[ovs-dev] [PATCH] datapath: Set datapath device MTU to minimum of MTU of ports.

[Jesse Gross]

The MTU of the local port should be no larger than the minimum of
the MTUs of the ports attached to the bridge, overwise packets may be
dropped.  We already prevent changes to the MTU that would violate
this constraint but don't actuallly proactively set the MTU.  This
changes makes everything consistent and matches the behavior of
the bridge.
---
 datapath/datapath.c  |   24 ++++++++++++++++++++++++
 datapath/datapath.h  |    1 +
 datapath/dp_notify.c |    8 ++++++++
 3 files changed, 33 insertions(+), 0 deletions(-)

diff --git a/datapath/datapath.c b/datapath/datapath.c
index 539859a..116fd98 100644
--- a/datapath/datapath.c
+++ b/datapath/datapath.c
@@ -419,6 +419,7 @@ got_port_no:
 	if (err)
 		goto out_put;
 
+	set_dp_devs_mtu(dp, dev);
 	dp_sysfs_add_if(dp->ports[port_no]);
 
 	err = __put_user(port_no, &port.port);
@@ -1319,6 +1320,29 @@ int dp_min_mtu(const struct datapath *dp)
 	return mtu ? mtu : ETH_DATA_LEN;
 }
 
+/* Sets the MTU of all datapath devices to the minimum of the ports. 'dev'
+ * is the device whose MTU may have changed.  Must be called with RTNL lock
+ * and dp_mutex. */
+void set_dp_devs_mtu(const struct datapath *dp, struct net_device *dev)
+{
+	struct net_bridge_port *p;
+	int mtu;
+
+	ASSERT_RTNL();
+
+	if (is_dp_dev(dev))
+		return;
+
+	mtu = dp_min_mtu(dp);
+
+	list_for_each_entry_rcu (p, &dp->port_list, node) {
+		struct net_device *br_dev = p->dev;
+
+		if (is_dp_dev(br_dev))
+			dev_set_mtu(br_dev, mtu);
+	}
+}
+
 static int
 put_port(const struct net_bridge_port *p, struct odp_port __user *uop)
 {
diff --git a/datapath/datapath.h b/datapath/datapath.h
index 7548ba2..d6883db 100644
--- a/datapath/datapath.h
+++ b/datapath/datapath.h
@@ -151,6 +151,7 @@ void dp_process_received_packet(struct sk_buff *, struct net_bridge_port *);
 int dp_del_port(struct net_bridge_port *);
 int dp_output_control(struct datapath *, struct sk_buff *, int, u32 arg);
 int dp_min_mtu(const struct datapath *dp);
+void set_dp_devs_mtu(const struct datapath *dp, struct net_device *dev);
 
 struct datapath *get_dp(int dp_idx);
 
diff --git a/datapath/dp_notify.c b/datapath/dp_notify.c
index d5a2749..8f77881 100644
--- a/datapath/dp_notify.c
+++ b/datapath/dp_notify.c
@@ -45,6 +45,14 @@ static int dp_device_event(struct notifier_block *unused, unsigned long event,
 			mutex_unlock(&dp->mutex);
 		}
 		break;
+
+	case NETDEV_CHANGEMTU:
+		if (p->port_no != ODPP_LOCAL) {
+			mutex_lock(&dp->mutex);
+			set_dp_devs_mtu(dp, dev);
+			mutex_unlock(&dp->mutex);
+		}
+		break;
 	}
 	return NOTIFY_DONE;
 }
-- 
1.6.3.3