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

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?