netdev - skb_checksum

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Date:	Thu, 12 Jan 2012 20:42:10 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	netdev <netdev@...r.kernel.org>,
	Stephen Hemminger <shemminger@...tta.com>,
	netfilter-devel <netfilter-devel@...r.kernel.org>
Subject: skb_checksum_help() vs GSO

skb_checksum_help() does:

	if (unlikely(skb_shinfo(skb)->gso_size)) {
		/* Let GSO fix up the checksum. */
		goto out_set_summed;
	}
...
out_set_summed:
	skb->ip_summed = CHECKSUM_NONE;
out:
	return ret;

but skb_gso_segment() requires that skb->ip_summed == CHECKSUM_PARTIAL
and WARNs if not.  I don't think there's any case where it's valid to
call both.  Shouldn't skb_checksum_help() also WARN and return an error
code instead of muddling on?

Inspecting the callers of skb_checksum_help(), it looks like sch_netem's
'corrupt' option and xt_CHECKSUM might trigger this case.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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