Re: Stimulating domains to send gratuitous ARPs

[Jeremy Fitzhardinge <jeremy@goop.org>]

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Ian Pratt wrote:
>> Whilst I might agree that from a purist point of view having netfront do
>> this is a violation of layering, it's already accepted in some other
>> upstream drivers 
>>     
>
> It's pretty clear it's not going to be accepted in the netfront that goes into upstream Linux, at least not without sedating various LKML folk first :)
>   

Stephen Hemminger posted a patch to add this capability generically so 
it wouldn't be a netfront-specific piece of behaviour.  I have not 
submitted it for upstream yet, mainly because nobody has 
confirmed/tested that it really does what we need.  But it looks 
reasonable, and it should be accepted once we confirm its correct.

    J

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Subject: ARP notify option

This adds another inet device option to enable gratuitous ARP
when device is brought up or address change. This is handy for
clusters or virtualization.

Tested on a normal device (not Xen).

Signed-off-by: Stephen Hemminger <shemminge@linux-foundation.org>

---
 Documentation/networking/ip-sysctl.txt |    6 ++++++
 include/linux/inetdevice.h             |    2 ++
 include/linux/sysctl.h                 |    1 +
 net/ipv4/devinet.c                     |   16 ++++++++++++++++
 4 files changed, 25 insertions(+)

===================================================================
--- net-2.6.22.orig/Documentation/networking/ip-sysctl.txt
+++ net-2.6.22/Documentation/networking/ip-sysctl.txt
@@ -732,6 +732,12 @@
 	The max value from conf/{all,interface}/arp_ignore is used
 	when ARP request is received on the {interface}
 
+arp_notify - BOOLEAN
+	Define mode for notification of address and device changes.
+	0 - (default): do nothing
+	1 - Generate gratuitous arp replies when device is brought up
+	    or hardware address changes.
+
 arp_accept - BOOLEAN
 	Define behavior when gratuitous arp replies are received:
 	0 - drop gratuitous arp frames
===================================================================
--- net-2.6.22.orig/include/linux/inetdevice.h
+++ net-2.6.22/include/linux/inetdevice.h
@@ -26,6 +26,7 @@
 	int	arp_announce;
 	int	arp_ignore;
 	int	arp_accept;
+	int	arp_notify;
 	int	medium_id;
 	int	no_xfrm;
 	int	no_policy;
@@ -84,6 +85,7 @@
 #define IN_DEV_ARPFILTER(in_dev)	(ipv4_devconf.arp_filter || (in_dev)->cnf.arp_filter)
 #define IN_DEV_ARP_ANNOUNCE(in_dev)	(max(ipv4_devconf.arp_announce, (in_dev)->cnf.arp_announce))
 #define IN_DEV_ARP_IGNORE(in_dev)	(max(ipv4_devconf.arp_ignore, (in_dev)->cnf.arp_ignore))
+#define IN_DEV_ARP_NOTIFY(in_dev)	(ipv4_devconf.arp_notify || (in_dev)->cnf.arp_notify)
 
 struct in_ifaddr
 {
===================================================================
--- net-2.6.22.orig/include/linux/sysctl.h
+++ net-2.6.22/include/linux/sysctl.h
@@ -495,6 +495,7 @@
 	NET_IPV4_CONF_ARP_IGNORE=19,
 	NET_IPV4_CONF_PROMOTE_SECONDARIES=20,
 	NET_IPV4_CONF_ARP_ACCEPT=21,
+	NET_IPV4_CONF_ARP_NOTIFY=22,
 	__NET_IPV4_CONF_MAX
 };
 
===================================================================
--- net-2.6.22.orig/net/ipv4/devinet.c
+++ net-2.6.22/net/ipv4/devinet.c
@@ -1089,6 +1089,14 @@
 			}
 		}
 		ip_mc_up(in_dev);
+		/* fall through */
+	case NETDEV_CHANGEADDR:
+		if (IN_DEV_ARP_NOTIFY(in_dev))
+			arp_send(ARPOP_REQUEST, ETH_P_ARP,
+				 in_dev->ifa_list->ifa_address,
+				 dev,
+				 in_dev->ifa_list->ifa_address,
+				 NULL, dev->dev_addr, NULL);
 		break;
 	case NETDEV_DOWN:
 		ip_mc_down(in_dev);
@@ -1495,6 +1503,14 @@
 			.proc_handler	= &proc_dointvec,
 		},
 		{
+			.ctl_name	= NET_IPV4_CONF_ARP_NOTIFY,
+			.procname	= "arp_notify",
+			.data		= &ipv4_devconf.arp_notify,
+			.maxlen		= sizeof(int),
+			.mode		= 0644,
+			.proc_handler	= &proc_dointvec,
+		},
+		{
 			.ctl_name	= NET_IPV4_CONF_NOXFRM,
 			.procname	= "disable_xfrm",
 			.data		= &ipv4_devconf.no_xfrm,

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