netdev - Re: [RFC PATCH] powerpc/pseries/mobility: notify network peers after migration

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Date:   Wed, 06 Nov 2019 16:14:03 -0600
From:   Nathan Lynch <nathanl@...ux.ibm.com>
To:     Thomas Falcon <tlfalcon@...ux.ibm.com>
Cc:     netdev@...r.kernel.org, tyreld@...ux.ibm.com, msuchanek@...e.com,
        linuxppc-dev@...abs.org
Subject: Re: [RFC PATCH] powerpc/pseries/mobility: notify network peers after migration

Hi Tom,

Thomas Falcon <tlfalcon@...ux.ibm.com> writes:
> After a migration, it is necessary to send a gratuitous ARP
> from all running interfaces so that the rest of the network
> is aware of its new location. However, some supported network
> devices are unaware that they have been migrated. To avoid network
> interruptions and other unwanted behavior, force a GARP on all
> valid, running interfaces as part of the post_mobility_fixup
> routine.

[...]

> @@ -331,6 +334,8 @@ void post_mobility_fixup(void)
>  {
>  	int rc;
>  	int activate_fw_token;
> +	struct net_device *netdev;
> +	struct net *net;
>  
>  	activate_fw_token = rtas_token("ibm,activate-firmware");
>  	if (activate_fw_token == RTAS_UNKNOWN_SERVICE) {
> @@ -371,6 +376,21 @@ void post_mobility_fixup(void)
>  	/* Possibly switch to a new RFI flush type */
>  	pseries_setup_rfi_flush();
>  
> +	/* need to force a gratuitous ARP on running interfaces */
> +	rtnl_lock();
> +	for_each_net(net) {
> +		for_each_netdev(net, netdev) {
> +			if (netif_device_present(netdev) &&
> +			    netif_running(netdev) &&
> +			    !(netdev->flags & (IFF_NOARP | IFF_LOOPBACK)))
> +				call_netdevice_notifiers(NETDEV_NOTIFY_PEERS,
> +							 netdev);
> +				call_netdevice_notifiers(NETDEV_RESEND_IGMP,
> +							 netdev);
> +		}
> +	}
> +	rtnl_unlock();
> +

This isn't an outright nak, but this is not nice. It illustrates the
need to rethink the pseries partition migration code. There is no
mechanism for drivers and other interested code to prepare for a
migration or to adjust to the destination. So post_mobility_fixup() will
continue to grow into a fragile collection of calls into unrelated
subsystems until there is a better design -- either a pseries-specific
notification/callback mechanism, or something based on the pm framework.

My understanding is that this is needed specifically for ibmveth and,
unlike ibmvnic, the platform does not provide any notification to that
driver that a migration has occurred, right?