netdev - Re: [PATCH net-next v2 3/3] net: bridge: Add a configurable default FDB learning limit

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Date: Tue, 20 Jun 2023 09:56:06 +0300
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: Johannes Nixdorf <jnixdorf-oss@....de>, bridge@...ts.linux-foundation.org
Cc: netdev@...r.kernel.org, David Ahern <dsahern@...il.com>,
 Vladimir Oltean <vladimir.oltean@....com>, Andrew Lunn <andrew@...n.ch>,
 Florian Fainelli <f.fainelli@...il.com>,
 Oleksij Rempel <linux@...pel-privat.de>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Roopa Prabhu <roopa@...dia.com>, Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next v2 3/3] net: bridge: Add a configurable default
 FDB learning limit

On 6/19/23 10:14, Johannes Nixdorf wrote:
> This adds 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 overridable per bridge
> using netlink.
> 
> Signed-off-by: Johannes Nixdorf <jnixdorf-oss@....de>
> 
> ---
> 
> Changes since v1:
>   - Added a default limit in Kconfig. (deemed acceptable in review
>     comments)
> 
>   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 8eca8a5c80c6..93f081ce8195 100644
> --- a/net/bridge/br_device.c
> +++ b/net/bridge/br_device.c
> @@ -530,6 +530,8 @@ 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_entries = CONFIG_BRIDGE_DEFAULT_FDB_MAX_LEARNED;
> +
>   	br_netfilter_rtable_init(br);
>   	br_stp_timer_init(br);
>   	br_multicast_init(br);

IMO this is pointless, noone will set the kconfig option except very 
specific users. I prefer if we leave it to the distribution to set a 
maximum on bridge creation, i.e. make it a distro policy.