If bridge have no sub-interfaces, it's status may be still with 'RUNNING'

Hi, all

I made this test on ubuntu 14.04 with kernel 3,19-rc7:

1. brctl addbr br0

2. ifconfig br0 up

3. ifconfig br0 (br0's status is with 'RUNNING')

4. brctl addif br0 eth0

5. brctl delif br0 eth0

6. ifconfig br0 (br0's status is without 'RUNNING')

When there is no sub-interface, the flag "RUNNING" is missing after the last sub-interface is removed.

As such, should we keep "RUNNING" flag after the last sub-interface is removed?

Thanks a lot.
Zhu Yanjun

Add the maintainer of bridge.

Any reply is appreciated.

Zhu Yanjun

This is intentional. If there are no active ports in bridge, then we want to tell applications that packets will go nowhere.

Hi Stephen,
When we up a bridge without sub-interfaces, it has "RUNNING" flag as below. Is it correct or not?

1. brctl addbr br0
2. ifconfig br0 up
3. ifconfig br0
br0 Link encap:Ethernet HWaddr e6:6c:84:a6:fc:64
inet6 addr: fe80::e46c:84ff:fea6:fc64/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:2 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0
RX bytes:0 (0.0 B) TX bytes:168 (168.0 B)

Best Regards
Kuaikuai Wu

-----Original Message-----
From: Stephen Hemminger [mailto:[email protected]]
Sent: Saturday, February 14, 2015 2:31 AM
To: Zhu, Yanjun
Cc: netdev; Wu, Kuaikuai; Tao, Yue
Subject: Re: If bridge have no sub-interfaces, it's status may be still with 'RUNNING'

This is intentional. If there are no active ports in bridge, then we want to tell applications that packets will go nowhere.

Hi, Stephen

Follow your advice, I made a new patch. This patch will turn off carrier when a new bridge interface is created. Please comment on it.

Thanks a lot.
Zhu Yanjun

From: Zhu Yanjun <[email protected]>
Date: Mon, 16 Feb 2015 12:45:36 +0800
Subject: [PATCH 1/1] bridge: turn off carrier when the bridge is created

When a bridge interface is created, there is no any sub interface in it. In this case, the packets should not go to this bridge interface. As such, carrier is turned off.

---
 net/bridge/br_device.c | 5 +++++
 1 file changed, 5 insertions(+)

index ffd379d..2d60474 100644
@@ -394,4 +394,9 @@ void br_dev_setup(struct net_device *dev)
 	br_netfilter_rtable_init(br);
 	br_stp_timer_init(br);
 	br_multicast_init(br);
+
+	/* Shutdown bridge to avoid packets */
+	if (netif_carrier_ok(dev)) {
+		netif_carrier_off(dev);
+	}
 }

1.9.1

I do not see that behavior with Fedora 21 and 3.18.5-201.fc21.x86_64. ie., after interface is removed br0 is still in up state. Perhaps a regression with 3.19.

It changes current behavior with respect to tcpdump. Today I can launch tcpdump on a bridge interface before starting a VM. With this change I will not be able to do that.

David

Originally bridge code would start with carrier off, but there were users using bridge as a form of dummy device and this broke them. Therefore it was decided (like 5 yrs ago), that bridge should start with carrier on.

Hi, all

We should make it compatible. So I made a patch to turn on carrier on this bridge interface when the last sub interface is removed.

Hi, David

Please make tests with this latest patch. Thanks a lot.

Best Regards!
Zhu Yanjun
________________________________________
From: Stephen Hemminger [[email protected]]
Sent: Monday, February 16, 2015 8:51 AM
To: David Ahern
Cc: Zhu, Yanjun; netdev; Wu, Kuaikuai; Tao, Yue
Subject: Re: If bridge have no sub-interfaces, it's status may be still with 'RUNNING'

Originally bridge code would start with carrier off, but there were users using bridge as a form of dummy device and this broke them. Therefore it was decided (like 5 yrs ago), that bridge should start with carrier on.

From 0d16f302f23c9f5101f849450abc073045a193de Mon Sep 17 00:00:00 2001
From: Zhu Yanjun <[email protected]>
Date: Tue, 17 Feb 2015 23:59:08 +0800
Subject: [PATCH 1/1] bridge: turn on carrier after removing the last sub
interface

When the last sub interface is removed from the bridge, the bridge turn off the carrier. Maybe it is not compatible with firstly created bridge without any sub interface. At that time, the carrier of this bridge is turned on.

---
 net/bridge/br_if.c | 6 ++++++
 1 file changed, 6 insertions(+)

index ed307db..f391f8c 100644
@@ -565,6 +565,12 @@ int br_del_if(struct net_bridge *br, struct net_device *dev)
 
 	netdev_update_features(br->dev);
 
+	/* No sub interface in bridge, turn on carrier */
+	if (list_empty(&br->port_list)) {
+		eth_hw_addr_random(br->dev);
+		netif_carrier_on(br->dev);
+	}
+
 	return 0;
 }
 

1.9.1

Hi, Stephen && David

Any update?

Zhu Yanjun

As I mentioned in my last response I see no problem with the existing behavior -- 3.18, 3.19 and 4.0-rc1. With all of them the bridge stays in the running state after all interfaces are removed.

David

Hi, David

I made tests on kernel 3.19-rc7.

1. brctl addbr br0

2. ifconfig br0 up

3. ifconfig br0 (br0's status is with 'RUNNING')

br0 Link encap:Ethernet HWaddr 0a:70:0b:06:34:8f
inet6 addr: fe80::870:bff:fe06:348f/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:16 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0
RX bytes:0 (0.0 B) TX bytes:5054 (5.0 KB)

4. brctl addif br0 eth1

5. brctl delif br0 eth1

6. ifconfig br0 (br0's status is without 'RUNNING')

br0 Link encap:Ethernet HWaddr 00:00:00:00:00:00
inet6 addr: fe80::870:bff:fe06:348f/64 Scope:Link UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:328 errors:0 dropped:5 overruns:0 frame:0 TX packets:19 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0
RX bytes:39997 (39.9 KB) TX bytes:5760 (5.7 KB)

Please compare with the outputs of step 3 and step 6, we can find the difference.

uname:

Linux wind-virtual-machine 3.19.0-rc7 #2 SMP Wed Jan 28 18:36:44 CST 2015 x86_64 x86_64 x86_64 GNU/Linux

So I think we should apply the latest patch to make consistent.

Any reply is appreciated.

Zhu Yanjun

NAK.
We need to keep the current behavior to not break corner case users.

Hi, Stephen && David

Any update ?

Best Regards!
Zhu Yanjun