Terry Lambert writes:
> Andrew Gallatin wrote:
> > I imagine that this was done to follow alignment constraints on
> > non-i386 platforms where having the ip header misaligned is fatal.
> > (the tulip is not capable of byte granularity DMA, so you can't
> > intentionally misalign the ethernet header & end up with an aligned IP
> > header)
>
> This is the reason: the ethernet header is 14 bytes.
>
>
> > I imagine the i386 should be made an exception. See rev 1.17 of
> > sys/dev/nge/if_nge.c
>
> I disagree with this code; the elemenets in the header
> are referenced multiple times. If you are doing the
> checksum check, you might as well be relocating the data,
> as well. The change I would make would be to integrate
> the checksum calculation with the m_devget(), to ensure
> a single pass, in the case that m_devget() must be used
> to get aligned packet payload, and the checksum has not
> been offloaded to hardware.
Interesting idea... However, what if you're a bridge or a router?
You've just done a whole lot of work for nothing. I imagine its just
this case that Luigi cares about.
If you want to integrate a checksum & a copy, it should really be done
at the copyout() stage.
Drew
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