After the very useful feedback from Nikolay, i threw away what i had, and started again. To recap:
The linux bridge supports IGMP snooping. It will listen to IGMP reports on bridge ports and keep track of which groups have been joined on an interface. It will then forward multicast based on this group membership. When the bridge adds or removed groups from an interface, it uses switchdev to request the hardware add an mdb to a port, so the hardware can perform the selective forwarding between ports. What is not covered by the current bridge code, is IGMP joins/leaves from the host on the brX interface. These are not reported via switchdev so that hardware knows the local host is interested in the multicast frames. Luckily, the bridge does track joins/leaves on the brX interface. The code is obfusticated, which is why i missed it with my first attempt. So the first patch tries to remove this obfustication. Currently, there is no notifications sent when the bridge interface joins a group. The second patch adds them. bridge monitor then shows joins/leaves in the same way as for other ports of the bridge. Then starts the work passing down to the hardware that the host has joined/left a group. The existing switchdev mdb object cannot be used, since the semantics are different. The existing SWITCHDEV_OBJ_ID_PORT_MDB is used to indicate a specific multicast group should be forwarded out that port of the switch. However here we require the exact opposite. We want multicast frames for the group received on the port to the forwarded to the host. Hence add a new object SWITCHDEV_OBJ_ID_HOST_MDB, a multicast database entry to forward to the host. This new object is then propagated through the DSA layers. No DSA driver changes should be needed, this should just work... Getting the frames to the bridge as requested turned up an issue or three. The offload_fwd_mark is not being set by DSA, so the bridge floods the received frames back to the switch ports, resulting in duplication since the hardware has already flooded the packet. Fixing that turned up an issue with the meaning of SWITCHDEV_ATTR_ID_PORT_PARENT_ID in DSA. A DSA fabric of three switches needs to look to the software bridge as a single switch. Otherwise the offload_fwd_mark does not work, and we get duplication on the non-ingress switch. But each switch returned a different value. And they were not unique. The third and last issue will be explained in a followup email. Open questions: Is sending notifications going to break userspace? Is this new switchdev object O.K. for the few non-DSA switches that exist? Is the SWITCHDEV_ATTR_ID_PORT_PARENT_ID change acceptable? Andrew Andrew Lunn (8): net: bridge: Rename mglist to host_joined net: bridge: Send notification when host join/leaves a group net: bridge: Add/del switchdev object on host join/leave net: dsa: slave: Handle switchdev host mdb add/del net: dsa: switch: handle host mdb add/remove net: dsa: switch: Don't add CPU port to an mdb by default net: dsa: set offload_fwd_mark on received packets net: dsa: Fix SWITCHDEV_ATTR_ID_PORT_PARENT_ID include/net/switchdev.h | 1 + net/bridge/br_input.c | 2 +- net/bridge/br_mdb.c | 50 +++++++++++++++++++++++++++++--- net/bridge/br_multicast.c | 18 +++++++----- net/bridge/br_private.h | 2 +- net/dsa/dsa.c | 1 + net/dsa/dsa_priv.h | 7 +++++ net/dsa/port.c | 26 +++++++++++++++++ net/dsa/slave.c | 16 ++++++++--- net/dsa/switch.c | 72 +++++++++++++++++++++++++++++++++++++++-------- net/switchdev/switchdev.c | 2 ++ 11 files changed, 168 insertions(+), 29 deletions(-) -- 2.14.1
