[NETLINK]: fib_lookup() via netlink

Below is a more generic patch to do fib_lookup via netlink. For others 
we should say that we discussed this as a way to verify route selection.
It's also possible there are others uses for this.

In short the fist half of struct fib_result_nl is filled in by caller 
and netlink call fills in the other half and returns it.

In case anyone is interested there is a corresponding user app to compare 
the full routing table this was used to test implementation of the LC-trie. 

Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netlink.h

@@ -14,6 +14,7 @@
 #define NETLINK_SELINUX		7	/* SELinux event notifications */
 #define NETLINK_ARPD		8
 #define NETLINK_AUDIT		9	/* auditing */
+#define NETLINK_FIB_LOOKUP	10	
 #define NETLINK_ROUTE6		11	/* af_inet6 route comm channel */
 #define NETLINK_IP6_FW		13
 #define NETLINK_DNRTMSG		14	/* DECnet routing messages */

include/net/ip_fib.h

@@ -109,6 +109,20 @@ struct fib_result {
 #endif
 };
 
+struct fib_result_nl {
+	u32		fl_addr;   /* To be looked up*/ 
+	u32		fl_fwmark; 
+	unsigned char	fl_tos;
+	unsigned char   fl_scope;
+	unsigned char   tb_id_in;
+
+	unsigned char   tb_id;      /* Results */
+	unsigned char	prefixlen;
+	unsigned char	nh_sel;
+	unsigned char	type;
+	unsigned char	scope;
+	int             err;      
+};
 
 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 

net/ipv4/fib_frontend.c

@@ -516,6 +516,60 @@ static void fib_del_ifaddr(struct in_ifaddr *ifa)
 #undef BRD1_OK
 }
 
+static void nl_fib_lookup(struct fib_result_nl *frn, struct fib_table *tb )
+{
+
+	struct fib_result       res;
+	struct flowi            fl = { .nl_u = { .ip4_u = { .daddr = frn->fl_addr, 
+							    .fwmark = frn->fl_fwmark,
+							    .tos = frn->fl_tos,
+							    .scope = frn->fl_scope } } };
+	if (tb) {
+		local_bh_disable();
+
+		frn->tb_id = tb->tb_id;
+		frn->err = tb->tb_lookup(tb, &fl, &res);
+
+		if (!frn->err) {
+			frn->prefixlen = res.prefixlen;
+			frn->nh_sel = res.nh_sel;
+			frn->type = res.type;
+			frn->scope = res.scope;
+		}
+		local_bh_enable();
+	}
+}
+
+static void nl_fib_input(struct sock *sk, int len)
+{
+	struct sk_buff *skb = NULL;
+        struct nlmsghdr *nlh = NULL;
+	struct fib_result_nl *frn;
+	int err;
+	u32 pid;     
+	struct fib_table *tb;
+
+	skb = skb_recv_datagram(sk, 0, 0, &err);
+	nlh = (struct nlmsghdr *)skb->data;
+
+	frn = (struct fib_result_nl *) NLMSG_DATA(nlh);
+	tb = fib_get_table(frn->tb_id_in);
+
+	nl_fib_lookup(frn, tb);
+
+	pid = nlh->nlmsg_pid;           /*pid of sending process */
+	NETLINK_CB(skb).groups = 0;     /* not in mcast group */
+	NETLINK_CB(skb).pid = 0;         /* from kernel */
+	NETLINK_CB(skb).dst_pid = pid;
+	NETLINK_CB(skb).dst_groups = 0;  /* unicast */
+	netlink_unicast(sk, skb, pid, MSG_DONTWAIT);
+}    
+
+static void nl_fib_lookup_init(void)
+{
+      netlink_kernel_create(NETLINK_FIB_LOOKUP, nl_fib_input);
+}
+
 static void fib_disable_ip(struct net_device *dev, int force)
 {
 	if (fib_sync_down(0, dev, force))
@@ -604,6 +658,7 @@ void __init ip_fib_init(void)
 
 	register_netdevice_notifier(&fib_netdev_notifier);
 	register_inetaddr_notifier(&fib_inetaddr_notifier);
+	nl_fib_lookup_init();
 }
 
 EXPORT_SYMBOL(inet_addr_type);