Re: [PATCH v18 06/10] virtio_ring: add a new API, virtqueue_add_one_desc

[Wei Wang <wei.w.wang@intel.com>]

On 12/01/2017 03:38 AM, Michael S. Tsirkin wrote:
> On Wed, Nov 29, 2017 at 09:55:22PM +0800, Wei Wang wrote:
> > Current virtqueue_add API implementation is based on the scatterlist
> > struct, which uses kaddr. This is inadequate to all the use case of
> > vring. For example:
> > - Some usages don't use IOMMU, in this case the user can directly pass
> >    in a physical address in hand, instead of going through the sg
> >    implementation (e.g. the VIRTIO_BALLOON_F_SG feature)
> > - Sometimes, a guest physical page may not have a kaddr (e.g. high
> >    memory) but need to use vring (e.g. the VIRTIO_BALLOON_F_FREE_PAGE_VQ
> >    feature)
> >
> > The new API virtqueue_add_one_desc enables the caller to assign a vring
> > desc with a physical address and len. Also, factor out the common code
> > with virtqueue_add in vring_set_avail.
> >
> > Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> > Cc: Michael S. Tsirkin <mst@redhat.com>
> You previously managed without this patch, and it's preferable
> IMHO since this patchset is already too big.
>
> I don't really understand what is wrong with virtio_add_sgs + sg_set_page.
> I don't think is assumes a kaddr.

OK, I will use the previous method to send sgs.
Please have a check if there are other things need to be improved.

Best,
Wei