struct ltt_ust_session *session,
 struct ltt_ust_session *trace_ust_create_session(uint64_t session_id);
 struct ltt_ust_channel *trace_ust_create_channel(struct lttng_channel *attr,
 		enum lttng_domain_type domain);
+
 enum lttng_error_code trace_ust_create_event(struct lttng_event *ev,
 		char *filter_expression,
 		struct lttng_filter_bytecode *filter,
diff --git a/src/common/Makefile.am b/src/common/Makefile.am
index ca9c70d80..8b698c921 100644
--- a/src/common/Makefile.am
+++ b/src/common/Makefile.am
@@ -33,6 +33,7 @@ libcommon_lgpl_la_SOURCES = \
 	action.c \
 	buffer-view.h buffer-view.c \
 	buffer-usage.c \
+	channel.c \
 	credentials.h \
 	condition.c \
 	defaults.c \
diff --git a/src/common/channel.c b/src/common/channel.c
new file mode 100644
index 000000000..4a237e471
--- /dev/null
+++ b/src/common/channel.c
@@ -0,0 +1,467 @@
+/*
+ * Copyright (C) 2021 Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
+ *
+ * SPDX-License-Identifier: LGPL-2.1-only
+ *
+ */
+
+#include <common/macros.h>
+#include <lttng/channel.h>
+#include <lttng/constant.h>
+#include <lttng/channel-internal.h>
+#include <lttng/userspace-probe-internal.h>
+#include <common/dynamic-buffer.h>
+#include <common/error.h>
+#include <assert.h>
+#include <string.h>
+#include <common/sessiond-comm/sessiond-comm.h>
+#include <common/dynamic-array.h>
+#include <common/buffer-view.h>
+
+static enum lttng_error_code flatten_lttng_channels(
+		struct lttng_dynamic_pointer_array *channels,
+		struct lttng_channel **flattened_channels);
+
+static enum lttng_error_code channel_list_create_from_buffer(
+		const struct lttng_buffer_view *buffer,
+		uint32_t count,
+		struct lttng_dynamic_pointer_array *channel_list);
+
+static void channel_list_destructor(void *ptr)
+{
+	struct lttng_channel *element = (struct lttng_channel *) ptr;
+
+	lttng_channel_destroy(element);
+}
+
+LTTNG_HIDDEN
+struct lttng_channel *lttng_channel_copy(const struct lttng_channel *src)
+{
+	struct lttng_channel_extended *extended = NULL;
+	struct lttng_channel *channel = NULL, *ret = NULL;
+
+	channel = zmalloc(sizeof(*channel));
+	if (!channel) {
+		goto end;
+	}
+
+	memcpy(channel, src, sizeof(*channel));
+
+	if (src->attr.extended.ptr) {
+		extended = zmalloc(sizeof(*extended));
+		if (!extended) {
+			goto end;
+		}
+		memcpy(extended, src->attr.extended.ptr, sizeof(*extended));
+		channel->attr.extended.ptr = extended;
+		extended = NULL;
+	}
+
+	ret = channel;
+	channel = NULL;
+end:
+	free(channel);
+	free(extended);
+	return ret;
+}
+
+/*
+ * The channel object is NOT populated.
+ */
+LTTNG_HIDDEN
+struct lttng_channel *lttng_channel_create_internal(void)
+{
+	struct lttng_channel *local_channel = NULL, *ret = NULL;
+	struct lttng_channel_extended *extended = NULL;
+
+	local_channel = zmalloc(sizeof(struct lttng_channel));
+	if (!local_channel) {
+		goto end;
+	}
+
+	/* Extended struct */
+	extended = zmalloc(sizeof(*extended));
+	if (!extended) {
+		goto end;
+	}
+
+	local_channel->attr.extended.ptr = extended;
+	extended = NULL;
+
+	ret = local_channel;
+	local_channel = NULL;
+end:
+	free(extended);
+	free(local_channel);
+	return ret;
+}
+
+LTTNG_HIDDEN
+ssize_t lttng_channel_create_from_buffer(const struct lttng_buffer_view *view,
+		struct lttng_channel **channel)
+{
+	ssize_t ret, offset = 0;
+	struct lttng_channel *local_channel = NULL;
+	const struct lttng_channel_comm *channel_comm;
+	struct lttng_channel_extended *extended = NULL;
+
+	assert(channel);
+
+	if (!view || !channel) {
+		ret = -1;
+		goto end;
+	}
+
+	/*
+	 * Create an 'internal' channel since `lttng_create_channel` requires a
+	 * domain and we cannot infer the domain from the payload.
+	 */
+	local_channel = lttng_channel_create_internal();
+	if (!local_channel) {
+		ret = -1;
+		goto end;
+	}
+
+	extended = (typeof(extended)) local_channel->attr.extended.ptr;
+
+	/* lttng_trigger_comm header */
+	{
+		const struct lttng_buffer_view comm_view =
+				lttng_buffer_view_from_view(view, offset,
+						sizeof(*channel_comm));
+
+		if (!lttng_buffer_view_is_valid(&comm_view)) {
+			ret = -1;
+			goto end;
+		}
+
+		channel_comm = (const struct lttng_channel_comm *)
+					       comm_view.data;
+		offset += sizeof(*channel_comm);
+	}
+
+	{
+		const char *name;
+		const struct lttng_buffer_view name_view =
+				lttng_buffer_view_from_view(view, offset,
+						channel_comm->name_len);
+
+		if (channel_comm->name_len > LTTNG_SYMBOL_NAME_LEN - 1) {
+			ret = -1;
+			goto end;
+		}
+
+		name = name_view.data;
+		if (!lttng_buffer_view_contains_string(
+				    &name_view, name, channel_comm->name_len)) {
+			ret = -1;
+			goto end;
+		}
+
+		strcpy(local_channel->name, name);
+		offset += channel_comm->name_len;
+	}
+
+	/* Populate the channel */
+	local_channel->enabled = channel_comm->enabled;
+
+	/* attr */
+	local_channel->attr.overwrite = channel_comm->overwrite;
+	local_channel->attr.subbuf_size = channel_comm->subbuf_size;
+	local_channel->attr.num_subbuf = channel_comm->num_subbuf;
+	local_channel->attr.switch_timer_interval =
+			channel_comm->switch_timer_interval;
+	local_channel->attr.read_timer_interval =
+			channel_comm->read_timer_interval;
+	local_channel->attr.output = channel_comm->output;
+	local_channel->attr.tracefile_size = channel_comm->tracefile_size;
+	local_channel->attr.tracefile_count = channel_comm->tracefile_count;
+	local_channel->attr.live_timer_interval =
+			channel_comm->live_timer_interval;
+
+	extended->discarded_events = channel_comm->discarded_events;
+	extended->lost_packets = channel_comm->lost_packets;
+	extended->monitor_timer_interval = channel_comm->monitor_timer_interval;
+	extended->blocking_timeout = channel_comm->blocking_timeout;
+
+	*channel = local_channel;
+	local_channel = NULL;
+
+	ret = offset;
+end:
+	lttng_channel_destroy(local_channel);
+	return ret;
+}
+
+LTTNG_HIDDEN
+int lttng_channel_serialize(
+		struct lttng_channel *channel, struct lttng_dynamic_buffer *buf)
+{
+	int ret;
+	size_t name_len;
+	struct lttng_channel_comm channel_comm = { 0 };
+	struct lttng_channel_extended *extended;
+
+	assert(channel);
+	assert(buf);
+
+	extended = channel->attr.extended.ptr;
+
+	name_len = lttng_strnlen(channel->name, LTTNG_SYMBOL_NAME_LEN);
+	if (name_len == LTTNG_SYMBOL_NAME_LEN) {
+		/* channel name is not NULL-terminated. */
+		ret = -1;
+		goto end;
+	}
+
+	/* Include string termination. */
+	name_len += 1;
+
+	/* Base field */
+	channel_comm.name_len = (uint32_t) name_len;
+	channel_comm.enabled = channel->enabled;
+
+	/* attr */
+	channel_comm.overwrite = channel->attr.overwrite;
+	channel_comm.subbuf_size = channel->attr.subbuf_size;
+	channel_comm.num_subbuf = channel->attr.num_subbuf;
+	channel_comm.switch_timer_interval =
+			channel->attr.switch_timer_interval;
+	channel_comm.read_timer_interval = channel->attr.read_timer_interval;
+	channel_comm.output = channel->attr.output;
+	channel_comm.tracefile_size = channel->attr.tracefile_size;
+	channel_comm.tracefile_count = channel->attr.tracefile_count;
+	channel_comm.live_timer_interval = channel->attr.live_timer_interval;
+
+	/* Extended struct */
+	channel_comm.discarded_events = extended->discarded_events;
+	channel_comm.lost_packets = extended->lost_packets;
+	channel_comm.monitor_timer_interval = extended->monitor_timer_interval;
+	channel_comm.blocking_timeout = extended->blocking_timeout;
+
+	/* Header */
+	ret = lttng_dynamic_buffer_append(
+			buf, &channel_comm, sizeof(channel_comm));
+	if (ret) {
+		goto end;
+	}
+
+	/* channel name */
+	ret = lttng_dynamic_buffer_append(buf, channel->name, name_len);
+	if (ret) {
+		goto end;
+	}
+end:
+	return ret;
+}
+
+LTTNG_HIDDEN
+void lttng_channel_set_default_extended_attr(struct lttng_domain *domain,
+		struct lttng_channel_extended *extended_attr)
+{
+	assert(domain);
+	assert(extended_attr);
+
+	memset(extended_attr, 0, sizeof(*extended_attr));
+
+	switch (domain->type) {
+	case LTTNG_DOMAIN_KERNEL:
+		extended_attr->monitor_timer_interval =
+				DEFAULT_KERNEL_CHANNEL_MONITOR_TIMER;
+		extended_attr->blocking_timeout =
+				DEFAULT_KERNEL_CHANNEL_BLOCKING_TIMEOUT;
+		break;
+	case LTTNG_DOMAIN_UST:
+		switch (domain->buf_type) {
+		case LTTNG_BUFFER_PER_UID:
+			extended_attr->monitor_timer_interval =
+					DEFAULT_UST_UID_CHANNEL_MONITOR_TIMER;
+			extended_attr->blocking_timeout =
+					DEFAULT_UST_UID_CHANNEL_BLOCKING_TIMEOUT;
+			break;
+		case LTTNG_BUFFER_PER_PID:
+		default:
+			if (extended_attr) {
+				extended_attr->monitor_timer_interval =
+						DEFAULT_UST_PID_CHANNEL_MONITOR_TIMER;
+				extended_attr->blocking_timeout =
+						DEFAULT_UST_PID_CHANNEL_BLOCKING_TIMEOUT;
+			}
+			break;
+		}
+	default:
+		/* Default behavior: leave set to 0. */
+		break;
+	}
+}
+
+static enum lttng_error_code channel_list_create_from_buffer(
+		const struct lttng_buffer_view *view,
+		unsigned int count,
+		struct lttng_dynamic_pointer_array *channel_list)
+{
+	enum lttng_error_code ret_code;
+	int ret, i;
+	int offset = 0;
+
+	assert(view);
+	assert(channel_list);
+
+	for (i = 0; i < count; i++) {
+		ssize_t channel_size;
+		struct lttng_channel *channel = NULL;
+		const struct lttng_buffer_view channel_view =
+				lttng_buffer_view_from_view(view, offset, -1);
+
+		channel_size = lttng_channel_create_from_buffer(
+				&channel_view, &channel);
+		if (channel_size < 0) {
+			ret_code = LTTNG_ERR_INVALID;
+			goto end;
+		}
+
+		/* Lifetime and management of the object is now bound to the array. */
+		ret = lttng_dynamic_pointer_array_add_pointer(channel_list, channel);
+		if (ret) {
+			lttng_channel_destroy(channel);
+			ret_code = LTTNG_ERR_NOMEM;
+			goto end;
+		}
+		offset += channel_size;
+	}
+
+	if (view->size != offset) {
+		ret_code = LTTNG_ERR_INVALID;
+		goto end;
+	}
+
+	ret_code = LTTNG_OK;
+
+end:
+	return ret_code;
+}
+
+static enum lttng_error_code flatten_lttng_channels(struct lttng_dynamic_pointer_array *channels,
+		struct lttng_channel **flattened_channels)
+{
+	enum lttng_error_code ret_code;
+	int ret, i;
+	size_t storage_req = 0;
+	struct lttng_dynamic_buffer local_flattened_channels;
+	int nb_channels;
+
+	assert(channels);
+	assert(flattened_channels);
+
+	lttng_dynamic_buffer_init(&local_flattened_channels);
+	nb_channels = lttng_dynamic_pointer_array_get_count(channels);
+
+	storage_req += sizeof(struct lttng_channel) * nb_channels;
+	storage_req += sizeof(struct lttng_channel_extended) * nb_channels;
+
+	/*
+	 * We must ensure that "local_flattened_channels" is never resized so as
+	 * to preserve the validity of the flattened objects.
+	 */
+	ret = lttng_dynamic_buffer_set_capacity(
+			&local_flattened_channels, storage_req);
+	if (ret) {
+		ret_code = LTTNG_ERR_NOMEM;
+		goto end;
+	}
+
+	/* Start by laying the struct lttng_channel */
+	for (i = 0; i < nb_channels; i++) {
+		const struct lttng_channel *element =
+				lttng_dynamic_pointer_array_get_pointer(
+						channels, i);
+
+		if (!element) {
+			ret_code = LTTNG_ERR_FATAL;
+			goto end;
+		}
+		ret = lttng_dynamic_buffer_append(&local_flattened_channels,
+				element, sizeof(struct lttng_channel));
+		if (ret) {
+			ret_code = LTTNG_ERR_NOMEM;
+			goto end;
+		}
+	}
+
+	/* Flatten the extended data */
+	for (i = 0; i < nb_channels; i++) {
+		const struct lttng_channel *element =
+				lttng_dynamic_pointer_array_get_pointer(
+						channels, i);
+		/*
+		 * Sample the location of the flattened channel we are about
+		 * to modify
+		 */
+		 struct lttng_channel *channel = (struct lttng_channel *)
+			(local_flattened_channels.data + (sizeof(struct lttng_channel) * i));
+		/*
+		 * Sample the location of the extended attributes we are about
+		 * to add.
+		 */
+		struct lttng_channel_extended *channel_extended =
+			(struct lttng_channel_extended *)
+				(local_flattened_channels.data + local_flattened_channels.size);
+
+		if (!element) {
+			ret_code = LTTNG_ERR_FATAL;
+			goto end;
+		}
+
+		ret = lttng_dynamic_buffer_append(&local_flattened_channels,
+				element->attr.extended.ptr,
+				sizeof(struct lttng_channel_extended));
+		if (ret) {
+			ret_code = LTTNG_ERR_NOMEM;
+			goto end;
+		}
+
+		/*
+		 * Update the flattened lttng_channel object with its flattened
+		 * extended object location.
+		 */
+		channel->attr.extended.ptr = channel_extended;
+	}
+
+	/* Don't reset local_flattened_channels buffer as we return its content. */
+	*flattened_channels = (struct lttng_channel *) local_flattened_channels.data;
+	lttng_dynamic_buffer_init(&local_flattened_channels);
+	ret_code = LTTNG_OK;
+end:
+	lttng_dynamic_buffer_reset(&local_flattened_channels);
+	return ret_code;
+}
+
+LTTNG_HIDDEN
+enum lttng_error_code lttng_channels_create_and_flatten_from_buffer(
+		const struct lttng_buffer_view *view,
+		uint32_t count,
+		struct lttng_channel **channels)
+{
+	enum lttng_error_code ret_code;
+	struct lttng_dynamic_pointer_array local_channels;
+
+	lttng_dynamic_pointer_array_init(&local_channels, channel_list_destructor);
+
+	/* Deserialize the channels */
+	{
+		const struct lttng_buffer_view channels_view =
+				lttng_buffer_view_from_view(view, 0, -1);
+
+		ret_code = channel_list_create_from_buffer(
+				&channels_view, count, &local_channels);
+		if (ret_code != LTTNG_OK) {
+			goto end;
+		}
+	}
+
+	ret_code = flatten_lttng_channels(&local_channels, channels);
+
+end:
+	lttng_dynamic_pointer_array_reset(&local_channels);
+	return ret_code;
+}
diff --git a/src/common/sessiond-comm/sessiond-comm.h b/src/common/sessiond-comm/sessiond-comm.h
index b9ab05bcb..0d3e374b3 100644
--- a/src/common/sessiond-comm/sessiond-comm.h
+++ b/src/common/sessiond-comm/sessiond-comm.h
@@ -311,9 +311,7 @@ struct lttcomm_session_msg {
 		} LTTNG_PACKED disable;
 		/* Create channel */
 		struct {
-			struct lttng_channel chan LTTNG_PACKED;
-			/* struct lttng_channel_extended is already packed. */
-			struct lttng_channel_extended extended;
+			uint32_t length;
 		} LTTNG_PACKED channel;
 		/* Context */
 		struct {
@@ -453,6 +451,14 @@ struct lttcomm_event_command_header {
 	uint32_t nb_events;
 } LTTNG_PACKED;
 
+/*
+ * Listing command header.
+ */
+struct lttcomm_list_command_header {
+	/* Number of elements */
+	uint32_t count;
+} LTTNG_PACKED;
+
 /*
  * Event extended info header. This is the structure preceding each
  * extended info data.
diff --git a/src/lib/lttng-ctl/lttng-ctl.c b/src/lib/lttng-ctl/lttng-ctl.c
index 5cdc2b011..622a2bd04 100644
--- a/src/lib/lttng-ctl/lttng-ctl.c
+++ b/src/lib/lttng-ctl/lttng-ctl.c
@@ -1509,10 +1509,9 @@ end:
 struct lttng_channel *lttng_channel_create(struct lttng_domain *domain)
 {
 	struct lttng_channel *channel = NULL;
-	struct lttng_channel_extended *extended = NULL;
 
 	if (!domain) {
-		goto error;
+		goto end;
 	}
 
 	/* Validate domain. */
@@ -1523,36 +1522,26 @@ struct lttng_channel *lttng_channel_create(struct lttng_domain *domain)
 		case LTTNG_BUFFER_PER_PID:
 			break;
 		default:
-			goto error;
+			goto end;
 		}
 		break;
 	case LTTNG_DOMAIN_KERNEL:
 		if (domain->buf_type != LTTNG_BUFFER_GLOBAL) {
-			goto error;
+			goto end;
 		}
 		break;
 	default:
-		goto error;
+		goto end;
 	}
 
-	channel = zmalloc(sizeof(*channel));
+	channel = lttng_channel_create_internal();
 	if (!channel) {
-		goto error;
-	}
-
-	extended = zmalloc(sizeof(*extended));
-	if (!extended) {
-		goto error;
+		goto end;
 	}
 
-	channel->attr.extended.ptr = extended;
-
 	lttng_channel_set_default_attr(domain, &channel->attr);
+end:
 	return channel;
-error:
-	free(channel);
-	free(extended);
-	return NULL;
 }
 
 void lttng_channel_destroy(struct lttng_channel *channel)
@@ -1576,56 +1565,32 @@ int lttng_enable_channel(struct lttng_handle *handle,
 {
 	enum lttng_error_code ret_code;
 	int ret;
+	struct lttng_dynamic_buffer buffer;
 	struct lttcomm_session_msg lsm;
 	uint64_t total_buffer_size_needed_per_cpu = 0;
+	struct lttng_channel *channel = NULL;
+
+	lttng_dynamic_buffer_init(&buffer);
 
 	/* 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));
+		ret = -LTTNG_ERR_INVALID;
+		goto end;
 	}
 
 	/*
 	 * Verify that the amount of memory required to create the requested
 	 * buffer is available on the system at the moment.
 	 */
-	if (lsm.u.channel.chan.attr.num_subbuf >
-			UINT64_MAX / lsm.u.channel.chan.attr.subbuf_size) {
+	if (in_chan->attr.num_subbuf >
+			UINT64_MAX / in_chan->attr.subbuf_size) {
 		/* Overflow */
 		ret = -LTTNG_ERR_OVERFLOW;
 		goto end;
 	}
 
-	total_buffer_size_needed_per_cpu = lsm.u.channel.chan.attr.num_subbuf *
-		lsm.u.channel.chan.attr.subbuf_size;
+	total_buffer_size_needed_per_cpu =
+			in_chan->attr.num_subbuf * in_chan->attr.subbuf_size;
 	ret_code = check_enough_available_memory(
 			total_buffer_size_needed_per_cpu);
 	if (ret_code != LTTNG_OK) {
@@ -1633,6 +1598,30 @@ int lttng_enable_channel(struct lttng_handle *handle,
 		goto end;
 	}
 
+	/* Copy the channel for easier manipulation. */
+	channel = lttng_channel_copy(in_chan);
+	if (!channel) {
+		ret = -LTTNG_ERR_NOMEM;
+		goto end;
+	}
+
+	/* Populate the channel extended attribute if necessary. */
+	if (!channel->attr.extended.ptr) {
+		struct lttng_channel_extended *extended =
+				zmalloc(sizeof(*extended));
+
+		if (!extended) {
+			ret = -LTTNG_ERR_NOMEM;
+			goto end;
+		}
+		lttng_channel_set_default_extended_attr(
+				&handle->domain, extended);
+		channel->attr.extended.ptr = extended;
+	}
+
+	/* Prepare the payload */
+	memset(&lsm, 0, sizeof(lsm));
+
 	lsm.cmd_type = LTTNG_ENABLE_CHANNEL;
 	COPY_DOMAIN_PACKED(lsm.domain, handle->domain);
 
@@ -1643,8 +1632,19 @@ int lttng_enable_channel(struct lttng_handle *handle,
 		goto end;
 	}
 
-	ret = lttng_ctl_ask_sessiond(&lsm, NULL);
+	ret = lttng_channel_serialize(channel, &buffer);
+	if (ret) {
+		ret = -LTTNG_ERR_FATAL;
+		goto end;
+	}
+
+	lsm.u.channel.length = buffer.size;
+
+	ret = lttng_ctl_ask_sessiond_varlen_no_cmd_header(
+			&lsm, buffer.data, buffer.size, NULL);
 end:
+	lttng_channel_destroy(channel);
+	lttng_dynamic_buffer_reset(&buffer);
 	return ret;
 }
 
@@ -2242,12 +2242,14 @@ error:
 int lttng_list_channels(struct lttng_handle *handle,
 		struct lttng_channel **channels)
 {
-	int ret;
-	size_t channel_count, i;
-	const size_t channel_size = sizeof(struct lttng_channel) +
-			sizeof(struct lttng_channel_extended);
+	int ret, total_payload_received;
 	struct lttcomm_session_msg lsm;
-	void *extended_at;
+	char *reception_buffer = NULL;
+	size_t cmd_header_len = 0;
+	struct lttcomm_list_command_header *cmd_header = NULL;
+	struct lttng_dynamic_buffer tmp_buffer;
+
+	lttng_dynamic_buffer_init(&tmp_buffer);
 
 	if (handle == NULL) {
 		ret = -LTTNG_ERR_INVALID;
@@ -2265,31 +2267,48 @@ int lttng_list_channels(struct lttng_handle *handle,
 
 	COPY_DOMAIN_PACKED(lsm.domain, handle->domain);
 
-	ret = lttng_ctl_ask_sessiond(&lsm, (void**) channels);
+	ret = lttng_ctl_ask_sessiond_fds_varlen(&lsm, NULL, 0, NULL, 0,
+			(void **) &reception_buffer, (void **) &cmd_header,
+			&cmd_header_len);
 	if (ret < 0) {
 		goto end;
 	}
 
-	if (ret % channel_size) {
-		ret = -LTTNG_ERR_UNK;
-		free(*channels);
-		*channels = NULL;
+	total_payload_received = ret;
+
+	if (cmd_header_len != sizeof(*cmd_header)) {
+		ret = -LTTNG_ERR_FATAL;
+		goto end;
+	}
+
+	if (!cmd_header) {
+		ret = LTTNG_ERR_UNK;
+		goto end;
+	}
+
+	if (cmd_header->count > INT_MAX) {
+		ret = -LTTNG_ERR_OVERFLOW;
 		goto end;
 	}
-	channel_count = (size_t) ret / channel_size;
 
-	/* Set extended info pointers */
-	extended_at = ((void *) *channels) +
-			channel_count * sizeof(struct lttng_channel);
-	for (i = 0; i < channel_count; i++) {
-		struct lttng_channel *chan = &(*channels)[i];
+	{
+		enum lttng_error_code ret_code;
+		const struct lttng_buffer_view events_view =
+				lttng_buffer_view_init(reception_buffer, 0,
+						total_payload_received);
 
-		chan->attr.extended.ptr = extended_at;
-		extended_at += sizeof(struct lttng_channel_extended);
+		ret_code = lttng_channels_create_and_flatten_from_buffer(
+				&events_view, cmd_header->count, channels);
+		if (ret_code != LTTNG_OK) {
+			ret = -ret_code;
+			goto end;
+		}
 	}
 
-	ret = (int) channel_count;
+	ret = (int) cmd_header->count;
 end:
+	free(cmd_header);
+	free(reception_buffer);
 	return ret;
 }
 
@@ -2598,6 +2617,7 @@ void lttng_channel_set_default_attr(struct lttng_domain *domain,
 		return;
 	}
 
+	/* Save the pointer for later use */
 	extended = (struct lttng_channel_extended *) attr->extended.ptr;
 	memset(attr, 0, sizeof(struct lttng_channel_attr));
 
@@ -2614,12 +2634,6 @@ void lttng_channel_set_default_attr(struct lttng_domain *domain,
 		attr->subbuf_size = default_get_kernel_channel_subbuf_size();
 		attr->num_subbuf = DEFAULT_KERNEL_CHANNEL_SUBBUF_NUM;
 		attr->output = DEFAULT_KERNEL_CHANNEL_OUTPUT;
-		if (extended) {
-			extended->monitor_timer_interval =
-					DEFAULT_KERNEL_CHANNEL_MONITOR_TIMER;
-			extended->blocking_timeout =
-					DEFAULT_KERNEL_CHANNEL_BLOCKING_TIMEOUT;
-		}
 		break;
 	case LTTNG_DOMAIN_UST:
 		switch (domain->buf_type) {
@@ -2631,12 +2645,6 @@ void lttng_channel_set_default_attr(struct lttng_domain *domain,
 					DEFAULT_UST_UID_CHANNEL_SWITCH_TIMER;
 			attr->read_timer_interval =
 					DEFAULT_UST_UID_CHANNEL_READ_TIMER;
-			if (extended) {
-				extended->monitor_timer_interval =
-						DEFAULT_UST_UID_CHANNEL_MONITOR_TIMER;
-				extended->blocking_timeout =
-						DEFAULT_UST_UID_CHANNEL_BLOCKING_TIMEOUT;
-			}
 			break;
 		case LTTNG_BUFFER_PER_PID:
 		default:
@@ -2647,12 +2655,6 @@ void lttng_channel_set_default_attr(struct lttng_domain *domain,
 					DEFAULT_UST_PID_CHANNEL_SWITCH_TIMER;
 			attr->read_timer_interval =
 					DEFAULT_UST_PID_CHANNEL_READ_TIMER;
-			if (extended) {
-				extended->monitor_timer_interval =
-						DEFAULT_UST_PID_CHANNEL_MONITOR_TIMER;
-				extended->blocking_timeout =
-						DEFAULT_UST_PID_CHANNEL_BLOCKING_TIMEOUT;
-			}
 			break;
 		}
 	default:
@@ -2660,6 +2662,11 @@ void lttng_channel_set_default_attr(struct lttng_domain *domain,
 		break;
 	}
 
+	if (extended) {
+		lttng_channel_set_default_extended_attr(domain, extended);
+	}
+
+	/* Reassign the extended pointer. */
 	attr->extended.ptr = extended;
 }