Linux Virtualization - May 2008 - [PATCH 3/3] virtio_net: Fix skb->csum_start computation

On Tue, May 27, 2008 at 12:20:47PM +0100, Mark McLoughlin
wrote:
> hdr->csum_start is the offset from the start of the ethernet
> header to the transport layer checksum field. skb->csum_start
> is the offset from skb->head.
> 
> skb_partial_csum_set() assumes that skb->data points to the
> ethernet header - i.e. it computes skb->csum_start by adding
> the headroom to hdr->csum_start.
> 
> Since eth_type_trans() skb_pull()s the ethernet header,
> skb_partial_csum_set() should be called before
> eth_type_trans().
> 
> Signed-off-by: Mark McLoughlin <markmc at redhat.com>
Good catch! Clearly shows I never ran this across a real Ethernet
device :)

Acked-by: Herbert Xu <herbert at gondor.apana.org.au>

Thanks,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert at gondor.apana.org.au>
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On Tuesday 27 May 2008 21:20:47 Mark McLoughlin wrote:
> hdr->csum_start is the offset from the start of the ethernet
> header to the transport layer checksum field. skb->csum_start
> is the offset from skb->head.
>
> skb_partial_csum_set() assumes that skb->data points to the
> ethernet header - i.e. it computes skb->csum_start by adding
> the headroom to hdr->csum_start.
>
> Since eth_type_trans() skb_pull()s the ethernet header,
> skb_partial_csum_set() should be called before
> eth_type_trans().
As should the rx_bytes += skb->len.  Thanks for this!

Applied (and 1/3, the typo patch).

I'll backport this to -stable, as well.

Thanks,
Rusty.