[lttng-tools.git] / src / bin / lttng-sessiond / notification-thread-events.c

/*
 * Copyright (C) 2017 Jérémie Galarneau <jeremie.galarneau@efficios.com>
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 */

#define _LGPL_SOURCE
#include <urcu.h>
#include <urcu/rculfhash.h>

#include <common/defaults.h>
#include <common/error.h>
#include <common/futex.h>
#include <common/unix.h>
#include <common/dynamic-buffer.h>
#include <common/hashtable/utils.h>
#include <common/sessiond-comm/sessiond-comm.h>
#include <common/macros.h>
#include <lttng/condition/condition.h>
#include <lttng/action/action-internal.h>
#include <lttng/notification/notification-internal.h>
#include <lttng/condition/condition-internal.h>
#include <lttng/condition/buffer-usage-internal.h>
#include <lttng/condition/session-consumed-size-internal.h>
#include <lttng/condition/session-rotation-internal.h>
#include <lttng/notification/channel-internal.h>

#include <time.h>
#include <unistd.h>
#include <assert.h>
#include <inttypes.h>
#include <fcntl.h>

#include "notification-thread.h"
#include "notification-thread-events.h"
#include "notification-thread-commands.h"
#include "lttng-sessiond.h"
#include "kernel.h"

#define CLIENT_POLL_MASK_IN (LPOLLIN | LPOLLERR | LPOLLHUP | LPOLLRDHUP)
#define CLIENT_POLL_MASK_IN_OUT (CLIENT_POLL_MASK_IN | LPOLLOUT)

enum lttng_object_type {
	LTTNG_OBJECT_TYPE_UNKNOWN,
	LTTNG_OBJECT_TYPE_NONE,
	LTTNG_OBJECT_TYPE_CHANNEL,
	LTTNG_OBJECT_TYPE_SESSION,
};

struct lttng_trigger_list_element {
	/* No ownership of the trigger object is assumed. */
	const struct lttng_trigger *trigger;
	struct cds_list_head node;
};

struct lttng_channel_trigger_list {
	struct channel_key channel_key;
	/* List of struct lttng_trigger_list_element. */
	struct cds_list_head list;
	/* Node in the channel_triggers_ht */
	struct cds_lfht_node channel_triggers_ht_node;
	/* call_rcu delayed reclaim. */
	struct rcu_head rcu_node;
};

/*
 * List of triggers applying to a given session.
 *
 * See:
 *   - lttng_session_trigger_list_create()
 *   - lttng_session_trigger_list_build()
 *   - lttng_session_trigger_list_destroy()
 *   - lttng_session_trigger_list_add()
 */
struct lttng_session_trigger_list {
	/*
	 * Not owned by this; points to the session_info structure's
	 * session name.
	 */
	const char *session_name;
	/* List of struct lttng_trigger_list_element. */
	struct cds_list_head list;
	/* Node in the session_triggers_ht */
	struct cds_lfht_node session_triggers_ht_node;
	/*
	 * Weak reference to the notification system's session triggers
	 * hashtable.
	 *
	 * The session trigger list structure structure is owned by
	 * the session's session_info.
	 *
	 * The session_info is kept alive the the channel_infos holding a
	 * reference to it (reference counting). When those channels are
	 * destroyed (at runtime or on teardown), the reference they hold
	 * to the session_info are released. On destruction of session_info,
	 * session_info_destroy() will remove the list of triggers applying
	 * to this session from the notification system's state.
	 *
	 * This implies that the session_triggers_ht must be destroyed
	 * after the channels.
	 */
	struct cds_lfht *session_triggers_ht;
	/* Used for delayed RCU reclaim. */
	struct rcu_head rcu_node;
};

struct lttng_trigger_ht_element {
	struct lttng_trigger *trigger;
	struct cds_lfht_node node;
	/* call_rcu delayed reclaim. */
	struct rcu_head rcu_node;
};

struct lttng_condition_list_element {
	struct lttng_condition *condition;
	struct cds_list_head node;
};

struct notification_client_list_element {
	struct notification_client *client;
	struct cds_list_head node;
};

/*
 * Thread safety of notification_client and notification_client_list.
 *
 * The notification thread (main thread) and the action executor
 * interact through client lists. Hence, when the action executor
 * thread looks-up the list of clients subscribed to a given
 * condition, it will acquire a reference to the list and lock it
 * while attempting to communicate with the various clients.
 *
 * It is not necessary to reference-count clients as they are guaranteed
 * to be 'alive' if they are present in a list and that list is locked. Indeed,
 * removing references to the client from those subscription lists is part of
 * the work performed on destruction of a client.
 *
 * No provision for other access scenarios are taken into account;
 * this is the bare minimum to make these accesses safe and the
 * notification thread's state is _not_ "thread-safe" in any general
 * sense.
 */
struct notification_client_list {
	pthread_mutex_t lock;
	struct urcu_ref ref;
	const struct lttng_trigger *trigger;
	struct cds_list_head list;
	/* Weak reference to container. */
	struct cds_lfht *notification_trigger_clients_ht;
	struct cds_lfht_node notification_trigger_clients_ht_node;
	/* call_rcu delayed reclaim. */
	struct rcu_head rcu_node;
};

struct notification_client {
	/* Nests within the notification_client_list lock. */
	pthread_mutex_t lock;
	notification_client_id id;
	int socket;
	/* Client protocol version. */
	uint8_t major, minor;
	uid_t uid;
	gid_t gid;
	/*
	 * Indicates if the credentials and versions of the client have been
	 * checked.
	 */
	bool validated;
	/*
	 * Conditions to which the client's notification channel is subscribed.
	 * List of struct lttng_condition_list_node. The condition member is
	 * owned by the client.
	 */
	struct cds_list_head condition_list;
	struct cds_lfht_node client_socket_ht_node;
	struct cds_lfht_node client_id_ht_node;
	struct {
		/*
		 * If a client's communication is inactive, it means that a
		 * fatal error has occurred (could be either a protocol error or
		 * the socket API returned a fatal error). No further
		 * communication should be attempted; the client is queued for
		 * clean-up.
		 */
		bool active;
		struct {
			/*
			 * During the reception of a message, the reception
			 * buffers' "size" is set to contain the current
			 * message's complete payload.
			 */
			struct lttng_dynamic_buffer buffer;
			/* Bytes left to receive for the current message. */
			size_t bytes_to_receive;
			/* Type of the message being received. */
			enum lttng_notification_channel_message_type msg_type;
			/*
			 * Indicates whether or not credentials are expected
			 * from the client.
			 */
			bool expect_creds;
			/*
			 * Indicates whether or not credentials were received
			 * from the client.
			 */
			bool creds_received;
			/* Only used during credentials reception. */
			lttng_sock_cred creds;
		} inbound;
		struct {
			/*
			 * Indicates whether or not a notification addressed to
			 * this client was dropped because a command reply was
			 * already buffered.
			 *
			 * A notification is dropped whenever the buffer is not
			 * empty.
			 */
			bool dropped_notification;
			/*
			 * Indicates whether or not a command reply is already
			 * buffered. In this case, it means that the client is
			 * not consuming command replies before emitting a new
			 * one. This could be caused by a protocol error or a
			 * misbehaving/malicious client.
			 */
			bool queued_command_reply;
			struct lttng_dynamic_buffer buffer;
		} outbound;
	} communication;
	/* call_rcu delayed reclaim. */
	struct rcu_head rcu_node;
};

struct channel_state_sample {
	struct channel_key key;
	struct cds_lfht_node channel_state_ht_node;
	uint64_t highest_usage;
	uint64_t lowest_usage;
	uint64_t channel_total_consumed;
	/* call_rcu delayed reclaim. */
	struct rcu_head rcu_node;
};

static unsigned long hash_channel_key(struct channel_key *key);
static int evaluate_buffer_condition(const struct lttng_condition *condition,
		struct lttng_evaluation **evaluation,
		const struct notification_thread_state *state,
		const struct channel_state_sample *previous_sample,
		const struct channel_state_sample *latest_sample,
		uint64_t previous_session_consumed_total,
		uint64_t latest_session_consumed_total,
		struct channel_info *channel_info);
static
int send_evaluation_to_clients(const struct lttng_trigger *trigger,
		const struct lttng_evaluation *evaluation,
		struct notification_client_list *client_list,
		struct notification_thread_state *state,
		uid_t channel_uid, gid_t channel_gid);


/* session_info API */
static
void session_info_destroy(void *_data);
static
void session_info_get(struct session_info *session_info);
static
void session_info_put(struct session_info *session_info);
static
struct session_info *session_info_create(const char *name,
		uid_t uid, gid_t gid,
		struct lttng_session_trigger_list *trigger_list,
		struct cds_lfht *sessions_ht);
static
void session_info_add_channel(struct session_info *session_info,
		struct channel_info *channel_info);
static
void session_info_remove_channel(struct session_info *session_info,
		struct channel_info *channel_info);

/* lttng_session_trigger_list API */
static
struct lttng_session_trigger_list *lttng_session_trigger_list_create(
		const char *session_name,
		struct cds_lfht *session_triggers_ht);
static
struct lttng_session_trigger_list *lttng_session_trigger_list_build(
		const struct notification_thread_state *state,
		const char *session_name);
static
void lttng_session_trigger_list_destroy(
		struct lttng_session_trigger_list *list);
static
int lttng_session_trigger_list_add(struct lttng_session_trigger_list *list,
		const struct lttng_trigger *trigger);


static
int match_client_socket(struct cds_lfht_node *node, const void *key)
{
	/* This double-cast is intended to supress pointer-to-cast warning. */
	const int socket = (int) (intptr_t) key;
	const struct notification_client *client = caa_container_of(node,
			struct notification_client, client_socket_ht_node);

	return client->socket == socket;
}

static
int match_client_id(struct cds_lfht_node *node, const void *key)
{
	/* This double-cast is intended to supress pointer-to-cast warning. */
	const notification_client_id id = *((notification_client_id *) key);
	const struct notification_client *client = caa_container_of(
			node, struct notification_client, client_id_ht_node);

	return client->id == id;
}

static
int match_channel_trigger_list(struct cds_lfht_node *node, const void *key)
{
	struct channel_key *channel_key = (struct channel_key *) key;
	struct lttng_channel_trigger_list *trigger_list;

	trigger_list = caa_container_of(node, struct lttng_channel_trigger_list,
			channel_triggers_ht_node);

	return !!((channel_key->key == trigger_list->channel_key.key) &&
			(channel_key->domain == trigger_list->channel_key.domain));
}

static
int match_session_trigger_list(struct cds_lfht_node *node, const void *key)
{
	const char *session_name = (const char *) key;
	struct lttng_session_trigger_list *trigger_list;

	trigger_list = caa_container_of(node, struct lttng_session_trigger_list,
			session_triggers_ht_node);

	return !!(strcmp(trigger_list->session_name, session_name) == 0);
}

static
int match_channel_state_sample(struct cds_lfht_node *node, const void *key)
{
	struct channel_key *channel_key = (struct channel_key *) key;
	struct channel_state_sample *sample;

	sample = caa_container_of(node, struct channel_state_sample,
			channel_state_ht_node);

	return !!((channel_key->key == sample->key.key) &&
			(channel_key->domain == sample->key.domain));
}

static
int match_channel_info(struct cds_lfht_node *node, const void *key)
{
	struct channel_key *channel_key = (struct channel_key *) key;
	struct channel_info *channel_info;

	channel_info = caa_container_of(node, struct channel_info,
			channels_ht_node);

	return !!((channel_key->key == channel_info->key.key) &&
			(channel_key->domain == channel_info->key.domain));
}

static
int match_condition(struct cds_lfht_node *node, const void *key)
{
	struct lttng_condition *condition_key = (struct lttng_condition *) key;
	struct lttng_trigger_ht_element *trigger;
	struct lttng_condition *condition;

	trigger = caa_container_of(node, struct lttng_trigger_ht_element,
			node);
	condition = lttng_trigger_get_condition(trigger->trigger);
	assert(condition);

	return !!lttng_condition_is_equal(condition_key, condition);
}

static
int match_client_list_condition(struct cds_lfht_node *node, const void *key)
{
	struct lttng_condition *condition_key = (struct lttng_condition *) key;
	struct notification_client_list *client_list;
	const struct lttng_condition *condition;

	assert(condition_key);

	client_list = caa_container_of(node, struct notification_client_list,
			notification_trigger_clients_ht_node);
	condition = lttng_trigger_get_const_condition(client_list->trigger);

	return !!lttng_condition_is_equal(condition_key, condition);
}

static
int match_session(struct cds_lfht_node *node, const void *key)
{
	const char *name = key;
	struct session_info *session_info = caa_container_of(
		node, struct session_info, sessions_ht_node);

	return !strcmp(session_info->name, name);
}

static
unsigned long lttng_condition_buffer_usage_hash(
	const struct lttng_condition *_condition)
{
	unsigned long hash;
	unsigned long condition_type;
	struct lttng_condition_buffer_usage *condition;

	condition = container_of(_condition,
			struct lttng_condition_buffer_usage, parent);

	condition_type = (unsigned long) condition->parent.type;
	hash = hash_key_ulong((void *) condition_type, lttng_ht_seed);
	if (condition->session_name) {
		hash ^= hash_key_str(condition->session_name, lttng_ht_seed);
	}
	if (condition->channel_name) {
		hash ^= hash_key_str(condition->channel_name, lttng_ht_seed);
	}
	if (condition->domain.set) {
		hash ^= hash_key_ulong(
				(void *) condition->domain.type,
				lttng_ht_seed);
	}
	if (condition->threshold_ratio.set) {
		uint64_t val;

		val = condition->threshold_ratio.value * (double) UINT32_MAX;
		hash ^= hash_key_u64(&val, lttng_ht_seed);
	} else if (condition->threshold_bytes.set) {
		uint64_t val;

		val = condition->threshold_bytes.value;
		hash ^= hash_key_u64(&val, lttng_ht_seed);
	}
	return hash;
}

static
unsigned long lttng_condition_session_consumed_size_hash(
	const struct lttng_condition *_condition)
{
	unsigned long hash;
	unsigned long condition_type =
			(unsigned long) LTTNG_CONDITION_TYPE_SESSION_CONSUMED_SIZE;
	struct lttng_condition_session_consumed_size *condition;
	uint64_t val;

	condition = container_of(_condition,
			struct lttng_condition_session_consumed_size, parent);

	hash = hash_key_ulong((void *) condition_type, lttng_ht_seed);
	if (condition->session_name) {
		hash ^= hash_key_str(condition->session_name, lttng_ht_seed);
	}
	val = condition->consumed_threshold_bytes.value;
	hash ^= hash_key_u64(&val, lttng_ht_seed);
	return hash;
}

static
unsigned long lttng_condition_session_rotation_hash(
	const struct lttng_condition *_condition)
{
	unsigned long hash, condition_type;
	struct lttng_condition_session_rotation *condition;

	condition = container_of(_condition,
			struct lttng_condition_session_rotation, parent);
	condition_type = (unsigned long) condition->parent.type;
	hash = hash_key_ulong((void *) condition_type, lttng_ht_seed);
	assert(condition->session_name);
	hash ^= hash_key_str(condition->session_name, lttng_ht_seed);
	return hash;
}

/*
 * The lttng_condition hashing code is kept in this file (rather than
 * condition.c) since it makes use of GPLv2 code (hashtable utils), which we
 * don't want to link in liblttng-ctl.
 */
static
unsigned long lttng_condition_hash(const struct lttng_condition *condition)
{
	switch (condition->type) {
	case LTTNG_CONDITION_TYPE_BUFFER_USAGE_LOW:
	case LTTNG_CONDITION_TYPE_BUFFER_USAGE_HIGH:
		return lttng_condition_buffer_usage_hash(condition);
	case LTTNG_CONDITION_TYPE_SESSION_CONSUMED_SIZE:
		return lttng_condition_session_consumed_size_hash(condition);
	case LTTNG_CONDITION_TYPE_SESSION_ROTATION_ONGOING:
	case LTTNG_CONDITION_TYPE_SESSION_ROTATION_COMPLETED:
		return lttng_condition_session_rotation_hash(condition);
	default:
		ERR("[notification-thread] Unexpected condition type caught");
		abort();
	}
}

static
unsigned long hash_channel_key(struct channel_key *key)
{
	unsigned long key_hash = hash_key_u64(&key->key, lttng_ht_seed);
	unsigned long domain_hash = hash_key_ulong(
		(void *) (unsigned long) key->domain, lttng_ht_seed);

	return key_hash ^ domain_hash;
}

static
unsigned long hash_client_socket(int socket)
{
	return hash_key_ulong((void *) (unsigned long) socket, lttng_ht_seed);
}

static
unsigned long hash_client_id(notification_client_id id)
{
	return hash_key_u64(&id, lttng_ht_seed);
}

/*
 * Get the type of object to which a given condition applies. Bindings let
 * the notification system evaluate a trigger's condition when a given
 * object's state is updated.
 *
 * For instance, a condition bound to a channel will be evaluated everytime
 * the channel's state is changed by a channel monitoring sample.
 */
static
enum lttng_object_type get_condition_binding_object(
		const struct lttng_condition *condition)
{
	switch (lttng_condition_get_type(condition)) {
	case LTTNG_CONDITION_TYPE_BUFFER_USAGE_LOW:
	case LTTNG_CONDITION_TYPE_BUFFER_USAGE_HIGH:
	case LTTNG_CONDITION_TYPE_SESSION_CONSUMED_SIZE:
		return LTTNG_OBJECT_TYPE_CHANNEL;
	case LTTNG_CONDITION_TYPE_SESSION_ROTATION_ONGOING:
	case LTTNG_CONDITION_TYPE_SESSION_ROTATION_COMPLETED:
		return LTTNG_OBJECT_TYPE_SESSION;
	default:
		return LTTNG_OBJECT_TYPE_UNKNOWN;
	}
}

static
void free_channel_info_rcu(struct rcu_head *node)
{
	free(caa_container_of(node, struct channel_info, rcu_node));
}

static
void channel_info_destroy(struct channel_info *channel_info)
{
	if (!channel_info) {
		return;
	}

	if (channel_info->session_info) {
		session_info_remove_channel(channel_info->session_info,
				channel_info);
		session_info_put(channel_info->session_info);
	}
	if (channel_info->name) {
		free(channel_info->name);
	}
	call_rcu(&channel_info->rcu_node, free_channel_info_rcu);
}

static
void free_session_info_rcu(struct rcu_head *node)
{
	free(caa_container_of(node, struct session_info, rcu_node));
}

/* Don't call directly, use the ref-counting mechanism. */
static
void session_info_destroy(void *_data)
{
	struct session_info *session_info = _data;
	int ret;

	assert(session_info);
	if (session_info->channel_infos_ht) {
		ret = cds_lfht_destroy(session_info->channel_infos_ht, NULL);
		if (ret) {
			ERR("[notification-thread] Failed to destroy channel information hash table");
		}
	}
	lttng_session_trigger_list_destroy(session_info->trigger_list);

	rcu_read_lock();
	cds_lfht_del(session_info->sessions_ht,
			&session_info->sessions_ht_node);
	rcu_read_unlock();
	free(session_info->name);
	call_rcu(&session_info->rcu_node, free_session_info_rcu);
}

static
void session_info_get(struct session_info *session_info)
{
	if (!session_info) {
		return;
	}
	lttng_ref_get(&session_info->ref);
}

static
void session_info_put(struct session_info *session_info)
{
	if (!session_info) {
		return;
	}
	lttng_ref_put(&session_info->ref);
}

static
struct session_info *session_info_create(const char *name, uid_t uid, gid_t gid,
		struct lttng_session_trigger_list *trigger_list,
		struct cds_lfht *sessions_ht)
{
	struct session_info *session_info;

	assert(name);

	session_info = zmalloc(sizeof(*session_info));
	if (!session_info) {
		goto end;
	}
	lttng_ref_init(&session_info->ref, session_info_destroy);

	session_info->channel_infos_ht = cds_lfht_new(DEFAULT_HT_SIZE,
			1, 0, CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);
	if (!session_info->channel_infos_ht) {
		goto error;
	}

	cds_lfht_node_init(&session_info->sessions_ht_node);
	session_info->name = strdup(name);
	if (!session_info->name) {
		goto error;
	}
	session_info->uid = uid;
	session_info->gid = gid;
	session_info->trigger_list = trigger_list;
	session_info->sessions_ht = sessions_ht;
end:
	return session_info;
error:
	session_info_put(session_info);
	return NULL;
}

static
void session_info_add_channel(struct session_info *session_info,
		struct channel_info *channel_info)
{
	rcu_read_lock();
	cds_lfht_add(session_info->channel_infos_ht,
			hash_channel_key(&channel_info->key),
			&channel_info->session_info_channels_ht_node);
	rcu_read_unlock();
}

static
void session_info_remove_channel(struct session_info *session_info,
		struct channel_info *channel_info)
{
	rcu_read_lock();
	cds_lfht_del(session_info->channel_infos_ht,
			&channel_info->session_info_channels_ht_node);
	rcu_read_unlock();
}

static
struct channel_info *channel_info_create(const char *channel_name,
		struct channel_key *channel_key, uint64_t channel_capacity,
		struct session_info *session_info)
{
	struct channel_info *channel_info = zmalloc(sizeof(*channel_info));

	if (!channel_info) {
		goto end;
	}

	cds_lfht_node_init(&channel_info->channels_ht_node);
	cds_lfht_node_init(&channel_info->session_info_channels_ht_node);
	memcpy(&channel_info->key, channel_key, sizeof(*channel_key));
	channel_info->capacity = channel_capacity;

	channel_info->name = strdup(channel_name);
	if (!channel_info->name) {
		goto error;
	}

	/*
	 * Set the references between session and channel infos:
	 *   - channel_info holds a strong reference to session_info
	 *   - session_info holds a weak reference to channel_info
	 */
	session_info_get(session_info);
	session_info_add_channel(session_info, channel_info);
	channel_info->session_info = session_info;
end:
	return channel_info;
error:
	channel_info_destroy(channel_info);
	return NULL;
}

static
bool notification_client_list_get(struct notification_client_list *list)
{
	return urcu_ref_get_unless_zero(&list->ref);
}

static
void free_notification_client_list_rcu(struct rcu_head *node)
{
	free(caa_container_of(node, struct notification_client_list,
			rcu_node));
}

static
void notification_client_list_release(struct urcu_ref *list_ref)
{
	struct notification_client_list *list =
			container_of(list_ref, typeof(*list), ref);
	struct notification_client_list_element *client_list_element, *tmp;

	if (list->notification_trigger_clients_ht) {
		rcu_read_lock();
		cds_lfht_del(list->notification_trigger_clients_ht,
				&list->notification_trigger_clients_ht_node);
		rcu_read_unlock();
		list->notification_trigger_clients_ht = NULL;
	}
	cds_list_for_each_entry_safe(client_list_element, tmp,
				     &list->list, node) {
		free(client_list_element);
	}
	pthread_mutex_destroy(&list->lock);
	call_rcu(&list->rcu_node, free_notification_client_list_rcu);
}

static
struct notification_client_list *notification_client_list_create(
		const struct lttng_trigger *trigger)
{
	struct notification_client_list *client_list =
			zmalloc(sizeof(*client_list));

	if (!client_list) {
		goto error;
	}
	pthread_mutex_init(&client_list->lock, NULL);
	urcu_ref_init(&client_list->ref);
	cds_lfht_node_init(&client_list->notification_trigger_clients_ht_node);
	CDS_INIT_LIST_HEAD(&client_list->list);
	client_list->trigger = trigger;
error:
	return client_list;
}

static
void publish_notification_client_list(
		struct notification_thread_state *state,
		struct notification_client_list *list)
{
	const struct lttng_condition *condition =
			lttng_trigger_get_const_condition(list->trigger);

	assert(!list->notification_trigger_clients_ht);

	list->notification_trigger_clients_ht =
			state->notification_trigger_clients_ht;

	rcu_read_lock();
	cds_lfht_add(state->notification_trigger_clients_ht,
			lttng_condition_hash(condition),
			&list->notification_trigger_clients_ht_node);
	rcu_read_unlock();
}

static
void notification_client_list_put(struct notification_client_list *list)
{
	if (!list) {
		return;
	}
	return urcu_ref_put(&list->ref, notification_client_list_release);
}

/* Provides a reference to the returned list. */
static
struct notification_client_list *get_client_list_from_condition(
	struct notification_thread_state *state,
	const struct lttng_condition *condition)
{
	struct cds_lfht_node *node;
	struct cds_lfht_iter iter;
	struct notification_client_list *list = NULL;

	rcu_read_lock();
	cds_lfht_lookup(state->notification_trigger_clients_ht,
			lttng_condition_hash(condition),
			match_client_list_condition,
			condition,
			&iter);
	node = cds_lfht_iter_get_node(&iter);
	if (node) {
		list = container_of(node, struct notification_client_list,
				notification_trigger_clients_ht_node);
		list = notification_client_list_get(list) ? list : NULL;
	}

	rcu_read_unlock();
	return list;
}

static
int evaluate_channel_condition_for_client(
		const struct lttng_condition *condition,
		struct notification_thread_state *state,
		struct lttng_evaluation **evaluation,
		uid_t *session_uid, gid_t *session_gid)
{
	int ret;
	struct cds_lfht_iter iter;
	struct cds_lfht_node *node;
	struct channel_info *channel_info = NULL;
	struct channel_key *channel_key = NULL;
	struct channel_state_sample *last_sample = NULL;
	struct lttng_channel_trigger_list *channel_trigger_list = NULL;

	rcu_read_lock();

	/* Find the channel associated with the condition. */
	cds_lfht_for_each_entry(state->channel_triggers_ht, &iter,
			channel_trigger_list, channel_triggers_ht_node) {
		struct lttng_trigger_list_element *element;

		cds_list_for_each_entry(element, &channel_trigger_list->list, node) {
			const struct lttng_condition *current_condition =
					lttng_trigger_get_const_condition(
						element->trigger);

			assert(current_condition);
			if (!lttng_condition_is_equal(condition,
					current_condition)) {
				continue;
			}

			/* Found the trigger, save the channel key. */
			channel_key = &channel_trigger_list->channel_key;
			break;
		}
		if (channel_key) {
			/* The channel key was found stop iteration. */
			break;
		}
	}

	if (!channel_key){
		/* No channel found; normal exit. */
		DBG("[notification-thread] No known channel associated with newly subscribed-to condition");
		ret = 0;
		goto end;
	}

	/* Fetch channel info for the matching channel. */
	cds_lfht_lookup(state->channels_ht,
			hash_channel_key(channel_key),
			match_channel_info,
			channel_key,
			&iter);
	node = cds_lfht_iter_get_node(&iter);
	assert(node);
	channel_info = caa_container_of(node, struct channel_info,
			channels_ht_node);

	/* Retrieve the channel's last sample, if it exists. */
	cds_lfht_lookup(state->channel_state_ht,
			hash_channel_key(channel_key),
			match_channel_state_sample,
			channel_key,
			&iter);
	node = cds_lfht_iter_get_node(&iter);
	if (node) {
		last_sample = caa_container_of(node,
				struct channel_state_sample,
				channel_state_ht_node);
	} else {
		/* Nothing to evaluate, no sample was ever taken. Normal exit */
		DBG("[notification-thread] No channel sample associated with newly subscribed-to condition");
		ret = 0;
		goto end;
	}

	ret = evaluate_buffer_condition(condition, evaluation, state,
			NULL, last_sample,
			0, channel_info->session_info->consumed_data_size,
			channel_info);
	if (ret) {
		WARN("[notification-thread] Fatal error occurred while evaluating a newly subscribed-to condition");
		goto end;
	}

	*session_uid = channel_info->session_info->uid;
	*session_gid = channel_info->session_info->gid;
end:
	rcu_read_unlock();
	return ret;
}

static
const char *get_condition_session_name(const struct lttng_condition *condition)
{
	const char *session_name = NULL;
	enum lttng_condition_status status;

	switch (lttng_condition_get_type(condition)) {
	case LTTNG_CONDITION_TYPE_BUFFER_USAGE_LOW:
	case LTTNG_CONDITION_TYPE_BUFFER_USAGE_HIGH:
		status = lttng_condition_buffer_usage_get_session_name(
				condition, &session_name);
		break;
	case LTTNG_CONDITION_TYPE_SESSION_CONSUMED_SIZE:
		status = lttng_condition_session_consumed_size_get_session_name(
				condition, &session_name);
		break;
	case LTTNG_CONDITION_TYPE_SESSION_ROTATION_ONGOING:
	case LTTNG_CONDITION_TYPE_SESSION_ROTATION_COMPLETED:
		status = lttng_condition_session_rotation_get_session_name(
				condition, &session_name);
		break;
	default:
		abort();
	}
	if (status != LTTNG_CONDITION_STATUS_OK) {
		ERR("[notification-thread] Failed to retrieve session rotation condition's session name");
		goto end;
	}
end:
	return session_name;
}

static
int evaluate_session_condition_for_client(
		const struct lttng_condition *condition,
		struct notification_thread_state *state,
		struct lttng_evaluation **evaluation,
		uid_t *session_uid, gid_t *session_gid)
{
	int ret;
	struct cds_lfht_iter iter;
	struct cds_lfht_node *node;
	const char *session_name;
	struct session_info *session_info = NULL;

	rcu_read_lock();
	session_name = get_condition_session_name(condition);

	/* Find the session associated with the trigger. */
	cds_lfht_lookup(state->sessions_ht,
			hash_key_str(session_name, lttng_ht_seed),
			match_session,
			session_name,
			&iter);
	node = cds_lfht_iter_get_node(&iter);
	if (!node) {
		DBG("[notification-thread] No known session matching name \"%s\"",
				session_name);
		ret = 0;
		goto end;
	}

	session_info = caa_container_of(node, struct session_info,
			sessions_ht_node);
	session_info_get(session_info);

	/*
	 * Evaluation is performed in-line here since only one type of
	 * session-bound condition is handled for the moment.
	 */
	switch (lttng_condition_get_type(condition)) {
	case LTTNG_CONDITION_TYPE_SESSION_ROTATION_ONGOING:
		if (!session_info->rotation.ongoing) {
			ret = 0;
			goto end_session_put;
		}

		*evaluation = lttng_evaluation_session_rotation_ongoing_create(
				session_info->rotation.id);
		if (!*evaluation) {
			/* Fatal error. */
			ERR("[notification-thread] Failed to create session rotation ongoing evaluation for session \"%s\"",
					session_info->name);
			ret = -1;
			goto end_session_put;
		}
		ret = 0;
		break;
	default:
		ret = 0;
		goto end_session_put;
	}

	*session_uid = session_info->uid;
	*session_gid = session_info->gid;

end_session_put:
	session_info_put(session_info);
end:
	rcu_read_unlock();
	return ret;
}

static
int evaluate_condition_for_client(const struct lttng_trigger *trigger,
		const struct lttng_condition *condition,
		struct notification_client *client,
		struct notification_thread_state *state)
{
	int ret;
	struct lttng_evaluation *evaluation = NULL;
	struct notification_client_list client_list = {
		.lock = PTHREAD_MUTEX_INITIALIZER,
	};
	struct notification_client_list_element client_list_element = { 0 };
	uid_t object_uid = 0;
	gid_t object_gid = 0;

	assert(trigger);
	assert(condition);
	assert(client);
	assert(state);

	switch (get_condition_binding_object(condition)) {
	case LTTNG_OBJECT_TYPE_SESSION:
		ret = evaluate_session_condition_for_client(condition, state,
				&evaluation, &object_uid, &object_gid);
		break;
	case LTTNG_OBJECT_TYPE_CHANNEL:
		ret = evaluate_channel_condition_for_client(condition, state,
				&evaluation, &object_uid, &object_gid);
		break;
	case LTTNG_OBJECT_TYPE_NONE:
		ret = 0;
		goto end;
	case LTTNG_OBJECT_TYPE_UNKNOWN:
	default:
		ret = -1;
		goto end;
	}
	if (ret) {
		/* Fatal error. */
		goto end;
	}
	if (!evaluation) {
		/* Evaluation yielded nothing. Normal exit. */
		DBG("[notification-thread] Newly subscribed-to condition evaluated to false, nothing to report to client");
		ret = 0;
		goto end;
	}

	/*
	 * Create a temporary client list with the client currently
	 * subscribing.
	 */
	cds_lfht_node_init(&client_list.notification_trigger_clients_ht_node);
	CDS_INIT_LIST_HEAD(&client_list.list);
	client_list.trigger = trigger;

	CDS_INIT_LIST_HEAD(&client_list_element.node);
	client_list_element.client = client;
	cds_list_add(&client_list_element.node, &client_list.list);

	/* Send evaluation result to the newly-subscribed client. */
	DBG("[notification-thread] Newly subscribed-to condition evaluated to true, notifying client");
	ret = send_evaluation_to_clients(trigger, evaluation, &client_list,
			state, object_uid, object_gid);

end:
	return ret;
}

static
int notification_thread_client_subscribe(struct notification_client *client,
		struct lttng_condition *condition,
		struct notification_thread_state *state,
		enum lttng_notification_channel_status *_status)
{
	int ret = 0;
	struct notification_client_list *client_list = NULL;
	struct lttng_condition_list_element *condition_list_element = NULL;
	struct notification_client_list_element *client_list_element = NULL;
	enum lttng_notification_channel_status status =
			LTTNG_NOTIFICATION_CHANNEL_STATUS_OK;

	/*
	 * Ensure that the client has not already subscribed to this condition
	 * before.
	 */
	cds_list_for_each_entry(condition_list_element, &client->condition_list, node) {
		if (lttng_condition_is_equal(condition_list_element->condition,
				condition)) {
			status = LTTNG_NOTIFICATION_CHANNEL_STATUS_ALREADY_SUBSCRIBED;
			goto end;
		}
	}

	condition_list_element = zmalloc(sizeof(*condition_list_element));
	if (!condition_list_element) {
		ret = -1;
		goto error;
	}
	client_list_element = zmalloc(sizeof(*client_list_element));
	if (!client_list_element) {
		ret = -1;
		goto error;
	}

	/*
	 * Add the newly-subscribed condition to the client's subscription list.
	 */
	CDS_INIT_LIST_HEAD(&condition_list_element->node);
	condition_list_element->condition = condition;
	cds_list_add(&condition_list_element->node, &client->condition_list);

	client_list = get_client_list_from_condition(state, condition);
	if (!client_list) {
		/*
		 * No notification-emiting trigger registered with this
		 * condition. We don't evaluate the condition right away
		 * since this trigger is not registered yet.
		 */
		free(client_list_element);
		goto end;
	}

	/*
	 * The condition to which the client just subscribed is evaluated
	 * at this point so that conditions that are already TRUE result
	 * in a notification being sent out.
	 *
	 * The client_list's trigger is used without locking the list itself.
	 * This is correct since the list doesn't own the trigger and the
	 * object is immutable.
	 */
	if (evaluate_condition_for_client(client_list->trigger, condition,
			client, state)) {
		WARN("[notification-thread] Evaluation of a condition on client subscription failed, aborting.");
		ret = -1;
		free(client_list_element);
		goto end;
	}

	/*
	 * Add the client to the list of clients interested in a given trigger
	 * if a "notification" trigger with a corresponding condition was
	 * added prior.
	 */
	client_list_element->client = client;
	CDS_INIT_LIST_HEAD(&client_list_element->node);

	pthread_mutex_lock(&client_list->lock);
	cds_list_add(&client_list_element->node, &client_list->list);
	pthread_mutex_unlock(&client_list->lock);
end:
	if (_status) {
		*_status = status;
	}
	if (client_list) {
		notification_client_list_put(client_list);
	}
	return ret;
error:
	free(condition_list_element);
	free(client_list_element);
	return ret;
}

static
int notification_thread_client_unsubscribe(
		struct notification_client *client,
		struct lttng_condition *condition,
		struct notification_thread_state *state,
		enum lttng_notification_channel_status *_status)
{
	struct notification_client_list *client_list;
	struct lttng_condition_list_element *condition_list_element,
			*condition_tmp;
	struct notification_client_list_element *client_list_element,
			*client_tmp;
	bool condition_found = false;
	enum lttng_notification_channel_status status =
			LTTNG_NOTIFICATION_CHANNEL_STATUS_OK;

	/* Remove the condition from the client's condition list. */
	cds_list_for_each_entry_safe(condition_list_element, condition_tmp,
			&client->condition_list, node) {
		if (!lttng_condition_is_equal(condition_list_element->condition,
				condition)) {
			continue;
		}

		cds_list_del(&condition_list_element->node);
		/*
		 * The caller may be iterating on the client's conditions to
		 * tear down a client's connection. In this case, the condition
		 * will be destroyed at the end.
		 */
		if (condition != condition_list_element->condition) {
			lttng_condition_destroy(
					condition_list_element->condition);
		}
		free(condition_list_element);
		condition_found = true;
		break;
	}

	if (!condition_found) {
		status = LTTNG_NOTIFICATION_CHANNEL_STATUS_UNKNOWN_CONDITION;
		goto end;
	}

	/*
	 * Remove the client from the list of clients interested the trigger
	 * matching the condition.
	 */
	client_list = get_client_list_from_condition(state, condition);
	if (!client_list) {
		goto end;
	}

	pthread_mutex_lock(&client_list->lock);
	cds_list_for_each_entry_safe(client_list_element, client_tmp,
			&client_list->list, node) {
		if (client_list_element->client->id != client->id) {
			continue;
		}
		cds_list_del(&client_list_element->node);
		free(client_list_element);
		break;
	}
	pthread_mutex_unlock(&client_list->lock);
	notification_client_list_put(client_list);
	client_list = NULL;
end:
	lttng_condition_destroy(condition);
	if (_status) {
		*_status = status;
	}
	return 0;
}

static
void free_notification_client_rcu(struct rcu_head *node)
{
	free(caa_container_of(node, struct notification_client, rcu_node));
}

static
void notification_client_destroy(struct notification_client *client,
		struct notification_thread_state *state)
{
	if (!client) {
		return;
	}

	/*
	 * The client object is not reachable by other threads, no need to lock
	 * the client here.
	 */
	if (client->socket >= 0) {
		(void) lttcomm_close_unix_sock(client->socket);
		client->socket = -1;
	}
	client->communication.active = false;
	lttng_dynamic_buffer_reset(&client->communication.inbound.buffer);
	lttng_dynamic_buffer_reset(&client->communication.outbound.buffer);
	pthread_mutex_destroy(&client->lock);
	call_rcu(&client->rcu_node, free_notification_client_rcu);
}

/*
 * Call with rcu_read_lock held (and hold for the lifetime of the returned
 * client pointer).
 */
static
struct notification_client *get_client_from_socket(int socket,
		struct notification_thread_state *state)
{
	struct cds_lfht_iter iter;
	struct cds_lfht_node *node;
	struct notification_client *client = NULL;

	cds_lfht_lookup(state->client_socket_ht,
			hash_client_socket(socket),
			match_client_socket,
			(void *) (unsigned long) socket,
			&iter);
	node = cds_lfht_iter_get_node(&iter);
	if (!node) {
		goto end;
	}

	client = caa_container_of(node, struct notification_client,
			client_socket_ht_node);
end:
	return client;
}

static
bool buffer_usage_condition_applies_to_channel(
		const struct lttng_condition *condition,
		const struct channel_info *channel_info)
{
	enum lttng_condition_status status;
	enum lttng_domain_type condition_domain;
	const char *condition_session_name = NULL;
	const char *condition_channel_name = NULL;

	status = lttng_condition_buffer_usage_get_domain_type(condition,
			&condition_domain);
	assert(status == LTTNG_CONDITION_STATUS_OK);
	if (channel_info->key.domain != condition_domain) {
		goto fail;
	}

	status = lttng_condition_buffer_usage_get_session_name(
			condition, &condition_session_name);
	assert((status == LTTNG_CONDITION_STATUS_OK) && condition_session_name);

	status = lttng_condition_buffer_usage_get_channel_name(
			condition, &condition_channel_name);
	assert((status == LTTNG_CONDITION_STATUS_OK) && condition_channel_name);

	if (strcmp(channel_info->session_info->name, condition_session_name)) {
		goto fail;
	}
	if (strcmp(channel_info->name, condition_channel_name)) {
		goto fail;
	}

	return true;
fail:
	return false;
}

static
bool session_consumed_size_condition_applies_to_channel(
		const struct lttng_condition *condition,
		const struct channel_info *channel_info)
{
	enum lttng_condition_status status;
	const char *condition_session_name = NULL;

	status = lttng_condition_session_consumed_size_get_session_name(
			condition, &condition_session_name);
	assert((status == LTTNG_CONDITION_STATUS_OK) && condition_session_name);

	if (strcmp(channel_info->session_info->name, condition_session_name)) {
		goto fail;
	}

	return true;
fail:
	return false;
}

static
bool trigger_applies_to_channel(const struct lttng_trigger *trigger,
		const struct channel_info *channel_info)
{
	const struct lttng_condition *condition;
	bool trigger_applies;

	condition = lttng_trigger_get_const_condition(trigger);
	if (!condition) {
		goto fail;
	}

	switch (lttng_condition_get_type(condition)) {
	case LTTNG_CONDITION_TYPE_BUFFER_USAGE_LOW:
	case LTTNG_CONDITION_TYPE_BUFFER_USAGE_HIGH:
		trigger_applies = buffer_usage_condition_applies_to_channel(
				condition, channel_info);
		break;
	case LTTNG_CONDITION_TYPE_SESSION_CONSUMED_SIZE:
		trigger_applies = session_consumed_size_condition_applies_to_channel(
				condition, channel_info);
		break;
	default:
		goto fail;
	}

	return trigger_applies;
fail:
	return false;
}

static
bool trigger_applies_to_client(struct lttng_trigger *trigger,
		struct notification_client *client)
{
	bool applies = false;
	struct lttng_condition_list_element *condition_list_element;

	cds_list_for_each_entry(condition_list_element, &client->condition_list,
			node) {
		applies = lttng_condition_is_equal(
				condition_list_element->condition,
				lttng_trigger_get_condition(trigger));
		if (applies) {
			break;
		}
	}
	return applies;
}

/* Must be called with RCU read lock held. */
static
struct lttng_session_trigger_list *get_session_trigger_list(
		struct notification_thread_state *state,
		const char *session_name)
{
	struct lttng_session_trigger_list *list = NULL;
	struct cds_lfht_node *node;
	struct cds_lfht_iter iter;

	cds_lfht_lookup(state->session_triggers_ht,
			hash_key_str(session_name, lttng_ht_seed),
			match_session_trigger_list,
			session_name,
			&iter);
	node = cds_lfht_iter_get_node(&iter);
	if (!node) {
		/*
		 * Not an error, the list of triggers applying to that session
		 * will be initialized when the session is created.
		 */
		DBG("[notification-thread] No trigger list found for session \"%s\" as it is not yet known to the notification system",
				session_name);
		goto end;
	}

	list = caa_container_of(node,
			struct lttng_session_trigger_list,
			session_triggers_ht_node);
end:
	return list;
}

/*
 * Allocate an empty lttng_session_trigger_list for the session named
 * 'session_name'.
 *
 * No ownership of 'session_name' is assumed by the session trigger list.
 * It is the caller's responsability to ensure the session name is alive
 * for as long as this list is.
 */
static
struct lttng_session_trigger_list *lttng_session_trigger_list_create(
		const char *session_name,
		struct cds_lfht *session_triggers_ht)
{
	struct lttng_session_trigger_list *list;

	list = zmalloc(sizeof(*list));
	if (!list) {
		goto end;
	}
	list->session_name = session_name;
	CDS_INIT_LIST_HEAD(&list->list);
	cds_lfht_node_init(&list->session_triggers_ht_node);
	list->session_triggers_ht = session_triggers_ht;

	rcu_read_lock();
	/* Publish the list through the session_triggers_ht. */
	cds_lfht_add(session_triggers_ht,
			hash_key_str(session_name, lttng_ht_seed),
			&list->session_triggers_ht_node);
	rcu_read_unlock();
end:
	return list;
}

static
void free_session_trigger_list_rcu(struct rcu_head *node)
{
	free(caa_container_of(node, struct lttng_session_trigger_list,
			rcu_node));
}

static
void lttng_session_trigger_list_destroy(struct lttng_session_trigger_list *list)
{
	struct lttng_trigger_list_element *trigger_list_element, *tmp;

	/* Empty the list element by element, and then free the list itself. */
	cds_list_for_each_entry_safe(trigger_list_element, tmp,
			&list->list, node) {
		cds_list_del(&trigger_list_element->node);
		free(trigger_list_element);
	}
	rcu_read_lock();
	/* Unpublish the list from the session_triggers_ht. */
	cds_lfht_del(list->session_triggers_ht,
			&list->session_triggers_ht_node);
	rcu_read_unlock();
	call_rcu(&list->rcu_node, free_session_trigger_list_rcu);
}

static
int lttng_session_trigger_list_add(struct lttng_session_trigger_list *list,
		const struct lttng_trigger *trigger)
{
	int ret = 0;
	struct lttng_trigger_list_element *new_element =
			zmalloc(sizeof(*new_element));

	if (!new_element) {
		ret = -1;
		goto end;
	}
	CDS_INIT_LIST_HEAD(&new_element->node);
	new_element->trigger = trigger;
	cds_list_add(&new_element->node, &list->list);
end:
	return ret;
}

static
bool trigger_applies_to_session(const struct lttng_trigger *trigger,
		const char *session_name)
{
	bool applies = false;
	const struct lttng_condition *condition;

	condition = lttng_trigger_get_const_condition(trigger);
	switch (lttng_condition_get_type(condition)) {
	case LTTNG_CONDITION_TYPE_SESSION_ROTATION_ONGOING:
	case LTTNG_CONDITION_TYPE_SESSION_ROTATION_COMPLETED:
	{
		enum lttng_condition_status condition_status;
		const char *condition_session_name;

		condition_status = lttng_condition_session_rotation_get_session_name(
			condition, &condition_session_name);
		if (condition_status != LTTNG_CONDITION_STATUS_OK) {
			ERR("[notification-thread] Failed to retrieve session rotation condition's session name");
			goto end;
		}

		assert(condition_session_name);
		applies = !strcmp(condition_session_name, session_name);
		break;
	}
	default:
		goto end;
	}
end:
	return applies;
}

/*
 * Allocate and initialize an lttng_session_trigger_list which contains
 * all triggers that apply to the session named 'session_name'.
 *
 * No ownership of 'session_name' is assumed by the session trigger list.
 * It is the caller's responsability to ensure the session name is alive
 * for as long as this list is.
 */
static
struct lttng_session_trigger_list *lttng_session_trigger_list_build(
		const struct notification_thread_state *state,
		const char *session_name)
{
	int trigger_count = 0;
	struct lttng_session_trigger_list *session_trigger_list = NULL;
	struct lttng_trigger_ht_element *trigger_ht_element = NULL;
	struct cds_lfht_iter iter;

	session_trigger_list = lttng_session_trigger_list_create(session_name,
			state->session_triggers_ht);

	/* Add all triggers applying to the session named 'session_name'. */
	cds_lfht_for_each_entry(state->triggers_ht, &iter, trigger_ht_element,
			node) {
		int ret;

		if (!trigger_applies_to_session(trigger_ht_element->trigger,
				session_name)) {
			continue;
		}

		ret = lttng_session_trigger_list_add(session_trigger_list,
				trigger_ht_element->trigger);
		if (ret) {
			goto error;
		}

		trigger_count++;
	}

	DBG("[notification-thread] Found %i triggers that apply to newly created session",
			trigger_count);
	return session_trigger_list;
error:
	lttng_session_trigger_list_destroy(session_trigger_list);
	return NULL;
}

static
struct session_info *find_or_create_session_info(
		struct notification_thread_state *state,
		const char *name, uid_t uid, gid_t gid)
{
	struct session_info *session = NULL;
	struct cds_lfht_node *node;
	struct cds_lfht_iter iter;
	struct lttng_session_trigger_list *trigger_list;

	rcu_read_lock();
	cds_lfht_lookup(state->sessions_ht,
			hash_key_str(name, lttng_ht_seed),
			match_session,
			name,
			&iter);
	node = cds_lfht_iter_get_node(&iter);
	if (node) {
		DBG("[notification-thread] Found session info of session \"%s\" (uid = %i, gid = %i)",
				name, uid, gid);
		session = caa_container_of(node, struct session_info,
				sessions_ht_node);
		assert(session->uid == uid);
		assert(session->gid == gid);
		session_info_get(session);
		goto end;
	}

	trigger_list = lttng_session_trigger_list_build(state, name);
	if (!trigger_list) {
		goto error;
	}

	session = session_info_create(name, uid, gid, trigger_list,
			state->sessions_ht);
	if (!session) {
		ERR("[notification-thread] Failed to allocation session info for session \"%s\" (uid = %i, gid = %i)",
				name, uid, gid);
		lttng_session_trigger_list_destroy(trigger_list);
		goto error;
	}
	trigger_list = NULL;

	cds_lfht_add(state->sessions_ht, hash_key_str(name, lttng_ht_seed),
			&session->sessions_ht_node);
end:
	rcu_read_unlock();
	return session;
error:
	rcu_read_unlock();
	session_info_put(session);
	return NULL;
}

static
int handle_notification_thread_command_add_channel(
		struct notification_thread_state *state,
		const char *session_name, uid_t session_uid, gid_t session_gid,
		const char *channel_name, enum lttng_domain_type channel_domain,
		uint64_t channel_key_int, uint64_t channel_capacity,
		enum lttng_error_code *cmd_result)
{
	struct cds_list_head trigger_list;
	struct channel_info *new_channel_info = NULL;
	struct channel_key channel_key = {
		.key = channel_key_int,
		.domain = channel_domain,
	};
	struct lttng_channel_trigger_list *channel_trigger_list = NULL;
	struct lttng_trigger_ht_element *trigger_ht_element = NULL;
	int trigger_count = 0;
	struct cds_lfht_iter iter;
	struct session_info *session_info = NULL;

	DBG("[notification-thread] Adding channel %s from session %s, channel key = %" PRIu64 " in %s domain",
			channel_name, session_name, channel_key_int,
			channel_domain == LTTNG_DOMAIN_KERNEL ? "kernel" : "user space");

	CDS_INIT_LIST_HEAD(&trigger_list);

	session_info = find_or_create_session_info(state, session_name,
			session_uid, session_gid);
	if (!session_info) {
		/* Allocation error or an internal error occurred. */
		goto error;
	}

	new_channel_info = channel_info_create(channel_name, &channel_key,
			channel_capacity, session_info);
	if (!new_channel_info) {
		goto error;
	}

	rcu_read_lock();
	/* Build a list of all triggers applying to the new channel. */
	cds_lfht_for_each_entry(state->triggers_ht, &iter, trigger_ht_element,
			node) {
		struct lttng_trigger_list_element *new_element;

		if (!trigger_applies_to_channel(trigger_ht_element->trigger,
				new_channel_info)) {
			continue;
		}

		new_element = zmalloc(sizeof(*new_element));
		if (!new_element) {
			rcu_read_unlock();
			goto error;
		}
		CDS_INIT_LIST_HEAD(&new_element->node);
		new_element->trigger = trigger_ht_element->trigger;
		cds_list_add(&new_element->node, &trigger_list);
		trigger_count++;
	}
	rcu_read_unlock();

	DBG("[notification-thread] Found %i triggers that apply to newly added channel",
			trigger_count);
	channel_trigger_list = zmalloc(sizeof(*channel_trigger_list));
	if (!channel_trigger_list) {
		goto error;
	}
	channel_trigger_list->channel_key = new_channel_info->key;
	CDS_INIT_LIST_HEAD(&channel_trigger_list->list);
	cds_lfht_node_init(&channel_trigger_list->channel_triggers_ht_node);
	cds_list_splice(&trigger_list, &channel_trigger_list->list);

	rcu_read_lock();
	/* Add channel to the channel_ht which owns the channel_infos. */
	cds_lfht_add(state->channels_ht,
			hash_channel_key(&new_channel_info->key),
			&new_channel_info->channels_ht_node);
	/*
	 * Add the list of triggers associated with this channel to the
	 * channel_triggers_ht.
	 */
	cds_lfht_add(state->channel_triggers_ht,
			hash_channel_key(&new_channel_info->key),
			&channel_trigger_list->channel_triggers_ht_node);
	rcu_read_unlock();
	session_info_put(session_info);
	*cmd_result = LTTNG_OK;
	return 0;
error:
	channel_info_destroy(new_channel_info);
	session_info_put(session_info);
	return 1;
}

static
void free_channel_trigger_list_rcu(struct rcu_head *node)
{
	free(caa_container_of(node, struct lttng_channel_trigger_list,
			rcu_node));
}

static
void free_channel_state_sample_rcu(struct rcu_head *node)
{
	free(caa_container_of(node, struct channel_state_sample,
			rcu_node));
}

static
int handle_notification_thread_command_remove_channel(
	struct notification_thread_state *state,
	uint64_t channel_key, enum lttng_domain_type domain,
	enum lttng_error_code *cmd_result)
{
	struct cds_lfht_node *node;
	struct cds_lfht_iter iter;
	struct lttng_channel_trigger_list *trigger_list;
	struct lttng_trigger_list_element *trigger_list_element, *tmp;
	struct channel_key key = { .key = channel_key, .domain = domain };
	struct channel_info *channel_info;

	DBG("[notification-thread] Removing channel key = %" PRIu64 " in %s domain",
			channel_key, domain == LTTNG_DOMAIN_KERNEL ? "kernel" : "user space");

	rcu_read_lock();

	cds_lfht_lookup(state->channel_triggers_ht,
			hash_channel_key(&key),
			match_channel_trigger_list,
			&key,
			&iter);
	node = cds_lfht_iter_get_node(&iter);
	/*
	 * There is a severe internal error if we are being asked to remove a
	 * channel that doesn't exist.
	 */
	if (!node) {
		ERR("[notification-thread] Channel being removed is unknown to the notification thread");
		goto end;
	}

	/* Free the list of triggers associated with this channel. */
	trigger_list = caa_container_of(node, struct lttng_channel_trigger_list,
			channel_triggers_ht_node);
	cds_list_for_each_entry_safe(trigger_list_element, tmp,
			&trigger_list->list, node) {
		cds_list_del(&trigger_list_element->node);
		free(trigger_list_element);
	}
	cds_lfht_del(state->channel_triggers_ht, node);
	call_rcu(&trigger_list->rcu_node, free_channel_trigger_list_rcu);

	/* Free sampled channel state. */
	cds_lfht_lookup(state->channel_state_ht,
			hash_channel_key(&key),
			match_channel_state_sample,
			&key,
			&iter);
	node = cds_lfht_iter_get_node(&iter);
	/*
	 * This is expected to be NULL if the channel is destroyed before we
	 * received a sample.
	 */
	if (node) {
		struct channel_state_sample *sample = caa_container_of(node,
				struct channel_state_sample,
				channel_state_ht_node);

		cds_lfht_del(state->channel_state_ht, node);
		call_rcu(&sample->rcu_node, free_channel_state_sample_rcu);
	}

	/* Remove the channel from the channels_ht and free it. */
	cds_lfht_lookup(state->channels_ht,
			hash_channel_key(&key),
			match_channel_info,
			&key,
			&iter);
	node = cds_lfht_iter_get_node(&iter);
	assert(node);
	channel_info = caa_container_of(node, struct channel_info,
			channels_ht_node);
	cds_lfht_del(state->channels_ht, node);
	channel_info_destroy(channel_info);
end:
	rcu_read_unlock();
	*cmd_result = LTTNG_OK;
	return 0;
}

static
int handle_notification_thread_command_session_rotation(
	struct notification_thread_state *state,
	enum notification_thread_command_type cmd_type,
	const char *session_name, uid_t session_uid, gid_t session_gid,
	uint64_t trace_archive_chunk_id,
	struct lttng_trace_archive_location *location,
	enum lttng_error_code *_cmd_result)
{
	int ret = 0;
	enum lttng_error_code cmd_result = LTTNG_OK;
	struct lttng_session_trigger_list *trigger_list;
	struct lttng_trigger_list_element *trigger_list_element;
	struct session_info *session_info;

	rcu_read_lock();

	session_info = find_or_create_session_info(state, session_name,
			session_uid, session_gid);
	if (!session_info) {
		/* Allocation error or an internal error occurred. */
		ret = -1;
		cmd_result = LTTNG_ERR_NOMEM;
		goto end;
	}

	session_info->rotation.ongoing =
			cmd_type == NOTIFICATION_COMMAND_TYPE_SESSION_ROTATION_ONGOING;
	session_info->rotation.id = trace_archive_chunk_id;
	trigger_list = get_session_trigger_list(state, session_name);
	if (!trigger_list) {
		DBG("[notification-thread] No triggers applying to session \"%s\" found",
				session_name);
		goto end;
	}

	cds_list_for_each_entry(trigger_list_element, &trigger_list->list,
			node) {
		const struct lttng_condition *condition;
		const struct lttng_action *action;
		const struct lttng_trigger *trigger;
		struct notification_client_list *client_list;
		struct lttng_evaluation *evaluation = NULL;
		enum lttng_condition_type condition_type;
		bool client_list_is_empty;

		trigger = trigger_list_element->trigger;
		condition = lttng_trigger_get_const_condition(trigger);
		assert(condition);
		condition_type = lttng_condition_get_type(condition);

		if (condition_type == LTTNG_CONDITION_TYPE_SESSION_ROTATION_ONGOING &&
				cmd_type != NOTIFICATION_COMMAND_TYPE_SESSION_ROTATION_ONGOING) {
			continue;
		} else if (condition_type == LTTNG_CONDITION_TYPE_SESSION_ROTATION_COMPLETED &&
				cmd_type != NOTIFICATION_COMMAND_TYPE_SESSION_ROTATION_COMPLETED) {
			continue;
		}

		action = lttng_trigger_get_const_action(trigger);

		/* Notify actions are the only type currently supported. */
		assert(lttng_action_get_type_const(action) ==
				LTTNG_ACTION_TYPE_NOTIFY);

		client_list = get_client_list_from_condition(state, condition);
		assert(client_list);

		pthread_mutex_lock(&client_list->lock);
		client_list_is_empty = cds_list_empty(&client_list->list);
		pthread_mutex_unlock(&client_list->lock);
		if (client_list_is_empty) {
			/*
			 * No clients interested in the evaluation's result,
			 * skip it.
			 */
			continue;
		}

		if (cmd_type == NOTIFICATION_COMMAND_TYPE_SESSION_ROTATION_ONGOING) {
			evaluation = lttng_evaluation_session_rotation_ongoing_create(
					trace_archive_chunk_id);
		} else {
			evaluation = lttng_evaluation_session_rotation_completed_create(
					trace_archive_chunk_id, location);
		}

		if (!evaluation) {
			/* Internal error */
			ret = -1;
			cmd_result = LTTNG_ERR_UNK;
			goto put_list;
		}

		/* Dispatch evaluation result to all clients. */
		ret = send_evaluation_to_clients(trigger_list_element->trigger,
				evaluation, client_list, state,
				session_info->uid,
				session_info->gid);
		lttng_evaluation_destroy(evaluation);
put_list:
		notification_client_list_put(client_list);
		if (caa_unlikely(ret)) {
			break;
		}
	}
end:
	session_info_put(session_info);
	*_cmd_result = cmd_result;
	rcu_read_unlock();
	return ret;
}

static
int condition_is_supported(struct lttng_condition *condition)
{
	int ret;

	switch (lttng_condition_get_type(condition)) {
	case LTTNG_CONDITION_TYPE_BUFFER_USAGE_LOW:
	case LTTNG_CONDITION_TYPE_BUFFER_USAGE_HIGH:
	{
		enum lttng_domain_type domain;

		ret = lttng_condition_buffer_usage_get_domain_type(condition,
				&domain);
		if (ret) {
			ret = -1;
			goto end;
		}

		if (domain != LTTNG_DOMAIN_KERNEL) {
			ret = 1;
			goto end;
		}

		/*
		 * Older kernel tracers don't expose the API to monitor their
		 * buffers. Therefore, we reject triggers that require that
		 * mechanism to be available to be evaluated.
		 */
		ret = kernel_supports_ring_buffer_snapshot_sample_positions();
		break;
	}
	default:
		ret = 1;
	}
end:
	return ret;
}

/* Must be called with RCU read lock held. */
static
int bind_trigger_to_matching_session(const struct lttng_trigger *trigger,
		struct notification_thread_state *state)
{
	int ret = 0;
	const struct lttng_condition *condition;
	const char *session_name;
	struct lttng_session_trigger_list *trigger_list;

	condition = lttng_trigger_get_const_condition(trigger);
	switch (lttng_condition_get_type(condition)) {
	case LTTNG_CONDITION_TYPE_SESSION_ROTATION_ONGOING:
	case LTTNG_CONDITION_TYPE_SESSION_ROTATION_COMPLETED:
	{
		enum lttng_condition_status status;

		status = lttng_condition_session_rotation_get_session_name(
				condition, &session_name);
		if (status != LTTNG_CONDITION_STATUS_OK) {
			ERR("[notification-thread] Failed to bind trigger to session: unable to get 'session_rotation' condition's session name");
			ret = -1;
			goto end;
		}
		break;
	}
	default:
		ret = -1;
		goto end;
	}

	trigger_list = get_session_trigger_list(state, session_name);
	if (!trigger_list) {
		DBG("[notification-thread] Unable to bind trigger applying to session \"%s\" as it is not yet known to the notification system",
				session_name);
		goto end;

	}

	DBG("[notification-thread] Newly registered trigger bound to session \"%s\"",
			session_name);
	ret = lttng_session_trigger_list_add(trigger_list, trigger);
end:
	return ret;
}

/* Must be called with RCU read lock held. */
static
int bind_trigger_to_matching_channels(const struct lttng_trigger *trigger,
		struct notification_thread_state *state)
{
	int ret = 0;
	struct cds_lfht_node *node;
	struct cds_lfht_iter iter;
	struct channel_info *channel;

	cds_lfht_for_each_entry(state->channels_ht, &iter, channel,
			channels_ht_node) {
		struct lttng_trigger_list_element *trigger_list_element;
		struct lttng_channel_trigger_list *trigger_list;
		struct cds_lfht_iter lookup_iter;

		if (!trigger_applies_to_channel(trigger, channel)) {
			continue;
		}

		cds_lfht_lookup(state->channel_triggers_ht,
				hash_channel_key(&channel->key),
				match_channel_trigger_list,
				&channel->key,
				&lookup_iter);
		node = cds_lfht_iter_get_node(&lookup_iter);
		assert(node);
		trigger_list = caa_container_of(node,
				struct lttng_channel_trigger_list,
				channel_triggers_ht_node);

		trigger_list_element = zmalloc(sizeof(*trigger_list_element));
		if (!trigger_list_element) {
			ret = -1;
			goto end;
		}
		CDS_INIT_LIST_HEAD(&trigger_list_element->node);
		trigger_list_element->trigger = trigger;
		cds_list_add(&trigger_list_element->node, &trigger_list->list);
		DBG("[notification-thread] Newly registered trigger bound to channel \"%s\"",
				channel->name);
	}
end:
	return ret;
}

/*
 * FIXME A client's credentials are not checked when registering a trigger, nor
 *       are they stored alongside with the trigger.
 *
 * The effects of this are benign since:
 *     - The client will succeed in registering the trigger, as it is valid,
 *     - The trigger will, internally, be bound to the channel/session,
 *     - The notifications will not be sent since the client's credentials
 *       are checked against the channel at that moment.
 *
 * If this function returns a non-zero value, it means something is
 * fundamentally broken and the whole subsystem/thread will be torn down.
 *
 * If a non-fatal error occurs, just set the cmd_result to the appropriate
 * error code.
 */
static
int handle_notification_thread_command_register_trigger(
		struct notification_thread_state *state,
		struct lttng_trigger *trigger,
		enum lttng_error_code *cmd_result)
{
	int ret = 0;
	struct lttng_condition *condition;
	struct notification_client *client;
	struct notification_client_list *client_list = NULL;
	struct lttng_trigger_ht_element *trigger_ht_element = NULL;
	struct notification_client_list_element *client_list_element, *tmp;
	struct cds_lfht_node *node;
	struct cds_lfht_iter iter;
	bool free_trigger = true;

	rcu_read_lock();

	condition = lttng_trigger_get_condition(trigger);
	assert(condition);

	ret = condition_is_supported(condition);
	if (ret < 0) {
		goto error;
	} else if (ret == 0) {
		*cmd_result = LTTNG_ERR_NOT_SUPPORTED;
		goto error;
	} else {
		/* Feature is supported, continue. */
		ret = 0;
	}

	trigger_ht_element = zmalloc(sizeof(*trigger_ht_element));
	if (!trigger_ht_element) {
		ret = -1;
		goto error;
	}

	/* Add trigger to the trigger_ht. */
	cds_lfht_node_init(&trigger_ht_element->node);
	trigger_ht_element->trigger = trigger;

	node = cds_lfht_add_unique(state->triggers_ht,
			lttng_condition_hash(condition),
			match_condition,
			condition,
			&trigger_ht_element->node);
	if (node != &trigger_ht_element->node) {
		/* Not a fatal error, simply report it to the client. */
		*cmd_result = LTTNG_ERR_TRIGGER_EXISTS;
		goto error_free_ht_element;
	}

	/*
	 * Ownership of the trigger and of its wrapper was transfered to
	 * the triggers_ht.
	 */
	trigger_ht_element = NULL;
	free_trigger = false;

	/*
	 * The rest only applies to triggers that have a "notify" action.
	 * It is not skipped as this is the only action type currently
	 * supported.
	 */
	client_list = notification_client_list_create(trigger);
	if (!client_list) {
		ret = -1;
		goto error_free_ht_element;
	}

	/* Build a list of clients to which this new trigger applies. */
	cds_lfht_for_each_entry(state->client_socket_ht, &iter, client,
			client_socket_ht_node) {
		if (!trigger_applies_to_client(trigger, client)) {
			continue;
		}

		client_list_element = zmalloc(sizeof(*client_list_element));
		if (!client_list_element) {
			ret = -1;
			goto error_put_client_list;
		}
		CDS_INIT_LIST_HEAD(&client_list_element->node);
		client_list_element->client = client;
		cds_list_add(&client_list_element->node, &client_list->list);
	}

	switch (get_condition_binding_object(condition)) {
	case LTTNG_OBJECT_TYPE_SESSION:
		/* Add the trigger to the list if it matches a known session. */
		ret = bind_trigger_to_matching_session(trigger, state);
		if (ret) {
			goto error_put_client_list;
		}
		break;
	case LTTNG_OBJECT_TYPE_CHANNEL:
		/*
		 * Add the trigger to list of triggers bound to the channels
		 * currently known.
		 */
		ret = bind_trigger_to_matching_channels(trigger, state);
		if (ret) {
			goto error_put_client_list;
		}
		break;
	case LTTNG_OBJECT_TYPE_NONE:
		break;
	default:
		ERR("[notification-thread] Unknown object type on which to bind a newly registered trigger was encountered");
		ret = -1;
		goto error_put_client_list;
	}

	/*
	 * Since there is nothing preventing clients from subscribing to a
	 * condition before the corresponding trigger is registered, we have
	 * to evaluate this new condition right away.
	 *
	 * At some point, we were waiting for the next "evaluation" (e.g. on
	 * reception of a channel sample) to evaluate this new condition, but
	 * that was broken.
	 *
	 * The reason it was broken is that waiting for the next sample
	 * does not allow us to properly handle transitions for edge-triggered
	 * conditions.
	 *
	 * Consider this example: when we handle a new channel sample, we
	 * evaluate each conditions twice: once with the previous state, and
	 * again with the newest state. We then use those two results to
	 * determine whether a state change happened: a condition was false and
	 * became true. If a state change happened, we have to notify clients.
	 *
	 * Now, if a client subscribes to a given notification and registers
	 * a trigger *after* that subscription, we have to make sure the
	 * condition is evaluated at this point while considering only the
	 * current state. Otherwise, the next evaluation cycle may only see
	 * that the evaluations remain the same (true for samples n-1 and n) and
	 * the client will never know that the condition has been met.
	 *
	 * No need to lock the list here as it has not been published yet.
	 */
	cds_list_for_each_entry_safe(client_list_element, tmp,
			&client_list->list, node) {
		ret = evaluate_condition_for_client(trigger, condition,
				client_list_element->client, state);
		if (ret) {
			goto error_put_client_list;
		}
	}

	/*
	 * Client list ownership transferred to the
	 * notification_trigger_clients_ht.
	 */
	publish_notification_client_list(state, client_list);
	client_list = NULL;

	*cmd_result = LTTNG_OK;

error_put_client_list:
	notification_client_list_put(client_list);

error_free_ht_element:
	free(trigger_ht_element);
error:
	if (free_trigger) {
		lttng_trigger_destroy(trigger);
	}
	rcu_read_unlock();
	return ret;
}

static
void free_lttng_trigger_ht_element_rcu(struct rcu_head *node)
{
	free(caa_container_of(node, struct lttng_trigger_ht_element,
			rcu_node));
}

static
int handle_notification_thread_command_unregister_trigger(
		struct notification_thread_state *state,
		struct lttng_trigger *trigger,
		enum lttng_error_code *_cmd_reply)
{
	struct cds_lfht_iter iter;
	struct cds_lfht_node *triggers_ht_node;
	struct lttng_channel_trigger_list *trigger_list;
	struct notification_client_list *client_list;
	struct lttng_trigger_ht_element *trigger_ht_element = NULL;
	struct lttng_condition *condition = lttng_trigger_get_condition(
			trigger);
	enum lttng_error_code cmd_reply;

	rcu_read_lock();

	cds_lfht_lookup(state->triggers_ht,
			lttng_condition_hash(condition),
			match_condition,
			condition,
			&iter);
	triggers_ht_node = cds_lfht_iter_get_node(&iter);
	if (!triggers_ht_node) {
		cmd_reply = LTTNG_ERR_TRIGGER_NOT_FOUND;
		goto end;
	} else {
		cmd_reply = LTTNG_OK;
	}

	/* Remove trigger from channel_triggers_ht. */
	cds_lfht_for_each_entry(state->channel_triggers_ht, &iter, trigger_list,
			channel_triggers_ht_node) {
		struct lttng_trigger_list_element *trigger_element, *tmp;

		cds_list_for_each_entry_safe(trigger_element, tmp,
				&trigger_list->list, node) {
			const struct lttng_condition *current_condition =
					lttng_trigger_get_const_condition(
						trigger_element->trigger);

			assert(current_condition);
			if (!lttng_condition_is_equal(condition,
					current_condition)) {
				continue;
			}

			DBG("[notification-thread] Removed trigger from channel_triggers_ht");
			cds_list_del(&trigger_element->node);
			/* A trigger can only appear once per channel */
			break;
		}
	}

	/*
	 * Remove and release the client list from
	 * notification_trigger_clients_ht.
	 */
	client_list = get_client_list_from_condition(state, condition);
	assert(client_list);

	/* Put new reference and the hashtable's reference. */
	notification_client_list_put(client_list);
	notification_client_list_put(client_list);
	client_list = NULL;

	/* Remove trigger from triggers_ht. */
	trigger_ht_element = caa_container_of(triggers_ht_node,
			struct lttng_trigger_ht_element, node);
	cds_lfht_del(state->triggers_ht, triggers_ht_node);

	/* Release the ownership of the trigger. */
	lttng_trigger_destroy(trigger_ht_element->trigger);
	call_rcu(&trigger_ht_element->rcu_node, free_lttng_trigger_ht_element_rcu);
end:
	rcu_read_unlock();
	if (_cmd_reply) {
		*_cmd_reply = cmd_reply;
	}
	return 0;
}

/* Returns 0 on success, 1 on exit requested, negative value on error. */
int handle_notification_thread_command(
		struct notification_thread_handle *handle,
		struct notification_thread_state *state)
{
	int ret;
	uint64_t counter;
	struct notification_thread_command *cmd;

	/* Read the event pipe to put it back into a quiescent state. */
	ret = lttng_read(lttng_pipe_get_readfd(handle->cmd_queue.event_pipe), &counter,
			sizeof(counter));
	if (ret != sizeof(counter)) {
		goto error;
	}

	pthread_mutex_lock(&handle->cmd_queue.lock);
	cmd = cds_list_first_entry(&handle->cmd_queue.list,
			struct notification_thread_command, cmd_list_node);
	switch (cmd->type) {
	case NOTIFICATION_COMMAND_TYPE_REGISTER_TRIGGER:
		DBG("[notification-thread] Received register trigger command");
		ret = handle_notification_thread_command_register_trigger(
				state, cmd->parameters.trigger,
				&cmd->reply_code);
		break;
	case NOTIFICATION_COMMAND_TYPE_UNREGISTER_TRIGGER:
		DBG("[notification-thread] Received unregister trigger command");
		ret = handle_notification_thread_command_unregister_trigger(
				state, cmd->parameters.trigger,
				&cmd->reply_code);
		break;
	case NOTIFICATION_COMMAND_TYPE_ADD_CHANNEL:
		DBG("[notification-thread] Received add channel command");
		ret = handle_notification_thread_command_add_channel(
				state,
				cmd->parameters.add_channel.session.name,
				cmd->parameters.add_channel.session.uid,
				cmd->parameters.add_channel.session.gid,
				cmd->parameters.add_channel.channel.name,
				cmd->parameters.add_channel.channel.domain,
				cmd->parameters.add_channel.channel.key,
				cmd->parameters.add_channel.channel.capacity,
				&cmd->reply_code);
		break;
	case NOTIFICATION_COMMAND_TYPE_REMOVE_CHANNEL:
		DBG("[notification-thread] Received remove channel command");
		ret = handle_notification_thread_command_remove_channel(
				state, cmd->parameters.remove_channel.key,
				cmd->parameters.remove_channel.domain,
				&cmd->reply_code);
		break;
	case NOTIFICATION_COMMAND_TYPE_SESSION_ROTATION_ONGOING:
	case NOTIFICATION_COMMAND_TYPE_SESSION_ROTATION_COMPLETED:
		DBG("[notification-thread] Received session rotation %s command",
				cmd->type == NOTIFICATION_COMMAND_TYPE_SESSION_ROTATION_ONGOING ?
				"ongoing" : "completed");
		ret = handle_notification_thread_command_session_rotation(
				state,
				cmd->type,
				cmd->parameters.session_rotation.session_name,
				cmd->parameters.session_rotation.uid,
				cmd->parameters.session_rotation.gid,
				cmd->parameters.session_rotation.trace_archive_chunk_id,
				cmd->parameters.session_rotation.location,
				&cmd->reply_code);
		break;
	case NOTIFICATION_COMMAND_TYPE_QUIT:
		DBG("[notification-thread] Received quit command");
		cmd->reply_code = LTTNG_OK;
		ret = 1;
		goto end;
	default:
		ERR("[notification-thread] Unknown internal command received");
		goto error_unlock;
	}

	if (ret) {
		goto error_unlock;
	}
end:
	cds_list_del(&cmd->cmd_list_node);
	lttng_waiter_wake_up(&cmd->reply_waiter);
	pthread_mutex_unlock(&handle->cmd_queue.lock);
	return ret;
error_unlock:
	/* Wake-up and return a fatal error to the calling thread. */
	lttng_waiter_wake_up(&cmd->reply_waiter);
	pthread_mutex_unlock(&handle->cmd_queue.lock);
	cmd->reply_code = LTTNG_ERR_FATAL;
error:
	/* Indicate a fatal error to the caller. */
	return -1;
}

static
int socket_set_non_blocking(int socket)
{
	int ret, flags;

	/* Set the pipe as non-blocking. */
	ret = fcntl(socket, F_GETFL, 0);
	if (ret == -1) {
		PERROR("fcntl get socket flags");
		goto end;
	}
	flags = ret;

	ret = fcntl(socket, F_SETFL, flags | O_NONBLOCK);
	if (ret == -1) {
		PERROR("fcntl set O_NONBLOCK socket flag");
		goto end;
	}
	DBG("Client socket (fd = %i) set as non-blocking", socket);
end:
	return ret;
}

/* Client lock must be acquired by caller. */
static
int client_reset_inbound_state(struct notification_client *client)
{
	int ret;

	ASSERT_LOCKED(client->lock);

	ret = lttng_dynamic_buffer_set_size(
			&client->communication.inbound.buffer, 0);
	assert(!ret);

	client->communication.inbound.bytes_to_receive =
			sizeof(struct lttng_notification_channel_message);
	client->communication.inbound.msg_type =
			LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_UNKNOWN;
	LTTNG_SOCK_SET_UID_CRED(&client->communication.inbound.creds, -1);
	LTTNG_SOCK_SET_GID_CRED(&client->communication.inbound.creds, -1);
	ret = lttng_dynamic_buffer_set_size(
			&client->communication.inbound.buffer,
			client->communication.inbound.bytes_to_receive);
	return ret;
}

int handle_notification_thread_client_connect(
		struct notification_thread_state *state)
{
	int ret;
	struct notification_client *client;

	DBG("[notification-thread] Handling new notification channel client connection");

	client = zmalloc(sizeof(*client));
	if (!client) {
		/* Fatal error. */
		ret = -1;
		goto error;
	}
	pthread_mutex_init(&client->lock, NULL);
	client->id = state->next_notification_client_id++;
	CDS_INIT_LIST_HEAD(&client->condition_list);
	lttng_dynamic_buffer_init(&client->communication.inbound.buffer);
	lttng_dynamic_buffer_init(&client->communication.outbound.buffer);
	client->communication.inbound.expect_creds = true;

	pthread_mutex_lock(&client->lock);
	ret = client_reset_inbound_state(client);
	pthread_mutex_unlock(&client->lock);
	if (ret) {
		ERR("[notification-thread] Failed to reset client communication's inbound state");
		ret = 0;
		goto error;
	}

	ret = lttcomm_accept_unix_sock(state->notification_channel_socket);
	if (ret < 0) {
		ERR("[notification-thread] Failed to accept new notification channel client connection");
		ret = 0;
		goto error;
	}

	client->socket = ret;

	ret = socket_set_non_blocking(client->socket);
	if (ret) {
		ERR("[notification-thread] Failed to set new notification channel client connection socket as non-blocking");
		goto error;
	}

	ret = lttcomm_setsockopt_creds_unix_sock(client->socket);
	if (ret < 0) {
		ERR("[notification-thread] Failed to set socket options on new notification channel client socket");
		ret = 0;
		goto error;
	}

	ret = lttng_poll_add(&state->events, client->socket,
			LPOLLIN | LPOLLERR |
			LPOLLHUP | LPOLLRDHUP);
	if (ret < 0) {
		ERR("[notification-thread] Failed to add notification channel client socket to poll set");
		ret = 0;
		goto error;
	}
	DBG("[notification-thread] Added new notification channel client socket (%i) to poll set",
			client->socket);

	rcu_read_lock();
	cds_lfht_add(state->client_socket_ht,
			hash_client_socket(client->socket),
			&client->client_socket_ht_node);
	cds_lfht_add(state->client_id_ht,
			hash_client_id(client->id),
			&client->client_id_ht_node);
	rcu_read_unlock();

	return ret;
error:
	notification_client_destroy(client, state);
	return ret;
}

/* RCU read-lock must be held by the caller. */
/* Client lock must be held by the caller */
static
int notification_thread_client_disconnect(
		struct notification_client *client,
		struct notification_thread_state *state)
{
	int ret;
	struct lttng_condition_list_element *condition_list_element, *tmp;

	/* Acquire the client lock to disable its communication atomically. */
	client->communication.active = false;
	ret = lttng_poll_del(&state->events, client->socket);
	if (ret) {
		ERR("[notification-thread] Failed to remove client socket %d from poll set",
				client->socket);
	}

	cds_lfht_del(state->client_socket_ht, &client->client_socket_ht_node);
	cds_lfht_del(state->client_id_ht, &client->client_id_ht_node);

	/* Release all conditions to which the client was subscribed. */
	cds_list_for_each_entry_safe(condition_list_element, tmp,
			&client->condition_list, node) {
		(void) notification_thread_client_unsubscribe(client,
				condition_list_element->condition, state, NULL);
	}

	/*
	 * Client no longer accessible to other threads (through the
	 * client lists).
	 */
	notification_client_destroy(client, state);
	return ret;
}

int handle_notification_thread_client_disconnect(
		int client_socket, struct notification_thread_state *state)
{
	int ret = 0;
	struct notification_client *client;

	rcu_read_lock();
	DBG("[notification-thread] Closing client connection (socket fd = %i)",
			client_socket);
	client = get_client_from_socket(client_socket, state);
	if (!client) {
		/* Internal state corruption, fatal error. */
		ERR("[notification-thread] Unable to find client (socket fd = %i)",
				client_socket);
		ret = -1;
		goto end;
	}

	pthread_mutex_lock(&client->lock);
	ret = notification_thread_client_disconnect(client, state);
	pthread_mutex_unlock(&client->lock);
end:
	rcu_read_unlock();
	return ret;
}

int handle_notification_thread_client_disconnect_all(
		struct notification_thread_state *state)
{
	struct cds_lfht_iter iter;
	struct notification_client *client;
	bool error_encoutered = false;

	rcu_read_lock();
	DBG("[notification-thread] Closing all client connections");
	cds_lfht_for_each_entry(state->client_socket_ht, &iter, client,
			client_socket_ht_node) {
		int ret;

		pthread_mutex_lock(&client->lock);
		ret = notification_thread_client_disconnect(
				client, state);
		pthread_mutex_unlock(&client->lock);
		if (ret) {
			error_encoutered = true;
		}
	}
	rcu_read_unlock();
	return error_encoutered ? 1 : 0;
}

int handle_notification_thread_trigger_unregister_all(
		struct notification_thread_state *state)
{
	bool error_occurred = false;
	struct cds_lfht_iter iter;
	struct lttng_trigger_ht_element *trigger_ht_element;

	rcu_read_lock();
	cds_lfht_for_each_entry(state->triggers_ht, &iter, trigger_ht_element,
			node) {
		int ret = handle_notification_thread_command_unregister_trigger(
				state, trigger_ht_element->trigger, NULL);
		if (ret) {
			error_occurred = true;
		}
	}
	rcu_read_unlock();
	return error_occurred ? -1 : 0;
}

/* Client lock must be acquired by caller. */
static
int client_flush_outgoing_queue(struct notification_client *client,
		struct notification_thread_state *state)
{
	ssize_t ret;
	size_t to_send_count;

	ASSERT_LOCKED(client->lock);

	assert(client->communication.outbound.buffer.size != 0);
	to_send_count = client->communication.outbound.buffer.size;
	DBG("[notification-thread] Flushing client (socket fd = %i) outgoing queue",
			client->socket);

	ret = lttcomm_send_unix_sock_non_block(client->socket,
			client->communication.outbound.buffer.data,
			to_send_count);
	if ((ret >= 0 && ret < to_send_count)) {
		DBG("[notification-thread] Client (socket fd = %i) outgoing queue could not be completely flushed",
				client->socket);
		to_send_count -= max(ret, 0);

		memcpy(client->communication.outbound.buffer.data,
				client->communication.outbound.buffer.data +
				client->communication.outbound.buffer.size - to_send_count,
				to_send_count);
		ret = lttng_dynamic_buffer_set_size(
				&client->communication.outbound.buffer,
				to_send_count);
		if (ret) {
			goto error;
		}

		/*
		 * We want to be notified whenever there is buffer space
		 * available to send the rest of the payload.
		 */
		ret = lttng_poll_mod(&state->events, client->socket,
				CLIENT_POLL_MASK_IN_OUT);
		if (ret) {
			goto error;
		}
	} else if (ret < 0) {
		/* Generic error, disconnect the client. */
		ERR("[notification-thread] Failed to send flush outgoing queue, disconnecting client (socket fd = %i)",
				client->socket);
		ret = notification_thread_client_disconnect(client, state);
		if (ret) {
			goto error;
		}
	} else {
		/* No error and flushed the queue completely. */
		ret = lttng_dynamic_buffer_set_size(
				&client->communication.outbound.buffer, 0);
		if (ret) {
			goto error;
		}
		ret = lttng_poll_mod(&state->events, client->socket,
				CLIENT_POLL_MASK_IN);
		if (ret) {
			goto error;
		}

		client->communication.outbound.queued_command_reply = false;
		client->communication.outbound.dropped_notification = false;
	}

	return 0;
error:
	return -1;
}

/* Client lock must be acquired by caller. */
static
int client_send_command_reply(struct notification_client *client,
		struct notification_thread_state *state,
		enum lttng_notification_channel_status status)
{
	int ret;
	struct lttng_notification_channel_command_reply reply = {
		.status = (int8_t) status,
	};
	struct lttng_notification_channel_message msg = {
		.type = (int8_t) LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_COMMAND_REPLY,
		.size = sizeof(reply),
	};
	char buffer[sizeof(msg) + sizeof(reply)];

	ASSERT_LOCKED(client->lock);

	if (client->communication.outbound.queued_command_reply) {
		/* Protocol error. */
		goto error;
	}

	memcpy(buffer, &msg, sizeof(msg));
	memcpy(buffer + sizeof(msg), &reply, sizeof(reply));
	DBG("[notification-thread] Send command reply (%i)", (int) status);

	/* Enqueue buffer to outgoing queue and flush it. */
	ret = lttng_dynamic_buffer_append(
			&client->communication.outbound.buffer,
			buffer, sizeof(buffer));
	if (ret) {
		goto error;
	}

	ret = client_flush_outgoing_queue(client, state);
	if (ret) {
		goto error;
	}

	if (client->communication.outbound.buffer.size != 0) {
		/* Queue could not be emptied. */
		client->communication.outbound.queued_command_reply = true;
	}

	return 0;
error:
	return -1;
}

static
int client_handle_message_unknown(struct notification_client *client,
		struct notification_thread_state *state)
{
	int ret;

	pthread_mutex_lock(&client->lock);

	/*
	 * Receiving message header. The function will be called again
	 * once the rest of the message as been received and can be
	 * interpreted.
	 */
	const struct lttng_notification_channel_message *msg;

	assert(sizeof(*msg) == client->communication.inbound.buffer.size);
	msg = (const struct lttng_notification_channel_message *)
			      client->communication.inbound.buffer.data;

	if (msg->size == 0 ||
			msg->size > DEFAULT_MAX_NOTIFICATION_CLIENT_MESSAGE_PAYLOAD_SIZE) {
		ERR("[notification-thread] Invalid notification channel message: length = %u",
				msg->size);
		ret = -1;
		goto end;
	}

	switch (msg->type) {
	case LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_SUBSCRIBE:
	case LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_UNSUBSCRIBE:
	case LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_HANDSHAKE:
		break;
	default:
		ret = -1;
		ERR("[notification-thread] Invalid notification channel message: unexpected message type");
		goto end;
	}

	client->communication.inbound.bytes_to_receive = msg->size;
	client->communication.inbound.msg_type =
			(enum lttng_notification_channel_message_type) msg->type;
	ret = lttng_dynamic_buffer_set_size(
			&client->communication.inbound.buffer, msg->size);
end:
	pthread_mutex_unlock(&client->lock);
	return ret;
}

static
int client_handle_message_handshake(struct notification_client *client,
		struct notification_thread_state *state)
{
	int ret;
	struct lttng_notification_channel_command_handshake *handshake_client;
	const struct lttng_notification_channel_command_handshake handshake_reply = {
			.major = LTTNG_NOTIFICATION_CHANNEL_VERSION_MAJOR,
			.minor = LTTNG_NOTIFICATION_CHANNEL_VERSION_MINOR,
	};
	const struct lttng_notification_channel_message msg_header = {
			.type = LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_HANDSHAKE,
			.size = sizeof(handshake_reply),
	};
	enum lttng_notification_channel_status status =
			LTTNG_NOTIFICATION_CHANNEL_STATUS_OK;
	char send_buffer[sizeof(msg_header) + sizeof(handshake_reply)];

	pthread_mutex_lock(&client->lock);

	memcpy(send_buffer, &msg_header, sizeof(msg_header));
	memcpy(send_buffer + sizeof(msg_header), &handshake_reply,
			sizeof(handshake_reply));

	handshake_client =
			(struct lttng_notification_channel_command_handshake *)
					client->communication.inbound.buffer
							.data;
	client->major = handshake_client->major;
	client->minor = handshake_client->minor;
	if (!client->communication.inbound.creds_received) {
		ERR("[notification-thread] No credentials received from client");
		ret = -1;
		goto end;
	}

	client->uid = LTTNG_SOCK_GET_UID_CRED(
			&client->communication.inbound.creds);
	client->gid = LTTNG_SOCK_GET_GID_CRED(
			&client->communication.inbound.creds);
	DBG("[notification-thread] Received handshake from client (uid = %u, gid = %u) with version %i.%i",
			client->uid, client->gid, (int) client->major,
			(int) client->minor);

	if (handshake_client->major !=
			LTTNG_NOTIFICATION_CHANNEL_VERSION_MAJOR) {
		status = LTTNG_NOTIFICATION_CHANNEL_STATUS_UNSUPPORTED_VERSION;
	}

	ret = lttng_dynamic_buffer_append(
			&client->communication.outbound.buffer, send_buffer,
			sizeof(send_buffer));
	if (ret) {
		ERR("[notification-thread] Failed to send protocol version to notification channel client");
		goto end;
	}

	client->validated = true;
	client->communication.active = true;

	ret = client_flush_outgoing_queue(client, state);
	if (ret) {
		goto end;
	}

	ret = client_send_command_reply(client, state, status);
	if (ret) {
		ERR("[notification-thread] Failed to send reply to notification channel client");
		goto end;
	}

	/* Set reception state to receive the next message header. */
	ret = client_reset_inbound_state(client);
	if (ret) {
		ERR("[notification-thread] Failed to reset client communication's inbound state");
		goto end;
	}

end:
	pthread_mutex_unlock(&client->lock);
	return ret;
}

static
int client_handle_message_subscription(
		struct notification_client *client,
		enum lttng_notification_channel_message_type msg_type,
		struct notification_thread_state *state)
{
	int ret;
	struct lttng_condition *condition;
	enum lttng_notification_channel_status status =
			LTTNG_NOTIFICATION_CHANNEL_STATUS_OK;
	struct lttng_payload_view condition_view =
			lttng_payload_view_from_dynamic_buffer(
					&client->communication.inbound.buffer,
					0, -1);
	size_t expected_condition_size;

	pthread_mutex_lock(&client->lock);
	expected_condition_size = client->communication.inbound.buffer.size;
	pthread_mutex_unlock(&client->lock);

	ret = lttng_condition_create_from_payload(&condition_view, &condition);
	if (ret != expected_condition_size) {
		ERR("[notification-thread] Malformed condition received from client");
		goto end;
	}

	if (msg_type == LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_SUBSCRIBE) {
		ret = notification_thread_client_subscribe(
				client, condition, state, &status);
	} else {
		ret = notification_thread_client_unsubscribe(
				client, condition, state, &status);
	}
	if (ret) {
		goto end;
	}

	pthread_mutex_lock(&client->lock);
	ret = client_send_command_reply(client, state, status);
	if (ret) {
		ERR("[notification-thread] Failed to send reply to notification channel client");
		goto end_unlock;
	}

	/* Set reception state to receive the next message header. */
	ret = client_reset_inbound_state(client);
	if (ret) {
		ERR("[notification-thread] Failed to reset client communication's inbound state");
		goto end_unlock;
	}

end_unlock:
	pthread_mutex_unlock(&client->lock);
end:
	return ret;
}

static
int client_dispatch_message(struct notification_client *client,
		struct notification_thread_state *state)
{
	int ret = 0;

	if (client->communication.inbound.msg_type !=
			LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_HANDSHAKE &&
			client->communication.inbound.msg_type !=
				LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_UNKNOWN &&
			!client->validated) {
		WARN("[notification-thread] client attempted a command before handshake");
		ret = -1;
		goto end;
	}

	switch (client->communication.inbound.msg_type) {
	case LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_UNKNOWN:
	{
		ret = client_handle_message_unknown(client, state);
		break;
	}
	case LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_HANDSHAKE:
	{
		ret = client_handle_message_handshake(client, state);
		break;
	}
	case LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_SUBSCRIBE:
	case LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_UNSUBSCRIBE:
	{
		ret = client_handle_message_subscription(client,
				client->communication.inbound.msg_type, state);
		break;
	}
	default:
		abort();
	}
end:
	return ret;
}

/* Incoming data from client. */
int handle_notification_thread_client_in(
		struct notification_thread_state *state, int socket)
{
	int ret = 0;
	struct notification_client *client;
	ssize_t recv_ret;
	size_t offset;
	bool message_is_complete = false;

	client = get_client_from_socket(socket, state);
	if (!client) {
		/* Internal error, abort. */
		ret = -1;
		goto end;
	}

	pthread_mutex_lock(&client->lock);
	offset = client->communication.inbound.buffer.size -
			client->communication.inbound.bytes_to_receive;
	if (client->communication.inbound.expect_creds) {
		recv_ret = lttcomm_recv_creds_unix_sock(socket,
				client->communication.inbound.buffer.data + offset,
				client->communication.inbound.bytes_to_receive,
				&client->communication.inbound.creds);
		if (recv_ret > 0) {
			client->communication.inbound.expect_creds = false;
			client->communication.inbound.creds_received = true;
		}
	} else {
		recv_ret = lttcomm_recv_unix_sock_non_block(socket,
				client->communication.inbound.buffer.data + offset,
				client->communication.inbound.bytes_to_receive);
	}
	if (recv_ret >= 0) {
		client->communication.inbound.bytes_to_receive -= recv_ret;
		message_is_complete = client->communication.inbound
						      .bytes_to_receive == 0;
	}
	pthread_mutex_unlock(&client->lock);
	if (recv_ret < 0) {
		goto error_disconnect_client;
	}

	if (message_is_complete) {
		ret = client_dispatch_message(client, state);
		if (ret) {
			/*
			 * Only returns an error if this client must be
			 * disconnected.
			 */
			goto error_disconnect_client;
		}
	}
end:
	return ret;
error_disconnect_client:
	pthread_mutex_lock(&client->lock);
	ret = notification_thread_client_disconnect(client, state);
	pthread_mutex_unlock(&client->lock);
	return ret;
}

/* Client ready to receive outgoing data. */
int handle_notification_thread_client_out(
		struct notification_thread_state *state, int socket)
{
	int ret;
	struct notification_client *client;

	client = get_client_from_socket(socket, state);
	if (!client) {
		/* Internal error, abort. */
		ret = -1;
		goto end;
	}

	pthread_mutex_lock(&client->lock);
	ret = client_flush_outgoing_queue(client, state);
	pthread_mutex_unlock(&client->lock);
	if (ret) {
		goto end;
	}
end:
	return ret;
}

static
bool evaluate_buffer_usage_condition(const struct lttng_condition *condition,
		const struct channel_state_sample *sample,
		uint64_t buffer_capacity)
{
	bool result = false;
	uint64_t threshold;
	enum lttng_condition_type condition_type;
	const struct lttng_condition_buffer_usage *use_condition = container_of(
			condition, struct lttng_condition_buffer_usage,
			parent);

	if (use_condition->threshold_bytes.set) {
		threshold = use_condition->threshold_bytes.value;
	} else {
		/*
		 * Threshold was expressed as a ratio.
		 *
		 * TODO the threshold (in bytes) of conditions expressed
		 * as a ratio of total buffer size could be cached to
		 * forego this double-multiplication or it could be performed
		 * as fixed-point math.
		 *
		 * Note that caching should accommodates the case where the
		 * condition applies to multiple channels (i.e. don't assume
		 * that all channels matching my_chann* have the same size...)
		 */
		threshold = (uint64_t) (use_condition->threshold_ratio.value *
				(double) buffer_capacity);
	}

	condition_type = lttng_condition_get_type(condition);
	if (condition_type == LTTNG_CONDITION_TYPE_BUFFER_USAGE_LOW) {
		DBG("[notification-thread] Low buffer usage condition being evaluated: threshold = %" PRIu64 ", highest usage = %" PRIu64,
				threshold, sample->highest_usage);

		/*
		 * The low condition should only be triggered once _all_ of the
		 * streams in a channel have gone below the "low" threshold.
		 */
		if (sample->highest_usage <= threshold) {
			result = true;
		}
	} else {
		DBG("[notification-thread] High buffer usage condition being evaluated: threshold = %" PRIu64 ", highest usage = %" PRIu64,
				threshold, sample->highest_usage);

		/*
		 * For high buffer usage scenarios, we want to trigger whenever
		 * _any_ of the streams has reached the "high" threshold.
		 */
		if (sample->highest_usage >= threshold) {
			result = true;
		}
	}

	return result;
}

static
bool evaluate_session_consumed_size_condition(
		const struct lttng_condition *condition,
		uint64_t session_consumed_size)
{
	uint64_t threshold;
	const struct lttng_condition_session_consumed_size *size_condition =
			container_of(condition,
				struct lttng_condition_session_consumed_size,
				parent);

	threshold = size_condition->consumed_threshold_bytes.value;
	DBG("[notification-thread] Session consumed size condition being evaluated: threshold = %" PRIu64 ", current size = %" PRIu64,
			threshold, session_consumed_size);
	return session_consumed_size >= threshold;
}

static
int evaluate_buffer_condition(const struct lttng_condition *condition,
		struct lttng_evaluation **evaluation,
		const struct notification_thread_state *state,
		const struct channel_state_sample *previous_sample,
		const struct channel_state_sample *latest_sample,
		uint64_t previous_session_consumed_total,
		uint64_t latest_session_consumed_total,
		struct channel_info *channel_info)
{
	int ret = 0;
	enum lttng_condition_type condition_type;
	const bool previous_sample_available = !!previous_sample;
	bool previous_sample_result = false;
	bool latest_sample_result;

	condition_type = lttng_condition_get_type(condition);

	switch (condition_type) {
	case LTTNG_CONDITION_TYPE_BUFFER_USAGE_LOW:
	case LTTNG_CONDITION_TYPE_BUFFER_USAGE_HIGH:
		if (caa_likely(previous_sample_available)) {
			previous_sample_result =
				evaluate_buffer_usage_condition(condition,
					previous_sample, channel_info->capacity);
		}
		latest_sample_result = evaluate_buffer_usage_condition(
				condition, latest_sample,
				channel_info->capacity);
		break;
	case LTTNG_CONDITION_TYPE_SESSION_CONSUMED_SIZE:
		if (caa_likely(previous_sample_available)) {
			previous_sample_result =
				evaluate_session_consumed_size_condition(
					condition,
					previous_session_consumed_total);
		}
		latest_sample_result =
				evaluate_session_consumed_size_condition(
					condition,
					latest_session_consumed_total);
		break;
	default:
		/* Unknown condition type; internal error. */
		abort();
	}

	if (!latest_sample_result ||
			(previous_sample_result == latest_sample_result)) {
		/*
		 * Only trigger on a condition evaluation transition.
		 *
		 * NOTE: This edge-triggered logic may not be appropriate for
		 * future condition types.
		 */
		goto end;
	}

	if (!evaluation || !latest_sample_result) {
		goto end;
	}

	switch (condition_type) {
	case LTTNG_CONDITION_TYPE_BUFFER_USAGE_LOW:
	case LTTNG_CONDITION_TYPE_BUFFER_USAGE_HIGH:
		*evaluation = lttng_evaluation_buffer_usage_create(
				condition_type,
				latest_sample->highest_usage,
				channel_info->capacity);
		break;
	case LTTNG_CONDITION_TYPE_SESSION_CONSUMED_SIZE:
		*evaluation = lttng_evaluation_session_consumed_size_create(
				latest_session_consumed_total);
		break;
	default:
		abort();
	}

	if (!*evaluation) {
		ret = -1;
		goto end;
	}
end:
	return ret;
}

static
int client_enqueue_dropped_notification(struct notification_client *client)
{
	int ret;
	struct lttng_notification_channel_message msg = {
		.type = (int8_t) LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_NOTIFICATION_DROPPED,
		.size = 0,
	};

	ASSERT_LOCKED(client->lock);

	ret = lttng_dynamic_buffer_append(
			&client->communication.outbound.buffer, &msg,
			sizeof(msg));
	return ret;
}

/*
 * Permission checks relative to notification channel clients are performed
 * here. Notice how object, client, and trigger credentials are involved in
 * this check.
 *
 * The `object` credentials are the credentials associated with the "subject"
 * of a condition. For instance, a `rotation completed` condition applies
 * to a session. When that condition is met, it will produce an evaluation
 * against a session. Hence, in this case, the `object` credentials are the
 * credentials of the "subject" session.
 *
 * The `trigger` credentials are the credentials of the user that registered the
 * trigger.
 *
 * The `client` credentials are the credentials of the user that created a given
 * notification channel.
 *
 * In terms of visibility, it is expected that non-privilieged users can only
 * register triggers against "their" objects (their own sessions and
 * applications they are allowed to interact with). They can then open a
 * notification channel and subscribe to notifications associated with those
 * triggers.
 *
 * As for privilieged users, they can register triggers against the objects of
 * other users. They can then subscribe to the notifications associated to their
 * triggers. Privilieged users _can't_ subscribe to the notifications of
 * triggers owned by other users; they must create their own triggers.
 *
 * This is more a concern of usability than security. It would be difficult for
 * a root user reliably subscribe to a specific set of conditions without
 * interference from external users (those could, for instance, unregister
 * their triggers).
 */
static
int send_evaluation_to_clients(const struct lttng_trigger *trigger,
		const struct lttng_evaluation *evaluation,
		struct notification_client_list* client_list,
		struct notification_thread_state *state,
		uid_t object_uid, gid_t object_gid)
{
	int ret = 0;
	struct lttng_payload msg_payload;
	struct notification_client_list_element *client_list_element, *tmp;
	const struct lttng_notification notification = {
		.condition = (struct lttng_condition *) lttng_trigger_get_const_condition(trigger),
		.evaluation = (struct lttng_evaluation *) evaluation,
	};
	struct lttng_notification_channel_message msg_header = {
		.type = (int8_t) LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_NOTIFICATION,
	};
	const struct lttng_credentials *trigger_creds = lttng_trigger_get_credentials(trigger);

	lttng_payload_init(&msg_payload);

	ret = lttng_dynamic_buffer_append(&msg_payload.buffer, &msg_header,
			sizeof(msg_header));
	if (ret) {
		goto end;
	}

	ret = lttng_notification_serialize(&notification, &msg_payload);
	if (ret) {
		ERR("[notification-thread] Failed to serialize notification");
		ret = -1;
		goto end;
	}

	/* Update payload size. */
	((struct lttng_notification_channel_message *) msg_payload.buffer.data)
			->size = (uint32_t)(
			msg_payload.buffer.size - sizeof(msg_header));

	pthread_mutex_lock(&client_list->lock);
	cds_list_for_each_entry_safe(client_list_element, tmp,
			&client_list->list, node) {
		struct notification_client *client =
				client_list_element->client;

		ret = 0;
		pthread_mutex_lock(&client->lock);
		if (client->uid != object_uid && client->gid != object_gid &&
				client->uid != 0) {
			/* Client is not allowed to monitor this channel. */
			DBG("[notification-thread] Skipping client at it does not have the object permission to receive notification for this trigger");
			goto unlock_client;
		}

		if (client->uid != trigger_creds->uid && client->gid != trigger_creds->gid) {
			DBG("[notification-thread] Skipping client at it does not have the permission to receive notification for this trigger");
			goto unlock_client;
		}

		DBG("[notification-thread] Sending notification to client (fd = %i, %zu bytes)",
				client->socket, msg_payload.buffer.size);
		if (client->communication.outbound.buffer.size) {
			/*
			 * Outgoing data is already buffered for this client;
			 * drop the notification and enqueue a "dropped
			 * notification" message if this is the first dropped
			 * notification since the socket spilled-over to the
			 * queue.
			 */
			DBG("[notification-thread] Dropping notification addressed to client (socket fd = %i)",
					client->socket);
			if (!client->communication.outbound.dropped_notification) {
				client->communication.outbound.dropped_notification = true;
				ret = client_enqueue_dropped_notification(
						client);
				if (ret) {
					goto unlock_client;
				}
			}
			goto unlock_client;
		}

		ret = lttng_dynamic_buffer_append_buffer(
				&client->communication.outbound.buffer,
				&msg_payload.buffer);
		if (ret) {
			goto unlock_client;
		}

		ret = client_flush_outgoing_queue(client, state);
		if (ret) {
			goto unlock_client;
		}
unlock_client:
		pthread_mutex_unlock(&client->lock);
		if (ret) {
			goto end_unlock_list;
		}
	}
	ret = 0;

end_unlock_list:
	pthread_mutex_unlock(&client_list->lock);
end:
	lttng_payload_reset(&msg_payload);
	return ret;
}

int handle_notification_thread_channel_sample(
		struct notification_thread_state *state, int pipe,
		enum lttng_domain_type domain)
{
	int ret = 0;
	struct lttcomm_consumer_channel_monitor_msg sample_msg;
	struct channel_info *channel_info;
	struct cds_lfht_node *node;
	struct cds_lfht_iter iter;
	struct lttng_channel_trigger_list *trigger_list;
	struct lttng_trigger_list_element *trigger_list_element;
	bool previous_sample_available = false;
	struct channel_state_sample previous_sample, latest_sample;
	uint64_t previous_session_consumed_total, latest_session_consumed_total;

	/*
	 * The monitoring pipe only holds messages smaller than PIPE_BUF,
	 * ensuring that read/write of sampling messages are atomic.
	 */
	ret = lttng_read(pipe, &sample_msg, sizeof(sample_msg));
	if (ret != sizeof(sample_msg)) {
		ERR("[notification-thread] Failed to read from monitoring pipe (fd = %i)",
				pipe);
		ret = -1;
		goto end;
	}

	ret = 0;
	latest_sample.key.key = sample_msg.key;
	latest_sample.key.domain = domain;
	latest_sample.highest_usage = sample_msg.highest;
	latest_sample.lowest_usage = sample_msg.lowest;
	latest_sample.channel_total_consumed = sample_msg.total_consumed;

	rcu_read_lock();

	/* Retrieve the channel's informations */
	cds_lfht_lookup(state->channels_ht,
			hash_channel_key(&latest_sample.key),
			match_channel_info,
			&latest_sample.key,
			&iter);
	node = cds_lfht_iter_get_node(&iter);
	if (caa_unlikely(!node)) {
		/*
		 * Not an error since the consumer can push a sample to the pipe
		 * and the rest of the session daemon could notify us of the
		 * channel's destruction before we get a chance to process that
		 * sample.
		 */
		DBG("[notification-thread] Received a sample for an unknown channel from consumerd, key = %" PRIu64 " in %s domain",
				latest_sample.key.key,
				domain == LTTNG_DOMAIN_KERNEL ? "kernel" :
					"user space");
		goto end_unlock;
	}
	channel_info = caa_container_of(node, struct channel_info,
			channels_ht_node);
	DBG("[notification-thread] Handling channel sample for channel %s (key = %" PRIu64 ") in session %s (highest usage = %" PRIu64 ", lowest usage = %" PRIu64", total consumed = %" PRIu64")",
			channel_info->name,
			latest_sample.key.key,
			channel_info->session_info->name,
			latest_sample.highest_usage,
			latest_sample.lowest_usage,
			latest_sample.channel_total_consumed);

	previous_session_consumed_total =
			channel_info->session_info->consumed_data_size;

	/* Retrieve the channel's last sample, if it exists, and update it. */
	cds_lfht_lookup(state->channel_state_ht,
			hash_channel_key(&latest_sample.key),
			match_channel_state_sample,
			&latest_sample.key,
			&iter);
	node = cds_lfht_iter_get_node(&iter);
	if (caa_likely(node)) {
		struct channel_state_sample *stored_sample;

		/* Update the sample stored. */
		stored_sample = caa_container_of(node,
				struct channel_state_sample,
				channel_state_ht_node);

		memcpy(&previous_sample, stored_sample,
				sizeof(previous_sample));
		stored_sample->highest_usage = latest_sample.highest_usage;
		stored_sample->lowest_usage = latest_sample.lowest_usage;
		stored_sample->channel_total_consumed = latest_sample.channel_total_consumed;
		previous_sample_available = true;

		latest_session_consumed_total =
				previous_session_consumed_total +
				(latest_sample.channel_total_consumed - previous_sample.channel_total_consumed);
	} else {
		/*
		 * This is the channel's first sample, allocate space for and
		 * store the new sample.
		 */
		struct channel_state_sample *stored_sample;

		stored_sample = zmalloc(sizeof(*stored_sample));
		if (!stored_sample) {
			ret = -1;
			goto end_unlock;
		}

		memcpy(stored_sample, &latest_sample, sizeof(*stored_sample));
		cds_lfht_node_init(&stored_sample->channel_state_ht_node);
		cds_lfht_add(state->channel_state_ht,
				hash_channel_key(&stored_sample->key),
				&stored_sample->channel_state_ht_node);

		latest_session_consumed_total =
				previous_session_consumed_total +
				latest_sample.channel_total_consumed;
	}

	channel_info->session_info->consumed_data_size =
			latest_session_consumed_total;

	/* Find triggers associated with this channel. */
	cds_lfht_lookup(state->channel_triggers_ht,
			hash_channel_key(&latest_sample.key),
			match_channel_trigger_list,
			&latest_sample.key,
			&iter);
	node = cds_lfht_iter_get_node(&iter);
	if (caa_likely(!node)) {
		goto end_unlock;
	}

	trigger_list = caa_container_of(node, struct lttng_channel_trigger_list,
			channel_triggers_ht_node);
	cds_list_for_each_entry(trigger_list_element, &trigger_list->list,
			node) {
		const struct lttng_condition *condition;
		const struct lttng_action *action;
		const struct lttng_trigger *trigger;
		struct notification_client_list *client_list = NULL;
		struct lttng_evaluation *evaluation = NULL;
		bool client_list_is_empty;

		ret = 0;
		trigger = trigger_list_element->trigger;
		condition = lttng_trigger_get_const_condition(trigger);
		assert(condition);
		action = lttng_trigger_get_const_action(trigger);

		/* Notify actions are the only type currently supported. */
		assert(lttng_action_get_type_const(action) ==
				LTTNG_ACTION_TYPE_NOTIFY);

		/*
		 * Check if any client is subscribed to the result of this
		 * evaluation.
		 */
		client_list = get_client_list_from_condition(state, condition);
		assert(client_list);
		client_list_is_empty = cds_list_empty(&client_list->list);
		if (client_list_is_empty) {
			/*
			 * No clients interested in the evaluation's result,
			 * skip it.
			 */
			goto put_list;
		}

		ret = evaluate_buffer_condition(condition, &evaluation, state,
				previous_sample_available ? &previous_sample : NULL,
				&latest_sample,
				previous_session_consumed_total,
				latest_session_consumed_total,
				channel_info);
		if (caa_unlikely(ret)) {
			goto put_list;
		}

		if (caa_likely(!evaluation)) {
			goto put_list;
		}

		/* Dispatch evaluation result to all clients. */
		ret = send_evaluation_to_clients(trigger_list_element->trigger,
				evaluation, client_list, state,
				channel_info->session_info->uid,
				channel_info->session_info->gid);
		lttng_evaluation_destroy(evaluation);
put_list:
		notification_client_list_put(client_list);
		if (caa_unlikely(ret)) {
			break;
		}
	}
end_unlock:
	rcu_read_unlock();
end:
	return ret;
}