Re: Need some help with IP/TCP Checksum Offload

From: Benjamin LaHaise (bcrl@redhat.com)
Date: Fri Feb 22 2002 - 18:52:22 EST


On Fri, Feb 22, 2002 at 02:57:22PM -0800, harish.vasudeva@amd.com wrote:
>
> Then, in my start_xmit( ) routine, i am parsing for the right
> headers & when i get the IP/TCP header, i print out the checksum
> & it is already the right checksum. When does the OS/Protocol
> offload this task? Am i missing something here?

The network stack generates checksums for packets while copying,
so the checksum offload feature is only used for packets that are
not copied. The easiest way to generate packets of this nature
is to use the sendfile() syscall to transmit data from the page
cache directly onto the wire. If you need a couple of test
programs I can forward a few to you offline. Cheers,

                -ben
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