Re: [Xen-devel] [PATCH] xen/netfront: handle compound page fragments on transmit

[ANNIE LI <annie.li@xxxxxxxxxx>]

On 2012-11-20 19:40, Ian Campbell wrote:
> An SKB paged fragment can consist of a compound page with order>  0.
> However the netchannel protocol deals only in PAGE_SIZE frames.
>
> Handle this in xennet_make_frags by iterating over the frames which
> make up the page.
>
> This is the netfront equivalent to 6a8ed462f16b for netback.
>
> Signed-off-by: Ian Campbell<ian.campbell@xxxxxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx
> Cc: xen-devel@xxxxxxxxxxxxx
> Cc: Eric Dumazet<edumazet@xxxxxxxxxx>
> Cc: Konrad Rzeszutek Wilk<konrad@xxxxxxxxxx>
> Cc: ANNIE LI<annie.li@xxxxxxxxxx>
> Cc: Sander Eikelenboom<linux@xxxxxxxxxxxxxx>
> Cc: Stefan Bader<stefan.bader@xxxxxxxxxxxxx>
> ---
>   drivers/net/xen-netfront.c |   58 +++++++++++++++++++++++++++++++++----------
>   1 files changed, 44 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index caa0110..a12b99a 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -452,24 +452,54 @@ static void xennet_make_frags(struct sk_buff *skb, struct 
> net_device *dev,
>         /* Grant backend access to each skb fragment page. */
>         for (i = 0; i<  frags; i++) {
>                 skb_frag_t *frag = skb_shinfo(skb)->frags + i;
> +               struct page *page = skb_frag_page(frag);
> +               unsigned long size = skb_frag_size(frag);
> +               unsigned long offset = frag->page_offset;
There are following definitions at the beginning of xennet_make_frags,

        unsigned int offset = offset_in_page(data);
        unsigned int len = skb_headlen(skb);

Is it better to reuse those definitions, and not define new size and 
offset again in this for loop? And unsigned int is enough here, right?
> -               tx->flags |= XEN_NETTXF_more_data;
> +               /* Data must not cross a page boundary. */
> +               BUG_ON(size + offset>  PAGE_SIZE<<compound_order(page));
>
> -               id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
> -               np->tx_skbs[id].skb = skb_get(skb);
> -               tx = RING_GET_REQUEST(&np->tx, prod++);
> -               tx->id = id;
> -               ref = gnttab_claim_grant_reference(&np->gref_tx_head);
> -               BUG_ON((signed short)ref<  0);
> +               /* Skip unused frames from start of page */
> +               page += offset>>  PAGE_SHIFT;
> +               offset&= ~PAGE_MASK;
>
> -               mfn = pfn_to_mfn(page_to_pfn(skb_frag_page(frag)));
> -               gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
> -                                               mfn, GNTMAP_readonly);
> +               while (size>  0) {
> +                       unsigned long bytes;
>
> -               tx->gref = np->grant_tx_ref[id] = ref;
> -               tx->offset = frag->page_offset;
> -               tx->size = skb_frag_size(frag);
> -               tx->flags = 0;
> +                       BUG_ON(offset>= PAGE_SIZE);
> +
> +                       bytes = PAGE_SIZE - offset;
> +                       if (bytes>  size)
> +                               bytes = size;
> +
> +                       tx->flags |= XEN_NETTXF_more_data;
> +
> +                       id = get_id_from_freelist(&np->tx_skb_freelist, 
> np->tx_skbs);
Over 80 characters?
> +                       np->tx_skbs[id].skb = skb_get(skb);
> +                       tx = RING_GET_REQUEST(&np->tx, prod++);
> +                       tx->id = id;
> +                       ref = gnttab_claim_grant_reference(&np->gref_tx_head);
> +                       BUG_ON((signed short)ref<  0);
> +
> +                       mfn = pfn_to_mfn(page_to_pfn(page));
> +                       gnttab_grant_foreign_access_ref(ref, 
> np->xbdev->otherend_id,
> +                                                       mfn, GNTMAP_readonly);
Over 80 characters?

Thanks
Annie
> +
> +                       tx->gref = np->grant_tx_ref[id] = ref;
> +                       tx->offset = offset;
> +                       tx->size = bytes;
> +                       tx->flags = 0;
> +
> +                       offset += bytes;
> +                       size -= bytes;
> +
> +                       /* Next frame */
> +                       if (offset == PAGE_SIZE&&  size) {
> +                               BUG_ON(!PageCompound(page));
> +                               page++;
> +                               offset = 0;
> +                       }
> +               }
>         }
>
>         np->tx.req_prod_pvt = prod;
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