[IPV4]: Primary and secondary addresses

Add an option to make secondary IP addresses get promoted
when primary IP addresses are removed from the device.
It defaults to off to preserve existing behavior.

Signed-off-by: Harald Welte <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/inetdevice.h

···
 	int	no_xfrm;
 	int	no_policy;
 	int	force_igmp_version;
+	int	promote_secondaries;
 	void	*sysctl;
 };
 
···
 #define IN_DEV_SEC_REDIRECTS(in_dev)	(ipv4_devconf.secure_redirects || (in_dev)->cnf.secure_redirects)
 #define IN_DEV_IDTAG(in_dev)		((in_dev)->cnf.tag)
 #define IN_DEV_MEDIUM_ID(in_dev)	((in_dev)->cnf.medium_id)
+#define IN_DEV_PROMOTE_SECONDARIES(in_dev)	(ipv4_devconf.promote_secondaries || (in_dev)->cnf.promote_secondaries)
 
 #define IN_DEV_RX_REDIRECTS(in_dev) \
 	((IN_DEV_FORWARD(in_dev) && \

include/linux/sysctl.h

···
 	NET_IPV4_CONF_FORCE_IGMP_VERSION=17,
 	NET_IPV4_CONF_ARP_ANNOUNCE=18,
 	NET_IPV4_CONF_ARP_IGNORE=19,
+	NET_IPV4_CONF_PROMOTE_SECONDARIES=20,
 	__NET_IPV4_CONF_MAX
 };
 

net/ipv4/devinet.c

···
 static void inet_del_ifa(struct in_device *in_dev, struct in_ifaddr **ifap,
 			 int destroy)
 {
+	struct in_ifaddr *promote = NULL;
 	struct in_ifaddr *ifa1 = *ifap;
 
 	ASSERT_RTNL();
 
-	/* 1. Deleting primary ifaddr forces deletion all secondaries */
+	/* 1. Deleting primary ifaddr forces deletion all secondaries 
+	 * unless alias promotion is set
+	 **/
 
 	if (!(ifa1->ifa_flags & IFA_F_SECONDARY)) {
 		struct in_ifaddr *ifa;
···
 				continue;
 			}
 
-			*ifap1 = ifa->ifa_next;
+			if (!IN_DEV_PROMOTE_SECONDARIES(in_dev)) {
+				*ifap1 = ifa->ifa_next;
 
-			rtmsg_ifa(RTM_DELADDR, ifa);
-			notifier_call_chain(&inetaddr_chain, NETDEV_DOWN, ifa);
-			inet_free_ifa(ifa);
+				rtmsg_ifa(RTM_DELADDR, ifa);
+				notifier_call_chain(&inetaddr_chain, NETDEV_DOWN, ifa);
+				inet_free_ifa(ifa);
+			} else {
+				promote = ifa;
+				break;
+			}
 		}
 	}
 
···
 
 		if (!in_dev->ifa_list)
 			inetdev_destroy(in_dev);
+	}
+
+	if (promote && IN_DEV_PROMOTE_SECONDARIES(in_dev)) {
+		/* not sure if we should send a delete notify first? */
+		promote->ifa_flags &= ~IFA_F_SECONDARY;
+		rtmsg_ifa(RTM_NEWADDR, promote);
+		notifier_call_chain(&inetaddr_chain, NETDEV_UP, promote);
 	}
 }
 
···
 			.ctl_name	= NET_IPV4_CONF_FORCE_IGMP_VERSION,
 			.procname	= "force_igmp_version",
 			.data		= &ipv4_devconf.force_igmp_version,
+			.maxlen		= sizeof(int),
+			.mode		= 0644,
+			.proc_handler	= &ipv4_doint_and_flush,
+			.strategy	= &ipv4_doint_and_flush_strategy,
+		},
+		{
+			.ctl_name	= NET_IPV4_CONF_PROMOTE_SECONDARIES,
+			.procname	= "promote_secondaries",
+			.data		= &ipv4_devconf.promote_secondaries,
 			.maxlen		= sizeof(int),
 			.mode		= 0644,
 			.proc_handler	= &ipv4_doint_and_flush,