Re: [PATCH RFC 3/3] Virtio draft III: example block driver

Avi Kivity
2007-06-17T14:25:21Z

Rusty Russell wrote:
> +static bool do_read(request_queue_t *q, struct virtio_blk *vblk,
> + struct virtblk_req *vbr)
> +{
> + unsigned long num;
> +
> + vbr->out_hdr.type |= VIRTIO_BLK_T_READ;
> +
> + /* Set up for reply. */
> + vblk->sg[0].page = virt_to_page(&vbr->in_hdr);
> + vblk->sg[0].offset = offset_in_page(&vbr->in_hdr);
> + vblk->sg[0].length = sizeof(vbr->in_hdr);
> + num = blk_rq_map_sg(q, vbr->req, vblk->sg+1);
> + vbr->out_hdr.id = vblk->vdev->ops->add_inbuf(vblk->vdev, vblk->sg,
> + 1+num, vbr);
> + if (IS_ERR_VALUE(vbr->out_hdr.id))
> + goto full;
> +
> + vblk->sg[0].page = virt_to_page(&vbr->out_hdr);
> + vblk->sg[0].offset = offset_in_page(&vbr->out_hdr);
> + vblk->sg[0].length = sizeof(vbr->out_hdr);
> +
> + vbr->out_id = vblk->vdev->ops->add_outbuf(vblk->vdev, vblk->sg, 1,
> + vbr);
>

This strikes me as wasteful. Why not set up a single descriptor which
contains both placement and the data itself?

--
error compiling committee.c: too many arguments to function