[RTNETLINK]: Add rtnetlink notification interface

Adds rtnl_notify() to send rtnetlink notification messages and
rtnl_set_sk_err() to report notification errors as socket
errors in order to indicate the need of a resync due to loss
of events.

nlmsg_report() is added to properly document the meaning of
NLM_F_ECHO.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/rtnetlink.h

@@ -585,6 +585,9 @@ struct rtnetlink_link
 extern struct rtnetlink_link * rtnetlink_links[NPROTO];
 extern int rtnetlink_send(struct sk_buff *skb, u32 pid, u32 group, int echo);
 extern int rtnl_unicast(struct sk_buff *skb, u32 pid);
+extern int rtnl_notify(struct sk_buff *skb, u32 pid, u32 group,
+		       struct nlmsghdr *nlh, gfp_t flags);
+extern void rtnl_set_sk_err(u32 group, int error);
 extern int rtnetlink_put_metrics(struct sk_buff *skb, u32 *metrics);
 
 extern void __rta_fill(struct sk_buff *skb, int attrtype, int attrlen, const void *data);

include/net/netlink.h

@@ -65,6 +65,9 @@
  *   nlmsg_validate()			validate netlink message incl. attrs
  *   nlmsg_for_each_attr()		loop over all attributes
  *
+ * Misc:
+ *   nlmsg_report()			report back to application?
+ *
  * ------------------------------------------------------------------------
  *                          Attributes Interface
  * ------------------------------------------------------------------------
@@ -194,6 +197,9 @@ extern void		netlink_run_queue(struct sock *sk, unsigned int *qlen,
 						    struct nlmsghdr *, int *));
 extern void		netlink_queue_skip(struct nlmsghdr *nlh,
 					   struct sk_buff *skb);
+extern int		nlmsg_notify(struct sock *sk, struct sk_buff *skb,
+				     u32 pid, unsigned int group, int report,
+				     gfp_t flags);
 
 extern int		nla_validate(struct nlattr *head, int len, int maxtype,
 				     struct nla_policy *policy);
@@ -375,6 +381,17 @@ static inline int nlmsg_validate(struct nlmsghdr *nlh, int hdrlen, int maxtype,
 			    nlmsg_attrlen(nlh, hdrlen), maxtype, policy);
 }
 
+/**
+ * nlmsg_report - need to report back to application?
+ * @nlh: netlink message header
+ *
+ * Returns 1 if a report back to the application is requested.
+ */
+static inline int nlmsg_report(struct nlmsghdr *nlh)
+{
+	return !!(nlh->nlmsg_flags & NLM_F_ECHO);
+}
+
 /**
  * nlmsg_for_each_attr - iterate over a stream of attributes
  * @pos: loop counter, set to current attribute

net/core/rtnetlink.c

@@ -171,6 +171,22 @@ int rtnl_unicast(struct sk_buff *skb, u32 pid)
 	return nlmsg_unicast(rtnl, skb, pid);
 }
 
+int rtnl_notify(struct sk_buff *skb, u32 pid, u32 group,
+		struct nlmsghdr *nlh, gfp_t flags)
+{
+	int report = 0;
+
+	if (nlh)
+		report = nlmsg_report(nlh);
+
+	return nlmsg_notify(rtnl, skb, pid, group, report, flags);
+}
+
+void rtnl_set_sk_err(u32 group, int error)
+{
+	netlink_set_err(rtnl, 0, group, error);
+}
+
 int rtnetlink_put_metrics(struct sk_buff *skb, u32 *metrics)
 {
 	struct rtattr *mx = (struct rtattr*)skb->tail;
@@ -829,3 +845,5 @@ EXPORT_SYMBOL(rtnl_lock);
 EXPORT_SYMBOL(rtnl_trylock);
 EXPORT_SYMBOL(rtnl_unlock);
 EXPORT_SYMBOL(rtnl_unicast);
+EXPORT_SYMBOL(rtnl_notify);
+EXPORT_SYMBOL(rtnl_set_sk_err);