netdev - Re: [PATCH net] net: Clear local_df only if crossing namespace.

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Message-ID: <CALnjE+ogMJ=axPo6Xq3a7xO2W5fLY1utwcACRdeoCPgYv4EQsg@mail.gmail.com>
Date:	Wed, 12 Feb 2014 09:05:55 -0800
From:	Pravin Shelar <pshelar@...ira.com>
To:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	"Templin, Fred L" <Fred.L.Templin@...ing.com>,
	Steffen Klassert <steffen.klassert@...unet.com>
Subject: Re: [PATCH net] net: Clear local_df only if crossing namespace.

On Wed, Feb 12, 2014 at 1:32 AM, Nicolas Dichtel
<nicolas.dichtel@...nd.com> wrote:
> Le 12/02/2014 05:26, Pravin Shelar a écrit :
>
>> On Mon, Feb 10, 2014 at 6:11 PM, Hannes Frederic Sowa
>> <hannes@...essinduktion.org> wrote:
>>>
>>> On Mon, Feb 10, 2014 at 01:00:14PM -0800, Pravin Shelar wrote:
>>>>
>>>> On Fri, Feb 7, 2014 at 4:58 PM, Hannes Frederic Sowa
>>>> <hannes@...essinduktion.org> wrote:
>>>>>
>>>>> May I know because of wich vport, vxlan or gre, you did this change?
>>>>>
>>>> It affects both gre and vxlan.
>>>
>>>
>>> Ok, thanks.
>>>
>>>>> I am feeling a bit uncomfortable handling remote and local packets that
>>>>> differently on lower tunnel output (local_df is mostly set on locally
>>>>> originating packets).
>>>>
>>>>
>>>> For ip traffic it make sense to turn on local_df only for local
>>>> traffic, since for remote case we can send icmp (frag-needed) back to
>>>> source. No such thing exist for OVS tunnels. ICMP packet are not
>>>> returned to source for the tunnels. That is why to be on safe side,
>>>> local_df is turned on for tunnels in OVS.
>>>
>>>
>>> I have a proposal:
>>>
>>> I don't like it that much because of the many arguments. But I currently
>>> don't see another easy solution. Maybe we should make bool xnet an enum
>>> and
>>> test with bitops?
>>>
>>> I left the clearing of local_df in skb_scrub_packet as we need it for the
>>> dev_forward_skb case and it should be done that in any case.
>>>
>>> This diff is slightly compile tested. ;)
>>>
>>> I can test and make proper submit if you agree.
>>>
>>> What do you think?
>>>
>>
>> I am not sure why the caller can not just set skb->local_df before
>> calling iptunnel_xmit() rather than passing extra arg to this
>> function?
>> There are not that many caller of this function.
>
> The benefit is that it ensures that future callers will think about this
> point
> ;-)
>

But that add extra test cases in fast path.
For example OVS we can not reset skb->mark in skb_scrub_packet(). I am
going to send patch for that too. Do you think I should add another
argument for skb-mark clear too ?
We can not make code every piece of code future proof. thats why we
have review process.
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