xnu-7195.101.1.tar.gz

[apple/xnu.git] / bsd / kern / tty_ptmx.c

/*
 * Copyright (c) 1997-2019 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
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 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * Copyright (c) 1982, 1986, 1989, 1993
 *      The Regents of the University of California.  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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 *
 *	@(#)tty_pty.c	8.4 (Berkeley) 2/20/95
 */

/*
 * Pseudo-teletype Driver
 * (Actually two drivers, requiring two entries in 'cdevsw')
 */
#include "pty.h"                /* XXX */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/ioctl.h>
#include <sys/proc_internal.h>
#include <sys/kauth.h>
#include <sys/tty.h>
#include <sys/conf.h>
#include <sys/file_internal.h>
#include <sys/uio_internal.h>
#include <sys/kernel.h>
#include <sys/vnode.h>
#include <sys/user.h>
#include <sys/signalvar.h>
#include <sys/sysctl.h>
#include <miscfs/devfs/devfs.h>
#include <miscfs/devfs/devfsdefs.h>     /* DEVFS_LOCK()/DEVFS_UNLOCK() */
#include <libkern/section_keywords.h>

#if CONFIG_MACF
#include <security/mac_framework.h>
#endif

#include "tty_dev.h"

/*
 * Forward declarations
 */
int ptmx_init(int n_ptys);
static struct ptmx_ioctl *ptmx_get_ioctl(int minor, int open_flag);
static int ptmx_free_ioctl(int minor, int open_flag);
static int ptmx_get_name(int minor, char *buffer, size_t size);
static void ptsd_revoke_knotes(int minor, struct tty *tp);

extern  d_open_t        ptsopen;
extern  d_close_t       ptsclose;
extern  d_read_t        ptsread;
extern  d_write_t       ptswrite;
extern  d_ioctl_t       ptyioctl;
extern  d_stop_t        ptsstop;
extern  d_reset_t       ptsreset;
extern  d_select_t      ptsselect;

extern  d_open_t        ptcopen;
extern  d_close_t       ptcclose;
extern  d_read_t        ptcread;
extern  d_write_t       ptcwrite;
extern  d_stop_t        ptcstop;
extern  d_reset_t       ptcreset;
extern  d_select_t      ptcselect;

static int ptmx_major;          /* dynamically assigned major number */
static const struct cdevsw ptmx_cdev = {
	.d_open       = ptcopen,
	.d_close      = ptcclose,
	.d_read       = ptcread,
	.d_write      = ptcwrite,
	.d_ioctl      = ptyioctl,
	.d_stop       = ptcstop,
	.d_reset      = ptcreset,
	.d_ttys       = NULL,
	.d_select     = ptcselect,
	.d_mmap       = eno_mmap,
	.d_strategy   = eno_strat,
	.d_reserved_1 = eno_getc,
	.d_reserved_2 = eno_putc,
	.d_type       = D_TTY
};

static int ptsd_major;          /* dynamically assigned major number */
static const struct cdevsw ptsd_cdev = {
	.d_open       = ptsopen,
	.d_close      = ptsclose,
	.d_read       = ptsread,
	.d_write      = ptswrite,
	.d_ioctl      = ptyioctl,
	.d_stop       = ptsstop,
	.d_reset      = ptsreset,
	.d_ttys       = NULL,
	.d_select     = ptsselect,
	.d_mmap       = eno_mmap,
	.d_strategy   = eno_strat,
	.d_reserved_1 = eno_getc,
	.d_reserved_2 = eno_putc,
	.d_type       = D_TTY
};

/*
 * ptmx == /dev/ptmx
 * ptsd == /dev/pts[0123456789]{3}
 */
#define PTMX_TEMPLATE   "ptmx"
#define PTSD_TEMPLATE   "ttys%03d"

/*
 * System-wide limit on the max number of cloned ptys
 */
#define PTMX_MAX_DEFAULT        511     /* 512 entries */
#define PTMX_MAX_HARD           999     /* 1000 entries, due to PTSD_TEMPLATE */

static int ptmx_max = PTMX_MAX_DEFAULT; /* default # of clones we allow */

/* Range enforcement for the sysctl */
static int
sysctl_ptmx_max(__unused struct sysctl_oid *oidp, __unused void *arg1,
    __unused int arg2, struct sysctl_req *req)
{
	int new_value, changed;
	int error = sysctl_io_number(req, ptmx_max, sizeof(int), &new_value, &changed);
	if (changed) {
		if (new_value > 0 && new_value <= PTMX_MAX_HARD) {
			ptmx_max = new_value;
		} else {
			error = EINVAL;
		}
	}
	return error;
}

SYSCTL_NODE(_kern, KERN_TTY, tty, CTLFLAG_RW | CTLFLAG_LOCKED, 0, "TTY");
SYSCTL_PROC(_kern_tty, OID_AUTO, ptmx_max,
    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
    &ptmx_max, 0, &sysctl_ptmx_max, "I", "ptmx_max");

static int      ptmx_clone(dev_t dev, int minor);

static struct tty_dev_t _ptmx_driver;

int
ptmx_init( __unused int config_count)
{
	/*
	 * We start looking at slot 10, since there are inits that will
	 * stomp explicit slots (e.g. vndevice stomps 1) below that.
	 */

	/* Get a major number for /dev/ptmx */
	if ((ptmx_major = cdevsw_add(-15, &ptmx_cdev)) == -1) {
		printf("ptmx_init: failed to obtain /dev/ptmx major number\n");
		return ENOENT;
	}

	if (cdevsw_setkqueueok(ptmx_major, &ptmx_cdev, CDEVSW_IS_PTC) == -1) {
		panic("Failed to set flags on ptmx cdevsw entry.");
	}

	/* Get a major number for /dev/pts/nnn */
	if ((ptsd_major = cdevsw_add(-15, &ptsd_cdev)) == -1) {
		(void)cdevsw_remove(ptmx_major, &ptmx_cdev);
		printf("ptmx_init: failed to obtain /dev/ptmx major number\n");
		return ENOENT;
	}

	if (cdevsw_setkqueueok(ptsd_major, &ptsd_cdev, CDEVSW_IS_PTS) == -1) {
		panic("Failed to set flags on ptmx cdevsw entry.");
	}

	/* Create the /dev/ptmx device {<major>,0} */
	(void)devfs_make_node_clone(makedev(ptmx_major, 0),
	    DEVFS_CHAR, UID_ROOT, GID_TTY, 0666,
	    ptmx_clone, PTMX_TEMPLATE);

	_ptmx_driver.master = ptmx_major;
	_ptmx_driver.slave = ptsd_major;
	_ptmx_driver.fix_7828447 = 1;
	_ptmx_driver.fix_7070978 = 1;
#if CONFIG_MACF
	_ptmx_driver.mac_notify = 1;
#endif
	_ptmx_driver.open = &ptmx_get_ioctl;
	_ptmx_driver.free = &ptmx_free_ioctl;
	_ptmx_driver.name = &ptmx_get_name;
	_ptmx_driver.revoke = &ptsd_revoke_knotes;
	tty_dev_register(&_ptmx_driver);

	return 0;
}


static struct _ptmx_ioctl_state {
	struct ptmx_ioctl       **pis_ioctl_list;       /* pointer vector */
	int                     pis_total;              /* total slots */
	int                     pis_free;               /* free slots */
} _state;
#define PTMX_GROW_VECTOR        16      /* Grow by this many slots at a time */

/*
 * Given a minor number, return the corresponding structure for that minor
 * number.  If there isn't one, and the create flag is specified, we create
 * one if possible.
 *
 * Parameters:	minor			Minor number of ptmx device
 *		open_flag		PF_OPEN_M	First open of master
 *					PF_OPEN_S	First open of slave
 *					0		Just want ioctl struct
 *
 * Returns:	NULL			Did not exist/could not create
 *		!NULL			structure corresponding minor number
 *
 * Locks:	tty_lock() on ptmx_ioctl->pt_tty NOT held on entry or exit.
 */
static struct ptmx_ioctl *
ptmx_get_ioctl(int minor, int open_flag)
{
	struct ptmx_ioctl *ptmx_ioctl = NULL;

	if (open_flag & PF_OPEN_M) {
		struct ptmx_ioctl *new_ptmx_ioctl;

		DEVFS_LOCK();
		/*
		 * If we are about to allocate more memory, but we have
		 * already hit the administrative limit, then fail the
		 * operation.
		 *
		 * Note:	Subtract free from total when making this
		 *		check to allow unit increments, rather than
		 *		snapping to the nearest PTMX_GROW_VECTOR...
		 */
		if ((_state.pis_total - _state.pis_free) >= ptmx_max) {
			DEVFS_UNLOCK();
			return NULL;
		}
		DEVFS_UNLOCK();

		new_ptmx_ioctl = kheap_alloc(KM_TTYS, sizeof(struct ptmx_ioctl),
		    Z_WAITOK | Z_ZERO);
		if (new_ptmx_ioctl == NULL) {
			return NULL;
		}

		if ((new_ptmx_ioctl->pt_tty = ttymalloc()) == NULL) {
			kheap_free(KM_TTYS, new_ptmx_ioctl, sizeof(struct ptmx_ioctl));
			return NULL;
		}

		/*
		 * Hold the DEVFS_LOCK() over this whole operation; devfs
		 * itself does this over malloc/free as well, so this should
		 * be safe to do.  We hold it longer than we want to, but
		 * doing so avoids a reallocation race on the minor number.
		 */
		DEVFS_LOCK();

		/*
		 * Check again to ensure the limit is not reached after initial check
		 * when the lock was dropped momentarily for malloc.
		 */
		if ((_state.pis_total - _state.pis_free) >= ptmx_max) {
			ttyfree(new_ptmx_ioctl->pt_tty);
			DEVFS_UNLOCK();
			kheap_free(KM_TTYS, new_ptmx_ioctl, sizeof(struct ptmx_ioctl));
			return NULL;
		}

		/* Need to allocate a larger vector? */
		if (_state.pis_free == 0) {
			struct ptmx_ioctl **new_pis_ioctl_list;
			struct ptmx_ioctl **old_pis_ioctl_list = NULL;
			size_t old_pis_total = 0;

			/* Yes. */
			new_pis_ioctl_list = kheap_alloc(KM_TTYS,
			    sizeof(struct ptmx_ioctl *) * (_state.pis_total + PTMX_GROW_VECTOR),
			    Z_WAITOK | Z_ZERO);
			if (new_pis_ioctl_list == NULL) {
				ttyfree(new_ptmx_ioctl->pt_tty);
				DEVFS_UNLOCK();
				kheap_free(KM_TTYS, new_ptmx_ioctl, sizeof(struct ptmx_ioctl));
				return NULL;
			}

			/* If this is not the first time, copy the old over */
			bcopy(_state.pis_ioctl_list, new_pis_ioctl_list, sizeof(struct ptmx_ioctl *) * _state.pis_total);
			old_pis_ioctl_list = _state.pis_ioctl_list;
			old_pis_total = _state.pis_total;
			_state.pis_ioctl_list = new_pis_ioctl_list;
			_state.pis_free += PTMX_GROW_VECTOR;
			_state.pis_total += PTMX_GROW_VECTOR;
			kheap_free(KM_TTYS, old_pis_ioctl_list,
			    sizeof(struct ptmx_ioctl *) * old_pis_total);
		}

		/* is minor in range now? */
		if (minor < 0 || minor >= _state.pis_total) {
			ttyfree(new_ptmx_ioctl->pt_tty);
			DEVFS_UNLOCK();
			kheap_free(KM_TTYS, new_ptmx_ioctl, sizeof(struct ptmx_ioctl));
			return NULL;
		}

		if (_state.pis_ioctl_list[minor] != NULL) {
			ttyfree(new_ptmx_ioctl->pt_tty);
			DEVFS_UNLOCK();
			kheap_free(KM_TTYS, new_ptmx_ioctl, sizeof(struct ptmx_ioctl));

			/* Special error value so we know to redrive the open, we've been raced */
			return (struct ptmx_ioctl*)-1;
		}

		/* Vector is large enough; grab a new ptmx_ioctl */

		/* Now grab a free slot... */
		_state.pis_ioctl_list[minor] = new_ptmx_ioctl;

		/* reduce free count */
		_state.pis_free--;

		_state.pis_ioctl_list[minor]->pt_flags |= PF_OPEN_M;
		DEVFS_UNLOCK();

		/* Create the /dev/ttysXXX device {<major>,XXX} */
		_state.pis_ioctl_list[minor]->pt_devhandle = devfs_make_node(
			makedev(ptsd_major, minor),
			DEVFS_CHAR, UID_ROOT, GID_TTY, 0620,
			PTSD_TEMPLATE, minor);
		if (_state.pis_ioctl_list[minor]->pt_devhandle == NULL) {
			printf("devfs_make_node() call failed for ptmx_get_ioctl()!!!!\n");
		}
	}

	/*
	 * Lock is held here to protect race when the 'pis_ioctl_list' array is
	 * being reallocated to increase its slots.
	 */
	DEVFS_LOCK();
	if (minor >= 0 && minor < _state.pis_total) {
		ptmx_ioctl = _state.pis_ioctl_list[minor];
	}
	DEVFS_UNLOCK();

	return ptmx_ioctl;
}

/*
 * Locks:	tty_lock() of old_ptmx_ioctl->pt_tty NOT held for this call.
 */
static int
ptmx_free_ioctl(int minor, int open_flag)
{
	struct ptmx_ioctl *old_ptmx_ioctl = NULL;

	DEVFS_LOCK();

	if (minor < 0 || minor >= _state.pis_total) {
		DEVFS_UNLOCK();
		return -1;
	}

	_state.pis_ioctl_list[minor]->pt_flags &= ~(open_flag);

	/*
	 * Was this the last close?  We will recognize it because we only get
	 * a notification on the last close of a device, and we will have
	 * cleared both the master and the slave open bits in the flags.
	 */
	if (!(_state.pis_ioctl_list[minor]->pt_flags & (PF_OPEN_M | PF_OPEN_S))) {
		/* Mark as free so it can be reallocated later */
		old_ptmx_ioctl = _state.pis_ioctl_list[minor];
		_state.pis_ioctl_list[minor] = NULL;
		_state.pis_free++;
	}
	DEVFS_UNLOCK();

	/* Free old after dropping lock */
	if (old_ptmx_ioctl != NULL) {
		/*
		 * XXX See <rdar://5348651> and <rdar://4854638>
		 *
		 * XXX Conditional to be removed when/if tty/pty reference
		 * XXX counting and mutex implemented.
		 */
		if (old_ptmx_ioctl->pt_devhandle != NULL) {
			devfs_remove(old_ptmx_ioctl->pt_devhandle);
		}
		ttyfree(old_ptmx_ioctl->pt_tty);
		kheap_free(KM_TTYS, old_ptmx_ioctl, sizeof(struct ptmx_ioctl));
	}

	return 0;     /* Success */
}

static int
ptmx_get_name(int minor, char *buffer, size_t size)
{
	return snprintf(buffer, size, "/dev/" PTSD_TEMPLATE, minor);
}



/*
 * Given the dev entry that's being opened, we clone the device.  This driver
 * doesn't actually use the dev entry, since we alreaqdy know who we are by
 * being called from this code.  This routine is a callback registered from
 * devfs_make_node_clone() in ptmx_init(); it's purpose is to provide a new
 * minor number, or to return -1, if one can't be provided.
 *
 * Parameters:	dev			The device we are cloning from
 *
 * Returns:	>= 0			A new minor device number
 *		-1			Error: ENOMEM ("Can't alloc device")
 *
 * NOTE:	Called with DEVFS_LOCK() held
 */
static int
ptmx_clone(__unused dev_t dev, int action)
{
	int i;

	if (action == DEVFS_CLONE_ALLOC) {
		/* First one */
		if (_state.pis_total == 0) {
			return 0;
		}

		/*
		 * Note: We can add hinting on free slots, if this linear search
		 * ends up being a performance bottleneck...
		 */
		for (i = 0; i < _state.pis_total; i++) {
			if (_state.pis_ioctl_list[i] == NULL) {
				break;
			}
		}

		/*
		 * XXX We fall off the end here; if we did this twice at the
		 * XXX same time, we could return the same minor to two
		 * XXX callers; we should probably exand the pointer vector
		 * XXX here, but I need more information on the MALLOC/FREE
		 * XXX locking to ensure against a deadlock.  Maybe we can
		 * XXX just high watermark it at 1/2 of PTMX_GROW_VECTOR?
		 * XXX That would require returning &minor as implict return
		 * XXX and an error code ("EAGAIN/ERESTART") or 0 as our
		 * XXX explicit return.
		 */

		return i;     /* empty slot or next slot */
	}
	return -1;
}


/*
 * kqueue support.
 */
int ptsd_kqfilter(dev_t dev, struct knote *kn);
static void ptsd_kqops_detach(struct knote *);
static int ptsd_kqops_event(struct knote *, long);
static int ptsd_kqops_touch(struct knote *kn, struct kevent_qos_s *kev);
static int ptsd_kqops_process(struct knote *kn, struct kevent_qos_s *kev);

SECURITY_READ_ONLY_EARLY(struct filterops) ptsd_kqops = {
	.f_isfd = 1,
	/* attach is handled by ptsd_kqfilter -- the dev node must be passed in */
	.f_detach = ptsd_kqops_detach,
	.f_event = ptsd_kqops_event,
	.f_touch = ptsd_kqops_touch,
	.f_process = ptsd_kqops_process,
};

/*
 * In the normal case, by the time the driver_close() routine is called
 * on the slave, all knotes have been detached.  However in the revoke(2)
 * case, the driver's close routine is called while there are knotes active
 * that reference the handlers below.  And we have no obvious means to
 * reach from the driver out to the kqueue's that reference them to get
 * them to stop.
 */

static void
ptsd_kqops_detach(struct knote *kn)
{
	struct tty *tp = kn->kn_hook;

	tty_lock(tp);

	/*
	 * Only detach knotes from open ttys -- ttyclose detaches all knotes
	 * under the lock and unsets TS_ISOPEN.
	 */
	if (tp->t_state & TS_ISOPEN) {
		switch (kn->kn_filter) {
		case EVFILT_READ:
			KNOTE_DETACH(&tp->t_rsel.si_note, kn);
			break;
		case EVFILT_WRITE:
			KNOTE_DETACH(&tp->t_wsel.si_note, kn);
			break;
		default:
			panic("invalid knote %p detach, filter: %d", kn, kn->kn_filter);
			break;
		}
	}

	tty_unlock(tp);
	ttyfree(tp);
}

static int
ptsd_kqops_common(struct knote *kn, struct kevent_qos_s *kev, struct tty *tp)
{
	int retval = 0;
	int64_t data = 0;

	TTY_LOCK_OWNED(tp);

	switch (kn->kn_filter) {
	case EVFILT_READ:
		/*
		 * ttnread can change the tty state,
		 * hence must be done upfront, before any other check.
		 */
		data = ttnread(tp);
		retval = (data > 0);
		break;

	case EVFILT_WRITE:
		if ((tp->t_outq.c_cc <= tp->t_lowat) &&
		    (tp->t_state & TS_CONNECTED)) {
			data = tp->t_outq.c_cn - tp->t_outq.c_cc;
			retval = 1;
		}
		break;

	default:
		panic("ptsd kevent: unexpected filter: %d, kn = %p, tty = %p",
		    kn->kn_filter, kn, tp);
		break;
	}

	if (tp->t_state & TS_ZOMBIE) {
		kn->kn_flags |= EV_EOF;
	}
	if (kn->kn_flags & EV_EOF) {
		retval = 1;
	}
	if (retval && kev) {
		knote_fill_kevent(kn, kev, data);
	}
	return retval;
}

static int
ptsd_kqops_event(struct knote *kn, long hint)
{
	struct tty *tp = kn->kn_hook;
	int ret;

	TTY_LOCK_OWNED(tp);

	if (hint & NOTE_REVOKE) {
		kn->kn_flags |= EV_EOF | EV_ONESHOT;
		ret = 1;
	} else {
		ret = ptsd_kqops_common(kn, NULL, tp);
	}

	return ret;
}

static int
ptsd_kqops_touch(struct knote *kn, struct kevent_qos_s *kev)
{
	struct tty *tp = kn->kn_hook;
	int ret;

	tty_lock(tp);

	/* accept new kevent state */
	kn->kn_sfflags = kev->fflags;
	kn->kn_sdata = kev->data;

	/* recapture fired state of knote */
	ret = ptsd_kqops_common(kn, NULL, tp);

	tty_unlock(tp);

	return ret;
}

static int
ptsd_kqops_process(struct knote *kn, struct kevent_qos_s *kev)
{
	struct tty *tp = kn->kn_hook;
	int ret;

	tty_lock(tp);
	ret = ptsd_kqops_common(kn, kev, tp);
	tty_unlock(tp);

	return ret;
}

int
ptsd_kqfilter(dev_t dev, struct knote *kn)
{
	struct tty *tp = NULL;
	struct ptmx_ioctl *pti = NULL;
	int ret;

	/* make sure we're talking about the right device type */
	if (cdevsw[major(dev)].d_open != ptsopen) {
		knote_set_error(kn, ENODEV);
		return 0;
	}

	if ((pti = ptmx_get_ioctl(minor(dev), 0)) == NULL) {
		knote_set_error(kn, ENXIO);
		return 0;
	}

	tp = pti->pt_tty;
	tty_lock(tp);

	assert(tp->t_state & TS_ISOPEN);

	kn->kn_filtid = EVFILTID_PTSD;
	/* the tty will be freed when detaching the knote */
	ttyhold(tp);
	kn->kn_hook = tp;

	switch (kn->kn_filter) {
	case EVFILT_READ:
		KNOTE_ATTACH(&tp->t_rsel.si_note, kn);
		break;
	case EVFILT_WRITE:
		KNOTE_ATTACH(&tp->t_wsel.si_note, kn);
		break;
	default:
		panic("ptsd kevent: unexpected filter: %d, kn = %p, tty = %p",
		    kn->kn_filter, kn, tp);
		break;
	}

	/* capture current event state */
	ret = ptsd_kqops_common(kn, NULL, tp);

	tty_unlock(tp);

	return ret;
}

/*
 * Support for revoke(2).
 */
static void
ptsd_revoke_knotes(__unused int minor, struct tty *tp)
{
	tty_lock(tp);

	ttwakeup(tp);
	assert((tp->t_rsel.si_flags & SI_KNPOSTING) == 0);
	KNOTE(&tp->t_rsel.si_note, NOTE_REVOKE);

	ttwwakeup(tp);
	assert((tp->t_wsel.si_flags & SI_KNPOSTING) == 0);
	KNOTE(&tp->t_wsel.si_note, NOTE_REVOKE);

	tty_unlock(tp);
}

/*
 * kevent filter routines for the master side of a pty, a ptmx.
 *
 * Stuff the ptmx_ioctl structure into the hook for ptmx knotes.  Use the
 * embedded tty's lock for synchronization.
 */

int ptmx_kqfilter(dev_t dev, struct knote *kn);
static void ptmx_kqops_detach(struct knote *);
static int ptmx_kqops_event(struct knote *, long);
static int ptmx_kqops_touch(struct knote *kn, struct kevent_qos_s *kev);
static int ptmx_kqops_process(struct knote *kn, struct kevent_qos_s *kev);
static int ptmx_kqops_common(struct knote *kn, struct kevent_qos_s *kev,
    struct ptmx_ioctl *pti, struct tty *tp);

SECURITY_READ_ONLY_EARLY(struct filterops) ptmx_kqops = {
	.f_isfd = 1,
	/* attach is handled by ptmx_kqfilter -- the dev node must be passed in */
	.f_detach = ptmx_kqops_detach,
	.f_event = ptmx_kqops_event,
	.f_touch = ptmx_kqops_touch,
	.f_process = ptmx_kqops_process,
};

static struct ptmx_ioctl *
ptmx_knote_ioctl(struct knote *kn)
{
	return (struct ptmx_ioctl *)kn->kn_hook;
}

static struct tty *
ptmx_knote_tty(struct knote *kn)
{
	return ptmx_knote_ioctl(kn)->pt_tty;
}

int
ptmx_kqfilter(dev_t dev, struct knote *kn)
{
	struct tty *tp = NULL;
	struct ptmx_ioctl *pti = NULL;
	int ret;

	/* make sure we're talking about the right device type */
	if (cdevsw[major(dev)].d_open != ptcopen) {
		knote_set_error(kn, ENODEV);
		return 0;
	}

	if ((pti = ptmx_get_ioctl(minor(dev), 0)) == NULL) {
		knote_set_error(kn, ENXIO);
		return 0;
	}

	tp = pti->pt_tty;
	tty_lock(tp);

	kn->kn_filtid = EVFILTID_PTMX;
	/* the tty will be freed when detaching the knote */
	ttyhold(tp);
	kn->kn_hook = pti;

	/*
	 * Attach to the ptmx's selinfo structures.  This is the major difference
	 * to the ptsd filtops, which use the selinfo structures in the tty
	 * structure.
	 */
	switch (kn->kn_filter) {
	case EVFILT_READ:
		KNOTE_ATTACH(&pti->pt_selr.si_note, kn);
		break;
	case EVFILT_WRITE:
		KNOTE_ATTACH(&pti->pt_selw.si_note, kn);
		break;
	default:
		panic("ptmx kevent: unexpected filter: %d, kn = %p, tty = %p",
		    kn->kn_filter, kn, tp);
		break;
	}

	/* capture current event state */
	ret = ptmx_kqops_common(kn, NULL, pti, tp);

	tty_unlock(tp);

	return ret;
}

static void
ptmx_kqops_detach(struct knote *kn)
{
	struct ptmx_ioctl *pti = kn->kn_hook;
	struct tty *tp = pti->pt_tty;

	tty_lock(tp);

	switch (kn->kn_filter) {
	case EVFILT_READ:
		KNOTE_DETACH(&pti->pt_selr.si_note, kn);
		break;
	case EVFILT_WRITE:
		KNOTE_DETACH(&pti->pt_selw.si_note, kn);
		break;
	default:
		panic("invalid knote %p detach, filter: %d", kn, kn->kn_filter);
		break;
	}

	tty_unlock(tp);
	ttyfree(tp);
}

static int
ptmx_kqops_common(struct knote *kn, struct kevent_qos_s *kev,
    struct ptmx_ioctl *pti, struct tty *tp)
{
	int retval = 0;
	int64_t data = 0;

	TTY_LOCK_OWNED(tp);

	switch (kn->kn_filter) {
	case EVFILT_READ:
		/* there's data on the TTY and it's not stopped */
		if (tp->t_outq.c_cc && !(tp->t_state & TS_TTSTOP)) {
			data = tp->t_outq.c_cc;
			retval = data > 0;
		} else if (((pti->pt_flags & PF_PKT) && pti->pt_send) ||
		    ((pti->pt_flags & PF_UCNTL) && pti->pt_ucntl)) {
			retval = 1;
		}
		break;

	case EVFILT_WRITE:
		if (pti->pt_flags & PF_REMOTE) {
			if (tp->t_canq.c_cc == 0) {
				retval = TTYHOG - 1;
			}
		} else {
			retval = (TTYHOG - 2) - (tp->t_rawq.c_cc + tp->t_canq.c_cc);
			if (tp->t_canq.c_cc == 0 && (tp->t_lflag & ICANON)) {
				retval = 1;
			}
			if (retval < 0) {
				retval = 0;
			}
		}
		break;

	default:
		panic("ptmx kevent: unexpected filter: %d, kn = %p, tty = %p",
		    kn->kn_filter, kn, tp);
		break;
	}

	/* disconnects should force a wakeup (EOF) */
	if (!(tp->t_state & TS_CONNECTED) || (tp->t_state & TS_ZOMBIE)) {
		kn->kn_flags |= EV_EOF;
	}
	if (kn->kn_flags & EV_EOF) {
		retval = 1;
	}
	if (retval && kev) {
		knote_fill_kevent(kn, kev, data);
	}
	return retval;
}

static int
ptmx_kqops_event(struct knote *kn, long hint)
{
	struct ptmx_ioctl *pti = ptmx_knote_ioctl(kn);
	struct tty *tp = ptmx_knote_tty(kn);
	int ret;

	TTY_LOCK_OWNED(tp);

	if (hint & NOTE_REVOKE) {
		kn->kn_flags |= EV_EOF | EV_ONESHOT;
		ret = 1;
	} else {
		ret = ptmx_kqops_common(kn, NULL, pti, tp);
	}

	return ret;
}

static int
ptmx_kqops_touch(struct knote *kn, struct kevent_qos_s *kev)
{
	struct ptmx_ioctl *pti = ptmx_knote_ioctl(kn);
	struct tty *tp = ptmx_knote_tty(kn);
	int ret;

	tty_lock(tp);

	/* accept new kevent state */
	kn->kn_sfflags = kev->fflags;
	kn->kn_sdata = kev->data;

	/* recapture fired state of knote */
	ret = ptmx_kqops_common(kn, NULL, pti, tp);

	tty_unlock(tp);

	return ret;
}

static int
ptmx_kqops_process(struct knote *kn, struct kevent_qos_s *kev)
{
	struct ptmx_ioctl *pti = ptmx_knote_ioctl(kn);
	struct tty *tp = ptmx_knote_tty(kn);
	int ret;

	tty_lock(tp);
	ret = ptmx_kqops_common(kn, kev, pti, tp);
	tty_unlock(tp);

	return ret;
}