/*

 * tcpprobe - Observe the TCP flow with kprobes.

 *

 * The idea for this came from Werner Almesberger's umlsim

 * Copyright (C) 2004, Stephen Hemminger <shemminger@osdl.org>

 *

 * 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.

 *

 * 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.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

 */

#include <linux/kernel.h>

#include <linux/kprobes.h>

#include <linux/socket.h>

#include <linux/tcp.h>

#include <linux/proc_fs.h>

#include <linux/module.h>

#include <linux/ktime.h>

#include <linux/time.h>

#include <net/net_namespace.h>

#include <net/tcp.h>

MODULE_AUTHOR("Stephen Hemminger <shemminger@linux-foundation.org>");

MODULE_DESCRIPTION("TCP cwnd snooper");

MODULE_LICENSE("GPL");

MODULE_VERSION("1.1");

static int port __read_mostly = 0;

MODULE_PARM_DESC(port, "Port to match (0=all)");

module_param(port, int, 0);

static int bufsize __read_mostly = 4096;

MODULE_PARM_DESC(bufsize, "Log buffer size in packets (4096)");

module_param(bufsize, int, 0);

static int full __read_mostly;

MODULE_PARM_DESC(full, "Full log (1=every ack packet received,  0=only cwnd changes)");

module_param(full, int, 0);

static const char procname[] = "tcpprobe";

struct tcp_log {

	ktime_t tstamp;

	__be32	saddr, daddr;

	__be16	sport, dport;

	u16	length;

	u32	snd_nxt;

	u32	snd_una;

	u32	snd_wnd;

	u32	snd_cwnd;

	u32	ssthresh;

	u32	srtt;

};

static struct {

	spinlock_t	lock;

	wait_queue_head_t wait;

	ktime_t		start;

	u32		lastcwnd;

	unsigned long	head, tail;

	struct tcp_log	*log;

} tcp_probe;

static inline int tcp_probe_used(void)

{

	return (tcp_probe.head - tcp_probe.tail) % bufsize;

}

static inline int tcp_probe_avail(void)

{

	return bufsize - tcp_probe_used();

}

/*

 * Hook inserted to be called before each receive packet.

 * Note: arguments must match tcp_rcv_established()!

 */

static int jtcp_rcv_established(struct sock *sk, struct sk_buff *skb,

			       struct tcphdr *th, unsigned len)

{

	const struct tcp_sock *tp = tcp_sk(sk);

	const struct inet_sock *inet = inet_sk(sk);

	/* Only update if port matches */

	if ((port == 0 || ntohs(inet->dport) == port || ntohs(inet->sport) == port)

	    && (full || tp->snd_cwnd != tcp_probe.lastcwnd)) {

		spin_lock(&tcp_probe.lock);

		/* If log fills, just silently drop */

		if (tcp_probe_avail() > 1) {

			struct tcp_log *p = tcp_probe.log + tcp_probe.head;

			p->tstamp = ktime_get();

			p->saddr = inet->saddr;

			p->sport = inet->sport;

			p->daddr = inet->daddr;

			p->dport = inet->dport;

			p->length = skb->len;

			p->snd_nxt = tp->snd_nxt;

			p->snd_una = tp->snd_una;

			p->snd_cwnd = tp->snd_cwnd;

			p->snd_wnd = tp->snd_wnd;

			p->ssthresh = tcp_current_ssthresh(sk);

			p->srtt = tp->srtt >> 3;

			tcp_probe.head = (tcp_probe.head + 1) % bufsize;

		}

		tcp_probe.lastcwnd = tp->snd_cwnd;

		spin_unlock(&tcp_probe.lock);

		wake_up(&tcp_probe.wait);

	}

	jprobe_return();

	return 0;

}

static struct jprobe tcp_jprobe = {

	.kp = {

		.symbol_name	= "tcp_rcv_established",

	},

	.entry	= jtcp_rcv_established,

};

static int tcpprobe_open(struct inode * inode, struct file * file)

{

	/* Reset (empty) log */

	spin_lock_bh(&tcp_probe.lock);

	tcp_probe.head = tcp_probe.tail = 0;

	tcp_probe.start = ktime_get();

	spin_unlock_bh(&tcp_probe.lock);

	return 0;

}

static int tcpprobe_sprint(char *tbuf, int n)

{

	const struct tcp_log *p

		= tcp_probe.log + tcp_probe.tail % bufsize;

	struct timespec tv

		= ktime_to_timespec(ktime_sub(p->tstamp, tcp_probe.start));

	return snprintf(tbuf, n,

			(unsigned long) tv.tv_sec,

			(unsigned long) tv.tv_nsec,

			p->length, p->snd_nxt, p->snd_una,

			p->snd_cwnd, p->ssthresh, p->snd_wnd, p->srtt);

}

static ssize_t tcpprobe_read(struct file *file, char __user *buf,

			     size_t len, loff_t *ppos)

{

	int error = 0, cnt = 0;

	if (!buf || len < 0)

		return -EINVAL;

	while (cnt < len) {

		char tbuf[128];

		int width;

		/* Wait for data in buffer */

		error = wait_event_interruptible(tcp_probe.wait,

						 tcp_probe_used() > 0);

		if (error)

			break;

		spin_lock_bh(&tcp_probe.lock);

		if (tcp_probe.head == tcp_probe.tail) {

			/* multiple readers race? */

			spin_unlock_bh(&tcp_probe.lock);

			continue;

		}

		width = tcpprobe_sprint(tbuf, sizeof(tbuf));

		if (cnt + width < len)

			tcp_probe.tail = (tcp_probe.tail + 1) % bufsize;

		spin_unlock_bh(&tcp_probe.lock);

		/* if record greater than space available

		   return partial buffer (so far) */

		if (cnt + width >= len)

			break;

		if (copy_to_user(buf + cnt, tbuf, width))

			return -EFAULT;

		cnt += width;

	}

	return cnt == 0 ? error : cnt;

}

static const struct file_operations tcpprobe_fops = {

	.owner	 = THIS_MODULE,

	.open	 = tcpprobe_open,

	.read    = tcpprobe_read,

};

static __init int tcpprobe_init(void)

{

	int ret = -ENOMEM;

	init_waitqueue_head(&tcp_probe.wait);

	spin_lock_init(&tcp_probe.lock);

	if (bufsize < 0)

		return -EINVAL;

	tcp_probe.log = kcalloc(bufsize, sizeof(struct tcp_log), GFP_KERNEL);

	if (!tcp_probe.log)

		goto err0;

	if (!proc_net_fops_create(&init_net, procname, S_IRUSR, &tcpprobe_fops))

		goto err0;

	ret = register_jprobe(&tcp_jprobe);

	if (ret)

		goto err1;

	pr_info("TCP probe registered (port=%d)\n", port);

	return 0;

 err1:

	proc_net_remove(&init_net, procname);

 err0:

	kfree(tcp_probe.log);

	return ret;

}

module_init(tcpprobe_init);

static __exit void tcpprobe_exit(void)

{

	proc_net_remove(&init_net, procname);

	unregister_jprobe(&tcp_jprobe);

	kfree(tcp_probe.log);

}

module_exit(tcpprobe_exit);