[PATCH net-next v9 07/15] rtnl: add helper to check if group has listeners

[Jamal Hadi Salim <jhs@mojatatu.com>]

As of today, rtnl code creates a new skb and unconditionally fills and
broadcasts it to the relevant group. For most operations this is okay
and doesn't waste resources in general.

For P4TC, it's interesting to know if the TC group has any listeners
when adding/updating/deleting table entries as we can optimize for the
most likely case it contains none. This not only improves our processing
speed, it also reduces pressure on the system memory as we completely
avoid the broadcast skb allocation.

Co-developed-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Co-developed-by: Pedro Tammela <pctammela@mojatatu.com>
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
---
 include/linux/rtnetlink.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index 971055e66..487e45f8a 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -142,4 +142,11 @@ extern int ndo_dflt_bridge_getlink(struct sk_buff *skb, u32 pid, u32 seq,
 
 extern void rtnl_offload_xstats_notify(struct net_device *dev);
 
+static inline int rtnl_has_listeners(const struct net *net, u32 group)
+{
+	struct sock *rtnl = net->rtnl;
+
+	return netlink_has_listeners(rtnl, group);
+}
+
 #endif	/* __LINUX_RTNETLINK_H */
-- 
2.34.1