netdev - Re: [PATCH net-next] bridge: Fix incorrect judgment of promisc

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Date:	Thu, 05 Jun 2014 11:06:07 -0400
From:	Vlad Yasevich <vyasevich@...il.com>
To:	David Laight <David.Laight@...LAB.COM>,
	'Toshiaki Makita' <makita.toshiaki@....ntt.co.jp>,
	"David S . Miller" <davem@...emloft.net>,
	Stephen Hemminger <stephen@...workplumber.org>
CC:	Vlad Yasevich <vyasevic@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"bridge@...ts.linux-foundation.org" 
	<bridge@...ts.linux-foundation.org>
Subject: Re: [PATCH net-next] bridge: Fix incorrect judgment of promisc

On 06/05/2014 08:55 AM, David Laight wrote:
> From: Toshiaki Makita
>> (2014/06/05 20:03), David Laight wrote:
>>> From: Toshiaki Makita
>>>> br_manage_promisc() incorrectly expects br_auto_port() to return only 0
>>>> or 1, while it actually returns flags, i.e., a subset of BR_AUTO_MASK.
>>>>
>>>> Signed-off-by: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
>>>> ---
>>>>  net/bridge/br_if.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
>>>> index a08d2b8..6a07a40 100644
>>>> --- a/net/bridge/br_if.c
>>>> +++ b/net/bridge/br_if.c
>>>> @@ -153,7 +153,7 @@ void br_manage_promisc(struct net_bridge *br)
>>>>  			 * This lets us disable promiscuous mode and write
>>>>  			 * this config to hw.
>>>>  			 */
>>>> -			if (br->auto_cnt <= br_auto_port(p))
>>>> +			if (br->auto_cnt <= !!br_auto_port(p))
>>>>  				br_port_clear_promisc(p);
>>>>  			else
>>>>  				br_port_set_promisc(p);
>>>
>>> Why not the less confusing:
>>> 			if (br->auto_cnt || br_auto_port(p))
>>> and reverse the then/else lines?
>>
>> I'm respecting the original style, but I'm not particular about this style.
>> I'll make less confusing one, thanks :)
>>
>> (Your suggested condition is not exactly the same as current one, even
>> if reversing if/else. v2 will be different than it. Anyway, thanks.)
> 
> A quick truth table:
> 	auto_cnt	auto_port	set/clear
> 		0		0	clear
> 		0		1	clear
               Can't happen

> 		1		0	set
              Can't happen
> 		1		1	clear
> 		2+		0/1	clear
> 
> So you want:
> 	if (br->auto_cnt && !br_auto_port(p))
> 		br_port_set_promisc(p);
> 	else
> 		br_port_clear_promisc(p);

Some versions of the series that added this had
an explicit check for count.  Essentially, the
expanded condition is this:

  if (count == 0)
     clear
  else if (count == 1 && auto_port(p))
     clear
  else
     set

The suggestion was that we could use a boolean (0|1)
to check reduce the above to
  if (count <= auto_port(p))
     clear
  else
     set

Personally, I prefer the extended version since it
is much clearer and is easy to understand.

-vlad

> 
> Does seem like a strange condition.
> 
> 	David
> 
> 	
> 
> 
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