kernel - kqueue - refactor kqueue_scan(), rename tick to ustick

[dragonfly.git] / sys / kern / kern_event.c

/*-
 * Copyright (c) 1999,2000,2001 Jonathan Lemon <jlemon@FreeBSD.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $FreeBSD: src/sys/kern/kern_event.c,v 1.2.2.10 2004/04/04 07:03:14 cperciva Exp $
 * $DragonFly: src/sys/kern/kern_event.c,v 1.33 2007/02/03 17:05:57 corecode Exp $
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/malloc.h> 
#include <sys/unistd.h>
#include <sys/file.h>
#include <sys/lock.h>
#include <sys/fcntl.h>
#include <sys/select.h>
#include <sys/queue.h>
#include <sys/event.h>
#include <sys/eventvar.h>
#include <sys/poll.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/stat.h>
#include <sys/sysctl.h>
#include <sys/sysproto.h>
#include <sys/uio.h>
#include <sys/signalvar.h>
#include <sys/filio.h>

#include <sys/thread2.h>
#include <sys/file2.h>
#include <sys/mplock2.h>

#include <vm/vm_zone.h>

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

static int      kqueue_scan(struct kqueue *kq, struct kevent *kevp, int count,
                    struct timespec *tsp, int *errorp);
static int      kqueue_read(struct file *fp, struct uio *uio,
                    struct ucred *cred, int flags);
static int      kqueue_write(struct file *fp, struct uio *uio,
                    struct ucred *cred, int flags);
static int      kqueue_ioctl(struct file *fp, u_long com, caddr_t data,
                    struct ucred *cred, struct sysmsg *msg);
static int      kqueue_poll(struct file *fp, int events, struct ucred *cred);
static int      kqueue_kqfilter(struct file *fp, struct knote *kn);
static int      kqueue_stat(struct file *fp, struct stat *st,
                    struct ucred *cred);
static int      kqueue_close(struct file *fp);
static void     kqueue_wakeup(struct kqueue *kq);

/*
 * MPSAFE
 */
static struct fileops kqueueops = {
        .fo_read = kqueue_read,
        .fo_write = kqueue_write,
        .fo_ioctl = kqueue_ioctl,
        .fo_poll = kqueue_poll,
        .fo_kqfilter = kqueue_kqfilter,
        .fo_stat = kqueue_stat,
        .fo_close = kqueue_close,
        .fo_shutdown = nofo_shutdown
};

static void     knote_attach(struct knote *kn);
static void     knote_drop(struct knote *kn);
static void     knote_enqueue(struct knote *kn);
static void     knote_dequeue(struct knote *kn);
static void     knote_init(void);
static struct   knote *knote_alloc(void);
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 struct filterops file_filtops =
        { 1, filt_fileattach, NULL, NULL };
static struct filterops kqread_filtops =
        { 1, NULL, filt_kqdetach, filt_kqueue };
static struct filterops proc_filtops =
        { 0, filt_procattach, filt_procdetach, filt_proc };
static struct filterops timer_filtops =
        { 0, filt_timerattach, filt_timerdetach, filt_timer };

static vm_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");

#define KNOTE_ACTIVATE(kn) do {                                         \
        kn->kn_status |= KN_ACTIVE;                                     \
        if ((kn->kn_status & (KN_QUEUED | KN_DISABLED)) == 0)           \
                knote_enqueue(kn);                                      \
} while(0)

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

extern struct filterops aio_filtops;
extern struct filterops sig_filtops;

/*
 * Table for for all system-defined filters.
 */
static struct filterops *sysfilt_ops[] = {
        &file_filtops,                  /* EVFILT_READ */
        &file_filtops,                  /* EVFILT_WRITE */
        &aio_filtops,                   /* EVFILT_AIO */
        &file_filtops,                  /* EVFILT_VNODE */
        &proc_filtops,                  /* EVFILT_PROC */
        &sig_filtops,                   /* EVFILT_SIGNAL */
        &timer_filtops,                 /* EVFILT_TIMER */
};

static int
filt_fileattach(struct knote *kn)
{
        return (fo_kqfilter(kn->kn_fp, kn));
}

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

        get_mplock();
        if (kn->kn_filter != EVFILT_READ) {
                rel_mplock();
                return (1);
        }

        kn->kn_fop = &kqread_filtops;
        SLIST_INSERT_HEAD(&kq->kq_sel.si_note, kn, kn_selnext);
        rel_mplock();
        return (0);
}

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

        SLIST_REMOVE(&kq->kq_sel.si_note, kn, knote, kn_selnext);
}

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

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

static int
filt_procattach(struct knote *kn)
{
        struct proc *p;
        int immediate;

        immediate = 0;
        p = pfind(kn->kn_id);
        if (p == NULL && (kn->kn_sfflags & NOTE_EXIT)) {
                p = zpfind(kn->kn_id);
                immediate = 1;
        }
        if (p == NULL)
                return (ESRCH);
        if (!PRISON_CHECK(curthread->td_ucred, p->p_ucred))
                return (EACCES);

        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;
        }

        /* XXX lock the proc here while adding to the list? */
        SLIST_INSERT_HEAD(&p->p_klist, kn, kn_selnext);

        /*
         * 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);

        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.
 */
static void
filt_procdetach(struct knote *kn)
{
        struct proc *p;

        if (kn->kn_status & KN_DETACHED)
                return;
        /* XXX locking?  this might modify another process. */
        p = kn->kn_ptr.p_proc;
        SLIST_REMOVE(&p->p_klist, kn, knote, kn_selnext);
}

static int
filt_proc(struct knote *kn, long hint)
{
        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.  Detach the
         * knote from the process now because the process will be poof,
         * gone later on.
         */
        if (event == NOTE_EXIT) {
                struct proc *p = kn->kn_ptr.p_proc;
                if ((kn->kn_status & KN_DETACHED) == 0) {
                        SLIST_REMOVE(&p->p_klist, kn, knote, kn_selnext);
                        kn->kn_status |= KN_DETACHED;
                        kn->kn_data = p->p_xstat;
                        kn->kn_ptr.p_proc = NULL;
                }
                kn->kn_flags |= (EV_EOF | EV_ONESHOT); 
                return (1);
        }

        /*
         * process forked, and user wants to track the new process,
         * so attach a new knote to it, and immediately report an
         * event with the parent's pid.
         */
        if ((event == NOTE_FORK) && (kn->kn_sfflags & NOTE_TRACK)) {
                struct kevent kev;
                int error;

                /*
                 * register knote with new process.
                 */
                kev.ident = hint & NOTE_PDATAMASK;      /* 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(kn->kn_kq, &kev);
                if (error)
                        kn->kn_fflags |= NOTE_TRACKERR;
        }

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

static void
filt_timerexpire(void *knx)
{
        struct knote *kn = knx;
        struct callout *calloutp;
        struct timeval tv;
        int tticks;

        kn->kn_data++;
        KNOTE_ACTIVATE(kn);

        if ((kn->kn_flags & EV_ONESHOT) == 0) {
                tv.tv_sec = kn->kn_sdata / 1000;
                tv.tv_usec = (kn->kn_sdata % 1000) * 1000;
                tticks = tvtohz_high(&tv);
                calloutp = (struct callout *)kn->kn_hook;
                callout_reset(calloutp, tticks, filt_timerexpire, kn);
        }
}

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

        if (kq_ncallouts >= kq_calloutmax)
                return (ENOMEM);
        kq_ncallouts++;

        tv.tv_sec = kn->kn_sdata / 1000;
        tv.tv_usec = (kn->kn_sdata % 1000) * 1000;
        tticks = tvtohz_high(&tv);

        kn->kn_flags |= EV_CLEAR;               /* automatically set */
        MALLOC(calloutp, struct callout *, sizeof(*calloutp),
            M_KQUEUE, M_WAITOK);
        callout_init(calloutp);
        kn->kn_hook = (caddr_t)calloutp;
        callout_reset(calloutp, tticks, filt_timerexpire, kn);

        return (0);
}

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

        calloutp = (struct callout *)kn->kn_hook;
        callout_stop(calloutp);
        FREE(calloutp, M_KQUEUE);
        kq_ncallouts--;
}

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

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

/*
 * Initialize a kqueue.
 *
 * NOTE: The lwp/proc code initializes a kqueue for select/poll ops.
 *
 * MPSAFE
 */
void
kqueue_init(struct kqueue *kq, struct filedesc *fdp)
{
        TAILQ_INIT(&kq->kq_knpend);
        TAILQ_INIT(&kq->kq_knlist);
        kq->kq_fdp = fdp;
}

/*
 * Terminate a kqueue.  Freeing the actual kq itself is left up to the
 * caller (it might be embedded in a lwp so we don't do it here).
 */
void
kqueue_terminate(struct kqueue *kq)
{
        struct knote *kn;
        struct klist *list;
        int hv;

        while ((kn = TAILQ_FIRST(&kq->kq_knlist)) != NULL) {
                kn->kn_fop->f_detach(kn);
                if (kn->kn_fop->f_isfd) {
                        list = &kn->kn_fp->f_klist;
                        SLIST_REMOVE(list, kn, knote, kn_link);
                        fdrop(kn->kn_fp);
                        kn->kn_fp = NULL;
                } else {
                        hv = KN_HASH(kn->kn_id, kq->kq_knhashmask);
                        list = &kq->kq_knhash[hv];
                        SLIST_REMOVE(list, kn, knote, kn_link);
                }
                TAILQ_REMOVE(&kq->kq_knlist, kn, kn_kqlink);
                if (kn->kn_status & KN_QUEUED)
                        knote_dequeue(kn);
                knote_free(kn);
        }

        if (kq->kq_knhash) {
                kfree(kq->kq_knhash, M_KQUEUE);
                kq->kq_knhash = NULL;
                kq->kq_knhashmask = 0;
        }
}

/*
 * MPSAFE
 */
int
sys_kqueue(struct kqueue_args *uap)
{
        struct thread *td = curthread;
        struct kqueue *kq;
        struct file *fp;
        int fd, error;

        error = falloc(td->td_lwp, &fp, &fd);
        if (error)
                return (error);
        fp->f_flag = FREAD | FWRITE;
        fp->f_type = DTYPE_KQUEUE;
        fp->f_ops = &kqueueops;

        kq = kmalloc(sizeof(struct kqueue), M_KQUEUE, M_WAITOK | M_ZERO);
        kqueue_init(kq, td->td_proc->p_fd);
        fp->f_data = kq;

        fsetfd(kq->kq_fdp, fp, fd);
        uap->sysmsg_result = fd;
        fdrop(fp);
        return (error);
}

/*
 * MPALMOSTSAFE
 */
int
sys_kevent(struct kevent_args *uap)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;
        struct kevent *kevp;
        struct kqueue *kq;
        struct file *fp = NULL;
        struct timespec ts;
        struct timespec *tsp;
        int i, n, total, nerrors, error;
        struct kevent kev[KQ_NEVENTS];

        fp = holdfp(p->p_fd, uap->fd, -1);
        if (fp == NULL)
                return (EBADF);
        if (fp->f_type != DTYPE_KQUEUE) {
                fdrop(fp);
                return (EBADF);
        }

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

        kq = (struct kqueue *)fp->f_data;
        nerrors = 0;

        get_mplock();
        while (uap->nchanges > 0) {
                n = uap->nchanges > KQ_NEVENTS ? KQ_NEVENTS : uap->nchanges;
                error = copyin(uap->changelist, kev, n * sizeof(struct kevent));
                if (error)
                        goto done;
                for (i = 0; i < n; i++) {
                        kevp = &kev[i];
                        kevp->flags &= ~EV_SYSFLAGS;
                        error = kqueue_register(kq, kevp);
                        if (error) {
                                if (uap->nevents != 0) {
                                        kevp->flags = EV_ERROR;
                                        kevp->data = error;
                                        copyout(kevp, uap->eventlist,
                                                sizeof(*kevp));
                                        uap->eventlist++;
                                        uap->nevents--;
                                        nerrors++;
                                } else {
                                        goto done;
                                }
                        }
                }
                uap->nchanges -= n;
                uap->changelist += n;
        }
        if (nerrors) {
                uap->sysmsg_result = nerrors;
                error = 0;
                goto done;
        }

        /*
         * Acquire/wait for events - setup timeout
         */
        if (tsp != NULL) {
                struct timespec ats;

                if (tsp->tv_sec || tsp->tv_nsec) {
                        nanouptime(&ats);
                        timespecadd(tsp, &ats);         /* tsp = target time */
                }
        }

        /*
         * Loop as required.
         *
         * Collect as many events as we can.  The timeout on successive
         * loops is disabled (kqueue_scan() becomes non-blocking).
         */
        total = 0;
        error = 0;
        while ((n = uap->nevents - total) > 0) {
                if (n > KQ_NEVENTS)
                        n = KQ_NEVENTS;
                i = kqueue_scan(kq, kev, n, tsp, &error);
                if (i == 0)
                        break;
                error = copyout(kev, uap->eventlist + total,
                                (size_t)i * sizeof(struct kevent));
                total += i;
                if (error || i != n)
                        break;
                tsp = &ts;              /* successive loops non-blocking */
                tsp->tv_sec = 0;
                tsp->tv_nsec = 0;
        }
        uap->sysmsg_result = total;
done:
        rel_mplock();
        if (fp != NULL)
                fdrop(fp);
        return (error);
}

int
kqueue_register(struct kqueue *kq, struct kevent *kev)
{
        struct filedesc *fdp = kq->kq_fdp;
        struct filterops *fops;
        struct file *fp = NULL;
        struct knote *kn = NULL;
        int error = 0;

        if (kev->filter < 0) {
                if (kev->filter + EVFILT_SYSCOUNT < 0)
                        return (EINVAL);
                fops = sysfilt_ops[~kev->filter];       /* to 0-base index */
        } else {
                /*
                 * XXX
                 * filter attach routine is responsible for insuring that
                 * the identifier can be attached to it.
                 */
                kprintf("unknown filter: %d\n", kev->filter);
                return (EINVAL);
        }

        if (fops->f_isfd) {
                /* validate descriptor */
                fp = holdfp(fdp, kev->ident, -1);
                if (fp == NULL)
                        return (EBADF);

                SLIST_FOREACH(kn, &fp->f_klist, kn_link) {
                        if (kn->kn_kq == kq &&
                            kn->kn_filter == kev->filter &&
                            kn->kn_id == kev->ident) {
                                break;
                        }
                }
        } else {
                if (kq->kq_knhashmask) {
                        struct klist *list;
                        
                        list = &kq->kq_knhash[
                            KN_HASH((u_long)kev->ident, kq->kq_knhashmask)];
                        SLIST_FOREACH(kn, list, kn_link) {
                                if (kn->kn_id == kev->ident &&
                                    kn->kn_filter == kev->filter)
                                        break;
                        }
                }
        }

        if (kn == NULL && ((kev->flags & EV_ADD) == 0)) {
                error = ENOENT;
                goto done;
        }

        /*
         * kn now contains the matching knote, or NULL if no match
         */
        if (kev->flags & EV_ADD) {
                if (kn == NULL) {
                        kn = knote_alloc();
                        if (kn == NULL) {
                                error = ENOMEM;
                                goto done;
                        }
                        kn->kn_fp = fp;
                        kn->kn_kq = kq;
                        kn->kn_fop = fops;

                        /*
                         * apply reference count to knote structure, and
                         * do not release it at the end of this routine.
                         */
                        fp = NULL;

                        kn->kn_sfflags = kev->fflags;
                        kn->kn_sdata = kev->data;
                        kev->fflags = 0;
                        kev->data = 0;
                        kn->kn_kevent = *kev;

                        knote_attach(kn);
                        if ((error = fops->f_attach(kn)) != 0) {
                                knote_drop(kn);
                                goto done;
                        }
                } else {
                        /*
                         * The user may change some filter values after the
                         * initial EV_ADD, but doing so will not reset any 
                         * filter which have already been triggered.
                         */
                        kn->kn_sfflags = kev->fflags;
                        kn->kn_sdata = kev->data;
                        kn->kn_kevent.udata = kev->udata;
                }

                crit_enter();
                if (kn->kn_fop->f_event(kn, 0))
                        KNOTE_ACTIVATE(kn);
                crit_exit();
        } else if (kev->flags & EV_DELETE) {
                kn->kn_fop->f_detach(kn);
                knote_drop(kn);
                goto done;
        }

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

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

done:
        if (fp != NULL)
                fdrop(fp);
        return (error);
}

/*
 * Scan the kqueue, blocking if necessary until the target time is reached.
 * If tsp is NULL we block indefinitely.  If tsp->ts_secs/nsecs are both
 * 0 we do not block at all.
 */
static int
kqueue_scan(struct kqueue *kq, struct kevent *kevp, int count,
            struct timespec *tsp, int *errorp)
{
        struct knote *kn, marker;
        int total;

        total = 0;
again:
        crit_enter();
        if (kq->kq_count == 0) {
                if (tsp == NULL) {
                        kq->kq_state |= KQ_SLEEP;
                        *errorp = tsleep(kq, PCATCH, "kqread", 0);
                } else if (tsp->tv_sec == 0 && tsp->tv_nsec == 0) {
                        *errorp = EWOULDBLOCK;
                } else {
                        struct timespec ats;
                        struct timespec atx = *tsp;
                        int timeout;

                        nanouptime(&ats);
                        timespecsub(&atx, &ats);
                        if (ats.tv_sec < 0) {
                                *errorp = EWOULDBLOCK;
                        } else {
                                timeout = atx.tv_sec > 24 * 60 * 60 ?
                                        24 * 60 * 60 * hz : tstohz_high(&atx);
                                kq->kq_state |= KQ_SLEEP;
                                *errorp = tsleep(kq, PCATCH, "kqread", timeout);
                        }
                }
                crit_exit();
                if (*errorp == 0)
                        goto again;
                /* don't restart after signals... */
                if (*errorp == ERESTART)
                        *errorp = EINTR;
                else if (*errorp == EWOULDBLOCK)
                        *errorp = 0;
                goto done;
        }

        /*
         * Collect events
         */
        TAILQ_INSERT_TAIL(&kq->kq_knpend, &marker, kn_tqe);
        while (count) {
                kn = TAILQ_FIRST(&kq->kq_knpend);
                TAILQ_REMOVE(&kq->kq_knpend, kn, kn_tqe);
                if (kn == &marker)
                        break;
                if (kn->kn_status & KN_DISABLED) {
                        kn->kn_status &= ~KN_QUEUED;
                        kq->kq_count--;
                        continue;
                }
                if ((kn->kn_flags & EV_ONESHOT) == 0 &&
                    kn->kn_fop->f_event(kn, 0) == 0) {
                        kn->kn_status &= ~(KN_QUEUED | KN_ACTIVE);
                        kq->kq_count--;
                        continue;
                }
                *kevp++ = kn->kn_kevent;
                ++total;
                --count;

                /*
                 * Post-event action on the note
                 */
                if (kn->kn_flags & EV_ONESHOT) {
                        kn->kn_status &= ~KN_QUEUED;
                        kq->kq_count--;
                        crit_exit();
                        kn->kn_fop->f_detach(kn);
                        knote_drop(kn);
                        crit_enter();
                } else if (kn->kn_flags & EV_CLEAR) {
                        kn->kn_data = 0;
                        kn->kn_fflags = 0;
                        kn->kn_status &= ~(KN_QUEUED | KN_ACTIVE);
                        kq->kq_count--;
                } else {
                        TAILQ_INSERT_TAIL(&kq->kq_knpend, kn, kn_tqe);
                }
        }
        TAILQ_REMOVE(&kq->kq_knpend, &marker, kn_tqe);
        crit_exit();
        if (total == 0)
                goto again;
done:
        return (total);
}

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

/*
 * MPSAFE
 */
static int
kqueue_write(struct file *fp, struct uio *uio, struct ucred *cred, int flags)
{
        return (ENXIO);
}

/*
 * MPSAFE
 */
static int
kqueue_ioctl(struct file *fp, u_long com, caddr_t data,
             struct ucred *cred, struct sysmsg *msg)
{
        struct kqueue *kq;
        int error;

        get_mplock();
        kq = (struct kqueue *)fp->f_data;

        switch(com) {
        case FIOASYNC:
                if (*(int *)data)
                        kq->kq_state |= KQ_ASYNC;
                else
                        kq->kq_state &= ~KQ_ASYNC;
                error = 0;
                break;
        case FIOSETOWN:
                error = fsetown(*(int *)data, &kq->kq_sigio);
                break;
        default:
                error = ENOTTY;
                break;
        }
        rel_mplock();
        return (error);
}

/*
 * MPALMOSTSAFE - acquires mplock
 */
static int
kqueue_poll(struct file *fp, int events, struct ucred *cred)
{
        struct kqueue *kq = (struct kqueue *)fp->f_data;
        int revents = 0;

        get_mplock();
        crit_enter();
        if (events & (POLLIN | POLLRDNORM)) {
                if (kq->kq_count) {
                        revents |= events & (POLLIN | POLLRDNORM);
                } else {
                        selrecord(curthread, &kq->kq_sel);
                        kq->kq_state |= KQ_SEL;
                }
        }
        crit_exit();
        rel_mplock();
        return (revents);
}

/*
 * MPSAFE
 */
static int
kqueue_stat(struct file *fp, struct stat *st, struct ucred *cred)
{
        struct kqueue *kq = (struct kqueue *)fp->f_data;

        bzero((void *)st, sizeof(*st));
        st->st_size = kq->kq_count;
        st->st_blksize = sizeof(struct kevent);
        st->st_mode = S_IFIFO;
        return (0);
}

/*
 * MPALMOSTSAFE - acquires mplock
 */
static int
kqueue_close(struct file *fp)
{
        struct kqueue *kq = (struct kqueue *)fp->f_data;

        get_mplock();

        kqueue_terminate(kq);

        fp->f_data = NULL;
        funsetown(kq->kq_sigio);
        rel_mplock();

        kfree(kq, M_KQUEUE);
        return (0);
}

static void
kqueue_wakeup(struct kqueue *kq)
{
        if (kq->kq_state & KQ_SLEEP) {
                kq->kq_state &= ~KQ_SLEEP;
                wakeup(kq);
        }
        if (kq->kq_state & KQ_SEL) {
                kq->kq_state &= ~KQ_SEL;
                selwakeup(&kq->kq_sel);
        }
        KNOTE(&kq->kq_sel.si_note, 0);
}

/*
 * walk down a list of knotes, activating them if their event has triggered.
 */
void
knote(struct klist *list, long hint)
{
        struct knote *kn;

        SLIST_FOREACH(kn, list, kn_selnext)
                if (kn->kn_fop->f_event(kn, hint))
                        KNOTE_ACTIVATE(kn);
}

/*
 * remove all knotes from a specified klist
 */
void
knote_remove(struct klist *list)
{
        struct knote *kn;

        while ((kn = SLIST_FIRST(list)) != NULL) {
                kn->kn_fop->f_detach(kn);
                knote_drop(kn);
        }
}

/*
 * remove all knotes referencing a specified fd
 */
void
knote_fdclose(struct file *fp, struct filedesc *fdp, int fd)
{
        struct knote *kn;

restart:
        SLIST_FOREACH(kn, &fp->f_klist, kn_link) {
                if (kn->kn_kq->kq_fdp == fdp && kn->kn_id == fd) {
                        kn->kn_fop->f_detach(kn);
                        knote_drop(kn);
                        goto restart;
                }
        }
}

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

        if (kn->kn_fop->f_isfd) {
                KKASSERT(kn->kn_fp);
                list = &kn->kn_fp->f_klist;
        } else {
                if (kq->kq_knhashmask == 0)
                        kq->kq_knhash = hashinit(KN_HASHSIZE, M_KQUEUE,
                                                 &kq->kq_knhashmask);
                list = &kq->kq_knhash[KN_HASH(kn->kn_id, kq->kq_knhashmask)];
        }
        SLIST_INSERT_HEAD(list, kn, kn_link);
        TAILQ_INSERT_HEAD(&kq->kq_knlist, kn, kn_kqlink);
        kn->kn_status = 0;
}

/*
 * should be called outside of a critical section, since we don't want to
 * hold a critical section while calling fdrop and free.
 */
static void
knote_drop(struct knote *kn)
{
        struct kqueue *kq;
        struct klist *list;

        kq = kn->kn_kq;

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

        SLIST_REMOVE(list, kn, knote, kn_link);
        TAILQ_REMOVE(&kq->kq_knlist, kn, kn_kqlink);
        if (kn->kn_status & KN_QUEUED)
                knote_dequeue(kn);
        if (kn->kn_fop->f_isfd)
                fdrop(kn->kn_fp);
        knote_free(kn);
}


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

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

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

        /*
         * Send SIGIO on request (typically set up as a mailbox signal)
         */
        if (kq->kq_sigio && (kq->kq_state & KQ_ASYNC) && kq->kq_count == 1)
                pgsigio(kq->kq_sigio, SIGIO, 0);
        crit_exit();
        kqueue_wakeup(kq);
}

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

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

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

static void
knote_init(void)
{
        knote_zone = zinit("KNOTE", sizeof(struct knote), 0, 0, 1);
}
SYSINIT(knote, SI_SUB_PSEUDO, SI_ORDER_ANY, knote_init, NULL)

static struct knote *
knote_alloc(void)
{
        return ((struct knote *)zalloc(knote_zone));
}

static void
knote_free(struct knote *kn)
{
        zfree(knote_zone, kn);
}