Re: [Qemu-devel] [PATCH v4 09/11] virtio-net: update the head descriptor in a chain lastly

[Jason Wang]

On 2019/2/20 下午12:01, Wei Xu wrote:
> > > AFAICT, virtqueue_fill() is a generic API for all relevant userspace virtio
> > > devices that do not support batching , without touching virtqueue_fill(),
> > > supporting batching changes the meaning of the parameter 'idx' which should
> > > be kept overall.
> > >
> > > To fix it, I got two proposals so far:
> > > 1). batching support(two APIs needed to keep compatibility)
> > > 2). save a head elem for a vq instead of caching an array of elems like vhost,
> > >      and introduce a new API(virtqueue_chain_fill()) functioning with an
> > >      additional parameter 'more' to the current virtqueue_fill() to indicate if
> > >      there are more descriptor(s) coming in a chain.
> > >
> > > Either way it changes the API somehow and it does not seem to be clean and clear
> > > as wanted.
> > It's as simple as accepting an array of elems in e.g
> > virtqueue_fill_batched()?
> It is trivial for both, my concern is an array elements need to be allocated 
> dynamically
> due to vq size which no any other devices are using, a head would be enough for 
> 2.

Do you see any issue for this?

Thanks