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     e->initialized = true;
  33 }
  34 #endif
  35
  36 int event_notifier_init(EventNotifier *e, int active)
  37 {
  38     int fds[2];
  39     int ret;
  40
  41 #ifdef CONFIG_EVENTFD
  42     ret = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
  43 #else
  44     ret = -1;
  45     errno = ENOSYS;
  46 #endif
  47     if (ret >= 0) {
  48         e->rfd = e->wfd = ret;
  49     } else {
  50         if (errno != ENOSYS) {
  51             return -errno;
  52         }
  53         if (qemu_pipe(fds) < 0) {
  54             return -errno;
  55         }
  56         ret = fcntl_setfl(fds[0], O_NONBLOCK);
  57         if (ret < 0) {
  58             ret = -errno;
  59             goto fail;
  60         }
  61         ret = fcntl_setfl(fds[1], O_NONBLOCK);
  62         if (ret < 0) {
  63             ret = -errno;
  64             goto fail;
  65         }
  66         e->rfd = fds[0];
  67         e->wfd = fds[1];
  68     }
  69     e->initialized = true;
  70     if (active) {
  71         event_notifier_set(e);
  72     }
  73     return 0;
  74
  75 fail:
  76     close(fds[0]);
  77     close(fds[1]);
  78     return ret;
  79 }
  80
  81 void event_notifier_cleanup(EventNotifier *e)
  82 {
  83     if (!e->initialized) {
  84         return;
  85     }
  86
  87     if (e->rfd != e->wfd) {
  88         close(e->rfd);
  89     }
  90
  91     e->rfd = -1;
  92     close(e->wfd);
  93     e->wfd = -1;
  94     e->initialized = false;
  95 }
  96
  97 int event_notifier_get_fd(const EventNotifier *e)
  98 {
  99     return e->rfd;
 100 }
 101
 102 int event_notifier_set(EventNotifier *e)
 103 {
 104     static const uint64_t value = 1;
 105     ssize_t ret;
 106
 107     if (!e->initialized) {
 108         return -1;
 109     }
 110
 111     do {
 112         ret = write(e->wfd, &value, sizeof(value));
 113     } while (ret < 0 && errno == EINTR);
 114
 115     /* EAGAIN is fine, a read must be pending.  */
 116     if (ret < 0 && errno != EAGAIN) {
 117         return -errno;
 118     }
 119     return 0;
 120 }
 121
 122 int event_notifier_test_and_clear(EventNotifier *e)
 123 {
 124     int value;
 125     ssize_t len;
 126     char buffer[512];
 127
 128     if (!e->initialized) {
 129         return 0;
 130     }
 131
 132     /* Drain the notify pipe.  For eventfd, only 8 bytes will be read.  */
 133     value = 0;
 134     do {
 135         len = read(e->rfd, buffer, sizeof(buffer));
 136         value |= (len > 0);
 137     } while ((len == -1 && errno == EINTR) || len == sizeof(buffer));
 138
 139     return value;
 140 }