VRING_DESC_F_NEXT
while (dp->flags & vq_gtoh16(vq, VRING_DESC_F_NEXT)) {
dp->flags |= vq_gtoh16(vq, VRING_DESC_F_NEXT);
if ((vp->flags & VRING_DESC_F_NEXT) == 0)
if ((vdir->flags & VRING_DESC_F_NEXT) == 0)