Re: [Xen-devel] [PATCH V2] xen: netback: handle compound page fragments on transmit.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Oct 10, 2012 at 02:48:42PM +0100, 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 netbk_gop_frag_copy and xen_netbk_count_skb_slots by
> iterating over the frames which make up the page.
> 
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>

Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

> Cc: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
> ---
> v2: Only move to next frame if there is data remaining.
> ---
>  drivers/net/xen-netback/netback.c |   40 ++++++++++++++++++++++++++++++++----
>  1 files changed, 35 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/xen-netback/netback.c 
> b/drivers/net/xen-netback/netback.c
> index 4ebfcf3..f2d6b78 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -335,21 +335,35 @@ unsigned int xen_netbk_count_skb_slots(struct xenvif 
> *vif, struct sk_buff *skb)
>  
>       for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
>               unsigned long size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
> +             unsigned long offset = skb_shinfo(skb)->frags[i].page_offset;
>               unsigned long bytes;
> +
> +             offset &= ~PAGE_MASK;
> +
>               while (size > 0) {
> +                     BUG_ON(offset >= PAGE_SIZE);
>                       BUG_ON(copy_off > MAX_BUFFER_OFFSET);
>  
> -                     if (start_new_rx_buffer(copy_off, size, 0)) {
> +                     bytes = PAGE_SIZE - offset;
> +
> +                     if (bytes > size)
> +                             bytes = size;
> +
> +                     if (start_new_rx_buffer(copy_off, bytes, 0)) {
>                               count++;
>                               copy_off = 0;
>                       }
>  
> -                     bytes = size;
>                       if (copy_off + bytes > MAX_BUFFER_OFFSET)
>                               bytes = MAX_BUFFER_OFFSET - copy_off;
>  
>                       copy_off += bytes;
> +
> +                     offset += bytes;
>                       size -= bytes;
> +
> +                     if (offset == PAGE_SIZE)
> +                             offset = 0;
>               }
>       }
>       return count;
> @@ -403,14 +417,24 @@ static void netbk_gop_frag_copy(struct xenvif *vif, 
> struct sk_buff *skb,
>       unsigned long bytes;
>  
>       /* Data must not cross a page boundary. */
> -     BUG_ON(size + offset > PAGE_SIZE);
> +     BUG_ON(size + offset > PAGE_SIZE<<compound_order(page));
>  
>       meta = npo->meta + npo->meta_prod - 1;
>  
> +     /* Skip unused frames from start of page */
> +     page += offset >> PAGE_SHIFT;
> +     offset &= ~PAGE_MASK;
> +
>       while (size > 0) {
> +             BUG_ON(offset >= PAGE_SIZE);
>               BUG_ON(npo->copy_off > MAX_BUFFER_OFFSET);
>  
> -             if (start_new_rx_buffer(npo->copy_off, size, *head)) {
> +             bytes = PAGE_SIZE - offset;
> +
> +             if (bytes > size)
> +                     bytes = size;
> +
> +             if (start_new_rx_buffer(npo->copy_off, bytes, *head)) {
>                       /*
>                        * Netfront requires there to be some data in the head
>                        * buffer.
> @@ -420,7 +444,6 @@ static void netbk_gop_frag_copy(struct xenvif *vif, 
> struct sk_buff *skb,
>                       meta = get_next_rx_buffer(vif, npo);
>               }
>  
> -             bytes = size;
>               if (npo->copy_off + bytes > MAX_BUFFER_OFFSET)
>                       bytes = MAX_BUFFER_OFFSET - npo->copy_off;
>  
> @@ -453,6 +476,13 @@ static void netbk_gop_frag_copy(struct xenvif *vif, 
> struct sk_buff *skb,
>               offset += bytes;
>               size -= bytes;
>  
> +             /* Next frame */
> +             if (offset == PAGE_SIZE && size) {
> +                     BUG_ON(!PageCompound(page));
> +                     page++;
> +                     offset = 0;
> +             }
> +
>               /* Leave a gap for the GSO descriptor. */
>               if (*head && skb_shinfo(skb)->gso_size && !vif->gso_prefix)
>                       vif->rx.req_cons++;
> -- 
> 1.7.2.5
> 
> 
> _______________________________________________
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> Xen-devel@xxxxxxxxxxxxx
> http://lists.xen.org/xen-devel
> 

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