[Qemu-devel] Re: [PATCHv3] virtio-net: correct packet length math

[Amit Shah]

On (Thu) Jun 24 2010 [18:54:07], Michael S. Tsirkin wrote:
> We were requesting too much when checking buffer
> length: size already includes host header length.
> 
> Further, we should not exit if we get a packet that
> is too long, since this might not be under control
> of the guest. Just drop the packet.

control of the host?

> @@ -579,19 +581,32 @@ static ssize_t virtio_net_receive(VLANClientState *nc, 
> const uint8_t *buf, size_
>                  mhdr = (struct virtio_net_hdr_mrg_rxbuf *)sg[0].iov_base;
>  
>              offset += receive_header(n, sg, elem.in_num,
> -                                     buf + offset, size - offset, hdr_len);
> -            total += hdr_len;
> +                                     buf + offset, size - offset, 
> guest_hdr_len);
> +            total += guest_hdr_len;
>          }
>  
>          /* copy in packet.  ugh */
>          len = iov_from_buf(sg, elem.in_num,
>                             buf + offset, size - offset);
>          total += len;
> +        offset += len;
> +        /* If buffers can't be merged, at this point we
> +         * must have consumed the complete packet.
> +         * Otherwise, drop it. */
> +        if (!n->mergeable_rx_bufs && offset < size) {
> +#if 0
> +            fprintf(stderr, "virtio-net truncated non-mergeable packet: "
> +
> +                    "i %zd mergeable %d offset %zd, size %zd, "
> +                    "guest hdr len %zd, host hdr len %zd\n",
> +                    i, n->mergeable_rx_bufs,
> +                    offset, size, guest_hdr_len, host_hdr_len);
> +#endif
> +            return size;
> +        }

Before returning, won't you have to finish off the virtqueue operations
-- fill, flush, kick, etc.?

                Amit