Re: [Qemu-devel] [PATCH] Use qemu_eventfd for POSIX AIO

[Anthony Liguori]

On 09/27/2011 09:22 AM, Jan Kiszka wrote:
> On 2011-09-27 16:19, Anthony Liguori wrote:
> > On 09/27/2011 09:11 AM, Avi Kivity wrote:
> > > On 09/27/2011 05:07 PM, Anthony Liguori wrote:
> > > > You don't expect to handle EAGAIN with eventfd() whereas you have to handle it
> > > > with pipe().
> > > >
> > > > Moreover, the eventfd() counter is not lossy (practically speaking) whereas if
> > > > you use pipe() as a counter, it will be lossy in practice.
> > > >
> > > > This is why posix aio uses pipe() and not eventfd().
> > >
> > > We could define a qemu_event mechanism that satisfies the least common
> > > denominator, and is implemented by eventfd when available.
> > >
> > > qemu_event_create()
> > > qemu_event_signal()
> > > qemu_event_wait()
> > > qemu_event_poll_add() // registers in main loop
> > > qemu_event_poll_del()
> >
> > See hw/event_notifier.[ch].
>
> That code looks suspicious, btw. It claims things ("we use
> EFD_SEMAPHORE") it does not do.

Indeed.

But the interface appears to be the right one IMHO.

Regards,

Anthony Liguori

> Jan