netdev - Re: [PATCH net-next 2/4] net: dev: don't set the same mac address for netdev

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Message-ID: <53904BB6.7030803@lab.ntt.co.jp>
Date:	Thu, 05 Jun 2014 19:51:34 +0900
From:	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:	Ding Tianhong <dingtianhong@...wei.com>, kaber@...sh.net,
	davem@...emloft.net, edumazet@...gle.com, vyasevic@...hat.com
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/4] net: dev: don't set the same mac address
 for netdev

(2014/06/05 18:50), Ding Tianhong wrote:
> On 2014/6/5 17:09, Toshiaki Makita wrote:
>> (2014/06/05 15:50), Ding Tianhong wrote:
>>> Most of netdev just like bond, team, vlan will set the mac address
>>> and propagate to the upperdev or lowerdev regardless the mac address
>>> is  same or not, I could not find that the same mac address could
>>> make affect, so add equal check when set mac address.
>>>
>>> Signed-off-by: Ding Tianhong <dingtianhong@...wei.com>
>>> ---
>>>  net/core/dev.c | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/net/core/dev.c b/net/core/dev.c
>>> index 5367bfb..4008a51 100644
>>> --- a/net/core/dev.c
>>> +++ b/net/core/dev.c
>>> @@ -5570,6 +5570,8 @@ int dev_set_mac_address(struct net_device *dev, struct sockaddr *sa)
>>>  		return -EINVAL;
>>>  	if (!netif_device_present(dev))
>>>  		return -ENODEV;
>>> +	if (ether_addr_equal_64bits(dev->dev_addr, sa->sa_data))
>>> +		return 0;
>>>  	err = ops->ndo_set_mac_address(dev, sa);
>>>  	if (err)
>>>  		return err;
>>>
>>
>> Bridge uses addr_assign_type to check if bridge_id can be propageted by
>> bridge ports. If user set mac address, and even if it is the same as
>> current one, bridge uses the fact that the mac address is set by user.
>>
> 
> OK
> 
>> Although I'm not aware of a driver that needs calling of
>> ndo_set_mac_address() for the same mac address, this change looks a bit
>> risky to me.
>> (For example, old bridge code needed this call because it managed
>> BR_SET_MAC_ADDR in bridge flags.)
>>
> Except the old bridge, I still don't think any other driver need to call ndo_set_mac_address()
> for the same mac address, if the dev_set_mac_address() don't do anything for the same address,
> I think some drivers should ignore the same mac address themselves just like bonding, macvlan, vlan and so on.

Though I don't know why you think this is safe, looking over some
drivers, br2684_mac_addr() seems to use a logic similar to old bridge's.

Thanks,
Toshiaki Makita
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