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Date:	Wed, 7 Oct 2015 10:19:19 -0700
From:	Pravin Shelar <>
To:	Jiri Benc <>
Cc:	netdev <>
Subject: Re: [PATCH net] openvswitch: Fix egress tunnel info.

On Wed, Oct 7, 2015 at 1:09 AM, Jiri Benc <> wrote:
> On Tue, 6 Oct 2015 14:16:02 -0700, Pravin Shelar wrote:
>> When OVS needs to add a vxlan tunnel device, OVS can create the vxlan
>> device and check the parameters for the flag. If the flag does not
>> exist then fallback to vport-create.
> You omitted the very important step, delete the device before falling
> back.
> This means that with older kernels, there will be an interface created
> and destroyed shortly after. With all netlink notifications sent, all
> tools listening for netlink events seeing the interface appear and go,
> with this being logged in various places, etc. Sounds very hacky and
> confusing to anyone watching their logs or output of such tools. That
> is the confusion I was talking about.
>> This only needs to be done for
>> very first tunnel device. Thats how most of features are supported in
>> OVS.
> The big difference to the other features is this cannot be detected
> until half way through the setup.
> What I'm proposing instead is to introduce a way to clearly and
> unambiguously detect whether lwtunnels are supported or not. We'll need
> this anyway: kernel 4.3 won't really support IPv6 tunneling with ovs,
> yet there's currently no way to determine whether it's supported or not
> (and, unlike with lwtunnel detection, there's not even a hacky way).
> Querying the datapath for the supported features is needed
> nevertheless; it's only logical to use it for the lwtunnel vs. old
> vport decision, too.
> I don't understand why you're opposed to this: it's much cleaner and
> there's no problem with lwtunnels not being used with the 4.3 kernel,
> everything should work just fine.

I don't want to add more flags to OVS for features which can be
derived from other APIs. But if creating and destroying single virtual
device is such big deal then I am fine with the alternative approach.
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