Re: [PATCH vhost v4 03/10] virtio_ring: packed: structure the indirect desc table

[Jason Wang <jasowang@redhat.com>]

On Thu, Mar 21, 2024 at 4:29 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>
> On Thu, 21 Mar 2024 12:47:18 +0800, Jason Wang <jasowang@redhat.com> wrote:
> > On Tue, Mar 12, 2024 at 11:36 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> > >
> > > This commit structure the indirect desc table.
> > > Then we can get the desc num directly when doing unmap.
> > >
> > > And save the dma info to the struct, then the indirect
> > > will not use the dma fields of the desc_extra. The subsequent
> > > commits will make the dma fields are optional. But for
> > > the indirect case, we must record the dma info.
> > >
> > > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > > ---
> > >  drivers/virtio/virtio_ring.c | 66 +++++++++++++++++++++---------------
> > >  1 file changed, 38 insertions(+), 28 deletions(-)
> > >
> > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > index 0dfbd17e5a87..22a588bba166 100644
> > > --- a/drivers/virtio/virtio_ring.c
> > > +++ b/drivers/virtio/virtio_ring.c
> > > @@ -72,9 +72,16 @@ struct vring_desc_state_split {
> > >         struct vring_desc *indir_desc;  /* Indirect descriptor, if any. */
> > >  };
> > >
> > > +struct vring_packed_desc_indir {
> > > +       dma_addr_t addr;                /* Descriptor Array DMA addr. */
> > > +       u32 len;                        /* Descriptor Array length. */
> > > +       u32 num;
> > > +       struct vring_packed_desc desc[];
> > > +};
> > > +
> > >  struct vring_desc_state_packed {
> > >         void *data;                     /* Data for callback. */
> > > -       struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */
> > > +       struct vring_packed_desc_indir *indir_desc; /* Indirect descriptor, if any. */
> >
> > Maybe it's better just to have a vring_desc_extra here.
>
>
> Do you mean replacing vring_packed_desc_indir by vring_desc_extra?

Just add a vring_desc_extra in vring_desc_state_packed.

>
> I am ok for that. But vring_desc_extra has two extra items:
>
>         u16 flags;                      /* Descriptor flags. */
>         u16 next;                       /* The next desc state in a list. */
>
> vring_packed_desc_indir has "desc". I think that is more convenient.
>
> So, I think vring_packed_desc_indir is appropriate.

It reuses the existing structure so we had the chance to reuse the
helper. And it could be used for future chained indirect (if it turns
out to be necessary).

Thanks

> Or I missed something.
>
>
> Thanks.
>
>
> >
> > Thanks
> >
>