Subject: Re: [PATCH 12/21] bridge: slight optimization of addr compare

From: Toshiaki Makita <[email-masked]>
Date: Mon, 23 Dec 2013 17:33:47 +0900

On Mon, 2013-12-23 at 13:10 +0800, Ding Tianhong wrote:
> Use the recently added and possibly more efficient
> ether_addr_equal_unaligned to instead of memcmp.
> 
> Cc: Stephen Hemminger <[email-masked]>
> Cc: David Miller <[email-masked]>
> Cc: [email-masked]
> Cc: [email-masked]
> Signed-off-by: Wang Weidong <[email-masked]>
> Signed-off-by: Ding Tianhong <[email-masked]>
> ---
>  net/bridge/br_stp_if.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
> index 656a6f3..04217d1 100644
> --- a/net/bridge/br_stp_if.c
> +++ b/net/bridge/br_stp_if.c
> @@ -229,7 +229,7 @@ bool br_stp_recalculate_bridge_id(struct net_bridge *br)
>  
>  	list_for_each_entry(p, &br->port_list, list) {
>  		if (addr == br_mac_zero ||
> -		    memcmp(p->dev->dev_addr, addr, ETH_ALEN) < 0)
> +		    !ether_addr_equal_unaligned(p->dev->dev_addr, addr) < 0)
>  			addr = p->dev->dev_addr;
>  
>  	}

We cannot do this change.
!ether_addr_equal() isn't identical to memcmp().
memcmp() can return negative value but ether_addr_equal() cannot.
br_stp_recalculate_bridge_id() is searching the smallest address among
its ports. This change breaks it.

Thanks,
Toshiaki Makita