[NETFILTER]: ctnetlink: avoid unneccessary event message generation

Avoid unneccessary event message generation by checking for netlink
listeners before building a message.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 15 insertions, 6 deletions

diff --git a/include/linux/netfilter/nfnetlink.h b/include/linux/netfilter/nfnetlink.h
index 934a2479f160..9f5b12cf489b 100644
--- a/include/linux/netfilter/nfnetlink.h
+++ b/include/linux/netfilter/nfnetlink.h
@@ -164,6 +164,7 @@ extern void nfattr_parse(struct nfattr *tb[], int maxattr,
         __res;                                                          \
 })
 
+extern int nfnetlink_has_listeners(unsigned int group);
 extern int nfnetlink_send(struct sk_buff *skb, u32 pid, unsigned group, 
                           int echo);
 extern int nfnetlink_unicast(struct sk_buff *skb, u_int32_t pid, int flags);
diff --git a/net/ipv4/netfilter/ip_conntrack_netlink.c b/net/ipv4/netfilter/ip_conntrack_netlink.c
index e0b5926c76f9..5ce2e3fc2c7f 100644
--- a/net/ipv4/netfilter/ip_conntrack_netlink.c
+++ b/net/ipv4/netfilter/ip_conntrack_netlink.c
@@ -327,9 +327,10 @@ static int ctnetlink_conntrack_event(struct notifier_block *this,
                 group = NFNLGRP_CONNTRACK_UPDATE;
         } else 
                 return NOTIFY_DONE;
-        
-  /* FIXME: Check if there are any listeners before, don't hurt performance */
-        
+
+        if (!nfnetlink_has_listeners(group))
+                return NOTIFY_DONE;
+
         skb = alloc_skb(NLMSG_GOODSIZE, GFP_ATOMIC);
         if (!skb)
                 return NOTIFY_DONE;
diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index aef3cb41131f..5eadf009bb15 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -338,9 +338,10 @@ static int ctnetlink_conntrack_event(struct notifier_block *this,
                 group = NFNLGRP_CONNTRACK_UPDATE;
         } else
                 return NOTIFY_DONE;
-        
-  /* FIXME: Check if there are any listeners before, don't hurt performance */
-        
+
+        if (!nfnetlink_has_listeners(group))
+                return NOTIFY_DONE;
+
         skb = alloc_skb(NLMSG_GOODSIZE, GFP_ATOMIC);
         if (!skb)
                 return NOTIFY_DONE;
diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
index f6063e8f0050..b88e82a1a987 100644
--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -191,6 +191,12 @@ nfnetlink_check_attributes(struct nfnetlink_subsystem *subsys,
         return 0;
 }
 
+int nfnetlink_has_listeners(unsigned int group)
+{
+        return netlink_has_listeners(nfnl, group);
+}
+EXPORT_SYMBOL_GPL(nfnetlink_has_listeners);
+
 int nfnetlink_send(struct sk_buff *skb, u32 pid, unsigned group, int echo)
 {
         gfp_t allocation = in_interrupt() ? GFP_ATOMIC : GFP_KERNEL;