netdev - RE: [net 2/2] net: fix a bug of dropping FCoE frames when disabling tx ip checksum

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Date:	Wed, 14 Mar 2012 18:54:32 +0000
From:	"Zou, Yi" <yi.zou@...el.com>
To:	Stephen Hemminger <shemminger@...tta.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"gospo@...hat.com" <gospo@...hat.com>,
	"sassmann@...hat.com" <sassmann@...hat.com>
Subject: RE: [net 2/2] net: fix a bug of dropping FCoE frames when disabling
 tx ip checksum

> 
> On Wed, 14 Mar 2012 00:01:58 -0700
> Jeff Kirsher <jeffrey.t.kirsher@...el.com> wrote:
> 
> > From: Yi Zou <yi.zou@...el.com>
> >
> > Fix a bug when using 'ethtool -K ethx tx off' to turn off tx ip
> checksum,
> > FCoE CRC offload should not be impacte. The skb_checksum_help() is
> needed
> > only if it's not FCoE traffic for ip checksum, regardless of ethtool
> toggling
> > the tx ip checksum on or off.
> >
> > Signed-off-by: Yi Zou <yi.zou@...el.com>
> > Tested-by: Ross Brattain <ross.b.brattain@...el.com>
> > Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> > ---
> >  net/core/dev.c |    3 +++
> >  1 files changed, 3 insertions(+), 0 deletions(-)
> >
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index 6ca32f6..9e378009 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -1913,6 +1913,9 @@ int skb_checksum_help(struct sk_buff *skb)
> >  	__wsum csum;
> >  	int ret = 0, offset;
> >
> > +	if (skb->protocol == htons(ETH_P_FCOE))
> > +		goto out;
> > +
> >  	if (skb->ip_summed == CHECKSUM_COMPLETE)
> >  		goto out_set_summed;
> >
> 
> Shouldn't this be done in the offending driver rather than the core?
Well, yes and no, the driver is already using NETIF_F_FCOE_CRC to indicate
the FCoE CRC offload capability, and can_checksum_protocol() indicates that.
The fcoe protocol stack then uses CHECKSUM_PARTIAL and NETIF_F_FCOE_CRC to
pass through netdev w/o doing skb_checksum(), which is not captured here
in dev_hard_start_xmit() as it looks at NETIF_F_ALL_CSUM only before calling
skb_checksum_help().

Yi

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