util/event_notifier-posix.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 or later.
  10  * See the COPYING file in the top-level directory.
  11  */
  12
  13 #include "qemu/osdep.h"
  14 #include "qemu-common.h"
  15 #include "qemu/cutils.h"
  16 #include "qemu/event_notifier.h"
  17 #include "qemu/main-loop.h"
  18
  19 #ifdef CONFIG_EVENTFD
  20 #include <sys/eventfd.h>
  21 #endif
  22
  23 #ifdef CONFIG_EVENTFD
  24 /*
  25  * Initialize @e with existing file descriptor @fd.
  26  * @fd must be a genuine eventfd object, emulation with pipe won't do.
  27  */
  28 void event_notifier_init_fd(EventNotifier *e, int fd)
  29 {
  30     e->rfd = fd;
  31     e->wfd = fd;
  32 }
  33 #endif
  34
  35 int event_notifier_init(EventNotifier *e, int active)
  36 {
  37     int fds[2];
  38     int ret;
  39
  40 #ifdef CONFIG_EVENTFD
  41     ret = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
  42 #else
  43     ret = -1;
  44     errno = ENOSYS;
  45 #endif
  46     if (ret >= 0) {
  47         e->rfd = e->wfd = ret;
  48     } else {
  49         if (errno != ENOSYS) {
  50             return -errno;
  51         }
  52         if (qemu_pipe(fds) < 0) {
  53             return -errno;
  54         }
  55         ret = fcntl_setfl(fds[0], O_NONBLOCK);
  56         if (ret < 0) {
  57             ret = -errno;
  58             goto fail;
  59         }
  60         ret = fcntl_setfl(fds[1], O_NONBLOCK);
  61         if (ret < 0) {
  62             ret = -errno;
  63             goto fail;
  64         }
  65         e->rfd = fds[0];
  66         e->wfd = fds[1];
  67     }
  68     if (active) {
  69         event_notifier_set(e);
  70     }
  71     return 0;
  72
  73 fail:
  74     close(fds[0]);
  75     close(fds[1]);
  76     return ret;
  77 }
  78
  79 void event_notifier_cleanup(EventNotifier *e)
  80 {
  81     if (e->rfd != e->wfd) {
  82         close(e->rfd);
  83     }
  84     e->rfd = -1;
  85     close(e->wfd);
  86     e->wfd = -1;
  87 }
  88
  89 int event_notifier_get_fd(const EventNotifier *e)
  90 {
  91     return e->rfd;
  92 }
  93
  94 int event_notifier_set(EventNotifier *e)
  95 {
  96     static const uint64_t value = 1;
  97     ssize_t ret;
  98
  99     do {
 100         ret = write(e->wfd, &value, sizeof(value));
 101     } while (ret < 0 && errno == EINTR);
 102
 103     /* EAGAIN is fine, a read must be pending.  */
 104     if (ret < 0 && errno != EAGAIN) {
 105         return -errno;
 106     }
 107     return 0;
 108 }
 109
 110 int event_notifier_test_and_clear(EventNotifier *e)
 111 {
 112     int value;
 113     ssize_t len;
 114     char buffer[512];
 115
 116     /* Drain the notify pipe.  For eventfd, only 8 bytes will be read.  */
 117     value = 0;
 118     do {
 119         len = read(e->rfd, buffer, sizeof(buffer));
 120         value |= (len > 0);
 121     } while ((len == -1 && errno == EINTR) || len == sizeof(buffer));
 122
 123     return value;
 124 }