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Re: wireless vs. alignment requirements

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Stephen Hemminger wrote:
Herbert Xu wrote:
On Sat, Nov 24, 2007 at 02:49:36PM +0100, Johannes Berg wrote:
Right. I just didn't think that would be a valid value for an
architecture to set.

OK.  Let me clarify this a bit more.  We require at least one
of the following rules to be met:

* the IPv4/IPv6 header is aligned by 8 bytes on reception;
* or the platform provides unaligned exception handlers.

So if your platform violates both rules then it won't work with
the IP stack, simple as that.  Fortunately I don't think such a
platform exists currently on Linux.

Cheers,

Then what about hardware that can't dma ethernet to non-aligned address.
Sky2 hardware breaks if DMA is not 8 byte aligned. IMHO the IP stack should handle any alignment, and do the appropriate memove if the CPU requires alignment.

I wrote a patch for the IP stack to realign packets if necessary at one point. I should dredge it up again and submit it for collective flamage.

	-hpa

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