Re: [PATCH net-next v4 5/6] net: bridge: Add a configurable default FDB learning limit

Nikolay Aleksandrov
2023-09-20T11:00:38Z

On 9/19/23 11:12, Johannes Nixdorf wrote:
> Add a Kconfig option to configure a default FDB learning limit system
> wide, so a distributor building a special purpose kernel can limit all
> created bridges by default.
>
> The limit is only a soft default setting and overrideable on a per bridge
> basis using netlink.
>
> Signed-off-by: Johannes Nixdorf <jnixdorf-oss@avm.de>
> ---
> net/bridge/Kconfig | 13 +++++++++++++
> net/bridge/br_device.c | 2 ++
> 2 files changed, 15 insertions(+)
>
> diff --git a/net/bridge/Kconfig b/net/bridge/Kconfig
> index 3c8ded7d3e84..c0d9c08088c4 100644
> --- a/net/bridge/Kconfig
> +++ b/net/bridge/Kconfig
> @@ -84,3 +84,16 @@ config BRIDGE_CFM
> Say N to exclude this support and reduce the binary size.
>
> If unsure, say N.
> +
> +config BRIDGE_DEFAULT_FDB_MAX_LEARNED
> + int "Default FDB learning limit"
> + default 0
> + depends on BRIDGE
> + help
> + Sets a default limit on the number of learned FDB entries on
> + new bridges. This limit can be overwritten via netlink on a
> + per bridge basis.
> +
> + The default of 0 disables the limit.
> +
> + If unsure, say 0.
> diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
> index 9a5ea06236bd..3214391c15a0 100644
> --- a/net/bridge/br_device.c
> +++ b/net/bridge/br_device.c
> @@ -531,6 +531,8 @@ void br_dev_setup(struct net_device *dev)
> br->bridge_ageing_time = br->ageing_time = BR_DEFAULT_AGEING_TIME;
> dev->max_mtu = ETH_MAX_MTU;
>
> + br->fdb_max_learned = CONFIG_BRIDGE_DEFAULT_FDB_MAX_LEARNED;
> +
> br_netfilter_rtable_init(br);
> br_stp_timer_init(br);
> br_multicast_init(br);
>

This one I'm not sure about at all. Distributions can just create the
bridge with a predefined limit. This is not flexible and just adds
one more kconfig option that is rather unnecessary. Why having a kconfig
knob is better than bridge creation time limit setting? You still have
to create the bridge, so why not set the limit then?