src/bin/lttng-sessiond/notification-thread.h

   1 /*
   2  * Copyright (C) 2017 Jérémie Galarneau <jeremie.galarneau@efficios.com>
   3  *
   4  * SPDX-License-Identifier: GPL-2.0-only
   5  *
   6  */
   7
   8 #ifndef NOTIFICATION_THREAD_H
   9 #define NOTIFICATION_THREAD_H
  10
  11 #include <urcu/list.h>
  12 #include <urcu.h>
  13 #include <urcu/rculfhash.h>
  14 #include <lttng/trigger/trigger.h>
  15 #include <common/pipe.h>
  16 #include <common/compat/poll.h>
  17 #include <common/hashtable/hashtable.h>
  18 #include <pthread.h>
  19 #include <semaphore.h>
  20 #include "thread.h"
  21
  22 struct notification_thread_handle {
  23         /*
  24          * Queue of struct notification command.
  25          * event_pipe must be WRITE(2) to signal that a new command
  26          * has been enqueued.
  27          */
  28         struct {
  29                 struct lttng_pipe *event_pipe;
  30                 struct cds_list_head list;
  31                 pthread_mutex_t lock;
  32         } cmd_queue;
  33         /*
  34          * Read side of pipes used to receive channel status info collected
  35          * by the various consumer daemons.
  36          */
  37         struct {
  38                 int ust32_consumer;
  39                 int ust64_consumer;
  40                 int kernel_consumer;
  41         } channel_monitoring_pipes;
  42         /* Used to wait for the launch of the notification thread. */
  43         sem_t ready;
  44 };
  45
  46 /**
  47  * This thread maintains an internal state associating clients and triggers.
  48  *
  49  * In order to speed-up and simplify queries, hash tables providing the
  50  * following associations are maintained:
  51  *
  52  *   - client_socket_ht: associate a client's socket (fd) to its "struct client"
  53  *             This hash table owns the "struct client" which must thus be
  54  *             disposed-of on removal from the hash table.
  55  *
  56  *   - channel_triggers_ht:
  57  *             associates a channel key to a list of
  58  *             struct lttng_trigger_list_nodes. The triggers in this list are
  59  *             those that have conditions that apply to a particular channel.
  60  *             A channel entry is only created when a channel is added; the
  61  *             list of triggers applying to such a channel is built at that
  62  *             moment.
  63  *             This hash table owns the list, but not the triggers themselves.
  64  *
  65  *   - session_triggers_ht:
  66  *             associates a session name to a list of
  67  *             struct lttng_trigger_list_nodes. The triggers in this list are
  68  *             those that have conditions that apply to a particular session.
  69  *             A session entry is only created when a session is created; the
  70  *             list of triggers applying to this new session is built at that
  71  *             moment. This happens at the time of creation of a session_info.
  72  *             Likewise, the list is destroyed at the time of the session_info's
  73  *             destruction.
  74  *
  75  *   - channel_state_ht:
  76  *             associates a pair (channel key, channel domain) to its last
  77  *             sampled state received from the consumer daemon
  78  *             (struct channel_state).
  79  *             This previous sample is kept to implement edge-triggered
  80  *             conditions as we need to detect the state transitions.
  81  *             This hash table owns the channel state.
  82  *
  83  *   - notification_trigger_clients_ht:
  84  *             associates notification-emitting triggers to clients
  85  *             (struct notification_client_list) subscribed to those
  86  *             conditions.
  87  *             The condition's hash and match functions are used directly since
  88  *             all triggers in this hash table have the "notify" action.
  89  *             This hash table holds no ownership.
  90  *
  91  *   - channels_ht:
  92  *             associates a channel_key to a struct channel_info. The hash table
  93  *             holds the ownership of the struct channel_info.
  94  *
  95  *   - sessions_ht:
  96  *             associates a session_name (hash) to a struct session_info. The
  97  *             hash table holds no ownership of the struct session_info;
  98  *             the session_info structure is owned by the session's various
  99  *             channels through their struct channel_info (ref-counting is used).
 100  *
 101  *   - triggers_ht:
 102  *             associates a condition to a struct lttng_trigger_ht_element.
 103  *             The hash table holds the ownership of the
 104  *             lttng_trigger_ht_elements along with the triggers themselves.
 105  *
 106  * The thread reacts to the following internal events:
 107  *   1) creation of a tracing channel,
 108  *   2) destruction of a tracing channel,
 109  *   3) registration of a trigger,
 110  *   4) unregistration of a trigger,
 111  *   5) reception of a channel monitor sample from the consumer daemon.
 112  *   6) Session rotation ongoing
 113  *   7) Session rotation completed
 114  *
 115  * Events specific to notification-emitting triggers:
 116  *   8) connection of a notification client,
 117  *   9) disconnection of a notification client,
 118  *   10) subscription of a client to a conditions' notifications,
 119  *   11) unsubscription of a client from a conditions' notifications,
 120  *
 121  *
 122  * 1) Creation of a tracing channel
 123  *    - notification_trigger_clients_ht is traversed to identify
 124  *      triggers which apply to this new channel,
 125  *      - triggers identified are added to the channel_triggers_ht.
 126  *    - add channel to channels_ht
 127  *    - if it is the first channel of a session, a session_info is created and
 128  *      added to the sessions_ht. A list of the triggers associated with that
 129  *      session is built, and it is added to session_triggers_ht.
 130  *
 131  * 2) Destruction of a tracing channel
 132  *    - remove entry from channel_triggers_ht, releasing the list wrapper and
 133  *      elements,
 134  *    - remove entry from the channel_state_ht.
 135  *    - remove channel from channels_ht
 136  *    - if it was the last known channel of a session, the session_info
 137  *      structure is torndown, which in return destroys the list of triggers
 138  *      applying to that session.
 139  *
 140  * 3) Registration of a trigger
 141  *    - if the trigger's action is of type "notify",
 142  *      - traverse the list of conditions of every client to build a list of
 143  *        clients which have to be notified when this trigger's condition is met,
 144  *        - add list of clients (even if it is empty) to the
 145  *          notification_trigger_clients_ht,
 146  *    - add trigger to channel_triggers_ht (if applicable),
 147  *    - add trigger to session_triggers_ht (if applicable),
 148  *    - add trigger to triggers_ht
 149  *    - evaluate the trigger's condition right away to react if that condition
 150  *      is true from the beginning.
 151  *
 152  * 4) Unregistration of a trigger
 153  *    - if the trigger's action is of type "notify",
 154  *      - remove the trigger from the notification_trigger_clients_ht,
 155  *    - remove trigger from channel_triggers_ht (if applicable),
 156  *    - remove trigger from session_triggers_ht (if applicable),
 157  *    - remove trigger from triggers_ht
 158  *
 159  * 5) Reception of a channel monitor sample from the consumer daemon
 160  *    - evaluate the conditions associated with the triggers found in
 161  *      the channel_triggers_ht,
 162  *      - if a condition evaluates to "true" and the condition is of type
 163  *        "notify", query the notification_trigger_clients_ht and send
 164  *        a notification to the clients.
 165  *
 166  * 6) Session rotation ongoing
 167  *
 168  * 7) Session rotation completed
 169  *
 170  * 8) Connection of a client
 171  *    - add client socket to the client_socket_ht.
 172  *
 173  * 9) Disconnection of a client
 174  *    - remove client socket from the client_socket_ht,
 175  *    - traverse all conditions to which the client is subscribed and remove
 176  *      the client from the notification_trigger_clients_ht.
 177  *
 178  * 10) Subscription of a client to a condition's notifications
 179  *    - Add the condition to the client's list of subscribed conditions,
 180  *    - Look-up notification_trigger_clients_ht and add the client to
 181  *      list of clients.
 182  *    - Evaluate the condition for the client that subscribed if the trigger
 183  *      was already registered.
 184  *
 185  * 11) Unsubscription of a client to a condition's notifications
 186  *    - Remove the condition from the client's list of subscribed conditions,
 187  *    - Look-up notification_trigger_clients_ht and remove the client
 188  *      from the list of clients.
 189  */
 190 struct notification_thread_state {
 191         int notification_channel_socket;
 192         struct lttng_poll_event events;
 193         struct cds_lfht *client_socket_ht;
 194         struct cds_lfht *channel_triggers_ht;
 195         struct cds_lfht *session_triggers_ht;
 196         struct cds_lfht *channel_state_ht;
 197         struct cds_lfht *notification_trigger_clients_ht;
 198         struct cds_lfht *channels_ht;
 199         struct cds_lfht *sessions_ht;
 200         struct cds_lfht *triggers_ht;
 201 };
 202
 203 /* notification_thread_data takes ownership of the channel monitor pipes. */
 204 struct notification_thread_handle *notification_thread_handle_create(
 205                 struct lttng_pipe *ust32_channel_monitor_pipe,
 206                 struct lttng_pipe *ust64_channel_monitor_pipe,
 207                 struct lttng_pipe *kernel_channel_monitor_pipe);
 208 void notification_thread_handle_destroy(
 209                 struct notification_thread_handle *handle);
 210 struct lttng_thread *launch_notification_thread(
 211                 struct notification_thread_handle *handle);
 212
 213 #endif /* NOTIFICATION_THREAD_H */