Subject: Re: [PATCH net-next 1/2] bridge: Add flag to control mac learning.

From: Vlad Yasevich <[email-masked]>
Date: Mon, 29 Apr 2013 12:33:24 -0400

On 04/29/2013 12:11 PM, Michael S. Tsirkin wrote:
> On Mon, Apr 29, 2013 at 11:58:21AM -0400, Vlad Yasevich wrote:
>> Allow user to control whether mac learning is enabled on the port.
>> By default, mac learning is enabled.  Disabling mac learning will
>> cause new dynamic FDB entries to not be created for a particular port.
>>
>> Signed-off-by: Vlad Yasevich <[email-masked]>
>> ---
>>   include/uapi/linux/if_link.h |    1 +
>>   net/bridge/br_fdb.c          |    4 ++++
>>   net/bridge/br_if.c           |    2 +-
>>   net/bridge/br_netlink.c      |    6 +++++-
>>   net/bridge/br_private.h      |    1 +
>>   net/bridge/br_sysfs_if.c     |    2 ++
>>   6 files changed, 14 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
>> index e316354..80fad7f 100644
>> --- a/include/uapi/linux/if_link.h
>> +++ b/include/uapi/linux/if_link.h
>> @@ -221,6 +221,7 @@ enum {
>>   	IFLA_BRPORT_GUARD,	/* bpdu guard              */
>>   	IFLA_BRPORT_PROTECT,	/* root port protection    */
>>   	IFLA_BRPORT_FAST_LEAVE,	/* multicast fast leave    */
>> +	IFLA_BRPORT_LEARNING,	/* mac learning */
>>   	__IFLA_BRPORT_MAX
>>   };
>>   #define IFLA_BRPORT_MAX (__IFLA_BRPORT_MAX - 1)
>> diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
>> index c581f12..9c4fe65 100644
>> --- a/net/bridge/br_fdb.c
>> +++ b/net/bridge/br_fdb.c
>> @@ -477,10 +477,14 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
>>   	} else {
>>   		spin_lock(&br->hash_lock);
>>   		if (likely(!fdb_find(head, addr, vid))) {
>> +			if (!(source->flags & BR_LEARNING))
>> +				goto unlock;
>> +
>>   			fdb = fdb_create(head, source, addr, vid);
>>   			if (fdb)
>>   				fdb_notify(br, fdb, RTM_NEWNEIGH);
>>   		}
>> +unlock:
>>   		/* else  we lose race and someone else inserts
>>   		 * it first, don't bother updating
>>   		 */
>
> Wait a second, this will affect adding fdbs using RTM_NEWNEIGH, won't it?

Hm..  Yes, I missed this.  But this has got me thinking of whether it is 
correct to allow 'creation' of an entry if NTF_USE is set.

Consider, that the current behavior is rather broken in that
if someone sets  NLM_F_CREATE|NLM_F_EXCL and NTF_USE, we will update
the FDB (which is technically wrong since we ignore the exclusivity).
Also, if someone doesn't specify NLM_F_CREATE, we create anyway.

I think that may be I'll fix the above inconsistencies first.

-vlad

> And let's not bother with lookups if learning is off.
> So I imagine we need something like the below instead
> (in addition to the sysfs/netlink part of the patch which
> look fine):
>
> Signed-off-by: Michael S. Tsirkin <[email-masked]>
>

> ---
>
> diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
> index bab338e..30eaa6b 100644
> --- a/net/bridge/br_fdb.c
> +++ b/net/bridge/br_fdb.c
> @@ -448,8 +448,9 @@ int br_fdb_insert(struct net_bridge *br, struct net_bridge_port *source,
>   	return ret;
>   }
>
> -void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
> -		   const unsigned char *addr, u16 vid)
> +static
> +void __br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
> +		     const unsigned char *addr, u16 vid)
>   {
>   	struct hlist_head *head = &br->hash[br_mac_hash(addr, vid)];
>   	struct net_bridge_fdb_entry *fdb;
> @@ -490,6 +491,14 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
>   	}
>   }
>
> +void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
> +		     const unsigned char *addr, u16 vid)
> +{
> +	if (!(source->flags & BR_LEARNING))
> +		return;
> +	__br_fdb_update(br, source, addr, vid);
> +}
> +
>   static int fdb_to_nud(const struct net_bridge_fdb_entry *fdb)
>   {
>   	if (fdb->is_local)
> @@ -655,7 +664,7 @@ static int __br_fdb_add(struct ndmsg *ndm, struct net_bridge_port *p,
>
>   	if (ndm->ndm_flags & NTF_USE) {
>   		rcu_read_lock();
> -		br_fdb_update(p->br, p, addr, vid);
> +		__br_fdb_update(p->br, p, addr, vid);
>   		rcu_read_unlock();
>   	} else {
>   		spin_lock_bh(&p->br->hash_lock);
>
>