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

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Message-ID: <539033BC.3000703@lab.ntt.co.jp>
Date:	Thu, 05 Jun 2014 18:09:16 +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 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.

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.)

Thanks,
Toshiaki Makita
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