event_notifier.c

   1 /*
   2  * event notifier support
   3  *
   4  * Copyright Red Hat, Inc. 2010
   5  *
   6  * Authors:
   7  *  Michael S. Tsirkin <mst@redhat.com>
   8  *
   9  * This work is licensed under the terms of the GNU GPL, version 2.  See
  10  * the COPYING file in the top-level directory.
  11  */
  12
  13 #include "event_notifier.h"
  14 #ifdef CONFIG_EVENTFD
  15 #include <sys/eventfd.h>
  16 #endif
  17
  18 int event_notifier_init(EventNotifier *e, int active)
  19 {
  20 #ifdef CONFIG_EVENTFD
  21     int fd = eventfd(!!active, EFD_NONBLOCK | EFD_CLOEXEC);
  22     if (fd < 0)
  23         return -errno;
  24     e->fd = fd;
  25     return 0;
  26 #else
  27     return -ENOSYS;
  28 #endif
  29 }
  30
  31 void event_notifier_cleanup(EventNotifier *e)
  32 {
  33     close(e->fd);
  34 }
  35
  36 int event_notifier_get_fd(EventNotifier *e)
  37 {
  38     return e->fd;
  39 }
  40
  41 int event_notifier_test_and_clear(EventNotifier *e)
  42 {
  43     uint64_t value;
  44     int r = read(e->fd, &value, sizeof(value));
  45     return r == sizeof(value);
  46 }
  47
  48 int event_notifier_test(EventNotifier *e)
  49 {
  50     uint64_t value;
  51     int r = read(e->fd, &value, sizeof(value));
  52     if (r == sizeof(value)) {
  53         /* restore previous value. */
  54         int s = write(e->fd, &value, sizeof(value));
  55         /* never blocks because we use EFD_SEMAPHORE.
  56          * If we didn't we'd get EAGAIN on overflow
  57          * and we'd have to write code to ignore it. */
  58         assert(s == sizeof(value));
  59     }
  60     return r == sizeof(value);
  61 }