netdev - Re: [PATCH v2] openvswitch: Trim off padding before L3+ netfilter processing

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Date:   Mon, 8 Jan 2018 16:05:32 -0800
From:   Pravin Shelar <pshelar@....org>
To:     Ed Swierk <eswierk@...portsystems.com>
Cc:     ovs-dev <ovs-dev@...nvswitch.org>, netdev <netdev@...r.kernel.org>,
        Benjamin Warren <ben@...portsystems.com>,
        Keith Holleman <holleman@...portsystems.com>
Subject: Re: [PATCH v2] openvswitch: Trim off padding before L3+ netfilter processing

On Sat, Jan 6, 2018 at 10:57 AM, Pravin Shelar <pshelar@....org> wrote:
> On Fri, Jan 5, 2018 at 10:59 PM, Ed Swierk <eswierk@...portsystems.com> wrote:
>>
>>
>> On Jan 5, 2018 22:17, "Pravin Shelar" <pshelar@....org> wrote:
>>
>> On Fri, Jan 5, 2018 at 3:20 PM, Ed Swierk <eswierk@...portsystems.com>
>> wrote:
>>> On Fri, Jan 5, 2018 at 10:14 AM, Ed Swierk <eswierk@...portsystems.com>
>>> wrote:
>>>> On Thu, Jan 4, 2018 at 7:36 PM, Pravin Shelar <pshelar@....org> wrote:
>>>>> OVS already pull all required headers in skb linear data, so no need
>>>>> to redo all of it. only check required is the ip-checksum validation.
>>>>> I think we could avoid it in most of cases by checking skb length to
>>>>> ipheader length before verifying the ip header-checksum.
>>>>
>>>> Shouldn't the IP header checksum be verified even earlier, like in
>>>> key_extract(), before actually using any of the fields in the IP
>>>> header?
>>>
>>> Something like this for verifying the IP header checksum (not tested):
>>>
>> AFAIU openflow does not need this verification, so it is not required
>> in flow extract.
>>
>>
>> Okay. How about my proposed trimming implementation, caching the pad length
>> in the ovs cb?
>>
> Caching the length is not that simple, OVS actions can change the
> length. Keeping it consistent with packet would be more work, so lets
> calculate it in ovs-ct function.

You could make it specific for skb-len-trimming, something like
boolean flag. so that it is easy to reason with.