netdev - Re: [PATCH] tcp: Set CHECKSUM_UNNECESSARY in tcp_init_nondata

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Message-ID: <20100408114928.GA23459@gondor.apana.org.au>
Date:	Thu, 8 Apr 2010 19:49:28 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] tcp: Set CHECKSUM_UNNECESSARY in tcp_init_nondata_skb

On Thu, Apr 08, 2010 at 01:26:17AM -0700, David Miller wrote:
> 
> Back in commit 04a0551c87363f100b04d28d7a15a632b70e18e7
> ("loopback: Drop obsolete ip_summed setting") we stopped
> setting CHECKSUM_UNNECESSARY in the loopback xmit.
> 
> This is because such a setting was a lie since it implies that the
> checksum field of the packet is properly filled in.
> 
> Instead what happens normally is that CHECKSUM_PARTIAL is set and
> skb->csum is calculated as needed.
> 
> But this was only happening for TCP data packets (via the
> skb->ip_summed assignment done in tcp_sendmsg()).  It doesn't
> happen for non-data packets like ACKs etc.

I don't understand.  If said packet was going across the network,
how could it possibly have worked?

Cheers,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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