Re: [Qemu-devel] [PATCH 02/17] event_notifier: enable it to use pipes

[Stefan Hajnoczi <stefanha@gmail.com>]

On Tue, Sep 25, 2012 at 02:55:48PM +0200, Paolo Bonzini wrote:
>  int event_notifier_init(EventNotifier *e, int active)
>  {
> +    int fds[2];
> +    int ret;
> +
>  #ifdef CONFIG_EVENTFD
> -    int fd = eventfd(!!active, EFD_NONBLOCK | EFD_CLOEXEC);
> -    if (fd < 0)
> -        return -errno;
> -    e->fd = fd;
> -    return 0;
> +    ret = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
>  #else
> -    return -ENOSYS;
> +    ret = -1;
> +    errno = ENOSYS;
>  #endif
> +    if (ret >= 0) {
> +        e->rfd = e->wfd = ret;
> +    } else {
> +        if (errno != ENOSYS) {
> +            return -errno;
> +        }
> +        if (qemu_pipe(fds) < 0) {
> +            return -errno;
> +        }
> +        ret = fcntl_setfl(fds[0], O_NONBLOCK);
> +        if (ret < 0) {

ret = -errno;

> +            goto fail;
> +        }
> +        ret = fcntl_setfl(fds[1], O_NONBLOCK);
> +        if (ret < 0) {

ret = -errno;

> +            goto fail;
> +        }
> +        e->rfd = fds[0];
> +        e->wfd = fds[1];
> +    }
> +    if (active) {
> +        event_notifier_set(e);
> +    }
> +    return 0;
> +
> +fail:
> +    close(fds[0]);
> +    close(fds[1]);
> +    return ret;
>  }
>  
>  void event_notifier_cleanup(EventNotifier *e)
>  {
> -    close(e->fd);
> +    if (e->rfd != e->wfd) {
> +        close(e->rfd);
> +    }
> +    close(e->wfd);
>  }
>  
>  int event_notifier_get_fd(EventNotifier *e)
>  {
> -    return e->fd;
> +    return e->rfd;
>  }
>  
>  int event_notifier_set_handler(EventNotifier *e,
>                                 EventNotifierHandler *handler)
>  {
> -    return qemu_set_fd_handler(e->fd, (IOHandler *)handler, NULL, e);
> +    return qemu_set_fd_handler(e->rfd, (IOHandler *)handler, NULL, e);
>  }
>  
>  int event_notifier_set(EventNotifier *e)
>  {
> -    uint64_t value = 1;
> -    int r = write(e->fd, &value, sizeof(value));
> -    return r == sizeof(value);
> +    static const uint64_t value = 1;
> +    ssize_t ret;
> +
> +    do {
> +        ret = write(e->wfd, &value, sizeof(value));
> +    } while (ret < 0 && errno == EINTR);
> +
> +    /* EAGAIN is fine, a read must be pending.  */
> +    if (ret < 0 && errno != EAGAIN) {
> +        return -1;

If we're changing the return value representation, then we might as well:

return -errno;

But no caller actually checks the return value.