Re: [Qemu-devel] [PATCH 5/8] virtio-serial-bus: Add support for buffering guest output, throttling guests

[Anthony Liguori]

On 01/12/2010 09:49 AM, Amit Shah wrote:
> On (Tue) Jan 12 2010 [09:46:55], Anthony Liguori wrote:
>    
> > On 01/12/2010 09:13 AM, Amit Shah wrote:
> >      
> > > On (Tue) Jan 12 2010 [09:00:52], Anthony Liguori wrote:
> > >
> > >        
> > > > On 01/12/2010 01:16 AM, Amit Shah wrote:
> > > >
> > > >          
> > > > > BTW I don't really want this too, I can get rid of it if everyone agrees
> > > > > we won't support clipboard writes>    4k over vnc or if there's a better
> > > > > idea.
> > > > >
> > > > >
> > > > >            
> > > > Why bother trying to preserve message boundaries?   I think that's the
> > > > fundamental question.
> > > >
> > > >          
> > > For the vnc clipboard copy-paste case, I explained that in the couple of
> > > mails before in this thread.
> > >
> > >        
> > It didn't make sense to me.  I think the assumption has to be that the
> > client can send corrupt data and the host has to handle it.
> >      
> You mean if the guest kernel sends the wrong flags? Or doesn't set the
> flags? Can you explain what scenario you're talking about?
>    

It's very likely that you'll have to implement some sort of protocol on 
top of virtio-serial.  It won't always just be simple strings.

If you have a simple datagram protocol, that contains two ints and a 
string, it's going to have to be encoded like <int a><int b><int 
len><char data[len]>.  You need to validate that len fits within the 
boundaries and deal with len being less than the boundary.

If you've got a command protocol where the you send the guest something 
and then expect a response, you have to deal with the fact that the 
guest may never respond.  Having well defined message boundaries does 
not help the general problem and it only helps in the most trivial cases.

Basically, it boils down to a lot of complexity for something that isn't 
going to be helpful in most circumstances.

Regards,

Anthony Liguori

>                 Amit
>