net-tcp: Fast Open base

This patch impelements the common code for both the client and server.

1. TCP Fast Open option processing. Since Fast Open does not have an
option number assigned by IANA yet, it shares the experiment option
code 254 by implementing draft-ietf-tcpm-experimental-options
with a 16 bits magic number 0xF989. This enables global experiments
without clashing the scarce(2) experimental options available for TCP.

When the draft status becomes standard (maybe), the client should
switch to the new option number assigned while the server supports
both numbers for transistion.

2. The new sysctl tcp_fastopen

3. A place holder init function

Signed-off-by: Yuchung Cheng <[e-mail]>
Acked-by: Eric Dumazet <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/tcp.h

···
 	return (tcp_hdr(skb)->doff - 5) * 4;
 }
 
+/* TCP Fast Open */
+#define TCP_FASTOPEN_COOKIE_MIN	4	/* Min Fast Open Cookie size in bytes */
+#define TCP_FASTOPEN_COOKIE_MAX	16	/* Max Fast Open Cookie size in bytes */
+
+/* TCP Fast Open Cookie as stored in memory */
+struct tcp_fastopen_cookie {
+	s8	len;
+	u8	val[TCP_FASTOPEN_COOKIE_MAX];
+};
+
 /* This defines a selective acknowledgement block. */
 struct tcp_sack_block_wire {
 	__be32	start_seq;

include/net/tcp.h

···
 #define TCPOPT_TIMESTAMP	8	/* Better RTT estimations/PAWS */
 #define TCPOPT_MD5SIG		19	/* MD5 Signature (RFC2385) */
 #define TCPOPT_COOKIE		253	/* Cookie extension (experimental) */
+#define TCPOPT_EXP		254	/* Experimental */
+/* Magic number to be after the option value for sharing TCP
+ * experimental options. See draft-ietf-tcpm-experimental-options-00.txt
+ */
+#define TCPOPT_FASTOPEN_MAGIC	0xF989
 
 /*
  *     TCP option lengths
···
 #define TCPOLEN_SACK_PERM      2
 #define TCPOLEN_TIMESTAMP      10
 #define TCPOLEN_MD5SIG         18
+#define TCPOLEN_EXP_FASTOPEN_BASE  4
 #define TCPOLEN_COOKIE_BASE    2	/* Cookie-less header extension */
 #define TCPOLEN_COOKIE_PAIR    3	/* Cookie pair header extension */
 #define TCPOLEN_COOKIE_MIN     (TCPOLEN_COOKIE_BASE+TCP_COOKIE_MIN)
···
 extern int sysctl_tcp_retries2;
 extern int sysctl_tcp_orphan_retries;
 extern int sysctl_tcp_syncookies;
+extern int sysctl_tcp_fastopen;
 extern int sysctl_tcp_retrans_collapse;
 extern int sysctl_tcp_stdurg;
 extern int sysctl_tcp_rfc1337;
···
 		       size_t len, int nonblock, int flags, int *addr_len);
 extern void tcp_parse_options(const struct sk_buff *skb,
 			      struct tcp_options_received *opt_rx, const u8 **hvpp,
-			      int estab);
+			      int estab, struct tcp_fastopen_cookie *foc);
 extern const u8 *tcp_parse_md5sig_option(const struct tcphdr *th);
 
 /*

net/ipv4/Makefile

···
 	     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_minisocks.o tcp_cong.o tcp_metrics.o tcp_fastopen.o \
 	     datagram.o raw.o udp.o udplite.o \
 	     arp.o icmp.o devinet.o af_inet.o  igmp.o \
 	     fib_frontend.o fib_semantics.o fib_trie.o \

net/ipv4/syncookies.c

···
 
 	/* check for timestamp cookie support */
 	memset(&tcp_opt, 0, sizeof(tcp_opt));
-	tcp_parse_options(skb, &tcp_opt, &hash_location, 0);
+	tcp_parse_options(skb, &tcp_opt, &hash_location, 0, NULL);
 
 	if (!cookie_check_timestamp(&tcp_opt, &ecn_ok))
 		goto out;

net/ipv4/sysctl_net_ipv4.c

···
 	},
 #endif
 	{
+		.procname	= "tcp_fastopen",
+		.data		= &sysctl_tcp_fastopen,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
+	{
 		.procname	= "tcp_tw_recycle",
 		.data		= &tcp_death_row.sysctl_tw_recycle,
 		.maxlen		= sizeof(int),

net/ipv4/tcp_fastopen.c

···
+#include <linux/init.h>
+#include <linux/kernel.h>
+
+int sysctl_tcp_fastopen;
+
+static int __init tcp_fastopen_init(void)
+{
+	return 0;
+}
+
+late_initcall(tcp_fastopen_init);

net/ipv4/tcp_input.c

···
  * the fast version below fails.
  */
 void tcp_parse_options(const struct sk_buff *skb, struct tcp_options_received *opt_rx,
-		       const u8 **hvpp, int estab)
+		       const u8 **hvpp, int estab,
+		       struct tcp_fastopen_cookie *foc)
 {
 	const unsigned char *ptr;
 	const struct tcphdr *th = tcp_hdr(skb);
···
 					break;
 				}
 				break;
-			}
 
+			case TCPOPT_EXP:
+				/* Fast Open option shares code 254 using a
+				 * 16 bits magic number. It's valid only in
+				 * SYN or SYN-ACK with an even size.
+				 */
+				if (opsize < TCPOLEN_EXP_FASTOPEN_BASE ||
+				    get_unaligned_be16(ptr) != TCPOPT_FASTOPEN_MAGIC ||
+				    foc == NULL || !th->syn || (opsize & 1))
+					break;
+				foc->len = opsize - TCPOLEN_EXP_FASTOPEN_BASE;
+				if (foc->len >= TCP_FASTOPEN_COOKIE_MIN &&
+				    foc->len <= TCP_FASTOPEN_COOKIE_MAX)
+					memcpy(foc->val, ptr + 2, foc->len);
+				else if (foc->len != 0)
+					foc->len = -1;
+				break;
+
+			}
 			ptr += opsize-2;
 			length -= opsize;
 		}
···
 		if (tcp_parse_aligned_timestamp(tp, th))
 			return true;
 	}
-	tcp_parse_options(skb, &tp->rx_opt, hvpp, 1);
+	tcp_parse_options(skb, &tp->rx_opt, hvpp, 1, NULL);
 	return true;
 }
 
···
 	struct tcp_cookie_values *cvp = tp->cookie_values;
 	int saved_clamp = tp->rx_opt.mss_clamp;
 
-	tcp_parse_options(skb, &tp->rx_opt, &hash_location, 0);
+	tcp_parse_options(skb, &tp->rx_opt, &hash_location, 0, NULL);
 
 	if (th->ack) {
 		/* rfc793:

net/ipv4/tcp_ipv4.c

···
 	tcp_clear_options(&tmp_opt);
 	tmp_opt.mss_clamp = TCP_MSS_DEFAULT;
 	tmp_opt.user_mss  = tp->rx_opt.user_mss;
-	tcp_parse_options(skb, &tmp_opt, &hash_location, 0);
+	tcp_parse_options(skb, &tmp_opt, &hash_location, 0, NULL);
 
 	if (tmp_opt.cookie_plus > 0 &&
 	    tmp_opt.saw_tstamp &&

net/ipv4/tcp_minisocks.c

···
 
 	tmp_opt.saw_tstamp = 0;
 	if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
-		tcp_parse_options(skb, &tmp_opt, &hash_location, 0);
+		tcp_parse_options(skb, &tmp_opt, &hash_location, 0, NULL);
 
 		if (tmp_opt.saw_tstamp) {
 			tmp_opt.ts_recent	= tcptw->tw_ts_recent;
···
 
 	tmp_opt.saw_tstamp = 0;
 	if (th->doff > (sizeof(struct tcphdr)>>2)) {
-		tcp_parse_options(skb, &tmp_opt, &hash_location, 0);
+		tcp_parse_options(skb, &tmp_opt, &hash_location, 0, NULL);
 
 		if (tmp_opt.saw_tstamp) {
 			tmp_opt.ts_recent = req->ts_recent;

net/ipv4/tcp_output.c

···
 #define OPTION_MD5		(1 << 2)
 #define OPTION_WSCALE		(1 << 3)
 #define OPTION_COOKIE_EXTENSION	(1 << 4)
+#define OPTION_FAST_OPEN_COOKIE	(1 << 8)
 
 struct tcp_out_options {
-	u8 options;		/* bit field of OPTION_* */
+	u16 options;		/* bit field of OPTION_* */
+	u16 mss;		/* 0 to disable */
 	u8 ws;			/* window scale, 0 to disable */
 	u8 num_sack_blocks;	/* number of SACK blocks to include */
 	u8 hash_size;		/* bytes in hash_location */
-	u16 mss;		/* 0 to disable */
-	__u32 tsval, tsecr;	/* need to include OPTION_TS */
 	__u8 *hash_location;	/* temporary pointer, overloaded */
+	__u32 tsval, tsecr;	/* need to include OPTION_TS */
+	struct tcp_fastopen_cookie *fastopen_cookie;	/* Fast open cookie */
 };
 
 /* The sysctl int routines are generic, so check consistency here.
···
 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
 			      struct tcp_out_options *opts)
 {
-	u8 options = opts->options;	/* mungable copy */
+	u16 options = opts->options;	/* mungable copy */
 
 	/* Having both authentication and cookies for security is redundant,
 	 * and there's certainly not enough room.  Instead, the cookie-less
···
 		}
 
 		tp->rx_opt.dsack = 0;
+	}
+
+	if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
+		struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
+
+		*ptr++ = htonl((TCPOPT_EXP << 24) |
+			       ((TCPOLEN_EXP_FASTOPEN_BASE + foc->len) << 16) |
+			       TCPOPT_FASTOPEN_MAGIC);
+
+		memcpy(ptr, foc->val, foc->len);
+		if ((foc->len & 3) == 2) {
+			u8 *align = ((u8 *)ptr) + foc->len;
+			align[0] = align[1] = TCPOPT_NOP;
+		}
+		ptr += (foc->len + 3) >> 2;
 	}
 }
 

net/ipv6/syncookies.c

···
 
 	/* check for timestamp cookie support */
 	memset(&tcp_opt, 0, sizeof(tcp_opt));
-	tcp_parse_options(skb, &tcp_opt, &hash_location, 0);
+	tcp_parse_options(skb, &tcp_opt, &hash_location, 0, NULL);
 
 	if (!cookie_check_timestamp(&tcp_opt, &ecn_ok))
 		goto out;

net/ipv6/tcp_ipv6.c

···
 	tcp_clear_options(&tmp_opt);
 	tmp_opt.mss_clamp = IPV6_MIN_MTU - sizeof(struct tcphdr) - sizeof(struct ipv6hdr);
 	tmp_opt.user_mss = tp->rx_opt.user_mss;
-	tcp_parse_options(skb, &tmp_opt, &hash_location, 0);
+	tcp_parse_options(skb, &tmp_opt, &hash_location, 0, NULL);
 
 	if (tmp_opt.cookie_plus > 0 &&
 	    tmp_opt.saw_tstamp &&