liblttng-ust/event-notifier-notification.c

   1 /*
   2  * event-notifier-notification.c
   3  *
   4  * Copyright (C) 2020 Francis Deslauriers <francis.deslauriers@efficios.com>
   5  *
   6  * This library is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public
   8  * License as published by the Free Software Foundation; only
   9  * version 2.1 of the License.
  10  *
  11  * This library is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public
  17  * License along with this library; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  19  */
  20
  21 #define _LGPL_SOURCE
  22
  23 #include <errno.h>
  24 #include <lttng/ust-events.h>
  25 #include <usterr-signal-safe.h>
  26
  27 #include "share.h"
  28
  29 void lttng_event_notifier_notification_send(
  30                 struct lttng_event_notifier *event_notifier)
  31 {
  32         /*
  33          * We want this write to be atomic AND non-blocking, meaning that we
  34          * want to write either everything OR nothing.
  35          * According to `pipe(7)`, writes that are smaller that the `PIPE_BUF`
  36          * value must be atomic, so we assert that the message we send is less
  37          * than PIPE_BUF.
  38          */
  39         struct lttng_ust_event_notifier_notification notif;
  40         ssize_t ret;
  41
  42         assert(event_notifier);
  43         assert(event_notifier->group);
  44         assert(sizeof(notif) <= PIPE_BUF);
  45
  46         notif.token = event_notifier->user_token;
  47
  48         ret = patient_write(event_notifier->group->notification_fd, &notif,
  49                 sizeof(notif));
  50         if (ret == -1) {
  51                 if (errno == EAGAIN) {
  52                         DBG("Cannot send event notifier notification without blocking: %s",
  53                                 strerror(errno));
  54                 } else {
  55                         DBG("Error to sending event notifier notification: %s",
  56                                 strerror(errno));
  57                         abort();
  58                 }
  59         }
  60 }