Merge ^/head r343712 through r343806.

[FreeBSD/FreeBSD.git] / sys / netinet / tcp_log_buf.c

/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2016-2018 Netflix, Inc.
 *
 * 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.
 *
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mutex.h>
#include <sys/queue.h>
#include <sys/refcount.h>
#include <sys/rwlock.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/sysctl.h>
#include <sys/tree.h>
#include <sys/counter.h>

#include <dev/tcp_log/tcp_log_dev.h>

#include <net/if.h>
#include <net/if_var.h>
#include <net/vnet.h>

#include <netinet/in.h>
#include <netinet/in_pcb.h>
#include <netinet/in_var.h>
#include <netinet/tcp_var.h>
#include <netinet/tcp_log_buf.h>

/* Default expiry time */
#define TCP_LOG_EXPIRE_TIME     ((sbintime_t)60 * SBT_1S)

/* Max interval at which to run the expiry timer */
#define TCP_LOG_EXPIRE_INTVL    ((sbintime_t)5 * SBT_1S)

bool    tcp_log_verbose;
static uma_zone_t tcp_log_bucket_zone, tcp_log_node_zone, tcp_log_zone;
static int      tcp_log_session_limit = TCP_LOG_BUF_DEFAULT_SESSION_LIMIT;
static uint32_t tcp_log_version = TCP_LOG_BUF_VER;
RB_HEAD(tcp_log_id_tree, tcp_log_id_bucket);
static struct tcp_log_id_tree tcp_log_id_head;
static STAILQ_HEAD(, tcp_log_id_node) tcp_log_expireq_head =
    STAILQ_HEAD_INITIALIZER(tcp_log_expireq_head);
static struct mtx tcp_log_expireq_mtx;
static struct callout tcp_log_expireq_callout;
static u_long tcp_log_auto_ratio = 0;
static volatile u_long tcp_log_auto_ratio_cur = 0;
static uint32_t tcp_log_auto_mode = TCP_LOG_STATE_TAIL;
static bool tcp_log_auto_all = false;

RB_PROTOTYPE_STATIC(tcp_log_id_tree, tcp_log_id_bucket, tlb_rb, tcp_log_id_cmp)

SYSCTL_NODE(_net_inet_tcp, OID_AUTO, bb, CTLFLAG_RW, 0, "TCP Black Box controls");

SYSCTL_BOOL(_net_inet_tcp_bb, OID_AUTO, log_verbose, CTLFLAG_RW, &tcp_log_verbose,
    0, "Force verbose logging for TCP traces");

SYSCTL_INT(_net_inet_tcp_bb, OID_AUTO, log_session_limit,
    CTLFLAG_RW, &tcp_log_session_limit, 0,
    "Maximum number of events maintained for each TCP session");

SYSCTL_UMA_MAX(_net_inet_tcp_bb, OID_AUTO, log_global_limit, CTLFLAG_RW,
    &tcp_log_zone, "Maximum number of events maintained for all TCP sessions");

SYSCTL_UMA_CUR(_net_inet_tcp_bb, OID_AUTO, log_global_entries, CTLFLAG_RD,
    &tcp_log_zone, "Current number of events maintained for all TCP sessions");

SYSCTL_UMA_MAX(_net_inet_tcp_bb, OID_AUTO, log_id_limit, CTLFLAG_RW,
    &tcp_log_bucket_zone, "Maximum number of log IDs");

SYSCTL_UMA_CUR(_net_inet_tcp_bb, OID_AUTO, log_id_entries, CTLFLAG_RD,
    &tcp_log_bucket_zone, "Current number of log IDs");

SYSCTL_UMA_MAX(_net_inet_tcp_bb, OID_AUTO, log_id_tcpcb_limit, CTLFLAG_RW,
    &tcp_log_node_zone, "Maximum number of tcpcbs with log IDs");

SYSCTL_UMA_CUR(_net_inet_tcp_bb, OID_AUTO, log_id_tcpcb_entries, CTLFLAG_RD,
    &tcp_log_node_zone, "Current number of tcpcbs with log IDs");

SYSCTL_U32(_net_inet_tcp_bb, OID_AUTO, log_version, CTLFLAG_RD, &tcp_log_version,
    0, "Version of log formats exported");

SYSCTL_ULONG(_net_inet_tcp_bb, OID_AUTO, log_auto_ratio, CTLFLAG_RW,
    &tcp_log_auto_ratio, 0, "Do auto capturing for 1 out of N sessions");

SYSCTL_U32(_net_inet_tcp_bb, OID_AUTO, log_auto_mode, CTLFLAG_RW,
    &tcp_log_auto_mode, TCP_LOG_STATE_HEAD_AUTO,
    "Logging mode for auto-selected sessions (default is TCP_LOG_STATE_HEAD_AUTO)");

SYSCTL_BOOL(_net_inet_tcp_bb, OID_AUTO, log_auto_all, CTLFLAG_RW,
    &tcp_log_auto_all, false,
    "Auto-select from all sessions (rather than just those with IDs)");

#ifdef TCPLOG_DEBUG_COUNTERS
counter_u64_t tcp_log_queued;
counter_u64_t tcp_log_que_fail1;
counter_u64_t tcp_log_que_fail2;
counter_u64_t tcp_log_que_fail3;
counter_u64_t tcp_log_que_fail4;
counter_u64_t tcp_log_que_fail5;
counter_u64_t tcp_log_que_copyout;
counter_u64_t tcp_log_que_read;
counter_u64_t tcp_log_que_freed;

SYSCTL_COUNTER_U64(_net_inet_tcp_bb, OID_AUTO, queued, CTLFLAG_RD,
    &tcp_log_queued, "Number of entries queued");
SYSCTL_COUNTER_U64(_net_inet_tcp_bb, OID_AUTO, fail1, CTLFLAG_RD,
    &tcp_log_que_fail1, "Number of entries queued but fail 1");
SYSCTL_COUNTER_U64(_net_inet_tcp_bb, OID_AUTO, fail2, CTLFLAG_RD,
    &tcp_log_que_fail2, "Number of entries queued but fail 2");
SYSCTL_COUNTER_U64(_net_inet_tcp_bb, OID_AUTO, fail3, CTLFLAG_RD,
    &tcp_log_que_fail3, "Number of entries queued but fail 3");
SYSCTL_COUNTER_U64(_net_inet_tcp_bb, OID_AUTO, fail4, CTLFLAG_RD,
    &tcp_log_que_fail4, "Number of entries queued but fail 4");
SYSCTL_COUNTER_U64(_net_inet_tcp_bb, OID_AUTO, fail5, CTLFLAG_RD,
    &tcp_log_que_fail5, "Number of entries queued but fail 4");
SYSCTL_COUNTER_U64(_net_inet_tcp_bb, OID_AUTO, copyout, CTLFLAG_RD,
    &tcp_log_que_copyout, "Number of entries copied out");
SYSCTL_COUNTER_U64(_net_inet_tcp_bb, OID_AUTO, read, CTLFLAG_RD,
    &tcp_log_que_read, "Number of entries read from the queue");
SYSCTL_COUNTER_U64(_net_inet_tcp_bb, OID_AUTO, freed, CTLFLAG_RD,
    &tcp_log_que_freed, "Number of entries freed after reading");
#endif

#ifdef INVARIANTS
#define TCPLOG_DEBUG_RINGBUF
#endif

struct tcp_log_mem
{
        STAILQ_ENTRY(tcp_log_mem) tlm_queue;
        struct tcp_log_buffer   tlm_buf;
        struct tcp_log_verbose  tlm_v;
#ifdef TCPLOG_DEBUG_RINGBUF
        volatile int            tlm_refcnt;
#endif
};

/* 60 bytes for the header, + 16 bytes for padding */
static uint8_t  zerobuf[76];

/*
 * Lock order:
 * 1. TCPID_TREE
 * 2. TCPID_BUCKET
 * 3. INP
 *
 * Rules:
 * A. You need a lock on the Tree to add/remove buckets.
 * B. You need a lock on the bucket to add/remove nodes from the bucket.
 * C. To change information in a node, you need the INP lock if the tln_closed
 *    field is false. Otherwise, you need the bucket lock. (Note that the
 *    tln_closed field can change at any point, so you need to recheck the
 *    entry after acquiring the INP lock.)
 * D. To remove a node from the bucket, you must have that entry locked,
 *    according to the criteria of Rule C. Also, the node must not be on
 *    the expiry queue.
 * E. The exception to C is the expiry queue fields, which are locked by
 *    the TCPLOG_EXPIREQ lock.
 *
 * Buckets have a reference count. Each node is a reference. Further,
 * other callers may add reference counts to keep a bucket from disappearing.
 * You can add a reference as long as you own a lock sufficient to keep the
 * bucket from disappearing. For example, a common use is:
 *   a. Have a locked INP, but need to lock the TCPID_BUCKET.
 *   b. Add a refcount on the bucket. (Safe because the INP lock prevents
 *      the TCPID_BUCKET from going away.)
 *   c. Drop the INP lock.
 *   d. Acquire a lock on the TCPID_BUCKET.
 *   e. Acquire a lock on the INP.
 *   f. Drop the refcount on the bucket.
 *      (At this point, the bucket may disappear.)
 *
 * Expire queue lock:
 * You can acquire this with either the bucket or INP lock. Don't reverse it.
 * When the expire code has committed to freeing a node, it resets the expiry
 * time to SBT_MAX. That is the signal to everyone else that they should
 * leave that node alone.
 */
static struct rwlock tcp_id_tree_lock;
#define TCPID_TREE_WLOCK()              rw_wlock(&tcp_id_tree_lock)
#define TCPID_TREE_RLOCK()              rw_rlock(&tcp_id_tree_lock)
#define TCPID_TREE_UPGRADE()            rw_try_upgrade(&tcp_id_tree_lock)
#define TCPID_TREE_WUNLOCK()            rw_wunlock(&tcp_id_tree_lock)
#define TCPID_TREE_RUNLOCK()            rw_runlock(&tcp_id_tree_lock)
#define TCPID_TREE_WLOCK_ASSERT()       rw_assert(&tcp_id_tree_lock, RA_WLOCKED)
#define TCPID_TREE_RLOCK_ASSERT()       rw_assert(&tcp_id_tree_lock, RA_RLOCKED)
#define TCPID_TREE_UNLOCK_ASSERT()      rw_assert(&tcp_id_tree_lock, RA_UNLOCKED)

#define TCPID_BUCKET_LOCK_INIT(tlb)     mtx_init(&((tlb)->tlb_mtx), "tcp log id bucket", NULL, MTX_DEF)
#define TCPID_BUCKET_LOCK_DESTROY(tlb)  mtx_destroy(&((tlb)->tlb_mtx))
#define TCPID_BUCKET_LOCK(tlb)          mtx_lock(&((tlb)->tlb_mtx))
#define TCPID_BUCKET_UNLOCK(tlb)        mtx_unlock(&((tlb)->tlb_mtx))
#define TCPID_BUCKET_LOCK_ASSERT(tlb)   mtx_assert(&((tlb)->tlb_mtx), MA_OWNED)
#define TCPID_BUCKET_UNLOCK_ASSERT(tlb) mtx_assert(&((tlb)->tlb_mtx), MA_NOTOWNED)

#define TCPID_BUCKET_REF(tlb)           refcount_acquire(&((tlb)->tlb_refcnt))
#define TCPID_BUCKET_UNREF(tlb)         refcount_release(&((tlb)->tlb_refcnt))

#define TCPLOG_EXPIREQ_LOCK()           mtx_lock(&tcp_log_expireq_mtx)
#define TCPLOG_EXPIREQ_UNLOCK()         mtx_unlock(&tcp_log_expireq_mtx)

SLIST_HEAD(tcp_log_id_head, tcp_log_id_node);

struct tcp_log_id_bucket
{
        /*
         * tlb_id must be first. This lets us use strcmp on
         * (struct tcp_log_id_bucket *) and (char *) interchangeably.
         */
        char                            tlb_id[TCP_LOG_ID_LEN];
        RB_ENTRY(tcp_log_id_bucket)     tlb_rb;
        struct tcp_log_id_head          tlb_head;
        struct mtx                      tlb_mtx;
        volatile u_int                  tlb_refcnt;
};

struct tcp_log_id_node
{
        SLIST_ENTRY(tcp_log_id_node) tln_list;
        STAILQ_ENTRY(tcp_log_id_node) tln_expireq; /* Locked by the expireq lock */
        sbintime_t              tln_expiretime; /* Locked by the expireq lock */

        /*
         * If INP is NULL, that means the connection has closed. We've
         * saved the connection endpoint information and the log entries
         * in the tln_ie and tln_entries members. We've also saved a pointer
         * to the enclosing bucket here. If INP is not NULL, the information is
         * in the PCB and not here.
         */
        struct inpcb            *tln_inp;
        struct tcpcb            *tln_tp;
        struct tcp_log_id_bucket *tln_bucket;
        struct in_endpoints     tln_ie;
        struct tcp_log_stailq   tln_entries;
        int                     tln_count;
        volatile int            tln_closed;
        uint8_t                 tln_af;
};

enum tree_lock_state {
        TREE_UNLOCKED = 0,
        TREE_RLOCKED,
        TREE_WLOCKED,
};

/* Do we want to select this session for auto-logging? */
static __inline bool
tcp_log_selectauto(void)
{

        /*
         * If we are doing auto-capturing, figure out whether we will capture
         * this session.
         */
        if (tcp_log_auto_ratio &&
            (atomic_fetchadd_long(&tcp_log_auto_ratio_cur, 1) %
            tcp_log_auto_ratio) == 0)
                return (true);
        return (false);
}

static __inline int
tcp_log_id_cmp(struct tcp_log_id_bucket *a, struct tcp_log_id_bucket *b)
{
        KASSERT(a != NULL, ("tcp_log_id_cmp: argument a is unexpectedly NULL"));
        KASSERT(b != NULL, ("tcp_log_id_cmp: argument b is unexpectedly NULL"));
        return strncmp(a->tlb_id, b->tlb_id, TCP_LOG_ID_LEN);
}

RB_GENERATE_STATIC(tcp_log_id_tree, tcp_log_id_bucket, tlb_rb, tcp_log_id_cmp)

static __inline void
tcp_log_id_validate_tree_lock(int tree_locked)
{

#ifdef INVARIANTS
        switch (tree_locked) {
        case TREE_WLOCKED:
                TCPID_TREE_WLOCK_ASSERT();
                break;
        case TREE_RLOCKED:
                TCPID_TREE_RLOCK_ASSERT();
                break;
        case TREE_UNLOCKED:
                TCPID_TREE_UNLOCK_ASSERT();
                break;
        default:
                kassert_panic("%s:%d: unknown tree lock state", __func__,
                    __LINE__);
        }
#endif
}

static __inline void
tcp_log_remove_bucket(struct tcp_log_id_bucket *tlb)
{

        TCPID_TREE_WLOCK_ASSERT();
        KASSERT(SLIST_EMPTY(&tlb->tlb_head),
            ("%s: Attempt to remove non-empty bucket", __func__));
        if (RB_REMOVE(tcp_log_id_tree, &tcp_log_id_head, tlb) == NULL) {
#ifdef INVARIANTS
                kassert_panic("%s:%d: error removing element from tree",
                            __func__, __LINE__);
#endif
        }
        TCPID_BUCKET_LOCK_DESTROY(tlb);
        uma_zfree(tcp_log_bucket_zone, tlb);
}

/*
 * Call with a referenced and locked bucket.
 * Will return true if the bucket was freed; otherwise, false.
 * tlb: The bucket to unreference.
 * tree_locked: A pointer to the state of the tree lock. If the tree lock
 *    state changes, the function will update it.
 * inp: If not NULL and the function needs to drop the inp lock to relock the
 *    tree, it will do so. (The caller must ensure inp will not become invalid,
 *    probably by holding a reference to it.)
 */
static bool
tcp_log_unref_bucket(struct tcp_log_id_bucket *tlb, int *tree_locked,
    struct inpcb *inp)
{

        KASSERT(tlb != NULL, ("%s: called with NULL tlb", __func__));
        KASSERT(tree_locked != NULL, ("%s: called with NULL tree_locked",
            __func__));

        tcp_log_id_validate_tree_lock(*tree_locked);

        /*
         * Did we hold the last reference on the tlb? If so, we may need
         * to free it. (Note that we can realistically only execute the
         * loop twice: once without a write lock and once with a write
         * lock.)
         */
        while (TCPID_BUCKET_UNREF(tlb)) {
                /*
                 * We need a write lock on the tree to free this.
                 * If we can upgrade the tree lock, this is "easy". If we
                 * can't upgrade the tree lock, we need to do this the
                 * "hard" way: unwind all our locks and relock everything.
                 * In the meantime, anything could have changed. We even
                 * need to validate that we still need to free the bucket.
                 */
                if (*tree_locked == TREE_RLOCKED && TCPID_TREE_UPGRADE())
                        *tree_locked = TREE_WLOCKED;
                else if (*tree_locked != TREE_WLOCKED) {
                        TCPID_BUCKET_REF(tlb);
                        if (inp != NULL)
                                INP_WUNLOCK(inp);
                        TCPID_BUCKET_UNLOCK(tlb);
                        if (*tree_locked == TREE_RLOCKED)
                                TCPID_TREE_RUNLOCK();
                        TCPID_TREE_WLOCK();
                        *tree_locked = TREE_WLOCKED;
                        TCPID_BUCKET_LOCK(tlb);
                        if (inp != NULL)
                                INP_WLOCK(inp);
                        continue;
                }

                /*
                 * We have an empty bucket and a write lock on the tree.
                 * Remove the empty bucket.
                 */
                tcp_log_remove_bucket(tlb);
                return (true);
        }
        return (false);
}

/*
 * Call with a locked bucket. This function will release the lock on the
 * bucket before returning.
 *
 * The caller is responsible for freeing the tp->t_lin/tln node!
 *
 * Note: one of tp or both tlb and tln must be supplied.
 *
 * inp: A pointer to the inp. If the function needs to drop the inp lock to
 *    acquire the tree write lock, it will do so. (The caller must ensure inp
 *    will not become invalid, probably by holding a reference to it.)
 * tp: A pointer to the tcpcb. (optional; if specified, tlb and tln are ignored)
 * tlb: A pointer to the bucket. (optional; ignored if tp is specified)
 * tln: A pointer to the node. (optional; ignored if tp is specified)
 * tree_locked: A pointer to the state of the tree lock. If the tree lock
 *    state changes, the function will update it.
 *
 * Will return true if the INP lock was reacquired; otherwise, false.
 */
static bool
tcp_log_remove_id_node(struct inpcb *inp, struct tcpcb *tp,
    struct tcp_log_id_bucket *tlb, struct tcp_log_id_node *tln,
    int *tree_locked)
{
        int orig_tree_locked;

        KASSERT(tp != NULL || (tlb != NULL && tln != NULL),
            ("%s: called with tp=%p, tlb=%p, tln=%p", __func__,
            tp, tlb, tln));
        KASSERT(tree_locked != NULL, ("%s: called with NULL tree_locked",
            __func__));

        if (tp != NULL) {
                tlb = tp->t_lib;
                tln = tp->t_lin;
                KASSERT(tlb != NULL, ("%s: unexpectedly NULL tlb", __func__));
                KASSERT(tln != NULL, ("%s: unexpectedly NULL tln", __func__));
        }

        tcp_log_id_validate_tree_lock(*tree_locked);
        TCPID_BUCKET_LOCK_ASSERT(tlb);

        /*
         * Remove the node, clear the log bucket and node from the TCPCB, and
         * decrement the bucket refcount. In the process, if this is the
         * last reference, the bucket will be freed.
         */
        SLIST_REMOVE(&tlb->tlb_head, tln, tcp_log_id_node, tln_list);
        if (tp != NULL) {
                tp->t_lib = NULL;
                tp->t_lin = NULL;
        }
        orig_tree_locked = *tree_locked;
        if (!tcp_log_unref_bucket(tlb, tree_locked, inp))
                TCPID_BUCKET_UNLOCK(tlb);
        return (*tree_locked != orig_tree_locked);
}

#define RECHECK_INP_CLEAN(cleanup)      do {                    \
        if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {    \
                rv = ECONNRESET;                                \
                cleanup;                                        \
                goto done;                                      \
        }                                                       \
        tp = intotcpcb(inp);                                    \
} while (0)

#define RECHECK_INP()   RECHECK_INP_CLEAN(/* noop */)

static void
tcp_log_grow_tlb(char *tlb_id, struct tcpcb *tp)
{

        INP_WLOCK_ASSERT(tp->t_inpcb);

#ifdef NETFLIX
        if (V_tcp_perconn_stats_enable == 2 && tp->t_stats == NULL)
                (void)tcp_stats_sample_rollthedice(tp, tlb_id, strlen(tlb_id));
#endif
}

/*
 * Set the TCP log ID for a TCPCB.
 * Called with INPCB locked. Returns with it unlocked.
 */
int
tcp_log_set_id(struct tcpcb *tp, char *id)
{
        struct tcp_log_id_bucket *tlb, *tmp_tlb;
        struct tcp_log_id_node *tln;
        struct inpcb *inp;
        int tree_locked, rv;
        bool bucket_locked;

        tlb = NULL;
        tln = NULL;
        inp = tp->t_inpcb;
        tree_locked = TREE_UNLOCKED;
        bucket_locked = false;

restart:
        INP_WLOCK_ASSERT(inp);

        /* See if the ID is unchanged. */
        if ((tp->t_lib != NULL && !strcmp(tp->t_lib->tlb_id, id)) ||
            (tp->t_lib == NULL && *id == 0)) {
                rv = 0;
                goto done;
        }

        /*
         * If the TCPCB had a previous ID, we need to extricate it from
         * the previous list.
         *
         * Drop the TCPCB lock and lock the tree and the bucket.
         * Because this is called in the socket context, we (theoretically)
         * don't need to worry about the INPCB completely going away
         * while we are gone.
         */
        if (tp->t_lib != NULL) {
                tlb = tp->t_lib;
                TCPID_BUCKET_REF(tlb);
                INP_WUNLOCK(inp);

                if (tree_locked == TREE_UNLOCKED) {
                        TCPID_TREE_RLOCK();
                        tree_locked = TREE_RLOCKED;
                }
                TCPID_BUCKET_LOCK(tlb);
                bucket_locked = true;
                INP_WLOCK(inp);

                /*
                 * Unreference the bucket. If our bucket went away, it is no
                 * longer locked or valid.
                 */
                if (tcp_log_unref_bucket(tlb, &tree_locked, inp)) {
                        bucket_locked = false;
                        tlb = NULL;
                }

                /* Validate the INP. */
                RECHECK_INP();

                /*
                 * Evaluate whether the bucket changed while we were unlocked.
                 *
                 * Possible scenarios here:
                 * 1. Bucket is unchanged and the same one we started with.
                 * 2. The TCPCB no longer has a bucket and our bucket was
                 *    freed.
                 * 3. The TCPCB has a new bucket, whether ours was freed.
                 * 4. The TCPCB no longer has a bucket and our bucket was
                 *    not freed.
                 *
                 * In cases 2-4, we will start over. In case 1, we will
                 * proceed here to remove the bucket.
                 */
                if (tlb == NULL || tp->t_lib != tlb) {
                        KASSERT(bucket_locked || tlb == NULL,
                            ("%s: bucket_locked (%d) and tlb (%p) are "
                            "inconsistent", __func__, bucket_locked, tlb));
                        
                        if (bucket_locked) {
                                TCPID_BUCKET_UNLOCK(tlb);
                                bucket_locked = false;
                                tlb = NULL;
                        }
                        goto restart;
                }

                /*
                 * Store the (struct tcp_log_id_node) for reuse. Then, remove
                 * it from the bucket. In the process, we may end up relocking.
                 * If so, we need to validate that the INP is still valid, and
                 * the TCPCB entries match we expect.
                 *
                 * We will clear tlb and change the bucket_locked state just
                 * before calling tcp_log_remove_id_node(), since that function
                 * will unlock the bucket.
                 */
                if (tln != NULL)
                        uma_zfree(tcp_log_node_zone, tln);
                tln = tp->t_lin;
                tlb = NULL;
                bucket_locked = false;
                if (tcp_log_remove_id_node(inp, tp, NULL, NULL, &tree_locked)) {
                        RECHECK_INP();

                        /*
                         * If the TCPCB moved to a new bucket while we had
                         * dropped the lock, restart.
                         */
                        if (tp->t_lib != NULL || tp->t_lin != NULL)
                                goto restart;
                }

                /*
                 * Yay! We successfully removed the TCPCB from its old
                 * bucket. Phew!
                 *
                 * On to bigger and better things...
                 */
        }

        /* At this point, the TCPCB should not be in any bucket. */
        KASSERT(tp->t_lib == NULL, ("%s: tp->t_lib is not NULL", __func__));

        /*
         * If the new ID is not empty, we need to now assign this TCPCB to a
         * new bucket.
         */
        if (*id) {
                /* Get a new tln, if we don't already have one to reuse. */
                if (tln == NULL) {
                        tln = uma_zalloc(tcp_log_node_zone, M_NOWAIT | M_ZERO);
                        if (tln == NULL) {
                                rv = ENOBUFS;
                                goto done;
                        }
                        tln->tln_inp = inp;
                        tln->tln_tp = tp;
                }

                /*
                 * Drop the INP lock for a bit. We don't need it, and dropping
                 * it prevents lock order reversals.
                 */
                INP_WUNLOCK(inp);

                /* Make sure we have at least a read lock on the tree. */
                tcp_log_id_validate_tree_lock(tree_locked);
                if (tree_locked == TREE_UNLOCKED) {
                        TCPID_TREE_RLOCK();
                        tree_locked = TREE_RLOCKED;
                }

refind:
                /*
                 * Remember that we constructed (struct tcp_log_id_node) so
                 * we can safely cast the id to it for the purposes of finding.
                 */
                KASSERT(tlb == NULL, ("%s:%d tlb unexpectedly non-NULL", 
                    __func__, __LINE__));
                tmp_tlb = RB_FIND(tcp_log_id_tree, &tcp_log_id_head,
                    (struct tcp_log_id_bucket *) id);

                /*
                 * If we didn't find a matching bucket, we need to add a new
                 * one. This requires a write lock. But, of course, we will
                 * need to recheck some things when we re-acquire the lock.
                 */
                if (tmp_tlb == NULL && tree_locked != TREE_WLOCKED) {
                        tree_locked = TREE_WLOCKED;
                        if (!TCPID_TREE_UPGRADE()) {
                                TCPID_TREE_RUNLOCK();
                                TCPID_TREE_WLOCK();

                                /*
                                 * The tree may have changed while we were
                                 * unlocked.
                                 */
                                goto refind;
                        }
                }

                /* If we need to add a new bucket, do it now. */
                if (tmp_tlb == NULL) {
                        /* Allocate new bucket. */
                        tlb = uma_zalloc(tcp_log_bucket_zone, M_NOWAIT);
                        if (tlb == NULL) {
                                rv = ENOBUFS;
                                goto done_noinp;
                        }

                        /*
                         * Copy the ID to the bucket.
                         * NB: Don't use strlcpy() unless you are sure
                         * we've always validated NULL termination.
                         *
                         * TODO: When I'm done writing this, see if we
                         * we have correctly validated NULL termination and
                         * can use strlcpy(). :-)
                         */
                        strncpy(tlb->tlb_id, id, TCP_LOG_ID_LEN - 1);
                        tlb->tlb_id[TCP_LOG_ID_LEN - 1] = '\0';

                        /*
                         * Take the refcount for the first node and go ahead
                         * and lock this. Note that we zero the tlb_mtx
                         * structure, since 0xdeadc0de flips the right bits
                         * for the code to think that this mutex has already
                         * been initialized. :-(
                         */
                        SLIST_INIT(&tlb->tlb_head);
                        refcount_init(&tlb->tlb_refcnt, 1);
                        memset(&tlb->tlb_mtx, 0, sizeof(struct mtx));
                        TCPID_BUCKET_LOCK_INIT(tlb);
                        TCPID_BUCKET_LOCK(tlb);
                        bucket_locked = true;

#define FREE_NEW_TLB()  do {                            \
        TCPID_BUCKET_LOCK_DESTROY(tlb);                 \
        uma_zfree(tcp_log_bucket_zone, tlb);            \
        bucket_locked = false;                          \
        tlb = NULL;                                     \
} while (0)
                        /*
                         * Relock the INP and make sure we are still
                         * unassigned.
                         */
                        INP_WLOCK(inp);
                        RECHECK_INP_CLEAN(FREE_NEW_TLB());
                        if (tp->t_lib != NULL) {
                                FREE_NEW_TLB();
                                goto restart;
                        }

                        /* Add the new bucket to the tree. */
                        tmp_tlb = RB_INSERT(tcp_log_id_tree, &tcp_log_id_head,
                            tlb);
                        KASSERT(tmp_tlb == NULL,
                            ("%s: Unexpected conflicting bucket (%p) while "
                            "adding new bucket (%p)", __func__, tmp_tlb, tlb));

                        /*
                         * If we found a conflicting bucket, free the new
                         * one we made and fall through to use the existing
                         * bucket.
                         */
                        if (tmp_tlb != NULL) {
                                FREE_NEW_TLB();
                                INP_WUNLOCK(inp);
                        }
#undef  FREE_NEW_TLB
                }

                /* If we found an existing bucket, use it. */
                if (tmp_tlb != NULL) {
                        tlb = tmp_tlb;
                        TCPID_BUCKET_LOCK(tlb);
                        bucket_locked = true;

                        /*
                         * Relock the INP and make sure we are still
                         * unassigned.
                         */
                        INP_UNLOCK_ASSERT(inp);
                        INP_WLOCK(inp);
                        RECHECK_INP();
                        if (tp->t_lib != NULL) {
                                TCPID_BUCKET_UNLOCK(tlb);
                                tlb = NULL;
                                goto restart;
                        }

                        /* Take a reference on the bucket. */
                        TCPID_BUCKET_REF(tlb);
                }

                tcp_log_grow_tlb(tlb->tlb_id, tp);

                /* Add the new node to the list. */
                SLIST_INSERT_HEAD(&tlb->tlb_head, tln, tln_list);
                tp->t_lib = tlb;
                tp->t_lin = tln;
                tln = NULL;
        }

        rv = 0;

done:
        /* Unlock things, as needed, and return. */
        INP_WUNLOCK(inp);
done_noinp:
        INP_UNLOCK_ASSERT(inp);
        if (bucket_locked) {
                TCPID_BUCKET_LOCK_ASSERT(tlb);
                TCPID_BUCKET_UNLOCK(tlb);
        } else if (tlb != NULL)
                TCPID_BUCKET_UNLOCK_ASSERT(tlb);
        if (tree_locked == TREE_WLOCKED) {
                TCPID_TREE_WLOCK_ASSERT();
                TCPID_TREE_WUNLOCK();
        } else if (tree_locked == TREE_RLOCKED) {
                TCPID_TREE_RLOCK_ASSERT();
                TCPID_TREE_RUNLOCK();
        } else
                TCPID_TREE_UNLOCK_ASSERT();
        if (tln != NULL)
                uma_zfree(tcp_log_node_zone, tln);
        return (rv);
}

/*
 * Get the TCP log ID for a TCPCB.
 * Called with INPCB locked.
 * 'buf' must point to a buffer that is at least TCP_LOG_ID_LEN bytes long.
 * Returns number of bytes copied.
 */
size_t
tcp_log_get_id(struct tcpcb *tp, char *buf)
{
        size_t len;

        INP_LOCK_ASSERT(tp->t_inpcb);
        if (tp->t_lib != NULL) {
                len = strlcpy(buf, tp->t_lib->tlb_id, TCP_LOG_ID_LEN);
                KASSERT(len < TCP_LOG_ID_LEN,
                    ("%s:%d: tp->t_lib->tlb_id too long (%zu)",
                    __func__, __LINE__, len));
        } else {
                *buf = '\0';
                len = 0;
        }
        return (len);
}

/*
 * Get number of connections with the same log ID.
 * Log ID is taken from given TCPCB.
 * Called with INPCB locked.
 */
u_int
tcp_log_get_id_cnt(struct tcpcb *tp)
{

        INP_WLOCK_ASSERT(tp->t_inpcb);
        return ((tp->t_lib == NULL) ? 0 : tp->t_lib->tlb_refcnt);
}

#ifdef TCPLOG_DEBUG_RINGBUF
/*
 * Functions/macros to increment/decrement reference count for a log
 * entry. This should catch when we do a double-free/double-remove or
 * a double-add.
 */
static inline void
_tcp_log_entry_refcnt_add(struct tcp_log_mem *log_entry, const char *func,
    int line)
{
        int refcnt;

        refcnt = atomic_fetchadd_int(&log_entry->tlm_refcnt, 1);
        if (refcnt != 0)
                panic("%s:%d: log_entry(%p)->tlm_refcnt is %d (expected 0)",
                    func, line, log_entry, refcnt);
}
#define tcp_log_entry_refcnt_add(l)     \
    _tcp_log_entry_refcnt_add((l), __func__, __LINE__)

static inline void
_tcp_log_entry_refcnt_rem(struct tcp_log_mem *log_entry, const char *func,
    int line)
{
        int refcnt;

        refcnt = atomic_fetchadd_int(&log_entry->tlm_refcnt, -1);
        if (refcnt != 1)
                panic("%s:%d: log_entry(%p)->tlm_refcnt is %d (expected 1)",
                    func, line, log_entry, refcnt);
}
#define tcp_log_entry_refcnt_rem(l)     \
    _tcp_log_entry_refcnt_rem((l), __func__, __LINE__)

#else /* !TCPLOG_DEBUG_RINGBUF */

#define tcp_log_entry_refcnt_add(l)
#define tcp_log_entry_refcnt_rem(l)

#endif

/*
 * Cleanup after removing a log entry, but only decrement the count if we
 * are running INVARIANTS.
 */
static inline void
tcp_log_free_log_common(struct tcp_log_mem *log_entry, int *count __unused)
{

        uma_zfree(tcp_log_zone, log_entry);
#ifdef INVARIANTS
        (*count)--;
        KASSERT(*count >= 0,
            ("%s: count unexpectedly negative", __func__));
#endif
}

static void
tcp_log_free_entries(struct tcp_log_stailq *head, int *count)
{
        struct tcp_log_mem *log_entry;

        /* Free the entries. */
        while ((log_entry = STAILQ_FIRST(head)) != NULL) {
                STAILQ_REMOVE_HEAD(head, tlm_queue);
                tcp_log_entry_refcnt_rem(log_entry);
                tcp_log_free_log_common(log_entry, count);
        }
}

/* Cleanup after removing a log entry. */
static inline void
tcp_log_remove_log_cleanup(struct tcpcb *tp, struct tcp_log_mem *log_entry)
{
        uma_zfree(tcp_log_zone, log_entry);
        tp->t_lognum--;
        KASSERT(tp->t_lognum >= 0,
            ("%s: tp->t_lognum unexpectedly negative", __func__));
}

/* Remove a log entry from the head of a list. */
static inline void
tcp_log_remove_log_head(struct tcpcb *tp, struct tcp_log_mem *log_entry)
{

        KASSERT(log_entry == STAILQ_FIRST(&tp->t_logs),
            ("%s: attempt to remove non-HEAD log entry", __func__));
        STAILQ_REMOVE_HEAD(&tp->t_logs, tlm_queue);
        tcp_log_entry_refcnt_rem(log_entry);
        tcp_log_remove_log_cleanup(tp, log_entry);
}

#ifdef TCPLOG_DEBUG_RINGBUF
/*
 * Initialize the log entry's reference count, which we want to
 * survive allocations.
 */
static int
tcp_log_zone_init(void *mem, int size, int flags __unused)
{
        struct tcp_log_mem *tlm;

        KASSERT(size >= sizeof(struct tcp_log_mem),
            ("%s: unexpectedly short (%d) allocation", __func__, size));
        tlm = (struct tcp_log_mem *)mem;
        tlm->tlm_refcnt = 0;
        return (0);
}

/*
 * Double check that the refcnt is zero on allocation and return.
 */
static int
tcp_log_zone_ctor(void *mem, int size, void *args __unused, int flags __unused)
{
        struct tcp_log_mem *tlm;

        KASSERT(size >= sizeof(struct tcp_log_mem),
            ("%s: unexpectedly short (%d) allocation", __func__, size));
        tlm = (struct tcp_log_mem *)mem;
        if (tlm->tlm_refcnt != 0)
                panic("%s:%d: tlm(%p)->tlm_refcnt is %d (expected 0)",
                    __func__, __LINE__, tlm, tlm->tlm_refcnt);
        return (0);
}

static void
tcp_log_zone_dtor(void *mem, int size, void *args __unused)
{
        struct tcp_log_mem *tlm;

        KASSERT(size >= sizeof(struct tcp_log_mem),
            ("%s: unexpectedly short (%d) allocation", __func__, size));
        tlm = (struct tcp_log_mem *)mem;
        if (tlm->tlm_refcnt != 0)
                panic("%s:%d: tlm(%p)->tlm_refcnt is %d (expected 0)",
                    __func__, __LINE__, tlm, tlm->tlm_refcnt);
}
#endif /* TCPLOG_DEBUG_RINGBUF */

/* Do global initialization. */
void
tcp_log_init(void)
{

        tcp_log_zone = uma_zcreate("tcp_log", sizeof(struct tcp_log_mem),
#ifdef TCPLOG_DEBUG_RINGBUF
            tcp_log_zone_ctor, tcp_log_zone_dtor, tcp_log_zone_init,
#else
            NULL, NULL, NULL,
#endif
            NULL, UMA_ALIGN_PTR, 0);
        (void)uma_zone_set_max(tcp_log_zone, TCP_LOG_BUF_DEFAULT_GLOBAL_LIMIT);
        tcp_log_bucket_zone = uma_zcreate("tcp_log_bucket",
            sizeof(struct tcp_log_id_bucket), NULL, NULL, NULL, NULL,
            UMA_ALIGN_PTR, 0);
        tcp_log_node_zone = uma_zcreate("tcp_log_node",
            sizeof(struct tcp_log_id_node), NULL, NULL, NULL, NULL,
            UMA_ALIGN_PTR, 0);
#ifdef TCPLOG_DEBUG_COUNTERS
        tcp_log_queued = counter_u64_alloc(M_WAITOK);
        tcp_log_que_fail1 = counter_u64_alloc(M_WAITOK);
        tcp_log_que_fail2 = counter_u64_alloc(M_WAITOK);
        tcp_log_que_fail3 = counter_u64_alloc(M_WAITOK);
        tcp_log_que_fail4 = counter_u64_alloc(M_WAITOK);
        tcp_log_que_fail5 = counter_u64_alloc(M_WAITOK);
        tcp_log_que_copyout = counter_u64_alloc(M_WAITOK);
        tcp_log_que_read = counter_u64_alloc(M_WAITOK);
        tcp_log_que_freed = counter_u64_alloc(M_WAITOK);
#endif

        rw_init_flags(&tcp_id_tree_lock, "TCP ID tree", RW_NEW);
        mtx_init(&tcp_log_expireq_mtx, "TCP log expireq", NULL, MTX_DEF);
        callout_init(&tcp_log_expireq_callout, 1);
}

/* Do per-TCPCB initialization. */
void
tcp_log_tcpcbinit(struct tcpcb *tp)
{

        /* A new TCPCB should start out zero-initialized. */
        STAILQ_INIT(&tp->t_logs);

        /*
         * If we are doing auto-capturing, figure out whether we will capture
         * this session.
         */
        if (tcp_log_selectauto()) {
                tp->t_logstate = tcp_log_auto_mode;
                tp->t_flags2 |= TF2_LOG_AUTO;
        }
}


/* Remove entries */
static void
tcp_log_expire(void *unused __unused)
{
        struct tcp_log_id_bucket *tlb;
        struct tcp_log_id_node *tln;
        sbintime_t expiry_limit;
        int tree_locked;

        TCPLOG_EXPIREQ_LOCK();
        if (callout_pending(&tcp_log_expireq_callout)) {
                /* Callout was reset. */
                TCPLOG_EXPIREQ_UNLOCK();
                return;
        }

        /*
         * Process entries until we reach one that expires too far in the
         * future. Look one second in the future.
         */
        expiry_limit = getsbinuptime() + SBT_1S;
        tree_locked = TREE_UNLOCKED;

        while ((tln = STAILQ_FIRST(&tcp_log_expireq_head)) != NULL &&
            tln->tln_expiretime <= expiry_limit) {
                if (!callout_active(&tcp_log_expireq_callout)) {
                        /*
                         * Callout was stopped. I guess we should
                         * just quit at this point.
                         */
                        TCPLOG_EXPIREQ_UNLOCK();
                        return;
                }

                /*
                 * Remove the node from the head of the list and unlock
                 * the list. Change the expiry time to SBT_MAX as a signal
                 * to other threads that we now own this.
                 */
                STAILQ_REMOVE_HEAD(&tcp_log_expireq_head, tln_expireq);
                tln->tln_expiretime = SBT_MAX;
                TCPLOG_EXPIREQ_UNLOCK();

                /*
                 * Remove the node from the bucket.
                 */
                tlb = tln->tln_bucket;
                TCPID_BUCKET_LOCK(tlb);
                if (tcp_log_remove_id_node(NULL, NULL, tlb, tln, &tree_locked)) {
                        tcp_log_id_validate_tree_lock(tree_locked);
                        if (tree_locked == TREE_WLOCKED)
                                TCPID_TREE_WUNLOCK();
                        else
                                TCPID_TREE_RUNLOCK();
                        tree_locked = TREE_UNLOCKED;
                }

                /* Drop the INP reference. */
                INP_WLOCK(tln->tln_inp);
                if (!in_pcbrele_wlocked(tln->tln_inp))
                        INP_WUNLOCK(tln->tln_inp);

                /* Free the log records. */
                tcp_log_free_entries(&tln->tln_entries, &tln->tln_count);

                /* Free the node. */
                uma_zfree(tcp_log_node_zone, tln);

                /* Relock the expiry queue. */
                TCPLOG_EXPIREQ_LOCK();
        }

        /*
         * We've expired all the entries we can. Do we need to reschedule
         * ourselves?
         */
        callout_deactivate(&tcp_log_expireq_callout);
        if (tln != NULL) {
                /*
                 * Get max(now + TCP_LOG_EXPIRE_INTVL, tln->tln_expiretime) and
                 * set the next callout to that. (This helps ensure we generally
                 * run the callout no more often than desired.)
                 */
                expiry_limit = getsbinuptime() + TCP_LOG_EXPIRE_INTVL;
                if (expiry_limit < tln->tln_expiretime)
                        expiry_limit = tln->tln_expiretime;
                callout_reset_sbt(&tcp_log_expireq_callout, expiry_limit,
                    SBT_1S, tcp_log_expire, NULL, C_ABSOLUTE);
        }

        /* We're done. */
        TCPLOG_EXPIREQ_UNLOCK();
        return;
}

/*
 * Move log data from the TCPCB to a new node. This will reset the TCPCB log
 * entries and log count; however, it will not touch other things from the
 * TCPCB (e.g. t_lin, t_lib).
 *
 * NOTE: Must hold a lock on the INP.
 */
static void
tcp_log_move_tp_to_node(struct tcpcb *tp, struct tcp_log_id_node *tln)
{

        INP_WLOCK_ASSERT(tp->t_inpcb);

        tln->tln_ie = tp->t_inpcb->inp_inc.inc_ie;
        if (tp->t_inpcb->inp_inc.inc_flags & INC_ISIPV6)
                tln->tln_af = AF_INET6;
        else
                tln->tln_af = AF_INET;
        tln->tln_entries = tp->t_logs;
        tln->tln_count = tp->t_lognum;
        tln->tln_bucket = tp->t_lib;

        /* Clear information from the PCB. */
        STAILQ_INIT(&tp->t_logs);
        tp->t_lognum = 0;
}

/* Do per-TCPCB cleanup */
void
tcp_log_tcpcbfini(struct tcpcb *tp)
{
        struct tcp_log_id_node *tln, *tln_first;
        struct tcp_log_mem *log_entry;
        sbintime_t callouttime;

        INP_WLOCK_ASSERT(tp->t_inpcb);

        /*
         * If we were gathering packets to be automatically dumped, try to do
         * it now. If this succeeds, the log information in the TCPCB will be
         * cleared. Otherwise, we'll handle the log information as we do
         * for other states.
         */
        switch(tp->t_logstate) {
        case TCP_LOG_STATE_HEAD_AUTO:
                (void)tcp_log_dump_tp_logbuf(tp, "auto-dumped from head",
                    M_NOWAIT, false);
                break;
        case TCP_LOG_STATE_TAIL_AUTO:
                (void)tcp_log_dump_tp_logbuf(tp, "auto-dumped from tail",
                    M_NOWAIT, false);
                break;
        case TCP_LOG_STATE_CONTINUAL:
                (void)tcp_log_dump_tp_logbuf(tp, "auto-dumped from continual",
                    M_NOWAIT, false);
                break;
        }

        /*
         * There are two ways we could keep logs: per-socket or per-ID. If
         * we are tracking logs with an ID, then the logs survive the
         * destruction of the TCPCB.
         * 
         * If the TCPCB is associated with an ID node, move the logs from the
         * TCPCB to the ID node. In theory, this is safe, for reasons which I
         * will now explain for my own benefit when I next need to figure out
         * this code. :-)
         *
         * We own the INP lock. Therefore, no one else can change the contents
         * of this node (Rule C). Further, no one can remove this node from
         * the bucket while we hold the lock (Rule D). Basically, no one can
         * mess with this node. That leaves two states in which we could be:
         * 
         * 1. Another thread is currently waiting to acquire the INP lock, with
         *    plans to do something with this node. When we drop the INP lock,
         *    they will have a chance to do that. They will recheck the
         *    tln_closed field (see note to Rule C) and then acquire the
         *    bucket lock before proceeding further.
         *
         * 2. Another thread will try to acquire a lock at some point in the
         *    future. If they try to acquire a lock before we set the
         *    tln_closed field, they will follow state #1. If they try to
         *    acquire a lock after we set the tln_closed field, they will be
         *    able to make changes to the node, at will, following Rule C.
         *
         * Therefore, we currently own this node and can make any changes
         * we want. But, as soon as we set the tln_closed field to true, we
         * have effectively dropped our lock on the node. (For this reason, we
         * also need to make sure our writes are ordered correctly. An atomic
         * operation with "release" semantics should be sufficient.)
         */

        if (tp->t_lin != NULL) {
                /* Copy the relevant information to the log entry. */
                tln = tp->t_lin;
                KASSERT(tln->tln_inp == tp->t_inpcb,
                    ("%s: Mismatched inp (tln->tln_inp=%p, tp->t_inpcb=%p)",
                    __func__, tln->tln_inp, tp->t_inpcb));
                tcp_log_move_tp_to_node(tp, tln);

                /* Clear information from the PCB. */
                tp->t_lin = NULL;
                tp->t_lib = NULL;

                /*
                 * Take a reference on the INP. This ensures that the INP
                 * remains valid while the node is on the expiry queue. This
                 * ensures the INP is valid for other threads that may be
                 * racing to lock this node when we move it to the expire
                 * queue.
                 */
                in_pcbref(tp->t_inpcb);

                /*
                 * Store the entry on the expiry list. The exact behavior
                 * depends on whether we have entries to keep. If so, we
                 * put the entry at the tail of the list and expire in
                 * TCP_LOG_EXPIRE_TIME. Otherwise, we expire "now" and put
                 * the entry at the head of the list. (Handling the cleanup
                 * via the expiry timer lets us avoid locking messy-ness here.)
                 */
                tln->tln_expiretime = getsbinuptime();
                TCPLOG_EXPIREQ_LOCK();
                if (tln->tln_count) {
                        tln->tln_expiretime += TCP_LOG_EXPIRE_TIME;
                        if (STAILQ_EMPTY(&tcp_log_expireq_head) &&
                            !callout_active(&tcp_log_expireq_callout)) {
                                /*
                                 * We are adding the first entry and a callout
                                 * is not currently scheduled; therefore, we
                                 * need to schedule one.
                                 */
                                callout_reset_sbt(&tcp_log_expireq_callout,
                                    tln->tln_expiretime, SBT_1S, tcp_log_expire,
                                    NULL, C_ABSOLUTE);
                        }
                        STAILQ_INSERT_TAIL(&tcp_log_expireq_head, tln,
                            tln_expireq);
                } else {
                        callouttime = tln->tln_expiretime +
                            TCP_LOG_EXPIRE_INTVL;
                        tln_first = STAILQ_FIRST(&tcp_log_expireq_head);

                        if ((tln_first == NULL ||
                            callouttime < tln_first->tln_expiretime) &&
                            (callout_pending(&tcp_log_expireq_callout) ||
                            !callout_active(&tcp_log_expireq_callout))) {
                                /*
                                 * The list is empty, or we want to run the
                                 * expire code before the first entry's timer
                                 * fires. Also, we are in a case where a callout
                                 * is not actively running. We want to reset
                                 * the callout to occur sooner.
                                 */
                                callout_reset_sbt(&tcp_log_expireq_callout,
                                    callouttime, SBT_1S, tcp_log_expire, NULL,
                                    C_ABSOLUTE);
                        }

                        /*
                         * Insert to the head, or just after the head, as
                         * appropriate. (This might result in small
                         * mis-orderings as a bunch of "expire now" entries
                         * gather at the start of the list, but that should
                         * not produce big problems, since the expire timer
                         * will walk through all of them.)
                         */
                        if (tln_first == NULL ||
                            tln->tln_expiretime < tln_first->tln_expiretime)
                                STAILQ_INSERT_HEAD(&tcp_log_expireq_head, tln,
                                    tln_expireq);
                        else
                                STAILQ_INSERT_AFTER(&tcp_log_expireq_head,
                                    tln_first, tln, tln_expireq);
                }
                TCPLOG_EXPIREQ_UNLOCK();

                /*
                 * We are done messing with the tln. After this point, we
                 * can't touch it. (Note that the "release" semantics should
                 * be included with the TCPLOG_EXPIREQ_UNLOCK() call above.
                 * Therefore, they should be unnecessary here. However, it
                 * seems like a good idea to include them anyway, since we
                 * really are releasing a lock here.)
                 */
                atomic_store_rel_int(&tln->tln_closed, 1);
        } else {
                /* Remove log entries. */
                while ((log_entry = STAILQ_FIRST(&tp->t_logs)) != NULL)
                        tcp_log_remove_log_head(tp, log_entry);
                KASSERT(tp->t_lognum == 0,
                    ("%s: After freeing entries, tp->t_lognum=%d (expected 0)",
                        __func__, tp->t_lognum));
        }

        /*
         * Change the log state to off (just in case anything tries to sneak
         * in a last-minute log).
         */
        tp->t_logstate = TCP_LOG_STATE_OFF;
}

/*
 * This logs an event for a TCP socket. Normally, this is called via
 * TCP_LOG_EVENT or TCP_LOG_EVENT_VERBOSE. See the documentation for
 * TCP_LOG_EVENT().
 */

struct tcp_log_buffer *
tcp_log_event_(struct tcpcb *tp, struct tcphdr *th, struct sockbuf *rxbuf,
    struct sockbuf *txbuf, uint8_t eventid, int errornum, uint32_t len,
    union tcp_log_stackspecific *stackinfo, int th_hostorder,
    const char *output_caller, const char *func, int line, const struct timeval *itv)
{
        struct tcp_log_mem *log_entry;
        struct tcp_log_buffer *log_buf;
        int attempt_count = 0;
        struct tcp_log_verbose *log_verbose;
        uint32_t logsn;

        KASSERT((func == NULL && line == 0) || (func != NULL && line > 0),
            ("%s called with inconsistent func (%p) and line (%d) arguments",
                __func__, func, line));

        INP_WLOCK_ASSERT(tp->t_inpcb);

        KASSERT(tp->t_logstate == TCP_LOG_STATE_HEAD ||
            tp->t_logstate == TCP_LOG_STATE_TAIL ||
            tp->t_logstate == TCP_LOG_STATE_CONTINUAL ||
            tp->t_logstate == TCP_LOG_STATE_HEAD_AUTO ||
            tp->t_logstate == TCP_LOG_STATE_TAIL_AUTO,
            ("%s called with unexpected tp->t_logstate (%d)", __func__,
                tp->t_logstate));

        /*
         * Get the serial number. We do this early so it will
         * increment even if we end up skipping the log entry for some
         * reason.
         */
        logsn = tp->t_logsn++;

        /*
         * Can we get a new log entry? If so, increment the lognum counter
         * here.
         */
retry:
        if (tp->t_lognum < tcp_log_session_limit) {
                if ((log_entry = uma_zalloc(tcp_log_zone, M_NOWAIT)) != NULL)
                        tp->t_lognum++;
        } else
                log_entry = NULL;

        /* Do we need to try to reuse? */
        if (log_entry == NULL) {
                /*
                 * Sacrifice auto-logged sessions without a log ID if
                 * tcp_log_auto_all is false. (If they don't have a log
                 * ID by now, it is probable that either they won't get one
                 * or we are resource-constrained.)
                 */
                if (tp->t_lib == NULL && (tp->t_flags2 & TF2_LOG_AUTO) &&
                    !tcp_log_auto_all) {
                        if (tcp_log_state_change(tp, TCP_LOG_STATE_CLEAR)) {
#ifdef INVARIANTS
                                panic("%s:%d: tcp_log_state_change() failed "
                                    "to set tp %p to TCP_LOG_STATE_CLEAR",
                                    __func__, __LINE__, tp);
#endif
                                tp->t_logstate = TCP_LOG_STATE_OFF;
                        }
                        return (NULL);
                }
                /*
                 * If we are in TCP_LOG_STATE_HEAD_AUTO state, try to dump
                 * the buffers. If successful, deactivate tracing. Otherwise,
                 * leave it active so we will retry.
                 */
                if (tp->t_logstate == TCP_LOG_STATE_HEAD_AUTO &&
                    !tcp_log_dump_tp_logbuf(tp, "auto-dumped from head",
                    M_NOWAIT, false)) {
                        tp->t_logstate = TCP_LOG_STATE_OFF;
                        return(NULL);
                } else if ((tp->t_logstate == TCP_LOG_STATE_CONTINUAL) &&
                    !tcp_log_dump_tp_logbuf(tp, "auto-dumped from continual",
                    M_NOWAIT, false)) {
                        if (attempt_count == 0) {
                                attempt_count++;
                                goto retry;
                        }
#ifdef TCPLOG_DEBUG_COUNTERS
                        counter_u64_add(tcp_log_que_fail4, 1);
#endif
                        return(NULL);
                } else if (tp->t_logstate == TCP_LOG_STATE_HEAD_AUTO)
                        return(NULL);

                /* If in HEAD state, just deactivate the tracing and return. */
                if (tp->t_logstate == TCP_LOG_STATE_HEAD) {
                        tp->t_logstate = TCP_LOG_STATE_OFF;
                        return(NULL);
                }

                /*
                 * Get a buffer to reuse. If that fails, just give up.
                 * (We can't log anything without a buffer in which to
                 * put it.)
                 *
                 * Note that we don't change the t_lognum counter
                 * here. Because we are re-using the buffer, the total
                 * number won't change.
                 */
                if ((log_entry = STAILQ_FIRST(&tp->t_logs)) == NULL)
                        return(NULL);
                STAILQ_REMOVE_HEAD(&tp->t_logs, tlm_queue);
                tcp_log_entry_refcnt_rem(log_entry);
        }

        KASSERT(log_entry != NULL,
            ("%s: log_entry unexpectedly NULL", __func__));

        /* Extract the log buffer and verbose buffer pointers. */
        log_buf = &log_entry->tlm_buf;
        log_verbose = &log_entry->tlm_v;

        /* Basic entries. */
        if (itv == NULL)
                getmicrouptime(&log_buf->tlb_tv);
        else
                memcpy(&log_buf->tlb_tv, itv, sizeof(struct timeval));
        log_buf->tlb_ticks = ticks;
        log_buf->tlb_sn = logsn;
        log_buf->tlb_stackid = tp->t_fb->tfb_id;
        log_buf->tlb_eventid = eventid;
        log_buf->tlb_eventflags = 0;
        log_buf->tlb_errno = errornum;

        /* Socket buffers */
        if (rxbuf != NULL) {
                log_buf->tlb_eventflags |= TLB_FLAG_RXBUF;
                log_buf->tlb_rxbuf.tls_sb_acc = rxbuf->sb_acc;
                log_buf->tlb_rxbuf.tls_sb_ccc = rxbuf->sb_ccc;
                log_buf->tlb_rxbuf.tls_sb_spare = 0;
        }
        if (txbuf != NULL) {
                log_buf->tlb_eventflags |= TLB_FLAG_TXBUF;
                log_buf->tlb_txbuf.tls_sb_acc = txbuf->sb_acc;
                log_buf->tlb_txbuf.tls_sb_ccc = txbuf->sb_ccc;
                log_buf->tlb_txbuf.tls_sb_spare = 0;
        }
        /* Copy values from tp to the log entry. */
#define COPY_STAT(f)    log_buf->tlb_ ## f = tp->f
#define COPY_STAT_T(f)  log_buf->tlb_ ## f = tp->t_ ## f
        COPY_STAT_T(state);
        COPY_STAT_T(starttime);
        COPY_STAT(iss);
        COPY_STAT_T(flags);
        COPY_STAT(snd_una);
        COPY_STAT(snd_max);
        COPY_STAT(snd_cwnd);
        COPY_STAT(snd_nxt);
        COPY_STAT(snd_recover);
        COPY_STAT(snd_wnd);
        COPY_STAT(snd_ssthresh);
        COPY_STAT_T(srtt);
        COPY_STAT_T(rttvar);
        COPY_STAT(rcv_up);
        COPY_STAT(rcv_adv);
        COPY_STAT(rcv_nxt);
        COPY_STAT(sack_newdata);
        COPY_STAT(rcv_wnd);
        COPY_STAT_T(dupacks);
        COPY_STAT_T(segqlen);
        COPY_STAT(snd_numholes);
        COPY_STAT(snd_scale);
        COPY_STAT(rcv_scale);
#undef COPY_STAT
#undef COPY_STAT_T
        log_buf->tlb_flex1 = 0;
        log_buf->tlb_flex2 = 0;
        /* Copy stack-specific info. */
        if (stackinfo != NULL) {
                memcpy(&log_buf->tlb_stackinfo, stackinfo,
                    sizeof(log_buf->tlb_stackinfo));
                log_buf->tlb_eventflags |= TLB_FLAG_STACKINFO;
        }

        /* The packet */
        log_buf->tlb_len = len;
        if (th) {
                int optlen;

                log_buf->tlb_eventflags |= TLB_FLAG_HDR;
                log_buf->tlb_th = *th;
                if (th_hostorder)
                        tcp_fields_to_net(&log_buf->tlb_th);
                optlen = (th->th_off << 2) - sizeof (struct tcphdr);
                if (optlen > 0)
                        memcpy(log_buf->tlb_opts, th + 1, optlen);
        }

        /* Verbose information */
        if (func != NULL) {
                log_buf->tlb_eventflags |= TLB_FLAG_VERBOSE;
                if (output_caller != NULL)
                        strlcpy(log_verbose->tlv_snd_frm, output_caller,
                            TCP_FUNC_LEN);
                else
                        *log_verbose->tlv_snd_frm = 0;
                strlcpy(log_verbose->tlv_trace_func, func, TCP_FUNC_LEN);
                log_verbose->tlv_trace_line = line;
        }

        /* Insert the new log at the tail. */
        STAILQ_INSERT_TAIL(&tp->t_logs, log_entry, tlm_queue);
        tcp_log_entry_refcnt_add(log_entry);
        return (log_buf);
}

/*
 * Change the logging state for a TCPCB. Returns 0 on success or an
 * error code on failure.
 */
int
tcp_log_state_change(struct tcpcb *tp, int state)
{
        struct tcp_log_mem *log_entry;

        INP_WLOCK_ASSERT(tp->t_inpcb);
        switch(state) {
        case TCP_LOG_STATE_CLEAR:
                while ((log_entry = STAILQ_FIRST(&tp->t_logs)) != NULL)
                        tcp_log_remove_log_head(tp, log_entry);
                /* Fall through */

        case TCP_LOG_STATE_OFF:
                tp->t_logstate = TCP_LOG_STATE_OFF;
                break;

        case TCP_LOG_STATE_TAIL:
        case TCP_LOG_STATE_HEAD:
        case TCP_LOG_STATE_CONTINUAL:
        case TCP_LOG_STATE_HEAD_AUTO:
        case TCP_LOG_STATE_TAIL_AUTO:
                tp->t_logstate = state;
                break;

        default:
                return (EINVAL);
        }

        tp->t_flags2 &= ~(TF2_LOG_AUTO);

        return (0);
}

/* If tcp_drain() is called, flush half the log entries. */
void
tcp_log_drain(struct tcpcb *tp)
{
        struct tcp_log_mem *log_entry, *next;
        int target, skip;

        INP_WLOCK_ASSERT(tp->t_inpcb);
        if ((target = tp->t_lognum / 2) == 0)
                return;

        /*
         * If we are logging the "head" packets, we want to discard
         * from the tail of the queue. Otherwise, we want to discard
         * from the head.
         */
        if (tp->t_logstate == TCP_LOG_STATE_HEAD ||
            tp->t_logstate == TCP_LOG_STATE_HEAD_AUTO) {
                skip = tp->t_lognum - target;
                STAILQ_FOREACH(log_entry, &tp->t_logs, tlm_queue)
                        if (!--skip)
                                break;
                KASSERT(log_entry != NULL,
                    ("%s: skipped through all entries!", __func__));
                if (log_entry == NULL)
                        return;
                while ((next = STAILQ_NEXT(log_entry, tlm_queue)) != NULL) {
                        STAILQ_REMOVE_AFTER(&tp->t_logs, log_entry, tlm_queue);
                        tcp_log_entry_refcnt_rem(next);
                        tcp_log_remove_log_cleanup(tp, next);
#ifdef INVARIANTS
                        target--;
#endif
                }
                KASSERT(target == 0,
                    ("%s: After removing from tail, target was %d", __func__,
                        target));
        } else if (tp->t_logstate == TCP_LOG_STATE_CONTINUAL) {
                (void)tcp_log_dump_tp_logbuf(tp, "auto-dumped from continual",
                    M_NOWAIT, false);
        } else {
                while ((log_entry = STAILQ_FIRST(&tp->t_logs)) != NULL &&
                    target--)
                        tcp_log_remove_log_head(tp, log_entry);
                KASSERT(target <= 0,
                    ("%s: After removing from head, target was %d", __func__,
                        target));
                KASSERT(tp->t_lognum > 0,
                    ("%s: After removing from head, tp->t_lognum was %d",
                        __func__, target));
                KASSERT(log_entry != NULL,
                    ("%s: After removing from head, the tailq was empty",
                        __func__));
        }
}

static inline int
tcp_log_copyout(struct sockopt *sopt, void *src, void *dst, size_t len)
{

        if (sopt->sopt_td != NULL)
                return (copyout(src, dst, len));
        bcopy(src, dst, len);
        return (0);
}

static int
tcp_log_logs_to_buf(struct sockopt *sopt, struct tcp_log_stailq *log_tailqp,
    struct tcp_log_buffer **end, int count)
{
        struct tcp_log_buffer *out_entry;
        struct tcp_log_mem *log_entry;
        size_t entrysize;
        int error;
#ifdef INVARIANTS
        int orig_count = count;
#endif

        /* Copy the data out. */
        error = 0;
        out_entry = (struct tcp_log_buffer *) sopt->sopt_val;
        STAILQ_FOREACH(log_entry, log_tailqp, tlm_queue) {
                count--;
                KASSERT(count >= 0,
                    ("%s:%d: Exceeded expected count (%d) processing list %p",
                    __func__, __LINE__, orig_count, log_tailqp));

#ifdef TCPLOG_DEBUG_COUNTERS
                counter_u64_add(tcp_log_que_copyout, 1);
#endif

                /*
                 * Skip copying out the header if it isn't present.
                 * Instead, copy out zeros (to ensure we don't leak info).
                 * TODO: Make sure we truly do zero everything we don't
                 * explicitly set.
                 */
                if (log_entry->tlm_buf.tlb_eventflags & TLB_FLAG_HDR)
                        entrysize = sizeof(struct tcp_log_buffer);
                else
                        entrysize = offsetof(struct tcp_log_buffer, tlb_th);
                error = tcp_log_copyout(sopt, &log_entry->tlm_buf, out_entry,
                    entrysize);
                if (error)
                        break;
                if (!(log_entry->tlm_buf.tlb_eventflags & TLB_FLAG_HDR)) {
                        error = tcp_log_copyout(sopt, zerobuf,
                            ((uint8_t *)out_entry) + entrysize,
                            sizeof(struct tcp_log_buffer) - entrysize);
                }

                /*
                 * Copy out the verbose bit, if needed. Either way,
                 * increment the output pointer the correct amount.
                 */
                if (log_entry->tlm_buf.tlb_eventflags & TLB_FLAG_VERBOSE) {
                        error = tcp_log_copyout(sopt, &log_entry->tlm_v,
                            out_entry->tlb_verbose,
                            sizeof(struct tcp_log_verbose));
                        if (error)
                                break;
                        out_entry = (struct tcp_log_buffer *)
                            (((uint8_t *) (out_entry + 1)) +
                            sizeof(struct tcp_log_verbose));
                } else
                        out_entry++;
        }
        *end = out_entry;
        KASSERT(error || count == 0,
            ("%s:%d: Less than expected count (%d) processing list %p"
            " (%d remain)", __func__, __LINE__, orig_count,
            log_tailqp, count));

        return (error);
}

/*
 * Copy out the buffer. Note that we do incremental copying, so
 * sooptcopyout() won't work. However, the goal is to produce the same
 * end result as if we copied in the entire user buffer, updated it,
 * and then used sooptcopyout() to copy it out.
 *
 * NOTE: This should be called with a write lock on the PCB; however,
 * the function will drop it after it extracts the data from the TCPCB.
 */
int
tcp_log_getlogbuf(struct sockopt *sopt, struct tcpcb *tp)
{
        struct tcp_log_stailq log_tailq;
        struct tcp_log_mem *log_entry, *log_next;
        struct tcp_log_buffer *out_entry;
        struct inpcb *inp;
        size_t outsize, entrysize;
        int error, outnum;

        INP_WLOCK_ASSERT(tp->t_inpcb);
        inp = tp->t_inpcb;

        /*
         * Determine which log entries will fit in the buffer. As an
         * optimization, skip this if all the entries will clearly fit
         * in the buffer. (However, get an exact size if we are using
         * INVARIANTS.)
         */
#ifndef INVARIANTS
        if (sopt->sopt_valsize / (sizeof(struct tcp_log_buffer) +
            sizeof(struct tcp_log_verbose)) >= tp->t_lognum) {
                log_entry = STAILQ_LAST(&tp->t_logs, tcp_log_mem, tlm_queue);
                log_next = NULL;
                outsize = 0;
                outnum = tp->t_lognum;
        } else {
#endif
                outsize = outnum = 0;
                log_entry = NULL;
                STAILQ_FOREACH(log_next, &tp->t_logs, tlm_queue) {
                        entrysize = sizeof(struct tcp_log_buffer);
                        if (log_next->tlm_buf.tlb_eventflags &
                            TLB_FLAG_VERBOSE)
                                entrysize += sizeof(struct tcp_log_verbose);
                        if ((sopt->sopt_valsize - outsize) < entrysize)
                                break;
                        outsize += entrysize;
                        outnum++;
                        log_entry = log_next;
                }
                KASSERT(outsize <= sopt->sopt_valsize,
                    ("%s: calculated output size (%zu) greater than available"
                        "space (%zu)", __func__, outsize, sopt->sopt_valsize));
#ifndef INVARIANTS
        }
#endif

        /*
         * Copy traditional sooptcopyout() behavior: if sopt->sopt_val
         * is NULL, silently skip the copy. However, in this case, we
         * will leave the list alone and return. Functionally, this
         * gives userspace a way to poll for an approximate buffer
         * size they will need to get the log entries.
         */
        if (sopt->sopt_val == NULL) {
                INP_WUNLOCK(inp);
                if (outsize == 0) {
                        outsize = outnum * (sizeof(struct tcp_log_buffer) +
                            sizeof(struct tcp_log_verbose));
                }
                if (sopt->sopt_valsize > outsize)
                        sopt->sopt_valsize = outsize;
                return (0);
        }

        /*
         * Break apart the list. We'll save the ones we want to copy
         * out locally and remove them from the TCPCB list. We can
         * then drop the INPCB lock while we do the copyout.
         *
         * There are roughly three cases:
         * 1. There was nothing to copy out. That's easy: drop the
         * lock and return.
         * 2. We are copying out the entire list. Again, that's easy:
         * move the whole list.
         * 3. We are copying out a partial list. That's harder. We
         * need to update the list book-keeping entries.
         */
        if (log_entry != NULL && log_next == NULL) {
                /* Move entire list. */
                KASSERT(outnum == tp->t_lognum,
                    ("%s:%d: outnum (%d) should match tp->t_lognum (%d)",
                        __func__, __LINE__, outnum, tp->t_lognum));
                log_tailq = tp->t_logs;
                tp->t_lognum = 0;
                STAILQ_INIT(&tp->t_logs);
        } else if (log_entry != NULL) {
                /* Move partial list. */
                KASSERT(outnum < tp->t_lognum,
                    ("%s:%d: outnum (%d) not less than tp->t_lognum (%d)",
                        __func__, __LINE__, outnum, tp->t_lognum));
                STAILQ_FIRST(&log_tailq) = STAILQ_FIRST(&tp->t_logs);
                STAILQ_FIRST(&tp->t_logs) = STAILQ_NEXT(log_entry, tlm_queue);
                KASSERT(STAILQ_NEXT(log_entry, tlm_queue) != NULL,
                    ("%s:%d: tp->t_logs is unexpectedly shorter than expected"
                    "(tp: %p, log_tailq: %p, outnum: %d, tp->t_lognum: %d)",
                    __func__, __LINE__, tp, &log_tailq, outnum, tp->t_lognum));
                STAILQ_NEXT(log_entry, tlm_queue) = NULL;
                log_tailq.stqh_last = &STAILQ_NEXT(log_entry, tlm_queue);
                tp->t_lognum -= outnum;
        } else
                STAILQ_INIT(&log_tailq);

        /* Drop the PCB lock. */
        INP_WUNLOCK(inp);

        /* Copy the data out. */
        error = tcp_log_logs_to_buf(sopt, &log_tailq, &out_entry, outnum);

        if (error) {
                /* Restore list */
                INP_WLOCK(inp);
                if ((inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) == 0) {
                        tp = intotcpcb(inp);

                        /* Merge the two lists. */
                        STAILQ_CONCAT(&log_tailq, &tp->t_logs);
                        tp->t_logs = log_tailq;
                        tp->t_lognum += outnum;
                }
                INP_WUNLOCK(inp);
        } else {
                /* Sanity check entries */
                KASSERT(((caddr_t)out_entry - (caddr_t)sopt->sopt_val)  ==
                    outsize, ("%s: Actual output size (%zu) != "
                        "calculated output size (%zu)", __func__,
                        (size_t)((caddr_t)out_entry - (caddr_t)sopt->sopt_val),
                        outsize));

                /* Free the entries we just copied out. */
                STAILQ_FOREACH_SAFE(log_entry, &log_tailq, tlm_queue, log_next) {
                        tcp_log_entry_refcnt_rem(log_entry);
                        uma_zfree(tcp_log_zone, log_entry);
                }
        }

        sopt->sopt_valsize = (size_t)((caddr_t)out_entry -
            (caddr_t)sopt->sopt_val);
        return (error);
}

static void
tcp_log_free_queue(struct tcp_log_dev_queue *param)
{
        struct tcp_log_dev_log_queue *entry;

        KASSERT(param != NULL, ("%s: called with NULL param", __func__));
        if (param == NULL)
                return;

        entry = (struct tcp_log_dev_log_queue *)param;

        /* Free the entries. */
        tcp_log_free_entries(&entry->tldl_entries, &entry->tldl_count);

        /* Free the buffer, if it is allocated. */
        if (entry->tldl_common.tldq_buf != NULL)
                free(entry->tldl_common.tldq_buf, M_TCPLOGDEV);

        /* Free the queue entry. */
        free(entry, M_TCPLOGDEV);
}

static struct tcp_log_common_header *
tcp_log_expandlogbuf(struct tcp_log_dev_queue *param)
{
        struct tcp_log_dev_log_queue *entry;
        struct tcp_log_header *hdr;
        uint8_t *end;
        struct sockopt sopt;
        int error;

        entry = (struct tcp_log_dev_log_queue *)param;

        /* Take a worst-case guess at space needs. */
        sopt.sopt_valsize = sizeof(struct tcp_log_header) +
            entry->tldl_count * (sizeof(struct tcp_log_buffer) +
            sizeof(struct tcp_log_verbose));
        hdr = malloc(sopt.sopt_valsize, M_TCPLOGDEV, M_NOWAIT);
        if (hdr == NULL) {
#ifdef TCPLOG_DEBUG_COUNTERS
                counter_u64_add(tcp_log_que_fail5, entry->tldl_count);
#endif
                return (NULL);
        }
        sopt.sopt_val = hdr + 1;
        sopt.sopt_valsize -= sizeof(struct tcp_log_header);
        sopt.sopt_td = NULL;
        
        error = tcp_log_logs_to_buf(&sopt, &entry->tldl_entries,
            (struct tcp_log_buffer **)&end, entry->tldl_count);
        if (error) {
                free(hdr, M_TCPLOGDEV);
                return (NULL);
        }

        /* Free the entries. */
        tcp_log_free_entries(&entry->tldl_entries, &entry->tldl_count);
        entry->tldl_count = 0;

        memset(hdr, 0, sizeof(struct tcp_log_header));
        hdr->tlh_version = TCP_LOG_BUF_VER;
        hdr->tlh_type = TCP_LOG_DEV_TYPE_BBR;
        hdr->tlh_length = end - (uint8_t *)hdr;
        hdr->tlh_ie = entry->tldl_ie;
        hdr->tlh_af = entry->tldl_af;
        getboottime(&hdr->tlh_offset);
        strlcpy(hdr->tlh_id, entry->tldl_id, TCP_LOG_ID_LEN);
        strlcpy(hdr->tlh_reason, entry->tldl_reason, TCP_LOG_REASON_LEN);
        return ((struct tcp_log_common_header *)hdr);
}

/*
 * Queue the tcpcb's log buffer for transmission via the log buffer facility.
 *
 * NOTE: This should be called with a write lock on the PCB.
 *
 * how should be M_WAITOK or M_NOWAIT. If M_WAITOK, the function will drop
 * and reacquire the INP lock if it needs to do so.
 *
 * If force is false, this will only dump auto-logged sessions if
 * tcp_log_auto_all is true or if there is a log ID defined for the session.
 */
int
tcp_log_dump_tp_logbuf(struct tcpcb *tp, char *reason, int how, bool force)
{
        struct tcp_log_dev_log_queue *entry;
        struct inpcb *inp;
#ifdef TCPLOG_DEBUG_COUNTERS
        int num_entries;
#endif

        inp = tp->t_inpcb;
        INP_WLOCK_ASSERT(inp);

        /* If there are no log entries, there is nothing to do. */
        if (tp->t_lognum == 0)
                return (0);

        /* Check for a log ID. */
        if (tp->t_lib == NULL && (tp->t_flags2 & TF2_LOG_AUTO) &&
            !tcp_log_auto_all && !force) {
                struct tcp_log_mem *log_entry;

                /*
                 * We needed a log ID and none was found. Free the log entries
                 * and return success. Also, cancel further logging. If the
                 * session doesn't have a log ID by now, we'll assume it isn't
                 * going to get one.
                 */
                while ((log_entry = STAILQ_FIRST(&tp->t_logs)) != NULL)
                        tcp_log_remove_log_head(tp, log_entry);
                KASSERT(tp->t_lognum == 0,
                    ("%s: After freeing entries, tp->t_lognum=%d (expected 0)",
                        __func__, tp->t_lognum));
                tp->t_logstate = TCP_LOG_STATE_OFF;
                return (0);
        }

        /*
         * Allocate memory. If we must wait, we'll need to drop the locks
         * and reacquire them (and do all the related business that goes
         * along with that).
         */
        entry = malloc(sizeof(struct tcp_log_dev_log_queue), M_TCPLOGDEV,
            M_NOWAIT);
        if (entry == NULL && (how & M_NOWAIT)) {
#ifdef TCPLOG_DEBUG_COUNTERS
                counter_u64_add(tcp_log_que_fail3, 1);
#endif
                return (ENOBUFS);
        }
        if (entry == NULL) {
                INP_WUNLOCK(inp);
                entry = malloc(sizeof(struct tcp_log_dev_log_queue),
                    M_TCPLOGDEV, M_WAITOK);
                INP_WLOCK(inp);
                /*
                 * Note that this check is slightly overly-restrictive in
                 * that the TCB can survive either of these events.
                 * However, there is currently not a good way to ensure
                 * that is the case. So, if we hit this M_WAIT path, we
                 * may end up dropping some entries. That seems like a
                 * small price to pay for safety.
                 */
                if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
                        free(entry, M_TCPLOGDEV);
#ifdef TCPLOG_DEBUG_COUNTERS
                        counter_u64_add(tcp_log_que_fail2, 1);
#endif
                        return (ECONNRESET);
                }
                tp = intotcpcb(inp);
                if (tp->t_lognum == 0) {
                        free(entry, M_TCPLOGDEV);
                        return (0);
                }
        }

        /* Fill in the unique parts of the queue entry. */
        if (tp->t_lib != NULL)
                strlcpy(entry->tldl_id, tp->t_lib->tlb_id, TCP_LOG_ID_LEN);
        else
                strlcpy(entry->tldl_id, "UNKNOWN", TCP_LOG_ID_LEN);
        if (reason != NULL)
                strlcpy(entry->tldl_reason, reason, TCP_LOG_REASON_LEN);
        else
                strlcpy(entry->tldl_reason, "UNKNOWN", TCP_LOG_ID_LEN);
        entry->tldl_ie = inp->inp_inc.inc_ie;
        if (inp->inp_inc.inc_flags & INC_ISIPV6)
                entry->tldl_af = AF_INET6;
        else
                entry->tldl_af = AF_INET;
        entry->tldl_entries = tp->t_logs;
        entry->tldl_count = tp->t_lognum;

        /* Fill in the common parts of the queue entry. */
        entry->tldl_common.tldq_buf = NULL;
        entry->tldl_common.tldq_xform = tcp_log_expandlogbuf;
        entry->tldl_common.tldq_dtor = tcp_log_free_queue;

        /* Clear the log data from the TCPCB. */
#ifdef TCPLOG_DEBUG_COUNTERS
        num_entries = tp->t_lognum;
#endif
        tp->t_lognum = 0;
        STAILQ_INIT(&tp->t_logs);

        /* Add the entry. If no one is listening, free the entry. */
        if (tcp_log_dev_add_log((struct tcp_log_dev_queue *)entry)) {
                tcp_log_free_queue((struct tcp_log_dev_queue *)entry);
#ifdef TCPLOG_DEBUG_COUNTERS
                counter_u64_add(tcp_log_que_fail1, num_entries);
        } else {
                counter_u64_add(tcp_log_queued, num_entries);
#endif
        }
        return (0);
}

/*
 * Queue the log_id_node's log buffers for transmission via the log buffer
 * facility.
 *
 * NOTE: This should be called with the bucket locked and referenced.
 *
 * how should be M_WAITOK or M_NOWAIT. If M_WAITOK, the function will drop
 * and reacquire the bucket lock if it needs to do so. (The caller must
 * ensure that the tln is no longer on any lists so no one else will mess
 * with this while the lock is dropped!)
 */
static int
tcp_log_dump_node_logbuf(struct tcp_log_id_node *tln, char *reason, int how)
{
        struct tcp_log_dev_log_queue *entry;
        struct tcp_log_id_bucket *tlb;

        tlb = tln->tln_bucket;
        TCPID_BUCKET_LOCK_ASSERT(tlb);
        KASSERT(tlb->tlb_refcnt > 0,
            ("%s:%d: Called with unreferenced bucket (tln=%p, tlb=%p)",
            __func__, __LINE__, tln, tlb));
        KASSERT(tln->tln_closed,
            ("%s:%d: Called for node with tln_closed==false (tln=%p)",
            __func__, __LINE__, tln));

        /* If there are no log entries, there is nothing to do. */
        if (tln->tln_count == 0)
                return (0);

        /*
         * Allocate memory. If we must wait, we'll need to drop the locks
         * and reacquire them (and do all the related business that goes
         * along with that).
         */
        entry = malloc(sizeof(struct tcp_log_dev_log_queue), M_TCPLOGDEV,
            M_NOWAIT);
        if (entry == NULL && (how & M_NOWAIT))
                return (ENOBUFS);
        if (entry == NULL) {
                TCPID_BUCKET_UNLOCK(tlb);
                entry = malloc(sizeof(struct tcp_log_dev_log_queue),
                    M_TCPLOGDEV, M_WAITOK);
                TCPID_BUCKET_LOCK(tlb);
        }

        /* Fill in the common parts of the queue entry.. */
        entry->tldl_common.tldq_buf = NULL;
        entry->tldl_common.tldq_xform = tcp_log_expandlogbuf;
        entry->tldl_common.tldq_dtor = tcp_log_free_queue;

        /* Fill in the unique parts of the queue entry. */
        strlcpy(entry->tldl_id, tlb->tlb_id, TCP_LOG_ID_LEN);
        if (reason != NULL)
                strlcpy(entry->tldl_reason, reason, TCP_LOG_REASON_LEN);
        else
                strlcpy(entry->tldl_reason, "UNKNOWN", TCP_LOG_ID_LEN);
        entry->tldl_ie = tln->tln_ie;
        entry->tldl_entries = tln->tln_entries;
        entry->tldl_count = tln->tln_count;
        entry->tldl_af = tln->tln_af;

        /* Add the entry. If no one is listening, free the entry. */
        if (tcp_log_dev_add_log((struct tcp_log_dev_queue *)entry))
                tcp_log_free_queue((struct tcp_log_dev_queue *)entry);

        return (0);
}


/*
 * Queue the log buffers for all sessions in a bucket for transmissions via
 * the log buffer facility.
 *
 * NOTE: This should be called with a locked bucket; however, the function
 * will drop the lock.
 */
#define LOCAL_SAVE      10
static void
tcp_log_dumpbucketlogs(struct tcp_log_id_bucket *tlb, char *reason)
{
        struct tcp_log_id_node local_entries[LOCAL_SAVE];
        struct inpcb *inp;
        struct tcpcb *tp;
        struct tcp_log_id_node *cur_tln, *prev_tln, *tmp_tln;
        int i, num_local_entries, tree_locked;
        bool expireq_locked;

        TCPID_BUCKET_LOCK_ASSERT(tlb);

        /*
         * Take a reference on the bucket to keep it from disappearing until
         * we are done.
         */
        TCPID_BUCKET_REF(tlb);

        /*
         * We'll try to create these without dropping locks. However, we
         * might very well need to drop locks to get memory. If that's the
         * case, we'll save up to 10 on the stack, and sacrifice the rest.
         * (Otherwise, we need to worry about finding our place again in a
         * potentially changed list. It just doesn't seem worth the trouble
         * to do that.
         */
        expireq_locked = false;
        num_local_entries = 0;
        prev_tln = NULL;
        tree_locked = TREE_UNLOCKED;
        SLIST_FOREACH_SAFE(cur_tln, &tlb->tlb_head, tln_list, tmp_tln) {
                /*
                 * If this isn't associated with a TCPCB, we can pull it off
                 * the list now. We need to be careful that the expire timer
                 * hasn't already taken ownership (tln_expiretime == SBT_MAX).
                 * If so, we let the expire timer code free the data. 
                 */
                if (cur_tln->tln_closed) {
no_inp:
                        /*
                         * Get the expireq lock so we can get a consistent
                         * read of tln_expiretime and so we can remove this
                         * from the expireq.
                         */
                        if (!expireq_locked) {
                                TCPLOG_EXPIREQ_LOCK();
                                expireq_locked = true;
                        }

                        /*
                         * We ignore entries with tln_expiretime == SBT_MAX.
                         * The expire timer code already owns those.
                         */
                        KASSERT(cur_tln->tln_expiretime > (sbintime_t) 0,
                            ("%s:%d: node on the expire queue without positive "
                            "expire time", __func__, __LINE__));
                        if (cur_tln->tln_expiretime == SBT_MAX) {
                                prev_tln = cur_tln;
                                continue;
                        }

                        /* Remove the entry from the expireq. */
                        STAILQ_REMOVE(&tcp_log_expireq_head, cur_tln,
                            tcp_log_id_node, tln_expireq);

                        /* Remove the entry from the bucket. */
                        if (prev_tln != NULL)
                                SLIST_REMOVE_AFTER(prev_tln, tln_list);
                        else
                                SLIST_REMOVE_HEAD(&tlb->tlb_head, tln_list);

                        /*
                         * Drop the INP and bucket reference counts. Due to
                         * lock-ordering rules, we need to drop the expire
                         * queue lock.
                         */
                        TCPLOG_EXPIREQ_UNLOCK();
                        expireq_locked = false;

                        /* Drop the INP reference. */
                        INP_WLOCK(cur_tln->tln_inp);
                        if (!in_pcbrele_wlocked(cur_tln->tln_inp))
                                INP_WUNLOCK(cur_tln->tln_inp);

                        if (tcp_log_unref_bucket(tlb, &tree_locked, NULL)) {
#ifdef INVARIANTS
                                panic("%s: Bucket refcount unexpectedly 0.",
                                    __func__);
#endif
                                /*
                                 * Recover as best we can: free the entry we
                                 * own.
                                 */
                                tcp_log_free_entries(&cur_tln->tln_entries,
                                    &cur_tln->tln_count);
                                uma_zfree(tcp_log_node_zone, cur_tln);
                                goto done;
                        }

                        if (tcp_log_dump_node_logbuf(cur_tln, reason,
                            M_NOWAIT)) {
                                /*
                                 * If we have sapce, save the entries locally.
                                 * Otherwise, free them.
                                 */
                                if (num_local_entries < LOCAL_SAVE) {
                                        local_entries[num_local_entries] =
                                            *cur_tln;
                                        num_local_entries++;
                                } else {
                                        tcp_log_free_entries(
                                            &cur_tln->tln_entries,
                                            &cur_tln->tln_count);
                                }
                        }

                        /* No matter what, we are done with the node now. */
                        uma_zfree(tcp_log_node_zone, cur_tln);

                        /*
                         * Because we removed this entry from the list, prev_tln
                         * (which tracks the previous entry still on the tlb
                         * list) remains unchanged.
                         */
                        continue;
                }

                /*
                 * If we get to this point, the session data is still held in
                 * the TCPCB. So, we need to pull the data out of that.
                 *
                 * We will need to drop the expireq lock so we can lock the INP.
                 * We can then try to extract the data the "easy" way. If that
                 * fails, we'll save the log entries for later.
                 */
                if (expireq_locked) {
                        TCPLOG_EXPIREQ_UNLOCK();
                        expireq_locked = false;
                }

                /* Lock the INP and then re-check the state. */
                inp = cur_tln->tln_inp;
                INP_WLOCK(inp);
                /*
                 * If we caught this while it was transitioning, the data
                 * might have moved from the TCPCB to the tln (signified by
                 * setting tln_closed to true. If so, treat this like an
                 * inactive connection.
                 */
                if (cur_tln->tln_closed) {
                        /*
                         * It looks like we may have caught this connection
                         * while it was transitioning from active to inactive.
                         * Treat this like an inactive connection.
                         */
                        INP_WUNLOCK(inp);
                        goto no_inp;
                }

                /*
                 * Try to dump the data from the tp without dropping the lock.
                 * If this fails, try to save off the data locally.
                 */
                tp = cur_tln->tln_tp;
                if (tcp_log_dump_tp_logbuf(tp, reason, M_NOWAIT, true) &&
                    num_local_entries < LOCAL_SAVE) {
                        tcp_log_move_tp_to_node(tp,
                            &local_entries[num_local_entries]);
                        local_entries[num_local_entries].tln_closed = 1;
                        KASSERT(local_entries[num_local_entries].tln_bucket ==
                            tlb, ("%s: %d: bucket mismatch for node %p",
                            __func__, __LINE__, cur_tln));
                        num_local_entries++;
                }

                INP_WUNLOCK(inp);

                /*
                 * We are goint to leave the current tln on the list. It will
                 * become the previous tln.
                 */
                prev_tln = cur_tln;
        }

        /* Drop our locks, if any. */
        KASSERT(tree_locked == TREE_UNLOCKED,
            ("%s: %d: tree unexpectedly locked", __func__, __LINE__));
        switch (tree_locked) {
        case TREE_WLOCKED:
                TCPID_TREE_WUNLOCK();
                tree_locked = TREE_UNLOCKED;
                break;
        case TREE_RLOCKED:
                TCPID_TREE_RUNLOCK();
                tree_locked = TREE_UNLOCKED;
                break;
        }
        if (expireq_locked) {
                TCPLOG_EXPIREQ_UNLOCK();
                expireq_locked = false;
        }

        /*
         * Try again for any saved entries. tcp_log_dump_node_logbuf() is
         * guaranteed to free the log entries within the node. And, since
         * the node itself is on our stack, we don't need to free it.
         */
        for (i = 0; i < num_local_entries; i++)
                tcp_log_dump_node_logbuf(&local_entries[i], reason, M_WAITOK);

        /* Drop our reference. */
        if (!tcp_log_unref_bucket(tlb, &tree_locked, NULL))
                TCPID_BUCKET_UNLOCK(tlb);

done:
        /* Drop our locks, if any. */
        switch (tree_locked) {
        case TREE_WLOCKED:
                TCPID_TREE_WUNLOCK();
                break;
        case TREE_RLOCKED:
                TCPID_TREE_RUNLOCK();
                break;
        }
        if (expireq_locked)
                TCPLOG_EXPIREQ_UNLOCK();
}
#undef  LOCAL_SAVE


/*
 * Queue the log buffers for all sessions in a bucket for transmissions via
 * the log buffer facility.
 *
 * NOTE: This should be called with a locked INP; however, the function
 * will drop the lock.
 */
void
tcp_log_dump_tp_bucket_logbufs(struct tcpcb *tp, char *reason)
{
        struct tcp_log_id_bucket *tlb;
        int tree_locked;

        /* Figure out our bucket and lock it. */
        INP_WLOCK_ASSERT(tp->t_inpcb);
        tlb = tp->t_lib;
        if (tlb == NULL) {
                /*
                 * No bucket; treat this like a request to dump a single
                 * session's traces.
                 */
                (void)tcp_log_dump_tp_logbuf(tp, reason, M_WAITOK, true);
                INP_WUNLOCK(tp->t_inpcb);
                return;
        }
        TCPID_BUCKET_REF(tlb);
        INP_WUNLOCK(tp->t_inpcb);
        TCPID_BUCKET_LOCK(tlb);

        /* If we are the last reference, we have nothing more to do here. */
        tree_locked = TREE_UNLOCKED;
        if (tcp_log_unref_bucket(tlb, &tree_locked, NULL)) {
                switch (tree_locked) {
                case TREE_WLOCKED:
                        TCPID_TREE_WUNLOCK();
                        break;
                case TREE_RLOCKED:
                        TCPID_TREE_RUNLOCK();
                        break;
                }
                return;
        }

        /* Turn this over to tcp_log_dumpbucketlogs() to finish the work. */ 
        tcp_log_dumpbucketlogs(tlb, reason);
}

/*
 * Mark the end of a flow with the current stack. A stack can add
 * stack-specific info to this trace event by overriding this
 * function (see bbr_log_flowend() for example).
 */
void
tcp_log_flowend(struct tcpcb *tp)
{
        if (tp->t_logstate != TCP_LOG_STATE_OFF) {
                struct socket *so = tp->t_inpcb->inp_socket;
                TCP_LOG_EVENT(tp, NULL, &so->so_rcv, &so->so_snd,
                                TCP_LOG_FLOWEND, 0, 0, NULL, false);
        }
}