freebsd-dev/sys/compat/linux/linux_event.c

/*-
 * Copyright (c) 2007 Roman Divacky
 * Copyright (c) 2014 Dmitry Chagin
 * 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_compat.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/imgact.h>
#include <sys/kernel.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/capability.h>
#include <sys/types.h>
#include <sys/user.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/errno.h>
#include <sys/event.h>
#include <sys/poll.h>
#include <sys/proc.h>
#include <sys/selinfo.h>
#include <sys/sx.h>
#include <sys/syscallsubr.h>
#include <sys/timespec.h>

#ifdef COMPAT_LINUX32
#include <machine/../linux32/linux.h>
#include <machine/../linux32/linux32_proto.h>
#else
#include <machine/../linux/linux.h>
#include <machine/../linux/linux_proto.h>
#endif

#include <compat/linux/linux_emul.h>
#include <compat/linux/linux_event.h>
#include <compat/linux/linux_file.h>
#include <compat/linux/linux_util.h>

/*
 * epoll defines 'struct epoll_event' with the field 'data' as 64 bits
 * on all architectures. But on 32 bit architectures BSD 'struct kevent' only
 * has 32 bit opaque pointer as 'udata' field. So we can't pass epoll supplied
 * data verbatuim. Therefore we allocate 64-bit memory block to pass
 * user supplied data for every file descriptor.
 */

typedef uint64_t	epoll_udata_t;

struct epoll_emuldata {
	uint32_t	fdc;		/* epoll udata max index */
	epoll_udata_t	udata[1];	/* epoll user data vector */
};

#define	EPOLL_DEF_SZ		16
#define	EPOLL_SIZE(fdn)			\
	(sizeof(struct epoll_emuldata)+(fdn) * sizeof(epoll_udata_t))

struct epoll_event {
	uint32_t	events;
	epoll_udata_t	data;
}
#if defined(__amd64__)
__attribute__((packed))
#endif
;

#define	LINUX_MAX_EVENTS	(INT_MAX / sizeof(struct epoll_event))

static void	epoll_fd_install(struct thread *td, int fd, epoll_udata_t udata);
static int	epoll_to_kevent(struct thread *td, struct file *epfp,
		    int fd, struct epoll_event *l_event, int *kev_flags,
		    struct kevent *kevent, int *nkevents);
static void	kevent_to_epoll(struct kevent *kevent, struct epoll_event *l_event);
static int	epoll_kev_copyout(void *arg, struct kevent *kevp, int count);
static int	epoll_kev_copyin(void *arg, struct kevent *kevp, int count);
static int	epoll_delete_event(struct thread *td, struct file *epfp,
		    int fd, int filter);
static int	epoll_delete_all_events(struct thread *td, struct file *epfp,
		    int fd);

struct epoll_copyin_args {
	struct kevent	*changelist;
};

struct epoll_copyout_args {
	struct epoll_event	*leventlist;
	struct proc		*p;
	uint32_t		count;
	int			error;
};

/* eventfd */
typedef uint64_t	eventfd_t;

static fo_rdwr_t	eventfd_read;
static fo_rdwr_t	eventfd_write;
static fo_truncate_t	eventfd_truncate;
static fo_ioctl_t	eventfd_ioctl;
static fo_poll_t	eventfd_poll;
static fo_kqfilter_t	eventfd_kqfilter;
static fo_stat_t	eventfd_stat;
static fo_close_t	eventfd_close;
static fo_fill_kinfo_t	eventfd_fill_kinfo;

static struct fileops eventfdops = {
	.fo_read = eventfd_read,
	.fo_write = eventfd_write,
	.fo_truncate = eventfd_truncate,
	.fo_ioctl = eventfd_ioctl,
	.fo_poll = eventfd_poll,
	.fo_kqfilter = eventfd_kqfilter,
	.fo_stat = eventfd_stat,
	.fo_close = eventfd_close,
	.fo_chmod = invfo_chmod,
	.fo_chown = invfo_chown,
	.fo_sendfile = invfo_sendfile,
	.fo_fill_kinfo = eventfd_fill_kinfo,
	.fo_flags = DFLAG_PASSABLE
};

static void	filt_eventfddetach(struct knote *kn);
static int	filt_eventfdread(struct knote *kn, long hint);
static int	filt_eventfdwrite(struct knote *kn, long hint);

static struct filterops eventfd_rfiltops = {
	.f_isfd = 1,
	.f_detach = filt_eventfddetach,
	.f_event = filt_eventfdread
};
static struct filterops eventfd_wfiltops = {
	.f_isfd = 1,
	.f_detach = filt_eventfddetach,
	.f_event = filt_eventfdwrite
};

struct eventfd {
	eventfd_t	efd_count;
	uint32_t	efd_flags;
	struct selinfo	efd_sel;
	struct mtx	efd_lock;
};

static int	eventfd_create(struct thread *td, uint32_t initval, int flags);


static void
epoll_fd_install(struct thread *td, int fd, epoll_udata_t udata)
{
	struct linux_pemuldata *pem;
	struct epoll_emuldata *emd;
	struct proc *p;

	p = td->td_proc;

	pem = pem_find(p);
	KASSERT(pem != NULL, ("epoll proc emuldata not found.\n"));

	LINUX_PEM_XLOCK(pem);
	if (pem->epoll == NULL) {
		emd = malloc(EPOLL_SIZE(fd), M_EPOLL, M_WAITOK);
		emd->fdc = fd;
		pem->epoll = emd;
	} else {
		emd = pem->epoll;
		if (fd > emd->fdc) {
			emd = realloc(emd, EPOLL_SIZE(fd), M_EPOLL, M_WAITOK);
			emd->fdc = fd;
			pem->epoll = emd;
		}
	}
	emd->udata[fd] = udata;
	LINUX_PEM_XUNLOCK(pem);
}

static int
epoll_create_common(struct thread *td, int flags)
{
	int error;

	error = kern_kqueue(td, flags, NULL);
	if (error)
		return (error);

	epoll_fd_install(td, EPOLL_DEF_SZ, 0);

	return (0);
}

int
linux_epoll_create(struct thread *td, struct linux_epoll_create_args *args)
{

	/*
	 * args->size is unused. Linux just tests it
	 * and then forgets it as well.
	 */
	if (args->size <= 0)
		return (EINVAL);

	return (epoll_create_common(td, 0));
}

int
linux_epoll_create1(struct thread *td, struct linux_epoll_create1_args *args)
{
	int flags;

	if ((args->flags & ~(LINUX_O_CLOEXEC)) != 0)
		return (EINVAL);

	flags = 0;
	if ((args->flags & LINUX_O_CLOEXEC) != 0)
		flags |= O_CLOEXEC;

	return (epoll_create_common(td, flags));
}

/* Structure converting function from epoll to kevent. */
static int
epoll_to_kevent(struct thread *td, struct file *epfp,
    int fd, struct epoll_event *l_event, int *kev_flags,
    struct kevent *kevent, int *nkevents)
{
	uint32_t levents = l_event->events;
	struct linux_pemuldata *pem;
	struct proc *p;

	/* flags related to how event is registered */
	if ((levents & LINUX_EPOLLONESHOT) != 0)
		*kev_flags |= EV_ONESHOT;
	if ((levents & LINUX_EPOLLET) != 0)
		*kev_flags |= EV_CLEAR;
	if ((levents & LINUX_EPOLLERR) != 0)
		*kev_flags |= EV_ERROR;
	if ((levents & LINUX_EPOLLRDHUP) != 0)
		*kev_flags |= EV_EOF;

	/* flags related to what event is registered */
	if ((levents & LINUX_EPOLL_EVRD) != 0) {
		EV_SET(kevent++, fd, EVFILT_READ, *kev_flags, 0, 0, 0);
		++(*nkevents);
	}
	if ((levents & LINUX_EPOLL_EVWR) != 0) {
		EV_SET(kevent++, fd, EVFILT_WRITE, *kev_flags, 0, 0, 0);
		++(*nkevents);
	}

	if ((levents & ~(LINUX_EPOLL_EVSUP)) != 0) {
		p = td->td_proc;

		pem = pem_find(p);
		KASSERT(pem != NULL, ("epoll proc emuldata not found.\n"));
		KASSERT(pem->epoll != NULL, ("epoll proc epolldata not found.\n"));

		LINUX_PEM_XLOCK(pem);
		if ((pem->flags & LINUX_XUNSUP_EPOLL) == 0) {
			pem->flags |= LINUX_XUNSUP_EPOLL;
			LINUX_PEM_XUNLOCK(pem);
			linux_msg(td, "epoll_ctl unsupported flags: 0x%x\n",
			    levents);
		} else
			LINUX_PEM_XUNLOCK(pem);
		return (EINVAL);
	}

	return (0);
}

/* 
 * Structure converting function from kevent to epoll. In a case
 * this is called on error in registration we store the error in
 * event->data and pick it up later in linux_epoll_ctl().
 */
static void
kevent_to_epoll(struct kevent *kevent, struct epoll_event *l_event)
{

	if ((kevent->flags & EV_ERROR) != 0) {
		l_event->events = LINUX_EPOLLERR;
		return;
	}

	switch (kevent->filter) {
	case EVFILT_READ:
		l_event->events = LINUX_EPOLLIN|LINUX_EPOLLRDNORM|LINUX_EPOLLPRI;
		if ((kevent->flags & EV_EOF) != 0)
			l_event->events |= LINUX_EPOLLRDHUP;
	break;
	case EVFILT_WRITE:
		l_event->events = LINUX_EPOLLOUT|LINUX_EPOLLWRNORM;
	break;
	}
}

/* 
 * Copyout callback used by kevent. This converts kevent
 * events to epoll events and copies them back to the
 * userspace. This is also called on error on registering
 * of the filter.
 */
static int
epoll_kev_copyout(void *arg, struct kevent *kevp, int count)
{
	struct epoll_copyout_args *args;
	struct linux_pemuldata *pem;
	struct epoll_emuldata *emd;
	struct epoll_event *eep;
	int error, fd, i;

	args = (struct epoll_copyout_args*) arg;
	eep = malloc(sizeof(*eep) * count, M_EPOLL, M_WAITOK | M_ZERO);

	pem = pem_find(args->p);
	KASSERT(pem != NULL, ("epoll proc emuldata not found.\n"));
	LINUX_PEM_SLOCK(pem);
	emd = pem->epoll;
	KASSERT(emd != NULL, ("epoll proc epolldata not found.\n"));

	for (i = 0; i < count; i++) {
		kevent_to_epoll(&kevp[i], &eep[i]);

		fd = kevp[i].ident;
		KASSERT(fd <= emd->fdc, ("epoll user data vector"
						    " is too small.\n"));
		eep[i].data = emd->udata[fd];
	}
	LINUX_PEM_SUNLOCK(pem);

	error = copyout(eep, args->leventlist, count * sizeof(*eep));
	if (error == 0) {
		args->leventlist += count;
		args->count += count;
	} else if (args->error == 0)
		args->error = error;

	free(eep, M_EPOLL);
	return (error);
}

/*
 * Copyin callback used by kevent. This copies already
 * converted filters from kernel memory to the kevent 
 * internal kernel memory. Hence the memcpy instead of
 * copyin.
 */
static int
epoll_kev_copyin(void *arg, struct kevent *kevp, int count)
{
	struct epoll_copyin_args *args;

	args = (struct epoll_copyin_args*) arg;
	
	memcpy(kevp, args->changelist, count * sizeof(*kevp));
	args->changelist += count;

	return (0);
}

/*
 * Load epoll filter, convert it to kevent filter
 * and load it into kevent subsystem.
 */
int
linux_epoll_ctl(struct thread *td, struct linux_epoll_ctl_args *args)
{
	struct file *epfp, *fp;
	struct epoll_copyin_args ciargs;
	struct kevent kev[2];
	struct kevent_copyops k_ops = { &ciargs,
					NULL,
					epoll_kev_copyin};
	struct epoll_event le;
	cap_rights_t rights;
	int kev_flags;
	int nchanges = 0;
	int error;

	if (args->op != LINUX_EPOLL_CTL_DEL) {
		error = copyin(args->event, &le, sizeof(le));
		if (error != 0)
			return (error);
	}

	error = fget(td, args->epfd,
	    cap_rights_init(&rights, CAP_KQUEUE_CHANGE), &epfp);
	if (error != 0)
		return (error);
	if (epfp->f_type != DTYPE_KQUEUE)
		goto leave1;

	 /* Protect user data vector from incorrectly supplied fd. */
	error = fget(td, args->fd, cap_rights_init(&rights, CAP_POLL_EVENT), &fp);
	if (error != 0)
		goto leave1;

	/* Linux disallows spying on himself */
	if (epfp == fp) {
		error = EINVAL;
		goto leave0;
	}

	ciargs.changelist = kev;

	switch (args->op) {
	case LINUX_EPOLL_CTL_MOD:
		/*
		 * We don't memorize which events were set for this FD
		 * on this level, so just delete all we could have set:
		 * EVFILT_READ and EVFILT_WRITE, ignoring any errors
		 */
		error = epoll_delete_all_events(td, epfp, args->fd);
		if (error)
			goto leave0;
		/* FALLTHROUGH */

	case LINUX_EPOLL_CTL_ADD:
			kev_flags = EV_ADD | EV_ENABLE;
		break;

	case LINUX_EPOLL_CTL_DEL:
		/* CTL_DEL means unregister this fd with this epoll */
		error = epoll_delete_all_events(td, epfp, args->fd);
		goto leave0;

	default:
		error = EINVAL;
		goto leave0;
	}

	error = epoll_to_kevent(td, epfp, args->fd, &le, &kev_flags,
	    kev, &nchanges);
	if (error)
		goto leave0;

	epoll_fd_install(td, args->fd, le.data);

	error = kern_kevent_fp(td, epfp, nchanges, 0, &k_ops, NULL);

leave0:
	fdrop(fp, td);

leave1:
	fdrop(epfp, td);
	return (error);
}

/*
 * Wait for a filter to be triggered on the epoll file descriptor.
 */
static int
linux_epoll_wait_common(struct thread *td, int epfd, struct epoll_event *events,
    int maxevents, int timeout, sigset_t *uset)
{
	struct file *epfp;
	struct timespec ts, *tsp;
	cap_rights_t rights;
	struct epoll_copyout_args coargs;
	struct kevent_copyops k_ops = { &coargs,
					epoll_kev_copyout,
					NULL};
	int error;

	if (maxevents <= 0 || maxevents > LINUX_MAX_EVENTS)
		return (EINVAL);

	if (uset != NULL) {
		error = kern_sigprocmask(td, SIG_SETMASK, uset,
		    &td->td_oldsigmask, 0);
		if (error != 0)
			return (error);
		td->td_pflags |= TDP_OLDMASK;
		/*
		 * Make sure that ast() is called on return to
		 * usermode and TDP_OLDMASK is cleared, restoring old
		 * sigmask.
		 */
		thread_lock(td);
		td->td_flags |= TDF_ASTPENDING;
		thread_unlock(td);
	}

	error = fget(td, epfd,
	    cap_rights_init(&rights, CAP_KQUEUE_EVENT), &epfp);
	if (error != 0)
		return (error);

	coargs.leventlist = events;
	coargs.p = td->td_proc;
	coargs.count = 0;
	coargs.error = 0;

	if (timeout != -1) {
		if (timeout < 0) {
			error = EINVAL;
			goto leave;
		}
		/* Convert from milliseconds to timespec. */
		ts.tv_sec = timeout / 1000;
		ts.tv_nsec = (timeout % 1000) * 1000000;
		tsp = &ts;
	} else {
		tsp = NULL;
	}

	error = kern_kevent_fp(td, epfp, 0, maxevents, &k_ops, tsp);
	if (error == 0 && coargs.error != 0)
		error = coargs.error;

	/* 
	 * kern_kevent might return ENOMEM which is not expected from epoll_wait.
	 * Maybe we should translate that but I don't think it matters at all.
	 */
	if (error == 0)
		td->td_retval[0] = coargs.count;
leave:
	fdrop(epfp, td);
	return (error);
}

int
linux_epoll_wait(struct thread *td, struct linux_epoll_wait_args *args)
{

	return (linux_epoll_wait_common(td, args->epfd, args->events,
	    args->maxevents, args->timeout, NULL));
}

int
linux_epoll_pwait(struct thread *td, struct linux_epoll_pwait_args *args)
{
	sigset_t mask, *pmask;
	l_sigset_t lmask;
	int error;

	if (args->mask != NULL) {
		error = copyin(args->mask, &lmask, sizeof(l_sigset_t));
		if (error != 0)
			return (error);
		linux_to_bsd_sigset(&lmask, &mask);
		pmask = &mask;
	} else
		pmask = NULL;
	return (linux_epoll_wait_common(td, args->epfd, args->events,
	    args->maxevents, args->timeout, pmask));
}

static int
epoll_delete_event(struct thread *td, struct file *epfp, int fd, int filter)
{
	struct epoll_copyin_args ciargs;
	struct kevent kev;
	struct kevent_copyops k_ops = { &ciargs,
					NULL,
					epoll_kev_copyin};
	int error;

	ciargs.changelist = &kev;
	EV_SET(&kev, fd, filter, EV_DELETE | EV_DISABLE, 0, 0, 0);

	error = kern_kevent_fp(td, epfp, 1, 0, &k_ops, NULL);

	/*
	 * here we ignore ENONT, because we don't keep track of events here
	 */
	if (error == ENOENT)
		error = 0;
	return (error);
}

static int
epoll_delete_all_events(struct thread *td, struct file *epfp, int fd)
{
	int error1, error2;

	error1 = epoll_delete_event(td, epfp, fd, EVFILT_READ);
	error2 = epoll_delete_event(td, epfp, fd, EVFILT_WRITE);

	/* report any errors we got */
	return (error1 == 0 ? error2 : error1);
}

static int
eventfd_create(struct thread *td, uint32_t initval, int flags)
{
	struct filedesc *fdp;
	struct eventfd *efd;
	struct file *fp;
	int fflags, fd, error;

	fflags = 0;
	if ((flags & LINUX_O_CLOEXEC) != 0)
		fflags |= O_CLOEXEC;

	fdp = td->td_proc->p_fd;
	error = falloc(td, &fp, &fd, fflags);
	if (error)
		return (error);

	efd = malloc(sizeof(*efd), M_EPOLL, M_WAITOK | M_ZERO);
	efd->efd_flags = flags;
	efd->efd_count = initval;
	mtx_init(&efd->efd_lock, "eventfd", NULL, MTX_DEF);

	knlist_init_mtx(&efd->efd_sel.si_note, &efd->efd_lock);

	fflags = FREAD | FWRITE; 
	if ((flags & LINUX_O_NONBLOCK) != 0)
		fflags |= FNONBLOCK;

	finit(fp, fflags, DTYPE_LINUXEFD, efd, &eventfdops);
	fdrop(fp, td);

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

int
linux_eventfd(struct thread *td, struct linux_eventfd_args *args)
{

	return (eventfd_create(td, args->initval, 0));
}

int
linux_eventfd2(struct thread *td, struct linux_eventfd2_args *args)
{

	if ((args->flags & ~(LINUX_O_CLOEXEC|LINUX_O_NONBLOCK|LINUX_EFD_SEMAPHORE)) != 0)
		return (EINVAL);

	return (eventfd_create(td, args->initval, args->flags));
}

static int
eventfd_close(struct file *fp, struct thread *td)
{
	struct eventfd *efd;

	efd = fp->f_data;
	if (fp->f_type != DTYPE_LINUXEFD || efd == NULL)
		return (EBADF);

	seldrain(&efd->efd_sel);
	knlist_destroy(&efd->efd_sel.si_note);

	fp->f_ops = &badfileops;
	mtx_destroy(&efd->efd_lock);
	free(efd, M_EPOLL);

	return (0);
}

static int
eventfd_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
	int flags, struct thread *td)
{
	struct eventfd *efd;
	eventfd_t count;
	int error;

	efd = fp->f_data;
	if (fp->f_type != DTYPE_LINUXEFD || efd == NULL)
		return (EBADF);

	if (uio->uio_resid < sizeof(eventfd_t))
		return (EINVAL);

	error = 0;
	mtx_lock(&efd->efd_lock);
retry:
	if (efd->efd_count == 0) {
		if ((efd->efd_flags & LINUX_O_NONBLOCK) != 0) {
			mtx_unlock(&efd->efd_lock);
			return (EAGAIN);
		}
		error = mtx_sleep(&efd->efd_count, &efd->efd_lock, PCATCH, "lefdrd", 0);
		if (error == 0)
			goto retry;
	}
	if (error == 0) {
		if ((efd->efd_flags & LINUX_EFD_SEMAPHORE) != 0) {
			count = 1;
			--efd->efd_count;
		} else {
			count = efd->efd_count;
			efd->efd_count = 0;
		}
		KNOTE_LOCKED(&efd->efd_sel.si_note, 0);
		selwakeup(&efd->efd_sel);
		wakeup(&efd->efd_count);
		mtx_unlock(&efd->efd_lock);
		error = uiomove(&count, sizeof(eventfd_t), uio);
	} else
		mtx_unlock(&efd->efd_lock);

	return (error);
}

static int
eventfd_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
	 int flags, struct thread *td)
{
	struct eventfd *efd;
	eventfd_t count;
	int error;

	efd = fp->f_data;
	if (fp->f_type != DTYPE_LINUXEFD || efd == NULL)
		return (EBADF);

	if (uio->uio_resid < sizeof(eventfd_t))
		return (EINVAL);

	error = uiomove(&count, sizeof(eventfd_t), uio);
	if (error)
		return (error);
	if (count == UINT64_MAX)
		return (EINVAL);

	mtx_lock(&efd->efd_lock);
retry:
	if (UINT64_MAX - efd->efd_count <= count) {
		if ((efd->efd_flags & LINUX_O_NONBLOCK) != 0) {
			mtx_unlock(&efd->efd_lock);
			return (EAGAIN);
		}
		error = mtx_sleep(&efd->efd_count, &efd->efd_lock,
		    PCATCH, "lefdwr", 0);
		if (error == 0)
			goto retry;
	}
	if (error == 0) {
		efd->efd_count += count;
		KNOTE_LOCKED(&efd->efd_sel.si_note, 0);
		selwakeup(&efd->efd_sel);
		wakeup(&efd->efd_count);
	}
	mtx_unlock(&efd->efd_lock);

	return (error);
}

static int
eventfd_poll(struct file *fp, int events, struct ucred *active_cred,
	struct thread *td)
{
	struct eventfd *efd;
	int revents = 0;

	efd = fp->f_data;
	if (fp->f_type != DTYPE_LINUXEFD || efd == NULL)
		return (POLLERR);

	mtx_lock(&efd->efd_lock);
	if ((events & (POLLIN|POLLRDNORM)) && efd->efd_count > 0)
		revents |= events & (POLLIN|POLLRDNORM);
	if ((events & (POLLOUT|POLLWRNORM)) && UINT64_MAX - 1 > efd->efd_count)
		revents |= events & (POLLOUT|POLLWRNORM);
	if (revents == 0)
		selrecord(td, &efd->efd_sel);
	mtx_unlock(&efd->efd_lock);

	return (revents);
}

/*ARGSUSED*/
static int
eventfd_kqfilter(struct file *fp, struct knote *kn)
{
	struct eventfd *efd;

	efd = fp->f_data;
	if (fp->f_type != DTYPE_LINUXEFD || efd == NULL)
		return (EINVAL);

	mtx_lock(&efd->efd_lock);
	switch (kn->kn_filter) {
	case EVFILT_READ:
		kn->kn_fop = &eventfd_rfiltops;
		break;
	case EVFILT_WRITE:
		kn->kn_fop = &eventfd_wfiltops;
		break;
	default:
		mtx_unlock(&efd->efd_lock);
		return (EINVAL);
	}

	kn->kn_hook = efd;
	knlist_add(&efd->efd_sel.si_note, kn, 1);
	mtx_unlock(&efd->efd_lock);

	return (0);
}

static void
filt_eventfddetach(struct knote *kn)
{
	struct eventfd *efd = kn->kn_hook;

	mtx_lock(&efd->efd_lock);
	knlist_remove(&efd->efd_sel.si_note, kn, 1);
	mtx_unlock(&efd->efd_lock);
}

/*ARGSUSED*/
static int
filt_eventfdread(struct knote *kn, long hint)
{
	struct eventfd *efd = kn->kn_hook;
	int ret;

	mtx_assert(&efd->efd_lock, MA_OWNED);
	ret = (efd->efd_count > 0);

	return (ret);
}

/*ARGSUSED*/
static int
filt_eventfdwrite(struct knote *kn, long hint)
{
	struct eventfd *efd = kn->kn_hook;
	int ret;

	mtx_assert(&efd->efd_lock, MA_OWNED);
	ret = (UINT64_MAX - 1 > efd->efd_count);

	return (ret);
}

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

	return (ENXIO);
}

/*ARGSUSED*/
static int
eventfd_ioctl(struct file *fp, u_long cmd, void *data,
	struct ucred *active_cred, struct thread *td)
{

	return (ENXIO);
}

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

	return (ENXIO);
}

/*ARGSUSED*/
static int
eventfd_fill_kinfo(struct file *fp, struct kinfo_file *kif, struct filedesc *fdp)
{

	kif->kf_type = KF_TYPE_UNKNOWN;
	return (0);
}