kern_event.c

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/*-
 * Copyright (c) 1999,2000,2001 Jonathan Lemon <jlemon@FreeBSD.org>
 * Copyright 2004 John-Mark Gurney <jmg@FreeBSD.org>
 * Copyright (c) 2009 Apple, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

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

#include "opt_ktrace.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/capability.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/malloc.h>
#include <sys/unistd.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/filio.h>
#include <sys/fcntl.h>
#include <sys/kthread.h>
#include <sys/selinfo.h>
#include <sys/queue.h>
#include <sys/event.h>
#include <sys/eventvar.h>
#include <sys/poll.h>
#include <sys/protosw.h>
#include <sys/sigio.h>
#include <sys/signalvar.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/stat.h>
#include <sys/sysctl.h>
#include <sys/sysproto.h>
#include <sys/syscallsubr.h>
#include <sys/taskqueue.h>
#include <sys/uio.h>
#ifdef KTRACE
#include <sys/ktrace.h>
#endif

#include <vm/uma.h>

static MALLOC_DEFINE(M_KQUEUE, "kqueue", "memory for kqueue system");

/*
 * This lock is used if multiple kq locks are required.  This possibly
 * should be made into a per proc lock.
 */
static struct mtx       kq_global;
MTX_SYSINIT(kq_global, &kq_global, "kqueue order", MTX_DEF);
#define KQ_GLOBAL_LOCK(lck, haslck)     do {    \
        if (!haslck)                            \
                mtx_lock(lck);                  \
        haslck = 1;                             \
} while (0)
#define KQ_GLOBAL_UNLOCK(lck, haslck)   do {    \
        if (haslck)                             \
                mtx_unlock(lck);                        \
        haslck = 0;                             \
} while (0)

TASKQUEUE_DEFINE_THREAD(kqueue);

static int      kevent_copyout(void *arg, struct kevent *kevp, int count);
static int      kevent_copyin(void *arg, struct kevent *kevp, int count);
static int      kqueue_register(struct kqueue *kq, struct kevent *kev,
                    struct thread *td, int waitok);
static int      kqueue_acquire(struct file *fp, struct kqueue **kqp);
static void     kqueue_release(struct kqueue *kq, int locked);
static int      kqueue_expand(struct kqueue *kq, struct filterops *fops,
                    uintptr_t ident, int waitok);
static void     kqueue_task(void *arg, int pending);
static int      kqueue_scan(struct kqueue *kq, int maxevents,
                    struct kevent_copyops *k_ops,
                    const struct timespec *timeout,
                    struct kevent *keva, struct thread *td);
static void     kqueue_wakeup(struct kqueue *kq);
static struct filterops *kqueue_fo_find(int filt);
static void     kqueue_fo_release(int filt);

static fo_rdwr_t        kqueue_read;
static fo_rdwr_t        kqueue_write;
static fo_truncate_t    kqueue_truncate;
static fo_ioctl_t       kqueue_ioctl;
static fo_poll_t        kqueue_poll;
static fo_kqfilter_t    kqueue_kqfilter;
static fo_stat_t        kqueue_stat;
static fo_close_t       kqueue_close;

static struct fileops kqueueops = {
        .fo_read = kqueue_read,
        .fo_write = kqueue_write,
        .fo_truncate = kqueue_truncate,
        .fo_ioctl = kqueue_ioctl,
        .fo_poll = kqueue_poll,
        .fo_kqfilter = kqueue_kqfilter,
        .fo_stat = kqueue_stat,
        .fo_close = kqueue_close,
        .fo_chmod = invfo_chmod,
        .fo_chown = invfo_chown,
};

static int      knote_attach(struct knote *kn, struct kqueue *kq);
static void     knote_drop(struct knote *kn, struct thread *td);
static void     knote_enqueue(struct knote *kn);
static void     knote_dequeue(struct knote *kn);
static void     knote_init(void);
static struct   knote *knote_alloc(int waitok);
static void     knote_free(struct knote *kn);

static void     filt_kqdetach(struct knote *kn);
static int      filt_kqueue(struct knote *kn, long hint);
static int      filt_procattach(struct knote *kn);
static void     filt_procdetach(struct knote *kn);
static int      filt_proc(struct knote *kn, long hint);
static int      filt_fileattach(struct knote *kn);
static void     filt_timerexpire(void *knx);
static int      filt_timerattach(struct knote *kn);
static void     filt_timerdetach(struct knote *kn);
static int      filt_timer(struct knote *kn, long hint);
static int      filt_userattach(struct knote *kn);
static void     filt_userdetach(struct knote *kn);
static int      filt_user(struct knote *kn, long hint);
static void     filt_usertouch(struct knote *kn, struct kevent *kev,
                    u_long type);

static struct filterops file_filtops = {
        .f_isfd = 1,
        .f_attach = filt_fileattach,
};
static struct filterops kqread_filtops = {
        .f_isfd = 1,
        .f_detach = filt_kqdetach,
        .f_event = filt_kqueue,
};
/* XXX - move to kern_proc.c?  */
static struct filterops proc_filtops = {
        .f_isfd = 0,
        .f_attach = filt_procattach,
        .f_detach = filt_procdetach,
        .f_event = filt_proc,
};
static struct filterops timer_filtops = {
        .f_isfd = 0,
        .f_attach = filt_timerattach,
        .f_detach = filt_timerdetach,
        .f_event = filt_timer,
};
static struct filterops user_filtops = {
        .f_attach = filt_userattach,
        .f_detach = filt_userdetach,
        .f_event = filt_user,
        .f_touch = filt_usertouch,
};

static uma_zone_t       knote_zone;
static int              kq_ncallouts = 0;
static int              kq_calloutmax = (4 * 1024);
SYSCTL_INT(_kern, OID_AUTO, kq_calloutmax, CTLFLAG_RW,
    &kq_calloutmax, 0, "Maximum number of callouts allocated for kqueue");

/* XXX - ensure not KN_INFLUX?? */
#define KNOTE_ACTIVATE(kn, islock) do {                                 \
        if ((islock))                                                   \
                mtx_assert(&(kn)->kn_kq->kq_lock, MA_OWNED);            \
        else                                                            \
                KQ_LOCK((kn)->kn_kq);                                   \
        (kn)->kn_status |= KN_ACTIVE;                                   \
        if (((kn)->kn_status & (KN_QUEUED | KN_DISABLED)) == 0)         \
                knote_enqueue((kn));                                    \
        if (!(islock))                                                  \
                KQ_UNLOCK((kn)->kn_kq);                                 \
} while(0)
#define KQ_LOCK(kq) do {                                                \
        mtx_lock(&(kq)->kq_lock);                                       \
} while (0)
#define KQ_FLUX_WAKEUP(kq) do {                                         \
        if (((kq)->kq_state & KQ_FLUXWAIT) == KQ_FLUXWAIT) {            \
                (kq)->kq_state &= ~KQ_FLUXWAIT;                         \
                wakeup((kq));                                           \
        }                                                               \
} while (0)
#define KQ_UNLOCK_FLUX(kq) do {                                         \
        KQ_FLUX_WAKEUP(kq);                                             \
        mtx_unlock(&(kq)->kq_lock);                                     \
} while (0)
#define KQ_UNLOCK(kq) do {                                              \
        mtx_unlock(&(kq)->kq_lock);                                     \
} while (0)
#define KQ_OWNED(kq) do {                                               \
        mtx_assert(&(kq)->kq_lock, MA_OWNED);                           \
} while (0)
#define KQ_NOTOWNED(kq) do {                                            \
        mtx_assert(&(kq)->kq_lock, MA_NOTOWNED);                        \
} while (0)
#define KN_LIST_LOCK(kn) do {                                           \
        if (kn->kn_knlist != NULL)                                      \
                kn->kn_knlist->kl_lock(kn->kn_knlist->kl_lockarg);      \
} while (0)
#define KN_LIST_UNLOCK(kn) do {                                         \
        if (kn->kn_knlist != NULL)                                      \
                kn->kn_knlist->kl_unlock(kn->kn_knlist->kl_lockarg);    \
} while (0)
#define KNL_ASSERT_LOCK(knl, islocked) do {                             \
        if (islocked)                                                   \
                KNL_ASSERT_LOCKED(knl);                         \
        else                                                            \
                KNL_ASSERT_UNLOCKED(knl);                               \
} while (0)
#ifdef INVARIANTS
#define KNL_ASSERT_LOCKED(knl) do {                                     \
        knl->kl_assert_locked((knl)->kl_lockarg);                       \
} while (0)
#define KNL_ASSERT_UNLOCKED(knl) do {                                   \
        knl->kl_assert_unlocked((knl)->kl_lockarg);                     \
} while (0)
#else /* !INVARIANTS */
#define KNL_ASSERT_LOCKED(knl) do {} while(0)
#define KNL_ASSERT_UNLOCKED(knl) do {} while (0)
#endif /* INVARIANTS */

#define KN_HASHSIZE             64              /* XXX should be tunable */
#define KN_HASH(val, mask)      (((val) ^ (val >> 8)) & (mask))

static int
filt_nullattach(struct knote *kn)
{

        return (ENXIO);
};

struct filterops null_filtops = {
        .f_isfd = 0,
        .f_attach = filt_nullattach,
};

/* XXX - make SYSINIT to add these, and move into respective modules. */
extern struct filterops sig_filtops;
extern struct filterops fs_filtops;

/*
 * Table for for all system-defined filters.
 */
static struct mtx       filterops_lock;
MTX_SYSINIT(kqueue_filterops, &filterops_lock, "protect sysfilt_ops",
        MTX_DEF);
static struct {
        struct filterops *for_fop;
        int for_refcnt;
} sysfilt_ops[EVFILT_SYSCOUNT] = {
        { &file_filtops },                      /* EVFILT_READ */
        { &file_filtops },                      /* EVFILT_WRITE */
        { &null_filtops },                      /* EVFILT_AIO */
        { &file_filtops },                      /* EVFILT_VNODE */
        { &proc_filtops },                      /* EVFILT_PROC */
        { &sig_filtops },                       /* EVFILT_SIGNAL */
        { &timer_filtops },                     /* EVFILT_TIMER */
        { &null_filtops },                      /* former EVFILT_NETDEV */
        { &fs_filtops },                        /* EVFILT_FS */
        { &null_filtops },                      /* EVFILT_LIO */
        { &user_filtops },                      /* EVFILT_USER */
};

/*
 * Simple redirection for all cdevsw style objects to call their fo_kqfilter
 * method.
 */
static int
filt_fileattach(struct knote *kn)
{

        return (fo_kqfilter(kn->kn_fp, kn));
}

/*ARGSUSED*/
static int
kqueue_kqfilter(struct file *fp, struct knote *kn)
{
        struct kqueue *kq = kn->kn_fp->f_data;

        if (kn->kn_filter != EVFILT_READ)
                return (EINVAL);

        kn->kn_status |= KN_KQUEUE;
        kn->kn_fop = &kqread_filtops;
        knlist_add(&kq->kq_sel.si_note, kn, 0);

        return (0);
}

static void
filt_kqdetach(struct knote *kn)
{
        struct kqueue *kq = kn->kn_fp->f_data;

        knlist_remove(&kq->kq_sel.si_note, kn, 0);
}

/*ARGSUSED*/
static int
filt_kqueue(struct knote *kn, long hint)
{
        struct kqueue *kq = kn->kn_fp->f_data;

        kn->kn_data = kq->kq_count;
        return (kn->kn_data > 0);
}

/* XXX - move to kern_proc.c?  */
static int
filt_procattach(struct knote *kn)
{
        struct proc *p;
        int immediate;
        int error;

        immediate = 0;
        p = pfind(kn->kn_id);
        if (p == NULL && (kn->kn_sfflags & NOTE_EXIT)) {
                p = zpfind(kn->kn_id);
                immediate = 1;
        } else if (p != NULL && (p->p_flag & P_WEXIT)) {
                immediate = 1;
        }

        if (p == NULL)
                return (ESRCH);
        if ((error = p_cansee(curthread, p))) {
                PROC_UNLOCK(p);
                return (error);
        }

        kn->kn_ptr.p_proc = p;
        kn->kn_flags |= EV_CLEAR;               /* automatically set */

        /*
         * internal flag indicating registration done by kernel
         */
        if (kn->kn_flags & EV_FLAG1) {
                kn->kn_data = kn->kn_sdata;             /* ppid */
                kn->kn_fflags = NOTE_CHILD;
                kn->kn_flags &= ~EV_FLAG1;
        }

        if (immediate == 0)
                knlist_add(&p->p_klist, kn, 1);

        /*
         * Immediately activate any exit notes if the target process is a
         * zombie.  This is necessary to handle the case where the target
         * process, e.g. a child, dies before the kevent is registered.
         */
        if (immediate && filt_proc(kn, NOTE_EXIT))
                KNOTE_ACTIVATE(kn, 0);

        PROC_UNLOCK(p);

        return (0);
}

/*
 * The knote may be attached to a different process, which may exit,
 * leaving nothing for the knote to be attached to.  So when the process
 * exits, the knote is marked as DETACHED and also flagged as ONESHOT so
 * it will be deleted when read out.  However, as part of the knote deletion,
 * this routine is called, so a check is needed to avoid actually performing
 * a detach, because the original process does not exist any more.
 */
/* XXX - move to kern_proc.c?  */
static void
filt_procdetach(struct knote *kn)
{
        struct proc *p;

        p = kn->kn_ptr.p_proc;
        knlist_remove(&p->p_klist, kn, 0);
        kn->kn_ptr.p_proc = NULL;
}

/* XXX - move to kern_proc.c?  */
static int
filt_proc(struct knote *kn, long hint)
{
        struct proc *p = kn->kn_ptr.p_proc;
        u_int event;

        /*
         * mask off extra data
         */
        event = (u_int)hint & NOTE_PCTRLMASK;

        /*
         * if the user is interested in this event, record it.
         */
        if (kn->kn_sfflags & event)
                kn->kn_fflags |= event;

        /*
         * process is gone, so flag the event as finished.
         */
        if (event == NOTE_EXIT) {
                if (!(kn->kn_status & KN_DETACHED))
                        knlist_remove_inevent(&p->p_klist, kn);
                kn->kn_flags |= (EV_EOF | EV_ONESHOT);
                kn->kn_ptr.p_proc = NULL;
                if (kn->kn_fflags & NOTE_EXIT)
                        kn->kn_data = p->p_xstat;
                if (kn->kn_fflags == 0)
                        kn->kn_flags |= EV_DROP;
                return (1);
        }

        return (kn->kn_fflags != 0);
}

/*
 * Called when the process forked. It mostly does the same as the
 * knote(), activating all knotes registered to be activated when the
 * process forked. Additionally, for each knote attached to the
 * parent, check whether user wants to track the new process. If so
 * attach a new knote to it, and immediately report an event with the
 * child's pid.
 */
void
knote_fork(struct knlist *list, int pid)
{
        struct kqueue *kq;
        struct knote *kn;
        struct kevent kev;
        int error;

        if (list == NULL)
                return;
        list->kl_lock(list->kl_lockarg);

        SLIST_FOREACH(kn, &list->kl_list, kn_selnext) {
                if ((kn->kn_status & KN_INFLUX) == KN_INFLUX)
                        continue;
                kq = kn->kn_kq;
                KQ_LOCK(kq);
                if ((kn->kn_status & (KN_INFLUX | KN_SCAN)) == KN_INFLUX) {
                        KQ_UNLOCK(kq);
                        continue;
                }

                /*
                 * The same as knote(), activate the event.
                 */
                if ((kn->kn_sfflags & NOTE_TRACK) == 0) {
                        kn->kn_status |= KN_HASKQLOCK;
                        if (kn->kn_fop->f_event(kn, NOTE_FORK))
                                KNOTE_ACTIVATE(kn, 1);
                        kn->kn_status &= ~KN_HASKQLOCK;
                        KQ_UNLOCK(kq);
                        continue;
                }

                /*
                 * The NOTE_TRACK case. In addition to the activation
                 * of the event, we need to register new event to
                 * track the child. Drop the locks in preparation for
                 * the call to kqueue_register().
                 */
                kn->kn_status |= KN_INFLUX;
                KQ_UNLOCK(kq);
                list->kl_unlock(list->kl_lockarg);

                /*
                 * Activate existing knote and register a knote with
                 * new process.
                 */
                kev.ident = pid;
                kev.filter = kn->kn_filter;
                kev.flags = kn->kn_flags | EV_ADD | EV_ENABLE | EV_FLAG1;
                kev.fflags = kn->kn_sfflags;
                kev.data = kn->kn_id;           /* parent */
                kev.udata = kn->kn_kevent.udata;/* preserve udata */
                error = kqueue_register(kq, &kev, NULL, 0);
                if (error)
                        kn->kn_fflags |= NOTE_TRACKERR;
                if (kn->kn_fop->f_event(kn, NOTE_FORK))
                        KNOTE_ACTIVATE(kn, 0);
                KQ_LOCK(kq);
                kn->kn_status &= ~KN_INFLUX;
                KQ_UNLOCK_FLUX(kq);
                list->kl_lock(list->kl_lockarg);
        }
        list->kl_unlock(list->kl_lockarg);
}

/*
 * XXX: EVFILT_TIMER should perhaps live in kern_time.c beside the
 * interval timer support code.
 */
static int
timertoticks(intptr_t data)
{
        struct timeval tv;
        int tticks;

        tv.tv_sec = data / 1000;
        tv.tv_usec = (data % 1000) * 1000;
        tticks = tvtohz(&tv);

        return tticks;
}

static void
filt_timerexpire(void *knx)
{
        struct knote *kn = knx;
        struct callout *calloutp;

        kn->kn_data++;
        KNOTE_ACTIVATE(kn, 0);  /* XXX - handle locking */

        /*
         * timertoticks() uses tvtohz() which always adds 1 to allow
         * for the time until the next clock interrupt being strictly
         * less than 1 clock tick.  We don't want that here since we
         * want to appear to be in sync with the clock interrupt even
         * when we're delayed.
         */
        if ((kn->kn_flags & EV_ONESHOT) != EV_ONESHOT) {
                calloutp = (struct callout *)kn->kn_hook;
                callout_reset_curcpu(calloutp, timertoticks(kn->kn_sdata) - 1,
                    filt_timerexpire, kn);
        }
}

/*
 * data contains amount of time to sleep, in milliseconds
 */
static int
filt_timerattach(struct knote *kn)
{
        struct callout *calloutp;

        atomic_add_int(&kq_ncallouts, 1);

        if (kq_ncallouts >= kq_calloutmax) {
                atomic_add_int(&kq_ncallouts, -1);
                return (ENOMEM);
        }

        kn->kn_flags |= EV_CLEAR;               /* automatically set */
        kn->kn_status &= ~KN_DETACHED;          /* knlist_add usually sets it */
        calloutp = malloc(sizeof(*calloutp), M_KQUEUE, M_WAITOK);
        callout_init(calloutp, CALLOUT_MPSAFE);
        kn->kn_hook = calloutp;
        callout_reset_curcpu(calloutp, timertoticks(kn->kn_sdata),
            filt_timerexpire, kn);

        return (0);
}

static void
filt_timerdetach(struct knote *kn)
{
        struct callout *calloutp;

        calloutp = (struct callout *)kn->kn_hook;
        callout_drain(calloutp);
        free(calloutp, M_KQUEUE);
        atomic_add_int(&kq_ncallouts, -1);
        kn->kn_status |= KN_DETACHED;   /* knlist_remove usually clears it */
}

static int
filt_timer(struct knote *kn, long hint)
{

        return (kn->kn_data != 0);
}

static int
filt_userattach(struct knote *kn)
{

        /* 
         * EVFILT_USER knotes are not attached to anything in the kernel.
         */ 
        kn->kn_hook = NULL;
        if (kn->kn_fflags & NOTE_TRIGGER)
                kn->kn_hookid = 1;
        else
                kn->kn_hookid = 0;
        return (0);
}

static void
filt_userdetach(__unused struct knote *kn)
{

        /*
         * EVFILT_USER knotes are not attached to anything in the kernel.
         */
}

static int
filt_user(struct knote *kn, __unused long hint)
{

        return (kn->kn_hookid);
}

static void
filt_usertouch(struct knote *kn, struct kevent *kev, u_long type)
{
        u_int ffctrl;

        switch (type) {
        case EVENT_REGISTER:
                if (kev->fflags & NOTE_TRIGGER)
                        kn->kn_hookid = 1;

                ffctrl = kev->fflags & NOTE_FFCTRLMASK;
                kev->fflags &= NOTE_FFLAGSMASK;
                switch (ffctrl) {
                case NOTE_FFNOP:
                        break;

                case NOTE_FFAND:
                        kn->kn_sfflags &= kev->fflags;
                        break;

                case NOTE_FFOR:
                        kn->kn_sfflags |= kev->fflags;
                        break;

                case NOTE_FFCOPY:
                        kn->kn_sfflags = kev->fflags;
                        break;

                default:
                        /* XXX Return error? */
                        break;
                }
                kn->kn_sdata = kev->data;
                if (kev->flags & EV_CLEAR) {
                        kn->kn_hookid = 0;
                        kn->kn_data = 0;
                        kn->kn_fflags = 0;
                }
                break;

        case EVENT_PROCESS:
                *kev = kn->kn_kevent;
                kev->fflags = kn->kn_sfflags;
                kev->data = kn->kn_sdata;
                if (kn->kn_flags & EV_CLEAR) {
                        kn->kn_hookid = 0;
                        kn->kn_data = 0;
                        kn->kn_fflags = 0;
                }
                break;

        default:
                panic("filt_usertouch() - invalid type (%ld)", type);
                break;
        }
}

int
sys_kqueue(struct thread *td, struct kqueue_args *uap)
{
        struct filedesc *fdp;
        struct kqueue *kq;
        struct file *fp;
        int fd, error;

        fdp = td->td_proc->p_fd;
        error = falloc(td, &fp, &fd, 0);
        if (error)
                goto done2;

        /* An extra reference on `nfp' has been held for us by falloc(). */
        kq = malloc(sizeof *kq, M_KQUEUE, M_WAITOK | M_ZERO);
        mtx_init(&kq->kq_lock, "kqueue", NULL, MTX_DEF|MTX_DUPOK);
        TAILQ_INIT(&kq->kq_head);
        kq->kq_fdp = fdp;
        knlist_init_mtx(&kq->kq_sel.si_note, &kq->kq_lock);
        TASK_INIT(&kq->kq_task, 0, kqueue_task, kq);

        FILEDESC_XLOCK(fdp);
        TAILQ_INSERT_HEAD(&fdp->fd_kqlist, kq, kq_list);
        FILEDESC_XUNLOCK(fdp);

        finit(fp, FREAD | FWRITE, DTYPE_KQUEUE, kq, &kqueueops);
        fdrop(fp, td);

        td->td_retval[0] = fd;
done2:
        return (error);
}

#ifndef _SYS_SYSPROTO_H_
struct kevent_args {
        int     fd;
        const struct kevent *changelist;
        int     nchanges;
        struct  kevent *eventlist;
        int     nevents;
        const struct timespec *timeout;
};
#endif
int
sys_kevent(struct thread *td, struct kevent_args *uap)
{
        struct timespec ts, *tsp;
        struct kevent_copyops k_ops = { uap,
                                        kevent_copyout,
                                        kevent_copyin};
        int error;
#ifdef KTRACE
        struct uio ktruio;
        struct iovec ktriov;
        struct uio *ktruioin = NULL;
        struct uio *ktruioout = NULL;
#endif

        if (uap->timeout != NULL) {
                error = copyin(uap->timeout, &ts, sizeof(ts));
                if (error)
                        return (error);
                tsp = &ts;
        } else
                tsp = NULL;

#ifdef KTRACE
        if (KTRPOINT(td, KTR_GENIO)) {
                ktriov.iov_base = uap->changelist;
                ktriov.iov_len = uap->nchanges * sizeof(struct kevent);
                ktruio = (struct uio){ .uio_iov = &ktriov, .uio_iovcnt = 1,
                    .uio_segflg = UIO_USERSPACE, .uio_rw = UIO_READ,
                    .uio_td = td };
                ktruioin = cloneuio(&ktruio);
                ktriov.iov_base = uap->eventlist;
                ktriov.iov_len = uap->nevents * sizeof(struct kevent);
                ktruioout = cloneuio(&ktruio);
        }
#endif

        error = kern_kevent(td, uap->fd, uap->nchanges, uap->nevents,
            &k_ops, tsp);

#ifdef KTRACE
        if (ktruioin != NULL) {
                ktruioin->uio_resid = uap->nchanges * sizeof(struct kevent);
                ktrgenio(uap->fd, UIO_WRITE, ktruioin, 0);
                ktruioout->uio_resid = td->td_retval[0] * sizeof(struct kevent);
                ktrgenio(uap->fd, UIO_READ, ktruioout, error);
        }
#endif

        return (error);
}

/*
 * Copy 'count' items into the destination list pointed to by uap->eventlist.
 */
static int
kevent_copyout(void *arg, struct kevent *kevp, int count)
{
        struct kevent_args *uap;
        int error;

        KASSERT(count <= KQ_NEVENTS, ("count (%d) > KQ_NEVENTS", count));
        uap = (struct kevent_args *)arg;

        error = copyout(kevp, uap->eventlist, count * sizeof *kevp);
        if (error == 0)
                uap->eventlist += count;
        return (error);
}

/*
 * Copy 'count' items from the list pointed to by uap->changelist.
 */
static int
kevent_copyin(void *arg, struct kevent *kevp, int count)
{
        struct kevent_args *uap;
        int error;

        KASSERT(count <= KQ_NEVENTS, ("count (%d) > KQ_NEVENTS", count));
        uap = (struct kevent_args *)arg;

        error = copyin(uap->changelist, kevp, count * sizeof *kevp);
        if (error == 0)
                uap->changelist += count;
        return (error);
}

int
kern_kevent(struct thread *td, int fd, int nchanges, int nevents,
    struct kevent_copyops *k_ops, const struct timespec *timeout)
{
        struct kevent keva[KQ_NEVENTS];
        struct kevent *kevp, *changes;
        struct kqueue *kq;
        struct file *fp;
        int i, n, nerrors, error;

        if ((error = fget(td, fd, CAP_POST_EVENT, &fp)) != 0)
                return (error);
        if ((error = kqueue_acquire(fp, &kq)) != 0)
                goto done_norel;

        nerrors = 0;

        while (nchanges > 0) {
                n = nchanges > KQ_NEVENTS ? KQ_NEVENTS : nchanges;
                error = k_ops->k_copyin(k_ops->arg, keva, n);
                if (error)
                        goto done;
                changes = keva;
                for (i = 0; i < n; i++) {
                        kevp = &changes[i];
                        if (!kevp->filter)
                                continue;
                        kevp->flags &= ~EV_SYSFLAGS;
                        error = kqueue_register(kq, kevp, td, 1);
                        if (error || (kevp->flags & EV_RECEIPT)) {
                                if (nevents != 0) {
                                        kevp->flags = EV_ERROR;
                                        kevp->data = error;
                                        (void) k_ops->k_copyout(k_ops->arg,
                                            kevp, 1);
                                        nevents--;
                                        nerrors++;
                                } else {
                                        goto done;
                                }
                        }
                }
                nchanges -= n;
        }
        if (nerrors) {
                td->td_retval[0] = nerrors;
                error = 0;
                goto done;
        }

        error = kqueue_scan(kq, nevents, k_ops, timeout, keva, td);
done:
        kqueue_release(kq, 0);
done_norel:
        fdrop(fp, td);
        return (error);
}

int
kqueue_add_filteropts(int filt, struct filterops *filtops)
{
        int error;

        error = 0;
        if (filt > 0 || filt + EVFILT_SYSCOUNT < 0) {
                printf(
"trying to add a filterop that is out of range: %d is beyond %d\n",
                    ~filt, EVFILT_SYSCOUNT);
                return EINVAL;
        }
        mtx_lock(&filterops_lock);
        if (sysfilt_ops[~filt].for_fop != &null_filtops &&
            sysfilt_ops[~filt].for_fop != NULL)
                error = EEXIST;
        else {
                sysfilt_ops[~filt].for_fop = filtops;
                sysfilt_ops[~filt].for_refcnt = 0;
        }
        mtx_unlock(&filterops_lock);

        return (error);
}

int
kqueue_del_filteropts(int filt)
{
        int error;

        error = 0;
        if (filt > 0 || filt + EVFILT_SYSCOUNT < 0)
                return EINVAL;

        mtx_lock(&filterops_lock);
        if (sysfilt_ops[~filt].for_fop == &null_filtops ||
            sysfilt_ops[~filt].for_fop == NULL)
                error = EINVAL;
        else if (sysfilt_ops[~filt].for_refcnt != 0)
                error = EBUSY;
        else {
                sysfilt_ops[~filt].for_fop = &null_filtops;
                sysfilt_ops[~filt].for_refcnt = 0;
        }
        mtx_unlock(&filterops_lock);

        return error;
}

static struct filterops *
kqueue_fo_find(int filt)
{

        if (filt > 0 || filt + EVFILT_SYSCOUNT < 0)
                return NULL;

        mtx_lock(&filterops_lock);
        sysfilt_ops[~filt].for_refcnt++;
        if (sysfilt_ops[~filt].for_fop == NULL)
                sysfilt_ops[~filt].for_fop = &null_filtops;
        mtx_unlock(&filterops_lock);

        return sysfilt_ops[~filt].for_fop;
}

static void
kqueue_fo_release(int filt)
{

        if (filt > 0 || filt + EVFILT_SYSCOUNT < 0)
                return;

        mtx_lock(&filterops_lock);
        KASSERT(sysfilt_ops[~filt].for_refcnt > 0,
            ("filter object refcount not valid on release"));
        sysfilt_ops[~filt].for_refcnt--;
        mtx_unlock(&filterops_lock);
}

/*
 * A ref to kq (obtained via kqueue_acquire) must be held.  waitok will
 * influence if memory allocation should wait.  Make sure it is 0 if you
 * hold any mutexes.
 */
static int
kqueue_register(struct kqueue *kq, struct kevent *kev, struct thread *td, int waitok)
{
        struct filterops *fops;
        struct file *fp;
        struct knote *kn, *tkn;
        int error, filt, event;
        int haskqglobal, filedesc_unlock;

        fp = NULL;
        kn = NULL;
        error = 0;
        haskqglobal = 0;
        filedesc_unlock = 0;

        filt = kev->filter;
        fops = kqueue_fo_find(filt);
        if (fops == NULL)
                return EINVAL;

        tkn = knote_alloc(waitok);              /* prevent waiting with locks */

findkn:
        if (fops->f_isfd) {
                KASSERT(td != NULL, ("td is NULL"));
                error = fget(td, kev->ident, CAP_POLL_EVENT, &fp);
                if (error)
                        goto done;

                if ((kev->flags & EV_ADD) == EV_ADD && kqueue_expand(kq, fops,
                    kev->ident, 0) != 0) {
                        /* try again */
                        fdrop(fp, td);
                        fp = NULL;
                        error = kqueue_expand(kq, fops, kev->ident, waitok);
                        if (error)
                                goto done;
                        goto findkn;
                }

                if (fp->f_type == DTYPE_KQUEUE) {
                        /*
                         * if we add some inteligence about what we are doing,
                         * we should be able to support events on ourselves.
                         * We need to know when we are doing this to prevent
                         * getting both the knlist lock and the kq lock since
                         * they are the same thing.
                         */
                        if (fp->f_data == kq) {
                                error = EINVAL;
                                goto done;
                        }

                        /*
                         * Pre-lock the filedesc before the global
                         * lock mutex, see the comment in
                         * kqueue_close().
                         */
                        FILEDESC_XLOCK(td->td_proc->p_fd);
                        filedesc_unlock = 1;
                        KQ_GLOBAL_LOCK(&kq_global, haskqglobal);
                }

                KQ_LOCK(kq);
                if (kev->ident < kq->kq_knlistsize) {
                        SLIST_FOREACH(kn, &kq->kq_knlist[kev->ident], kn_link)
                                if (kev->filter == kn->kn_filter)
                                        break;
                }
        } else {
                if ((kev->flags & EV_ADD) == EV_ADD)
                        kqueue_expand(kq, fops, kev->ident, waitok);

                KQ_LOCK(kq);
                if (kq->kq_knhashmask != 0) {
                        struct klist *list;

                        list = &kq->kq_knhash[
                            KN_HASH((u_long)kev->ident, kq->kq_knhashmask)];
                        SLIST_FOREACH(kn, list, kn_link)
                                if (kev->ident == kn->kn_id &&
                                    kev->filter == kn->kn_filter)
                                        break;
                }
        }

        /* knote is in the process of changing, wait for it to stablize. */
        if (kn != NULL && (kn->kn_status & KN_INFLUX) == KN_INFLUX) {
                KQ_GLOBAL_UNLOCK(&kq_global, haskqglobal);
                if (filedesc_unlock) {
                        FILEDESC_XUNLOCK(td->td_proc->p_fd);
                        filedesc_unlock = 0;
                }
                kq->kq_state |= KQ_FLUXWAIT;
                msleep(kq, &kq->kq_lock, PSOCK | PDROP, "kqflxwt", 0);
                if (fp != NULL) {
                        fdrop(fp, td);
                        fp = NULL;
                }
                goto findkn;
        }

        /*
         * kn now contains the matching knote, or NULL if no match
         */
        if (kn == NULL) {
                if (kev->flags & EV_ADD) {
                        kn = tkn;
                        tkn = NULL;
                        if (kn == NULL) {
                                KQ_UNLOCK(kq);
                                error = ENOMEM;
                                goto done;
                        }
                        kn->kn_fp = fp;
                        kn->kn_kq = kq;
                        kn->kn_fop = fops;
                        /*
                         * apply reference counts to knote structure, and
                         * do not release it at the end of this routine.
                         */
                        fops = NULL;
                        fp = NULL;

                        kn->kn_sfflags = kev->fflags;
                        kn->kn_sdata = kev->data;
                        kev->fflags = 0;
                        kev->data = 0;
                        kn->kn_kevent = *kev;
                        kn->kn_kevent.flags &= ~(EV_ADD | EV_DELETE |
                            EV_ENABLE | EV_DISABLE);
                        kn->kn_status = KN_INFLUX|KN_DETACHED;

                        error = knote_attach(kn, kq);
                        KQ_UNLOCK(kq);
                        if (error != 0) {
                                tkn = kn;
                                goto done;
                        }

                        if ((error = kn->kn_fop->f_attach(kn)) != 0) {
                                knote_drop(kn, td);
                                goto done;
                        }
                        KN_LIST_LOCK(kn);
                        goto done_ev_add;
                } else {
                        /* No matching knote and the EV_ADD flag is not set. */
                        KQ_UNLOCK(kq);
                        error = ENOENT;
                        goto done;
                }
        }
        
        if (kev->flags & EV_DELETE) {
                kn->kn_status |= KN_INFLUX;
                KQ_UNLOCK(kq);
                if (!(kn->kn_status & KN_DETACHED))
                        kn->kn_fop->f_detach(kn);
                knote_drop(kn, td);
                goto done;
        }

        /*
         * The user may change some filter values after the initial EV_ADD,
         * but doing so will not reset any filter which has already been
         * triggered.
         */
        kn->kn_status |= KN_INFLUX | KN_SCAN;
        KQ_UNLOCK(kq);
        KN_LIST_LOCK(kn);
        kn->kn_kevent.udata = kev->udata;
        if (!fops->f_isfd && fops->f_touch != NULL) {
                fops->f_touch(kn, kev, EVENT_REGISTER);
        } else {
                kn->kn_sfflags = kev->fflags;
                kn->kn_sdata = kev->data;
        }

        /*
         * We can get here with kn->kn_knlist == NULL.  This can happen when
         * the initial attach event decides that the event is "completed" 
         * already.  i.e. filt_procattach is called on a zombie process.  It
         * will call filt_proc which will remove it from the list, and NULL
         * kn_knlist.
         */
done_ev_add:
        event = kn->kn_fop->f_event(kn, 0);
        KQ_LOCK(kq);
        if (event)
                KNOTE_ACTIVATE(kn, 1);
        kn->kn_status &= ~(KN_INFLUX | KN_SCAN);
        KN_LIST_UNLOCK(kn);

        if ((kev->flags & EV_DISABLE) &&
            ((kn->kn_status & KN_DISABLED) == 0)) {
                kn->kn_status |= KN_DISABLED;
        }

        if ((kev->flags & EV_ENABLE) && (kn->kn_status & KN_DISABLED)) {
                kn->kn_status &= ~KN_DISABLED;
                if ((kn->kn_status & KN_ACTIVE) &&
                    ((kn->kn_status & KN_QUEUED) == 0))
                        knote_enqueue(kn);
        }
        KQ_UNLOCK_FLUX(kq);

done:
        KQ_GLOBAL_UNLOCK(&kq_global, haskqglobal);
        if (filedesc_unlock)
                FILEDESC_XUNLOCK(td->td_proc->p_fd);
        if (fp != NULL)
                fdrop(fp, td);
        if (tkn != NULL)
                knote_free(tkn);
        if (fops != NULL)
                kqueue_fo_release(filt);
        return (error);
}

static int
kqueue_acquire(struct file *fp, struct kqueue **kqp)
{
        int error;
        struct kqueue *kq;

        error = 0;

        kq = fp->f_data;
        if (fp->f_type != DTYPE_KQUEUE || kq == NULL)
                return (EBADF);
        *kqp = kq;
        KQ_LOCK(kq);
        if ((kq->kq_state & KQ_CLOSING) == KQ_CLOSING) {
                KQ_UNLOCK(kq);
                return (EBADF);
        }
        kq->kq_refcnt++;
        KQ_UNLOCK(kq);

        return error;
}

static void
kqueue_release(struct kqueue *kq, int locked)
{
        if (locked)
                KQ_OWNED(kq);
        else
                KQ_LOCK(kq);
        kq->kq_refcnt--;
        if (kq->kq_refcnt == 1)
                wakeup(&kq->kq_refcnt);
        if (!locked)
                KQ_UNLOCK(kq);
}

static void
kqueue_schedtask(struct kqueue *kq)
{

        KQ_OWNED(kq);
        KASSERT(((kq->kq_state & KQ_TASKDRAIN) != KQ_TASKDRAIN),
            ("scheduling kqueue task while draining"));

        if ((kq->kq_state & KQ_TASKSCHED) != KQ_TASKSCHED) {
                taskqueue_enqueue(taskqueue_kqueue, &kq->kq_task);
                kq->kq_state |= KQ_TASKSCHED;
        }
}

/*
 * Expand the kq to make sure we have storage for fops/ident pair.
 *
 * Return 0 on success (or no work necessary), return errno on failure.
 *
 * Not calling hashinit w/ waitok (proper malloc flag) should be safe.
 * If kqueue_register is called from a non-fd context, there usually/should
 * be no locks held.
 */
static int
kqueue_expand(struct kqueue *kq, struct filterops *fops, uintptr_t ident,
        int waitok)
{
        struct klist *list, *tmp_knhash, *to_free;
        u_long tmp_knhashmask;
        int size;
        int fd;
        int mflag = waitok ? M_WAITOK : M_NOWAIT;

        KQ_NOTOWNED(kq);

        to_free = NULL;
        if (fops->f_isfd) {
                fd = ident;
                if (kq->kq_knlistsize <= fd) {
                        size = kq->kq_knlistsize;
                        while (size <= fd)
                                size += KQEXTENT;
                        list = malloc(size * sizeof(*list), M_KQUEUE, mflag);
                        if (list == NULL)
                                return ENOMEM;
                        KQ_LOCK(kq);
                        if (kq->kq_knlistsize > fd) {
                                to_free = list;
                                list = NULL;
                        } else {
                                if (kq->kq_knlist != NULL) {
                                        bcopy(kq->kq_knlist, list,
                                            kq->kq_knlistsize * sizeof(*list));
                                        to_free = kq->kq_knlist;
                                        kq->kq_knlist = NULL;
                                }
                                bzero((caddr_t)list +
                                    kq->kq_knlistsize * sizeof(*list),
                                    (size - kq->kq_knlistsize) * sizeof(*list));
                                kq->kq_knlistsize = size;
                                kq->kq_knlist = list;
                        }
                        KQ_UNLOCK(kq);
                }
        } else {
                if (kq->kq_knhashmask == 0) {
                        tmp_knhash = hashinit(KN_HASHSIZE, M_KQUEUE,
                            &tmp_knhashmask);
                        if (tmp_knhash == NULL)
                                return ENOMEM;
                        KQ_LOCK(kq);
                        if (kq->kq_knhashmask == 0) {
                                kq->kq_knhash = tmp_knhash;
                                kq->kq_knhashmask = tmp_knhashmask;
                        } else {
                                to_free = tmp_knhash;
                        }
                        KQ_UNLOCK(kq);
                }
        }
        free(to_free, M_KQUEUE);

        KQ_NOTOWNED(kq);
        return 0;
}

static void
kqueue_task(void *arg, int pending)
{
        struct kqueue *kq;
        int haskqglobal;

        haskqglobal = 0;
        kq = arg;

        KQ_GLOBAL_LOCK(&kq_global, haskqglobal);
        KQ_LOCK(kq);

        KNOTE_LOCKED(&kq->kq_sel.si_note, 0);

        kq->kq_state &= ~KQ_TASKSCHED;
        if ((kq->kq_state & KQ_TASKDRAIN) == KQ_TASKDRAIN) {
                wakeup(&kq->kq_state);
        }
        KQ_UNLOCK(kq);
        KQ_GLOBAL_UNLOCK(&kq_global, haskqglobal);
}

/*
 * Scan, update kn_data (if not ONESHOT), and copyout triggered events.
 * We treat KN_MARKER knotes as if they are INFLUX.
 */
static int
kqueue_scan(struct kqueue *kq, int maxevents, struct kevent_copyops *k_ops,
    const struct timespec *tsp, struct kevent *keva, struct thread *td)
{
        struct kevent *kevp;
        struct timeval atv, rtv, ttv;
        struct knote *kn, *marker;
        int count, timeout, nkev, error, influx;
        int haskqglobal, touch;

        count = maxevents;
        nkev = 0;
        error = 0;
        haskqglobal = 0;

        if (maxevents == 0)
                goto done_nl;

        if (tsp != NULL) {
                TIMESPEC_TO_TIMEVAL(&atv, tsp);
                if (itimerfix(&atv)) {
                        error = EINVAL;
                        goto done_nl;
                }
                if (tsp->tv_sec == 0 && tsp->tv_nsec == 0)
                        timeout = -1;
                else
                        timeout = atv.tv_sec > 24 * 60 * 60 ?
                            24 * 60 * 60 * hz : tvtohz(&atv);
                getmicrouptime(&rtv);
                timevaladd(&atv, &rtv);
        } else {
                atv.tv_sec = 0;
                atv.tv_usec = 0;
                timeout = 0;
        }
        marker = knote_alloc(1);
        if (marker == NULL) {
                error = ENOMEM;
                goto done_nl;
        }
        marker->kn_status = KN_MARKER;
        KQ_LOCK(kq);
        goto start;

retry:
        if (atv.tv_sec || atv.tv_usec) {
                getmicrouptime(&rtv);
                if (timevalcmp(&rtv, &atv, >=))
                        goto done;
                ttv = atv;
                timevalsub(&ttv, &rtv);
                timeout = ttv.tv_sec > 24 * 60 * 60 ?
                        24 * 60 * 60 * hz : tvtohz(&ttv);
        }

start:
        kevp = keva;
        if (kq->kq_count == 0) {
                if (timeout < 0) {
                        error = EWOULDBLOCK;
                } else {
                        kq->kq_state |= KQ_SLEEP;
                        error = msleep(kq, &kq->kq_lock, PSOCK | PCATCH,
                            "kqread", timeout);
                }
                if (error == 0)
                        goto retry;
                /* don't restart after signals... */
                if (error == ERESTART)
                        error = EINTR;
                else if (error == EWOULDBLOCK)
                        error = 0;
                goto done;
        }

        TAILQ_INSERT_TAIL(&kq->kq_head, marker, kn_tqe);
        influx = 0;
        while (count) {
                KQ_OWNED(kq);
                kn = TAILQ_FIRST(&kq->kq_head);

                if ((kn->kn_status == KN_MARKER && kn != marker) ||
                    (kn->kn_status & KN_INFLUX) == KN_INFLUX) {
                        if (influx) {
                                influx = 0;
                                KQ_FLUX_WAKEUP(kq);
                        }
                        kq->kq_state |= KQ_FLUXWAIT;
                        error = msleep(kq, &kq->kq_lock, PSOCK,
                            "kqflxwt", 0);
                        continue;
                }

                TAILQ_REMOVE(&kq->kq_head, kn, kn_tqe);
                if ((kn->kn_status & KN_DISABLED) == KN_DISABLED) {
                        kn->kn_status &= ~KN_QUEUED;
                        kq->kq_count--;
                        continue;
                }
                if (kn == marker) {
                        KQ_FLUX_WAKEUP(kq);
                        if (count == maxevents)
                                goto retry;
                        goto done;
                }
                KASSERT((kn->kn_status & KN_INFLUX) == 0,
                    ("KN_INFLUX set when not suppose to be"));

                if ((kn->kn_flags & EV_DROP) == EV_DROP) {
                        kn->kn_status &= ~KN_QUEUED;
                        kn->kn_status |= KN_INFLUX;
                        kq->kq_count--;
                        KQ_UNLOCK(kq);
                        /*
                         * We don't need to lock the list since we've marked
                         * it _INFLUX.
                         */
                        if (!(kn->kn_status & KN_DETACHED))
                                kn->kn_fop->f_detach(kn);
                        knote_drop(kn, td);
                        KQ_LOCK(kq);
                        continue;
                } else if ((kn->kn_flags & EV_ONESHOT) == EV_ONESHOT) {
                        kn->kn_status &= ~KN_QUEUED;
                        kn->kn_status |= KN_INFLUX;
                        kq->kq_count--;
                        KQ_UNLOCK(kq);
                        /*
                         * We don't need to lock the list since we've marked
                         * it _INFLUX.
                         */
                        *kevp = kn->kn_kevent;
                        if (!(kn->kn_status & KN_DETACHED))
                                kn->kn_fop->f_detach(kn);
                        knote_drop(kn, td);
                        KQ_LOCK(kq);
                        kn = NULL;
                } else {
                        kn->kn_status |= KN_INFLUX | KN_SCAN;
                        KQ_UNLOCK(kq);
                        if ((kn->kn_status & KN_KQUEUE) == KN_KQUEUE)
                                KQ_GLOBAL_LOCK(&kq_global, haskqglobal);
                        KN_LIST_LOCK(kn);
                        if (kn->kn_fop->f_event(kn, 0) == 0) {
                                KQ_LOCK(kq);
                                KQ_GLOBAL_UNLOCK(&kq_global, haskqglobal);
                                kn->kn_status &=
                                    ~(KN_QUEUED | KN_ACTIVE | KN_INFLUX |
                                    KN_SCAN);
                                kq->kq_count--;
                                KN_LIST_UNLOCK(kn);
                                influx = 1;
                                continue;
                        }
                        touch = (!kn->kn_fop->f_isfd &&
                            kn->kn_fop->f_touch != NULL);
                        if (touch)
                                kn->kn_fop->f_touch(kn, kevp, EVENT_PROCESS);
                        else
                                *kevp = kn->kn_kevent;
                        KQ_LOCK(kq);
                        KQ_GLOBAL_UNLOCK(&kq_global, haskqglobal);
                        if (kn->kn_flags & (EV_CLEAR |  EV_DISPATCH)) {
                                /* 
                                 * Manually clear knotes who weren't 
                                 * 'touch'ed.
                                 */
                                if (touch == 0 && kn->kn_flags & EV_CLEAR) {
                                        kn->kn_data = 0;
                                        kn->kn_fflags = 0;
                                }
                                if (kn->kn_flags & EV_DISPATCH)
                                        kn->kn_status |= KN_DISABLED;
                                kn->kn_status &= ~(KN_QUEUED | KN_ACTIVE);
                                kq->kq_count--;
                        } else
                                TAILQ_INSERT_TAIL(&kq->kq_head, kn, kn_tqe);
                        
                        kn->kn_status &= ~(KN_INFLUX | KN_SCAN);
                        KN_LIST_UNLOCK(kn);
                        influx = 1;
                }

                /* we are returning a copy to the user */
                kevp++;
                nkev++;
                count--;

                if (nkev == KQ_NEVENTS) {
                        influx = 0;
                        KQ_UNLOCK_FLUX(kq);
                        error = k_ops->k_copyout(k_ops->arg, keva, nkev);
                        nkev = 0;
                        kevp = keva;
                        KQ_LOCK(kq);
                        if (error)
                                break;
                }
        }
        TAILQ_REMOVE(&kq->kq_head, marker, kn_tqe);
done:
        KQ_OWNED(kq);
        KQ_UNLOCK_FLUX(kq);
        knote_free(marker);
done_nl:
        KQ_NOTOWNED(kq);
        if (nkev != 0)
                error = k_ops->k_copyout(k_ops->arg, keva, nkev);
        td->td_retval[0] = maxevents - count;
        return (error);
}

/*
 * XXX
 * This could be expanded to call kqueue_scan, if desired.
 */
/*ARGSUSED*/
static int
kqueue_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
        int flags, struct thread *td)
{
        return (ENXIO);
}

/*ARGSUSED*/
static int
kqueue_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
         int flags, struct thread *td)
{
        return (ENXIO);
}

/*ARGSUSED*/
static int
kqueue_truncate(struct file *fp, off_t length, struct ucred *active_cred,
        struct thread *td)
{

        return (EINVAL);
}

/*ARGSUSED*/
static int
kqueue_ioctl(struct file *fp, u_long cmd, void *data,
        struct ucred *active_cred, struct thread *td)
{
        /*
         * Enabling sigio causes two major problems:
         * 1) infinite recursion:
         * Synopsys: kevent is being used to track signals and have FIOASYNC
         * set.  On receipt of a signal this will cause a kqueue to recurse
         * into itself over and over.  Sending the sigio causes the kqueue
         * to become ready, which in turn posts sigio again, forever.
         * Solution: this can be solved by setting a flag in the kqueue that
         * we have a SIGIO in progress.
         * 2) locking problems:
         * Synopsys: Kqueue is a leaf subsystem, but adding signalling puts
         * us above the proc and pgrp locks.
         * Solution: Post a signal using an async mechanism, being sure to
         * record a generation count in the delivery so that we do not deliver
         * a signal to the wrong process.
         *
         * Note, these two mechanisms are somewhat mutually exclusive!
         */
#if 0
        struct kqueue *kq;

        kq = fp->f_data;
        switch (cmd) {
        case FIOASYNC:
                if (*(int *)data) {
                        kq->kq_state |= KQ_ASYNC;
                } else {
                        kq->kq_state &= ~KQ_ASYNC;
                }
                return (0);

        case FIOSETOWN:
                return (fsetown(*(int *)data, &kq->kq_sigio));

        case FIOGETOWN:
                *(int *)data = fgetown(&kq->kq_sigio);
                return (0);
        }
#endif

        return (ENOTTY);
}

/*ARGSUSED*/
static int
kqueue_poll(struct file *fp, int events, struct ucred *active_cred,
        struct thread *td)
{
        struct kqueue *kq;
        int revents = 0;
        int error;

        if ((error = kqueue_acquire(fp, &kq)))
                return POLLERR;

        KQ_LOCK(kq);
        if (events & (POLLIN | POLLRDNORM)) {
                if (kq->kq_count) {
                        revents |= events & (POLLIN | POLLRDNORM);
                } else {
                        selrecord(td, &kq->kq_sel);
                        if (SEL_WAITING(&kq->kq_sel))
                                kq->kq_state |= KQ_SEL;
                }
        }
        kqueue_release(kq, 1);
        KQ_UNLOCK(kq);
        return (revents);
}

/*ARGSUSED*/
static int
kqueue_stat(struct file *fp, struct stat *st, struct ucred *active_cred,
        struct thread *td)
{

        bzero((void *)st, sizeof *st);
        /*
         * We no longer return kq_count because the unlocked value is useless.
         * If you spent all this time getting the count, why not spend your
         * syscall better by calling kevent?
         *
         * XXX - This is needed for libc_r.
         */
        st->st_mode = S_IFIFO;
        return (0);
}

/*ARGSUSED*/
static int
kqueue_close(struct file *fp, struct thread *td)
{
        struct kqueue *kq = fp->f_data;
        struct filedesc *fdp;
        struct knote *kn;
        int i;
        int error;
        int filedesc_unlock;

        if ((error = kqueue_acquire(fp, &kq)))
                return error;

        filedesc_unlock = 0;
        KQ_LOCK(kq);

        KASSERT((kq->kq_state & KQ_CLOSING) != KQ_CLOSING,
            ("kqueue already closing"));
        kq->kq_state |= KQ_CLOSING;
        if (kq->kq_refcnt > 1)
                msleep(&kq->kq_refcnt, &kq->kq_lock, PSOCK, "kqclose", 0);

        KASSERT(kq->kq_refcnt == 1, ("other refs are out there!"));
        fdp = kq->kq_fdp;

        KASSERT(knlist_empty(&kq->kq_sel.si_note),
            ("kqueue's knlist not empty"));

        for (i = 0; i < kq->kq_knlistsize; i++) {
                while ((kn = SLIST_FIRST(&kq->kq_knlist[i])) != NULL) {
                        if ((kn->kn_status & KN_INFLUX) == KN_INFLUX) {
                                kq->kq_state |= KQ_FLUXWAIT;
                                msleep(kq, &kq->kq_lock, PSOCK, "kqclo1", 0);
                                continue;
                        }
                        kn->kn_status |= KN_INFLUX;
                        KQ_UNLOCK(kq);
                        if (!(kn->kn_status & KN_DETACHED))
                                kn->kn_fop->f_detach(kn);
                        knote_drop(kn, td);
                        KQ_LOCK(kq);
                }
        }
        if (kq->kq_knhashmask != 0) {
                for (i = 0; i <= kq->kq_knhashmask; i++) {
                        while ((kn = SLIST_FIRST(&kq->kq_knhash[i])) != NULL) {
                                if ((kn->kn_status & KN_INFLUX) == KN_INFLUX) {
                                        kq->kq_state |= KQ_FLUXWAIT;
                                        msleep(kq, &kq->kq_lock, PSOCK,
                                               "kqclo2", 0);
                                        continue;
                                }
                                kn->kn_status |= KN_INFLUX;
                                KQ_UNLOCK(kq);
                                if (!(kn->kn_status & KN_DETACHED))
                                        kn->kn_fop->f_detach(kn);
                                knote_drop(kn, td);
                                KQ_LOCK(kq);
                        }
                }
        }

        if ((kq->kq_state & KQ_TASKSCHED) == KQ_TASKSCHED) {
                kq->kq_state |= KQ_TASKDRAIN;
                msleep(&kq->kq_state, &kq->kq_lock, PSOCK, "kqtqdr", 0);
        }

        if ((kq->kq_state & KQ_SEL) == KQ_SEL) {
                selwakeuppri(&kq->kq_sel, PSOCK);
                if (!SEL_WAITING(&kq->kq_sel))
                        kq->kq_state &= ~KQ_SEL;
        }

        KQ_UNLOCK(kq);

        /*
         * We could be called due to the knote_drop() doing fdrop(),
         * called from kqueue_register().  In this case the global
         * lock is owned, and filedesc sx is locked before, to not
         * take the sleepable lock after non-sleepable.
         */
        if (!sx_xlocked(FILEDESC_LOCK(fdp))) {
                FILEDESC_XLOCK(fdp);
                filedesc_unlock = 1;
        } else
                filedesc_unlock = 0;
        TAILQ_REMOVE(&fdp->fd_kqlist, kq, kq_list);
        if (filedesc_unlock)
                FILEDESC_XUNLOCK(fdp);

        seldrain(&kq->kq_sel);
        knlist_destroy(&kq->kq_sel.si_note);
        mtx_destroy(&kq->kq_lock);
        kq->kq_fdp = NULL;

        if (kq->kq_knhash != NULL)
                free(kq->kq_knhash, M_KQUEUE);
        if (kq->kq_knlist != NULL)
                free(kq->kq_knlist, M_KQUEUE);

        funsetown(&kq->kq_sigio);
        free(kq, M_KQUEUE);
        fp->f_data = NULL;

        return (0);
}

static void
kqueue_wakeup(struct kqueue *kq)
{
        KQ_OWNED(kq);

        if ((kq->kq_state & KQ_SLEEP) == KQ_SLEEP) {
                kq->kq_state &= ~KQ_SLEEP;
                wakeup(kq);
        }
        if ((kq->kq_state & KQ_SEL) == KQ_SEL) {
                selwakeuppri(&kq->kq_sel, PSOCK);
                if (!SEL_WAITING(&kq->kq_sel))
                        kq->kq_state &= ~KQ_SEL;
        }
        if (!knlist_empty(&kq->kq_sel.si_note))
                kqueue_schedtask(kq);
        if ((kq->kq_state & KQ_ASYNC) == KQ_ASYNC) {
                pgsigio(&kq->kq_sigio, SIGIO, 0);
        }
}

/*
 * Walk down a list of knotes, activating them if their event has triggered.
 *
 * There is a possibility to optimize in the case of one kq watching another.
 * Instead of scheduling a task to wake it up, you could pass enough state
 * down the chain to make up the parent kqueue.  Make this code functional
 * first.
 */
void
knote(struct knlist *list, long hint, int lockflags)
{
        struct kqueue *kq;
        struct knote *kn;
        int error;

        if (list == NULL)
                return;

        KNL_ASSERT_LOCK(list, lockflags & KNF_LISTLOCKED);

        if ((lockflags & KNF_LISTLOCKED) == 0)
                list->kl_lock(list->kl_lockarg); 

        /*
         * If we unlock the list lock (and set KN_INFLUX), we can eliminate
         * the kqueue scheduling, but this will introduce four
         * lock/unlock's for each knote to test.  If we do, continue to use
         * SLIST_FOREACH, SLIST_FOREACH_SAFE is not safe in our case, it is
         * only safe if you want to remove the current item, which we are
         * not doing.
         */
        SLIST_FOREACH(kn, &list->kl_list, kn_selnext) {
                kq = kn->kn_kq;
                KQ_LOCK(kq);
                if ((kn->kn_status & (KN_INFLUX | KN_SCAN)) == KN_INFLUX) {
                        /*
                         * Do not process the influx notes, except for
                         * the influx coming from the kq unlock in the
                         * kqueue_scan().  In the later case, we do
                         * not interfere with the scan, since the code
                         * fragment in kqueue_scan() locks the knlist,
                         * and cannot proceed until we finished.
                         */
                        KQ_UNLOCK(kq);
                } else if ((lockflags & KNF_NOKQLOCK) != 0) {
                        kn->kn_status |= KN_INFLUX;
                        KQ_UNLOCK(kq);
                        error = kn->kn_fop->f_event(kn, hint);
                        KQ_LOCK(kq);
                        kn->kn_status &= ~KN_INFLUX;
                        if (error)
                                KNOTE_ACTIVATE(kn, 1);
                        KQ_UNLOCK_FLUX(kq);
                } else {
                        kn->kn_status |= KN_HASKQLOCK;
                        if (kn->kn_fop->f_event(kn, hint))
                                KNOTE_ACTIVATE(kn, 1);
                        kn->kn_status &= ~KN_HASKQLOCK;
                        KQ_UNLOCK(kq);
                }
        }
        if ((lockflags & KNF_LISTLOCKED) == 0)
                list->kl_unlock(list->kl_lockarg); 
}

/*
 * add a knote to a knlist
 */
void
knlist_add(struct knlist *knl, struct knote *kn, int islocked)
{
        KNL_ASSERT_LOCK(knl, islocked);
        KQ_NOTOWNED(kn->kn_kq);
        KASSERT((kn->kn_status & (KN_INFLUX|KN_DETACHED)) ==
            (KN_INFLUX|KN_DETACHED), ("knote not KN_INFLUX and KN_DETACHED"));
        if (!islocked)
                knl->kl_lock(knl->kl_lockarg);
        SLIST_INSERT_HEAD(&knl->kl_list, kn, kn_selnext);
        if (!islocked)
                knl->kl_unlock(knl->kl_lockarg);
        KQ_LOCK(kn->kn_kq);
        kn->kn_knlist = knl;
        kn->kn_status &= ~KN_DETACHED;
        KQ_UNLOCK(kn->kn_kq);
}

static void
knlist_remove_kq(struct knlist *knl, struct knote *kn, int knlislocked, int kqislocked)
{
        KASSERT(!(!!kqislocked && !knlislocked), ("kq locked w/o knl locked"));
        KNL_ASSERT_LOCK(knl, knlislocked);
        mtx_assert(&kn->kn_kq->kq_lock, kqislocked ? MA_OWNED : MA_NOTOWNED);
        if (!kqislocked)
                KASSERT((kn->kn_status & (KN_INFLUX|KN_DETACHED)) == KN_INFLUX,
    ("knlist_remove called w/o knote being KN_INFLUX or already removed"));
        if (!knlislocked)
                knl->kl_lock(knl->kl_lockarg);
        SLIST_REMOVE(&knl->kl_list, kn, knote, kn_selnext);
        kn->kn_knlist = NULL;
        if (!knlislocked)
                knl->kl_unlock(knl->kl_lockarg);
        if (!kqislocked)
                KQ_LOCK(kn->kn_kq);
        kn->kn_status |= KN_DETACHED;
        if (!kqislocked)
                KQ_UNLOCK(kn->kn_kq);
}

/*
 * remove all knotes from a specified klist
 */
void
knlist_remove(struct knlist *knl, struct knote *kn, int islocked)
{

        knlist_remove_kq(knl, kn, islocked, 0);
}

/*
 * remove knote from a specified klist while in f_event handler.
 */
void
knlist_remove_inevent(struct knlist *knl, struct knote *kn)
{

        knlist_remove_kq(knl, kn, 1,
            (kn->kn_status & KN_HASKQLOCK) == KN_HASKQLOCK);
}

int
knlist_empty(struct knlist *knl)
{
        KNL_ASSERT_LOCKED(knl);
        return SLIST_EMPTY(&knl->kl_list);
}

static struct mtx       knlist_lock;
MTX_SYSINIT(knlist_lock, &knlist_lock, "knlist lock for lockless objects",
        MTX_DEF);
static void knlist_mtx_lock(void *arg);
static void knlist_mtx_unlock(void *arg);

static void
knlist_mtx_lock(void *arg)
{
        mtx_lock((struct mtx *)arg);
}

static void
knlist_mtx_unlock(void *arg)
{
        mtx_unlock((struct mtx *)arg);
}

static void
knlist_mtx_assert_locked(void *arg)
{
        mtx_assert((struct mtx *)arg, MA_OWNED);
}

static void
knlist_mtx_assert_unlocked(void *arg)
{
        mtx_assert((struct mtx *)arg, MA_NOTOWNED);
}

void
knlist_init(struct knlist *knl, void *lock, void (*kl_lock)(void *),
    void (*kl_unlock)(void *),
    void (*kl_assert_locked)(void *), void (*kl_assert_unlocked)(void *))
{

        if (lock == NULL)
                knl->kl_lockarg = &knlist_lock;
        else
                knl->kl_lockarg = lock;

        if (kl_lock == NULL)
                knl->kl_lock = knlist_mtx_lock;
        else
                knl->kl_lock = kl_lock;
        if (kl_unlock == NULL)
                knl->kl_unlock = knlist_mtx_unlock;
        else
                knl->kl_unlock = kl_unlock;
        if (kl_assert_locked == NULL)
                knl->kl_assert_locked = knlist_mtx_assert_locked;
        else
                knl->kl_assert_locked = kl_assert_locked;
        if (kl_assert_unlocked == NULL)
                knl->kl_assert_unlocked = knlist_mtx_assert_unlocked;
        else
                knl->kl_assert_unlocked = kl_assert_unlocked;

        SLIST_INIT(&knl->kl_list);
}

void
knlist_init_mtx(struct knlist *knl, struct mtx *lock)
{

        knlist_init(knl, lock, NULL, NULL, NULL, NULL);
}

void
knlist_destroy(struct knlist *knl)
{

#ifdef INVARIANTS
        /*
         * if we run across this error, we need to find the offending
         * driver and have it call knlist_clear.
         */
        if (!SLIST_EMPTY(&knl->kl_list))
                printf("WARNING: destroying knlist w/ knotes on it!\n");
#endif

        knl->kl_lockarg = knl->kl_lock = knl->kl_unlock = NULL;
        SLIST_INIT(&knl->kl_list);
}

/*
 * Even if we are locked, we may need to drop the lock to allow any influx
 * knotes time to "settle".
 */
void
knlist_cleardel(struct knlist *knl, struct thread *td, int islocked, int killkn)
{
        struct knote *kn, *kn2;
        struct kqueue *kq;

        if (islocked)
                KNL_ASSERT_LOCKED(knl);
        else {
                KNL_ASSERT_UNLOCKED(knl);
again:          /* need to reacquire lock since we have dropped it */
                knl->kl_lock(knl->kl_lockarg);
        }

        SLIST_FOREACH_SAFE(kn, &knl->kl_list, kn_selnext, kn2) {
                kq = kn->kn_kq;
                KQ_LOCK(kq);
                if ((kn->kn_status & KN_INFLUX)) {
                        KQ_UNLOCK(kq);
                        continue;
                }
                knlist_remove_kq(knl, kn, 1, 1);
                if (killkn) {
                        kn->kn_status |= KN_INFLUX | KN_DETACHED;
                        KQ_UNLOCK(kq);
                        knote_drop(kn, td);
                } else {
                        /* Make sure cleared knotes disappear soon */
                        kn->kn_flags |= (EV_EOF | EV_ONESHOT);
                        KQ_UNLOCK(kq);
                }
                kq = NULL;
        }

        if (!SLIST_EMPTY(&knl->kl_list)) {
                /* there are still KN_INFLUX remaining */
                kn = SLIST_FIRST(&knl->kl_list);
                kq = kn->kn_kq;
                KQ_LOCK(kq);
                KASSERT(kn->kn_status & KN_INFLUX,
                    ("knote removed w/o list lock"));
                knl->kl_unlock(knl->kl_lockarg);
                kq->kq_state |= KQ_FLUXWAIT;
                msleep(kq, &kq->kq_lock, PSOCK | PDROP, "kqkclr", 0);
                kq = NULL;
                goto again;
        }

        if (islocked)
                KNL_ASSERT_LOCKED(knl);
        else {
                knl->kl_unlock(knl->kl_lockarg);
                KNL_ASSERT_UNLOCKED(knl);
        }
}

/*
 * Remove all knotes referencing a specified fd must be called with FILEDESC
 * lock.  This prevents a race where a new fd comes along and occupies the
 * entry and we attach a knote to the fd.
 */
void
knote_fdclose(struct thread *td, int fd)
{
        struct filedesc *fdp = td->td_proc->p_fd;
        struct kqueue *kq;
        struct knote *kn;
        int influx;

        FILEDESC_XLOCK_ASSERT(fdp);

        /*
         * We shouldn't have to worry about new kevents appearing on fd
         * since filedesc is locked.
         */
        TAILQ_FOREACH(kq, &fdp->fd_kqlist, kq_list) {
                KQ_LOCK(kq);

again:
                influx = 0;
                while (kq->kq_knlistsize > fd &&
                    (kn = SLIST_FIRST(&kq->kq_knlist[fd])) != NULL) {
                        if (kn->kn_status & KN_INFLUX) {
                                /* someone else might be waiting on our knote */
                                if (influx)
                                        wakeup(kq);
                                kq->kq_state |= KQ_FLUXWAIT;
                                msleep(kq, &kq->kq_lock, PSOCK, "kqflxwt", 0);
                                goto again;
                        }
                        kn->kn_status |= KN_INFLUX;
                        KQ_UNLOCK(kq);
                        if (!(kn->kn_status & KN_DETACHED))
                                kn->kn_fop->f_detach(kn);
                        knote_drop(kn, td);
                        influx = 1;
                        KQ_LOCK(kq);
                }
                KQ_UNLOCK_FLUX(kq);
        }
}

static int
knote_attach(struct knote *kn, struct kqueue *kq)
{
        struct klist *list;

        KASSERT(kn->kn_status & KN_INFLUX, ("knote not marked INFLUX"));
        KQ_OWNED(kq);

        if (kn->kn_fop->f_isfd) {
                if (kn->kn_id >= kq->kq_knlistsize)
                        return ENOMEM;
                list = &kq->kq_knlist[kn->kn_id];
        } else {
                if (kq->kq_knhash == NULL)
                        return ENOMEM;
                list = &kq->kq_knhash[KN_HASH(kn->kn_id, kq->kq_knhashmask)];
        }

        SLIST_INSERT_HEAD(list, kn, kn_link);

        return 0;
}

/*
 * knote must already have been detached using the f_detach method.
 * no lock need to be held, it is assumed that the KN_INFLUX flag is set
 * to prevent other removal.
 */
static void
knote_drop(struct knote *kn, struct thread *td)
{
        struct kqueue *kq;
        struct klist *list;

        kq = kn->kn_kq;

        KQ_NOTOWNED(kq);
        KASSERT((kn->kn_status & KN_INFLUX) == KN_INFLUX,
            ("knote_drop called without KN_INFLUX set in kn_status"));

        KQ_LOCK(kq);
        if (kn->kn_fop->f_isfd)
                list = &kq->kq_knlist[kn->kn_id];
        else
                list = &kq->kq_knhash[KN_HASH(kn->kn_id, kq->kq_knhashmask)];

        if (!SLIST_EMPTY(list))
                SLIST_REMOVE(list, kn, knote, kn_link);
        if (kn->kn_status & KN_QUEUED)
                knote_dequeue(kn);
        KQ_UNLOCK_FLUX(kq);

        if (kn->kn_fop->f_isfd) {
                fdrop(kn->kn_fp, td);
                kn->kn_fp = NULL;
        }
        kqueue_fo_release(kn->kn_kevent.filter);
        kn->kn_fop = NULL;
        knote_free(kn);
}

static void
knote_enqueue(struct knote *kn)
{
        struct kqueue *kq = kn->kn_kq;

        KQ_OWNED(kn->kn_kq);
        KASSERT((kn->kn_status & KN_QUEUED) == 0, ("knote already queued"));

        TAILQ_INSERT_TAIL(&kq->kq_head, kn, kn_tqe);
        kn->kn_status |= KN_QUEUED;
        kq->kq_count++;
        kqueue_wakeup(kq);
}

static void
knote_dequeue(struct knote *kn)
{
        struct kqueue *kq = kn->kn_kq;

        KQ_OWNED(kn->kn_kq);
        KASSERT(kn->kn_status & KN_QUEUED, ("knote not queued"));

        TAILQ_REMOVE(&kq->kq_head, kn, kn_tqe);
        kn->kn_status &= ~KN_QUEUED;
        kq->kq_count--;
}

static void
knote_init(void)
{

        knote_zone = uma_zcreate("KNOTE", sizeof(struct knote), NULL, NULL,
            NULL, NULL, UMA_ALIGN_PTR, 0);
}
SYSINIT(knote, SI_SUB_PSEUDO, SI_ORDER_ANY, knote_init, NULL);

static struct knote *
knote_alloc(int waitok)
{
        return ((struct knote *)uma_zalloc(knote_zone,
            (waitok ? M_WAITOK : M_NOWAIT)|M_ZERO));
}

static void
knote_free(struct knote *kn)
{
        if (kn != NULL)
                uma_zfree(knote_zone, kn);
}

/*
 * Register the kev w/ the kq specified by fd.
 */
int 
kqfd_register(int fd, struct kevent *kev, struct thread *td, int waitok)
{
        struct kqueue *kq;
        struct file *fp;
        int error;

        if ((error = fget(td, fd, CAP_POST_EVENT, &fp)) != 0)
                return (error);
        if ((error = kqueue_acquire(fp, &kq)) != 0)
                goto noacquire;

        error = kqueue_register(kq, kev, td, waitok);

        kqueue_release(kq, 0);

noacquire:
        fdrop(fp, td);

        return error;
}