ipv4: provide addr and netconf dump consistency info

This patch takes benefit of dev_addr_genid and dev_base_seq to check if a change
occurs during a netlink dump. If a change is detected, the flag NLM_F_DUMP_INTR
is set in the first message after the dump was interrupted.

Note that seq and prev_seq must be reset between each family in rtnl_dump_all()
because they are specific to each family.
Reported-by: Junwei Zhang <junwei.zhang@6wind.com>
Reported-by: Hongjun Li <hongjun.li@6wind.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/rtnetlink.c

@@ -1929,8 +1929,11 @@ static int rtnl_dump_all(struct sk_buff *skb, struct netlink_callback *cb)
 		if (rtnl_msg_handlers[idx] == NULL ||
 		    rtnl_msg_handlers[idx][type].dumpit == NULL)
 			continue;
-		if (idx > s_idx)
+		if (idx > s_idx) {
 			memset(&cb->args[0], 0, sizeof(cb->args));
+			cb->prev_seq = 0;
+			cb->seq = 0;
+		}
 		if (rtnl_msg_handlers[idx][type].dumpit(skb, cb))
 			break;
 	}

net/ipv4/devinet.c

@@ -1499,6 +1499,8 @@ static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
 		idx = 0;
 		head = &net->dev_index_head[h];
 		rcu_read_lock();
+		cb->seq = atomic_read(&net->ipv4.dev_addr_genid) ^
+			  net->dev_base_seq;
 		hlist_for_each_entry_rcu(dev, head, index_hlist) {
 			if (idx < s_idx)
 				goto cont;
@@ -1519,6 +1521,7 @@ static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
 					rcu_read_unlock();
 					goto done;
 				}
+				nl_dump_check_consistent(cb, nlmsg_hdr(skb));
 			}
 cont:
 			idx++;
@@ -1807,6 +1810,8 @@ static int inet_netconf_dump_devconf(struct sk_buff *skb,
 		idx = 0;
 		head = &net->dev_index_head[h];
 		rcu_read_lock();
+		cb->seq = atomic_read(&net->ipv4.dev_addr_genid) ^
+			  net->dev_base_seq;
 		hlist_for_each_entry_rcu(dev, head, index_hlist) {
 			if (idx < s_idx)
 				goto cont;
@@ -1824,6 +1829,7 @@ static int inet_netconf_dump_devconf(struct sk_buff *skb,
 				rcu_read_unlock();
 				goto done;
 			}
+			nl_dump_check_consistent(cb, nlmsg_hdr(skb));
 cont:
 			idx++;
 		}