Re: [PATCH v3 net-next 00/12] Better support for sandwiched LAGs with bridge and DSA

[Nikolay Aleksandrov]

On 21/03/2021 00:34, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@xxxxxxx>
> 
> The objective of this series is to make LAG uppers on top of switchdev
> ports work regardless of which order we link interfaces to their masters
> (first make the port join the LAG, then the LAG join the bridge, or the
> other way around).
> 
> There was a design decision to be made in patches 2-4 on whether we
> should adopt the "push" model (which attempts to solve the problem
> centrally, in the bridge layer) where the driver just calls:
> 
>   switchdev_bridge_port_offloaded(brport_dev,
>                                   &atomic_notifier_block,
>                                   &blocking_notifier_block,
>                                   extack);
> 
> and the bridge just replays the entire collection of switchdev port
> attributes and objects that it has, in some predefined order and with
> some predefined error handling logic;
> 
> 
> or the "pull" model (which attempts to solve the problem by giving the
> driver the rope to hang itself), where the driver, apart from calling:
> 
>   switchdev_bridge_port_offloaded(brport_dev, extack);
> 
> has the task of "dumpster diving" (as Tobias puts it) through the bridge
> attributes and objects by itself, by calling:
> 
>   - br_vlan_replay
>   - br_fdb_replay
>   - br_mdb_replay
>   - br_vlan_enabled
>   - br_port_flag_is_set
>   - br_port_get_stp_state
>   - br_multicast_router
>   - br_get_ageing_time
> 
> (not necessarily all of them, and not necessarily in this order, and
> with driver-defined error handling).
> 
> Even though I'm not in love myself with the "pull" model, I chose it
> because there is a fundamental trick with replaying switchdev events
> like this:
> 
> ip link add br0 type bridge
> ip link add bond0 type bond
> ip link set bond0 master br0
> ip link set swp0 master bond0 <- this will replay the objects once for
>                                  the bond0 bridge port, and the swp0
>                                  switchdev port will process them
> ip link set swp1 master bond0 <- this will replay the objects again for
>                                  the bond0 bridge port, and the swp1
>                                  switchdev port will see them, but swp0
>                                  will see them for the second time now
> 
> Basically I believe that it is implementation defined whether the driver
> wants to error out on switchdev objects seen twice on a port, and the
> bridge should not enforce a certain model for that. For example, for FDB
> entries added to a bonding interface, the underling switchdev driver
> might have an abstraction for just that: an FDB entry pointing towards a
> logical (as opposed to physical) port. So when the second port joins the
> bridge, it doesn't realy need to replay FDB entries, since there is
> already at least one hardware port which has been receiving those
> events, and the FDB entries don't need to be added a second time to the
> same logical port.
> In the other corner, we have the drivers that handle switchdev port
> attributes on a LAG as individual switchdev port attributes on physical
> ports (example: VLAN filtering). In fact, the switchdev_handle_port_attr_set
> helper facilitates this: it is a fan-out from a single orig_dev towards
> multiple lowers that pass the check_cb().
> But that's the point: switchdev_handle_port_attr_set is just a helper
> which the driver _opts_ to use. The bridge can't enforce the "push"
> model, because that would assume that all drivers handle port attributes
> in the same way, which is probably false.
> 
> For this reason, I preferred to go with the "pull" mode for this patch
> set. Just to see how bad it is for other switchdev drivers to copy-paste
> this logic, I added the pull support to ocelot too, and I think it's
> pretty manageable.
> 
> Vladimir Oltean (12):
>   net: dsa: call dsa_port_bridge_join when joining a LAG that is already
>     in a bridge
>   net: dsa: pass extack to dsa_port_{bridge,lag}_join
>   net: dsa: inherit the actual bridge port flags at join time
>   net: dsa: sync up with bridge port's STP state when joining
>   net: dsa: sync up VLAN filtering state when joining the bridge
>   net: dsa: sync multicast router state when joining the bridge
>   net: dsa: sync ageing time when joining the bridge
>   net: dsa: replay port and host-joined mdb entries when joining the
>     bridge
>   net: dsa: replay port and local fdb entries when joining the bridge
>   net: dsa: replay VLANs installed on port when joining the bridge
>   net: ocelot: call ocelot_netdevice_bridge_join when joining a bridged
>     LAG
>   net: ocelot: replay switchdev events when joining bridge
> 
>  drivers/net/dsa/ocelot/felix.c         |   4 +-
>  drivers/net/ethernet/mscc/ocelot.c     |  18 +--
>  drivers/net/ethernet/mscc/ocelot_net.c | 208 +++++++++++++++++++++----
>  include/linux/if_bridge.h              |  40 +++++
>  include/net/switchdev.h                |   1 +
>  include/soc/mscc/ocelot.h              |   6 +-
>  net/bridge/br_fdb.c                    |  52 +++++++
>  net/bridge/br_mdb.c                    |  84 ++++++++++
>  net/bridge/br_stp.c                    |  27 ++++
>  net/bridge/br_vlan.c                   |  71 +++++++++
>  net/dsa/dsa_priv.h                     |   9 +-
>  net/dsa/port.c                         | 203 ++++++++++++++++++------
>  net/dsa/slave.c                        |  11 +-
>  13 files changed, 631 insertions(+), 103 deletions(-)
> 

Hi Vladimir,
Please pull all of the new bridge code into separate patches with the proper
bridge subsystems tagged in the subject.
I'll review the bridge changes in a minute.

Thanks,
 Nik