[Qemu-devel] Re: [PATCHv6 03/11] notifier: event notifier implementation

[Paolo Bonzini <pbonzini@redhat.com>]

On 03/17/2010 12:07 PM, Michael S. Tsirkin wrote:
> +{
> +#ifdef CONFIG_EVENTFD
> +    int fd = eventfd(!!active, EFD_NONBLOCK | EFD_CLOEXEC);

> +    uint64_t value;
> +    int r = read(e->fd,&value, sizeof(value));
> +    if (r == sizeof(value)) {
> +        /* restore previous value. */
> +        int s = write(e->fd,&value, sizeof(value));
> +        /* never blocks because we use EFD_SEMAPHORE.

No, we don't...

Also, it seems like this function as it is written now requires blocking 
operation of the eventfd, otherwise it would not be atomic when another 
thread calls event_notifier_test_and_clear.  Which makes everything more 
complicated.

But after all is unused, maybe it should be zapped?

Paolo