netdev - Re: [Patch net 3/3] team: use a larger struct for mac address

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Message-ID: <af281f03-e6a9-7197-c38c-d5f63abc3410@redhat.com>
Date:   Wed, 26 Apr 2017 13:59:00 -0400
From:   Jarod Wilson <jarod@...hat.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Jiri Pirko <jiri@...nulli.us>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [Patch net 3/3] team: use a larger struct for mac address

On 2017-04-26 1:28 PM, Cong Wang wrote:
> On Wed, Apr 26, 2017 at 9:46 AM, Jarod Wilson <jarod@...hat.com> wrote:
>> On 2017-04-26 12:11 PM, Cong Wang wrote:
>>>
>>> On Wed, Apr 26, 2017 at 8:55 AM, Jarod Wilson <jarod@...hat.com> wrote:
>>>>
>>>>
>>>> We already have struct sockaddr_storage that could be used throughout
>>>> this
>>>> set as well. We just converted a few pieces of the bonding driver over to
>>>> using it for better support of ipoib bonds, via commit
>>>> faeeb317a5615076dff1ff44b51e862e6064dbd0. Might be better to just use
>>>> that
>>>> in both bonding and team, rather than having different per-driver
>>>> structs,
>>>> or Yet Another Address Storage implementation.
>>>
>>>
>>> Technically, struct sockaddr_storage is not enough either, given the
>>> max is MAX_ADDR_LEN. This is why I gave up on sockaddr_storage.
>>
>>
>> Wait, what? Am I missing something? MAX_ADDR_LEN is 32, and sockaddr_storage
>> is a #define for __kernel_sockaddr_storage, which has it's __data member
>> defined as being of size 128 - sizeof(unsigned short).
> 
> My bad, I thought it is same with sizeof(in6addr) without looking into it.
> The question is, why do we waste 126 - 32 = 94 bytes on stack to just
> use struct sockaddr_storage?

That's a fair point.

> I totally understand we want a unified struct, but we already redefine
> it in multiple places in tree...

Something unified and centralized with a data storage of MAX_ADDR_LEN 
does seem reasonable to get both consistency and minimized waste, and I 
could certainly do a follow-up patch for the bonding driver to switch 
the bits now using sockaddr_storage over to whatever new struct gets added.

-- 
Jarod Wilson
jarod@...hat.com