Re: [PATCH v4 net-next 01/11] net: bridge: add helper for retrieving the current bridge port STP state

[Nikolay Aleksandrov]

On 23/03/2021 01:51, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@xxxxxxx>
> 
> It may happen that we have the following topology with DSA or any other
> switchdev driver with LAG offload:
> 
> ip link add br0 type bridge stp_state 1
> ip link add bond0 type bond
> ip link set bond0 master br0
> ip link set swp0 master bond0
> ip link set swp1 master bond0
> 
> STP decides that it should put bond0 into the BLOCKING state, and
> that's that. The ports that are actively listening for the switchdev
> port attributes emitted for the bond0 bridge port (because they are
> offloading it) and have the honor of seeing that switchdev port
> attribute can react to it, so we can program swp0 and swp1 into the
> BLOCKING state.
> 
> But if then we do:
> 
> ip link set swp2 master bond0
> 
> then as far as the bridge is concerned, nothing has changed: it still
> has one bridge port. But this new bridge port will not see any STP state
> change notification and will remain FORWARDING, which is how the
> standalone code leaves it in.
> 
> We need a function in the bridge driver which retrieves the current STP
> state, such that drivers can synchronize to it when they may have missed
> switchdev events.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
> Reviewed-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
> Reviewed-by: Tobias Waldekranz <tobias@xxxxxxxxxxxxxx>
> ---
>  include/linux/if_bridge.h |  6 ++++++
>  net/bridge/br_stp.c       | 14 ++++++++++++++
>  2 files changed, 20 insertions(+)
> 

Acked-by: Nikolay Aleksandrov <nikolay@xxxxxxxxxx>