netfilter: nf_tables: wrap tracing with a static key

Only needed when meta nftrace rule(s) were added.
The assumption is that no such rules are active, so the call to
nft_trace_init is "never" needed.

When nftrace rules are active, we always call the nft_trace_* functions,
but will only send netlink messages when all of the following are true:

 - traceinfo structure was initialised
 - skb->nf_trace == 1
 - at least one subscriber to trace group.

Adding an extra conditional
(static_branch ... && skb->nf_trace)
	nft_trace_init( ..)

Is possible but results in a larger nft_do_chain footprint.

Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/net/netfilter/nf_tables_trace.c b/net/netfilter/nf_tables_trace.c
index 36fd7ad6729a..e9e959f65d91 100644
--- a/net/netfilter/nf_tables_trace.c
+++ b/net/netfilter/nf_tables_trace.c
@@ -8,6 +8,7 @@
  */
 
 #include <linux/module.h>
+#include <linux/static_key.h>
 #include <linux/hash.h>
 #include <linux/jhash.h>
 #include <linux/if_vlan.h>
@@ -24,6 +25,9 @@
 #define NFT_TRACETYPE_NETWORK_HSIZE	40
 #define NFT_TRACETYPE_TRANSPORT_HSIZE	20
 
+DEFINE_STATIC_KEY_FALSE(nft_trace_enabled);
+EXPORT_SYMBOL_GPL(nft_trace_enabled);
+
 static int trace_fill_id(struct sk_buff *nlskb, struct sk_buff *skb)
 {
 	__be32 id;