kern_event.c
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kern_event.c
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	/*-
	* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
	*
	* 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("$FreeBSD$");

	#include "opt_ktrace.h"
	#include "opt_kqueue.h"

	#ifdef COMPAT_FREEBSD11
	#define _WANT_FREEBSD11_KEVENT
	#endif

	#include <sys/param.h>
	#include <sys/systm.h>
	#include <sys/capsicum.h>
	#include <sys/kernel.h>
	#include <sys/lock.h>
	#include <sys/mutex.h>
	#include <sys/rwlock.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/resourcevar.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>
	#include <sys/user.h>
	#ifdef KTRACE
	#include <sys/ktrace.h>
	#endif
	#include <machine/atomic.h>

	#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_ctx);

	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 void kqueue_destroy(struct kqueue *kq);
	static void kqueue_drain(struct kqueue kq, struct thread td);
	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);
	struct g_kevent_args;
	static int kern_kevent_generic(struct thread *td,
	struct g_kevent_args *uap,
	struct kevent_copyops k_ops, const char struct_name);

	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 fo_fill_kinfo_t kqueue_fill_kinfo;

	static struct fileops kqueueops = {
	.fo_read = invfo_rdwr,
	.fo_write = invfo_rdwr,
	.fo_truncate = invfo_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,
	.fo_sendfile = invfo_sendfile,
	.fo_fill_kinfo = kqueue_fill_kinfo,
	};

	static int knote_attach(struct knote kn, struct kqueue kq);
	static void knote_drop(struct knote kn, struct thread td);
	static void knote_drop_detached(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 void filt_timerstart(struct knote *kn, sbintime_t to);
	static void filt_timertouch(struct knote kn, struct kevent kev,
	u_long type);
	static int filt_timervalidate(struct knote kn, sbintime_t to);
	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,
	.f_touch = filt_timertouch,
	};
	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 unsigned int kq_ncallouts = 0;
	static unsigned int kq_calloutmax = 4 * 1024;
	SYSCTL_UINT(_kern, OID_AUTO, kq_calloutmax, CTLFLAG_RW,
	&kq_calloutmax, 0, "Maximum number of callouts allocated for kqueue");

	/* XXX - ensure not 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)

	static struct knlist *
	kn_list_lock(struct knote *kn)
	{
	struct knlist *knl;

	knl = kn->kn_knlist;
	if (knl != NULL)
	knl->kl_lock(knl->kl_lockarg);
	return (knl);
	}

	static void
	kn_list_unlock(struct knlist *knl)
	{
	bool do_free;

	if (knl == NULL)
	return;
	do_free = knl->kl_autodestroy && knlist_empty(knl);
	knl->kl_unlock(knl->kl_lockarg);
	if (do_free) {
	knlist_destroy(knl);
	free(knl, M_KQUEUE);
	}
	}

	static bool
	kn_in_flux(struct knote *kn)
	{

	return (kn->kn_influx > 0);
	}

	static void
	kn_enter_flux(struct knote *kn)
	{

	KQ_OWNED(kn->kn_kq);
	MPASS(kn->kn_influx < INT_MAX);
	kn->kn_influx++;
	}

	static bool
	kn_leave_flux(struct knote *kn)
	{

	KQ_OWNED(kn->kn_kq);
	MPASS(kn->kn_influx > 0);
	kn->kn_influx--;
	return (kn->kn_influx == 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 */

	#ifndef KN_HASHSIZE
	#define KN_HASHSIZE 64 /* XXX should be tunable */
	#endif

	#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_nolock;
	int for_refcnt;
	} sysfilt_ops[EVFILT_SYSCOUNT] = {
	{ &file_filtops, 1 }, /* EVFILT_READ */
	{ &file_filtops, 1 }, /* EVFILT_WRITE */
	{ &null_filtops }, /* EVFILT_AIO */
	{ &file_filtops, 1 }, /* EVFILT_VNODE */
	{ &proc_filtops, 1 }, /* EVFILT_PROC */
	{ &sig_filtops, 1 }, /* EVFILT_SIGNAL */
	{ &timer_filtops, 1 }, /* EVFILT_TIMER */
	{ &file_filtops, 1 }, /* EVFILT_PROCDESC */
	{ &fs_filtops, 1 }, /* EVFILT_FS */
	{ &null_filtops }, /* EVFILT_LIO */
	{ &user_filtops, 1 }, /* EVFILT_USER */
	{ &null_filtops }, /* EVFILT_SENDFILE */
	{ &file_filtops, 1 }, /* EVFILT_EMPTY */
	};

	/*
	* 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 error;
	bool exiting, immediate;

	exiting = immediate = false;
	if (kn->kn_sfflags & NOTE_EXIT)
	p = pfind_any(kn->kn_id);
	else
	p = pfind(kn->kn_id);
	if (p == NULL)
	return (ESRCH);
	if (p->p_flag & P_WEXIT)
	exiting = true;

	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 for the
	* purposes of getting a NOTE_CHILD notification.
	*/
	if (kn->kn_flags & EV_FLAG2) {
	kn->kn_flags &= ~EV_FLAG2;
	kn->kn_data = kn->kn_sdata; /* ppid */
	kn->kn_fflags = NOTE_CHILD;
	kn->kn_sfflags &= ~(NOTE_EXIT \| NOTE_EXEC \| NOTE_FORK);
	immediate = true; /* Force immediate activation of child note. */
	}
	/*
	* Internal flag indicating registration done by kernel (for other than
	* NOTE_CHILD).
	*/
	if (kn->kn_flags & EV_FLAG1) {
	kn->kn_flags &= ~EV_FLAG1;
	}

	knlist_add(p->p_klist, kn, 1);

	/*
	* Immediately activate any child notes or, in the case of a zombie
	* target process, exit notes. The latter is necessary to handle the
	* case where the target process, e.g. a child, dies before the kevent
	* is registered.
	*/
	if (immediate \|\| (exiting && 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)
	{

	knlist_remove(kn->kn_knlist, 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;
	u_int event;

	p = kn->kn_ptr.p_proc;
	if (p == NULL) /* already activated, from attach filter */
	return (0);

	/* 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) {
	kn->kn_flags \|= EV_EOF \| EV_ONESHOT;
	kn->kn_ptr.p_proc = NULL;
	if (kn->kn_fflags & NOTE_EXIT)
	kn->kn_data = KW_EXITCODE(p->p_xexit, p->p_xsig);
	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) {
	kq = kn->kn_kq;
	KQ_LOCK(kq);
	if (kn_in_flux(kn) && (kn->kn_status & KN_SCAN) == 0) {
	KQ_UNLOCK(kq);
	continue;
	}

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

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

	/*
	* Activate existing knote and register tracking knotes with
	* new process.
	*
	* First register a knote to get just the child notice. This
	* must be a separate note from a potential NOTE_EXIT
	* notification since both NOTE_CHILD and NOTE_EXIT are defined
	* to use the data field (in conflicting ways).
	*/
	kev.ident = pid;
	kev.filter = kn->kn_filter;
	kev.flags = kn->kn_flags \| EV_ADD \| EV_ENABLE \| EV_ONESHOT \|
	EV_FLAG2;
	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;

	/*
	* Then register another knote to track other potential events
	* from the 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_leave_flux(kn);
	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.
	*/

	#define NOTE_TIMER_PRECMASK \
	(NOTE_SECONDS \| NOTE_MSECONDS \| NOTE_USECONDS \| NOTE_NSECONDS)

	static sbintime_t
	timer2sbintime(intptr_t data, int flags)
	{
	int64_t secs;

	/*
	* Macros for converting to the fractional second portion of an
	* sbintime_t using 64bit multiplication to improve precision.
	*/
	#define NS_TO_SBT(ns) (((ns) * (((uint64_t)1 << 63) / 500000000)) >> 32)
	#define US_TO_SBT(us) (((us) * (((uint64_t)1 << 63) / 500000)) >> 32)
	#define MS_TO_SBT(ms) (((ms) * (((uint64_t)1 << 63) / 500)) >> 32)
	switch (flags & NOTE_TIMER_PRECMASK) {
	case NOTE_SECONDS:
	#ifdef __LP64__
	if (data > (SBT_MAX / SBT_1S))
	return (SBT_MAX);
	#endif
	return ((sbintime_t)data << 32);
	case NOTE_MSECONDS: /* FALLTHROUGH */
	case 0:
	if (data >= 1000) {
	secs = data / 1000;
	#ifdef __LP64__
	if (secs > (SBT_MAX / SBT_1S))
	return (SBT_MAX);
	#endif
	return (secs << 32 \| MS_TO_SBT(data % 1000));
	}
	return (MS_TO_SBT(data));
	case NOTE_USECONDS:
	if (data >= 1000000) {
	secs = data / 1000000;
	#ifdef __LP64__
	if (secs > (SBT_MAX / SBT_1S))
	return (SBT_MAX);
	#endif
	return (secs << 32 \| US_TO_SBT(data % 1000000));
	}
	return (US_TO_SBT(data));
	case NOTE_NSECONDS:
	if (data >= 1000000000) {
	secs = data / 1000000000;
	#ifdef __LP64__
	if (secs > (SBT_MAX / SBT_1S))
	return (SBT_MAX);
	#endif
	return (secs << 32 \| US_TO_SBT(data % 1000000000));
	}
	return (NS_TO_SBT(data));
	default:
	break;
	}
	return (-1);
	}

	struct kq_timer_cb_data {
	struct callout c;
	sbintime_t next; /* next timer event fires at */
	sbintime_t to; /* precalculated timer period, 0 for abs */
	};

	static void
	filt_timerexpire(void *knx)
	{
	struct knote *kn;
	struct kq_timer_cb_data *kc;

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

	if ((kn->kn_flags & EV_ONESHOT) != 0)
	return;
	kc = kn->kn_ptr.p_v;
	if (kc->to == 0)
	return;
	kc->next += kc->to;
	callout_reset_sbt_on(&kc->c, kc->next, 0, filt_timerexpire, kn,
	PCPU_GET(cpuid), C_ABSOLUTE);
	}

	/*
	* data contains amount of time to sleep
	*/
	static int
	filt_timervalidate(struct knote kn, sbintime_t to)
	{
	struct bintime bt;
	sbintime_t sbt;

	if (kn->kn_sdata < 0)
	return (EINVAL);
	if (kn->kn_sdata == 0 && (kn->kn_flags & EV_ONESHOT) == 0)
	kn->kn_sdata = 1;
	/*
	* The only fflags values supported are the timer unit
	* (precision) and the absolute time indicator.
	*/
	if ((kn->kn_sfflags & ~(NOTE_TIMER_PRECMASK \| NOTE_ABSTIME)) != 0)
	return (EINVAL);

	*to = timer2sbintime(kn->kn_sdata, kn->kn_sfflags);
	if ((kn->kn_sfflags & NOTE_ABSTIME) != 0) {
	getboottimebin(&bt);
	sbt = bttosbt(bt);
	*to -= sbt;
	}
	if (*to < 0)
	return (EINVAL);
	return (0);
	}

	static int
	filt_timerattach(struct knote *kn)
	{
	struct kq_timer_cb_data *kc;
	sbintime_t to;
	unsigned int ncallouts;
	int error;

	error = filt_timervalidate(kn, &to);
	if (error != 0)
	return (error);

	do {
	ncallouts = kq_ncallouts;
	if (ncallouts >= kq_calloutmax)
	return (ENOMEM);
	} while (!atomic_cmpset_int(&kq_ncallouts, ncallouts, ncallouts + 1));

	if ((kn->kn_sfflags & NOTE_ABSTIME) == 0)
	kn->kn_flags \|= EV_CLEAR; /* automatically set */
	kn->kn_status &= ~KN_DETACHED; /* knlist_add clears it */
	kn->kn_ptr.p_v = kc = malloc(sizeof(*kc), M_KQUEUE, M_WAITOK);
	callout_init(&kc->c, 1);
	filt_timerstart(kn, to);

	return (0);
	}

	static void
	filt_timerstart(struct knote *kn, sbintime_t to)
	{
	struct kq_timer_cb_data *kc;

	kc = kn->kn_ptr.p_v;
	if ((kn->kn_sfflags & NOTE_ABSTIME) != 0) {
	kc->next = to;
	kc->to = 0;
	} else {
	kc->next = to + sbinuptime();
	kc->to = to;
	}
	callout_reset_sbt_on(&kc->c, kc->next, 0, filt_timerexpire, kn,
	PCPU_GET(cpuid), C_ABSOLUTE);
	}

	static void
	filt_timerdetach(struct knote *kn)
	{
	struct kq_timer_cb_data *kc;
	unsigned int old __unused;

	kc = kn->kn_ptr.p_v;
	callout_drain(&kc->c);
	free(kc, M_KQUEUE);
	old = atomic_fetchadd_int(&kq_ncallouts, -1);
	KASSERT(old > 0, ("Number of callouts cannot become negative"));
	kn->kn_status \|= KN_DETACHED; /* knlist_remove sets it */
	}

	static void
	filt_timertouch(struct knote kn, struct kevent kev, u_long type)
	{
	struct kq_timer_cb_data *kc;
	struct kqueue *kq;
	sbintime_t to;
	int error;

	switch (type) {
	case EVENT_REGISTER:
	/* Handle re-added timers that update data/fflags */
	if (kev->flags & EV_ADD) {
	kc = kn->kn_ptr.p_v;

	/* Drain any existing callout. */
	callout_drain(&kc->c);

	/* Throw away any existing undelivered record
	* of the timer expiration. This is done under
	* the presumption that if a process is
	* re-adding this timer with new parameters,
	* it is no longer interested in what may have
	* happened under the old parameters. If it is
	* interested, it can wait for the expiration,
	* delete the old timer definition, and then
	* add the new one.
	*
	* This has to be done while the kq is locked:
	* - if enqueued, dequeue
	* - make it no longer active
	* - clear the count of expiration events
	*/
	kq = kn->kn_kq;
	KQ_LOCK(kq);
	if (kn->kn_status & KN_QUEUED)
	knote_dequeue(kn);

	kn->kn_status &= ~KN_ACTIVE;
	kn->kn_data = 0;
	KQ_UNLOCK(kq);

	/* Reschedule timer based on new data/fflags */
	kn->kn_sfflags = kev->fflags;
	kn->kn_sdata = kev->data;
	error = filt_timervalidate(kn, &to);
	if (error != 0) {
	kn->kn_flags \|= EV_ERROR;
	kn->kn_data = error;
	} else
	filt_timerstart(kn, to);
	}
	break;

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

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

	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)
	{

	return (kern_kqueue(td, 0, NULL));
	}

	static void
	kqueue_init(struct kqueue *kq)
	{

	mtx_init(&kq->kq_lock, "kqueue", NULL, MTX_DEF \| MTX_DUPOK);
	TAILQ_INIT(&kq->kq_head);
	knlist_init_mtx(&kq->kq_sel.si_note, &kq->kq_lock);
	TASK_INIT(&kq->kq_task, 0, kqueue_task, kq);
	}

	int
	kern_kqueue(struct thread td, int flags, struct filecaps fcaps)
	{
	struct filedesc *fdp;
	struct kqueue *kq;
	struct file *fp;
	struct ucred *cred;
	int fd, error;

	fdp = td->td_proc->p_fd;
	cred = td->td_ucred;
	if (!chgkqcnt(cred->cr_ruidinfo, 1, lim_cur(td, RLIMIT_KQUEUES)))
	return (ENOMEM);

	error = falloc_caps(td, &fp, &fd, flags, fcaps);
	if (error != 0) {
	chgkqcnt(cred->cr_ruidinfo, -1, 0);
	return (error);
	}

	/* An extra reference on `fp' has been held for us by falloc(). */
	kq = malloc(sizeof *kq, M_KQUEUE, M_WAITOK \| M_ZERO);
	kqueue_init(kq);
	kq->kq_fdp = fdp;
	kq->kq_cred = crhold(cred);

	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;
	return (0);
	}

	struct g_kevent_args {
	int fd;
	void *changelist;
	int nchanges;
	void *eventlist;
	int nevents;
	const struct timespec *timeout;
	};

	int
	sys_kevent(struct thread td, struct kevent_args uap)
	{
	struct kevent_copyops k_ops = {
	.arg = uap,
	.k_copyout = kevent_copyout,
	.k_copyin = kevent_copyin,
	.kevent_size = sizeof(struct kevent),
	};
	struct g_kevent_args gk_args = {
	.fd = uap->fd,
	.changelist = uap->changelist,
	.nchanges = uap->nchanges,
	.eventlist = uap->eventlist,
	.nevents = uap->nevents,
	.timeout = uap->timeout,
	};

	return (kern_kevent_generic(td, &gk_args, &k_ops, "kevent"));
	}

	static int
	kern_kevent_generic(struct thread td, struct g_kevent_args uap,
	struct kevent_copyops k_ops, const char struct_name)
	{
	struct timespec ts, *tsp;
	#ifdef KTRACE
	struct kevent *eventlist = uap->eventlist;
	#endif
	int error;

	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_STRUCT_ARRAY))
	ktrstructarray(struct_name, UIO_USERSPACE, uap->changelist,
	uap->nchanges, k_ops->kevent_size);
	#endif

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

	#ifdef KTRACE
	if (error == 0 && KTRPOINT(td, KTR_STRUCT_ARRAY))
	ktrstructarray(struct_name, UIO_USERSPACE, eventlist,
	td->td_retval[0], k_ops->kevent_size);
	#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);
	}

	#ifdef COMPAT_FREEBSD11
	static int
	kevent11_copyout(void arg, struct kevent kevp, int count)
	{
	struct freebsd11_kevent_args *uap;
	struct kevent_freebsd11 kev11;
	int error, i;

	KASSERT(count <= KQ_NEVENTS, ("count (%d) > KQ_NEVENTS", count));
	uap = (struct freebsd11_kevent_args *)arg;

	for (i = 0; i < count; i++) {
	kev11.ident = kevp->ident;
	kev11.filter = kevp->filter;
	kev11.flags = kevp->flags;
	kev11.fflags = kevp->fflags;
	kev11.data = kevp->data;
	kev11.udata = kevp->udata;
	error = copyout(&kev11, uap->eventlist, sizeof(kev11));
	if (error != 0)
	break;
	uap->eventlist++;
	kevp++;
	}
	return (error);
	}

	/*
	* Copy 'count' items from the list pointed to by uap->changelist.
	*/
	static int
	kevent11_copyin(void arg, struct kevent kevp, int count)
	{
	struct freebsd11_kevent_args *uap;
	struct kevent_freebsd11 kev11;
	int error, i;

	KASSERT(count <= KQ_NEVENTS, ("count (%d) > KQ_NEVENTS", count));
	uap = (struct freebsd11_kevent_args *)arg;

	for (i = 0; i < count; i++) {
	error = copyin(uap->changelist, &kev11, sizeof(kev11));
	if (error != 0)
	break;
	kevp->ident = kev11.ident;
	kevp->filter = kev11.filter;
	kevp->flags = kev11.flags;
	kevp->fflags = kev11.fflags;
	kevp->data = (uintptr_t)kev11.data;
	kevp->udata = kev11.udata;
	bzero(&kevp->ext, sizeof(kevp->ext));
	uap->changelist++;
	kevp++;
	}
	return (error);
	}

	int
	freebsd11_kevent(struct thread td, struct freebsd11_kevent_args uap)
	{
	struct kevent_copyops k_ops = {
	.arg = uap,
	.k_copyout = kevent11_copyout,
	.k_copyin = kevent11_copyin,
	.kevent_size = sizeof(struct kevent_freebsd11),
	};
	struct g_kevent_args gk_args = {
	.fd = uap->fd,
	.changelist = uap->changelist,
	.nchanges = uap->nchanges,
	.eventlist = uap->eventlist,
	.nevents = uap->nevents,
	.timeout = uap->timeout,
	};

	return (kern_kevent_generic(td, &gk_args, &k_ops, "kevent_freebsd11"));
	}
	#endif

	int
	kern_kevent(struct thread *td, int fd, int nchanges, int nevents,
	struct kevent_copyops k_ops, const struct timespec timeout)
	{
	cap_rights_t rights;
	struct file *fp;
	int error;

	cap_rights_init(&rights);
	if (nchanges > 0)
	cap_rights_set(&rights, CAP_KQUEUE_CHANGE);
	if (nevents > 0)
	cap_rights_set(&rights, CAP_KQUEUE_EVENT);
	error = fget(td, fd, &rights, &fp);
	if (error != 0)
	return (error);

	error = kern_kevent_fp(td, fp, nchanges, nevents, k_ops, timeout);
	fdrop(fp, td);

	return (error);
	}

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

	nerrors = 0;
	while (nchanges > 0) {
	n = nchanges > KQ_NEVENTS ? KQ_NEVENTS : nchanges;
	error = k_ops->k_copyin(k_ops->arg, keva, n);
	if (error)
	return (error);
	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)
	return (error);
	kevp->flags = EV_ERROR;
	kevp->data = error;
	(void)k_ops->k_copyout(k_ops->arg, kevp, 1);
	nevents--;
	nerrors++;
	}
	}
	nchanges -= n;
	}
	if (nerrors) {
	td->td_retval[0] = nerrors;
	return (0);
	}

	return (kqueue_scan(kq, nevents, k_ops, timeout, keva, td));
	}

	int
	kern_kevent_fp(struct thread td, struct file fp, int nchanges, int nevents,
	struct kevent_copyops k_ops, const struct timespec timeout)
	{
	struct kqueue *kq;
	int error;

	error = kqueue_acquire(fp, &kq);
	if (error != 0)
	return (error);
	error = kqueue_kevent(kq, td, nchanges, nevents, k_ops, timeout);
	kqueue_release(kq, 0);
	return (error);
	}

	/*
	* Performs a kevent() call on a temporarily created kqueue. This can be
	* used to perform one-shot polling, similar to poll() and select().
	*/
	int
	kern_kevent_anonymous(struct thread *td, int nevents,
	struct kevent_copyops *k_ops)
	{
	struct kqueue kq = {};
	int error;

	kqueue_init(&kq);
	kq.kq_refcnt = 1;
	error = kqueue_kevent(&kq, td, nevents, nevents, k_ops, NULL);
	kqueue_drain(&kq, td);
	kqueue_destroy(&kq);
	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;

	if (sysfilt_ops[~filt].for_nolock)
	return sysfilt_ops[~filt].for_fop;

	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;

	if (sysfilt_ops[~filt].for_nolock)
	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;
	struct knlist *knl;
	int error, filt, event;
	int haskqglobal, filedesc_unlock;

	if ((kev->flags & (EV_ENABLE \| EV_DISABLE)) == (EV_ENABLE \| EV_DISABLE))
	return (EINVAL);

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

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

	if (kev->flags & EV_ADD) {
	/*
	* Prevent waiting with locks. Non-sleepable
	* allocation failures are handled in the loop, only
	* if the spare knote appears to be actually required.
	*/
	tkn = knote_alloc(waitok);
	} else {
	tkn = NULL;
	}

	findkn:
	if (fops->f_isfd) {
	KASSERT(td != NULL, ("td is NULL"));
	if (kev->ident > INT_MAX)
	error = EBADF;
	else
	error = fget(td, kev->ident, &cap_event_rights, &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 intelligence 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 possible, find an existing knote to use for this kevent.
	*/
	if (kev->filter == EVFILT_PROC &&
	(kev->flags & (EV_FLAG1 \| EV_FLAG2)) != 0) {
	/* This is an internal creation of a process tracking
	* note. Don't attempt to coalesce this with an
	* existing note.
	*/
	;
	} else 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 stabilize. */
	if (kn != NULL && kn_in_flux(kn)) {
	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 \| EV_FORCEONESHOT);
	kn->kn_status = KN_DETACHED;
	kn_enter_flux(kn);

	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_detached(kn, td);
	goto done;
	}
	knl = 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_enter_flux(kn);
	KQ_UNLOCK(kq);
	knote_drop(kn, td);
	goto done;
	}

	if (kev->flags & EV_FORCEONESHOT) {
	kn->kn_flags \|= EV_ONESHOT;
	KNOTE_ACTIVATE(kn, 1);
	}

	/*
	* 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_SCAN;
	kn_enter_flux(kn);
	KQ_UNLOCK(kq);
	knl = 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:
	if ((kev->flags & EV_ENABLE) != 0)
	kn->kn_status &= ~KN_DISABLED;
	else if ((kev->flags & EV_DISABLE) != 0)
	kn->kn_status \|= KN_DISABLED;

	if ((kn->kn_status & KN_DISABLED) == 0)
	event = kn->kn_fop->f_event(kn, 0);
	else
	event = 0;

	KQ_LOCK(kq);
	if (event)
	kn->kn_status \|= KN_ACTIVE;
	if ((kn->kn_status & (KN_ACTIVE \| KN_DISABLED \| KN_QUEUED)) ==
	KN_ACTIVE)
	knote_enqueue(kn);
	kn->kn_status &= ~KN_SCAN;
	kn_leave_flux(kn);
	kn_list_unlock(knl);
	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);
	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_ctx, &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 in flux.
	*/
	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 knote kn, marker;
	struct knlist *knl;
	sbintime_t asbt, rsbt;
	int count, error, haskqglobal, influx, nkev, touch;

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

	if (maxevents == 0)
	goto done_nl;

	rsbt = 0;
	if (tsp != NULL) {
	if (tsp->tv_sec < 0 \|\| tsp->tv_nsec < 0 \|\|
	tsp->tv_nsec >= 1000000000) {
	error = EINVAL;
	goto done_nl;
	}
	if (timespecisset(tsp)) {
	if (tsp->tv_sec <= INT32_MAX) {
	rsbt = tstosbt(*tsp);
	if (TIMESEL(&asbt, rsbt))
	asbt += tc_tick_sbt;
	if (asbt <= SBT_MAX - rsbt)
	asbt += rsbt;
	else
	asbt = 0;
	rsbt >>= tc_precexp;
	} else
	asbt = 0;
	} else
	asbt = -1;
	} else
	asbt = 0;
	marker = knote_alloc(1);
	marker->kn_status = KN_MARKER;
	KQ_LOCK(kq);

	retry:
	kevp = keva;
	if (kq->kq_count == 0) {
	if (asbt == -1) {
	error = EWOULDBLOCK;
	} else {
	kq->kq_state \|= KQ_SLEEP;
	error = msleep_sbt(kq, &kq->kq_lock, PSOCK \| PCATCH,
	"kqread", asbt, rsbt, C_ABSOLUTE);
	}
	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_in_flux(kn)) {
	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_in_flux(kn),
	("knote %p is unexpectedly in flux", kn));

	if ((kn->kn_flags & EV_DROP) == EV_DROP) {
	kn->kn_status &= ~KN_QUEUED;
	kn_enter_flux(kn);
	kq->kq_count--;
	KQ_UNLOCK(kq);
	/*
	* We don't need to lock the list since we've
	* marked it as in flux.
	*/
	knote_drop(kn, td);
	KQ_LOCK(kq);
	continue;
	} else if ((kn->kn_flags & EV_ONESHOT) == EV_ONESHOT) {
	kn->kn_status &= ~KN_QUEUED;
	kn_enter_flux(kn);
	kq->kq_count--;
	KQ_UNLOCK(kq);
	/*
	* We don't need to lock the list since we've
	* marked the knote as being in flux.
	*/
	*kevp = kn->kn_kevent;
	knote_drop(kn, td);
	KQ_LOCK(kq);
	kn = NULL;
	} else {
	kn->kn_status \|= KN_SCAN;
	kn_enter_flux(kn);
	KQ_UNLOCK(kq);
	if ((kn->kn_status & KN_KQUEUE) == KN_KQUEUE)
	KQ_GLOBAL_LOCK(&kq_global, haskqglobal);
	knl = 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_SCAN);
	kn_leave_flux(kn);
	kq->kq_count--;
	kn_list_unlock(knl);
	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_SCAN;
	kn_leave_flux(kn);
	kn_list_unlock(knl);
	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);
	}

	/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);
	}

	static void
	kqueue_drain(struct kqueue kq, struct thread td)
	{
	struct knote *kn;
	int i;

	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!"));

	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_in_flux(kn)) {
	kq->kq_state \|= KQ_FLUXWAIT;
	msleep(kq, &kq->kq_lock, PSOCK, "kqclo1", 0);
	continue;
	}
	kn_enter_flux(kn);
	KQ_UNLOCK(kq);
	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_in_flux(kn)) {
	kq->kq_state \|= KQ_FLUXWAIT;
	msleep(kq, &kq->kq_lock, PSOCK,
	"kqclo2", 0);
	continue;
	}
	kn_enter_flux(kn);
	KQ_UNLOCK(kq);
	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);
	}

	static void
	kqueue_destroy(struct kqueue *kq)
	{

	KASSERT(kq->kq_fdp == NULL,
	("kqueue still attached to a file descriptor"));
	seldrain(&kq->kq_sel);
	knlist_destroy(&kq->kq_sel.si_note);
	mtx_destroy(&kq->kq_lock);

	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);
	}

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

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

	/*
	* 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.
	*/
	fdp = kq->kq_fdp;
	kq->kq_fdp = NULL;
	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);

	kqueue_destroy(kq);
	chgkqcnt(kq->kq_cred->cr_ruidinfo, -1, 0);
	crfree(kq->kq_cred);
	free(kq, M_KQUEUE);
	fp->f_data = NULL;

	return (0);
	}

	static int
	kqueue_fill_kinfo(struct file fp, struct kinfo_file kif, struct filedesc *fdp)
	{

	kif->kf_type = KF_TYPE_KQUEUE;
	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, tkn;
	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 enter influx), we can
	* eliminate the kqueue scheduling, but this will introduce
	* four lock/unlock's for each knote to test. Also, marker
	* would be needed to keep iteration position, since filters
	* or other threads could remove events.
	*/
	SLIST_FOREACH_SAFE(kn, &list->kl_list, kn_selnext, tkn) {
	kq = kn->kn_kq;
	KQ_LOCK(kq);
	if (kn_in_flux(kn) && (kn->kn_status & KN_SCAN) == 0) {
	/*
	* 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_enter_flux(kn);
	KQ_UNLOCK(kq);
	error = kn->kn_fop->f_event(kn, hint);
	KQ_LOCK(kq);
	kn_leave_flux(kn);
	if (error)
	KNOTE_ACTIVATE(kn, 1);
	KQ_UNLOCK_FLUX(kq);
	} else {
	if (kn->kn_fop->f_event(kn, hint))
	KNOTE_ACTIVATE(kn, 1);
	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_in_flux(kn), ("knote %p not in flux", kn));
	KASSERT((kn->kn_status & KN_DETACHED) != 0,
	("knote %p was not detached", kn));
	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);
	KASSERT(kqislocked \|\| kn_in_flux(kn), ("knote %p not in flux", kn));
	KASSERT((kn->kn_status & KN_DETACHED) == 0,
	("knote %p was already detached", kn));
	if (!knlislocked)
	knl->kl_lock(knl->kl_lockarg);
	SLIST_REMOVE(&knl->kl_list, kn, knote, kn_selnext);
	kn->kn_knlist = NULL;
	if (!knlislocked)
	kn_list_unlock(knl);
	if (!kqislocked)
	KQ_LOCK(kn->kn_kq);
	kn->kn_status \|= KN_DETACHED;
	if (!kqislocked)
	KQ_UNLOCK(kn->kn_kq);
	}

	/*
	* remove knote from the specified knlist
	*/
	void
	knlist_remove(struct knlist knl, struct knote kn, int islocked)
	{

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

	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);
	}

	static void
	knlist_rw_rlock(void *arg)
	{

	rw_rlock((struct rwlock *)arg);
	}

	static void
	knlist_rw_runlock(void *arg)
	{

	rw_runlock((struct rwlock *)arg);
	}

	static void
	knlist_rw_assert_locked(void *arg)
	{

	rw_assert((struct rwlock *)arg, RA_LOCKED);
	}

	static void
	knlist_rw_assert_unlocked(void *arg)
	{

	rw_assert((struct rwlock *)arg, RA_UNLOCKED);
	}

	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;

	knl->kl_autodestroy = 0;
	SLIST_INIT(&knl->kl_list);
	}

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

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

	struct knlist *
	knlist_alloc(struct mtx *lock)
	{
	struct knlist *knl;

	knl = malloc(sizeof(struct knlist), M_KQUEUE, M_WAITOK);
	knlist_init_mtx(knl, lock);
	return (knl);
	}

	void
	knlist_init_rw_reader(struct knlist knl, struct rwlock lock)
	{

	knlist_init(knl, lock, knlist_rw_rlock, knlist_rw_runlock,
	knlist_rw_assert_locked, knlist_rw_assert_unlocked);
	}

	void
	knlist_destroy(struct knlist *knl)
	{

	KASSERT(KNLIST_EMPTY(knl),
	("destroying knlist %p with knotes on it", knl));
	}

	void
	knlist_detach(struct knlist *knl)
	{

	KNL_ASSERT_LOCKED(knl);
	knl->kl_autodestroy = 1;
	if (knlist_empty(knl)) {
	knlist_destroy(knl);
	free(knl, M_KQUEUE);
	}
	}

	/*
	* 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;

	KASSERT(!knl->kl_autodestroy, ("cleardel for autodestroy %p", knl));
	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_in_flux(kn)) {
	KQ_UNLOCK(kq);
	continue;
	}
	knlist_remove_kq(knl, kn, 1, 1);
	if (killkn) {
	kn_enter_flux(kn);
	KQ_UNLOCK(kq);
	knote_drop_detached(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 in flux knotes remaining */
	kn = SLIST_FIRST(&knl->kl_list);
	kq = kn->kn_kq;
	KQ_LOCK(kq);
	KASSERT(kn_in_flux(kn), ("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_in_flux(kn)) {
	/* 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_enter_flux(kn);
	KQ_UNLOCK(kq);
	influx = 1;
	knote_drop(kn, td);
	KQ_LOCK(kq);
	}
	KQ_UNLOCK_FLUX(kq);
	}
	}

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

	KASSERT(kn_in_flux(kn), ("knote %p not marked influx", kn));
	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);
	}

	static void
	knote_drop(struct knote kn, struct thread td)
	{

	if ((kn->kn_status & KN_DETACHED) == 0)
	kn->kn_fop->f_detach(kn);
	knote_drop_detached(kn, td);
	}

	static void
	knote_drop_detached(struct knote kn, struct thread td)
	{
	struct kqueue *kq;
	struct klist *list;

	kq = kn->kn_kq;

	KASSERT((kn->kn_status & KN_DETACHED) != 0,
	("knote %p still attached", kn));
	KQ_NOTOWNED(kq);

	KQ_LOCK(kq);
	KASSERT(kn->kn_influx == 1,
	("knote_drop called on %p with influx %d", kn, kn->kn_influx));

	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 (uma_zalloc(knote_zone, (waitok ? M_WAITOK : M_NOWAIT) \|
	M_ZERO));
	}

	static void
	knote_free(struct knote *kn)
	{

	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;
	cap_rights_t rights;
	int error;

	error = fget(td, fd, cap_rights_init(&rights, CAP_KQUEUE_CHANGE), &fp);
	if (error != 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);
	}

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