include/lttng/notification/channel.h

   1 /*
   2  * Copyright (C) 2017 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
   3  *
   4  * This library is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU Lesser General Public License, version 2.1 only,
   6  * as published by the Free Software Foundation.
   7  *
   8  * This library is distributed in the hope that it will be useful, but WITHOUT
   9  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  10  * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
  11  * for more details.
  12  *
  13  * You should have received a copy of the GNU Lesser General Public License
  14  * along with this library; if not, write to the Free Software Foundation,
  15  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  16  */
  17
  18 #ifndef LTTNG_NOTIFICATION_CHANNEL_H
  19 #define LTTNG_NOTIFICATION_CHANNEL_H
  20
  21 #ifdef __cplusplus
  22 extern "C" {
  23 #endif
  24
  25 struct lttng_endpoint;
  26 struct lttng_condition;
  27 struct lttng_notification;
  28 struct lttng_notification_channel;
  29
  30 enum lttng_notification_channel_status {
  31         LTTNG_NOTIFICATION_CHANNEL_STATUS_NOTIFICATIONS_DROPPED = 1,
  32         LTTNG_NOTIFICATION_CHANNEL_STATUS_OK = 0,
  33         LTTNG_NOTIFICATION_CHANNEL_STATUS_ERROR = -1,
  34         LTTNG_NOTIFICATION_CHANNEL_STATUS_CLOSED = -2,
  35         LTTNG_NOTIFICATION_CHANNEL_STATUS_ALREADY_SUBSCRIBED = -3,
  36         /* Condition unknown. */
  37         LTTNG_NOTIFICATION_CHANNEL_STATUS_UNKNOWN_CONDITION = -4,
  38         LTTNG_NOTIFICATION_CHANNEL_STATUS_INVALID = -5,
  39         LTTNG_NOTIFICATION_CHANNEL_STATUS_UNSUPPORTED_VERSION = -6,
  40 };
  41
  42 /**
  43  * A notification channel is used to receive notifications from various
  44  * LTTng components.
  45  *
  46  * Notification channels connect a client to an LTTng endpoint
  47  * (see lttng/endpoint.h) and allows client to subscribe and unsubscribe
  48  * to various types of notifications which are associated to conditions.
  49  *
  50  * In order to emit a notification, a condition must be associated to a
  51  * notify action within a trigger. A client wishing to consume such
  52  * conditions must explicitly subscribe to them by using an equivalent
  53  * condition.
  54  */
  55
  56 /*
  57  * Create a notification channel connected to a given endpoint.
  58  *
  59  * The only supported endpoint, at the moment, is the
  60  * lttng_session_daemon_notification_endpoint, which is a singleton
  61  * declared in the lttng/endpoint.h header.
  62  *
  63  * Returns an lttng_notification_channel on success, NULL on failure.
  64  * The returned lttng_notification_channel must be destroyed using
  65  * the lttng_notification_channel_destroy() function.
  66  */
  67 extern struct lttng_notification_channel *lttng_notification_channel_create(
  68                 struct lttng_endpoint *endpoint);
  69
  70 /*
  71  * Get the next notification received on a notification channel.
  72  *
  73  * This call will block until a notification is received on the notification
  74  * channel or until the endpoint closes the connection.
  75  *
  76  * The returned notification's ownership is transferred to the caller and
  77  * it must be destroyed using lttng_notification_destroy().
  78  *
  79  * Notifications can be dropped if a client consumes the notifications sent
  80  * through the notification channel too slowly.
  81  *
  82  * Returns LTTNG_NOTIFICATION_CHANNEL_STATUS_OK and a notification on success,
  83  * LTTNG_NOTIFICATION_CHANNEL_STATUS_INVALID if an invalid parameter was
  84  * provided, or LTTNG_NOTIFICATION_CHANNEL_STATUS_NOTIFICATIONS_DROPPED if
  85  * notifications were dropped.
  86  */
  87 extern enum lttng_notification_channel_status
  88 lttng_notification_channel_get_next_notification(
  89                 struct lttng_notification_channel *channel,
  90                 struct lttng_notification **notification);
  91
  92 /*
  93  * Subscribe to notifications of a condition through a notification channel.
  94  *
  95  * The caller retains the ownership of the condition passed through this call
  96  * and it can be disposed-of at any moment after this call.
  97  *
  98  * An error will be reported if the client tries to subscribe to the same
  99  * condition multiple times without unsubscribing.
 100  *
 101  * Returns LTTNG_NOTIFICATION_CHANNEL_STATUS_OK on success,
 102  * LTTNG_NOTIFICATION_CHANNEL_STATUS_INVALID if an invalid parameter was
 103  * provided, or LTTNG_NOTIFICATION_CHANNEL_STATUS_ALREADY_SUBSCRIBED if the
 104  * client was already subscribed to the condition through this channel.
 105  */
 106 extern enum lttng_notification_channel_status
 107 lttng_notification_channel_subscribe(
 108                 struct lttng_notification_channel *channel,
 109                 const struct lttng_condition *condition);
 110
 111 /*
 112  * Unsubscribe to notifications of a condition through a notification channel.
 113  *
 114  * The caller retains the ownership of the condition passed through this call
 115  * and it can be disposed-of at any moment after this call.
 116  *
 117  * An error will be reported if the client tries to unsubscribe to from a
 118  * conditions' notifications to which it was not previously subscribed.
 119  *
 120  * Returns LTTNG_NOTIFICATION_CHANNEL_STATUS_OK on success,
 121  * LTTNG_NOTIFICATION_CHANNEL_STATUS_INVALID if an invalid parameter was
 122  * provided, or LTTNG_NOTIFICATION_CHANNEL_STATUS_UNKNOWN_CONDITION if the
 123  * client was not already subscribed to the condition through this channel.
 124  */
 125 extern enum lttng_notification_channel_status
 126 lttng_notification_channel_unsubscribe(
 127                 struct lttng_notification_channel *channel,
 128                 const struct lttng_condition *condition);
 129
 130 /*
 131  * Closes and destroys (frees) a notification channel.
 132  */
 133 extern void lttng_notification_channel_destroy(
 134                 struct lttng_notification_channel *channel);
 135
 136 #ifdef __cplusplus
 137 }
 138 #endif
 139
 140 #endif /* LTTNG_NOTIFICATION_CHANNEL_H */