--- /dev/null
+/*
+ * Copyright (C) 2017 Jérémie Galarneau <jeremie.galarneau@efficios.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-only
+ *
+ */
+
+#ifndef NOTIFICATION_THREAD_H
+#define NOTIFICATION_THREAD_H
+
+#include "action-executor.hpp"
+#include "thread.hpp"
+#include <common/compat/poll.hpp>
+#include <common/hashtable/hashtable.hpp>
+#include <common/pipe.hpp>
+#include <lttng/trigger/trigger.h>
+#include <lttng/domain.h>
+#include <pthread.h>
+#include <semaphore.h>
+#include <urcu.h>
+#include <urcu/list.h>
+#include <urcu/rculfhash.h>
+
+typedef uint64_t notification_client_id;
+
+/*
+ * The notification thread holds no ownership of the tracer event source pipe
+ * file descriptor. The tracer management logic must remove the event source
+ * from the notification thread (see external commands) before releasing
+ * this file descriptor.
+ */
+struct notification_event_tracer_event_source_element {
+ int fd;
+ /*
+ * A tracer event source can be removed from the notification thread's
+ * poll set before the end of its lifetime (for instance, when an error
+ * or hang-up is detected on its file descriptor). This is done to
+ * allow the notification thread to ignore follow-up events on this
+ * file descriptors.
+ *
+ * Under such circumstances, the notification thread still expects
+ * the normal clean-up to occur through the 'REMOVE_TRACER_EVENT_SOURCE'
+ * command.
+ */
+ bool is_fd_in_poll_set;
+ enum lttng_domain_type domain;
+ struct cds_list_head node;
+};
+
+struct notification_trigger_tokens_ht_element {
+ uint64_t token;
+ /* Weak reference to the trigger. */
+ struct lttng_trigger *trigger;
+ struct cds_lfht_node node;
+ /* call_rcu delayed reclaim. */
+ struct rcu_head rcu_node;
+};
+
+struct notification_thread_handle {
+ /*
+ * Queue of struct notification command.
+ * event_pipe must be WRITE(2) to signal that a new command
+ * has been enqueued.
+ */
+ struct {
+ struct lttng_pipe *event_pipe;
+ 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;
+ /* Used to wait for the launch of the notification thread. */
+ sem_t ready;
+};
+
+/**
+ * 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 notification_client".
+ * This hash table owns the "struct notification_client" which must
+ * thus be disposed-of on removal from the hash table.
+ *
+ * - client_id_ht: associate a client's id to its "struct notification_client"
+ * This hash table holds a _weak_ reference to the
+ * "struct notification_client".
+ *
+ * - 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 a particular channel.
+ * A channel entry is only created when a channel is added; the
+ * list of triggers applying to such a channel is built at that
+ * moment.
+ * This hash table owns the list, but not the triggers themselves.
+ *
+ * - session_triggers_ht:
+ * associates a session name to a list of
+ * struct lttng_trigger_list_nodes. The triggers in this list are
+ * those that have conditions that apply to a particular session.
+ * A session entry is only created when a session is created; the
+ * list of triggers applying to this new session is built at that
+ * moment. This happens at the time of creation of a session_info.
+ * Likewise, the list is destroyed at the time of the session_info's
+ * destruction.
+ *
+ * - 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_list) 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.
+ *
+ * - sessions_ht:
+ * associates a session_name (hash) to a struct session_info. The
+ * hash table holds no ownership of the struct session_info;
+ * the session_info structure is owned by the session's various
+ * channels through their struct channel_info (ref-counting is used).
+ *
+ * - triggers_ht:
+ * associates a trigger to a struct lttng_trigger_ht_element.
+ * The hash table holds the ownership of the
+ * lttng_trigger_ht_elements along with the triggers themselves.
+ * - triggers_by_name_uid_ht:
+ * associates a trigger (name, uid) tuple to
+ * a struct lttng_trigger_ht_element.
+ * The hash table does not hold any ownership and is used strictly
+ * for lookup on registration.
+ * - tracer_event_sources_list:
+ * A list of tracer event source (read side fd) of type
+* struct notification_event_tracer_event_source_element.
+*
+ *
+ * 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,
+ * 6) Session rotation ongoing,
+ * 7) Session rotation completed,
+ * 8) registration of a tracer event source,
+ * 9) unregistration of a tracer event source,
+ *
+ * Events specific to notification-emitting triggers:
+ * 9) connection of a notification client,
+ * 10) disconnection of a notification client,
+ * 11) subscription of a client to a conditions' notifications,
+ * 12) 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
+ * - if it is the first channel of a session, a session_info is created and
+ * added to the sessions_ht. A list of the triggers associated with that
+ * session is built, and it is added to session_triggers_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
+ * - if it was the last known channel of a session, the session_info
+ * structure is torndown, which in return destroys the list of triggers
+ * applying to that session.
+ *
+ * 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 session_triggers_ht (if applicable),
+ * - add trigger to triggers_by_name_uid_ht
+ * - add trigger to triggers_ht
+ * - evaluate the trigger's condition right away to react if that condition
+ * is true from the beginning.
+ *
+ * 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 session_triggers_ht (if applicable),
+ * - remove trigger from triggers_by_name_uid_ht
+ * - 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) Session rotation ongoing
+ *
+ * 7) Session rotation completed
+ *
+ * 8) Registration of a tracer event source
+ * - Add the tracer event source of the application to
+ * tracer_event_sources_list,
+ * - Add the trace event source to the pollset.
+ *
+ * 8) Unregistration of a tracer event source
+ * - Remove the tracer event source of the application from
+ * tracer_event_sources_list,
+ * - Remove the trace event source from the pollset.
+ *
+ * 10) Connection of a client
+ * - add client socket to the client_socket_ht,
+ * - add client socket to the client_id_ht.
+ *
+ * 11) Disconnection of a client
+ * - remove client socket from the client_id_ht,
+ * - 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.
+ *
+ * 12) 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.
+ * - Evaluate the condition for the client that subscribed if the trigger
+ * was already registered.
+ *
+ * 13) 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.
+ */
+struct notification_thread_state {
+ int notification_channel_socket;
+ struct lttng_poll_event events;
+ struct cds_lfht *client_socket_ht;
+ struct cds_lfht *client_id_ht;
+ struct cds_lfht *channel_triggers_ht;
+ struct cds_lfht *session_triggers_ht;
+ struct cds_lfht *channel_state_ht;
+ struct cds_lfht *notification_trigger_clients_ht;
+ struct cds_lfht *channels_ht;
+ struct cds_lfht *sessions_ht;
+ struct cds_lfht *triggers_ht;
+ struct cds_lfht *triggers_by_name_uid_ht;
+ struct cds_lfht *trigger_tokens_ht;
+ struct {
+ uint64_t next_tracer_token;
+ uint64_t name_offset;
+ } trigger_id;
+ /*
+ * Read side of the pipes used to receive tracer events. As their name
+ * implies, tracer event source activity originate from either
+ * registered applications (user space tracer) or from the kernel
+ * tracer.
+ *
+ * The list is not protected by a lock since add and remove operations
+ * are currently done only by the notification thread through in
+ * response to blocking commands.
+ */
+ struct cds_list_head tracer_event_sources_list;
+ notification_client_id next_notification_client_id;
+ struct action_executor *executor;
+
+ /*
+ * Indicates the thread to break for the poll event processing loop and
+ * call _poll_wait() again.
+ *
+ * This is necessary because some events on one fd might trigger the
+ * consumption of another fd.
+ * For example, a single _poll_wait() call can return notification
+ * thread commands and events from the tracer event source (event
+ * notifier).
+ * Picture a scenario where we receive two events:
+ * the first one is a _REMOVE_TRACER_EVENT_SOURCE command, and
+ * the second is an POLLIN on the tracer event source fd.
+ *
+ * The _REMOVE_TRACER_EVENT_SOURCE will read all the data of the
+ * removed tracer event source.
+ *
+ * The second event is now invalid has we consumed all the data for
+ * which we received the POLLIN.
+ *
+ * For this reason, we need to break for the event processing loop and
+ * call _poll_wait() again to get a clean view of the activity on the
+ * fds.
+ */
+ bool restart_poll;
+};
+
+/* 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);
+struct lttng_thread *launch_notification_thread(
+ struct notification_thread_handle *handle);
+
+#endif /* NOTIFICATION_THREAD_H */
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