Make it possible to build IP stack as a module

This is not pretty, but it works.

net/ipv4/Makefile

@@ -2,7 +2,9 @@
 # Makefile for the Linux TCP/IP (INET) layer.
 #
 
-obj-y     := route.o inetpeer.o protocol.o \
+obj-$(CONFIG_INET) += ipv4.o
+
+ipv4-y :=    route.o inetpeer.o protocol.o \
 	     ip_input.o ip_fragment.o ip_forward.o ip_options.o \
 	     ip_output.o ip_sockglue.o inet_hashtables.o \
 	     inet_timewait_sock.o inet_connection_sock.o \
@@ -13,17 +15,21 @@ obj-y     := route.o inetpeer.o protocol.o \
 	     fib_frontend.o fib_semantics.o fib_trie.o \
 	     inet_fragment.o ping.o
 
+ifeq ($(CONFIG_INET),m)
+ipv4-y += module_lib.o
+endif
+
 obj-$(CONFIG_NET_IP_TUNNEL) += ip_tunnel.o
-obj-$(CONFIG_SYSCTL) += sysctl_net_ipv4.o
-obj-$(CONFIG_SYSFS) += sysfs_net_ipv4.o
-obj-$(CONFIG_PROC_FS) += proc.o
-obj-$(CONFIG_IP_MULTIPLE_TABLES) += fib_rules.o
-obj-$(CONFIG_IP_MROUTE) += ipmr.o
+ipv4-$(CONFIG_SYSCTL) += sysctl_net_ipv4.o
+ipv4-$(CONFIG_SYSFS) += sysfs_net_ipv4.o
+ipv4-$(CONFIG_PROC_FS) += proc.o
+ipv4-$(CONFIG_IP_MULTIPLE_TABLES) += fib_rules.o
+ipv4-$(CONFIG_IP_MROUTE) += ipmr.o
 obj-$(CONFIG_NET_IPIP) += ipip.o
 obj-$(CONFIG_NET_IPGRE_DEMUX) += gre.o
 obj-$(CONFIG_NET_IPGRE) += ip_gre.o
 obj-$(CONFIG_NET_IPVTI) += ip_vti.o
-obj-$(CONFIG_SYN_COOKIES) += syncookies.o
+ipv4-$(CONFIG_SYN_COOKIES) += syncookies.o
 obj-$(CONFIG_INET_AH) += ah4.o
 obj-$(CONFIG_INET_ESP) += esp4.o
 obj-$(CONFIG_INET_IPCOMP) += ipcomp.o
@@ -33,8 +39,8 @@ obj-$(CONFIG_INET_LRO) += inet_lro.o
 obj-$(CONFIG_INET_TUNNEL) += tunnel4.o
 obj-$(CONFIG_INET_XFRM_MODE_TRANSPORT) += xfrm4_mode_transport.o
 obj-$(CONFIG_INET_XFRM_MODE_TUNNEL) += xfrm4_mode_tunnel.o
-obj-$(CONFIG_IP_PNP) += ipconfig.o
-obj-$(CONFIG_NETFILTER)	+= netfilter.o netfilter/
+ipv4-$(CONFIG_IP_PNP) += ipconfig.o
+ipv4-$(CONFIG_NETFILTER)	+= netfilter.o netfilter/
 obj-$(CONFIG_INET_DIAG) += inet_diag.o 
 obj-$(CONFIG_INET_TCP_DIAG) += tcp_diag.o
 obj-$(CONFIG_INET_UDP_DIAG) += udp_diag.o
@@ -51,8 +57,8 @@ obj-$(CONFIG_TCP_CONG_SCALABLE) += tcp_scalable.o
 obj-$(CONFIG_TCP_CONG_LP) += tcp_lp.o
 obj-$(CONFIG_TCP_CONG_YEAH) += tcp_yeah.o
 obj-$(CONFIG_TCP_CONG_ILLINOIS) += tcp_illinois.o
-obj-$(CONFIG_MEMCG_KMEM) += tcp_memcontrol.o
-obj-$(CONFIG_NETLABEL) += cipso_ipv4.o
+ipv4-$(CONFIG_MEMCG_KMEM) += tcp_memcontrol.o
+ipv4-$(CONFIG_NETLABEL) += cipso_ipv4.o
 
-obj-$(CONFIG_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \
+ipv4-$(CONFIG_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \
 		      xfrm4_output.o

net/ipv4/af_inet.c

@@ -119,6 +119,10 @@
 #include <linux/mroute.h>
 #endif
 
+MODULE_AUTHOR("Cast of dozens");
+MODULE_DESCRIPTION("IPv4 protocol stack for Linux");
+MODULE_LICENSE("GPL");
+
 #ifdef CONFIG_ANDROID_PARANOID_NETWORK
 #include <linux/android_aid.h>
 
@@ -1702,13 +1706,23 @@ static int __init ipv4_offload_init(void)
 	return 0;
 }
 
+#ifndef CONFIG_INET_MODULE
 fs_initcall(ipv4_offload_init);
+#endif
 
 static struct packet_type ip_packet_type __read_mostly = {
 	.type = cpu_to_be16(ETH_P_IP),
 	.func = ip_rcv,
 };
 
+#ifdef CONFIG_INET_MODULE
+int tcp_congestion_init(void);
+int tcp_fastopen_init(void);
+int sysctl_ipv4_init(void);
+int sysfs_ipv4_init(void);
+int tcp_memcontrol_init(void);
+#endif
+
 static int __init inet_init(void)
 {
 	struct inet_protosw *q;
@@ -1717,6 +1731,12 @@ static int __init inet_init(void)
 
 	BUILD_BUG_ON(sizeof(struct inet_skb_parm) > FIELD_SIZEOF(struct sk_buff, cb));
 
+#ifdef CONFIG_INET_MODULE
+	tcp_congestion_init();
+	tcp_fastopen_init();
+	ipv4_offload_init();
+#endif
+
 	sysctl_local_reserved_ports = kzalloc(65536 / 8, GFP_KERNEL);
 	if (!sysctl_local_reserved_ports)
 		goto out;
@@ -1823,6 +1843,21 @@ static int __init inet_init(void)
 
 	dev_add_pack(&ip_packet_type);
 
+#ifdef CONFIG_INET_MODULE
+#ifdef CONFIG_SYSCTL
+	sysctl_ipv4_init();
+#endif
+#ifdef CONFIG_SYSFS
+	sysfs_ipv4_init();
+#endif
+#ifdef CONFIG_MEMCG_KMEM
+	tcp_memcontrol_init();
+#endif
+
+	/* TODO: Implement unload logic */
+	try_module_get(THIS_MODULE);
+#endif
+
 	rc = 0;
 out:
 	return rc;

net/ipv4/inet_hashtables.c

@@ -582,6 +582,7 @@ out:
 		return ret;
 	}
 }
+EXPORT_SYMBOL(__inet_hash_connect);
 
 /*
  * Bind a port for a connect operation and hash it.

net/ipv4/inet_timewait_sock.c

@@ -65,6 +65,7 @@ int inet_twsk_bind_unhash(struct inet_timewait_sock *tw,
 	 */
 	return 1;
 }
+EXPORT_SYMBOL(inet_twsk_unhash);
 
 /* Must be called with locally disabled BHs. */
 static void __inet_twsk_kill(struct inet_timewait_sock *tw,

net/ipv4/proc.c

@@ -59,7 +59,9 @@ static int sockstat_seq_show(struct seq_file *seq, void *v)
 	sockets = proto_sockets_allocated_sum_positive(&tcp_prot);
 	local_bh_enable();
 
+#ifndef CONFIG_INET_MODULE
 	socket_seq_show(seq);
+#endif
 	seq_printf(seq, "TCP: inuse %d orphan %d tw %d alloc %d mem %ld\n",
 		   sock_prot_inuse_get(net, &tcp_prot), orphans,
 		   tcp_death_row.tw_count, sockets,

net/ipv4/sysctl_net_ipv4.c

@@ -958,7 +958,11 @@ static __net_initdata struct pernet_operations ipv4_sysctl_ops = {
 	.exit = ipv4_sysctl_exit_net,
 };
 
+#ifdef CONFIG_INET_MODULE
+int sysctl_ipv4_init(void)
+#else
 static __init int sysctl_ipv4_init(void)
+#endif
 {
 	struct ctl_table_header *hdr;
 	struct ctl_table *i;
@@ -984,4 +988,6 @@ static __init int sysctl_ipv4_init(void)
 	return 0;
 }
 
+#ifndef CONFIG_INET_MODULE
 __initcall(sysctl_ipv4_init);
+#endif

net/ipv4/sysfs_net_ipv4.c

@@ -67,7 +67,11 @@ static struct attribute_group ipv4_attr_group = {
 	.attrs = ipv4_attrs,
 };
 
+#ifdef CONFIG_INET_MODULE
+int sysfs_ipv4_init(void)
+#else
 static __init int sysfs_ipv4_init(void)
+#endif
 {
 	struct kobject *ipv4_kobject;
 	int ret;
@@ -85,4 +89,6 @@ static __init int sysfs_ipv4_init(void)
 	return 0;
 }
 
+#ifndef CONFIG_INET_MODULE
 subsys_initcall(sysfs_ipv4_init);
+#endif

net/ipv4/tcp.c

@@ -1245,8 +1245,10 @@ out:
 out_nopush:
 	release_sock(sk);
 
+#ifndef CONFIG_INET_MODULE
 	if (copied + copied_syn)
 		uid_stat_tcp_snd(current_uid(), copied + copied_syn);
+#endif
 	return copied + copied_syn;
 
 do_fault:
@@ -1551,7 +1553,9 @@ int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
 	if (copied > 0) {
 		tcp_recv_skb(sk, seq, &offset);
 		tcp_cleanup_rbuf(sk, copied);
+#ifndef CONFIG_INET_MODULE
 		uid_stat_tcp_rcv(current_uid(), copied);
+#endif
 	}
 	return copied;
 }
@@ -1957,8 +1961,10 @@ skip_copy:
 
 	release_sock(sk);
 
+#ifndef CONFIG_INET_MODULE
 	if (copied > 0)
 		uid_stat_tcp_rcv(current_uid(), copied);
+#endif
 	return copied;
 
 out:
@@ -1967,8 +1973,10 @@ out:
 
 recv_urg:
 	err = tcp_recv_urg(sk, msg, len, flags);
+#ifndef CONFIG_INET_MODULE
 	if (err > 0)
 		uid_stat_tcp_rcv(current_uid(), err);
+#endif
 	goto out;
 
 recv_sndq:

net/ipv4/tcp_cong.c

@@ -137,12 +137,19 @@ int tcp_set_default_congestion_control(const char *name)
 	return ret;
 }
 
+#ifdef CONFIG_INET_MODULE
+int tcp_congestion_init(void)
+#else
 /* Set default value from kernel configuration at bootup */
 static int __init tcp_congestion_default(void)
+#endif
 {
 	return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
 }
+
+#ifndef CONFIG_INET_MODULE
 late_initcall(tcp_congestion_default);
+#endif
 
 
 /* Build string with list of available congestion control values */

net/ipv4/tcp_fastopen.c

@@ -80,7 +80,11 @@ void tcp_fastopen_cookie_gen(__be32 addr, struct tcp_fastopen_cookie *foc)
 	rcu_read_unlock();
 }
 
+#ifdef CONFIG_INET_MODULE
+int tcp_fastopen_init(void)
+#else
 static int __init tcp_fastopen_init(void)
+#endif
 {
 	__u8 key[TCP_FASTOPEN_KEY_LENGTH];
 
@@ -89,4 +93,6 @@ static int __init tcp_fastopen_init(void)
 	return 0;
 }
 
+#ifndef CONFIG_INET_MODULE
 late_initcall(tcp_fastopen_init);
+#endif

net/ipv4/tcp_ipv4.c

@@ -2891,7 +2891,7 @@ struct proto tcp_prot = {
 	.compat_setsockopt	= compat_tcp_setsockopt,
 	.compat_getsockopt	= compat_tcp_getsockopt,
 #endif
-#ifdef CONFIG_MEMCG_KMEM
+#if defined(CONFIG_MEMCG_KMEM) && !defined(CONFIG_INET_MODULE)
 	.init_cgroup		= tcp_init_cgroup,
 	.destroy_cgroup		= tcp_destroy_cgroup,
 	.proto_cgroup		= tcp_proto_cgroup,

net/ipv4/tcp_memcontrol.c

@@ -280,9 +280,15 @@ static struct cftype tcp_files[] = {
 	{ }	/* terminate */
 };
 
+#ifdef CONFIG_INET_MODULE
+int tcp_memcontrol_init(void)
+#else
 static int __init tcp_memcontrol_init(void)
+#endif
 {
 	WARN_ON(cgroup_add_cftypes(&mem_cgroup_subsys, tcp_files));
 	return 0;
 }
+#ifndef CONFIG_INET_MODULE
 __initcall(tcp_memcontrol_init);
+#endif

net/ipv4/udp.c

@@ -1413,7 +1413,9 @@ static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 					 is_udplite);
 		UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
 		kfree_skb(skb);
+#ifndef CONFIG_INET_MODULE
 		trace_udp_fail_queue_rcv_skb(rc, sk);
+#endif
 		return -1;
 	}