[TCP]: TCP Probe congestion window tracing

This adds a new module for tracking TCP state variables non-intrusively
using kprobes.  It has a simple /proc interface that outputs one line
for each packet received. A sample usage is to collect congestion
window and ssthresh over time graphs.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 180 insertions, 0 deletions

diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile
index f30faefc2672..38b8039bdd55 100644
--- a/net/ipv4/Makefile
+++ b/net/ipv4/Makefile
@@ -36,6 +36,7 @@ obj-$(CONFIG_IP_VS) += ipvs/
 obj-$(CONFIG_INET_DIAG) += inet_diag.o 
 obj-$(CONFIG_IP_ROUTE_MULTIPATH_CACHED) += multipath.o
 obj-$(CONFIG_INET_TCP_DIAG) += tcp_diag.o
+obj-$(CONFIG_NET_TCPPROBE) += tcp_probe.o
 obj-$(CONFIG_TCP_CONG_BIC) += tcp_bic.o
 obj-$(CONFIG_TCP_CONG_CUBIC) += tcp_cubic.o
 obj-$(CONFIG_TCP_CONG_WESTWOOD) += tcp_westwood.o
diff --git a/net/ipv4/tcp_probe.c b/net/ipv4/tcp_probe.c
new file mode 100644
index 000000000000..be94d526c7cb
--- /dev/null
+++ b/net/ipv4/tcp_probe.c
@@ -0,0 +1,179 @@
+/*
+ * 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, 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.
+ *
+ * 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/kfifo.h>
+#include <linux/vmalloc.h>
+
+#include <net/tcp.h>
+
+MODULE_AUTHOR("Stephen Hemminger <shemminger@osdl.org>");
+MODULE_DESCRIPTION("TCP cwnd snooper");
+MODULE_LICENSE("GPL");
+
+static int port = 0;
+MODULE_PARM_DESC(port, "Port to match (0=all)");
+module_param(port, int, 0);
+
+static int bufsize = 64*1024;
+MODULE_PARM_DESC(bufsize, "Log buffer size (default 64k)");
+module_param(bufsize, int, 0);
+
+static const char procname[] = "tcpprobe";
+
+struct {
+        struct kfifo  *fifo;
+        spinlock_t    lock;
+        wait_queue_head_t wait;
+        struct timeval tstart;
+} tcpw;
+
+static void printl(const char *fmt, ...)
+{
+        va_list args;
+        int len;
+        struct timeval now;
+        char tbuf[256];
+
+        va_start(args, fmt);
+        do_gettimeofday(&now);
+
+        now.tv_sec -= tcpw.tstart.tv_sec;
+        now.tv_usec -= tcpw.tstart.tv_usec;
+        if (now.tv_usec < 0) {
+                --now.tv_sec;
+                now.tv_usec += 1000000;
+        }
+
+        len = sprintf(tbuf, "%lu.%06lu ", now.tv_sec, now.tv_usec);
+        len += vscnprintf(tbuf+len, sizeof(tbuf)-len, fmt, args);
+        va_end(args);
+
+        kfifo_put(tcpw.fifo, tbuf, len);
+        wake_up(&tcpw.wait);
+}
+
+static int jtcp_sendmsg(struct kiocb *iocb, struct sock *sk,
+                        struct msghdr *msg, size_t size)
+{
+        const struct tcp_sock *tp = tcp_sk(sk);
+        const struct inet_sock *inet = inet_sk(sk);
+
+        if (port == 0 || ntohs(inet->dport) == port ||
+            ntohs(inet->sport) == port) {
+                printl("%d.%d.%d.%d:%u %d.%d.%d.%d:%u %d %#x %#x %u %u %u\n",
+                       NIPQUAD(inet->saddr), ntohs(inet->sport),
+                       NIPQUAD(inet->daddr), ntohs(inet->dport),
+                       size, tp->snd_nxt, tp->snd_una,
+                       tp->snd_cwnd, tcp_current_ssthresh(sk),
+                       tp->snd_wnd);
+        }
+
+        jprobe_return();
+        return 0;
+}
+
+static struct jprobe tcp_send_probe = {
+        .kp = { .addr = (kprobe_opcode_t *) &tcp_sendmsg, },
+        .entry = (kprobe_opcode_t *) &jtcp_sendmsg,
+};
+
+
+static int tcpprobe_open(struct inode * inode, struct file * file)
+{
+        kfifo_reset(tcpw.fifo);
+        do_gettimeofday(&tcpw.tstart);
+        return 0;
+}
+
+static ssize_t tcpprobe_read(struct file *file, char __user *buf,
+                             size_t len, loff_t *ppos)
+{
+        int error = 0, cnt;
+        unsigned char *tbuf;
+
+        if (!buf || len < 0)
+                return -EINVAL;
+
+        if (len == 0)
+                return 0;
+
+        tbuf = vmalloc(len);
+        if (!tbuf)
+                return -ENOMEM;
+
+        error = wait_event_interruptible(tcpw.wait,
+                                         __kfifo_len(tcpw.fifo) != 0);
+        if (error)
+                return error;
+
+        cnt = kfifo_get(tcpw.fifo, tbuf, len);
+        error = copy_to_user(buf, tbuf, cnt);
+
+        vfree(tbuf);
+
+        return error ? error : cnt;
+}
+
+static 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(&tcpw.wait);
+        spin_lock_init(&tcpw.lock);
+        tcpw.fifo = kfifo_alloc(bufsize, GFP_KERNEL, &tcpw.lock);
+
+        if (!proc_net_fops_create(procname, S_IRUSR, &tcpprobe_fops))
+                goto err0;
+
+        ret = register_jprobe(&tcp_send_probe);
+        if (ret)
+                goto err1;
+
+        pr_info("TCP watch registered (port=%d)\n", port);
+        return 0;
+ err1:
+        proc_net_remove(procname);
+ err0:
+        kfifo_free(tcpw.fifo);
+        return ret;
+}
+module_init(tcpprobe_init);
+
+static __exit void tcpprobe_exit(void)
+{
+        kfifo_free(tcpw.fifo);
+        proc_net_remove(procname);
+        unregister_jprobe(&tcp_send_probe);
+
+}
+module_exit(tcpprobe_exit);