netdev - Re: [PATCH net] gso: do GSO for local skb with size bigger than MTU

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Message-ID: <CAEP_g=9BvhQfGKveCXgTa92vuWMp3-V8MHP+eiABvyzQFF08nA@mail.gmail.com>
Date:	Thu, 4 Dec 2014 15:19:47 -0800
From:	Jesse Gross <jesse@...ira.com>
To:	Thomas Graf <tgraf@...g.ch>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	"Du, Fan" <fan.du@...el.com>, Jason Wang <jasowang@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"fw@...len.de" <fw@...len.de>,
	"dev@...nvswitch.org" <dev@...nvswitch.org>,
	Pravin Shelar <pshelar@...ira.com>
Subject: Re: [PATCH net] gso: do GSO for local skb with size bigger than MTU

On Thu, Dec 4, 2014 at 1:26 AM, Thomas Graf <tgraf@...g.ch> wrote:
> On 12/03/14 at 05:51pm, Jesse Gross wrote:
>> I think it depends on where you put the PMTU check. If routing is
>> happening in OVS where it is decomposed in several discrete actions
>> like set MAC and decrement TTL then perhaps there is another explicit
>> action to check the MTU. If it is happening in the context of the IP
>> stack, then ICMP generation occurs automatically and if you get that
>> if you write a flow to send a packet there. In each case, it seems
>> like a flow would be steering you by way of an action to do routing so
>> you would have fine grained control. I don't see this as conflicting
>> with L3 ACLs in an L2 context in the same way that you don't have to
>> automatically decrement the TTL.
>
> OK, I was under the impression that you would detect L3 behaviour
> desire in OVS without an explicit action. Hence the worry on wrong
> classification for L3 ACLs.
>
> Whether we mark the packet and defer the MTU check or we check right
> in the action is an implementation detail in the end. I think we
> agree on concept level that we need an API to control behaviour.

Yes, I agree.
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