https://lkml.org/lkml/2014/5/5/674
Andi Kleen <ak@linux.intel.com>

diff -Nur linux-3.14.4.orig/include/linux/tcp.h linux-3.14.4/include/linux/tcp.h
--- linux-3.14.4.orig/include/linux/tcp.h	2014-05-13 13:33:14.000000000 +0200
+++ linux-3.14.4/include/linux/tcp.h	2014-05-29 21:30:07.000000000 +0200
@@ -359,6 +359,9 @@
 	return (struct tcp_timewait_sock *)sk;
 }
 
+extern void tcp_sock_destruct(struct sock *sk);
+
+#ifdef CONFIG_TCP_FASTOPEN
 static inline bool tcp_passive_fastopen(const struct sock *sk)
 {
 	return (sk->sk_state == TCP_SYN_RECV &&
@@ -370,8 +373,6 @@
 	return foc->len != -1;
 }
 
-extern void tcp_sock_destruct(struct sock *sk);
-
 static inline int fastopen_init_queue(struct sock *sk, int backlog)
 {
 	struct request_sock_queue *queue =
@@ -391,4 +392,13 @@
 	return 0;
 }
 
+#else
+static inline bool tcp_passive_fastopen(const struct sock *sk)
+{ return false; }
+static inline bool fastopen_cookie_present(struct tcp_fastopen_cookie *foc)
+{ return false; }
+static inline int fastopen_init_queue(struct sock *sk, int backlog)
+{ return 0; }
+#endif
+
 #endif	/* _LINUX_TCP_H */
diff -Nur linux-3.14.4.orig/include/net/request_sock.h linux-3.14.4/include/net/request_sock.h
--- linux-3.14.4.orig/include/net/request_sock.h	2014-05-13 13:33:14.000000000 +0200
+++ linux-3.14.4/include/net/request_sock.h	2014-05-29 21:30:07.000000000 +0200
@@ -168,8 +168,13 @@
 
 void __reqsk_queue_destroy(struct request_sock_queue *queue);
 void reqsk_queue_destroy(struct request_sock_queue *queue);
+#ifdef CONFIG_TCP_FASTOPEN
 void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
 			   bool reset);
+#else
+static inline void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
+			   bool reset) {}
+#endif
 
 static inline struct request_sock *
 	reqsk_queue_yank_acceptq(struct request_sock_queue *queue)
diff -Nur linux-3.14.4.orig/include/net/tcp.h linux-3.14.4/include/net/tcp.h
--- linux-3.14.4.orig/include/net/tcp.h	2014-05-13 13:33:14.000000000 +0200
+++ linux-3.14.4/include/net/tcp.h	2014-05-29 21:30:07.000000000 +0200
@@ -250,7 +250,11 @@
 extern int sysctl_tcp_retries2;
 extern int sysctl_tcp_orphan_retries;
 extern int sysctl_tcp_syncookies;
+#ifdef CONFIG_TCP_FASTOPEN
 extern int sysctl_tcp_fastopen;
+#else
+#define sysctl_tcp_fastopen 0
+#endif
 extern int sysctl_tcp_retrans_collapse;
 extern int sysctl_tcp_stdurg;
 extern int sysctl_tcp_rfc1337;
@@ -1307,7 +1311,12 @@
 	size_t				size;
 	int				copied;	/* queued in tcp_connect() */
 };
+
+#ifdef CONFIG_TCP_FASTOPEN
 void tcp_free_fastopen_req(struct tcp_sock *tp);
+#else
+static inline void tcp_free_fastopen_req(struct tcp_sock *tp) {}
+#endif
 
 extern struct tcp_fastopen_context __rcu *tcp_fastopen_ctx;
 int tcp_fastopen_reset_cipher(void *key, unsigned int len);
diff -Nur linux-3.14.4.orig/net/Kconfig linux-3.14.4/net/Kconfig
--- linux-3.14.4.orig/net/Kconfig	2014-05-13 13:33:14.000000000 +0200
+++ linux-3.14.4/net/Kconfig	2014-05-29 21:30:07.000000000 +0200
@@ -53,8 +53,8 @@
 
 config INET
 	bool "TCP/IP networking"
-	select CRYPTO
-	select CRYPTO_AES
+	select CRYPTO if TCP_FASTOPEN
+	select CRYPTO_AES if TCP_FASTOPEN
 	---help---
 	  These are the protocols used on the Internet and on most local
 	  Ethernets. It is highly recommended to say Y here (this will enlarge
diff -Nur linux-3.14.4.orig/net/core/request_sock.c linux-3.14.4/net/core/request_sock.c
--- linux-3.14.4.orig/net/core/request_sock.c	2014-05-13 13:33:14.000000000 +0200
+++ linux-3.14.4/net/core/request_sock.c	2014-05-29 21:30:07.000000000 +0200
@@ -131,6 +131,7 @@
 		kfree(lopt);
 }
 
+#ifdef CONFIG_TCP_FASTOPEN
 /*
  * This function is called to set a Fast Open socket's "fastopen_rsk" field
  * to NULL when a TFO socket no longer needs to access the request_sock.
@@ -223,3 +224,4 @@
 	sock_put(lsk);
 	return;
 }
+#endif
diff -Nur linux-3.14.4.orig/net/ipv4/Kconfig linux-3.14.4/net/ipv4/Kconfig
--- linux-3.14.4.orig/net/ipv4/Kconfig	2014-05-13 13:33:14.000000000 +0200
+++ linux-3.14.4/net/ipv4/Kconfig	2014-05-29 21:30:07.000000000 +0200
@@ -307,6 +307,10 @@
 	  the notion of a secure tunnel for IPSEC and then use routing protocol
 	  on top.
 
+config TCP_FASTOPEN
+	bool "Enable TCP fastopen"
+	default n
+
 config INET_AH
 	tristate "IP: AH transformation"
 	select XFRM_ALGO
diff -Nur linux-3.14.4.orig/net/ipv4/Makefile linux-3.14.4/net/ipv4/Makefile
--- linux-3.14.4.orig/net/ipv4/Makefile	2014-05-13 13:33:14.000000000 +0200
+++ linux-3.14.4/net/ipv4/Makefile	2014-05-29 21:30:51.000000000 +0200
@@ -7,7 +7,7 @@
 	     ip_output.o ip_sockglue.o inet_hashtables.o \
 	     inet_timewait_sock.o inet_connection_sock.o \
 	     tcp.o tcp_input.o tcp_output.o tcp_timer.o tcp_ipv4.o \
-	     tcp_minisocks.o tcp_cong.o tcp_metrics.o tcp_fastopen.o \
+	     tcp_minisocks.o tcp_cong.o tcp_metrics.o \
 	     tcp_offload.o datagram.o raw.o udp.o udplite.o \
 	     udp_offload.o arp.o icmp.o devinet.o af_inet.o igmp.o \
 	     fib_frontend.o fib_semantics.o fib_trie.o \
@@ -51,6 +51,7 @@
 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_TCP_FASTOPEN) += tcp_fastopen.o
 obj-$(CONFIG_MEMCG_KMEM) += tcp_memcontrol.o
 obj-$(CONFIG_NETLABEL) += cipso_ipv4.o
 
diff -Nur linux-3.14.4.orig/net/ipv4/sysctl_net_ipv4.c linux-3.14.4/net/ipv4/sysctl_net_ipv4.c
--- linux-3.14.4.orig/net/ipv4/sysctl_net_ipv4.c	2014-05-13 13:33:14.000000000 +0200
+++ linux-3.14.4/net/ipv4/sysctl_net_ipv4.c	2014-05-29 21:30:07.000000000 +0200
@@ -200,6 +200,7 @@
 	return ret;
 }
 
+#ifdef CONFIG_TCP_FASTOPEN
 static int proc_tcp_fastopen_key(struct ctl_table *ctl, int write,
 				 void __user *buffer, size_t *lenp,
 				 loff_t *ppos)
@@ -246,6 +247,7 @@
 	kfree(tbl.data);
 	return ret;
 }
+#endif
 
 static struct ctl_table ipv4_table[] = {
 	{
@@ -388,6 +390,7 @@
 		.proc_handler	= proc_dointvec
 	},
 #endif
+#ifdef CONFIG_TCP_FASTOPEN
 	{
 		.procname	= "tcp_fastopen",
 		.data		= &sysctl_tcp_fastopen,
@@ -401,6 +404,7 @@
 		.maxlen		= ((TCP_FASTOPEN_KEY_LENGTH * 2) + 10),
 		.proc_handler	= proc_tcp_fastopen_key,
 	},
+#endif
 	{
 		.procname	= "tcp_tw_recycle",
 		.data		= &tcp_death_row.sysctl_tw_recycle,
diff -Nur linux-3.14.4.orig/net/ipv4/tcp.c linux-3.14.4/net/ipv4/tcp.c
--- linux-3.14.4.orig/net/ipv4/tcp.c	2014-05-13 13:33:14.000000000 +0200
+++ linux-3.14.4/net/ipv4/tcp.c	2014-05-29 21:30:07.000000000 +0200
@@ -1036,6 +1036,7 @@
 	return tmp;
 }
 
+#ifdef CONFIG_TCP_FASTOPEN
 void tcp_free_fastopen_req(struct tcp_sock *tp)
 {
 	if (tp->fastopen_req != NULL) {
@@ -1069,6 +1070,7 @@
 	tcp_free_fastopen_req(tp);
 	return err;
 }
+#endif
 
 int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 		size_t size)
@@ -1084,6 +1086,7 @@
 	lock_sock(sk);
 
 	flags = msg->msg_flags;
+#ifdef CONFIG_TCP_FASTOPEN
 	if (flags & MSG_FASTOPEN) {
 		err = tcp_sendmsg_fastopen(sk, msg, &copied_syn, size);
 		if (err == -EINPROGRESS && copied_syn > 0)
@@ -1092,6 +1095,7 @@
 			goto out_err;
 		offset = copied_syn;
 	}
+#endif
 
 	timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);
 
diff -Nur linux-3.14.4.orig/net/ipv4/tcp_ipv4.c linux-3.14.4/net/ipv4/tcp_ipv4.c
--- linux-3.14.4.orig/net/ipv4/tcp_ipv4.c	2014-05-13 13:33:14.000000000 +0200
+++ linux-3.14.4/net/ipv4/tcp_ipv4.c	2014-05-29 21:30:07.000000000 +0200
@@ -1260,6 +1260,7 @@
 };
 #endif
 
+#ifdef CONFIG_TCP_FASTOPEN
 static bool tcp_fastopen_check(struct sock *sk, struct sk_buff *skb,
 			       struct request_sock *req,
 			       struct tcp_fastopen_cookie *foc,
@@ -1440,6 +1441,23 @@
 	WARN_ON(req->sk == NULL);
 	return 0;
 }
+#else
+static bool tcp_fastopen_check(struct sock *sk, struct sk_buff *skb,
+			       struct request_sock *req,
+			       struct tcp_fastopen_cookie *foc,
+			       struct tcp_fastopen_cookie *valid_foc)
+{
+	return false;
+}
+
+static int tcp_v4_conn_req_fastopen(struct sock *sk,
+				    struct sk_buff *skb,
+				    struct sk_buff *skb_synack,
+				    struct request_sock *req)
+{
+	return 0;
+}
+#endif
 
 int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
 {