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

Nikolay Aleksandrov
2023-09-21T20:27:53Z

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@avm.de>
> ---
> 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.