Re: [17/18] arp_notify: unconditionally send gratuitous ARP for NETDEV_NOTIFY_PEERS.

[Ian Campbell <Ian.Campbell@eu.citrix.com>]

On Sat, 2011-03-05 at 01:03 +0000, Greg KH wrote:
> 2.6.32-longterm review patch.  If anyone has any objections, please let us know.
> 
> ------------------
> 
> From: Ian Campbell <Ian.Campbell@citrix.com>
> 
> commit d11327ad6695db8117c78d70611e71102ceec2ac upstream.
> 
> NETDEV_NOTIFY_PEER is an explicit request by the driver to send a link
> notification while NETDEV_UP/NETDEV_CHANGEADDR generate link
> notifications as a sort of side effect.
> 
> In the later cases the sysctl option is present because link
> notification events can have undesired effects e.g. if the link is
> flapping. I don't think this applies in the case of an explicit
> request from a driver.
> 
> This patch makes NETDEV_NOTIFY_PEER unconditional, if preferred we
> could add a new sysctl for this case which defaults to on.
> 
> This change causes Xen post-migration ARP notifications (which cause
> switches to relearn their MAC tables etc) to be sent by default.
> 
> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> [reported to solve hyperv live migration problem - gkh]

I hadn't spotted this second caller of netif_notify_peers under
drivers/staging but, yes, I rather suspect it will help hyperv as well
as Xen given that 7c161d0b900ea9bd9fc5ea5d3fa9916e9eb0dd88 "staging: hv:
Enable sending GARP packet after live migration" is already in the
stable and longterm trees.

Ian.

> Cc: Haiyang Zhang <haiyangz@microsoft.com>
> Cc: Mike Surcouf <mike@surcouf.co.uk>
> Cc: Hank Janssen <hjanssen@microsoft.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
> 
> ---
>  net/ipv4/devinet.c |   30 ++++++++++++++++++++----------
>  1 file changed, 20 insertions(+), 10 deletions(-)
> 
> --- a/net/ipv4/devinet.c
> +++ b/net/ipv4/devinet.c
> @@ -1025,6 +1025,21 @@ static inline bool inetdev_valid_mtu(uns
>  	return mtu >= 68;
>  }
>  
> +static void inetdev_send_gratuitous_arp(struct net_device *dev,
> +					struct in_device *in_dev)
> +
> +{
> +	struct in_ifaddr *ifa = in_dev->ifa_list;
> +
> +	if (!ifa)
> +		return;
> +
> +	arp_send(ARPOP_REQUEST, ETH_P_ARP,
> +		 ifa->ifa_address, dev,
> +		 ifa->ifa_address, NULL,
> +		 dev->dev_addr, NULL);
> +}
> +
>  /* Called only under RTNL semaphore */
>  
>  static int inetdev_event(struct notifier_block *this, unsigned long event,
> @@ -1076,18 +1091,13 @@ static int inetdev_event(struct notifier
>  		}
>  		ip_mc_up(in_dev);
>  		/* fall through */
> -	case NETDEV_NOTIFY_PEERS:
>  	case NETDEV_CHANGEADDR:
> +		if (!IN_DEV_ARP_NOTIFY(in_dev))
> +			break;
> +		/* fall through */
> +	case NETDEV_NOTIFY_PEERS:
>  		/* Send gratuitous ARP to notify of link change */
> -		if (IN_DEV_ARP_NOTIFY(in_dev)) {
> -			struct in_ifaddr *ifa = in_dev->ifa_list;
> -
> -			if (ifa)
> -				arp_send(ARPOP_REQUEST, ETH_P_ARP,
> -					 ifa->ifa_address, dev,
> -					 ifa->ifa_address, NULL,
> -					 dev->dev_addr, NULL);
> -		}
> +		inetdev_send_gratuitous_arp(dev, in_dev);
>  		break;
>  	case NETDEV_DOWN:
>  		ip_mc_down(in_dev);
> 
>