Re: [RFC PATCH net-next 0/5] Replay and offload host VLAN entries in DSA

[Vladimir Oltean <vladimir.oltean@nxp.com>]

On Sun, Feb 13, 2022 at 10:02:55PM +0200, Vladimir Oltean wrote:
> (a) call br_vlan_get_info() from the DSA switchdev notification handler
>     to figure out whether the VLAN is new or not. As far as I can see in
>     __vlan_add(), br_switchdev_port_vlan_add() is called before the
>     insertion of the VLAN into &vg->vlan_hash, so the absence from there
>     could be used as an indicator that the VLAN is new, and that the
>     refcount needs to be bumped, regardless of knowing exactly which
>     bridge or bridge port the VLAN came from. The important part is that
>     it isn't just a flag change, for which we don't want to bump the
>     refcount, and that we can rely on the bridge database and not keep a
>     separate one. The disadvantage seems to be that the solution is a
>     bit fragile and puts a bit too much pressure on the bridge code
>     structure, if it even works (need to try).

Ah, this is too fragile, I thought of a case where it's broken already:
for VLAN replays, it's technically a 'new VLAN' not a changed one, yet
br_vlan_get_info() will still find it so it will get detected as changed.
So the bridge has to pass the information that the switchdev notifier is
just for a change of flags somehow.