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 20:45:40 +0000
From:	"Zou, Yi" <yi.zou@...el.com>
To:	Stephen Hemminger <shemminger@...tta.com>
CC:	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"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 18:54:32 +0000
> "Zou, Yi" <yi.zou@...el.com> wrote:
> 
> > >
> > > 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().
> 
> But your change would break any code (if there is any) generating this
> kind of packet and going through firewall, etc. For example a bridge or
> router for FCOE packets.

I don't know anything like that exists right now but in that case for fcoe,
you dan't want to use CHECKSUM_PARTIAL on output. Still, the point is the 
skb_checksum_help() only makes sense for ip checksum.

yi



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