netfilter: conntrack: make nf_conntrack_id callable without a module dependency

While nf_conntrack_id() doesn't need any functionaliy from conntrack, it
does reside in nf_conntrack_core.c -- callers add a module
dependency on conntrack.

Followup patch will need to compute the conntrack id from nf_tables_trace.c
to include it in nf_trace messages emitted to userspace via netlink.

I don't want to introduce a module dependency between nf_tables and
conntrack for this.

Since trace is slowpath, the added indirection is ok.

One alternative is to move nf_conntrack_id to the netfilter/core.c,
but I don't see a compelling reason so far.

Signed-off-by: Florian Westphal <[email protected]>
Signed-off-by: Pablo Neira Ayuso <[email protected]>

Author: Florian Westphal

include/linux/netfilter.h

@@ -470,6 +470,7 @@ struct nf_ct_hook {
 	void (*attach)(struct sk_buff *nskb, const struct sk_buff *skb);
 	void (*set_closing)(struct nf_conntrack *nfct);
 	int (*confirm)(struct sk_buff *skb);
+	u32 (*get_id)(const struct nf_conntrack *nfct);
 };
 extern const struct nf_ct_hook __rcu *nf_ct_hook;
 

net/netfilter/nf_conntrack_core.c

@@ -505,6 +505,11 @@ u32 nf_ct_get_id(const struct nf_conn *ct)
 }
 EXPORT_SYMBOL_GPL(nf_ct_get_id);
 
+static u32 nf_conntrack_get_id(const struct nf_conntrack *nfct)
+{
+	return nf_ct_get_id(nf_ct_to_nf_conn(nfct));
+}
+
 static void
 clean_from_lists(struct nf_conn *ct)
 {
@@ -2710,6 +2715,7 @@ static const struct nf_ct_hook nf_conntrack_hook = {
 	.attach		= nf_conntrack_attach,
 	.set_closing	= nf_conntrack_set_closing,
 	.confirm	= __nf_conntrack_confirm,
+	.get_id		= nf_conntrack_get_id,
 };
 
 void nf_conntrack_init_end(void)