Subject: Re: [PATCH 3/3] netdevice: order of synchronization of IFF_PROMISC and IFF_ALLMULTI

From: Wang Chen <[email-masked]>
Date: Mon, 16 Jun 2008 17:39:29 +0800

Patrick McHardy said the following on 2008-6-16 17:27:
> Wang Chen wrote:
>> IFF_PROMISC should be set before IFF_ALLMULTI.
>>
>> Signed-off-by: Wang Chen <[email-masked]>
>> ---
>>  net/8021q/vlan_dev.c |   25 +++++++++++++++++++------
>>  1 files changed, 19 insertions(+), 6 deletions(-)
>>
>> diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c
>> index 5d055c2..14742e3 100644
>> --- a/net/8021q/vlan_dev.c
>> +++ b/net/8021q/vlan_dev.c
>> @@ -547,10 +547,14 @@ static int vlan_dev_open(struct net_device *dev)
>>      }
>>      memcpy(vlan->real_dev_addr, real_dev->dev_addr, ETH_ALEN);
>>  
>> -    if (dev->flags & IFF_ALLMULTI)
>> -        dev_set_allmulti(real_dev, 1);
>> +    /* NOTE: order of synchronization of IFF_PROMISC and IFF_ALLMULTI
>> +       is important. Some (broken) drivers set IFF_PROMISC, when
>> +       IFF_ALLMULTI is requested not asking us and not reporting.
>> +     */
>>      if (dev->flags & IFF_PROMISC)
>>          dev_set_promiscuity(real_dev, 1);
>> +    if (dev->flags & IFF_ALLMULTI)
>> +        dev_set_allmulti(real_dev, 1);
> 
> 
> What exactly is the problem here? The VLAN code is obviously not
> one of the broken drivers, so why should it care what other drivers
> do?
> 

I think the problem is that allmulti is not valid if promis is not on.

And about the comment, I copy it from dev_change_flags() and think
it seems suit for here.
Did I misunderstand this comment?