netdev - Re: [PATCH net-next] bridge: Propagate NETDEV_NOTIFY

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Date:   Wed, 27 Jan 2021 12:15:21 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Nikolay Aleksandrov <nikolay@...dia.com>
Cc:     netdev@...r.kernel.org, Roopa Prabhu <roopa@...dia.com>,
        "David S . Miller" <davem@...emloft.net>,
        bridge@...ts.linux-foundation.org, Jarod Wilson <jarod@...hat.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Ivan Vecera <ivecera@...hat.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Ido Schimmel <idosch@...sch.org>
Subject: Re: [PATCH net-next] bridge: Propagate NETDEV_NOTIFY_PEERS notifier

On Tue, Jan 26, 2021 at 04:55:22PM +0200, Nikolay Aleksandrov wrote:
> >> Thanks for the reply. There are a few reasons I think the bridge should
> >> handle NETDEV_NOTIFY_PEERS:
> >>
> >> 1. Only a few devices will call NETDEV_NOTIFY_PEERS notifier: bond, team,
> >>    virtio, xen, 6lowpan. There should have no much notification message.
> > 
> > You can't send a broadcast to all ports because 1 bond's link status has changed.
> > That makes no sense, the GARP needs to be sent only on that bond. The bond devices
> > are heavily used with bridge setups, and in general the bridge is considered a switch
> > device, it shouldn't be broadcasting GARPs to all ports when one changes link state.
> > 
> 
> Scratch the last sentence, I guess you're talking about when the bond's mac causes
> the bridge to change mac address by br_stp_recalculate_bridge_id(). I was wondering

Yes, that's what I mean. Sorry I didn't make it clear in commit description.

> at first why would you need to send garp, but in fact, as Ido mentioned privately,
> it is already handled correctly, but you need to have set arp_notify sysctl.
> Then if the bridge's mac changes because of the bond flapping a NETDEV_NOTIFY_PEERS will be
> generated. Check:
> devinet.c inetdev_event() -> case NETDEV_CHANGEADDR

Yes, this is a generic work around. It will handle all mac changing instead of
failover.

For IGMP, although you said they are different. In my understanding, when
bridge mac changed, we need to re-join multicast group, while a gratuitous
ARP is also needed. I couldn't find a reason why IGMP message is OK but GARP
is not.

> 
> Alternatively you can always set the bridge mac address manually and then it won't be
> changed by such events.

Thanks for this tips. I'm not sure if administers like this way.

This remind me another issue. Should we resend IGMP when got port
NETDEV_RESEND_IGMP notify, Even the bridge mac address may not changed?
Shouldn't we only resend IGMP, GARP when bridge mac address changed, e.g.

diff --git a/net/bridge/br.c b/net/bridge/br.c
index 1b169f8e7491..74571f24bb18 100644
--- a/net/bridge/br.c
+++ b/net/bridge/br.c
@@ -80,8 +80,11 @@ static int br_device_event(struct notifier_block *unused, unsigned long event, v
 		changed_addr = br_stp_recalculate_bridge_id(br);
 		spin_unlock_bh(&br->lock);
 
-		if (changed_addr)
+		if (changed_addr) {
 			call_netdevice_notifiers(NETDEV_CHANGEADDR, br->dev);
+			call_netdevice_notifiers(NETDEV_RESEND_IGMP, br->dev);
+			call_netdevice_notifiers(NETDEV_NOTIFY_PEERS, br->dev);
+		}
 
 		break;
 
@@ -124,11 +127,6 @@ static int br_device_event(struct notifier_block *unused, unsigned long event, v
 	case NETDEV_PRE_TYPE_CHANGE:
 		/* Forbid underlaying device to change its type. */
 		return NOTIFY_BAD;
-
-	case NETDEV_RESEND_IGMP:
-		/* Propagate to master device */
-		call_netdevice_notifiers(event, br->dev);
-		break;
 	}
 
 	if (event != NETDEV_UNREGISTER)


Thanks
Hangbin