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

Toshiaki Makita
2013-12-23T08:33:55Z

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 <stephen@networkplumber.org>
> Cc: David Miller <davem@davemloft.net>
> Cc: bridge@lists.linux-foundation.org
> Cc: netdev@vger.kernel.org
> Signed-off-by: Wang Weidong <wangweidong1@huawei.com>
> Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
> ---
> 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