netdev - RE: [PATCH V1 net-next 1/1] hyperv: Properly handle checksum offload

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Date:	Mon, 28 Apr 2014 18:31:56 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	David Miller <davem@...emloft.net>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"stable@...nel.org" <stable@...nel.org>
Subject: RE: [PATCH V1 net-next 1/1] hyperv: Properly handle checksum offload



> -----Original Message-----
> From: David Miller [mailto:davem@...emloft.net]
> Sent: Monday, April 28, 2014 10:24 AM
> To: KY Srinivasan
> Cc: netdev@...r.kernel.org; linux-kernel@...r.kernel.org;
> devel@...uxdriverproject.org; olaf@...fle.de; apw@...onical.com;
> jasowang@...hat.com; stable@...nel.org
> Subject: Re: [PATCH V1 net-next 1/1] hyperv: Properly handle checksum
> offload
> 
> From: "K. Y. Srinivasan" <kys@...rosoft.com>
> Date: Fri, 25 Apr 2014 20:55:23 -0700
> 
> > @@ -467,6 +467,9 @@ static int netvsc_start_xmit(struct sk_buff *skb,
> struct net_device *net)
> >  	if (skb_is_gso(skb))
> >  		goto do_lso;
> >
> > +	if (skb->ip_summed != CHECKSUM_PARTIAL)
> > +		goto do_send;
> > +
> 
> There are many possible values of ip_summed, why would you go to
> do_send if for example it was set to CHECKSUM_COMPLETE?
> 
> I think you are just rushing this change, take your time and implement the fix
> properly.
> 
> For example, if you only expect two possible values here
> (CHECKSUM_PARTIAL and something else), design your test so that it only
> allows those two values and therefore you'll be documenting this invariant.

David,

I based this check on the check I see in tcp_v4_send_check() (and tcp_v6_send_check).
Looking at the code some more, it looks like if ip_summed is set to  CHECKSUM_NONE, the
software has computed the checksum and we can bypass the code for offloading the checksum.

Regards,

K. Y
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