netdev - Re: [PATCH net-next 2/2] bonding: make hard-coded defines configurable at build

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Message-ID: <CAADnVQJaUQsDF1--4ffnCUz=1Tw1Ox=kgUw3h1L1EnrDs0WQfw@mail.gmail.com>
Date:	Tue, 15 Jul 2014 09:45:36 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Veaceslav Falico <vfalico@...il.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Jay Vosburgh <j.vosburgh@...il.com>,
	Andy Gospodarek <andy@...yhouse.net>
Subject: Re: [PATCH net-next 2/2] bonding: make hard-coded defines
 configurable at build

On Tue, Jul 15, 2014 at 9:18 AM, Veaceslav Falico <vfalico@...il.com> wrote:
> On Tue, Jul 15, 2014 at 08:48:01AM -0700, Alexei Starovoitov wrote:
>>
>> On Tue, Jul 15, 2014 at 3:15 AM, Veaceslav Falico <vfalico@...il.com>
>> wrote:
>>>
>>> +
>>> +config BOND_MAX_VLAN_ENCAP
>>> +       int "Maximum number of stacked vlans on top of bonding"
>>> +       default "2"
>>> +
>>
>> I don't think we should allow changing these defaults so easily.
>> Not a single HW supports 3 vlan tags. There is no standard for it either.
>> Why you would ever change this?
>
> There have been discussions about vlan nestings for bonding, and the
> outcome was that more than 2 are possible. Also, iirc, no standard limits
> it to only 2.

standard doesn't say that the maximum is 2, but it doesn't specify what
should be done in such case, so all vlan-aware switches that I know will
be just dropping packets with 3 vlans.
Therefore for bond driver there is no reason to accept such packets
in the first place from user space, since they won't go too far in the network.

> These defaults are scalable by their nature, and there are people
> maintaining their own patches to change them. So making them available to
> be configured at compile time is a good thing to do, I think.

people keep a patch to support 3 vlans? what's the use case?
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