Re: [Xen-devel] Stimulating domains to send gratuitous ARPs

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

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

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@xxxxxxxxxxxxxxxxxxxx>

---
 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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