netdev - [PATCH net-next v2] bridge: also trigger RTM_NEWLINK when interface is released from bridge

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Date:   Sat, 16 Sep 2017 16:18:33 +0200
From:   Vincent Bernat <vincent@...nat.im>
To:     Stephen Hemminger <stephen@...workplumber.org>,
        "David S. Miller" <davem@...emloft.net>,
        bridge@...ts.linux-foundation.org, netdev@...r.kernel.org
Cc:     Vincent Bernat <vincent@...nat.im>
Subject: [PATCH net-next v2] bridge: also trigger RTM_NEWLINK when interface is released from bridge

Currently, when an interface is released from a bridge via
ioctl(), we get a RTM_DELLINK event through netlink:

Deleted 2: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 master bridge0 state UNKNOWN
    link/ether 6e:23:c2:54:3a:b3

Userspace has to interpret that as a removal from the bridge, not as a
complete removal of the interface. When an bridged interface is
completely removed, we get two events:

Deleted 2: dummy0: <BROADCAST,NOARP> mtu 1500 master bridge0 state DOWN
    link/ether 6e:23:c2:54:3a:b3
Deleted 2: dummy0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default
    link/ether 6e:23:c2:54:3a:b3 brd ff:ff:ff:ff:ff:ff

In constrast, when an interface is released from a bond, we get a
RTM_NEWLINK with only the new characteristics (no master):

3: dummy1: <BROADCAST,NOARP,SLAVE,UP,LOWER_UP> mtu 1500 qdisc noqueue master bond0 state UNKNOWN group default
    link/ether ae:dc:7a:8c:9a:3c brd ff:ff:ff:ff:ff:ff
3: dummy1: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default
    link/ether ae:dc:7a:8c:9a:3c brd ff:ff:ff:ff:ff:ff
4: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
    link/ether ae:dc:7a:8c:9a:3c brd ff:ff:ff:ff:ff:ff
3: dummy1: <BROADCAST,NOARP> mtu 1500 qdisc noqueue state DOWN group default
    link/ether ae:dc:7a:8c:9a:3c brd ff:ff:ff:ff:ff:ff
3: dummy1: <BROADCAST,NOARP> mtu 1500 qdisc noqueue state DOWN group default
    link/ether ca:c8:7b:66:f8:25 brd ff:ff:ff:ff:ff:ff
4: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
    link/ether ae:dc:7a:8c:9a:3c brd ff:ff:ff:ff:ff:ff

Userland may be confused by the fact we say a link is deleted while
its characteristics are only modified. A first solution would have
been to turn the RTM_DELLINK event in del_nbp() into a RTM_NEWLINK
event. However, maybe some piece of userland is relying on this
RTM_DELLINK to detect when a bridged interface is released. Instead,
we also emit a RTM_NEWLINK event once the interface is
released (without master info).

Deleted 2: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 master bridge0 state UNKNOWN
    link/ether 8a:bb:e7:94:b1:f8
2: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default
    link/ether 8a:bb:e7:94:b1:f8 brd ff:ff:ff:ff:ff:ff

This is done only when using ioctl(). When using Netlink, such an
event is already automatically emitted in do_setlink().

Signed-off-by: Vincent Bernat <vincent@...nat.im>
---
 net/bridge/br_ioctl.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/bridge/br_ioctl.c b/net/bridge/br_ioctl.c
index 7970f8540cbb..3148cb3a8e82 100644
--- a/net/bridge/br_ioctl.c
+++ b/net/bridge/br_ioctl.c
@@ -99,8 +99,10 @@ static int add_del_if(struct net_bridge *br, int ifindex, int isadd)
 
 	if (isadd)
 		ret = br_add_if(br, dev);
-	else
+	else {
 		ret = br_del_if(br, dev);
+		rtmsg_ifinfo(RTM_NEWLINK, dev, IFF_MASTER, GFP_KERNEL);
+	}
 
 	return ret;
 }
-- 
2.14.1