Author: hiren
Date: Wed Oct 14 00:35:37 2015
New Revision: 289276
URL: https://svnweb.freebsd.org/changeset/base/289276

Log:
  There are times when it would be really nice to have a record of the last few
  packets and/or state transitions from each TCP socket. That would help with
  narrowing down certain problems we see in the field that are hard to reproduce
  without understanding the history of how we got into a certain state. This
  change provides just that.
  
  It saves copies of the last N packets in a list in the tcpcb. When the tcpcb 
is
  destroyed, the list is freed. I thought this was likely to be more
  performance-friendly than saving copies of the tcpcb. Plus, with the packets,
  you should be able to reverse-engineer what happened to the tcpcb.
  
  To enable the feature, you will need to compile a kernel with the TCPPCAP
  option. Even then, the feature defaults to being deactivated. You can activate
  it by setting a positive value for the number of captured packets. You can do
  that on either a global basis or on a per-socket basis (via a setsockopt 
call).
  
  There is no way to get the packets out of the kernel other than using kmem or
  getting a coredump. I thought that would help some of the legal/privacy 
concerns
  regarding such a feature. However, it should be possible to add a future 
effort
  to export them in PCAP format.
  
  I tested this at low scale, and found that there were no mbuf leaks and the 
peak
  mbuf usage appeared to be unchanged with and without the feature.
  
  The main performance concern I can envision is the number of mbufs that would 
be
  used on systems with a large number of sockets. If you save five packets per
  direction per socket and have 3,000 sockets, that will consume at least 30,000
  mbufs just to keep these packets. I tried to reduce the concerns associated 
with
  this by limiting the number of clusters (not mbufs) that could be used for 
this
  feature. Again, in my testing, that appears to work correctly.
  
  Differential Revision:        D3100
  Submitted by:         Jonathan Looney <jlooney at juniper dot net>
  Reviewed by:          gnn, hiren

Added:
  head/sys/netinet/tcp_pcap.c   (contents, props changed)
  head/sys/netinet/tcp_pcap.h   (contents, props changed)
Modified:
  head/sys/conf/NOTES
  head/sys/conf/files
  head/sys/conf/options
  head/sys/kern/uipc_mbuf.c
  head/sys/netinet/tcp.h
  head/sys/netinet/tcp_input.c
  head/sys/netinet/tcp_output.c
  head/sys/netinet/tcp_subr.c
  head/sys/netinet/tcp_usrreq.c
  head/sys/netinet/tcp_var.h
  head/sys/sys/mbuf.h

Modified: head/sys/conf/NOTES
==============================================================================
--- head/sys/conf/NOTES Wed Oct 14 00:23:31 2015        (r289275)
+++ head/sys/conf/NOTES Wed Oct 14 00:35:37 2015        (r289276)
@@ -960,6 +960,9 @@ device              lagg
 # for sockets with the SO_DEBUG option set, which can then be examined
 # using the trpt(8) utility.
 #
+# TCPPCAP enables code which keeps the last n packets sent and received
+# on a TCP socket.
+#
 # RADIX_MPATH provides support for equal-cost multi-path routing.
 #
 options        MROUTING                # Multicast routing
@@ -976,6 +979,7 @@ options     IPFILTER_DEFAULT_BLOCK  #block a
 options        IPSTEALTH               #support for stealth forwarding
 options        PF_DEFAULT_TO_DROP      #drop everything by default
 options        TCPDEBUG
+options        TCPPCAP
 options        RADIX_MPATH
 
 # The MBUF_STRESS_TEST option enables options which create

Modified: head/sys/conf/files
==============================================================================
--- head/sys/conf/files Wed Oct 14 00:23:31 2015        (r289275)
+++ head/sys/conf/files Wed Oct 14 00:35:37 2015        (r289276)
@@ -3682,6 +3682,7 @@ netinet/tcp_input.c               optional inet | ine
 netinet/tcp_lro.c              optional inet | inet6
 netinet/tcp_output.c           optional inet | inet6
 netinet/tcp_offload.c          optional tcp_offload inet | tcp_offload inet6
+netinet/tcp_pcap.c             optional tcppcap
 netinet/tcp_reass.c            optional inet | inet6
 netinet/tcp_sack.c             optional inet | inet6
 netinet/tcp_subr.c             optional inet | inet6

Modified: head/sys/conf/options
==============================================================================
--- head/sys/conf/options       Wed Oct 14 00:23:31 2015        (r289275)
+++ head/sys/conf/options       Wed Oct 14 00:35:37 2015        (r289276)
@@ -436,6 +436,7 @@ ROUTETABLES         opt_route.h
 RSS                    opt_rss.h
 SLIP_IFF_OPTS          opt_slip.h
 TCPDEBUG
+TCPPCAP                opt_global.h
 SIFTR
 TCP_OFFLOAD            opt_inet.h # Enable code to dispatch TCP offloading
 TCP_SIGNATURE          opt_inet.h

Modified: head/sys/kern/uipc_mbuf.c
==============================================================================
--- head/sys/kern/uipc_mbuf.c   Wed Oct 14 00:23:31 2015        (r289275)
+++ head/sys/kern/uipc_mbuf.c   Wed Oct 14 00:35:37 2015        (r289276)
@@ -395,7 +395,7 @@ mb_free_ext(struct mbuf *m)
  * Attach the cluster from *m to *n, set up m_ext in *n
  * and bump the refcount of the cluster.
  */
-static void
+void
 mb_dupcl(struct mbuf *n, const struct mbuf *m)
 {
 

Modified: head/sys/netinet/tcp.h
==============================================================================
--- head/sys/netinet/tcp.h      Wed Oct 14 00:23:31 2015        (r289275)
+++ head/sys/netinet/tcp.h      Wed Oct 14 00:35:37 2015        (r289276)
@@ -165,6 +165,8 @@ struct tcphdr {
 #define        TCP_KEEPIDLE    256     /* L,N,X start keeplives after this 
period */
 #define        TCP_KEEPINTVL   512     /* L,N interval between keepalives */
 #define        TCP_KEEPCNT     1024    /* L,N number of keepalives before 
close */
+#define        TCP_PCAP_OUT    2048    /* number of output packets to keep */
+#define        TCP_PCAP_IN     4096    /* number of input packets to keep */
 
 /* Start of reserved space for third-party user-settable options. */
 #define        TCP_VENDOR      SO_VENDOR

Modified: head/sys/netinet/tcp_input.c
==============================================================================
--- head/sys/netinet/tcp_input.c        Wed Oct 14 00:23:31 2015        
(r289275)
+++ head/sys/netinet/tcp_input.c        Wed Oct 14 00:35:37 2015        
(r289276)
@@ -104,6 +104,9 @@ __FBSDID("$FreeBSD$");
 #include <netinet/tcp_var.h>
 #include <netinet6/tcp6_var.h>
 #include <netinet/tcpip.h>
+#ifdef TCPPCAP
+#include <netinet/tcp_pcap.h>
+#endif
 #include <netinet/tcp_syncache.h>
 #ifdef TCPDEBUG
 #include <netinet/tcp_debug.h>
@@ -1524,6 +1527,11 @@ tcp_do_segment(struct mbuf *m, struct tc
        KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
            __func__));
 
+#ifdef TCPPCAP
+       /* Save segment, if requested. */
+       tcp_pcap_add(th, m, &(tp->t_inpkts));
+#endif
+
        /*
         * Segment received on connection.
         * Reset idle time and keep-alive timer.

Modified: head/sys/netinet/tcp_output.c
==============================================================================
--- head/sys/netinet/tcp_output.c       Wed Oct 14 00:23:31 2015        
(r289275)
+++ head/sys/netinet/tcp_output.c       Wed Oct 14 00:35:37 2015        
(r289276)
@@ -74,6 +74,9 @@ __FBSDID("$FreeBSD$");
 #include <netinet/tcp_timer.h>
 #include <netinet/tcp_var.h>
 #include <netinet/tcpip.h>
+#ifdef TCPPCAP
+#include <netinet/tcp_pcap.h>
+#endif
 #ifdef TCPDEBUG
 #include <netinet/tcp_debug.h>
 #endif
@@ -1305,6 +1308,11 @@ send:
 
                TCP_PROBE5(send, NULL, tp, ip6, tp, th);
 
+#ifdef TCPPCAP
+               /* Save packet, if requested. */
+               tcp_pcap_add(th, m, &(tp->t_outpkts));
+#endif
+
                /* TODO: IPv6 IP6TOS_ECT bit on */
                error = ip6_output(m, tp->t_inpcb->in6p_outputopts, &ro,
                    ((so->so_options & SO_DONTROUTE) ?  IP_ROUTETOIF : 0),
@@ -1348,6 +1356,11 @@ send:
 
        TCP_PROBE5(send, NULL, tp, ip, tp, th);
 
+#ifdef TCPPCAP
+       /* Save packet, if requested. */
+       tcp_pcap_add(th, m, &(tp->t_outpkts));
+#endif
+
        error = ip_output(m, tp->t_inpcb->inp_options, &ro,
            ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
            tp->t_inpcb);

Added: head/sys/netinet/tcp_pcap.c
==============================================================================
--- /dev/null   00:00:00 1970   (empty, because file is newly added)
+++ head/sys/netinet/tcp_pcap.c Wed Oct 14 00:35:37 2015        (r289276)
@@ -0,0 +1,437 @@
+/*-
+ * Copyright (c) 2015
+ *     Jonathan Looney. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#include <sys/queue.h>
+#include <sys/param.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/socketvar.h>
+#include <sys/sysctl.h>
+#include <sys/systm.h>
+#include <sys/mbuf.h>
+#include <sys/eventhandler.h>
+#include <machine/atomic.h>
+#include <netinet/tcp_var.h>
+#include <netinet/tcp_pcap.h>
+
+#define M_LEADINGSPACE_NOWRITE(m)                                      \
+       ((m)->m_data - M_START(m))
+
+static int tcp_pcap_clusters_referenced_cur = 0;
+static int tcp_pcap_clusters_referenced_max = 0;
+
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_pcap_clusters_referenced_cur,
+       CTLFLAG_RD, &tcp_pcap_clusters_referenced_cur, 0,
+       "Number of clusters currently referenced on TCP PCAP queues");
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_pcap_clusters_referenced_max,
+       CTLFLAG_RW, &tcp_pcap_clusters_referenced_max, 0,
+       "Maximum number of clusters allowed to be referenced on TCP PCAP "
+       "queues");
+
+static int tcp_pcap_alloc_reuse_ext = 0;
+static int tcp_pcap_alloc_reuse_mbuf = 0;
+static int tcp_pcap_alloc_new_mbuf = 0;
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_pcap_alloc_reuse_ext,
+       CTLFLAG_RD, &tcp_pcap_alloc_reuse_ext, 0,
+       "Number of mbufs with external storage reused for the TCP PCAP "
+       "functionality");
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_pcap_alloc_reuse_mbuf,
+       CTLFLAG_RD, &tcp_pcap_alloc_reuse_mbuf, 0,
+       "Number of mbufs with internal storage reused for the TCP PCAP "
+       "functionality");
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_pcap_alloc_new_mbuf,
+       CTLFLAG_RD, &tcp_pcap_alloc_new_mbuf, 0,
+       "Number of new mbufs allocated for the TCP PCAP functionality");
+
+VNET_DEFINE(int, tcp_pcap_packets) = 0;
+#define V_tcp_pcap_packets     VNET(tcp_pcap_packets)
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_pcap_packets, CTLFLAG_RW,
+       &V_tcp_pcap_packets, 0, "Default number of packets saved per direction "
+       "per TCPCB");
+
+/* Initialize the values. */
+static void
+tcp_pcap_max_set() {
+       tcp_pcap_clusters_referenced_max = nmbclusters / 4;
+}
+
+void
+tcp_pcap_init() {
+       tcp_pcap_max_set();
+       EVENTHANDLER_REGISTER(nmbclusters_change, tcp_pcap_max_set,
+               NULL, EVENTHANDLER_PRI_ANY);
+}
+
+/*
+ * If we are below the maximum allowed cluster references,
+ * increment the reference count and return TRUE. Otherwise,
+ * leave the reference count alone and return FALSE.
+ */
+static __inline bool
+tcp_pcap_take_cluster_reference(void)
+{
+       if (atomic_fetchadd_int(&tcp_pcap_clusters_referenced_cur, 1) >=
+               tcp_pcap_clusters_referenced_max) {
+               atomic_add_int(&tcp_pcap_clusters_referenced_cur, -1);
+               return FALSE;
+       }
+       return TRUE;
+}
+
+/*
+ * For all the external entries in m, apply the given adjustment.
+ * This can be used to adjust the counter when an mbuf chain is
+ * copied or freed.
+ */
+static __inline void
+tcp_pcap_adj_cluster_reference(struct mbuf *m, int adj)
+{
+       while (m) {
+               if (m->m_flags & M_EXT)
+                       atomic_add_int(&tcp_pcap_clusters_referenced_cur, adj);
+
+               m = m->m_next;
+       }
+}
+
+/*
+ * Free all mbufs in a chain, decrementing the reference count as
+ * necessary.
+ *
+ * Functions in this file should use this instead of m_freem() when
+ * they are freeing mbuf chains that may contain clusters that were
+ * already included in tcp_pcap_clusters_referenced_cur.
+ */
+static void
+tcp_pcap_m_freem(struct mbuf *mb)
+{
+       while (mb != NULL) {
+               if (mb->m_flags & M_EXT)
+                       atomic_subtract_int(&tcp_pcap_clusters_referenced_cur,
+                           1);
+               mb = m_free(mb);
+       }
+}
+
+/*
+ * Copy data from m to n, where n cannot fit all the data we might
+ * want from m.
+ *
+ * Prioritize data like this:
+ * 1. TCP header
+ * 2. IP header
+ * 3. Data
+ */
+static void
+tcp_pcap_copy_bestfit(struct tcphdr *th, struct mbuf *m, struct mbuf *n)
+{
+       struct mbuf *m_cur = m;
+       int bytes_to_copy=0, trailing_data, skip=0, tcp_off;
+
+       /* Below, we assume these will be non-NULL. */
+       KASSERT(th, ("%s: called with th == NULL", __func__));
+       KASSERT(m, ("%s: called with m == NULL", __func__));
+       KASSERT(n, ("%s: called with n == NULL", __func__));
+
+       /* We assume this initialization occurred elsewhere. */
+       KASSERT(n->m_len == 0, ("%s: called with n->m_len=%d (expected 0)",
+               __func__, n->m_len));
+       KASSERT(n->m_data == M_START(n),
+               ("%s: called with n->m_data != M_START(n)", __func__));
+
+       /*
+        * Calculate the size of the TCP header. We use this often
+        * enough that it is worth just calculating at the start.
+        */
+       tcp_off = th->th_off << 2;
+
+       /* Trim off leading empty mbufs. */
+       while (m && m->m_len == 0)
+               m = m->m_next;
+
+       if (m) {
+               m_cur = m;
+       }
+       else {
+               /*
+                * No data? Highly unusual. We would expect to at
+                * least see a TCP header in the mbuf.
+                * As we have a pointer to the TCP header, I guess
+                * we should just copy that. (???)
+                */
+fallback:
+               bytes_to_copy = tcp_off;
+               if (bytes_to_copy > M_SIZE(n))
+                       bytes_to_copy = M_SIZE(n);
+               bcopy(th, n->m_data, bytes_to_copy);
+               n->m_len = bytes_to_copy;
+               return;
+       }
+
+       /*
+        * Find TCP header. Record the total number of bytes up to,
+        * and including, the TCP header.
+        */
+       while (m_cur) {
+               if ((caddr_t) th >= (caddr_t) m_cur->m_data &&
+                       (caddr_t) th < (caddr_t) (m_cur->m_data + m_cur->m_len))
+                       break;
+               bytes_to_copy += m_cur->m_len;
+               m_cur = m_cur->m_next;
+       }
+       if (m_cur)
+               bytes_to_copy += (caddr_t) th - (caddr_t) m_cur->m_data;
+       else
+               goto fallback;
+       bytes_to_copy += tcp_off;
+
+       /*
+        * If we already want to copy more bytes than we can hold
+        * in the destination mbuf, skip leading bytes and copy
+        * what we can.
+        *
+        * Otherwise, consider trailing data.
+        */
+       if (bytes_to_copy > M_SIZE(n)) {
+               skip  = bytes_to_copy - M_SIZE(n);
+               bytes_to_copy = M_SIZE(n);
+       }
+       else {
+               /*
+                * Determine how much trailing data is in the chain.
+                * We start with the length of this mbuf (the one
+                * containing th) and subtract the size of the TCP
+                * header (tcp_off) and the size of the data prior
+                * to th (th - m_cur->m_data).
+                *
+                * This *should not* be negative, as the TCP code
+                * should put the whole TCP header in a single
+                * mbuf. But, it isn't a problem if it is. We will
+                * simple work off our negative balance as we look
+                * at subsequent mbufs.
+                */
+               trailing_data = m_cur->m_len - tcp_off;
+               trailing_data -= (caddr_t) th - (caddr_t) m_cur->m_data;
+               m_cur = m_cur->m_next;
+               while (m_cur) {
+                       trailing_data += m_cur->m_len;
+                       m_cur = m_cur->m_next;
+               }
+               if ((bytes_to_copy + trailing_data) > M_SIZE(n))
+                       bytes_to_copy = M_SIZE(n);
+               else
+                       bytes_to_copy += trailing_data;
+       }
+
+       m_copydata(m, skip, bytes_to_copy, n->m_data);
+       n->m_len = bytes_to_copy;
+}
+
+void
+tcp_pcap_add(struct tcphdr *th, struct mbuf *m, struct mbufq *queue)
+{
+       struct mbuf *n = NULL, *mhead;
+
+       KASSERT(th, ("%s: called with th == NULL", __func__));
+       KASSERT(m, ("%s: called with m == NULL", __func__));
+       KASSERT(queue, ("%s: called with queue == NULL", __func__));
+
+       /* We only care about data packets. */
+       while (m && m->m_type != MT_DATA)
+               m = m->m_next;
+
+       /* We only need to do something if we still have an mbuf. */
+       if (!m)
+               return;
+
+       /* If we are not saving mbufs, return now. */
+       if (queue->mq_maxlen == 0)
+               return;
+
+       /*
+        * Check to see if we will need to recycle mbufs.
+        *
+        * If we need to get rid of mbufs to stay below
+        * our packet count, try to reuse the mbuf. Once
+        * we already have a new mbuf (n), then we can
+        * simply free subsequent mbufs.
+        *
+        * Note that most of the logic in here is to deal
+        * with the reuse. If we are fine with constant
+        * mbuf allocs/deallocs, we could ditch this logic.
+        * But, it only seems to make sense to reuse
+        * mbufs we already have.
+        */
+       while (mbufq_full(queue)) {
+               mhead = mbufq_dequeue(queue);
+
+               if (n) {
+                       tcp_pcap_m_freem(mhead);
+               }
+               else {
+                       /*
+                        * If this held an external cluster, try to
+                        * detach the cluster. But, if we held the
+                        * last reference, go through the normal
+                        * free-ing process.
+                        */
+                       if (mhead->m_flags & M_EXT) {
+                               switch (mhead->m_ext.ext_type) {
+                               case EXT_SFBUF:
+                                       /* Don't mess around with these. */
+                                       tcp_pcap_m_freem(mhead);
+                                       continue;
+                               default:
+                                       if (atomic_fetchadd_int(
+                                               mhead->m_ext.ext_cnt, -1) == 1)
+                                       {
+                                               /*
+                                                * We held the last reference
+                                                * on this cluster. Restore
+                                                * the reference count and put
+                                                * it back in the pool.
+                                                */
+                                               *(mhead->m_ext.ext_cnt) = 1;
+                                               tcp_pcap_m_freem(mhead);
+                                               continue;
+                                       }
+                                       /*
+                                        * We were able to cleanly free the
+                                        * reference.
+                                        */
+                                       atomic_subtract_int(
+                                           &tcp_pcap_clusters_referenced_cur,
+                                           1);
+                                       tcp_pcap_alloc_reuse_ext++;
+                                       break;
+                               }
+                       }
+                       else {
+                               tcp_pcap_alloc_reuse_mbuf++;
+                       }
+
+                       n = mhead;
+                       tcp_pcap_m_freem(n->m_next);
+                       m_init(n, NULL, 0, M_NOWAIT, MT_DATA, 0);
+               }
+       }
+
+       /* Check to see if we need to get a new mbuf. */
+       if (!n) {
+               if (!(n = m_get(M_NOWAIT, MT_DATA)))
+                       return;
+               tcp_pcap_alloc_new_mbuf++;
+       }
+
+       /*
+        * What are we dealing with? If a cluster, attach it. Otherwise,
+        * try to copy the data from the beginning of the mbuf to the
+        * end of data. (There may be data between the start of the data
+        * area and the current data pointer. We want to get this, because
+        * it may contain header information that is useful.)
+        * In cases where that isn't possible, settle for what we can
+        * get.
+        */
+       if ((m->m_flags & M_EXT) && tcp_pcap_take_cluster_reference()) {
+               n->m_data = m->m_data;
+               n->m_len = m->m_len;
+               mb_dupcl(n, m);
+       }
+       else if (((m->m_data + m->m_len) - M_START(m)) <= M_SIZE(n)) {
+               /*
+                * At this point, n is guaranteed to be a normal mbuf
+                * with no cluster and no packet header. Because the
+                * logic in this code block requires this, the assert
+                * is here to catch any instances where someone
+                * changes the logic to invalidate that assumption.
+                */
+               KASSERT((n->m_flags & (M_EXT | M_PKTHDR)) == 0,
+                       ("%s: Unexpected flags (%#x) for mbuf",
+                       __func__, n->m_flags));
+               n->m_data = n->m_dat + M_LEADINGSPACE_NOWRITE(m);
+               n->m_len = m->m_len;
+               bcopy(M_START(m), n->m_dat,
+                       m->m_len + M_LEADINGSPACE_NOWRITE(m));
+       }
+       else {
+               /*
+                * This is the case where we need to "settle for what
+                * we can get". The most probable way to this code
+                * path is that we've already taken references to the
+                * maximum number of mbuf clusters we can, and the data
+                * is too long to fit in an mbuf's internal storage.
+                * Try for a "best fit".
+                */
+               tcp_pcap_copy_bestfit(th, m, n);
+
+               /* Don't try to get additional data. */
+               goto add_to_queue;
+       }
+
+       if (m->m_next) {
+               n->m_next = m_copym(m->m_next, 0, M_COPYALL, M_NOWAIT);
+               tcp_pcap_adj_cluster_reference(n->m_next, 1);
+       }
+
+add_to_queue:
+       /* Add the new mbuf to the list. */
+       if (mbufq_enqueue(queue, n)) {
+               /* This shouldn't happen. If INVARIANTS is defined, panic. */
+               KASSERT(0, ("%s: mbufq was unexpectedly full!", __func__));
+               tcp_pcap_m_freem(n);
+       }
+}
+
+void
+tcp_pcap_drain(struct mbufq *queue)
+{
+       struct mbuf *m;
+       while ((m = mbufq_dequeue(queue)))
+               tcp_pcap_m_freem(m);
+}
+
+void
+tcp_pcap_tcpcb_init(struct tcpcb *tp)
+{
+       mbufq_init(&(tp->t_inpkts), V_tcp_pcap_packets);
+       mbufq_init(&(tp->t_outpkts), V_tcp_pcap_packets);
+}
+
+void
+tcp_pcap_set_sock_max(struct mbufq *queue, int newval)
+{
+       queue->mq_maxlen = newval;
+       while (queue->mq_len > queue->mq_maxlen)
+               tcp_pcap_m_freem(mbufq_dequeue(queue));
+}
+
+int
+tcp_pcap_get_sock_max(struct mbufq *queue)
+{
+       return queue->mq_maxlen;
+}

Added: head/sys/netinet/tcp_pcap.h
==============================================================================
--- /dev/null   00:00:00 1970   (empty, because file is newly added)
+++ head/sys/netinet/tcp_pcap.h Wed Oct 14 00:35:37 2015        (r289276)
@@ -0,0 +1,39 @@
+/*-
+ * Copyright (c) 2015
+ *     Jonathan Looney. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#ifndef _NETINET_TCP_PCAP_H_
+#define _NETINET_TCP_PCAP_H_
+
+void tcp_pcap_init(void);
+void tcp_pcap_add(struct tcphdr *th, struct mbuf *m, struct mbufq *queue);
+void tcp_pcap_drain(struct mbufq *queue);
+void tcp_pcap_tcpcb_init(struct tcpcb *tp);
+void tcp_pcap_set_sock_max(struct mbufq *queue, int newval);
+int tcp_pcap_get_sock_max(struct mbufq *queue);
+
+#endif /* _NETINET_TCP_PCAP_H_ */

Modified: head/sys/netinet/tcp_subr.c
==============================================================================
--- head/sys/netinet/tcp_subr.c Wed Oct 14 00:23:31 2015        (r289275)
+++ head/sys/netinet/tcp_subr.c Wed Oct 14 00:35:37 2015        (r289276)
@@ -92,6 +92,9 @@ __FBSDID("$FreeBSD$");
 #include <netinet6/tcp6_var.h>
 #endif
 #include <netinet/tcpip.h>
+#ifdef TCPPCAP
+#include <netinet/tcp_pcap.h>
+#endif
 #ifdef TCPDEBUG
 #include <netinet/tcp_debug.h>
 #endif
@@ -427,6 +430,9 @@ tcp_init(void)
                SHUTDOWN_PRI_DEFAULT);
        EVENTHANDLER_REGISTER(maxsockets_change, tcp_zone_change, NULL,
                EVENTHANDLER_PRI_ANY);
+#ifdef TCPPCAP
+       tcp_pcap_init();
+#endif
 }
 
 #ifdef VIMAGE
@@ -832,6 +838,12 @@ tcp_newtcpcb(struct inpcb *inp)
         */
        inp->inp_ip_ttl = V_ip_defttl;
        inp->inp_ppcb = tp;
+#ifdef TCPPCAP
+       /*
+        * Init the TCP PCAP queues.
+        */
+       tcp_pcap_tcpcb_init(tp);
+#endif
        return (tp);            /* XXX */
 }
 
@@ -1016,6 +1028,12 @@ tcp_discardcb(struct tcpcb *tp)
                
        tcp_free_sackholes(tp);
 
+#ifdef TCPPCAP
+       /* Free the TCP PCAP queues. */
+       tcp_pcap_drain(&(tp->t_inpkts));
+       tcp_pcap_drain(&(tp->t_outpkts));
+#endif
+
        /* Allow the CC algorithm to clean up after itself. */
        if (CC_ALGO(tp)->cb_destroy != NULL)
                CC_ALGO(tp)->cb_destroy(tp->ccv);

Modified: head/sys/netinet/tcp_usrreq.c
==============================================================================
--- head/sys/netinet/tcp_usrreq.c       Wed Oct 14 00:23:31 2015        
(r289275)
+++ head/sys/netinet/tcp_usrreq.c       Wed Oct 14 00:35:37 2015        
(r289276)
@@ -86,6 +86,9 @@ __FBSDID("$FreeBSD$");
 #include <netinet/tcp_timer.h>
 #include <netinet/tcp_var.h>
 #include <netinet/tcpip.h>
+#ifdef TCPPCAP
+#include <netinet/tcp_pcap.h>
+#endif
 #ifdef TCPDEBUG
 #include <netinet/tcp_debug.h>
 #endif
@@ -1577,6 +1580,25 @@ unlock_and_done:
                                    TP_MAXIDLE(tp));
                        goto unlock_and_done;
 
+#ifdef TCPPCAP
+               case TCP_PCAP_OUT:
+               case TCP_PCAP_IN:
+                       INP_WUNLOCK(inp);
+                       error = sooptcopyin(sopt, &optval, sizeof optval,
+                           sizeof optval);
+                       if (error)
+                               return (error);
+
+                       INP_WLOCK_RECHECK(inp);
+                       if (optval >= 0)
+                               tcp_pcap_set_sock_max(TCP_PCAP_OUT ?
+                                       &(tp->t_outpkts) : &(tp->t_inpkts),
+                                       optval);
+                       else
+                               error = EINVAL;
+                       goto unlock_and_done;
+#endif
+
                default:
                        INP_WUNLOCK(inp);
                        error = ENOPROTOOPT;
@@ -1647,6 +1669,15 @@ unlock_and_done:
                        INP_WUNLOCK(inp);
                        error = sooptcopyout(sopt, &ui, sizeof(ui));
                        break;
+#ifdef TCPPCAP
+               case TCP_PCAP_OUT:
+               case TCP_PCAP_IN:
+                       optval = tcp_pcap_get_sock_max(TCP_PCAP_OUT ?
+                                       &(tp->t_outpkts) : &(tp->t_inpkts));
+                       INP_WUNLOCK(inp);
+                       error = sooptcopyout(sopt, &optval, sizeof optval);
+                       break;
+#endif
                default:
                        INP_WUNLOCK(inp);
                        error = ENOPROTOOPT;

Modified: head/sys/netinet/tcp_var.h
==============================================================================
--- head/sys/netinet/tcp_var.h  Wed Oct 14 00:23:31 2015        (r289275)
+++ head/sys/netinet/tcp_var.h  Wed Oct 14 00:35:37 2015        (r289276)
@@ -37,6 +37,7 @@
 
 #ifdef _KERNEL
 #include <net/vnet.h>
+#include <sys/mbuf.h>
 
 /*
  * Kernel variables for tcp.
@@ -204,7 +205,17 @@ struct tcpcb {
 
        uint32_t t_ispare[8];           /* 5 UTO, 3 TBD */
        void    *t_pspare2[4];          /* 1 TCP_SIGNATURE, 3 TBD */
-       uint64_t _pad[6];               /* 6 TBD (1-2 CC/RTT?) */
+#if defined(_KERNEL) && defined(TCPPCAP)
+       struct mbufq t_inpkts;          /* List of saved input packets. */
+       struct mbufq t_outpkts;         /* List of saved output packets. */
+#ifdef _LP64
+       uint64_t _pad[0];               /* all used! */
+#else
+       uint64_t _pad[2];               /* 2 are available */
+#endif /* _LP64 */
+#else
+       uint64_t _pad[6];
+#endif /* defined(_KERNEL) && defined(TCPPCAP) */
 };
 
 /*

Modified: head/sys/sys/mbuf.h
==============================================================================
--- head/sys/sys/mbuf.h Wed Oct 14 00:23:31 2015        (r289275)
+++ head/sys/sys/mbuf.h Wed Oct 14 00:35:37 2015        (r289276)
@@ -524,6 +524,7 @@ extern uma_zone_t   zone_jumbo9;
 extern uma_zone_t      zone_jumbo16;
 extern uma_zone_t      zone_ext_refcnt;
 
+void            mb_dupcl(struct mbuf *, const struct mbuf *);
 void            mb_free_ext(struct mbuf *);
 int             m_pkthdr_init(struct mbuf *, int);
 
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