Add the sessiond notification-handling subsystem
authorJérémie Galarneau <jeremie.galarneau@efficios.com>
Fri, 5 May 2017 03:17:39 +0000 (23:17 -0400)
committerJérémie Galarneau <jeremie.galarneau@efficios.com>
Fri, 5 May 2017 04:15:02 +0000 (00:15 -0400)
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
src/bin/lttng-sessiond/Makefile.am
src/bin/lttng-sessiond/health-sessiond.h
src/bin/lttng-sessiond/notification-thread-commands.c [new file with mode: 0644]
src/bin/lttng-sessiond/notification-thread-commands.h [new file with mode: 0644]
src/bin/lttng-sessiond/notification-thread-events.c [new file with mode: 0644]
src/bin/lttng-sessiond/notification-thread-events.h [new file with mode: 0644]
src/bin/lttng-sessiond/notification-thread.c [new file with mode: 0644]
src/bin/lttng-sessiond/notification-thread.h [new file with mode: 0644]

index 4238661397275622c9cf79a6c8a9b1d6982a9894..0ac7506b440dc825151c32db1bbeca862c70613c 100644 (file)
@@ -30,7 +30,10 @@ lttng_sessiond_SOURCES = utils.c utils.h \
                        agent.c agent.h \
                        save.h save.c \
                        load-session-thread.h load-session-thread.c \
-                       syscall.h syscall.c
+                       syscall.h syscall.c \
+                       notification-thread.h notification-thread.c \
+                       notification-thread-commands.h notification-thread-commands.c \
+                       notification-thread-events.h notification-thread-events.c
 
 if HAVE_LIBLTTNG_UST_CTL
 lttng_sessiond_SOURCES += trace-ust.c ust-registry.c ust-app.c \
index 22ea1bb3e6de87635b5623c8fff8c5dc6163531a..5d94cc639e2e77476dba2502db5b58e222b5491a 100644 (file)
@@ -29,6 +29,7 @@ enum health_type_sessiond {
        HEALTH_SESSIOND_TYPE_HT_CLEANUP         = 5,
        HEALTH_SESSIOND_TYPE_APP_MANAGE_NOTIFY  = 6,
        HEALTH_SESSIOND_TYPE_APP_REG_DISPATCH   = 7,
+       HEALTH_SESSIOND_TYPE_NOTIFICATION       = 8,
 
        NR_HEALTH_SESSIOND_TYPES,
 };
diff --git a/src/bin/lttng-sessiond/notification-thread-commands.c b/src/bin/lttng-sessiond/notification-thread-commands.c
new file mode 100644 (file)
index 0000000..5483a31
--- /dev/null
@@ -0,0 +1,181 @@
+/*
+ * Copyright (C) 2017 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License, version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include <lttng/trigger/trigger.h>
+#include <lttng/lttng-error.h>
+#include "notification-thread.h"
+#include "notification-thread-commands.h"
+#include <common/error.h>
+#include <common/futex.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <inttypes.h>
+
+static
+void init_notification_thread_command(struct notification_thread_command *cmd)
+{
+       memset(cmd, 0, sizeof(*cmd));
+       CDS_INIT_LIST_HEAD(&cmd->cmd_list_node);
+}
+
+static
+int run_command_wait(struct notification_thread_handle *handle,
+               struct notification_thread_command *cmd)
+{
+       int ret;
+       uint64_t notification_counter = 1;
+
+       futex_nto1_prepare(&cmd->reply_futex);
+
+       pthread_mutex_lock(&handle->cmd_queue.lock);
+       /* Add to queue. */
+       cds_list_add_tail(&cmd->cmd_list_node,
+                       &handle->cmd_queue.list);
+       /* Wake-up thread. */
+       ret = write(handle->cmd_queue.event_fd,
+                       &notification_counter, sizeof(notification_counter));
+       if (ret < 0) {
+               PERROR("write to notification thread's queue event fd");
+               /*
+                * Remove the command from the list so the notification
+                * thread does not process it.
+                */
+               cds_list_del(&cmd->cmd_list_node);
+               goto error_unlock_queue;
+       }
+       pthread_mutex_unlock(&handle->cmd_queue.lock);
+
+       futex_nto1_wait(&cmd->reply_futex);
+       return 0;
+error_unlock_queue:
+       pthread_mutex_unlock(&handle->cmd_queue.lock);
+       return -1;
+}
+
+enum lttng_error_code notification_thread_command_register_trigger(
+               struct notification_thread_handle *handle,
+               struct lttng_trigger *trigger)
+{
+       int ret;
+       enum lttng_error_code ret_code;
+       struct notification_thread_command cmd;
+
+       init_notification_thread_command(&cmd);
+
+       cmd.type = NOTIFICATION_COMMAND_TYPE_REGISTER_TRIGGER;
+       cmd.parameters.trigger = trigger;
+
+       ret = run_command_wait(handle, &cmd);
+       if (ret) {
+               ret_code = LTTNG_ERR_UNK;
+               goto end;
+       }
+       ret_code = cmd.reply_code;
+end:
+       return ret_code;
+}
+
+enum lttng_error_code notification_thread_command_unregister_trigger(
+               struct notification_thread_handle *handle,
+               struct lttng_trigger *trigger)
+{
+       int ret;
+       enum lttng_error_code ret_code;
+       struct notification_thread_command cmd;
+
+       init_notification_thread_command(&cmd);
+
+       cmd.type = NOTIFICATION_COMMAND_TYPE_UNREGISTER_TRIGGER;
+       cmd.parameters.trigger = trigger;
+
+       ret = run_command_wait(handle, &cmd);
+       if (ret) {
+               ret_code = LTTNG_ERR_UNK;
+               goto end;
+       }
+       ret_code = cmd.reply_code;
+end:
+       return ret_code;
+}
+
+enum lttng_error_code notification_thread_command_add_channel(
+               struct notification_thread_handle *handle,
+               char *session_name, uid_t uid, gid_t gid,
+               char *channel_name, uint64_t key,
+               enum lttng_domain_type domain, uint64_t capacity)
+{
+       int ret;
+       enum lttng_error_code ret_code;
+       struct notification_thread_command cmd;
+
+       init_notification_thread_command(&cmd);
+
+       cmd.type = NOTIFICATION_COMMAND_TYPE_ADD_CHANNEL;
+       cmd.parameters.add_channel.session_name = session_name;
+       cmd.parameters.add_channel.uid = uid;
+       cmd.parameters.add_channel.gid = gid;
+       cmd.parameters.add_channel.channel_name = channel_name;
+       cmd.parameters.add_channel.key.key = key;
+       cmd.parameters.add_channel.key.domain = domain;
+       cmd.parameters.add_channel.capacity = capacity;
+
+       ret = run_command_wait(handle, &cmd);
+       if (ret) {
+               ret_code = LTTNG_ERR_UNK;
+               goto end;
+       }
+       ret_code = cmd.reply_code;
+end:
+       return ret_code;
+}
+
+enum lttng_error_code notification_thread_command_remove_channel(
+               struct notification_thread_handle *handle,
+               uint64_t key, enum lttng_domain_type domain)
+{
+       int ret;
+       enum lttng_error_code ret_code;
+       struct notification_thread_command cmd;
+
+       init_notification_thread_command(&cmd);
+
+       cmd.type = NOTIFICATION_COMMAND_TYPE_REMOVE_CHANNEL;
+       cmd.parameters.remove_channel.key = key;
+       cmd.parameters.remove_channel.domain = domain;
+
+       ret = run_command_wait(handle, &cmd);
+       if (ret) {
+               ret_code = LTTNG_ERR_UNK;
+               goto end;
+       }
+       ret_code = cmd.reply_code;
+end:
+       return ret_code;
+}
+
+void notification_thread_command_quit(
+               struct notification_thread_handle *handle)
+{
+       int ret;
+       struct notification_thread_command cmd;
+
+       init_notification_thread_command(&cmd);
+
+       cmd.type = NOTIFICATION_COMMAND_TYPE_QUIT;
+       ret = run_command_wait(handle, &cmd);
+       assert(!ret && cmd.reply_code == LTTNG_OK);
+}
diff --git a/src/bin/lttng-sessiond/notification-thread-commands.h b/src/bin/lttng-sessiond/notification-thread-commands.h
new file mode 100644 (file)
index 0000000..fc7e90b
--- /dev/null
@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2017 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License, version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef NOTIFICATION_THREAD_COMMANDS_H
+#define NOTIFICATION_THREAD_COMMANDS_H
+
+#include <lttng/domain.h>
+#include <lttng/lttng-error.h>
+#include <urcu/rculfhash.h>
+#include "notification-thread.h"
+
+struct notification_thread_data;
+struct lttng_trigger;
+
+enum notification_thread_command_type {
+       NOTIFICATION_COMMAND_TYPE_REGISTER_TRIGGER,
+       NOTIFICATION_COMMAND_TYPE_UNREGISTER_TRIGGER,
+       NOTIFICATION_COMMAND_TYPE_ADD_CHANNEL,
+       NOTIFICATION_COMMAND_TYPE_REMOVE_CHANNEL,
+       NOTIFICATION_COMMAND_TYPE_QUIT,
+};
+
+struct channel_key {
+       uint64_t key;
+       enum lttng_domain_type domain;
+};
+
+struct channel_info {
+       struct channel_key key;
+       char *session_name;
+       uid_t uid;
+       gid_t gid;
+       char *channel_name;
+       uint64_t capacity;
+       struct cds_lfht_node channels_ht_node;
+};
+
+struct notification_thread_command {
+       struct cds_list_head cmd_list_node;
+
+       enum notification_thread_command_type type;
+       union {
+               /* Register/Unregister trigger. */
+               struct lttng_trigger *trigger;
+               /* Add channel. */
+               struct channel_info add_channel;
+               /* Remove channel. */
+               struct {
+                       uint64_t key;
+                       enum lttng_domain_type domain;
+               } remove_channel;
+       } parameters;
+
+       /* Futex on which to wait for command reply (optional). */
+       int32_t reply_futex;
+       enum lttng_error_code reply_code;
+};
+
+enum lttng_error_code notification_thread_command_register_trigger(
+               struct notification_thread_handle *handle,
+               struct lttng_trigger *trigger);
+
+enum lttng_error_code notification_thread_command_unregister_trigger(
+               struct notification_thread_handle *handle,
+               struct lttng_trigger *trigger);
+
+enum lttng_error_code notification_thread_command_add_channel(
+               struct notification_thread_handle *handle,
+               char *session_name, uid_t uid, gid_t gid,
+               char *channel_name, uint64_t key,
+               enum lttng_domain_type domain, uint64_t capacity);
+
+enum lttng_error_code notification_thread_command_remove_channel(
+               struct notification_thread_handle *handle,
+               uint64_t key, enum lttng_domain_type domain);
+
+void notification_thread_command_quit(
+               struct notification_thread_handle *handle);
+
+#endif /* NOTIFICATION_THREAD_COMMANDS_H */
diff --git a/src/bin/lttng-sessiond/notification-thread-events.c b/src/bin/lttng-sessiond/notification-thread-events.c
new file mode 100644 (file)
index 0000000..7de6595
--- /dev/null
@@ -0,0 +1,2113 @@
+/*
+ * Copyright (C) 2017 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License, version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#define _LGPL_SOURCE
+#include <urcu.h>
+#include <urcu/rculfhash.h>
+
+#include "notification-thread.h"
+#include "notification-thread-events.h"
+#include "notification-thread-commands.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.h>
+#include <lttng/notification/notification-internal.h>
+#include <lttng/condition/condition-internal.h>
+#include <lttng/condition/buffer-usage-internal.h>
+#include <lttng/notification/channel-internal.h>
+#include <time.h>
+#include <unistd.h>
+#include <assert.h>
+#include <inttypes.h>
+
+#define CLIENT_POLL_MASK_IN (LPOLLIN | LPOLLERR | LPOLLHUP | LPOLLRDHUP)
+#define CLIENT_POLL_MASK_IN_OUT (CLIENT_POLL_MASK_IN | LPOLLOUT)
+
+struct lttng_trigger_list_element {
+       struct lttng_trigger *trigger;
+       struct cds_list_head node;
+};
+
+struct lttng_channel_trigger_list {
+       struct channel_key channel_key;
+       struct cds_list_head list;
+       struct cds_lfht_node channel_triggers_ht_node;
+};
+
+struct lttng_trigger_ht_element {
+       struct lttng_trigger *trigger;
+       struct cds_lfht_node 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;
+};
+
+struct notification_client_list {
+       struct lttng_trigger *trigger;
+       struct cds_list_head list;
+       struct cds_lfht_node notification_trigger_ht_node;
+};
+
+struct notification_client {
+       int socket;
+       /* Client protocol version. */
+       uint8_t major, minor;
+       uid_t uid;
+       gid_t gid;
+       /*
+        * Indicates if the credentials and versions of the client has 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 {
+               struct {
+                       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 receive_creds;
+                       /*
+                        * Indicates whether or not credentials were received
+                        * from the client.
+                        */
+                       bool creds_received;
+                       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;
+};
+
+struct channel_state_sample {
+       struct channel_key key;
+       struct cds_lfht_node channel_state_ht_node;
+       uint64_t highest_usage;
+       uint64_t lowest_usage;
+};
+
+static
+int match_client(struct cds_lfht_node *node, const void *key)
+{
+       /* This double-cast is intended to supress pointer-to-cast warning. */
+       int socket = (int) (intptr_t) key;
+       struct notification_client *client;
+
+       client = caa_container_of(node, struct notification_client,
+                       client_socket_ht_node);
+
+       return !!(client->socket == socket);
+}
+
+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_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(struct cds_lfht_node *node, const void *key)
+{
+       struct lttng_trigger *trigger_key = (struct lttng_trigger *) key;
+       struct notification_client_list *client_list;
+       struct lttng_condition *condition;
+       struct lttng_condition *condition_key = lttng_trigger_get_condition(
+                       trigger_key);
+
+       assert(condition_key);
+
+       client_list = caa_container_of(node, struct notification_client_list,
+                       notification_trigger_ht_node);
+       condition = lttng_trigger_get_condition(client_list->trigger);
+
+       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;
+       struct lttng_condition *condition;
+
+       assert(condition_key);
+
+       client_list = caa_container_of(node, struct notification_client_list,
+                       notification_trigger_ht_node);
+       condition = lttng_trigger_get_condition(client_list->trigger);
+
+       return !!lttng_condition_is_equal(condition_key, condition);
+}
+
+static
+unsigned long lttng_condition_buffer_usage_hash(
+       struct lttng_condition *_condition)
+{
+       unsigned long hash = 0;
+       struct lttng_condition_buffer_usage *condition;
+
+       condition = container_of(_condition,
+                       struct lttng_condition_buffer_usage, parent);
+
+       if (condition->session_name) {
+               hash ^= hash_key_str(condition->session_name, lttng_ht_seed);
+       }
+       if (condition->channel_name) {
+               hash ^= hash_key_str(condition->session_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_ratio.set) {
+               uint64_t val;
+
+               val = condition->threshold_bytes.value;
+               hash ^= hash_key_u64(&val, 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(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);
+       default:
+               ERR("[notification-thread] Unexpected condition type caught");
+               abort();
+       }
+}
+
+static
+void channel_info_destroy(struct channel_info *channel_info)
+{
+       if (!channel_info) {
+               return;
+       }
+
+       if (channel_info->session_name) {
+               free(channel_info->session_name);
+       }
+       if (channel_info->channel_name) {
+               free(channel_info->channel_name);
+       }
+       free(channel_info);
+}
+
+static
+struct channel_info *channel_info_copy(struct channel_info *channel_info)
+{
+       struct channel_info *copy = zmalloc(sizeof(*channel_info));
+
+       assert(channel_info);
+       assert(channel_info->session_name);
+       assert(channel_info->channel_name);
+
+       if (!copy) {
+               goto end;
+       }
+
+       memcpy(copy, channel_info, sizeof(*channel_info));
+       copy->session_name = NULL;
+       copy->channel_name = NULL;
+
+       copy->session_name = strdup(channel_info->session_name);
+       if (!copy->session_name) {
+               goto error;
+       }
+       copy->channel_name = strdup(channel_info->channel_name);
+       if (!copy->channel_name) {
+               goto error;
+       }
+       cds_lfht_node_init(&channel_info->channels_ht_node);
+end:
+       return copy;
+error:
+       channel_info_destroy(copy);
+       return NULL;
+}
+
+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 cds_lfht_iter iter;
+       struct cds_lfht_node *node;
+       struct notification_client_list *client_list;
+       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;
+       }
+
+       rcu_read_lock();
+
+       /*
+        * 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);
+
+       /*
+        * Add the client to the list of clients interested in a given trigger
+        * if a "notification" trigger with a corresponding condition was
+        * added prior.
+        */
+       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) {
+               goto end_unlock;
+       }
+
+       client_list = caa_container_of(node, struct notification_client_list,
+                       notification_trigger_ht_node);
+       client_list_element->client = client;
+       CDS_INIT_LIST_HEAD(&client_list_element->node);
+       cds_list_add(&client_list_element->node, &client_list->list);
+end_unlock:
+       rcu_read_unlock();
+end:
+       if (_status) {
+               *_status = status;
+       }
+       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 cds_lfht_iter iter;
+       struct cds_lfht_node *node;
+       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.
+        */
+       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) {
+               goto end_unlock;
+       }
+
+       client_list = caa_container_of(node, struct notification_client_list,
+                       notification_trigger_ht_node);
+       cds_list_for_each_entry_safe(client_list_element, client_tmp,
+                       &client_list->list, node) {
+               if (client_list_element->client->socket != client->socket) {
+                       continue;
+               }
+               cds_list_del(&client_list_element->node);
+               free(client_list_element);
+               break;
+       }
+end_unlock:
+       rcu_read_unlock();
+end:
+       lttng_condition_destroy(condition);
+       if (_status) {
+               *_status = status;
+       }
+       return 0;
+}
+
+static
+void notification_client_destroy(struct notification_client *client,
+               struct notification_thread_state *state)
+{
+       struct lttng_condition_list_element *condition_list_element, *tmp;
+
+       if (!client) {
+               return;
+       }
+
+       /* 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);
+       }
+
+       if (client->socket >= 0) {
+               (void) lttcomm_close_unix_sock(client->socket);
+       }
+       lttng_dynamic_buffer_reset(&client->communication.inbound.buffer);
+       lttng_dynamic_buffer_reset(&client->communication.outbound.buffer);
+       free(client);
+}
+
+/*
+ * 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_key_ulong((void *) (unsigned long) socket, lttng_ht_seed),
+                       match_client,
+                       (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 trigger_applies_to_channel(struct lttng_trigger *trigger,
+               struct channel_info *info)
+{
+       enum lttng_condition_status status;
+       struct lttng_condition *condition;
+       const char *trigger_session_name = NULL;
+       const char *trigger_channel_name = NULL;
+       enum lttng_domain_type trigger_domain;
+
+       condition = lttng_trigger_get_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:
+               break;
+       default:
+               goto fail;
+       }
+
+       status = lttng_condition_buffer_usage_get_domain_type(condition,
+                       &trigger_domain);
+       assert(status == LTTNG_CONDITION_STATUS_OK);
+       if (info->key.domain != trigger_domain) {
+               goto fail;
+       }
+
+       status = lttng_condition_buffer_usage_get_session_name(
+                       condition, &trigger_session_name);
+       assert((status == LTTNG_CONDITION_STATUS_OK) && trigger_session_name);
+
+       status = lttng_condition_buffer_usage_get_channel_name(
+                       condition, &trigger_channel_name);
+       assert((status == LTTNG_CONDITION_STATUS_OK) && trigger_channel_name);
+
+       if (strcmp(info->session_name, trigger_session_name)) {
+               goto fail;
+       }
+       if (strcmp(info->channel_name, trigger_channel_name)) {
+               goto fail;
+       }
+
+       return true;
+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;
+}
+
+static
+unsigned long hash_channel_key(struct channel_key *key)
+{
+       return hash_key_u64(&key->key, lttng_ht_seed) ^ hash_key_ulong(
+               (void *) (unsigned long) key->domain, lttng_ht_seed);
+}
+
+static
+int handle_notification_thread_command_add_channel(
+       struct notification_thread_state *state,
+       struct channel_info *channel_info,
+       enum lttng_error_code *cmd_result)
+{
+       struct cds_list_head trigger_list;
+       struct channel_info *new_channel_info;
+       struct channel_key *channel_key;
+       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;
+
+       DBG("[notification-thread] Adding channel %s from session %s, channel key = %" PRIu64 " in %s domain",
+                       channel_info->channel_name, channel_info->session_name,
+                       channel_info->key.key, channel_info->key.domain == LTTNG_DOMAIN_KERNEL ? "kernel" : "user space");
+
+       CDS_INIT_LIST_HEAD(&trigger_list);
+
+       new_channel_info = channel_info_copy(channel_info);
+       if (!new_channel_info) {
+               goto error;
+       }
+
+       channel_key = &new_channel_info->key;
+
+       /* 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,
+                               channel_info)) {
+                       continue;
+               }
+
+               new_element = zmalloc(sizeof(*new_element));
+               if (!new_element) {
+                       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++;
+       }
+
+       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 = *channel_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(channel_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(channel_key),
+                       &channel_trigger_list->channel_triggers_ht_node);
+       rcu_read_unlock();
+       *cmd_result = LTTNG_OK;
+       return 0;
+error:
+       /* Empty trigger list */
+       channel_info_destroy(new_channel_info);
+       return 1;
+}
+
+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);
+       free(trigger_list);
+
+       /* 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);
+               free(sample);
+       }
+
+       /* 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;
+}
+
+/*
+ * 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:
+ *     - The client will succeed in registering the trigger, as it is valid,
+ *     - The trigger will, internally, be bound to the channel,
+ *     - The notifications will not be sent since the client's credentials
+ *       are checked against the channel at that moment.
+ */
+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;
+       struct channel_info *channel;
+       bool free_trigger = true;
+
+       rcu_read_lock();
+
+       condition = lttng_trigger_get_condition(trigger);
+       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 = zmalloc(sizeof(*client_list));
+       if (!client_list) {
+               ret = -1;
+               goto error_free_ht_element;
+       }
+       cds_lfht_node_init(&client_list->notification_trigger_ht_node);
+       CDS_INIT_LIST_HEAD(&client_list->list);
+       client_list->trigger = trigger;
+
+       /* 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_free_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);
+       }
+
+       cds_lfht_add(state->notification_trigger_clients_ht,
+                       lttng_condition_hash(condition),
+                       &client_list->notification_trigger_ht_node);
+       /*
+        * Client list ownership transferred to the
+        * notification_trigger_clients_ht.
+        */
+       client_list = NULL;
+
+       /*
+        * Add the trigger to list of triggers bound to the channels currently
+        * known.
+        */
+       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;
+
+               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,
+                               &iter);
+               node = cds_lfht_iter_get_node(&iter);
+               assert(node);
+               /* Free the list of triggers associated with this channel. */
+               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 error_free_client_list;
+               }
+               CDS_INIT_LIST_HEAD(&trigger_list_element->node);
+               trigger_list_element->trigger = trigger;
+               cds_list_add(&trigger_list_element->node, &trigger_list->list);
+               /* A trigger can only apply to one channel. */
+               break;
+       }
+
+       *cmd_result = LTTNG_OK;
+error_free_client_list:
+       if (client_list) {
+               cds_list_for_each_entry_safe(client_list_element, tmp,
+                               &client_list->list, node) {
+                       free(client_list_element);
+               }
+               free(client_list);
+       }
+error_free_ht_element:
+       free(trigger_ht_element);
+error:
+       if (free_trigger) {
+               struct lttng_action *action = lttng_trigger_get_action(trigger);
+
+               lttng_condition_destroy(condition);
+               lttng_action_destroy(action);
+               lttng_trigger_destroy(trigger);
+       }
+       rcu_read_unlock();
+       return ret;
+}
+
+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 *node, *triggers_ht_node;
+       struct lttng_channel_trigger_list *trigger_list;
+       struct notification_client_list *client_list;
+       struct notification_client_list_element *client_list_element, *tmp;
+       struct lttng_trigger_ht_element *trigger_ht_element = NULL;
+       struct lttng_condition *condition = lttng_trigger_get_condition(
+                       trigger);
+       struct lttng_action *action;
+       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) {
+                       struct lttng_condition *current_condition =
+                                       lttng_trigger_get_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);
+               }
+       }
+
+       /*
+        * Remove and release the client list from
+        * notification_trigger_clients_ht.
+        */
+       cds_lfht_lookup(state->notification_trigger_clients_ht,
+                       lttng_condition_hash(condition),
+                       match_client_list,
+                       trigger,
+                       &iter);
+       node = cds_lfht_iter_get_node(&iter);
+       assert(node);
+       client_list = caa_container_of(node, struct notification_client_list,
+                       notification_trigger_ht_node);
+       cds_list_for_each_entry_safe(client_list_element, tmp,
+                       &client_list->list, node) {
+               free(client_list_element);
+       }
+       cds_lfht_del(state->notification_trigger_clients_ht, node);
+       free(client_list);
+
+       /* 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);
+
+       condition = lttng_trigger_get_condition(trigger_ht_element->trigger);
+       lttng_condition_destroy(condition);
+       action = lttng_trigger_get_action(trigger_ht_element->trigger);
+       lttng_action_destroy(action);
+       lttng_trigger_destroy(trigger_ht_element->trigger);
+       free(trigger_ht_element);
+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 event_fd to put it back into a quiescent state. */
+       ret = read(handle->cmd_queue.event_fd, &counter, sizeof(counter));
+       if (ret == -1) {
+               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,
+                               &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_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);
+       futex_nto1_wake(&cmd->reply_futex);
+       pthread_mutex_unlock(&handle->cmd_queue.lock);
+       return ret;
+error_unlock:
+       /* Wake-up and return a fatal error to the calling thread. */
+       futex_nto1_wake(&cmd->reply_futex);
+       pthread_mutex_unlock(&handle->cmd_queue.lock);
+       cmd->reply_code = LTTNG_ERR_FATAL;
+error:
+       /* Indicate a fatal error to the caller. */
+       return -1;
+}
+
+static
+unsigned long hash_client_socket(int socket)
+{
+       return hash_key_ulong((void *) (unsigned long) socket, lttng_ht_seed);
+}
+
+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;
+}
+
+static
+void client_reset_inbound_state(struct notification_client *client)
+{
+       int ret;
+
+       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;
+       client->communication.inbound.receive_creds = false;
+       LTTNG_SOCK_SET_UID_CRED(&client->communication.inbound.creds, -1);
+       LTTNG_SOCK_SET_GID_CRED(&client->communication.inbound.creds, -1);
+}
+
+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;
+       }
+       CDS_INIT_LIST_HEAD(&client->condition_list);
+       lttng_dynamic_buffer_init(&client->communication.inbound.buffer);
+       lttng_dynamic_buffer_init(&client->communication.outbound.buffer);
+       client_reset_inbound_state(client);
+
+       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);
+
+       /* Add to ht. */
+       rcu_read_lock();
+       cds_lfht_add(state->client_socket_ht,
+                       hash_client_socket(client->socket),
+                       &client->client_socket_ht_node);
+       rcu_read_unlock();
+
+       return ret;
+error:
+       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;
+       }
+
+       ret = lttng_poll_del(&state->events, client_socket);
+       if (ret) {
+               ERR("[notification-thread] Failed to remove client socket from poll set");
+       }
+        cds_lfht_del(state->client_socket_ht,
+                       &client->client_socket_ht_node);
+       notification_client_destroy(client, state);
+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;
+
+               ret = handle_notification_thread_client_disconnect(
+                               client->socket, state);
+               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_occured = false;
+       struct cds_lfht_iter iter;
+       struct lttng_trigger_ht_element *trigger_ht_element;
+
+       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_occured = true;
+               }
+       }
+       return error_occured ? -1 : 0;
+}
+
+static
+int client_flush_outgoing_queue(struct notification_client *client,
+               struct notification_thread_state *state)
+{
+       ssize_t ret;
+       size_t to_send_count;
+
+       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 && (errno == EAGAIN || errno == EWOULDBLOCK)) ||
+                       (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 = handle_notification_thread_client_disconnect(
+                               client->socket, 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;
+}
+
+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)];
+
+       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_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:
+       {
+               /*
+                * 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;
+               if (client->communication.inbound.msg_type ==
+                               LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_HANDSHAKE) {
+                       client->communication.inbound.receive_creds = true;
+               }
+               ret = lttng_dynamic_buffer_set_size(
+                               &client->communication.inbound.buffer, 0);
+               if (ret) {
+                       goto end;
+               }
+               break;
+       }
+       case LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_HANDSHAKE:
+       {
+               struct lttng_notification_channel_command_handshake *handshake_client;
+               struct lttng_notification_channel_command_handshake handshake_reply = {
+                       .major = LTTNG_NOTIFICATION_CHANNEL_VERSION_MAJOR,
+                       .minor = LTTNG_NOTIFICATION_CHANNEL_VERSION_MINOR,
+               };
+               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)];
+
+               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;
+               }
+
+               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. */
+               client_reset_inbound_state(client);
+               client->validated = true;
+               break;
+       }
+       case LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_SUBSCRIBE:
+       case LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_UNSUBSCRIBE:
+       {
+               struct lttng_condition *condition;
+               enum lttng_notification_channel_status status =
+                               LTTNG_NOTIFICATION_CHANNEL_STATUS_OK;
+               const struct lttng_buffer_view condition_view =
+                               lttng_buffer_view_from_dynamic_buffer(
+                                       &client->communication.inbound.buffer,
+                                       0, -1);
+               size_t expected_condition_size =
+                               client->communication.inbound.buffer.size;
+
+               ret = lttng_condition_create_from_buffer(&condition_view,
+                               &condition);
+               if (ret != expected_condition_size) {
+                       ERR("[notification-thread] Malformed condition received from client");
+                       goto end;
+               }
+
+               if (client->communication.inbound.msg_type ==
+                               LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_SUBSCRIBE) {
+                       /*
+                        * FIXME The current state should be evaluated on
+                        * subscription.
+                        */
+                       ret = notification_thread_client_subscribe(client,
+                                       condition, state, &status);
+               } else {
+                       ret = notification_thread_client_unsubscribe(client,
+                                       condition, state, &status);
+               }
+               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. */
+               client_reset_inbound_state(client);
+               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;
+       struct notification_client *client;
+       ssize_t recv_ret;
+       size_t offset;
+
+       client = get_client_from_socket(socket, state);
+       if (!client) {
+               /* Internal error, abort. */
+               ret = -1;
+               goto end;
+       }
+
+       offset = client->communication.inbound.buffer.size;
+       ret = lttng_dynamic_buffer_set_size(
+                       &client->communication.inbound.buffer,
+                       client->communication.inbound.bytes_to_receive);
+       if (ret) {
+               goto end;
+       }
+
+       if (client->communication.inbound.receive_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.receive_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) {
+               goto error_disconnect_client;
+       }
+
+       client->communication.inbound.bytes_to_receive -= recv_ret;
+       ret = lttng_dynamic_buffer_set_size(
+                       &client->communication.inbound.buffer,
+                       client->communication.inbound.buffer.size -
+                       client->communication.inbound.bytes_to_receive);
+       if (ret) {
+               goto end;
+       }
+
+       if (client->communication.inbound.bytes_to_receive == 0) {
+               ret = client_dispatch_message(client, state);
+               if (ret) {
+                       /*
+                        * Only returns an error if this client must be
+                        * disconnected.
+                        */
+                       goto error_disconnect_client;
+               }
+       } else {
+               goto end;
+       }
+end:
+       return ret;
+error_disconnect_client:
+       ret = handle_notification_thread_client_disconnect(socket, state);
+       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;
+       }
+
+       ret = client_flush_outgoing_queue(client, state);
+       if (ret) {
+               goto end;
+       }
+end:
+       return ret;
+}
+
+static
+bool evaluate_buffer_usage_condition(struct lttng_condition *condition,
+               struct channel_state_sample *sample, uint64_t buffer_capacity)
+{
+       bool result = false;
+       uint64_t threshold;
+       enum lttng_condition_type condition_type;
+       struct lttng_condition_buffer_usage *use_condition = container_of(
+                       condition, struct lttng_condition_buffer_usage,
+                       parent);
+
+       if (!sample) {
+               goto end;
+       }
+
+       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 accomodate 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;
+               }
+       }
+end:
+       return result;
+}
+
+static
+int evaluate_condition(struct lttng_condition *condition,
+               struct lttng_evaluation **evaluation,
+               struct notification_thread_state *state,
+               struct channel_state_sample *previous_sample,
+               struct channel_state_sample *latest_sample,
+               uint64_t buffer_capacity)
+{
+       int ret = 0;
+       enum lttng_condition_type condition_type;
+       bool previous_sample_result;
+       bool latest_sample_result;
+
+       condition_type = lttng_condition_get_type(condition);
+       /* No other condition type supported for the moment. */
+       assert(condition_type == LTTNG_CONDITION_TYPE_BUFFER_USAGE_LOW ||
+                       condition_type == LTTNG_CONDITION_TYPE_BUFFER_USAGE_HIGH);
+
+       previous_sample_result = evaluate_buffer_usage_condition(condition,
+                       previous_sample, buffer_capacity);
+       latest_sample_result = evaluate_buffer_usage_condition(condition,
+                       latest_sample, buffer_capacity);
+
+       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) {
+               *evaluation = lttng_evaluation_buffer_usage_create(
+                               condition_type,
+                               latest_sample->highest_usage,
+                               buffer_capacity);
+               if (!*evaluation) {
+                       ret = -1;
+                       goto end;
+               }
+       }
+end:
+       return ret;
+}
+
+static
+int client_enqueue_dropped_notification(struct notification_client *client,
+               struct notification_thread_state *state)
+{
+       int ret;
+       struct lttng_notification_channel_message msg = {
+               .type = (int8_t) LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_NOTIFICATION_DROPPED,
+               .size = 0,
+       };
+
+       ret = lttng_dynamic_buffer_append(
+                       &client->communication.outbound.buffer, &msg,
+                       sizeof(msg));
+       return ret;
+}
+
+static
+int send_evaluation_to_clients(struct lttng_trigger *trigger,
+               struct lttng_evaluation *evaluation,
+               struct notification_client_list* client_list,
+               struct notification_thread_state *state,
+               uid_t channel_uid, gid_t channel_gid)
+{
+       int ret = 0;
+       struct lttng_dynamic_buffer msg_buffer;
+       struct notification_client_list_element *client_list_element, *tmp;
+       struct lttng_notification *notification;
+       struct lttng_condition *condition;
+       ssize_t expected_notification_size, notification_size;
+       struct lttng_notification_channel_message msg;
+
+       lttng_dynamic_buffer_init(&msg_buffer);
+
+       condition = lttng_trigger_get_condition(trigger);
+       assert(condition);
+
+       notification = lttng_notification_create(condition, evaluation);
+       if (!notification) {
+               ret = -1;
+               goto end;
+       }
+
+       expected_notification_size = lttng_notification_serialize(notification,
+                       NULL);
+       if (expected_notification_size < 0) {
+               ERR("[notification-thread] Failed to get size of serialized notification");
+               ret = -1;
+               goto end;
+       }
+
+       msg.type = (int8_t) LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_NOTIFICATION;
+       msg.size = (uint32_t) expected_notification_size;
+       ret = lttng_dynamic_buffer_append(&msg_buffer, &msg, sizeof(msg));
+       if (ret) {
+               goto end;
+       }
+
+       ret = lttng_dynamic_buffer_set_size(&msg_buffer,
+                       msg_buffer.size + expected_notification_size);
+       if (ret) {
+               goto end;
+       }
+
+       notification_size = lttng_notification_serialize(notification,
+                       msg_buffer.data + sizeof(msg));
+       if (notification_size != expected_notification_size) {
+               ERR("[notification-thread] Failed to serialize notification");
+               ret = -1;
+               goto end;
+       }
+
+       cds_list_for_each_entry_safe(client_list_element, tmp,
+                       &client_list->list, node) {
+               struct notification_client *client =
+                               client_list_element->client;
+
+               if (client->uid != channel_uid && client->gid != channel_gid &&
+                               client->uid != 0) {
+                       /* Client is not allowed to monitor this channel. */
+                       DBG("[notification-thread] Skipping client at it does not have the permission to receive notification for this channel");
+                       continue;
+               }
+
+               DBG("[notification-thread] Sending notification to client (fd = %i, %zu bytes)",
+                               client->socket, msg_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, state);
+                               if (ret) {
+                                       goto end;
+                               }
+                       }
+                       continue;
+               }
+
+               ret = lttng_dynamic_buffer_append_buffer(
+                               &client->communication.outbound.buffer,
+                               &msg_buffer);
+               if (ret) {
+                       goto end;
+               }
+
+               ret = client_flush_outgoing_queue(client, state);
+               if (ret) {
+                       goto end;
+               }
+       }
+       ret = 0;
+end:
+       lttng_notification_destroy(notification);
+       lttng_dynamic_buffer_reset(&msg_buffer);
+       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_state_sample previous_sample, latest_sample;
+       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;
+
+       /*
+        * The monitoring pipe only holds messages smaller than PIPE_BUF,
+        * ensuring that read/write of sampling messages are atomic.
+        */
+       do {
+               ret = read(pipe, &sample_msg, sizeof(sample_msg));
+       } while (ret == -1 && errno == EINTR);
+       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;
+
+       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 (!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")",
+                       channel_info->channel_name,
+                       latest_sample.key.key,
+                       channel_info->session_name,
+                       latest_sample.highest_usage,
+                       latest_sample.lowest_usage);
+
+       /* 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 (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;
+               previous_sample_available = true;
+       } 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);
+       }
+
+       /* 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 (!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) {
+               struct lttng_condition *condition;
+               struct lttng_action *action;
+               struct lttng_trigger *trigger;
+               struct notification_client_list *client_list;
+               struct lttng_evaluation *evaluation = NULL;
+
+               trigger = trigger_list_element->trigger;
+               condition = lttng_trigger_get_condition(trigger);
+               assert(condition);
+               action = lttng_trigger_get_action(trigger);
+
+               /* Notify actions are the only type currently supported. */
+               assert(lttng_action_get_type(action) ==
+                               LTTNG_ACTION_TYPE_NOTIFY);
+
+               /*
+                * Check if any client is subscribed to the result of this
+                * evaluation.
+                */
+               cds_lfht_lookup(state->notification_trigger_clients_ht,
+                               lttng_condition_hash(condition),
+                               match_client_list,
+                               trigger,
+                               &iter);
+               node = cds_lfht_iter_get_node(&iter);
+               assert(node);
+
+               client_list = caa_container_of(node,
+                               struct notification_client_list,
+                               notification_trigger_ht_node);
+               if (cds_list_empty(&client_list->list)) {
+                       /*
+                        * No clients interested in the evaluation's result,
+                        * skip it.
+                        */
+                       continue;
+               }
+
+               ret = evaluate_condition(condition, &evaluation, state,
+                               previous_sample_available ? &previous_sample : NULL,
+                               &latest_sample, channel_info->capacity);
+               if (ret) {
+                       goto end_unlock;
+               }
+
+               if (!evaluation) {
+                       continue;
+               }
+
+               /* Dispatch evaluation result to all clients. */
+               ret = send_evaluation_to_clients(trigger_list_element->trigger,
+                               evaluation, client_list, state,
+                               channel_info->uid, channel_info->gid);
+               if (ret) {
+                       goto end_unlock;
+               }
+       }
+end_unlock:
+       rcu_read_unlock();
+end:
+       return ret;
+}
diff --git a/src/bin/lttng-sessiond/notification-thread-events.h b/src/bin/lttng-sessiond/notification-thread-events.h
new file mode 100644 (file)
index 0000000..a0795e4
--- /dev/null
@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2017 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License, version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef NOTIFICATION_THREAD_EVENTS_H
+#define NOTIFICATION_THREAD_EVENTS_H
+
+#include <lttng/domain.h>
+#include "notification-thread.h"
+
+/**
+ * Event handling function shall only return an error if
+ * the thread should be stopped.
+ */
+int handle_notification_thread_command(
+               struct notification_thread_handle *handle,
+               struct notification_thread_state *state);
+
+int handle_notification_thread_client_connect(
+               struct notification_thread_state *state);
+
+int handle_notification_thread_client_disconnect(
+               int client_fd,
+               struct notification_thread_state *state);
+
+int handle_notification_thread_client_disconnect_all(
+               struct notification_thread_state *state);
+
+int handle_notification_thread_trigger_unregister_all(
+               struct notification_thread_state *state);
+
+int handle_notification_thread_client_in(
+               struct notification_thread_state *state,
+               int socket);
+
+int handle_notification_thread_client_out(
+               struct notification_thread_state *state,
+               int socket);
+
+int handle_notification_thread_channel_sample(
+               struct notification_thread_state *state, int pipe,
+               enum lttng_domain_type domain);
+
+#endif /* NOTIFICATION_THREAD_EVENTS_H */
diff --git a/src/bin/lttng-sessiond/notification-thread.c b/src/bin/lttng-sessiond/notification-thread.c
new file mode 100644 (file)
index 0000000..58c3f2b
--- /dev/null
@@ -0,0 +1,722 @@
+/*
+ * Copyright (C) 2017 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License, version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#define _LGPL_SOURCE
+#include <lttng/trigger/trigger.h>
+#include <lttng/notification/channel-internal.h>
+#include <lttng/notification/notification-internal.h>
+#include <lttng/condition/condition-internal.h>
+#include <lttng/condition/buffer-usage-internal.h>
+#include <common/error.h>
+#include <common/config/session-config.h>
+#include <common/defaults.h>
+#include <common/utils.h>
+#include <common/futex.h>
+#include <common/align.h>
+#include <common/time.h>
+#include <sys/eventfd.h>
+#include <sys/stat.h>
+#include <time.h>
+#include <signal.h>
+
+#include "notification-thread.h"
+#include "notification-thread-events.h"
+#include "notification-thread-commands.h"
+#include "lttng-sessiond.h"
+#include "health-sessiond.h"
+
+#include <urcu.h>
+#include <urcu/list.h>
+#include <urcu/rculfhash.h>
+
+/**
+ * This thread maintains an internal state associating clients and triggers.
+ *
+ * In order to speed-up and simplify queries, hash tables providing the
+ * following associations are maintained:
+ *
+ *   - client_socket_ht: associate a client's socket (fd) to its "struct client"
+ *             This hash table owns the "struct client" which must thus be
+ *             disposed-of on removal from the hash table.
+ *
+ *   - channel_triggers_ht:
+ *             associates a channel key to a list of
+ *             struct lttng_trigger_list_nodes. The triggers in this list are
+ *             those that have conditions that apply to this channel.
+ *             This hash table owns the list, but not the triggers themselves.
+ *
+ *   - channel_state_ht:
+ *             associates a pair (channel key, channel domain) to its last
+ *             sampled state received from the consumer daemon
+ *             (struct channel_state).
+ *             This previous sample is kept to implement edge-triggered
+ *             conditions as we need to detect the state transitions.
+ *             This hash table owns the channel state.
+ *
+ *   - notification_trigger_clients_ht:
+ *             associates notification-emitting triggers to clients
+ *             (struct notification_client_ht_node) subscribed to those
+ *             conditions.
+ *             The condition's hash and match functions are used directly since
+ *             all triggers in this hash table have the "notify" action.
+ *             This hash table holds no ownership.
+ *
+ *   - channels_ht:
+ *             associates a channel_key to a struct channel_info. The hash table
+ *             holds the ownership of the struct channel_info.
+ *
+ *   - triggers_ht:
+ *             associated a condition to a struct lttng_trigger_ht_element.
+ *             The hash table holds the ownership of the
+ *             lttng_trigger_ht_elements along with the triggers themselves.
+ *
+ * The thread reacts to the following internal events:
+ *   1) creation of a tracing channel,
+ *   2) destruction of a tracing channel,
+ *   3) registration of a trigger,
+ *   4) unregistration of a trigger,
+ *   5) reception of a channel monitor sample from the consumer daemon.
+ *
+ * Events specific to notification-emitting triggers:
+ *   6) connection of a notification client,
+ *   7) disconnection of a notification client,
+ *   8) subscription of a client to a conditions' notifications,
+ *   9) unsubscription of a client from a conditions' notifications,
+ *
+ *
+ * 1) Creation of a tracing channel
+ *    - notification_trigger_clients_ht is traversed to identify
+ *      triggers which apply to this new channel,
+ *    - triggers identified are added to the channel_triggers_ht.
+ *    - add channel to channels_ht
+ *
+ * 2) Destruction of a tracing channel
+ *    - remove entry from channel_triggers_ht, releasing the list wrapper and
+ *      elements,
+ *    - remove entry from the channel_state_ht.
+ *    - remove channel from channels_ht
+ *
+ * 3) Registration of a trigger
+ *    - if the trigger's action is of type "notify",
+ *      - traverse the list of conditions of every client to build a list of
+ *        clients which have to be notified when this trigger's condition is met,
+ *        - add list of clients (even if it is empty) to the
+ *          notification_trigger_clients_ht,
+ *    - add trigger to channel_triggers_ht (if applicable),
+ *    - add trigger to triggers_ht
+ *
+ * 4) Unregistration of a trigger
+ *    - if the trigger's action is of type "notify",
+ *      - remove the trigger from the notification_trigger_clients_ht,
+ *    - remove trigger from channel_triggers_ht (if applicable),
+ *    - remove trigger from triggers_ht
+ *
+ * 5) Reception of a channel monitor sample from the consumer daemon
+ *    - evaluate the conditions associated with the triggers found in
+ *      the channel_triggers_ht,
+ *      - if a condition evaluates to "true" and the condition is of type
+ *        "notify", query the notification_trigger_clients_ht and send
+ *        a notification to the clients.
+ *
+ * 6) Connection of a client
+ *    - add client socket to the client_socket_ht.
+ *
+ * 7) Disconnection of a client
+ *    - remove client socket from the client_socket_ht,
+ *    - traverse all conditions to which the client is subscribed and remove
+ *      the client from the notification_trigger_clients_ht.
+ *
+ * 8) Subscription of a client to a condition's notifications
+ *    - Add the condition to the client's list of subscribed conditions,
+ *    - Look-up notification_trigger_clients_ht and add the client to
+ *      list of clients.
+ *
+ * 9) Unsubscription of a client to a condition's notifications
+ *    - Remove the condition from the client's list of subscribed conditions,
+ *    - Look-up notification_trigger_clients_ht and remove the client
+ *      from the list of clients.
+ */
+
+/*
+ * Destroy the thread data previously created by the init function.
+ */
+void notification_thread_handle_destroy(
+               struct notification_thread_handle *handle)
+{
+       int ret;
+       struct notification_thread_command *cmd, *tmp;
+
+       if (!handle) {
+               goto end;
+       }
+
+       if (handle->cmd_queue.event_fd < 0) {
+               goto end;
+       }
+       ret = close(handle->cmd_queue.event_fd);
+       if (ret < 0) {
+               PERROR("close notification command queue event_fd");
+       }
+
+       pthread_mutex_lock(&handle->cmd_queue.lock);
+       /* Purge queue of in-flight commands and mark them as cancelled. */
+       cds_list_for_each_entry_safe(cmd, tmp, &handle->cmd_queue.list,
+                       cmd_list_node) {
+               cds_list_del(&cmd->cmd_list_node);
+               cmd->reply_code = LTTNG_ERR_COMMAND_CANCELLED;
+               futex_nto1_wake(&cmd->reply_futex);
+       }
+       pthread_mutex_unlock(&handle->cmd_queue.lock);
+       pthread_mutex_destroy(&handle->cmd_queue.lock);
+
+       if (handle->channel_monitoring_pipes.ust32_consumer >= 0) {
+               ret = close(handle->channel_monitoring_pipes.ust32_consumer);
+               if (ret) {
+                       PERROR("close 32-bit consumer channel monitoring pipe");
+               }
+       }
+       if (handle->channel_monitoring_pipes.ust64_consumer >= 0) {
+               ret = close(handle->channel_monitoring_pipes.ust64_consumer);
+               if (ret) {
+                       PERROR("close 64-bit consumer channel monitoring pipe");
+               }
+       }
+       if (handle->channel_monitoring_pipes.kernel_consumer >= 0) {
+               ret = close(handle->channel_monitoring_pipes.kernel_consumer);
+               if (ret) {
+                       PERROR("close kernel consumer channel monitoring pipe");
+               }
+       }
+end:
+       free(handle);
+}
+
+struct notification_thread_handle *notification_thread_handle_create(
+               struct lttng_pipe *ust32_channel_monitor_pipe,
+               struct lttng_pipe *ust64_channel_monitor_pipe,
+               struct lttng_pipe *kernel_channel_monitor_pipe)
+{
+       int ret;
+       struct notification_thread_handle *handle;
+
+       handle = zmalloc(sizeof(*handle));
+       if (!handle) {
+               goto end;
+       }
+
+       /* FIXME Replace eventfd by a pipe to support older kernels. */
+       handle->cmd_queue.event_fd = eventfd(0, EFD_CLOEXEC);
+       if (handle->cmd_queue.event_fd < 0) {
+               PERROR("eventfd notification command queue");
+               goto error;
+       }
+       CDS_INIT_LIST_HEAD(&handle->cmd_queue.list);
+       ret = pthread_mutex_init(&handle->cmd_queue.lock, NULL);
+       if (ret) {
+               goto error;
+       }
+
+       if (ust32_channel_monitor_pipe) {
+               handle->channel_monitoring_pipes.ust32_consumer =
+                               lttng_pipe_release_readfd(
+                                       ust32_channel_monitor_pipe);
+               if (handle->channel_monitoring_pipes.ust32_consumer < 0) {
+                       goto error;
+               }
+       } else {
+               handle->channel_monitoring_pipes.ust32_consumer = -1;
+       }
+       if (ust64_channel_monitor_pipe) {
+               handle->channel_monitoring_pipes.ust64_consumer =
+                               lttng_pipe_release_readfd(
+                                       ust64_channel_monitor_pipe);
+               if (handle->channel_monitoring_pipes.ust64_consumer < 0) {
+                       goto error;
+               }
+       } else {
+               handle->channel_monitoring_pipes.ust64_consumer = -1;
+       }
+       if (kernel_channel_monitor_pipe) {
+               handle->channel_monitoring_pipes.kernel_consumer =
+                               lttng_pipe_release_readfd(
+                                       kernel_channel_monitor_pipe);
+               if (handle->channel_monitoring_pipes.kernel_consumer < 0) {
+                       goto error;
+               }
+       } else {
+               handle->channel_monitoring_pipes.kernel_consumer = -1;
+       }
+end:
+       return handle;
+error:
+       notification_thread_handle_destroy(handle);
+       return NULL;
+}
+
+static
+char *get_notification_channel_sock_path(void)
+{
+       int ret;
+       bool is_root = !getuid();
+       char *sock_path;
+
+       sock_path = zmalloc(LTTNG_PATH_MAX);
+       if (!sock_path) {
+               goto error;
+       }
+
+       if (is_root) {
+               ret = snprintf(sock_path, LTTNG_PATH_MAX,
+                               DEFAULT_GLOBAL_NOTIFICATION_CHANNEL_UNIX_SOCK);
+               if (ret < 0) {
+                       goto error;
+               }
+       } else {
+               char *home_path = utils_get_home_dir();
+
+               if (!home_path) {
+                       ERR("Can't get HOME directory for socket creation");
+                       goto error;
+               }
+
+               ret = snprintf(sock_path, LTTNG_PATH_MAX,
+                               DEFAULT_HOME_NOTIFICATION_CHANNEL_UNIX_SOCK,
+                               home_path);
+               if (ret < 0) {
+                       goto error;
+               }
+       }
+
+       return sock_path;
+error:
+       free(sock_path);
+       return NULL;
+}
+
+static
+void notification_channel_socket_destroy(int fd)
+{
+       int ret;
+       char *sock_path = get_notification_channel_sock_path();
+
+       DBG("[notification-thread] Destroying notification channel socket");
+
+       if (sock_path) {
+               ret = unlink(sock_path);
+               free(sock_path);
+               if (ret < 0) {
+                       PERROR("unlink notification channel socket");
+               }
+       }
+
+       ret = close(fd);
+       if (ret) {
+               PERROR("close notification channel socket");
+       }
+}
+
+static
+int notification_channel_socket_create(void)
+{
+       int fd = -1, ret;
+       char *sock_path = get_notification_channel_sock_path();
+
+       DBG("[notification-thread] Creating notification channel UNIX socket at %s",
+                       sock_path);
+
+       ret = lttcomm_create_unix_sock(sock_path);
+       if (ret < 0) {
+               ERR("[notification-thread] Failed to create notification socket");
+               goto error;
+       }
+       fd = ret;
+
+       ret = chmod(sock_path, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
+       if (ret < 0) {
+               ERR("Set file permissions failed: %s", sock_path);
+               PERROR("chmod notification channel socket");
+               goto error;
+       }
+
+       if (getuid() == 0) {
+               ret = chown(sock_path, 0,
+                               utils_get_group_id(tracing_group_name));
+               if (ret) {
+                       ERR("Failed to set the notification channel socket's group");
+                       ret = -1;
+                       goto error;
+               }
+       }
+
+       DBG("[notification-thread] Notification channel UNIX socket created (fd = %i)",
+                       fd);
+       free(sock_path);
+       return fd;
+error:
+       if (fd >= 0 && close(fd) < 0) {
+               PERROR("close notification channel socket");
+       }
+       free(sock_path);
+       return ret;
+}
+
+static
+int init_poll_set(struct lttng_poll_event *poll_set,
+               struct notification_thread_handle *handle,
+               int notification_channel_socket)
+{
+       int ret;
+
+       /*
+        * Create pollset with size 5:
+        *      - notification channel socket (listen for new connections),
+        *      - command queue event fd (internal sessiond commands),
+        *      - consumerd (32-bit user space) channel monitor pipe,
+        *      - consumerd (64-bit user space) channel monitor pipe,
+        *      - consumerd (kernel) channel monitor pipe.
+        */
+       ret = lttng_poll_create(poll_set, 5, LTTNG_CLOEXEC);
+       if (ret < 0) {
+               goto end;
+       }
+
+       ret = lttng_poll_add(poll_set, notification_channel_socket,
+                       LPOLLIN | LPOLLERR | LPOLLHUP | LPOLLRDHUP);
+       if (ret < 0) {
+               ERR("[notification-thread] Failed to add notification channel socket to pollset");
+               goto error;
+       }
+       ret = lttng_poll_add(poll_set, handle->cmd_queue.event_fd,
+                       LPOLLIN | LPOLLERR);
+       if (ret < 0) {
+               ERR("[notification-thread] Failed to add notification command queue event fd to pollset");
+               goto error;
+       }
+       ret = lttng_poll_add(poll_set,
+                       handle->channel_monitoring_pipes.ust32_consumer,
+                       LPOLLIN | LPOLLERR);
+       if (ret < 0) {
+               ERR("[notification-thread] Failed to add ust-32 channel monitoring pipe fd to pollset");
+               goto error;
+       }
+       ret = lttng_poll_add(poll_set,
+                       handle->channel_monitoring_pipes.ust64_consumer,
+                       LPOLLIN | LPOLLERR);
+       if (ret < 0) {
+               ERR("[notification-thread] Failed to add ust-64 channel monitoring pipe fd to pollset");
+               goto error;
+       }
+       if (handle->channel_monitoring_pipes.kernel_consumer < 0) {
+               goto end;
+       }
+       ret = lttng_poll_add(poll_set,
+                       handle->channel_monitoring_pipes.kernel_consumer,
+                       LPOLLIN | LPOLLERR);
+       if (ret < 0) {
+               ERR("[notification-thread] Failed to add kernel channel monitoring pipe fd to pollset");
+               goto error;
+       }
+end:
+       return ret;
+error:
+       lttng_poll_clean(poll_set);
+       return ret;
+}
+
+static
+void fini_thread_state(struct notification_thread_state *state)
+{
+       int ret;
+
+       if (state->client_socket_ht) {
+               ret = handle_notification_thread_client_disconnect_all(state);
+               assert(!ret);
+               ret = cds_lfht_destroy(state->client_socket_ht, NULL);
+               assert(!ret);
+       }
+       if (state->triggers_ht) {
+               ret = handle_notification_thread_trigger_unregister_all(state);
+               assert(!ret);
+               ret = cds_lfht_destroy(state->triggers_ht, NULL);
+               assert(!ret);
+       }
+       if (state->channel_triggers_ht) {
+               ret = cds_lfht_destroy(state->channel_triggers_ht, NULL);
+               assert(!ret);
+       }
+       if (state->channel_state_ht) {
+               ret = cds_lfht_destroy(state->channel_state_ht, NULL);
+               assert(!ret);
+       }
+       if (state->notification_trigger_clients_ht) {
+               ret = cds_lfht_destroy(state->notification_trigger_clients_ht,
+                               NULL);
+               assert(!ret);
+       }
+       if (state->channels_ht) {
+               ret = cds_lfht_destroy(state->channels_ht,
+                               NULL);
+               assert(!ret);
+       }
+
+       if (state->notification_channel_socket >= 0) {
+               notification_channel_socket_destroy(
+                               state->notification_channel_socket);
+       }
+       lttng_poll_clean(&state->events);
+}
+
+static
+int init_thread_state(struct notification_thread_handle *handle,
+               struct notification_thread_state *state)
+{
+       int ret;
+
+       memset(state, 0, sizeof(*state));
+       state->notification_channel_socket = -1;
+       lttng_poll_init(&state->events);
+
+       ret = notification_channel_socket_create();
+       if (ret < 0) {
+               goto end;
+       }
+       state->notification_channel_socket = ret;
+
+       ret = init_poll_set(&state->events, handle,
+                       state->notification_channel_socket);
+       if (ret) {
+               goto end;
+       }
+
+       DBG("[notification-thread] Listening on notification channel socket");
+       ret = lttcomm_listen_unix_sock(state->notification_channel_socket);
+       if (ret < 0) {
+               ERR("[notification-thread] Listen failed on notification channel socket");
+               goto error;
+       }
+
+       state->client_socket_ht = cds_lfht_new(DEFAULT_HT_SIZE, 1, 0,
+                       CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);
+       if (!state->client_socket_ht) {
+               goto error;
+       }
+
+       state->channel_triggers_ht = cds_lfht_new(DEFAULT_HT_SIZE, 1, 0,
+                       CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);
+       if (!state->channel_triggers_ht) {
+               goto error;
+       }
+
+       state->channel_state_ht = cds_lfht_new(DEFAULT_HT_SIZE, 1, 0,
+                       CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);
+       if (!state->channel_state_ht) {
+               goto error;
+       }
+
+       state->notification_trigger_clients_ht = cds_lfht_new(DEFAULT_HT_SIZE,
+                       1, 0, CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);
+       if (!state->notification_trigger_clients_ht) {
+               goto error;
+       }
+
+       state->channels_ht = cds_lfht_new(DEFAULT_HT_SIZE,
+                       1, 0, CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);
+       if (!state->channels_ht) {
+               goto error;
+       }
+
+       state->triggers_ht = cds_lfht_new(DEFAULT_HT_SIZE,
+                       1, 0, CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);
+       if (!state->triggers_ht) {
+               goto error;
+       }
+end:
+       return 0;
+error:
+       fini_thread_state(state);
+       return -1;
+}
+
+static
+int handle_channel_monitoring_pipe(int fd, uint32_t revents,
+               struct notification_thread_handle *handle,
+               struct notification_thread_state *state)
+{
+       int ret = 0;
+       enum lttng_domain_type domain;
+
+       if (fd == handle->channel_monitoring_pipes.ust32_consumer ||
+                       fd == handle->channel_monitoring_pipes.ust64_consumer) {
+               domain = LTTNG_DOMAIN_UST;
+       } else if (fd == handle->channel_monitoring_pipes.kernel_consumer) {
+               domain = LTTNG_DOMAIN_KERNEL;
+       } else {
+               abort();
+       }
+
+       if (revents & (LPOLLERR | LPOLLHUP | LPOLLRDHUP)) {
+               ret = lttng_poll_del(&state->events, fd);
+               if (ret) {
+                       ERR("[notification-thread] Failed to remove consumer monitoring pipe from poll set");
+               }
+               goto end;
+       }
+
+       ret = handle_notification_thread_channel_sample(
+                       state, fd, domain);
+       if (ret) {
+               ERR("[notification-thread] Consumer sample handling error occured");
+               ret = -1;
+               goto end;
+       }
+end:
+       return ret;
+}
+
+/*
+ * This thread services notification channel clients and commands received
+ * from various lttng-sessiond components over a command queue.
+ */
+void *thread_notification(void *data)
+{
+       int ret;
+       struct notification_thread_handle *handle = data;
+       struct notification_thread_state state;
+
+       DBG("[notification-thread] Started notification thread");
+
+       if (!handle) {
+               ERR("[notification-thread] Invalid thread context provided");
+               goto end;
+       }
+
+       rcu_register_thread();
+       rcu_thread_online();
+
+       health_register(health_sessiond, HEALTH_SESSIOND_TYPE_NOTIFICATION);
+       health_code_update();
+
+       ret = init_thread_state(handle, &state);
+       if (ret) {
+               goto end;
+       }
+
+       /* Ready to handle client connections. */
+       sessiond_notify_ready();
+
+       while (true) {
+               int fd_count, i;
+
+               health_poll_entry();
+               DBG("[notification-thread] Entering poll wait");
+               ret = lttng_poll_wait(&state.events, -1);
+               DBG("[notification-thread] Poll wait returned (%i)", ret);
+               health_poll_exit();
+               if (ret < 0) {
+                       /*
+                        * Restart interrupted system call.
+                        */
+                       if (errno == EINTR) {
+                               continue;
+                       }
+                       ERR("[notification-thread] Error encountered during lttng_poll_wait (%i)", ret);
+                       goto error;
+               }
+
+               fd_count = ret;
+               for (i = 0; i < fd_count; i++) {
+                       int fd = LTTNG_POLL_GETFD(&state.events, i);
+                       uint32_t revents = LTTNG_POLL_GETEV(&state.events, i);
+
+                       DBG("[notification-thread] Handling fd (%i) activity (%u)", fd, revents);
+
+                       if (fd == state.notification_channel_socket) {
+                               if (revents & LPOLLIN) {
+                                       ret = handle_notification_thread_client_connect(
+                                                       &state);
+                                       if (ret < 0) {
+                                               goto error;
+                                       }
+                               } else if (revents &
+                                               (LPOLLERR | LPOLLHUP | LPOLLRDHUP)) {
+                                       ERR("[notification-thread] Notification socket poll error");
+                                       goto error;
+                               } else {
+                                       ERR("[notification-thread] Unexpected poll events %u for notification socket %i", revents, fd);
+                                       goto error;
+                               }
+                       } else if (fd == handle->cmd_queue.event_fd) {
+                               ret = handle_notification_thread_command(handle,
+                                               &state);
+                               if (ret < 0) {
+                                       DBG("[notification-thread] Error encountered while servicing command queue");
+                                       goto error;
+                               } else if (ret > 0) {
+                                       goto exit;
+                               }
+                       } else if (fd == handle->channel_monitoring_pipes.ust32_consumer ||
+                                       fd == handle->channel_monitoring_pipes.ust64_consumer ||
+                                       fd == handle->channel_monitoring_pipes.kernel_consumer) {
+                               ret = handle_channel_monitoring_pipe(fd,
+                                               revents, handle, &state);
+                               if (ret) {
+                                       goto error;
+                               }
+                       } else {
+                               /* Activity on a client's socket. */
+                               if (revents & (LPOLLERR | LPOLLHUP | LPOLLRDHUP)) {
+                                       /*
+                                        * It doesn't matter if a command was
+                                        * pending on the client socket at this
+                                        * point since it now has no way to
+                                        * receive the notifications to which
+                                        * it was subscribing or unsubscribing.
+                                        */
+                                       ret = handle_notification_thread_client_disconnect(
+                                                       fd, &state);
+                                       if (ret) {
+                                               goto error;
+                                       }
+                               } else {
+                                       if (revents & LPOLLIN) {
+                                               ret = handle_notification_thread_client_in(
+                                                       &state, fd);
+                                               if (ret) {
+                                                       goto error;
+                                               }
+                                       }
+
+                                       if (revents & LPOLLOUT) {
+                                               ret = handle_notification_thread_client_out(
+                                                       &state, fd);
+                                               if (ret) {
+                                                       goto error;
+                                               }
+                                       }
+                               }
+                       }
+               }
+       }
+exit:
+error:
+       fini_thread_state(&state);
+       health_unregister(health_sessiond);
+       rcu_thread_offline();
+       rcu_unregister_thread();
+end:
+       return NULL;
+}
diff --git a/src/bin/lttng-sessiond/notification-thread.h b/src/bin/lttng-sessiond/notification-thread.h
new file mode 100644 (file)
index 0000000..c401b41
--- /dev/null
@@ -0,0 +1,73 @@
+/*
+ * Copyright (C) 2017 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License, version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef NOTIFICATION_THREAD_H
+#define NOTIFICATION_THREAD_H
+
+#include <urcu/list.h>
+#include <urcu.h>
+#include <urcu/rculfhash.h>
+#include <lttng/trigger/trigger.h>
+#include <common/pipe.h>
+#include <common/compat/poll.h>
+#include <common/hashtable/hashtable.h>
+#include <pthread.h>
+
+struct notification_thread_handle {
+       /*
+        * Queue of struct notification command.
+        * event_fd must be WRITE(2) to signal that a new command
+        * has been enqueued.
+        */
+       struct {
+               int event_fd;
+               struct cds_list_head list;
+               pthread_mutex_t lock;
+       } cmd_queue;
+       /*
+        * Read side of pipes used to receive channel status info collected
+        * by the various consumer daemons.
+        */
+       struct {
+               int ust32_consumer;
+               int ust64_consumer;
+               int kernel_consumer;
+       } channel_monitoring_pipes;
+};
+
+struct notification_thread_state {
+       int notification_channel_socket;
+       struct lttng_poll_event events;
+       struct cds_lfht *client_socket_ht;
+       struct cds_lfht *channel_triggers_ht;
+       struct cds_lfht *channel_state_ht;
+       struct cds_lfht *notification_trigger_clients_ht;
+       struct cds_lfht *channels_ht;
+       struct cds_lfht *triggers_ht;
+};
+
+/* notification_thread_data takes ownership of the channel monitor pipes. */
+struct notification_thread_handle *notification_thread_handle_create(
+               struct lttng_pipe *ust32_channel_monitor_pipe,
+               struct lttng_pipe *ust64_channel_monitor_pipe,
+               struct lttng_pipe *kernel_channel_monitor_pipe);
+void notification_thread_handle_destroy(
+               struct notification_thread_handle *handle);
+
+void *thread_notification(void *data);
+
+#endif /* NOTIFICATION_THREAD_H */
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