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

   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.hpp"
  12 #include "thread.hpp"
  13
  14 #include <common/compat/poll.hpp>
  15 #include <common/hashtable/hashtable.hpp>
  16 #include <common/pipe.hpp>
  17
  18 #include <lttng/domain.h>
  19 #include <lttng/trigger/trigger.h>
  20
  21 #include <pthread.h>
  22 #include <semaphore.h>
  23 #include <urcu.h>
  24 #include <urcu/list.h>
  25 #include <urcu/rculfhash.h>
  26
  27 using notification_client_id = uint64_t;
  28
  29 /*
  30  * The notification thread holds no ownership of the tracer event source pipe
  31  * file descriptor. The tracer management logic must remove the event source
  32  * from the notification thread (see external commands) before releasing
  33  * this file descriptor.
  34  */
  35 struct notification_event_tracer_event_source_element {
  36         int fd;
  37         /*
  38          * A tracer event source can be removed from the notification thread's
  39          * poll set before the end of its lifetime (for instance, when an error
  40          * or hang-up is detected on its file descriptor). This is done to
  41          * allow the notification thread to ignore follow-up events on this
  42          * file descriptors.
  43          *
  44          * Under such circumstances, the notification thread still expects
  45          * the normal clean-up to occur through the 'REMOVE_TRACER_EVENT_SOURCE'
  46          * command.
  47          */
  48         bool is_fd_in_poll_set;
  49         enum lttng_domain_type domain;
  50         struct cds_list_head node;
  51 };
  52
  53 struct notification_trigger_tokens_ht_element {
  54         uint64_t token;
  55         /* Weak reference to the trigger. */
  56         struct lttng_trigger *trigger;
  57         struct cds_lfht_node node;
  58         /* call_rcu delayed reclaim. */
  59         struct rcu_head rcu_node;
  60 };
  61
  62 struct notification_thread_handle {
  63         /*
  64          * Queue of struct notification command.
  65          * event_pipe must be WRITE(2) to signal that a new command
  66          * has been enqueued.
  67          */
  68         struct {
  69                 int event_fd;
  70                 struct cds_list_head list;
  71                 pthread_mutex_t lock;
  72         } cmd_queue;
  73         /*
  74          * Read side of pipes used to receive channel status info collected
  75          * by the various consumer daemons.
  76          */
  77         struct {
  78                 int ust32_consumer;
  79                 int ust64_consumer;
  80                 int kernel_consumer;
  81         } channel_monitoring_pipes;
  82         /* Used to wait for the launch of the notification thread. */
  83         sem_t ready;
  84 };
  85
  86 /**
  87  * This thread maintains an internal state associating clients and triggers.
  88  *
  89  * In order to speed-up and simplify queries, hash tables providing the
  90  * following associations are maintained:
  91  *
  92  *   - client_socket_ht: associate a client's socket (fd) to its
  93  *             "struct notification_client".
  94  *             This hash table owns the "struct notification_client" which must
  95  *             thus be disposed-of on removal from the hash table.
  96  *
  97  *   - client_id_ht: associate a client's id to its "struct notification_client"
  98  *             This hash table holds a _weak_ reference to the
  99  *             "struct notification_client".
 100  *
 101  *   - channel_triggers_ht:
 102  *             associates a channel key to a list of
 103  *             struct lttng_trigger_list_nodes. The triggers in this list are
 104  *             those that have conditions that apply to a particular channel.
 105  *             A channel entry is only created when a channel is added; the
 106  *             list of triggers applying to such a channel is built at that
 107  *             moment.
 108  *             This hash table owns the list, but not the triggers themselves.
 109  *
 110  *   - session_triggers_ht:
 111  *             associates a session name to a list of
 112  *             struct lttng_trigger_list_nodes. The triggers in this list are
 113  *             those that have conditions that apply to a particular session.
 114  *             A session entry is only created when a session is created; the
 115  *             list of triggers applying to this new session is built at that
 116  *             moment. This happens at the time of creation of a session_info.
 117  *             Likewise, the list is destroyed at the time of the session_info's
 118  *             destruction.
 119  *
 120  *   - channel_state_ht:
 121  *             associates a pair (channel key, channel domain) to its last
 122  *             sampled state received from the consumer daemon
 123  *             (struct channel_state).
 124  *             This previous sample is kept to implement edge-triggered
 125  *             conditions as we need to detect the state transitions.
 126  *             This hash table owns the channel state.
 127  *
 128  *   - notification_trigger_clients_ht:
 129  *             associates notification-emitting triggers to clients
 130  *             (struct notification_client_list) subscribed to those
 131  *             conditions.
 132  *             The condition's hash and match functions are used directly since
 133  *             all triggers in this hash table have the "notify" action.
 134  *             This hash table holds no ownership.
 135  *
 136  *   - channels_ht:
 137  *             associates a channel_key to a struct channel_info. The hash table
 138  *             holds the ownership of the struct channel_info.
 139  *
 140  *   - sessions_ht:
 141  *             associates a session_name (hash) to a struct session_info. The
 142  *             hash table holds no ownership of the struct session_info;
 143  *             the session_info structure is owned by the session's various
 144  *             channels through their struct channel_info (ref-counting is used).
 145  *
 146  *   - triggers_ht:
 147  *             associates a trigger to a struct lttng_trigger_ht_element.
 148  *             The hash table holds the ownership of the
 149  *             lttng_trigger_ht_elements along with the triggers themselves.
 150  *   - triggers_by_name_uid_ht:
 151  *             associates a trigger (name, uid) tuple to
 152  *             a struct lttng_trigger_ht_element.
 153  *             The hash table does not hold any ownership and is used strictly
 154  *             for lookup on registration.
 155  *   - tracer_event_sources_list:
 156  *             A list of tracer event source (read side fd) of type
 157  *              struct notification_event_tracer_event_source_element.
 158  *
 159  *
 160  * The thread reacts to the following internal events:
 161  *   1) creation of a tracing channel,
 162  *   2) destruction of a tracing channel,
 163  *   3) creation of a tracing session,
 164  *   4) destruction of a tracing session,
 165  *   5)  registration of a trigger,
 166  *   6)  unregistration of a trigger,
 167  *   7)  reception of a channel monitor sample from the consumer daemon,
 168  *   8)  Session rotation ongoing,
 169  *   9)  Session rotation completed,
 170  *   10) registration of a tracer event source,
 171  *   11) unregistration of a tracer event source,
 172  *
 173  * Events specific to notification-emitting triggers:
 174  *   9) connection of a notification client,
 175  *   10) disconnection of a notification client,
 176  *   11) subscription of a client to a conditions' notifications,
 177  *   12) unsubscription of a client from a conditions' notifications,
 178  *
 179  *
 180  * 1) Creation of a tracing channel
 181  *    - notification_trigger_clients_ht is traversed to identify
 182  *      triggers which apply to this new channel,
 183  *      - triggers identified are added to the channel_triggers_ht.
 184  *    - add channel to channels_ht
 185  *    - if it is the first channel of a session, a session_info is created and
 186  *      added to the sessions_ht. A list of the triggers associated with that
 187  *      session is built, and it is added to session_triggers_ht.
 188  *
 189  * 2) Destruction of a tracing channel
 190  *    - remove entry from channel_triggers_ht, releasing the list wrapper and
 191  *      elements,
 192  *    - remove entry from the channel_state_ht.
 193  *    - remove channel from channels_ht
 194  *    - if it was the last known channel of a session, the session_info
 195  *      structure is torndown, which in return destroys the list of triggers
 196  *      applying to that session.
 197  *
 198  * 3) Registration of a trigger
 199  *    - if the trigger's action is of type "notify",
 200  *      - traverse the list of conditions of every client to build a list of
 201  *        clients which have to be notified when this trigger's condition is met,
 202  *        - add list of clients (even if it is empty) to the
 203  *          notification_trigger_clients_ht,
 204  *    - add trigger to channel_triggers_ht (if applicable),
 205  *    - add trigger to session_triggers_ht (if applicable),
 206  *    - add trigger to triggers_by_name_uid_ht
 207  *    - add trigger to triggers_ht
 208  *    - evaluate the trigger's condition right away to react if that condition
 209  *      is true from the beginning.
 210  *
 211  * 4) Unregistration of a trigger
 212  *    - if the trigger's action is of type "notify",
 213  *      - remove the trigger from the notification_trigger_clients_ht,
 214  *    - remove trigger from channel_triggers_ht (if applicable),
 215  *    - remove trigger from session_triggers_ht (if applicable),
 216  *    - remove trigger from triggers_by_name_uid_ht
 217  *    - remove trigger from triggers_ht
 218  *
 219  * 5) Reception of a channel monitor sample from the consumer daemon
 220  *    - evaluate the conditions associated with the triggers found in
 221  *      the channel_triggers_ht,
 222  *      - if a condition evaluates to "true" and the condition is of type
 223  *        "notify", query the notification_trigger_clients_ht and send
 224  *        a notification to the clients.
 225  *
 226  * 6) Session rotation ongoing
 227  *
 228  * 7) Session rotation completed
 229  *
 230  * 8) Registration of a tracer event source
 231  *    - Add the tracer event source of the application to
 232  *      tracer_event_sources_list,
 233  *    - Add the trace event source to the pollset.
 234  *
 235  * 8) Unregistration of a tracer event source
 236  *    - Remove the tracer event source of the application from
 237  *      tracer_event_sources_list,
 238  *    - Remove the trace event source from the pollset.
 239  *
 240  * 10) Connection of a client
 241  *    - add client socket to the client_socket_ht,
 242  *    - add client socket to the client_id_ht.
 243  *
 244  * 11) Disconnection of a client
 245  *    - remove client socket from the client_id_ht,
 246  *    - remove client socket from the client_socket_ht,
 247  *    - traverse all conditions to which the client is subscribed and remove
 248  *      the client from the notification_trigger_clients_ht.
 249  *
 250  * 12) Subscription of a client to a condition's notifications
 251  *    - Add the condition to the client's list of subscribed conditions,
 252  *    - Look-up notification_trigger_clients_ht and add the client to
 253  *      list of clients.
 254  *    - Evaluate the condition for the client that subscribed if the trigger
 255  *      was already registered.
 256  *
 257  * 13) Unsubscription of a client to a condition's notifications
 258  *    - Remove the condition from the client's list of subscribed conditions,
 259  *    - Look-up notification_trigger_clients_ht and remove the client
 260  *      from the list of clients.
 261  */
 262 struct notification_thread_state {
 263         int notification_channel_socket;
 264         struct lttng_poll_event events;
 265         struct cds_lfht *client_socket_ht;
 266         struct cds_lfht *client_id_ht;
 267         struct cds_lfht *channel_triggers_ht;
 268         struct cds_lfht *session_triggers_ht;
 269         struct cds_lfht *channel_state_ht;
 270         struct cds_lfht *notification_trigger_clients_ht;
 271         struct cds_lfht *channels_ht;
 272         struct cds_lfht *sessions_ht;
 273         struct cds_lfht *triggers_ht;
 274         struct cds_lfht *triggers_by_name_uid_ht;
 275         struct cds_lfht *trigger_tokens_ht;
 276         struct {
 277                 uint64_t next_tracer_token;
 278                 uint64_t name_offset;
 279         } trigger_id;
 280         /*
 281          * Read side of the pipes used to receive tracer events. As their name
 282          * implies, tracer event source activity originate from either
 283          * registered applications (user space tracer) or from the kernel
 284          * tracer.
 285          *
 286          * The list is not protected by a lock since add and remove operations
 287          * are currently done only by the notification thread through in
 288          * response to blocking commands.
 289          */
 290         struct cds_list_head tracer_event_sources_list;
 291         notification_client_id next_notification_client_id;
 292         struct action_executor *executor;
 293
 294         /*
 295          * Indicates the thread to break for the poll event processing loop and
 296          * call _poll_wait() again.
 297          *
 298          * This is necessary because some events on one fd might trigger the
 299          * consumption of another fd.
 300          * For example, a single _poll_wait() call can return notification
 301          * thread commands and events from the tracer event source (event
 302          * notifier).
 303          * Picture a scenario where we receive two events:
 304          *  the first one is a _REMOVE_TRACER_EVENT_SOURCE command, and
 305          *  the second is an POLLIN on the tracer event source fd.
 306          *
 307          * The _REMOVE_TRACER_EVENT_SOURCE will read all the data of the
 308          * removed tracer event source.
 309          *
 310          * The second event is now invalid has we consumed all the data for
 311          * which we received the POLLIN.
 312          *
 313          * For this reason, we need to break for the event processing loop and
 314          * call _poll_wait() again to get a clean view of the activity on the
 315          * fds.
 316          */
 317         bool restart_poll;
 318 };
 319
 320 /* notification_thread_data takes ownership of the channel monitor pipes. */
 321 struct notification_thread_handle *
 322 notification_thread_handle_create(struct lttng_pipe *ust32_channel_monitor_pipe,
 323                                   struct lttng_pipe *ust64_channel_monitor_pipe,
 324                                   struct lttng_pipe *kernel_channel_monitor_pipe);
 325 void notification_thread_handle_destroy(struct notification_thread_handle *handle);
 326 struct lttng_thread *launch_notification_thread(struct notification_thread_handle *handle);
 327
 328 #endif /* NOTIFICATION_THREAD_H */