hw/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 "hw.h"
  14 #include "event_notifier.h"
  15 #ifdef CONFIG_EVENTFD
  16 #include <sys/eventfd.h>
  17 #endif
  18
  19 int event_notifier_init(EventNotifier *e, int active)
  20 {
  21 #ifdef CONFIG_EVENTFD
  22     int fd = eventfd(!!active, EFD_NONBLOCK | EFD_CLOEXEC);
  23     if (fd < 0)
  24         return -errno;
  25     e->fd = fd;
  26     return 0;
  27 #else
  28     return -ENOSYS;
  29 #endif
  30 }
  31
  32 void event_notifier_cleanup(EventNotifier *e)
  33 {
  34     close(e->fd);
  35 }
  36
  37 int event_notifier_get_fd(EventNotifier *e)
  38 {
  39     return e->fd;
  40 }
  41
  42 int event_notifier_test_and_clear(EventNotifier *e)
  43 {
  44     uint64_t value;
  45     int r = read(e->fd, &value, sizeof(value));
  46     return r == sizeof(value);
  47 }
  48
  49 int event_notifier_test(EventNotifier *e)
  50 {
  51     uint64_t value;
  52     int r = read(e->fd, &value, sizeof(value));
  53     if (r == sizeof(value)) {
  54         /* restore previous value. */
  55         int s = write(e->fd, &value, sizeof(value));
  56         /* never blocks because we use EFD_SEMAPHORE.
  57          * If we didn't we'd get EAGAIN on overflow
  58          * and we'd have to write code to ignore it. */
  59         assert(s == sizeof(value));
  60     }
  61     return r == sizeof(value);
  62 }