netdev - Re: [PATCH] r8169: fix offloaded tx checksum for small packets.

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Date:	Fri, 17 May 2013 00:00:49 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Francois Romieu <romieu@...zoreil.com>
CC:	"David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
	"Hayes Wang" <hayeswang@...ltek.com>,
	Stefan Bader <stefan.bader@...onical.com>,
	Holger Hoffstätte 
	<holger.hoffstaette@...glemail.com>
Subject: Re: [PATCH] r8169: fix offloaded tx checksum for small packets.

On Fri, 2013-05-17 at 00:38 +0200, Francois Romieu wrote:
> 8168evl offloaded checksums are wrong since
> e5195c1f31f399289347e043d6abf3ffa80f0005 pads small packets to
> 60 bytes (without ethernet checksum). Observed UDP checksums are
> typically wrong by the count of added bytes.
> 
> It isn't worth compensating. Let's checksum by hand, then pad.
[...]
> @@ -5869,13 +5877,24 @@ static inline void rtl8169_tso_csum(struct rtl8169_private *tp,
>  	} else if (skb->ip_summed == CHECKSUM_PARTIAL) {
>  		const struct iphdr *ip = ip_hdr(skb);
>  
> +		if (unlikely(skb->len < ETH_ZLEN &&
> +		    (tp->mac_version == RTL_GIGA_MAC_VER_34))) {
> +			skb_checksum_help(skb);
> +			return rtl_skb_pad(skb);
[...]

skb_checksum_help() can fail, though it is unlikely for such a short
packet.  So I think this should be:

			return skb_checksum_help(skb) == 0 && rtl_skb_pad(skb);

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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