Re: [RFC PATCH 13/27] vhost: Send buffers to device

[Stefan Hajnoczi]

On Wed, Dec 09, 2020 at 07:41:23PM +0100, Eugenio Perez Martin wrote:
> On Tue, Dec 8, 2020 at 9:16 AM Stefan Hajnoczi <stefanha@gmail.com> wrote:
> > On Fri, Nov 20, 2020 at 07:50:51PM +0100, Eugenio Pérez wrote:
> > > +        while (true) {
> > > +            int r;
> > > +            if (virtio_queue_full(vq)) {
> > > +                break;
> > > +            }
> >
> > Why is this check necessary? The guest cannot provide more descriptors
> > than there is ring space. If that happens somehow then it's a driver
> > error that is already reported in virtqueue_pop() below.
> >
> 
> It's just checked because virtqueue_pop prints an error on that case,
> and there is no way to tell the difference between a regular error and
> another caused by other causes. Maybe the right thing to do is just to
> not to print that error? Caller should do the error printing in that
> case. Should we return an error code?

The reason an error is printed today is because it's a guest error that
never happens with correct guest drivers. Something is broken and the
user should know about it.

Why is "virtio_queue_full" (I already forgot what that actually means,
it's not clear whether this is referring to avail elements or used
elements) a condition that should be silently ignored in shadow vqs?

Stefan

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