Re: [PATCH 3/3] virtio_ring: unify direct/indirect code paths.

Andy Lutomirski
2014-09-04T01:59:33Z

On Tue, Sep 2, 2014 at 9:29 PM, Rusty Russell <rusty@rustcorp.com.au> wrote:
> virtqueue_add() populates the virtqueue descriptor table from the sgs
> given. If it uses an indirect descriptor table, then it puts a single
> descriptor in the descriptor table pointing to the kmalloc'ed indirect
> table where the sg is populated.
>
> Previously vring_add_indirect() did the allocation and the simple
> linear layout. We replace that with alloc_indirect() which allocates
> the indirect table then chains it like the normal descriptor table so
> we can reuse the core logic.
>

> + if (vq->indirect && total_sg > 1 && vq->vq.num_free)
> + desc = alloc_indirect(total_sg, gfp);
> + else
> + desc = NULL;
> +
> + if (desc) {
> + /* Use a single buffer which doesn't continue */
> + vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
> + vq->vring.desc[head].addr = virt_to_phys(desc);
> + /* avoid kmemleak false positive (hidden by virt_to_phys) */
> + kmemleak_ignore(desc);
> + vq->vring.desc[head].len = total_sg * sizeof(struct vring_desc);
> +
> + /* Set up rest to use this indirect table. */
> + i = 0;
> + total_sg = 1;

This is a little too magical for me. Would it make sense to add a new
variable for this (total_root_descs or something)?

--Andy