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 "action-executor.h"
  12 #include "thread.h"
  13 #include <common/compat/poll.h>
  14 #include <common/hashtable/hashtable.h>
  15 #include <common/pipe.h>
  16 #include <lttng/trigger/trigger.h>
  17 #include <lttng/domain.h>
  18 #include <pthread.h>
  19 #include <semaphore.h>
  20 #include <urcu.h>
  21 #include <urcu/list.h>
  22 #include <urcu/rculfhash.h>
  23
  24 typedef uint64_t notification_client_id;
  25
  26 /*
  27  * The notification thread holds no ownership of the tracer event source pipe
  28  * file descriptor. The tracer management logic must remove the event source
  29  * from the notification thread (see external commands) before releasing
  30  * this file descriptor.
  31  */
  32 struct notification_event_tracer_event_source_element {
  33         int fd;
  34         /*
  35          * A tracer event source can be removed from the notification thread's
  36          * poll set before the end of its lifetime (for instance, when an error
  37          * or hang-up is detected on its file descriptor). This is done to
  38          * allow the notification thread to ignore follow-up events on this
  39          * file descriptors.
  40          *
  41          * Under such circumstances, the notification thread still expects
  42          * the normal clean-up to occur through the 'REMOVE_TRACER_EVENT_SOURCE'
  43          * command.
  44          */
  45         bool is_fd_in_poll_set;
  46         enum lttng_domain_type domain;
  47         struct cds_list_head node;
  48 };
  49
  50 struct notification_thread_handle {
  51         /*
  52          * Queue of struct notification command.
  53          * event_pipe must be WRITE(2) to signal that a new command
  54          * has been enqueued.
  55          */
  56         struct {
  57                 struct lttng_pipe *event_pipe;
  58                 struct cds_list_head list;
  59                 pthread_mutex_t lock;
  60         } cmd_queue;
  61         /*
  62          * Read side of pipes used to receive channel status info collected
  63          * by the various consumer daemons.
  64          */
  65         struct {
  66                 int ust32_consumer;
  67                 int ust64_consumer;
  68                 int kernel_consumer;
  69         } channel_monitoring_pipes;
  70         /* Used to wait for the launch of the notification thread. */
  71         sem_t ready;
  72 };
  73
  74 /**
  75  * This thread maintains an internal state associating clients and triggers.
  76  *
  77  * In order to speed-up and simplify queries, hash tables providing the
  78  * following associations are maintained:
  79  *
  80  *   - client_socket_ht: associate a client's socket (fd) to its
  81  *             "struct notification_client".
  82  *             This hash table owns the "struct notification_client" which must
  83  *             thus be disposed-of on removal from the hash table.
  84  *
  85  *   - client_id_ht: associate a client's id to its "struct notification_client"
  86  *             This hash table holds a _weak_ reference to the
  87  *             "struct notification_client".
  88  *
  89  *   - channel_triggers_ht:
  90  *             associates a channel key to a list of
  91  *             struct lttng_trigger_list_nodes. The triggers in this list are
  92  *             those that have conditions that apply to a particular channel.
  93  *             A channel entry is only created when a channel is added; the
  94  *             list of triggers applying to such a channel is built at that
  95  *             moment.
  96  *             This hash table owns the list, but not the triggers themselves.
  97  *
  98  *   - session_triggers_ht:
  99  *             associates a session name to a list of
 100  *             struct lttng_trigger_list_nodes. The triggers in this list are
 101  *             those that have conditions that apply to a particular session.
 102  *             A session entry is only created when a session is created; the
 103  *             list of triggers applying to this new session is built at that
 104  *             moment. This happens at the time of creation of a session_info.
 105  *             Likewise, the list is destroyed at the time of the session_info's
 106  *             destruction.
 107  *
 108  *   - channel_state_ht:
 109  *             associates a pair (channel key, channel domain) to its last
 110  *             sampled state received from the consumer daemon
 111  *             (struct channel_state).
 112  *             This previous sample is kept to implement edge-triggered
 113  *             conditions as we need to detect the state transitions.
 114  *             This hash table owns the channel state.
 115  *
 116  *   - notification_trigger_clients_ht:
 117  *             associates notification-emitting triggers to clients
 118  *             (struct notification_client_list) subscribed to those
 119  *             conditions.
 120  *             The condition's hash and match functions are used directly since
 121  *             all triggers in this hash table have the "notify" action.
 122  *             This hash table holds no ownership.
 123  *
 124  *   - channels_ht:
 125  *             associates a channel_key to a struct channel_info. The hash table
 126  *             holds the ownership of the struct channel_info.
 127  *
 128  *   - sessions_ht:
 129  *             associates a session_name (hash) to a struct session_info. The
 130  *             hash table holds no ownership of the struct session_info;
 131  *             the session_info structure is owned by the session's various
 132  *             channels through their struct channel_info (ref-counting is used).
 133  *
 134  *   - triggers_ht:
 135  *             associates a trigger to a struct lttng_trigger_ht_element.
 136  *             The hash table holds the ownership of the
 137  *             lttng_trigger_ht_elements along with the triggers themselves.
 138  *   - triggers_by_name_uid_ht:
 139  *             associates a trigger (name, uid) tuple to
 140  *             a struct lttng_trigger_ht_element.
 141  *             The hash table does not hold any ownership and is used strictly
 142  *             for lookup on registration.
 143  *   - tracer_event_sources_list:
 144  *             A list of tracer event source (read side fd) of type
 145 *              struct notification_event_tracer_event_source_element.
 146 *
 147  *
 148  * The thread reacts to the following internal events:
 149  *   1) creation of a tracing channel,
 150  *   2) destruction of a tracing channel,
 151  *   3) registration of a trigger,
 152  *   4) unregistration of a trigger,
 153  *   5) reception of a channel monitor sample from the consumer daemon,
 154  *   6) Session rotation ongoing,
 155  *   7) Session rotation completed,
 156  *   8) registration of a tracer event source,
 157  *   9) unregistration of a tracer event source,
 158  *
 159  * Events specific to notification-emitting triggers:
 160  *   9) connection of a notification client,
 161  *   10) disconnection of a notification client,
 162  *   11) subscription of a client to a conditions' notifications,
 163  *   12) unsubscription of a client from a conditions' notifications,
 164  *
 165  *
 166  * 1) Creation of a tracing channel
 167  *    - notification_trigger_clients_ht is traversed to identify
 168  *      triggers which apply to this new channel,
 169  *      - triggers identified are added to the channel_triggers_ht.
 170  *    - add channel to channels_ht
 171  *    - if it is the first channel of a session, a session_info is created and
 172  *      added to the sessions_ht. A list of the triggers associated with that
 173  *      session is built, and it is added to session_triggers_ht.
 174  *
 175  * 2) Destruction of a tracing channel
 176  *    - remove entry from channel_triggers_ht, releasing the list wrapper and
 177  *      elements,
 178  *    - remove entry from the channel_state_ht.
 179  *    - remove channel from channels_ht
 180  *    - if it was the last known channel of a session, the session_info
 181  *      structure is torndown, which in return destroys the list of triggers
 182  *      applying to that session.
 183  *
 184  * 3) Registration of a trigger
 185  *    - if the trigger's action is of type "notify",
 186  *      - traverse the list of conditions of every client to build a list of
 187  *        clients which have to be notified when this trigger's condition is met,
 188  *        - add list of clients (even if it is empty) to the
 189  *          notification_trigger_clients_ht,
 190  *    - add trigger to channel_triggers_ht (if applicable),
 191  *    - add trigger to session_triggers_ht (if applicable),
 192  *    - add trigger to triggers_by_name_uid_ht
 193  *    - add trigger to triggers_ht
 194  *    - evaluate the trigger's condition right away to react if that condition
 195  *      is true from the beginning.
 196  *
 197  * 4) Unregistration of a trigger
 198  *    - if the trigger's action is of type "notify",
 199  *      - remove the trigger from the notification_trigger_clients_ht,
 200  *    - remove trigger from channel_triggers_ht (if applicable),
 201  *    - remove trigger from session_triggers_ht (if applicable),
 202  *    - remove trigger from triggers_by_name_uid_ht
 203  *    - remove trigger from triggers_ht
 204  *
 205  * 5) Reception of a channel monitor sample from the consumer daemon
 206  *    - evaluate the conditions associated with the triggers found in
 207  *      the channel_triggers_ht,
 208  *      - if a condition evaluates to "true" and the condition is of type
 209  *        "notify", query the notification_trigger_clients_ht and send
 210  *        a notification to the clients.
 211  *
 212  * 6) Session rotation ongoing
 213  *
 214  * 7) Session rotation completed
 215  *
 216  * 8) Registration of a tracer event source
 217  *    - Add the tracer event source of the application to
 218  *      tracer_event_sources_list,
 219  *    - Add the trace event source to the pollset.
 220  *
 221  * 8) Unregistration of a tracer event source
 222  *    - Remove the tracer event source of the application from
 223  *      tracer_event_sources_list,
 224  *    - Remove the trace event source from the pollset.
 225  *
 226  * 10) Connection of a client
 227  *    - add client socket to the client_socket_ht,
 228  *    - add client socket to the client_id_ht.
 229  *
 230  * 11) Disconnection of a client
 231  *    - remove client socket from the client_id_ht,
 232  *    - remove client socket from the client_socket_ht,
 233  *    - traverse all conditions to which the client is subscribed and remove
 234  *      the client from the notification_trigger_clients_ht.
 235  *
 236  * 12) Subscription of a client to a condition's notifications
 237  *    - Add the condition to the client's list of subscribed conditions,
 238  *    - Look-up notification_trigger_clients_ht and add the client to
 239  *      list of clients.
 240  *    - Evaluate the condition for the client that subscribed if the trigger
 241  *      was already registered.
 242  *
 243  * 13) Unsubscription of a client to a condition's notifications
 244  *    - Remove the condition from the client's list of subscribed conditions,
 245  *    - Look-up notification_trigger_clients_ht and remove the client
 246  *      from the list of clients.
 247  */
 248 struct notification_thread_state {
 249         int notification_channel_socket;
 250         struct lttng_poll_event events;
 251         struct cds_lfht *client_socket_ht;
 252         struct cds_lfht *client_id_ht;
 253         struct cds_lfht *channel_triggers_ht;
 254         struct cds_lfht *session_triggers_ht;
 255         struct cds_lfht *channel_state_ht;
 256         struct cds_lfht *notification_trigger_clients_ht;
 257         struct cds_lfht *channels_ht;
 258         struct cds_lfht *sessions_ht;
 259         struct cds_lfht *triggers_ht;
 260         struct cds_lfht *triggers_by_name_uid_ht;
 261         struct {
 262                 uint64_t next_tracer_token;
 263                 uint64_t name_offset;
 264         } trigger_id;
 265         /*
 266          * Read side of the pipes used to receive tracer events. As their name
 267          * implies, tracer event source activity originate from either
 268          * registered applications (user space tracer) or from the kernel
 269          * tracer.
 270          *
 271          * The list is not protected by a lock since add and remove operations
 272          * are currently done only by the notification thread through in
 273          * response to blocking commands.
 274          */
 275         struct cds_list_head tracer_event_sources_list;
 276         notification_client_id next_notification_client_id;
 277         struct action_executor *executor;
 278 };
 279
 280 /* notification_thread_data takes ownership of the channel monitor pipes. */
 281 struct notification_thread_handle *notification_thread_handle_create(
 282                 struct lttng_pipe *ust32_channel_monitor_pipe,
 283                 struct lttng_pipe *ust64_channel_monitor_pipe,
 284                 struct lttng_pipe *kernel_channel_monitor_pipe);
 285 void notification_thread_handle_destroy(
 286                 struct notification_thread_handle *handle);
 287 struct lttng_thread *launch_notification_thread(
 288                 struct notification_thread_handle *handle);
 289
 290 #endif /* NOTIFICATION_THREAD_H */