Re: [Xen-devel] [PATCH] Network Checksum Removal

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 26 May 2005, at 00:41, Jon Mason wrote:

> The bridge device still is the device that the stack sees, and uses its
> features to determine what to do during transmission.  If you monitor 
> the
> skb->ip_summed flag going into netif_be_start_xmit(), you will see 
> that it is
> 0 (meaning that the stack did the checksum in software).  Now if you 
> add the
> following patch to the bridging device, you will notice that ip_summed 
> is now
> being used.
For local traffic transmitted via veth0, ip_summed is zero 
(CHECKSUM_NONE) at netif_be_start_xmit because the bridge forwarding 
code nobbles the ip_summed field. It does *not* checksum the packet: 
etherbridge never checksums packets it forwards because that is the 
destination's job (it's an end-to-end checksum at the protocol level).
If you transmit local traffic directly on the bridge device then yes, 
you need a patch because it does not advertise NETIF_F_*_CSUM.
 -- Keir


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