Re: [PATCH net-next v4 4/6] net: bridge: Add netlink knobs for number / max learned FDB entries

[Nikolay Aleksandrov]

On 9/19/23 11:12, Johannes Nixdorf wrote:
> The previous patch added accounting and a limit for the number of
> dynamically learned FDB entries per bridge. However it did not provide
> means to actually configure those bounds or read back the count. This
> patch does that.
>
> Two new netlink attributes are added for the accounting and limit of
> dynamically learned FDB entries:
>   - IFLA_BR_FDB_N_LEARNED (RO) for the number of entries accounted for
>     a single bridge.
>   - IFLA_BR_FDB_MAX_LEARNED (RW) for the configured limit of entries for
>     the bridge.
>
> The new attributes are used like this:
>
>   # ip link add name br up type bridge fdb_max_learned 256
>   # ip link add name v1 up master br type veth peer v2
>   # ip link set up dev v2
>   # mausezahn -a rand -c 1024 v2
>   0.01 seconds (90877 packets per second
>   # bridge fdb | grep -v permanent | wc -l
>   256
>   # ip -d link show dev br
>   13: br: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 [...]
>       [...] fdb_n_learned 256 fdb_max_learned 256
>
> Signed-off-by: Johannes Nixdorf <jnixdorf-oss@xxxxxx>
> ---
>   include/uapi/linux/if_link.h |  2 ++
>   net/bridge/br_netlink.c      | 15 ++++++++++++++-
>   2 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
> index ce3117df9cec..0486f314c176 100644
> --- a/include/uapi/linux/if_link.h
> +++ b/include/uapi/linux/if_link.h
> @@ -510,6 +510,8 @@ enum {
>   	IFLA_BR_VLAN_STATS_PER_PORT,
>   	IFLA_BR_MULTI_BOOLOPT,
>   	IFLA_BR_MCAST_QUERIER_STATE,
> +	IFLA_BR_FDB_N_LEARNED,
> +	IFLA_BR_FDB_MAX_LEARNED,
>   	__IFLA_BR_MAX,
>   };
>   
> diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
> index 505683ef9a26..f5d49a05e61b 100644
> --- a/net/bridge/br_netlink.c
> +++ b/net/bridge/br_netlink.c
> @@ -1267,6 +1267,8 @@ static const struct nla_policy br_policy[IFLA_BR_MAX + 1] = {
>   	[IFLA_BR_VLAN_STATS_PER_PORT] = { .type = NLA_U8 },
>   	[IFLA_BR_MULTI_BOOLOPT] =
>   		NLA_POLICY_EXACT_LEN(sizeof(struct br_boolopt_multi)),
> +	[IFLA_BR_FDB_N_LEARNED] = { .type = NLA_U32 },
> +	[IFLA_BR_FDB_MAX_LEARNED] = { .type = NLA_U32 },
>   };
>   
>   static int br_changelink(struct net_device *brdev, struct nlattr *tb[],
> @@ -1541,6 +1543,12 @@ static int br_changelink(struct net_device *brdev, struct nlattr *tb[],
>   			return err;
>   	}
>   
> +	if (data[IFLA_BR_FDB_MAX_LEARNED]) {
> +		u32 val = nla_get_u32(data[IFLA_BR_FDB_MAX_LEARNED]);
> +
> +		WRITE_ONCE(br->fdb_max_learned, val);
> +	}
> +
>   	return 0;
>   }
>   
> @@ -1595,6 +1603,8 @@ static size_t br_get_size(const struct net_device *brdev)
>   	       nla_total_size_64bit(sizeof(u64)) + /* IFLA_BR_TOPOLOGY_CHANGE_TIMER */
>   	       nla_total_size_64bit(sizeof(u64)) + /* IFLA_BR_GC_TIMER */
>   	       nla_total_size(ETH_ALEN) +       /* IFLA_BR_GROUP_ADDR */
> +	       nla_total_size(sizeof(u32)) +    /* IFLA_BR_FDB_N_LEARNED */
> +	       nla_total_size(sizeof(u32)) +    /* IFLA_BR_FDB_MAX_LEARNED */
>   #ifdef CONFIG_BRIDGE_IGMP_SNOOPING
>   	       nla_total_size(sizeof(u8)) +     /* IFLA_BR_MCAST_ROUTER */
>   	       nla_total_size(sizeof(u8)) +     /* IFLA_BR_MCAST_SNOOPING */
> @@ -1670,7 +1680,10 @@ static int br_fill_info(struct sk_buff *skb, const struct net_device *brdev)
>   	    nla_put_u8(skb, IFLA_BR_TOPOLOGY_CHANGE_DETECTED,
>   		       br->topology_change_detected) ||
>   	    nla_put(skb, IFLA_BR_GROUP_ADDR, ETH_ALEN, br->group_addr) ||
> -	    nla_put(skb, IFLA_BR_MULTI_BOOLOPT, sizeof(bm), &bm))
> +	    nla_put(skb, IFLA_BR_MULTI_BOOLOPT, sizeof(bm), &bm) ||
> +	    nla_put_u32(skb, IFLA_BR_FDB_N_LEARNED,
> +			atomic_read(&br->fdb_n_learned)) ||
> +	    nla_put_u32(skb, IFLA_BR_FDB_MAX_LEARNED, br->fdb_max_learned))
>   		return -EMSGSIZE;
>   
>   #ifdef CONFIG_BRIDGE_VLAN_FILTERING

Actually you're using atomic for counting, but using a u32 for the 
limit, you should cap it because the count can overflow. Or you should
use atomic64 for the counting.