Re: [Qemu-devel] [PATCH 01/12] event_notifier: enable it to use pipes

[Anthony Liguori <anthony@codemonkey.ws>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> This takes the eventfd emulation code from the main loop and adds it
> to EventNotifier.  When the EventNotifier is used for the main loop too,
> we need this compatibility code.
>
> Without CONFIG_EVENTFD, event_notifier_get_fd is only usable for the
> "read" side of the notifier, for example to set a select() handler.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  event_notifier.c |   83 +++++++++++++++++++++++++++++++++++++++++++-----------
>  event_notifier.h |    3 +-
>  2 files changed, 69 insertions(+), 17 deletions(-)
>
> diff --git a/event_notifier.c b/event_notifier.c
> index 2c207e1..dde2d32 100644
> --- a/event_notifier.c
> +++ b/event_notifier.c
> @@ -20,48 +20,99 @@
>  
>  void event_notifier_init_fd(EventNotifier *e, int fd)
>  {
> -    e->fd = fd;
> +    e->rfd = fd;
> +    e->wfd = fd;
>  }
>  
>  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, O_NONBLOCK);
>  #else
> -    return -ENOSYS;
> +    ret = -1;
> +    errno = ENOSYS;
>  #endif
> +    if (ret >= 0) {
> +        e->rfd = e->wfd = ret;
> +        qemu_set_cloexec(ret);

This is kind of redundant with EFD_CLOEXEC, no?

> +    } else {
> +        if (errno != ENOSYS) {
> +            return -errno;
> +        }
> +        if (qemu_pipe(fds) < 0) {
> +            return -errno;
> +        }
> +        ret = fcntl_setfl(fds[0], O_NONBLOCK);
> +        if (ret < 0) {
> +            goto fail;
> +        }
> +        ret = fcntl_setfl(fds[1], O_NONBLOCK);
> +        if (ret < 0) {
> +            goto fail;
> +        }
> +        e->rfd = fds[0];
> +        e->wfd = fds[1];
> +    }
> +    if (active)
> +        event_notifier_set(e);

Missing a curly..

The rest looks good.

Regards,

Anthony Liguori

> +    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;
> +    }
> +    return 0;
>  }
>  
>  int event_notifier_test_and_clear(EventNotifier *e)
>  {
> -    uint64_t value;
> -    int r = read(e->fd, &value, sizeof(value));
> -    return r == sizeof(value);
> +    int value;
> +    ssize_t len;
> +    char buffer[512];
> +
> +    /* Drain the notify pipe.  For eventfd, only 8 bytes will be read.  */
> +    value = 0;
> +    do {
> +        len = read(e->rfd, buffer, sizeof(buffer));
> +        value |= (len > 0);
> +    } while ((len == -1 && errno == EINTR) || len == sizeof(buffer));
> +
> +    return value;
>  }
> diff --git a/event_notifier.h b/event_notifier.h
> index f0ec2f2..f04d12d 100644
> --- a/event_notifier.h
> +++ b/event_notifier.h
> @@ -16,7 +16,8 @@
>  #include "qemu-common.h"
>  
>  struct EventNotifier {
> -    int fd;
> +    int rfd;
> +    int wfd;
>  };
>  
>  typedef void EventNotifierHandler(EventNotifier *);
> -- 
> 1.7.10.4