[PATCH 4/6] bridge: Force mcast_flooding for mrouter ports

[Joseph Huang]

When a port turns into an mrouter port, enable multicast flooding
on that port even if mcast_flood is disabled by user config. This
is necessary so that in a distributed system, the multicast packets
can be fowarded to the Querier when the multicast source is attached
to a Non-Querier bridge.

Consider the following scenario:

                 +--------------------+
                 |                    |
                 |      Snooping      |    +------------+
                 |      Bridge 1      |----| Listener 1 |
                 |     (Querier)      |    +------------+
                 |                    |
                 +--------------------+
                           |
                           |
                 +--------------------+
                 |    | mrouter |     |
+-----------+    |    +---------+     |
| MC Source |----|      Snooping      |
+-----------|    |      Bridge 2      |
                 |    (Non-Querier)   |
                 +--------------------+

In this scenario, Listener 1 will never receive multicast traffic
from MC Source if mcast_flood is disabled on the mrouter port on
Snooping Bridge 2.

Signed-off-by: Joseph Huang <Joseph.Huang@xxxxxxxxxx>
---
 net/bridge/br_multicast.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index d7fbe1f3af18..719ded3204a0 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -2680,6 +2680,21 @@ static void br_port_mc_router_state_change(struct net_bridge_port *port,
 
 	switchdev_port_attr_set(port->dev, &attr, NULL);
 
+	/* Force mcast_flood if mrouter port
+	 * this does not prevent netlink from changing it again
+	 */
+	if (is_mc_router && !(port->flags & BR_MCAST_FLOOD)) {
+		attr.id = SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS;
+		attr.u.brport_flags.val = BR_MCAST_FLOOD;
+		attr.u.brport_flags.mask = BR_MCAST_FLOOD;
+		switchdev_port_attr_set(port->dev, &attr, NULL);
+	} else if (!is_mc_router) {
+		attr.id = SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS;
+		attr.u.brport_flags.val = port->flags & BR_MCAST_FLOOD;
+		attr.u.brport_flags.mask = BR_MCAST_FLOOD;
+		switchdev_port_attr_set(port->dev, &attr, NULL);
+	}
+
 	/* Add/delete the router port to/from all multicast group
 	 * called whle br->multicast_lock is held
 	 */
-- 
2.17.1