On (Thu) Aug 27 2009 [20:36:07], Rusty Russell wrote:
> >
> > I'm missing something though: the value of 'num' changes in the loop and
> > the value of num when it will be compared will just have been used by
> > add_buf. The next iteration of the loop will probably use a different
> > value (-- from just reading the code, not going over the cases in which
> > this function is called).
>
> Here's the code:
>
> num = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
> skb_queue_head(&vi->recv, skb);
>
> err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, num, skb);
> if (err < 0) {
> skb_unlink(skb, &vi->recv);
> trim_pages(vi, skb);
> kfree_skb(skb);
> break;
> }
> vi->num++;
> } while (err >= num);
>
> Now, it turns out that we always allocate packets of the same size.
OK; works since the packet size is the same.
> So the number of descriptors required by the next packet will be the same as
> for this packet.
>
> Clear?
Thanks!
> Rusty.
Amit
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