[Qemu-devel] Re: [PATCH v6 18/18] virtio-serial-bus: wake up iothread upon guest read notification

[Anthony Liguori]

On 04/27/2010 12:58 PM, Marcelo Tosatti wrote:
> On Tue, Apr 27, 2010 at 12:41:27PM -0500, Anthony Liguori wrote:
>    
> > On 04/27/2010 07:34 AM, Amit Shah wrote:
> >      
> > > From: Marcelo Tosatti<address@hidden>
> > >
> > > Wake up iothread when buffers are consumed.
> > >
> > > Signed-off-by: Marcelo Tosatti<address@hidden>
> > > Signed-off-by: Amit Shah<address@hidden>
> > >        
> > What's the race here?  This looks very odd to me.
> >      
> We discussed this on the following thread:
>
> http://www.mail-archive.com/address@hidden/msg29249.html
>    

I don't think there was ever an adequate explanation of exactly what was 
happening.

My suspicion is that the real problem is due to the can_read() handlers 
whereas it's necessary to invoke the main loop for can_read() to be 
executed again to cause the event to be polled.  The better solution 
though is to not use the can_read() handler and instead explicitly 
register and deregister the read callbacks.

qemu_set_fd_handler() would require a notify call but that makes sense.

I think this is a good justification for removing uses of 
qemu_set_fd_handler2().

Regards,

Anthony Liguori