[PATCH 1/8] Add Reliable Asynchronous Transfer Protocol

[Sascha Hauer <s.hauer@pengutronix.de>]

This patch adds support for Reliable Asynchronous Transfer Protocol (RATP)
as described in RFC916.

Communication over RS232 is often unreliable as characters are lost or
misinterpreted. This protocol allows for a reliable packet based communication
over serial lines.

The implementation simply follows the state machine described in the RFC text.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 include/ratp.h |   22 +
 lib/Kconfig    |    8 +
 lib/Makefile   |    1 +
 lib/ratp.c     | 1834 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 1865 insertions(+)
 create mode 100644 include/ratp.h
 create mode 100644 lib/ratp.c

diff --git a/include/ratp.h b/include/ratp.h
new file mode 100644
index 0000000..b91d305
--- /dev/null
+++ b/include/ratp.h
@@ -0,0 +1,22 @@
+#ifndef __RATP_H
+#define __RATP_H
+
+struct ratp {
+	struct ratp_internal *internal;
+	int (*send)(struct ratp *, void *pkt, int len);
+	int (*recv)(struct ratp *, uint8_t *data);
+};
+
+int ratp_establish(struct ratp *ratp, bool active, int timeout_ms);
+void ratp_close(struct ratp *ratp);
+int ratp_recv(struct ratp *ratp, void **data, size_t *len);
+int ratp_send(struct ratp *ratp, const void *data, size_t len);
+int ratp_send_complete(struct ratp *ratp, const void *data, size_t len,
+		   void (*complete)(void *ctx, int status), void *complete_ctx);
+int ratp_poll(struct ratp *ratp);
+bool ratp_closed(struct ratp *ratp);
+bool ratp_busy(struct ratp *ratp);
+
+void ratp_run_command(void);
+
+#endif /* __RATP_H */
diff --git a/lib/Kconfig b/lib/Kconfig
index fbf9f0f..a7e067e 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -55,6 +55,14 @@ config LIBMTD
 config STMP_DEVICE
 	bool
 
+config RATP
+	select CRC16
+	bool
+	help
+	  Reliable Asynchronous Transfer Protocol (RATP) is a protocol for reliably
+	  transferring packets over serial links described in RFC916. This implementation
+	  is used for controlling barebox over serial ports.
+
 source lib/gui/Kconfig
 
 source lib/fonts/Kconfig
diff --git a/lib/Makefile b/lib/Makefile
index abb34cf..0694721 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -56,3 +56,4 @@ obj-y			+= gcd.o
 obj-y			+= hexdump.o
 obj-$(CONFIG_FONTS)	+= fonts/
 obj-$(CONFIG_BAREBOX_LOGO)     += logo/
+obj-$(CONFIG_RATP)	+= ratp.o
diff --git a/lib/ratp.c b/lib/ratp.c
new file mode 100644
index 0000000..d596a0e
--- /dev/null
+++ b/lib/ratp.c
@@ -0,0 +1,1834 @@
+/*
+ * barebox RATP implementation.
+ * This is the barebox implementation for the Reliable Asynchronous
+ * Transfer Protocol (RATP) as described in RFC916.
+ *
+ * Copyright (C) 2015 Pengutronix, Sascha Hauer <s.hauer@pengutronix.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#define pr_fmt(fmt)  "ratp: " fmt
+
+#include <common.h>
+#include <malloc.h>
+#include <getopt.h>
+#include <ratp.h>
+#include <crc.h>
+#include <clock.h>
+#include <asm/unaligned.h>
+
+/*
+ * RATP packet format:
+ *
+ * Byte No.
+ *
+ *        +-------------------------------+
+ *        |                               |
+ *    1   |          Synch Leader         | Hex 01
+ *        |                               |
+ *        +-------------------------------+
+ *        | S | A | F | R | S | A | E | S |
+ *    2   | Y | C | I | S | N | N | O | O | Control
+ *        | N | K | N | T |   |   | R |   |
+ *        +-------------------------------+
+ *        |                               |
+ *    3   |      Data length (0-255)      |
+ *        |                               |
+ *        +-------------------------------+
+ *        |                               |
+ *    4   |        Header Checksum        |
+ *        |                               |
+ *        +-------------------------------+
+ *
+ */
+
+struct ratp_header {
+	uint8_t	synch;
+	uint8_t	control;
+	uint8_t	data_length;
+	uint8_t	cksum;
+};
+
+#define RATP_CONTROL_SO		(1 << 0)
+#define RATP_CONTROL_EOR	(1 << 1)
+#define RATP_CONTROL_AN		(1 << 2)
+#define RATP_CONTROL_SN		(1 << 3)
+#define RATP_CONTROL_RST	(1 << 4)
+#define RATP_CONTROL_FIN	(1 << 5)
+#define RATP_CONTROL_ACK	(1 << 6)
+#define RATP_CONTROL_SYN	(1 << 7)
+
+enum ratp_state {
+	RATP_STATE_LISTEN,
+	RATP_STATE_SYN_SENT,
+	RATP_STATE_SYN_RECEIVED,
+	RATP_STATE_ESTABLISHED,
+	RATP_STATE_FIN_WAIT,
+	RATP_STATE_LAST_ACK,
+	RATP_STATE_CLOSING,
+	RATP_STATE_TIME_WAIT,
+	RATP_STATE_CLOSED,
+};
+
+struct ratp_message {
+	void *buf;
+	size_t len;
+	struct list_head list;
+	void (*complete)(void *ctx, int status);
+	void *complete_ctx;
+	int eor;
+};
+
+static char *ratp_state_str[] = {
+	[RATP_STATE_LISTEN]       = "LISTEN",
+	[RATP_STATE_SYN_SENT]     = "SYN_SENT",
+	[RATP_STATE_SYN_RECEIVED] = "SYN_RECEIVED",
+	[RATP_STATE_ESTABLISHED]  = "ESTABLISHED",
+	[RATP_STATE_FIN_WAIT]     = "FIN_WAIT",
+	[RATP_STATE_LAST_ACK]     = "LAST_ACK",
+	[RATP_STATE_CLOSING]      = "CLOSING",
+	[RATP_STATE_TIME_WAIT]    = "TIME_WAIT",
+	[RATP_STATE_CLOSED]       = "CLOSED",
+};
+
+struct ratp_internal {
+	struct ratp *ratp;
+
+	enum ratp_state state;
+	int sn_sent;
+	int sn_received;
+	int active;
+
+	void *recvbuf;
+	void *sendbuf;
+	int sendbuf_len;
+
+	struct list_head recvmsg;
+	struct list_head sendmsg;
+
+	struct ratp_message *sendmsg_current;
+
+	uint64_t timewait_timer_start;
+	uint64_t retransmission_timer_start;
+	int max_retransmission;
+	int retransmission_count;
+	int srtt;
+	int rto;
+
+	int status;
+
+	int in_ratp;
+};
+
+static bool ratp_sn(struct ratp_header *hdr)
+{
+	return hdr->control & RATP_CONTROL_SN ? 1 : 0;
+}
+
+static bool ratp_an(struct ratp_header *hdr)
+{
+	return hdr->control & RATP_CONTROL_AN ? 1 : 0;
+}
+
+#define ratp_set_sn(sn) (((sn) % 2) ? RATP_CONTROL_SN : 0)
+#define ratp_set_an(an) (((an) % 2) ? RATP_CONTROL_AN : 0)
+
+static inline int ratp_header_ok(struct ratp_internal *ri, struct ratp_header *h)
+{
+	uint8_t cksum;
+	int ret;
+
+	cksum = h->control;
+	cksum += h->data_length;
+	cksum += h->cksum;
+
+	ret = cksum == 0xff ? 1 : 0;
+
+	if (ret)
+		pr_vdebug("Header ok\n");
+	else
+		pr_vdebug("Header cksum failed: %02x\n", cksum);
+
+	return ret;
+}
+
+static bool ratp_has_data(struct ratp_header *hdr)
+{
+	if (hdr->control & RATP_CONTROL_SO)
+		return 1;
+	if (hdr->data_length)
+		return 1;
+	return 0;
+}
+
+static void ratp_print_header(struct ratp_internal *ri, struct ratp_header *hdr,
+		const char *prefix)
+{
+	uint8_t control = hdr->control;
+
+	pr_debug("%s>%s %s %s %s %s %s %s %s< len: %-3d\n",
+		prefix,
+		control & RATP_CONTROL_SO  ? "so" : "--",
+		control & RATP_CONTROL_EOR ? "eor" : "---",
+		control & RATP_CONTROL_AN ? "an" : "--",
+		control & RATP_CONTROL_SN ? "sn" : "--",
+		control & RATP_CONTROL_RST ? "rst" : "---",
+		control & RATP_CONTROL_FIN ? "fin" : "---",
+		control & RATP_CONTROL_ACK ? "ack" : "---",
+		control & RATP_CONTROL_SYN ? "syn" : "---",
+		hdr->data_length);
+
+#ifdef VERBOSE_DEBUG
+	if (hdr->data_length)
+		memory_display(hdr + 1, 0, hdr->data_length, 1, 0);
+#endif
+}
+
+static void ratp_create_packet(struct ratp_internal *ri, struct ratp_header *hdr,
+		uint8_t control, uint8_t length)
+{
+	hdr->synch = 0x1;
+	hdr->control = control;
+	hdr->data_length = length;
+	hdr->cksum = (control + length) ^ 0xff;
+}
+
+static void ratp_state_change(struct ratp_internal *ri, enum ratp_state state)
+{
+	pr_debug("state %-10s -> %-10s\n", ratp_state_str[ri->state],
+			ratp_state_str[state]);
+
+	ri->state = state;
+}
+
+#define RATP_CONTROL_SO		(1 << 0)
+#define RATP_CONTROL_EOR	(1 << 1)
+#define RATP_CONTROL_AN		(1 << 2)
+#define RATP_CONTROL_SN		(1 << 3)
+#define RATP_CONTROL_RST	(1 << 4)
+#define RATP_CONTROL_FIN	(1 << 5)
+#define RATP_CONTROL_ACK	(1 << 6)
+#define RATP_CONTROL_SYN	(1 << 7)
+
+static int ratp_send_pkt(struct ratp_internal *ri, void *pkt, int length)
+{
+	struct ratp_header *hdr = (void *)pkt;
+
+	ratp_print_header(ri, hdr, "send");
+
+	if (ratp_has_data(hdr) ||
+	    (hdr->control & (RATP_CONTROL_SYN | RATP_CONTROL_RST | RATP_CONTROL_FIN))) {
+		memcpy(ri->sendbuf, pkt, length);
+		ri->sn_sent = ratp_sn(hdr);
+		ri->sendbuf_len = length;
+		ri->retransmission_timer_start = get_time_ns();
+		ri->retransmission_count = 0;
+	}
+
+	return ri->ratp->send(ri->ratp, pkt, length);
+}
+
+static int ratp_send_hdr(struct ratp_internal *ri, uint8_t control)
+{
+	struct ratp_header hdr = {};
+
+	ratp_create_packet(ri, &hdr, control, 0);
+
+	return ratp_send_pkt(ri, &hdr, sizeof(hdr));
+}
+
+static int ratp_recv_char(struct ratp_internal *ri, uint8_t *data, int poll_timeout_ms)
+{
+	uint64_t start;
+	int ret;
+
+	start = get_time_ns();
+
+	while (1) {
+		ret = ri->ratp->recv(ri->ratp, data);
+		if (ret < 0 && ret != -EAGAIN)
+			return ret;
+
+		if (ret == 0)
+			return 0;
+
+		if (is_timeout(start, poll_timeout_ms * MSECOND))
+			return -EAGAIN;
+	}
+}
+
+static int ratp_recv_pkt_header(struct ratp_internal *ri, struct ratp_header *hdr,
+		int poll_timeout_ms)
+{
+	int ret;
+	uint8_t buf;
+
+	do {
+		ret = ratp_recv_char(ri, &buf, 0);
+		if (ret < 0)
+			return ret;
+		hdr->synch = buf;
+	} while (hdr->synch != 1);
+	ret = ratp_recv_char(ri, &buf, poll_timeout_ms);
+	if (ret < 0)
+		return ret;
+
+	hdr->control = buf;
+	ret = ratp_recv_char(ri, &buf, poll_timeout_ms);
+	if (ret < 0)
+		return ret;
+
+	hdr->data_length = buf;
+
+	ret = ratp_recv_char(ri, &buf, poll_timeout_ms);
+	if (ret < 0)
+		return ret;
+
+	hdr->cksum = buf;
+
+	if (!ratp_header_ok(ri, hdr))
+		return -EAGAIN;
+
+	return 0;
+}
+
+static int ratp_recv_pkt_data(struct ratp_internal *ri, void *data, uint8_t len,
+		int poll_timeout_ms)
+{
+	uint16_t crc_expect, crc_read;
+	int ret, i;
+
+	for (i = 0; i < len + 2; i++) {
+		ret = ratp_recv_char(ri, data + i, poll_timeout_ms);
+		if (ret < 0)
+			return ret;
+	}
+
+	crc_expect = cyg_crc16(data, len);
+
+	crc_read = get_unaligned_be16(data + len);
+
+	if (crc_expect != crc_read) {
+		pr_vdebug("Wrong CRC: expected: 0x%04x, got 0x%04x\n",
+				crc_expect, crc_read);
+		return -EBADMSG;
+	} else {
+		pr_vdebug("correct CRC: 0x%04x\n", crc_expect);
+	}
+
+	return 0;
+}
+
+static int ratp_recv_pkt(struct ratp_internal *ri, void *pkt, int poll_timeout_ms)
+{
+	struct ratp_header *hdr = pkt;
+	void *data = pkt + sizeof(struct ratp_header);
+	int ret;
+
+	ret = ratp_recv_pkt_header(ri, hdr, poll_timeout_ms);
+	if (ret < 0)
+		return ret;
+
+	if (hdr->control & (RATP_CONTROL_SO | RATP_CONTROL_RST | RATP_CONTROL_SYN |
+		RATP_CONTROL_FIN))
+		return 0;
+
+	if (hdr->data_length) {
+		ret = ratp_recv_pkt_data(ri, data, hdr->data_length,
+				poll_timeout_ms);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static bool ratp_an_expected(struct ratp_internal *ri, struct ratp_header *hdr)
+{
+	return ratp_an(hdr) == (ri->sn_sent + 1) % 2;
+}
+
+static bool ratp_sn_expected(struct ratp_internal *ri, struct ratp_header *hdr)
+{
+	return ratp_sn(hdr) != ri->sn_received;
+}
+
+static int ratp_send_ack(struct ratp_internal *ri, struct ratp_header *hdr)
+{
+	uint8_t control = RATP_CONTROL_ACK;
+	int ret;
+
+	if (hdr->control & RATP_CONTROL_SN)
+		control |= RATP_CONTROL_AN;
+	else
+		control |= 0;
+
+	ret = ratp_send_hdr(ri, control);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static int ratp_send_next_data(struct ratp_internal *ri)
+{
+	uint16_t crc;
+	uint8_t control = RATP_CONTROL_ACK;
+	struct ratp_header *hdr;
+	int pktlen;
+	struct ratp_message *msg;
+	int len;
+
+	if (ri->sendmsg_current) {
+		pr_err("%s: busy\n", __func__);
+		return -EBUSY;
+	}
+
+	if (list_empty(&ri->sendmsg))
+		return 0;
+
+	msg = list_first_entry(&ri->sendmsg, struct ratp_message, list);
+
+	ri->sendmsg_current = msg;
+
+	list_del(&msg->list);
+
+	len = msg->len;
+
+	control = ratp_set_sn(ri->sn_sent + 1) |
+		ratp_set_an(ri->sn_received + 1) |
+		RATP_CONTROL_ACK;
+
+	hdr = msg->buf;
+
+	if (msg->eor)
+		control |= RATP_CONTROL_EOR;
+
+	if (len > 1) {
+		void *data = hdr + 1;
+		pktlen = sizeof(*hdr) + len + 2;
+		crc = cyg_crc16(data, len);
+		put_unaligned_be16(crc, data + len);
+	} else {
+		pktlen = sizeof(struct ratp_header);
+		control |= RATP_CONTROL_SO;
+		len = 0;
+	}
+
+	ratp_create_packet(ri, hdr, control, len);
+
+	ri->retransmission_count = 0;
+
+	ratp_send_pkt(ri, msg->buf, pktlen);
+
+	return 0;
+}
+
+static void ratp_start_time_wait_timer(struct ratp_internal *ri)
+{
+	ri->timewait_timer_start = get_time_ns();
+}
+
+static void ratp_msg_done(struct ratp_internal *ri, struct ratp_message *msg, int status)
+{
+	int alpha, beta, rtt;
+
+	if (!status) {
+		rtt = (unsigned long)(get_time_ns() - ri->retransmission_timer_start) / MSECOND;
+
+		alpha = 8;
+		beta = 15;
+
+		ri->srtt = (alpha * ri->srtt + (10 - alpha) * rtt) / 10;
+		ri->rto = max(200, beta * ri->srtt / 10);
+
+		pr_debug("%s: done. SRTT: %dms RTO: %dms status: %d\n",
+			__func__, ri->srtt, ri->rto, ri->status);
+	}
+
+	if (msg->complete)
+		msg->complete(msg->complete_ctx, status);
+
+	free(msg->buf);
+	free(msg);
+}
+
+/*
+ * This procedure details the behavior of the LISTEN state.  First
+ * check the packet for the RST flag.  If it is set then packet is
+ * discarded and ignored, return and continue the processing
+ * associated with this state.
+ *
+ * We assume now that the RST flag was not set.  Check the packet
+ * for the ACK flag.  If it is set we have an illegal condition
+ * since no connection has yet been opened.  Send a RST packet
+ * with the correct response SN value:
+ *
+ * <SN=received AN><CTL=RST>
+ *
+ * Return to the current state without any further processing.
+ *
+ * We assume now that neither the RST nor the ACK flags were set.
+ * Check the packet for a SYN flag.  If it is set then an attempt
+ * is being made to open a connection.  Create a TCB for this
+ * connection.  The sender has placed its MDL in the LENGTH field,
+ * also specified is the sender's initial SN value.  Retrieve and
+ * place them into the TCB.  Note that the presence of the SO flag
+ * is ignored since it has no meaning when either of the SYN, RST,
+ * or FIN flags are set.
+ *
+ * Send a SYN packet which acknowledges the SYN received.  Choose
+ * the initial SN value and the MDL for this end of the
+ * connection:
+ *
+ * <SN=0><AN=received SN+1 modulo 2><CTL=SYN, ACK><LENGTH=MDL>
+ *
+ * and go to the RATP_STATE_SYN_RECEIVED state without any further
+ * processing.
+ *
+ * Any packet not satisfying the above tests is discarded and
+ * ignored.  Return to the current state without any further
+ * processing.
+ */
+static void ratp_behaviour_a(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+
+	pr_debug("%s\n", __func__);
+
+	if (hdr->control & RATP_CONTROL_RST)
+		return;
+
+	if (hdr->control & RATP_CONTROL_ACK) {
+		uint8_t control = RATP_CONTROL_RST;
+
+		if (hdr->control & RATP_CONTROL_AN)
+			control |= RATP_CONTROL_SN;
+
+		ratp_send_hdr(ri, control);
+
+		return;
+	}
+
+	if (hdr->control & RATP_CONTROL_SYN) {
+		struct ratp_header synack = {};
+		uint8_t control = RATP_CONTROL_SYN | RATP_CONTROL_ACK;
+
+		if (!(hdr->control & RATP_CONTROL_SN))
+			control |= RATP_CONTROL_AN;
+
+		ratp_create_packet(ri, &synack, control, 255);
+		ratp_send_pkt(ri, &synack, sizeof(synack));
+
+		ratp_state_change(ri, RATP_STATE_SYN_RECEIVED);
+	}
+}
+
+/*
+ * This procedure represents the behavior of the SYN-SENT state
+ * and is entered when this end of the connection decides to
+ * execute an active OPEN.
+ *
+ * First, check the packet for the ACK flag.  If the ACK flag is
+ * set then check to see if the AN value was as expected.  If it
+ * was continue below.  Otherwise the AN value was unexpected.  If
+ * the RST flag was set then discard the packet and return to the
+ * current state without any further processing, else send a
+ * reset:
+ *
+ * <SN=received AN><CTL=RST>
+ *
+ * Discard the packet and return to the current state without any
+ * further processing.
+ *
+ * At this point either the ACK flag was set and the AN value was
+ * as expected or ACK was not set.  Second, check the RST flag.
+ * If the RST flag is set there are two cases:
+ *
+ * . If the ACK flag is set then discard the packet, flush the
+ * retransmission queue, inform the user "Error: Connection
+ * refused", delete the TCB, and go to the CLOSED state without
+ * any further processing.
+ *
+ * 2. If the ACK flag was not set then discard the packet and
+ * return to this state without any further processing.
+ *
+ * At this point we assume the packet contained an ACK which was
+ * Ok, or there was no ACK, and there was no RST.  Now check the
+ * packet for the SYN flag.  If the ACK flag was set then our SYN
+ * has been acknowledged.  Store MDL received in the TCB.  At this
+ * point we are technically in the ESTABLISHED state.  Send an
+ * acknowledgment packet and any initial data which is queued to
+ * send:
+ *
+ * <SN=received AN><AN=received SN+1 modulo 2><CTL=ACK><DATA>
+ *
+ * Go to the ESTABLISHED state without any further processing.
+ *
+ * If the SYN flag was set but the ACK was not set then the other
+ * end of the connection has executed an active open also.
+ * Acknowledge the SYN, choose your MDL, and send:
+ *
+ * <SN=0><AN=received SN+1 modulo 2><CTL=SYN, ACK><LENGTH=MDL>
+ *
+ * Go to the SYN-RECEIVED state without any further processing.
+ *
+ * Any packet not satisfying the above tests is discarded and
+ * ignored.  Return to the current state without any further
+ * processing.
+ */
+static void ratp_behaviour_b(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+
+	pr_debug("%s\n", __func__);
+
+	if ((hdr->control & RATP_CONTROL_ACK) && !ratp_an_expected(ri, hdr)) {
+		if (!(hdr->control & RATP_CONTROL_RST)) {
+			uint8_t control = RATP_CONTROL_RST;
+
+			control = RATP_CONTROL_RST |
+				ratp_set_sn(ratp_an(hdr));
+
+			ratp_send_hdr(ri, control);
+		}
+		return;
+	}
+
+	if (hdr->control & RATP_CONTROL_RST) {
+		if (hdr->control & RATP_CONTROL_ACK) {
+			ri->status = -ECONNREFUSED;
+
+			pr_debug("Connection refused\n");
+
+			ratp_state_change(ri, RATP_STATE_CLOSED);
+
+		}
+		return;
+	}
+
+	if (hdr->control & RATP_CONTROL_SYN) {
+		uint8_t control;
+
+		if (hdr->control & RATP_CONTROL_ACK) {
+			control = ratp_set_sn(ratp_an(hdr)) |
+				ratp_set_an(!ratp_sn(hdr)) |
+				RATP_CONTROL_ACK;
+		} else {
+			control = ratp_set_an(!ratp_sn(hdr)) |
+				RATP_CONTROL_SYN |
+				RATP_CONTROL_ACK;
+
+		}
+
+		ri->sn_received = ratp_sn(hdr);
+
+		ratp_send_hdr(ri, control);
+		ratp_state_change(ri, RATP_STATE_ESTABLISHED);
+	}
+}
+
+/*
+ * Examine the received SN field value.  If the SN value was
+ * expected then return and continue the processing associated
+ * with this state.
+ *
+ * We now assume the SN value was not what was expected.
+ *
+ * If either RST or FIN were set discard the packet and return to
+ * the current state without any further processing.
+ *
+ * If neither RST nor FIN flags were set it is assumed that this
+ * packet is a duplicate of one already received.  Send an ACK
+ * back:
+ *
+ * <SN=received AN><AN=received SN+1 modulo 2><CTL=ACK>
+ *
+ * Discard the duplicate packet and return to the current state
+ * without any further processing.
+ */
+static int ratp_behaviour_c1(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+	int ret;
+
+	pr_debug("%s\n", __func__);
+
+	if (ratp_sn_expected(ri, hdr)) {
+		pr_vdebug("%s: sn is expected\n", __func__);
+		return 0;
+	}
+
+	if (!(hdr->control & RATP_CONTROL_RST) &&
+			!(hdr->control & RATP_CONTROL_FIN)) {
+		ret = ratp_send_ack(ri, hdr);
+		if (ret)
+			return ret;
+	}
+
+	return 1;
+
+}
+
+/*
+ * Examine the received SN field value.  If the SN value was
+ * expected then return and continue the processing associated
+ * with this state.
+ *
+ * We now assume the SN value was not what was expected.
+ *
+ * If either RST or FIN were set discard the packet and return to
+ * the current state without any further processing.
+ *
+ * If SYN was set we assume that the other end crashed and has
+ * attempted to open a new connection.  We respond by sending a
+ * legal reset:
+ *
+ * <SN=received AN><AN=received SN+1 modulo 2><CTL=RST, ACK>
+ *
+ * This will cause the other end, currently in the SYN-SENT state,
+ * to close.  Flush the retransmission queue, inform the user
+ * "Error: Connection reset", discard the packet, delete the TCB,
+ * and go to the CLOSED state without any further processing.
+ *
+ * If neither RST, FIN, nor SYN flags were set it is assumed that
+ * this packet is a duplicate of one already received.  Send an
+ * ACK back:
+ *
+ * <SN=received AN><AN=received SN+1 modulo 2><CTL=ACK>
+ *
+ * Discard the duplicate packet and return to the current state
+ * without any further processing.
+ */
+static int ratp_behaviour_c2(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+	int ret;
+
+	pr_debug("%s\n", __func__);
+
+	if (!ratp_has_data(hdr))
+		return 0;
+
+	if (ratp_sn_expected(ri, hdr))
+		return 0;
+
+	if ((hdr->control & RATP_CONTROL_RST) ||
+			(hdr->control & RATP_CONTROL_FIN))
+		return 1;
+
+	if (hdr->control & RATP_CONTROL_SYN) {
+		ri->status = -ECONNRESET;
+		pr_debug("Error: Connection reset\n");
+		ratp_state_change(ri, RATP_STATE_CLOSED);
+		return 1;
+	}
+
+	if (!ratp_has_data(hdr))
+		return 1;
+
+	pr_debug("Sending ack for duplicate message\n");
+	ret = ratp_send_ack(ri, hdr);
+	if (ret)
+		return ret;
+
+	return 1;
+}
+
+/*
+ * The packet is examined for a RST flag.  If RST is not set then
+ * return and continue the processing associated with this state.
+ *
+ * RST is now assumed to have been set.  If the connection was
+ * originally initiated from the LISTEN state (it was passively
+ * opened) then flush the retransmission queue, discard the
+ * packet, and go to the LISTEN state without any further
+ * processing.
+ *
+ * If instead the connection was initiated actively (came from the
+ * SYN-SENT state) then flush the retransmission queue, inform the
+ * user "Error: Connection refused", discard the packet, delete
+ * the TCB, and go to the CLOSED state without any further
+ * processing.
+ */
+static int ratp_behaviour_d1(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+
+	pr_debug("%s\n", __func__);
+
+	if (!(hdr->control & RATP_CONTROL_RST))
+		return 0;
+
+	if (!(ri->active)) {
+		ratp_state_change(ri, RATP_STATE_LISTEN);
+		return 1;
+	}
+
+	ri->status = -ECONNREFUSED;
+
+	pr_debug("Error: connection refused\n");
+
+	ratp_state_change(ri, RATP_STATE_CLOSED);
+
+	return 1;
+}
+
+/*
+ * The packet is examined for a RST flag.  If RST is not set then
+ * return and continue the processing associated with this state.
+ *
+ * RST is now assumed to have been set.  Any data remaining to be
+ * sent is flushed.  The retransmission queue is flushed, the user
+ * is informed "Error: Connection reset.", discard the packet,
+ * delete the TCB, and go to the CLOSED state without any further
+ * processing.
+ */
+static int ratp_behaviour_d2(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+
+	pr_debug("%s\n", __func__);
+
+	if (!(hdr->control & RATP_CONTROL_RST))
+		return 0;
+
+	ri->status = -ECONNRESET;
+
+	pr_debug("connection reset\n");
+
+	return 0;
+}
+
+/*
+ * The packet is examined for a RST flag.  If RST is not set then
+ * return and continue the processing associated with this state.
+ *
+ * RST is now assumed to have been set.  Discard the packet,
+ * delete the TCB, and go to the CLOSED state without any further
+ * processing.
+ */
+static int ratp_behaviour_d3(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+
+	pr_debug("%s\n", __func__);
+
+	if (!(hdr->control & RATP_CONTROL_RST))
+		return 0;
+
+	ratp_state_change(ri, RATP_STATE_CLOSED);
+
+	return 1;
+}
+
+/*
+ * Check the presence of the SYN flag.  If the SYN flag is not set
+ * then return and continue the processing associated with this
+ * state.
+ *
+ * We now assume that the SYN flag was set.  The presence of a SYN
+ * here is an error.  Flush the retransmission queue, send a legal
+ * RST packet.
+ *
+ * If the ACK flag was set then send:
+ *
+ * <SN=received AN><CTL=RST>
+ *
+ * If the ACK flag was not set then send:
+ *
+ * <SN=0><CTL=RST>
+ *
+ * The user should receive the message "Error: Connection reset.",
+ * then delete the TCB and go to the CLOSED state without any
+ * further processing.
+ */
+static int ratp_behaviour_e(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+	uint8_t control;
+
+	pr_debug("%s\n", __func__);
+
+	if (!(hdr->control & RATP_CONTROL_SYN))
+		return 0;
+
+	ri->status = -ECONNRESET;
+
+	control = RATP_CONTROL_RST;
+
+	if (hdr->control & RATP_CONTROL_ACK)
+		control |= ratp_set_sn(ratp_an(hdr));
+
+	ratp_send_hdr(ri, control);
+
+	pr_debug("connection reset\n");
+
+	ratp_state_change(ri, RATP_STATE_CLOSED);
+
+	return 1;
+}
+
+/*
+ * Check the presence of the ACK flag.  If ACK is not set then
+ * discard the packet and return without any further processing.
+ *
+ * We now assume that the ACK flag was set.  If the AN field value
+ * was as expected then return and continue the processing
+ * associated with this state.
+ *
+ * We now assume that the ACK flag was set and that the AN field
+ * value was unexpected.  If the connection was originally
+ * initiated from the LISTEN state (it was passively opened) then
+ * flush the retransmission queue, discard the packet, and send a
+ * legal RST packet:
+ *
+ * <SN=received AN><CTL=RST>
+ *
+ * Then delete the TCB and go to the LISTEN state without any
+ * further processing.
+ *
+ * Otherwise the connection was initiated actively (came from the
+ * SYN-SENT state) then inform the user "Error: Connection
+ * refused", flush the retransmission queue, discard the packet,
+ * and send a legal RST packet:
+ *
+ * <SN=received AN><CTL=RST>
+ *
+ * Then delete the TCB and go to the CLOSED state without any
+ * further processing.
+ */
+static int ratp_behaviour_f1(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+	uint8_t control;
+
+	pr_debug("%s\n", __func__);
+
+	if (!(hdr->control & RATP_CONTROL_ACK))
+		return 1;
+
+	if (ratp_an_expected(ri, hdr))
+		return 0;
+
+	control = RATP_CONTROL_RST | ratp_set_sn(ratp_an(hdr));
+	ratp_send_hdr(ri, control);
+
+	if (ri->active) {
+		ratp_state_change(ri, RATP_STATE_CLOSED);
+		ri->status = -ECONNREFUSED;
+
+		pr_debug("connection refused\n");
+	} else {
+		ratp_state_change(ri, RATP_STATE_LISTEN);
+	}
+
+	return 1;
+}
+
+/*
+ * Check the presence of the ACK flag.  If ACK is not set then
+ * discard the packet and return without any further processing.
+ *
+ * We now assume that the ACK flag was set.  If the AN field value
+ * was as expected then flush the retransmission queue and inform
+ * the user with an "Ok" if a buffer has been entirely
+ * acknowledged.  Another packet containing data may now be sent.
+ * Return and continue the processing associated with this state.
+ *
+ * We now assume that the ACK flag was set and that the AN field
+ * value was unexpected.  This is assumed to indicate a duplicate
+ * acknowledgment.  It is ignored, return and continue the
+ * processing associated with this state.
+ */
+static int ratp_behaviour_f2(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+
+	pr_debug("%s\n", __func__);
+
+	if (!(hdr->control & RATP_CONTROL_ACK))
+		return 1;
+
+	if (ratp_an_expected(ri, hdr)) {
+		pr_debug("Data succesfully sent\n");
+		if (ri->sendmsg_current)
+			ratp_msg_done(ri, ri->sendmsg_current, 0);
+		ri->sendmsg_current = NULL;
+		return 0;
+	} else {
+		pr_vdebug("%s: an not expected\n", __func__);
+	}
+
+	return 0;
+}
+
+/*
+ * Check the presence of the ACK flag.  If ACK is not set then
+ * discard the packet and return without any further processing.
+ *
+ * We now assume that the ACK flag was set.  If the AN field value
+ * was as expected then continue the processing associated with
+ * this state.
+ *
+ * We now assume that the ACK flag was set and that the AN field
+ * value was unexpected.  This is ignored, return and continue
+ * with the processing associated with this state.
+ */
+static int ratp_behaviour_f3(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+
+	pr_debug("%s\n", __func__);
+
+	if (!(hdr->control & RATP_CONTROL_ACK))
+		return 1;
+
+	return 0;
+}
+
+/*
+ * This procedure represents the behavior of the CLOSED state of a
+ * connection.  All incoming packets are discarded.  If the packet
+ * had the RST flag set take no action.  Otherwise it is necessary
+ * to build a RST packet.  Since this end is closed the other end
+ * of the connection has incorrect data about the state of the
+ * connection and should be so informed.
+ *
+ * If the ACK flag was set then send:
+ *
+ * <SN=received AN><CTL=RST>
+ *
+ * If the ACK flag was not set then send:
+ *
+ * <SN=0><AN=received SN+1 modulo 2><CTL=RST, ACK>
+ *
+ * After sending the reset packet return to the current state
+ * without any further processing.
+ */
+static int ratp_behaviour_g(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+	uint8_t control;
+
+	pr_debug("%s\n", __func__);
+
+	control = RATP_CONTROL_RST;
+
+	if (hdr->control & RATP_CONTROL_ACK)
+		control |= ratp_set_sn(ratp_an(hdr));
+	else
+		control = ratp_set_an(ratp_sn(hdr) + 1) | RATP_CONTROL_ACK;
+
+	ratp_send_hdr(ri, control);
+
+	return 0;
+}
+
+/*
+ * Our SYN has been acknowledged.  At this point we are
+ * technically in the ESTABLISHED state.  Send any initial data
+ * which is queued to send:
+ *
+ * <SN=received AN><AN=received SN+1 modulo 2><CTL=ACK><DATA>
+ *
+ * Go to the ESTABLISHED state and execute procedure I1 to process
+ * any data which might be in this packet.
+ *
+ * Any packet not satisfying the above tests is discarded and
+ * ignored.  Return to the current state without any further
+ * processing.
+ */
+static int ratp_behaviour_h1(struct ratp_internal *ri, void *pkt)
+{
+	pr_debug("%s\n", __func__);
+
+	ratp_state_change(ri, RATP_STATE_ESTABLISHED);
+
+	return 0;
+}
+
+/*
+ * Check the presence of the FIN flag.  If FIN is not set then
+ * continue the processing associated with this state.
+ *
+ * We now assume that the FIN flag was set.  This means the other
+ * end has decided to close the connection.  Flush the
+ * retransmission queue.  If any data remains to be sent then
+ * inform the user "Warning: Data left unsent."  The user must
+ * also be informed "Connection closing."  An acknowledgment for
+ * the FIN must be sent which also indicates this end is closing:
+ *
+ * <SN=received AN><AN=received SN + 1 modulo 2><CTL=FIN, ACK>
+ *
+ * Go to the LAST-ACK state without any further processing.
+ */
+static int ratp_behaviour_h2(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+	uint8_t control;
+
+	pr_debug("%s\n", __func__);
+
+	if (!(hdr->control & RATP_CONTROL_FIN))
+		return 0;
+
+	ri->status = -ENETDOWN;
+
+	control = ratp_set_sn(ratp_an(hdr)) |
+		ratp_set_an(ratp_sn(hdr) + 1) |
+		RATP_CONTROL_FIN |
+		RATP_CONTROL_ACK;
+
+	ratp_send_hdr(ri, control);
+
+	ratp_state_change(ri, RATP_STATE_LAST_ACK);
+
+	return 1;
+}
+
+/*
+ * This state represents the final behavior of the FIN-WAIT state.
+ *
+ * If the packet did not contain a FIN we assume this packet is a
+ * duplicate and that the other end of the connection has not seen
+ * the FIN packet we sent earlier.  Rely upon retransmission of
+ * our earlier FIN packet to inform the other end of our desire to
+ * close.  Discard the packet and return without any further
+ * processing.
+ *
+ * At this point we have a packet which should contain a FIN.  By
+ * the rules of this protocol an ACK of a FIN requires a FIN, ACK
+ * in response and no data.  If the packet contains data we have
+ * detected an illegal condition.  Send a reset:
+ * <SN=received AN><AN=received SN+1 modulo 2><CTL=RST, ACK>
+ *
+ * Discard the packet, flush the retransmission queue, inform the
+ * ser "Error: Connection reset.", delete the TCB, and go to the
+ * CLOSED state without any further processing.
+ *
+ * We now assume that the FIN flag was set and no data was
+ * contained in the packet.  If the AN field value was expected
+ * then this packet acknowledges a previously sent FIN packet.
+ * The other end of the connection is then also assumed to be
+ * closing and expects an acknowledgment.  Send an acknowledgment
+ * of the FIN:
+ *
+ * <SN=received AN><AN=received SN+1 modulo 2><CTL=ACK>
+ *
+ * Start the 2*SRTT timer associated with the TIME-WAIT state,
+ * discard the packet, and go to the TIME-WAIT state without any
+ * further processing.
+ *
+ * Otherwise the AN field value was unexpected.  This indicates a
+ * simultaneous closing by both sides of the connection.  Send an
+ * acknowledgment of the FIN:
+ *
+ * <SN=received AN><AN=received SN+1 modulo 2><CTL=ACK>
+ *
+ * Discard the packet, and go to the CLOSING state without any
+ * further processing.
+ */
+static int ratp_behaviour_h3(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+	uint8_t control;
+	int expected;
+
+	pr_debug("%s\n", __func__);
+
+	if (!(hdr->control & RATP_CONTROL_FIN))
+		return 1;
+
+	if (ratp_has_data(hdr)) {
+		control = ratp_set_sn(ratp_an(hdr)) |
+			ratp_set_an(ratp_sn(hdr) + 1) |
+			RATP_CONTROL_RST |
+			RATP_CONTROL_ACK;
+		ratp_send_hdr(ri, control);
+		ri->status = -ECONNRESET;
+		pr_debug("Error: Connection reset\n");
+		ratp_state_change(ri, RATP_STATE_CLOSED);
+		return 1;
+	}
+
+	control = ratp_set_sn(ratp_an(hdr)) |
+		ratp_set_an(ratp_sn(hdr) + 1) |
+		RATP_CONTROL_ACK;
+
+	expected = ratp_an_expected(ri, hdr);
+
+	ratp_send_hdr(ri, control);
+
+	if (expected) {
+		ratp_state_change(ri, RATP_STATE_TIME_WAIT);
+		ratp_start_time_wait_timer(ri);
+	} else {
+		ratp_state_change(ri, RATP_STATE_CLOSING);
+	}
+
+	return 1;
+}
+
+/*
+ * This state represents the final behavior of the LAST-ACK state.
+ *
+ * If the AN field value is expected then this ACK is in response
+ * to the FIN, ACK packet recently sent.  This is the final
+ * acknowledging message indicating both side's agreement to close
+ * the connection.  Discard the packet, flush all queues, delete
+ * the TCB, and go to the CLOSED state without any further
+ * processing.
+ *
+ * Otherwise the AN field value was unexpected.  Discard the
+ * packet and remain in the current state without any further
+ * processing.
+ */
+static int ratp_behaviour_h4(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+
+	pr_debug("%s\n", __func__);
+
+	if (ratp_an_expected(ri, hdr))
+		ratp_state_change(ri, RATP_STATE_CLOSED);
+
+	return 1;
+}
+
+/*
+ * This state represents the final behavior of the CLOSING state.
+ *
+ * If the AN field value was expected then this packet
+ * acknowledges the FIN packet recently sent.  This is the final
+ * acknowledging message indicating both side's agreement to close
+ * the connection.  Start the 2*SRTT timer associated with the
+ * TIME-WAIT state, discard the packet, and go to the TIME-WAIT
+ * state without any further processing.
+ *
+ * Otherwise the AN field value was unexpected.  Discard the
+ * packet and remain in the current state without any further
+ * processing.
+ */
+static int ratp_behaviour_h5(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+
+	pr_debug("%s\n", __func__);
+
+	if (ratp_an_expected(ri, hdr)) {
+		ratp_state_change(ri, RATP_STATE_TIME_WAIT);
+		ratp_start_time_wait_timer(ri);
+	}
+
+	return 0;
+}
+
+/*
+ * This state represents the behavior of the TIME-WAIT state.
+ * Check the presence of the ACK flag.  If ACK is not set then
+ * discard the packet and return without any further processing.
+ *
+ * Check the presence of the FIN flag.  If FIN is not set then
+ * discard the packet and return without any further processing.
+ *
+ * We now assume that the FIN flag was set.  This situation
+ * indicates that the last acknowledgment of the FIN packet sent
+ * by the other end of the connection did not arrive.  Resend the
+ * acknowledgment:
+ *
+ * <SN=received AN><AN=received SN+1 modulo 2><CTL=ACK>
+ *
+ * Restart the 2*SRTT timer, discard the packet, and remain in the
+ * current state without any further processing.
+ */
+static int ratp_behaviour_h6(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+	uint8_t control;
+
+	pr_debug("%s\n", __func__);
+
+	if (!(hdr->control & RATP_CONTROL_ACK))
+		return 1;
+
+	if (!(hdr->control & RATP_CONTROL_FIN))
+		return 1;
+
+	control = ratp_set_sn(ratp_an(hdr) + 1) | RATP_CONTROL_ACK;
+
+	ratp_send_hdr(ri, control);
+
+	ratp_start_time_wait_timer(ri);
+
+	return 0;
+}
+
+static int msg_recv(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+	struct ratp_message *msg;
+
+	pr_debug("%s: Put msg in receive queue\n", __func__);
+
+	msg = xzalloc(sizeof(*msg));
+	if (hdr->data_length) {
+		msg->len = hdr->data_length;
+		msg->buf = xzalloc(msg->len);
+		memcpy(msg->buf, pkt + sizeof(struct ratp_header), msg->len);
+	} else {
+		msg->len = 1;
+		msg->buf = xzalloc(1);
+		*(uint8_t *)msg->buf = hdr->data_length;
+	}
+
+	if (hdr->control & RATP_CONTROL_EOR)
+		msg->eor = 1;
+
+	list_add_tail(&msg->list, &ri->recvmsg);
+
+	return 0;
+}
+
+/*
+ * This represents that stage of processing in the ESTABLISHED
+ * state in which all the flag bits have been processed and only
+ * data may remain.  The packet is examined to see if it contains
+ * data.  If not the packet is now discarded, return to the
+ * current state without any further processing.
+ *
+ * We assume the packet contained data, that either the SO flag
+ * was set or LENGTH is positive.  That data is placed into the
+ * user's receive buffers.  As these become full the user should
+ * be informed "Receive buffer full."  An acknowledgment is sent:
+ *
+ * <SN=received AN><AN=received SN+1 modulo 2><CTL=ACK>
+ *
+ * If data is queued to send then it is most efficient to
+ * 'piggyback' this acknowledgment on that data packet.
+ *
+ * The packet is now discarded, return to the ESTABLISHED state
+ * without any further processing.
+ */
+static int ratp_behaviour_i1(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+	uint8_t control = 0;
+
+	if (!hdr->data_length && !(hdr->control & RATP_CONTROL_SO))
+		return 1;
+
+	pr_vdebug("%s **received** %d\n", __func__, hdr->data_length);
+
+	ri->sn_received = ratp_sn(hdr);
+
+	msg_recv(ri, pkt);
+
+	if (list_empty(&ri->sendmsg) || ri->sendmsg_current) {
+		control = ratp_set_sn(!ri->sn_sent) |
+			ratp_set_an(ri->sn_received + 1) |
+			RATP_CONTROL_ACK;
+
+		ratp_send_hdr(ri, control);
+	} else {
+		ratp_send_next_data(ri);
+	}
+
+	return 0;
+}
+
+/*
+ * State machine as desribed in RFC916
+ *
+ * STATE                BEHAVIOR
+ * =============+========================
+ * LISTEN       |  A
+ * -------------+------------------------
+ * SYN-SENT     |  B
+ * -------------+------------------------
+ * SYN-RECEIVED |  C1  D1  E  F1  H1
+ * -------------+------------------------
+ * ESTABLISHED  |  C2  D2  E  F2  H2  I1
+ * -------------+------------------------
+ * FIN-WAIT     |  C2  D2  E  F3  H3
+ * -------------+------------------------
+ * LAST-ACK     |  C2  D3  E  F3  H4
+ * -------------+------------------------
+ * CLOSING      |  C2  D3  E  F3  H5
+ * -------------+------------------------
+ * TIME-WAIT    |  D3  E  F3 H6
+ * -------------+------------------------
+ * CLOSED       |  G
+ * -------------+------------------------
+ */
+
+static int ratp_state_machine(struct ratp_internal *ri, void *pkt)
+{
+	struct ratp_header *hdr = pkt;
+	int ret;
+
+	ratp_print_header(ri, hdr, "                      recv");
+	pr_debug(" state %s\n", ratp_state_str[ri->state]);
+
+	switch (ri->state) {
+	case RATP_STATE_LISTEN:
+		ratp_behaviour_a(ri, pkt);
+		break;
+	case RATP_STATE_SYN_SENT:
+		ratp_behaviour_b(ri, pkt);
+		break;
+	case RATP_STATE_SYN_RECEIVED:
+		ret = ratp_behaviour_c1(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_d1(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_e(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_f1(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_h1(ri, pkt);
+		if (ret)
+			return ret;
+		break;
+	case RATP_STATE_ESTABLISHED:
+		ret = ratp_behaviour_c2(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_d2(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_e(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_f2(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_h2(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_i1(ri, pkt);
+		if (ret)
+			return ret;
+		break;
+	case RATP_STATE_FIN_WAIT:
+		ret = ratp_behaviour_c2(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_d2(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_e(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_f3(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_h3(ri, pkt);
+		if (ret)
+			return ret;
+		break;
+	case RATP_STATE_LAST_ACK:
+		ret = ratp_behaviour_c2(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_d3(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_e(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_f3(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_h4(ri, pkt);
+		if (ret)
+			return ret;
+		break;
+	case RATP_STATE_CLOSING:
+		ret = ratp_behaviour_c2(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_d3(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_e(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_f3(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_h5(ri, pkt);
+		if (ret)
+			return ret;
+		break;
+	case RATP_STATE_TIME_WAIT:
+		ret = ratp_behaviour_d3(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_e(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_f3(ri, pkt);
+		if (ret)
+			return ret;
+		ret = ratp_behaviour_h6(ri, pkt);
+		if (ret)
+			return ret;
+		break;
+	case RATP_STATE_CLOSED:
+		ratp_behaviour_g(ri, pkt);
+		break;
+	};
+
+	return 0;
+}
+
+/**
+ * ratp_closed() - Check if a connection is closed
+ *
+ * Return: true if a connection is closed, false otherwise
+ */
+bool ratp_closed(struct ratp *ratp)
+{
+	struct ratp_internal *ri = ratp->internal;
+
+	if (!ri)
+		return true;
+
+	return ri->state == RATP_STATE_CLOSED;
+}
+
+/**
+ * ratp_busy() - Check if we are inside the RATP code
+ *
+ * Needed for RATP debugging. The RATP console uses this to determine
+ * if it is called from inside the RATP code.
+ *
+ * Return: true if we are inside the RATP code, false otherwise
+ */
+bool ratp_busy(struct ratp *ratp)
+{
+	struct ratp_internal *ri = ratp->internal;
+
+	if (!ri)
+		return false;
+
+	return ri->in_ratp != 0;
+}
+
+/**
+ * ratp_poll() - Execute RATP state machine
+ * @ratp: The RATP link
+ *
+ * This function should be executed periodically to keep the RATP state
+ * machine going.
+ *
+ * Return: 0 if successful, a negative error code otherwise.
+ */
+int ratp_poll(struct ratp *ratp)
+{
+	struct ratp_internal *ri = ratp->internal;
+	int ret;
+
+	if (!ri)
+		return -ENETDOWN;
+
+	ri->in_ratp++;
+
+	ret = ratp_recv_pkt(ri, ri->recvbuf, 100);
+	if (ret == 0) {
+
+		if (ri->state == RATP_STATE_TIME_WAIT &&
+		    is_timeout(ri->timewait_timer_start, ri->srtt * 2 * MSECOND)) {
+			pr_debug("2*SRTT timer timed out\n");
+			ret = -ECONNRESET;
+			goto out;
+		}
+
+		ret = ratp_state_machine(ri, ri->recvbuf);
+		if (ret < 0)
+			goto out;
+
+		if (ri->status < 0) {
+			ret = ri->status;
+			goto out;
+		}
+	}
+
+	if (ri->sendmsg_current && is_timeout(ri->retransmission_timer_start,
+	    ri->rto * MSECOND)) {
+
+		ri->retransmission_count++;
+		if (ri->retransmission_count == ri->max_retransmission) {
+			ri->status = ret = -ETIMEDOUT;
+			ri->state = RATP_STATE_CLOSED;
+			goto out;
+		}
+
+		pr_debug("%s: retransmit\n", __func__);
+
+		ratp_print_header(ri, ri->sendbuf, "resend");
+
+		ri->retransmission_timer_start = get_time_ns();
+
+		ret = ri->ratp->send(ratp, ri->sendbuf, ri->sendbuf_len);
+		if (ret)
+			goto out;
+	}
+
+	if (!ri->sendmsg_current && !list_empty(&ri->sendmsg))
+		ratp_send_next_data(ri);
+
+	ret = 0;
+out:
+	ri->in_ratp--;
+
+	return ret;
+}
+
+/**
+ * ratp_establish(): Establish a RATP link
+ * @ratp: The RATP link
+ * @active: if true actively create a connection
+ * @timeout_ms: Timeout in ms to wait until a connection is established. If
+ *              0 wait forever.
+ *
+ * This function establishes a link with the remote end. It expects the
+ * send and receive functions to be set, all other struct ratp_internal members can
+ * be left uninitialized.
+ *
+ * Return: 0 if successful, a negative error code otherwise.
+ */
+int ratp_establish(struct ratp *ratp, bool active, int timeout_ms)
+{
+	struct ratp_internal *ri;
+	int ret;
+	uint64_t start;
+
+	ri = xzalloc(sizeof(*ri));
+	ri->ratp = ratp;
+	ratp->internal = ri;
+
+	ri->recvbuf = xmalloc(512);
+	ri->sendbuf = xmalloc(512);
+	INIT_LIST_HEAD(&ri->recvmsg);
+	INIT_LIST_HEAD(&ri->sendmsg);
+	ri->max_retransmission = 100;
+	ri->srtt = 100;
+	ri->rto = 100;
+	ri->active = active;
+
+	ri->in_ratp++;
+
+	if (ri->active) {
+		ratp_send_hdr(ri, RATP_CONTROL_SYN);
+
+		ratp_state_change(ri, RATP_STATE_SYN_SENT);
+	}
+
+	start = get_time_ns();
+
+	while (1) {
+		ret = ratp_poll(ri->ratp);
+		if (ret < 0)
+			goto out;
+
+		if (ri->state == RATP_STATE_ESTABLISHED) {
+			ret = 0;
+			goto out;
+		}
+
+		if (timeout_ms && is_timeout(start, MSECOND * timeout_ms)) {
+			ret = -ETIMEDOUT;
+			goto out;
+		}
+	}
+
+out:
+	if (ret) {
+		free(ri->recvbuf);
+		free(ri->sendbuf);
+		free(ri);
+		ratp->internal = NULL;
+	}
+
+	ri->in_ratp--;
+
+	return ret;
+}
+
+void ratp_close(struct ratp *ratp)
+{
+	struct ratp_internal *ri = ratp->internal;
+	struct ratp_message *msg, *tmp;
+	struct ratp_header fin = {};
+
+	if (!ri)
+		return;
+
+	if (ri->state == RATP_STATE_ESTABLISHED) {
+		uint64_t start;
+		u8 control;
+
+		pr_debug("Closing...\n");
+
+		ratp_state_change(ri, RATP_STATE_FIN_WAIT);
+
+		control = ratp_set_sn(!ri->sn_sent) |
+			ratp_set_an(ri->sn_received + 1) |
+			RATP_CONTROL_FIN | RATP_CONTROL_ACK;
+
+		ratp_create_packet(ri, &fin, control, 0);
+
+		ratp_send_pkt(ri, &fin, sizeof(fin));
+
+		start = get_time_ns();
+
+		while (!is_timeout(start, ri->srtt * MSECOND * 2))
+			ratp_poll(ratp);
+	}
+
+	list_for_each_entry_safe(msg, tmp, &ri->sendmsg, list)
+		ratp_msg_done(ri, msg, -ECONNRESET);
+
+	free(ri);
+	ratp->internal = NULL;
+
+	pr_info("Closed\n");
+}
+
+/**
+ * ratp_send_complete(): Send data over a RATP link
+ * @ratp: The RATP link
+ * @data: The data buffer
+ * @len: The length of the message to send
+ * @complete: The completion callback for the message
+ * @complete_ctx: context pointer for the completion callback
+ *
+ * Queue a RATP message for transmission. This only queues the message,
+ * ratp_poll has to be called to actually transfer the message.
+ * @complete will be called upon completion of the message.
+ *
+ * Return: 0 if successful, a negative error code otherwise.
+ */
+int ratp_send_complete(struct ratp *ratp, const void *data, size_t len,
+		   void (*complete)(void *ctx, int status), void *complete_ctx)
+{
+	struct ratp_internal *ri = ratp->internal;
+	struct ratp_message *msg;
+
+	if (!ri || ri->state != RATP_STATE_ESTABLISHED)
+		return -ENETDOWN;
+
+	if (!len)
+		return -EINVAL;
+
+	ri->in_ratp++;
+
+	while (len) {
+		int now = min((int)len, 255);
+
+		msg = xzalloc(sizeof(*msg));
+		msg->buf = xzalloc(sizeof(struct ratp_header) + now + 2);
+		msg->len = now;
+		memcpy(msg->buf + sizeof(struct ratp_header), data, now);
+
+		list_add_tail(&msg->list, &ri->sendmsg);
+
+		len -= now;
+	}
+
+	msg->eor = 1;
+	msg->complete = complete;
+	msg->complete_ctx = complete_ctx;
+
+	ri->in_ratp--;
+
+	return 0;
+}
+
+/**
+ * ratp_send(): Send data over a RATP link
+ * @ratp: The RATP link
+ * @data: The data buffer
+ * @len: The length of the message to send
+ *
+ * Queue a RATP message for transmission. This only queues the message,
+ * ratp_poll has to be called to actually transfer the message.
+ *
+ * Return: 0 if successful, a negative error code otherwise.
+ */
+int ratp_send(struct ratp *ratp, const void *data, size_t len)
+{
+	return ratp_send_complete(ratp, data, len, NULL, NULL);
+}
+
+/**
+ * ratp_recv() - Receive data from a RATP link
+ * @ratp: The RATP link
+ * @data: Pointer to data
+ * @len: The length of the data in bytes
+ *
+ * If a message is available it fills @data with a pointer to the data.
+ * This function does not wait for new messages. If no data is available
+ * -EAGAIN is returned. If data is received @data has to be freed by the
+ * caller.
+ *
+ * Return: 0 if successful, a negative error code otherwise.
+ */
+int ratp_recv(struct ratp *ratp, void **data, size_t *len)
+{
+	struct ratp_internal *ri = ratp->internal;
+	struct ratp_message *msg, *tmp;
+	void *pos;
+	int num = 0;
+
+	*len = 0;
+
+	if (!ri || ri->state != RATP_STATE_ESTABLISHED)
+		return -ENETDOWN;
+
+	if (list_empty(&ri->recvmsg))
+		return -EAGAIN;
+
+	list_for_each_entry(msg, &ri->recvmsg, list) {
+		*len += msg->len;
+		num++;
+		if (msg->eor)
+			goto eor;
+	}
+
+	return -EAGAIN;
+
+eor:
+	*data = malloc(*len);
+	if (!*data)
+		return -ENOMEM;
+
+	pos = *data;
+
+	list_for_each_entry_safe(msg, tmp, &ri->recvmsg, list) {
+		memcpy(pos, msg->buf, msg->len);
+		pos += msg->len;
+
+		list_del(&msg->list);
+
+		free(msg->buf);
+		free(msg);
+	}
+
+	return 0;
+}
\ No newline at end of file
-- 
2.6.4


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