netdev - Re: [net-next 02/10] udp: Expand UDP tunnel common APIs

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Date:	Tue, 22 Jul 2014 19:12:02 -0400
From:	Jesse Gross <jesse@...ira.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	Andy Zhou <azhou@...ira.com>, David Miller <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [net-next 02/10] udp: Expand UDP tunnel common APIs

On Tue, Jul 22, 2014 at 6:38 PM, Tom Herbert <therbert@...gle.com> wrote:
> On Tue, Jul 22, 2014 at 2:56 PM, Jesse Gross <jesse@...ira.com> wrote:
>> On Tue, Jul 22, 2014 at 5:16 PM, Tom Herbert <therbert@...gle.com> wrote:
>>> On Tue, Jul 22, 2014 at 2:02 PM, Andy Zhou <azhou@...ira.com> wrote:
>>>> On Tue, Jul 22, 2014 at 12:52 PM, Tom Herbert <therbert@...gle.com> wrote:
>>>>>> --- a/include/net/udp_tunnel.h
>>>>>> +++ b/include/net/udp_tunnel.h
>>>>>> @@ -1,7 +1,10 @@
>>>>>>  #ifndef __NET_UDP_TUNNEL_H
>>>>>>  #define __NET_UDP_TUNNEL_H
>>>>>>
>>>>>> -#define UDP_TUNNEL_TYPE_VXLAN 0x01
>>>>>> +#include <net/ip_tunnels.h>
>>>>>> +
>>>>>> +#define UDP_TUNNEL_TYPE_VXLAN  0x01
>>>>>> +#define UDP_TUNNEL_TYPE_GENEVE 0x02
>>>>>>
>>>>> Why do we need to define these? Caller should know what type of port is
>>>>> being opened and provide appropriate encap_rcv.
>>>>
>>>> Assume udp tunnel layer needs to keep track of open ports, should it
>>>> also keep track of the protocol associated with the port?
>>>>
>>> For what purpose? Other than for offloads and rcv_encap functions that
>>> provide the service function anyway, what need is there for UDP layer
>>> to know about this. More to the point, if I add a module to the kernel
>>> with a new flavor of UDP tunneling, I shouldn't have to touch any core
>>> code for things to work correctly. So by this line of thinking,
>>> neither the terms VXLAN nor GENEVE should appear in any common code.
>>
>> The hardware will need to know what the header format is so that it
>> can parse the packets on receive. And since the NIC can't exactly call
>> into a function pointer like GRO can, I'm not sure that there is a
>> solution that doesn't involve an identifier that needs to be listed
>> somewhere. This is a pretty minimal impact - it doesn't actually
>> appear in the core code.
>
> The hardware doesn't *need* to know this, it's must be optional and
> should have no bearing on the software stack. Suggest to put them in
> their own header file. Also, as HW features these should appear in
> NETIF_F_* list so that we can control on a per device level rather to
> enable this feature (something like how NETIF_F_GSO_* was done).

Right - I meant for hardware offload. Obviously, pure software
implementations should continue to work fine with the tunnel stack (as
it does here). I don't have any particular objection to moving them to
a different file (udp_offload.h?) but I agree with Alex that these are
slightly different than hardware feature flags.

> What about support for L2TP/UDP?

It should be possible to take advantage of the common UDP tunnel code
here as well. I believe that Andy is planning on doing it as a follow
up patch, which would be a good example of a pure software
implementation.
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