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 "sysemu/char.h"
  18 #include "qemu/main-loop.h"
  19
  20 #ifdef CONFIG_EVENTFD
  21 #include <sys/eventfd.h>
  22 #endif
  23
  24 #ifdef CONFIG_EVENTFD
  25 /*
  26  * Initialize @e with existing file descriptor @fd.
  27  * @fd must be a genuine eventfd object, emulation with pipe won't do.
  28  */
  29 void event_notifier_init_fd(EventNotifier *e, int fd)
  30 {
  31     e->rfd = fd;
  32     e->wfd = fd;
  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     if (active) {
  70         event_notifier_set(e);
  71     }
  72     return 0;
  73
  74 fail:
  75     close(fds[0]);
  76     close(fds[1]);
  77     return ret;
  78 }
  79
  80 void event_notifier_cleanup(EventNotifier *e)
  81 {
  82     if (e->rfd != e->wfd) {
  83         close(e->rfd);
  84         e->rfd = -1;
  85     }
  86     close(e->wfd);
  87     e->wfd = -1;
  88 }
  89
  90 int event_notifier_get_fd(const EventNotifier *e)
  91 {
  92     return e->rfd;
  93 }
  94
  95 int event_notifier_set(EventNotifier *e)
  96 {
  97     static const uint64_t value = 1;
  98     ssize_t ret;
  99
 100     do {
 101         ret = write(e->wfd, &value, sizeof(value));
 102     } while (ret < 0 && errno == EINTR);
 103
 104     /* EAGAIN is fine, a read must be pending.  */
 105     if (ret < 0 && errno != EAGAIN) {
 106         return -errno;
 107     }
 108     return 0;
 109 }
 110
 111 int event_notifier_test_and_clear(EventNotifier *e)
 112 {
 113     int value;
 114     ssize_t len;
 115     char buffer[512];
 116
 117     /* Drain the notify pipe.  For eventfd, only 8 bytes will be read.  */
 118     value = 0;
 119     do {
 120         len = read(e->rfd, buffer, sizeof(buffer));
 121         value |= (len > 0);
 122     } while ((len == -1 && errno == EINTR) || len == sizeof(buffer));
 123
 124     return value;
 125 }