xref: /xnu-8020.121.3/osfmk/ipc/ipc_port.c (revision fdd8201d7b966f0c3ea610489d29bd841d358941)

/*
 * Copyright (c) 2000-2019 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
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/*
 * @OSF_FREE_COPYRIGHT@
 */
/*
 * Mach Operating System
 * Copyright (c) 1991,1990,1989 Carnegie Mellon University
 * All Rights Reserved.
 *
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * Carnegie Mellon requests users of this software to return to
 *
 *  Software Distribution Coordinator  or  [email protected]
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie Mellon
 * the rights to redistribute these changes.
 */
/*
 * NOTICE: This file was modified by McAfee Research in 2004 to introduce
 * support for mandatory and extensible security protections.  This notice
 * is included in support of clause 2.2 (b) of the Apple Public License,
 * Version 2.0.
 */
/*
 */
/*
 *	File:	ipc/ipc_port.c
 *	Author:	Rich Draves
 *	Date:	1989
 *
 *	Functions to manipulate IPC ports.
 */

#include <mach_assert.h>

#include <mach/port.h>
#include <mach/kern_return.h>
#include <kern/backtrace.h>
#include <kern/debug.h>
#include <kern/ipc_kobject.h>
#include <kern/kcdata.h>
#include <kern/misc_protos.h>
#include <kern/policy_internal.h>
#include <kern/thread.h>
#include <kern/waitq.h>
#include <ipc/ipc_entry.h>
#include <ipc/ipc_space.h>
#include <ipc/ipc_object.h>
#include <ipc/ipc_right.h>
#include <ipc/ipc_port.h>
#include <ipc/ipc_pset.h>
#include <ipc/ipc_kmsg.h>
#include <ipc/ipc_mqueue.h>
#include <ipc/ipc_notify.h>
#include <ipc/ipc_table.h>
#include <ipc/ipc_importance.h>
#include <machine/limits.h>
#include <kern/turnstile.h>
#include <kern/machine.h>

#include <security/mac_mach_internal.h>
#include <ipc/ipc_service_port.h>

#include <string.h>

static TUNABLE(bool, prioritize_launch, "prioritize_launch", true);
TUNABLE_WRITEABLE(int, ipc_portbt, "ipc_portbt", false);

extern zone_t ipc_kobject_label_zone;

LCK_SPIN_DECLARE_ATTR(ipc_port_multiple_lock_data, &ipc_lck_grp, &ipc_lck_attr);
ipc_port_timestamp_t ipc_port_timestamp_data;

#if     MACH_ASSERT
static void ipc_port_init_debug(ipc_port_t, void *fp);
#endif  /* MACH_ASSERT */

void __abortlike
__ipc_port_inactive_panic(ipc_port_t port)
{
	panic("Using inactive port %p", port);
}

static __abortlike void
__ipc_port_translate_receive_panic(ipc_space_t space, ipc_port_t port)
{
	panic("found receive right in space %p for port %p owned by space %p",
	    space, port, ip_get_receiver(port));
}

static void
ipc_port_send_turnstile_recompute_push_locked(
	ipc_port_t port);

static thread_t
ipc_port_get_watchport_inheritor(
	ipc_port_t port);

static kern_return_t
ipc_port_update_qos_n_iotier(
	ipc_port_t port,
	uint8_t    qos,
	uint8_t    iotier);

void
ipc_port_release(ipc_port_t port)
{
	ip_release(port);
}

void
ipc_port_reference(ipc_port_t port)
{
	ip_reference(port);
}

/*
 *	Routine:	ipc_port_timestamp
 *	Purpose:
 *		Retrieve a timestamp value.
 */

ipc_port_timestamp_t
ipc_port_timestamp(void)
{
	return OSIncrementAtomic(&ipc_port_timestamp_data);
}


/*
 *	Routine:	ipc_port_translate_send
 *	Purpose:
 *		Look up a send right in a space.
 *	Conditions:
 *		Nothing locked before.  If successful, the object
 *		is returned active and locked.  The caller doesn't get a ref.
 *	Returns:
 *		KERN_SUCCESS		Object returned locked.
 *		KERN_INVALID_TASK	The space is dead.
 *		KERN_INVALID_NAME	The name doesn't denote a right
 *		KERN_INVALID_RIGHT	Name doesn't denote the correct right
 */
kern_return_t
ipc_port_translate_send(
	ipc_space_t                     space,
	mach_port_name_t                name,
	ipc_port_t                     *portp)
{
	ipc_port_t port = IP_NULL;
	ipc_object_t object;
	kern_return_t kr;

	kr = ipc_object_translate(space, name, MACH_PORT_RIGHT_SEND, &object);
	if (kr == KERN_SUCCESS) {
		port = ip_object_to_port(object);
	}
	*portp = port;
	return kr;
}


/*
 *	Routine:	ipc_port_translate_receive
 *	Purpose:
 *		Look up a receive right in a space.
 *		Performs some minimal security checks against tampering.
 *	Conditions:
 *		Nothing locked before.  If successful, the object
 *		is returned active and locked.  The caller doesn't get a ref.
 *	Returns:
 *		KERN_SUCCESS		Object returned locked.
 *		KERN_INVALID_TASK	The space is dead.
 *		KERN_INVALID_NAME	The name doesn't denote a right
 *		KERN_INVALID_RIGHT	Name doesn't denote the correct right
 */
kern_return_t
ipc_port_translate_receive(
	ipc_space_t                     space,
	mach_port_name_t                name,
	ipc_port_t                     *portp)
{
	ipc_port_t port = IP_NULL;
	ipc_object_t object;
	kern_return_t kr;

	kr = ipc_object_translate(space, name, MACH_PORT_RIGHT_RECEIVE, &object);
	if (kr == KERN_SUCCESS) {
		/* object is locked */
		port = ip_object_to_port(object);
		if (!ip_in_space(port, space)) {
			__ipc_port_translate_receive_panic(space, port);
		}
	}
	*portp = port;
	return kr;
}


/*
 *	Routine:	ipc_port_request_alloc
 *	Purpose:
 *		Try to allocate a request slot.
 *		If successful, returns the request index.
 *		Otherwise returns zero.
 *	Conditions:
 *		The port is locked and active.
 *	Returns:
 *		KERN_SUCCESS		A request index was found.
 *		KERN_NO_SPACE		No index allocated.
 */

#if IMPORTANCE_INHERITANCE
kern_return_t
ipc_port_request_alloc(
	ipc_port_t                      port,
	mach_port_name_t                name,
	ipc_port_t                      soright,
	boolean_t                       send_possible,
	boolean_t                       immediate,
	ipc_port_request_index_t        *indexp,
	boolean_t                       *importantp)
#else
kern_return_t
ipc_port_request_alloc(
	ipc_port_t                      port,
	mach_port_name_t                name,
	ipc_port_t                      soright,
	boolean_t                       send_possible,
	boolean_t                       immediate,
	ipc_port_request_index_t        *indexp)
#endif /* IMPORTANCE_INHERITANCE */
{
	ipc_port_request_t ipr, table;
	ipc_port_request_index_t index;
	uintptr_t mask = 0;

#if IMPORTANCE_INHERITANCE
	*importantp = FALSE;
#endif /* IMPORTANCE_INHERITANCE */

	require_ip_active(port);
	assert(name != MACH_PORT_NULL);
	assert(soright != IP_NULL);

	table = port->ip_requests;

	if (table == IPR_NULL) {
		return KERN_NO_SPACE;
	}

	index = table->ipr_next;
	if (index == 0) {
		return KERN_NO_SPACE;
	}

	ipr = &table[index];
	assert(ipr->ipr_name == MACH_PORT_NULL);

	table->ipr_next = ipr->ipr_next;
	ipr->ipr_name = name;

	if (send_possible) {
		mask |= IPR_SOR_SPREQ_MASK;
		if (immediate) {
			mask |= IPR_SOR_SPARM_MASK;
			if (port->ip_sprequests == 0) {
				port->ip_sprequests = 1;
#if IMPORTANCE_INHERITANCE
				/* TODO: Live importance support in send-possible */
				if (port->ip_impdonation != 0 &&
				    port->ip_spimportant == 0 &&
				    (task_is_importance_donor(current_task()))) {
					*importantp = TRUE;
				}
#endif /* IMPORTANCE_INHERTANCE */
			}
		}
	}
	ipr->ipr_soright = IPR_SOR_MAKE(soright, mask);

	*indexp = index;

	return KERN_SUCCESS;
}

/*
 *	Routine:	ipc_port_request_grow
 *	Purpose:
 *		Grow a port's table of requests.
 *	Conditions:
 *		The port must be locked and active.
 *		Nothing else locked; will allocate memory.
 *		Upon return the port is unlocked.
 *	Returns:
 *		KERN_SUCCESS		Grew the table.
 *		KERN_SUCCESS		Somebody else grew the table.
 *		KERN_SUCCESS		The port died.
 *		KERN_RESOURCE_SHORTAGE	Couldn't allocate new table.
 *		KERN_NO_SPACE		Couldn't grow to desired size
 */

kern_return_t
ipc_port_request_grow(
	ipc_port_t              port,
	ipc_table_elems_t       target_size)
{
	ipc_table_size_t its;
	ipc_port_request_t otable, ntable;
	require_ip_active(port);

	otable = port->ip_requests;
	if (otable == IPR_NULL) {
		its = &ipc_table_requests[0];
	} else {
		its = otable->ipr_size + 1;
	}

	if (target_size != ITS_SIZE_NONE) {
		if ((otable != IPR_NULL) &&
		    (target_size <= otable->ipr_size->its_size)) {
			ip_mq_unlock(port);
			return KERN_SUCCESS;
		}
		while ((its->its_size) && (its->its_size < target_size)) {
			its++;
		}
		if (its->its_size == 0) {
			ip_mq_unlock(port);
			return KERN_NO_SPACE;
		}
	}

	ip_reference(port);
	ip_mq_unlock(port);

	if ((its->its_size == 0) ||
	    ((ntable = it_requests_alloc(its)) == IPR_NULL)) {
		ip_release(port);
		return KERN_RESOURCE_SHORTAGE;
	}

	ip_mq_lock(port);

	/*
	 *	Check that port is still active and that nobody else
	 *	has slipped in and grown the table on us.  Note that
	 *	just checking if the current table pointer == otable
	 *	isn't sufficient; must check ipr_size.
	 */

	if (ip_active(port) && (port->ip_requests == otable) &&
	    ((otable == IPR_NULL) || (otable->ipr_size + 1 == its))) {
		ipc_table_size_t oits;
		ipc_table_elems_t osize, nsize;
		ipc_port_request_index_t free, i;

		/* copy old table to new table */

		if (otable != IPR_NULL) {
			oits = otable->ipr_size;
			osize = oits->its_size;
			free = otable->ipr_next;

			(void) memcpy((void *)(ntable + 1),
			    (const void *)(otable + 1),
			    (osize - 1) * sizeof(struct ipc_port_request));
		} else {
			osize = 1;
			oits = 0;
			free = 0;
		}

		nsize = its->its_size;
		assert(nsize > osize);

		/* add new elements to the new table's free list */

		for (i = osize; i < nsize; i++) {
			ipc_port_request_t ipr = &ntable[i];

			ipr->ipr_name = MACH_PORT_NULL;
			ipr->ipr_next = free;
			free = i;
		}

		ntable->ipr_next = free;
		ntable->ipr_size = its;
		port->ip_requests = ntable;
		ip_mq_unlock(port);
		ip_release(port);

		if (otable != IPR_NULL) {
			it_requests_free(oits, otable);
		}
	} else {
		ip_mq_unlock(port);
		ip_release(port);
		it_requests_free(its, ntable);
	}

	return KERN_SUCCESS;
}

/*
 *	Routine:	ipc_port_request_sparm
 *	Purpose:
 *		Arm delayed send-possible request.
 *	Conditions:
 *		The port must be locked and active.
 *
 *		Returns TRUE if the request was armed
 *		(or armed with importance in that version).
 */

boolean_t
ipc_port_request_sparm(
	ipc_port_t                      port,
	__assert_only mach_port_name_t  name,
	ipc_port_request_index_t        index,
	mach_msg_option_t               option,
	mach_msg_priority_t             priority)
{
	if (index != IE_REQ_NONE) {
		ipc_port_request_t ipr, table;

		require_ip_active(port);

		table = port->ip_requests;
		assert(table != IPR_NULL);

		ipr = &table[index];
		assert(ipr->ipr_name == name);

		/* Is there a valid destination? */
		if (IPR_SOR_SPREQ(ipr->ipr_soright)) {
			ipr->ipr_soright = IPR_SOR_MAKE(ipr->ipr_soright, IPR_SOR_SPARM_MASK);
			port->ip_sprequests = 1;

			if (option & MACH_SEND_OVERRIDE) {
				/* apply override to message queue */
				mach_msg_qos_t qos_ovr;
				if (mach_msg_priority_is_pthread_priority(priority)) {
					qos_ovr = _pthread_priority_thread_qos(priority);
				} else {
					qos_ovr = mach_msg_priority_overide_qos(priority);
				}
				if (qos_ovr) {
					ipc_mqueue_override_send_locked(&port->ip_messages, qos_ovr);
				}
			}

#if IMPORTANCE_INHERITANCE
			if (((option & MACH_SEND_NOIMPORTANCE) == 0) &&
			    (port->ip_impdonation != 0) &&
			    (port->ip_spimportant == 0) &&
			    (((option & MACH_SEND_IMPORTANCE) != 0) ||
			    (task_is_importance_donor(current_task())))) {
				return TRUE;
			}
#else
			return TRUE;
#endif /* IMPORTANCE_INHERITANCE */
		}
	}
	return FALSE;
}

/*
 *	Routine:	ipc_port_request_type
 *	Purpose:
 *		Determine the type(s) of port requests enabled for a name.
 *	Conditions:
 *		The port must be locked or inactive (to avoid table growth).
 *		The index must not be IE_REQ_NONE and for the name in question.
 */
mach_port_type_t
ipc_port_request_type(
	ipc_port_t                      port,
	__assert_only mach_port_name_t  name,
	ipc_port_request_index_t        index)
{
	ipc_port_request_t ipr, table;
	mach_port_type_t type = 0;

	table = port->ip_requests;
	assert(table != IPR_NULL);

	assert(index != IE_REQ_NONE);
	ipr = &table[index];
	assert(ipr->ipr_name == name);

	if (IP_VALID(IPR_SOR_PORT(ipr->ipr_soright))) {
		type |= MACH_PORT_TYPE_DNREQUEST;

		if (IPR_SOR_SPREQ(ipr->ipr_soright)) {
			type |= MACH_PORT_TYPE_SPREQUEST;

			if (!IPR_SOR_SPARMED(ipr->ipr_soright)) {
				type |= MACH_PORT_TYPE_SPREQUEST_DELAYED;
			}
		}
	}
	return type;
}

/*
 *	Routine:	ipc_port_request_cancel
 *	Purpose:
 *		Cancel a dead-name/send-possible request and return the send-once right.
 *	Conditions:
 *		The port must be locked and active.
 *		The index must not be IPR_REQ_NONE and must correspond with name.
 */

ipc_port_t
ipc_port_request_cancel(
	ipc_port_t                      port,
	__assert_only mach_port_name_t  name,
	ipc_port_request_index_t        index)
{
	ipc_port_request_t ipr, table;
	ipc_port_t request = IP_NULL;

	require_ip_active(port);
	table = port->ip_requests;
	assert(table != IPR_NULL);

	assert(index != IE_REQ_NONE);
	ipr = &table[index];
	assert(ipr->ipr_name == name);
	request = IPR_SOR_PORT(ipr->ipr_soright);

	/* return ipr to the free list inside the table */
	ipr->ipr_name = MACH_PORT_NULL;
	ipr->ipr_next = table->ipr_next;
	table->ipr_next = index;

	return request;
}


/*
 *	Routine:	ipc_port_nsrequest
 *	Purpose:
 *		Make a no-senders request, returning the
 *		previously registered send-once right.
 *		Just cancels the previous request if notify is IP_NULL.
 *	Conditions:
 *		The port is locked and active.  It is unlocked.
 *		Consumes a ref for notify (if non-null), and
 *		returns previous with a ref (if non-null).
 */

void
ipc_port_nsrequest(
	ipc_port_t              port,
	mach_port_mscount_t     sync,
	ipc_port_t              notify,
	ipc_port_t              *previousp)
{
	ipc_port_t previous;
	mach_port_mscount_t mscount;
	require_ip_active(port);

	assert(!ip_in_space(port, ipc_space_kernel));
	assert(port->ip_nsrequest != IP_KOBJECT_NSREQUEST_ARMED);

	previous = port->ip_nsrequest;
	mscount = port->ip_mscount;

	if ((port->ip_srights == 0) && (sync <= mscount) &&
	    (notify != IP_NULL)) {
		port->ip_nsrequest = IP_NULL;
		ip_mq_unlock(port);
		ipc_notify_no_senders(notify, mscount, /* kobject */ false);
	} else {
		port->ip_nsrequest = notify;
		ip_mq_unlock(port);
	}

	*previousp = previous;
}


/*
 *	Routine:	ipc_port_clear_receiver
 *	Purpose:
 *		Prepares a receive right for transmission/destruction,
 *		optionally performs mqueue destruction (with port lock held)
 *
 *	Conditions:
 *		The port is locked and active.
 *	Returns:
 *		If should_destroy is TRUE, then the return value indicates
 *		whether the caller needs to reap kmsg structures that should
 *		be destroyed (by calling ipc_kmsg_reap_delayed)
 *
 *              If should_destroy is FALSE, this always returns FALSE
 */

boolean_t
ipc_port_clear_receiver(
	ipc_port_t          port,
	boolean_t           should_destroy,
	waitq_link_list_t  *free_l)
{
	ipc_mqueue_t    mqueue = &port->ip_messages;
	boolean_t       reap_messages = FALSE;

	/*
	 * Pull ourselves out of any sets to which we belong.
	 * We hold the write space lock or the receive entry has
	 * been deleted, so even though this acquires and releases
	 * the port lock, we know we won't be added to any other sets.
	 */
	if (ip_in_pset(port)) {
		waitq_unlink_all_locked(&port->ip_waitq, NULL, free_l);
		assert(!ip_in_pset(port));
	}

	/*
	 * Send anyone waiting on the port's queue directly away.
	 * Also clear the mscount, seqno, guard bits
	 */
	if (ip_in_a_space(port)) {
		ipc_mqueue_changed(ip_get_receiver(port), &port->ip_waitq);
	} else {
		ipc_mqueue_changed(NULL, &port->ip_waitq);
	}
	port->ip_mscount = 0;
	mqueue->imq_seqno = 0;
	port->ip_context = port->ip_guarded = port->ip_strict_guard = 0;
	/*
	 * clear the immovable bit so the port can move back to anyone listening
	 * for the port destroy notification
	 */
	port->ip_immovable_receive = 0;

	if (should_destroy) {
		/*
		 * Mark the port and mqueue invalid, preventing further send/receive
		 * operations from succeeding. It's important for this to be
		 * done under the same lock hold as the ipc_mqueue_changed
		 * call to avoid additional threads blocking on an mqueue
		 * that's being destroyed.
		 *
		 * The port active bit needs to be guarded under mqueue lock for
		 * turnstiles
		 */

		/* port transitions to INACTIVE state */
		io_bits_andnot(ip_to_object(port), IO_BITS_ACTIVE);
		port->ip_receiver_name = MACH_PORT_NULL;
		port->ip_timestamp = ipc_port_timestamp();

		reap_messages = ipc_mqueue_destroy_locked(mqueue, free_l);
	} else {
		/* port transtions to IN-LIMBO state */
		port->ip_receiver_name = MACH_PORT_NULL;
		port->ip_destination = IP_NULL;
	}

	return reap_messages;
}

/*
 *	Routine:	ipc_port_init
 *	Purpose:
 *		Initializes a newly-allocated port.
 *
 *		The memory is expected to be zero initialized (allocated with Z_ZERO).
 */

void
ipc_port_init(
	ipc_port_t              port,
	ipc_space_t             space,
	ipc_port_init_flags_t   flags,
	mach_port_name_t        name)
{
	int policy = SYNC_POLICY_FIFO;

	/* the port has been 0 initialized when called */

	if (flags & IPC_PORT_INIT_FILTER_MESSAGE) {
		io_bits_or(ip_to_object(port), IP_BIT_FILTER_MSG);
	}
	if (flags & IPC_PORT_INIT_LOCKED) {
		policy |= SYNC_POLICY_INIT_LOCKED;
	}

	/* must be done first, many ip_* bits live inside the waitq */
	waitq_init(&port->ip_waitq, WQT_PORT, policy);
	if (flags & IPC_PORT_INIT_TG_BLOCK_TRACKING) {
		port->ip_tg_block_tracking = true;
	}
	if (flags & IPC_PORT_INIT_SPECIAL_REPLY) {
		port->ip_specialreply = true;
		port->ip_immovable_receive = true;
	}

	port->ip_kernel_qos_override = THREAD_QOS_UNSPECIFIED;
	port->ip_kernel_iotier_override = THROTTLE_LEVEL_END;

	ipc_mqueue_init(&port->ip_messages);
#if MACH_ASSERT
	ipc_port_init_debug(port, __builtin_frame_address(0));
#endif  /* MACH_ASSERT */

	/* port transitions to IN-SPACE state */
	port->ip_receiver_name = name;
	port->ip_receiver = space;

	if (flags & IPC_PORT_INIT_MAKE_SEND_RIGHT) {
		port->ip_srights = 1;
		port->ip_mscount = 1;
	}
}

/*
 *	Routine:	ipc_port_alloc
 *	Purpose:
 *		Allocate a port.
 *	Conditions:
 *		Nothing locked.  If successful, the port is returned
 *		locked.  (The caller doesn't have a reference.)
 *	Returns:
 *		KERN_SUCCESS		The port is allocated.
 *		KERN_INVALID_TASK	The space is dead.
 *		KERN_NO_SPACE		No room for an entry in the space.
 *		KERN_RESOURCE_SHORTAGE	Couldn't allocate memory.
 */

kern_return_t
ipc_port_alloc(
	ipc_space_t             space,
	ipc_port_init_flags_t   flags,
	mach_port_name_t        *namep,
	ipc_port_t              *portp)
{
	ipc_port_t port;
	mach_port_name_t name;
	kern_return_t kr;
	mach_port_type_t type = MACH_PORT_TYPE_RECEIVE;
	mach_port_urefs_t urefs = 0;

	if (flags & IPC_PORT_INIT_MAKE_SEND_RIGHT) {
		type |= MACH_PORT_TYPE_SEND;
		urefs = 1;
	}
	kr = ipc_object_alloc(space, IOT_PORT, type, urefs,
	    &name, (ipc_object_t *) &port);
	if (kr != KERN_SUCCESS) {
		return kr;
	}

	/* space is locked */
	ipc_port_init(port, space, flags | IPC_PORT_INIT_LOCKED, name);
	/* port is locked */
#if MACH_ASSERT
	ipc_port_init_debug(port, __builtin_frame_address(0));
#endif  /* MACH_ASSERT */

	/* unlock space after init */
	is_write_unlock(space);

	*namep = name;
	*portp = port;

	return KERN_SUCCESS;
}

/*
 *	Routine:	ipc_port_alloc_name
 *	Purpose:
 *		Allocate a port, with a specific name.
 *	Conditions:
 *		Nothing locked.  If successful, the port is returned
 *		locked.  (The caller doesn't have a reference.)
 *	Returns:
 *		KERN_SUCCESS		The port is allocated.
 *		KERN_INVALID_TASK	The space is dead.
 *		KERN_NAME_EXISTS	The name already denotes a right.
 *		KERN_RESOURCE_SHORTAGE	Couldn't allocate memory.
 */

kern_return_t
ipc_port_alloc_name(
	ipc_space_t             space,
	ipc_port_init_flags_t   flags,
	mach_port_name_t        name,
	ipc_port_t              *portp)
{
	mach_port_type_t type = MACH_PORT_TYPE_RECEIVE;
	mach_port_urefs_t urefs = 0;

	if (flags & IPC_PORT_INIT_MAKE_SEND_RIGHT) {
		type |= MACH_PORT_TYPE_SEND;
		urefs = 1;
	}
	flags |= IPC_PORT_INIT_LOCKED;

	return ipc_object_alloc_name(space, IOT_PORT, type, urefs,
	           name, (ipc_object_t *)portp, ^(ipc_object_t object){
		ipc_port_init(ip_object_to_port(object), space, flags, name);
	});
}

/*
 *      Routine:	ipc_port_spnotify
 *	Purpose:
 *		Generate send-possible port notifications.
 *	Conditions:
 *		Nothing locked, reference held on port.
 */
void
ipc_port_spnotify(
	ipc_port_t      port)
{
	ipc_port_request_index_t index = 0;
	ipc_table_elems_t size = 0;

	/*
	 * If the port has no send-possible request
	 * armed, don't bother to lock the port.
	 */
	if (port->ip_sprequests == 0) {
		return;
	}

	ip_mq_lock(port);

#if IMPORTANCE_INHERITANCE
	if (port->ip_spimportant != 0) {
		port->ip_spimportant = 0;
		if (ipc_port_importance_delta(port, IPID_OPTION_NORMAL, -1) == TRUE) {
			ip_mq_lock(port);
		}
	}
#endif /* IMPORTANCE_INHERITANCE */

	if (port->ip_sprequests == 0) {
		ip_mq_unlock(port);
		return;
	}
	port->ip_sprequests = 0;

revalidate:
	if (ip_active(port)) {
		ipc_port_request_t requests;

		/* table may change each time port unlocked (reload) */
		requests = port->ip_requests;
		assert(requests != IPR_NULL);

		/*
		 * no need to go beyond table size when first
		 * we entered - those are future notifications.
		 */
		if (size == 0) {
			size = requests->ipr_size->its_size;
		}

		/* no need to backtrack either */
		while (++index < size) {
			ipc_port_request_t ipr = &requests[index];
			mach_port_name_t name = ipr->ipr_name;
			ipc_port_t soright = IPR_SOR_PORT(ipr->ipr_soright);
			boolean_t armed = IPR_SOR_SPARMED(ipr->ipr_soright);

			if (MACH_PORT_VALID(name) && armed && IP_VALID(soright)) {
				/* claim send-once right - slot still inuse */
				ipr->ipr_soright = IP_NULL;
				ip_mq_unlock(port);

				ipc_notify_send_possible(soright, name);

				ip_mq_lock(port);
				goto revalidate;
			}
		}
	}
	ip_mq_unlock(port);
	return;
}

/*
 *      Routine:	ipc_port_dnnotify
 *	Purpose:
 *		Generate dead name notifications for
 *		all outstanding dead-name and send-
 *		possible requests.
 *	Conditions:
 *		Nothing locked.
 *		Port must be inactive.
 *		Reference held on port.
 */
void
ipc_port_dnnotify(
	ipc_port_t      port)
{
	ipc_port_request_t requests = port->ip_requests;

	assert(!ip_active(port));
	if (requests != IPR_NULL) {
		ipc_table_size_t its = requests->ipr_size;
		ipc_table_elems_t size = its->its_size;
		ipc_port_request_index_t index;
		for (index = 1; index < size; index++) {
			ipc_port_request_t ipr = &requests[index];
			mach_port_name_t name = ipr->ipr_name;
			ipc_port_t soright = IPR_SOR_PORT(ipr->ipr_soright);

			if (MACH_PORT_VALID(name) && IP_VALID(soright)) {
				ipc_notify_dead_name(soright, name);
			}
		}
	}
}

/*
 *	Routine:	ipc_port_destroy
 *	Purpose:
 *		Destroys a port.  Cleans up queued messages.
 *
 *		If the port has a backup, it doesn't get destroyed,
 *		but is sent in a port-destroyed notification to the backup.
 *	Conditions:
 *		The port is locked and alive; nothing else locked.
 *		The caller has a reference, which is consumed.
 *		Afterwards, the port is unlocked and dead.
 */

void
ipc_port_destroy(ipc_port_t port)
{
	bool special_reply = port->ip_specialreply;
	bool service_port  = port->ip_service_port;
	bool reap_msgs;

	ipc_port_t pdrequest = IP_NULL;
	struct task_watchport_elem *twe = NULL;
	waitq_link_list_t free_l = { };

#if IMPORTANCE_INHERITANCE
	ipc_importance_task_t release_imp_task = IIT_NULL;
	thread_t self = current_thread();
	boolean_t top = (self->ith_assertions == 0);
	natural_t assertcnt = 0;
#endif /* IMPORTANCE_INHERITANCE */

	require_ip_active(port);
	/* port->ip_receiver_name is garbage */
	/* port->ip_receiver/port->ip_destination is garbage */

	/* clear any reply-port context */
	port->ip_reply_context = 0;

	/* must be done before we access ip_pdrequest */
	twe = ipc_port_clear_watchport_elem_internal(port);
	assert(!port->ip_has_watchport);

	if (!special_reply) {
		/* we assume the ref for pdrequest */
		pdrequest = port->ip_pdrequest;
		port->ip_pdrequest = IP_NULL;
	} else if (port->ip_tempowner) {
		panic("ipc_port_destroy: invalid state");
	}

#if IMPORTANCE_INHERITANCE
	/* determine how many assertions to drop and from whom */
	if (port->ip_tempowner != 0) {
		assert(top);
		release_imp_task = ip_get_imp_task(port);
		if (IIT_NULL != release_imp_task) {
			port->ip_imp_task = IIT_NULL;
			assertcnt = port->ip_impcount;
		}
		/* Otherwise, nothing to drop */
	} else {
		assertcnt = port->ip_impcount;
		if (pdrequest != IP_NULL) {
			/* mark in limbo for the journey */
			port->ip_tempowner = 1;
		}
	}

	if (top) {
		self->ith_assertions = assertcnt;
	}
#endif /* IMPORTANCE_INHERITANCE */

	/*
	 * If no port-destroyed notification is armed, calling
	 * ipc_port_clear_receiver() will mark the port inactive
	 * and will wakeup any threads which may be blocked receiving on it.
	 */
	reap_msgs = ipc_port_clear_receiver(port, pdrequest == IP_NULL, &free_l);
	assert(!ip_in_pset(port));
	assert(port->ip_mscount == 0);

	/*
	 * Handle port-destroyed notification
	 */
	if (pdrequest != IP_NULL) {
		assert(reap_msgs == false);

		if (service_port) {
			assert(port->ip_splabel != NULL);
			if (ipc_service_port_label_is_special_pdrequest((ipc_service_port_label_t)port->ip_splabel)) {
				ipc_service_port_label_set_flag(port->ip_splabel, ISPL_FLAGS_SEND_PD_NOTIFICATION);
			}
		}

		ipc_port_send_turnstile_recompute_push_locked(port);
		/* port unlocked */

		/* consumes our refs for port and pdrequest */
		ipc_notify_port_destroyed(pdrequest, port);
	} else {
		ipc_service_port_label_t splabel = NULL;
		ipc_notify_nsenders_t nsrequest;

		nsrequest = ipc_notify_no_senders_prepare(port);

		if (!ip_is_kolabeled(port)) {
			splabel = port->ip_splabel;
			port->ip_splabel = NULL;
			port->ip_service_port = false;
		}

		ipc_port_send_turnstile_recompute_push_locked(port);
		/* port unlocked */

		/* unlink the kmsg from special reply port */
		if (special_reply) {
			ipc_port_adjust_special_reply_port(port,
			    IPC_PORT_ADJUST_SR_ALLOW_SYNC_LINKAGE);
		}

		/* Deallocate the service/connection port label */
		if (splabel) {
			ipc_service_port_label_dealloc(splabel, service_port);
			splabel = NULL;
		}

		if (reap_msgs) {
			ipc_kmsg_reap_delayed();
		}

		if (nsrequest.ns_notify) {
			/*
			 * ipc_notify_no_senders_prepare will consume
			 * the reference for kobjects.
			 */
			assert(!nsrequest.ns_is_kobject);
			ip_mq_lock(nsrequest.ns_notify);
			ipc_notify_send_once_and_unlock(nsrequest.ns_notify); /* consumes ref */
		}

		/* generate dead-name notifications */
		ipc_port_dnnotify(port);

		ipc_kobject_destroy(port);

		ip_release(port); /* consume caller's ref */
	}

	if (twe) {
		task_watchport_elem_deallocate(twe);
		twe = NULL;
	}

	waitq_link_free_list(WQT_PORT_SET, &free_l);

#if IMPORTANCE_INHERITANCE
	if (release_imp_task != IIT_NULL) {
		if (assertcnt > 0) {
			assert(top);
			self->ith_assertions = 0;
			assert(ipc_importance_task_is_any_receiver_type(release_imp_task));
			ipc_importance_task_drop_internal_assertion(release_imp_task, assertcnt);
		}
		ipc_importance_task_release(release_imp_task);
	} else if (assertcnt > 0) {
		if (top) {
			self->ith_assertions = 0;
			release_imp_task = current_task()->task_imp_base;
			if (ipc_importance_task_is_any_receiver_type(release_imp_task)) {
				ipc_importance_task_drop_internal_assertion(release_imp_task, assertcnt);
			}
		}
	}
#endif /* IMPORTANCE_INHERITANCE */
}

/*
 *	Routine:	ipc_port_destination_chain_lock
 *	Purpose:
 *		Search for the end of the chain (a port not in transit),
 *		acquiring locks along the way, and return it in `base`.
 *
 *		Returns true if a reference was taken on `base`
 *
 *	Conditions:
 *		No ports locked.
 *		ipc_port_multiple_lock held.
 */
boolean_t
ipc_port_destination_chain_lock(
	ipc_port_t port,
	ipc_port_t *base)
{
	for (;;) {
		ip_mq_lock(port);

		if (!ip_active(port)) {
			/*
			 * Active ports that are ip_mq_lock()ed cannot go away.
			 *
			 * But inactive ports at the end of walking
			 * an ip_destination chain are only protected
			 * from space termination cleanup while the entire
			 * chain of ports leading to them is held.
			 *
			 * Callers of this code tend to unlock the chain
			 * in the same order than this walk which doesn't
			 * protect `base` properly when it's inactive.
			 *
			 * In that case, take a reference that the caller
			 * is responsible for releasing.
			 */
			ip_reference(port);
			*base = port;
			return true;
		}

		/* port is active */
		if (!ip_in_transit(port)) {
			*base = port;
			return false;
		}

		port = ip_get_destination(port);
	}
}


/*
 *	Routine:	ipc_port_check_circularity
 *	Purpose:
 *		Check if queueing "port" in a message for "dest"
 *		would create a circular group of ports and messages.
 *
 *		If no circularity (FALSE returned), then "port"
 *		is changed from "in limbo" to "in transit".
 *
 *		That is, we want to set port->ip_destination == dest,
 *		but guaranteeing that this doesn't create a circle
 *		port->ip_destination->ip_destination->... == port
 *
 *	Conditions:
 *		No ports locked.  References held for "port" and "dest".
 */

boolean_t
ipc_port_check_circularity(
	ipc_port_t      port,
	ipc_port_t      dest)
{
#if IMPORTANCE_INHERITANCE
	/* adjust importance counts at the same time */
	return ipc_importance_check_circularity(port, dest);
#else
	ipc_port_t base;
	struct task_watchport_elem *watchport_elem = NULL;
	bool took_base_ref = false;

	assert(port != IP_NULL);
	assert(dest != IP_NULL);

	if (port == dest) {
		return TRUE;
	}
	base = dest;

	/* Check if destination needs a turnstile */
	ipc_port_send_turnstile_prepare(dest);

	/*
	 *	First try a quick check that can run in parallel.
	 *	No circularity if dest is not in transit.
	 */
	ip_mq_lock(port);
	if (ip_mq_lock_try(dest)) {
		if (!ip_in_transit(dest)) {
			goto not_circular;
		}

		/* dest is in transit; further checking necessary */

		ip_mq_unlock(dest);
	}
	ip_mq_unlock(port);

	ipc_port_multiple_lock(); /* massive serialization */

	/*
	 *	Search for the end of the chain (a port not in transit),
	 *	acquiring locks along the way.
	 */

	took_base_ref = ipc_port_destination_chain_lock(dest, &base);
	/* all ports in chain from dest to base, inclusive, are locked */

	if (port == base) {
		/* circularity detected! */

		ipc_port_multiple_unlock();

		/* port (== base) is in limbo */
		require_ip_active(port);
		assert(ip_in_limbo(port));
		assert(!took_base_ref);

		base = dest;
		while (base != IP_NULL) {
			ipc_port_t next;

			/* dest is in transit or in limbo */
			require_ip_active(base);
			assert(!ip_in_a_space(base));

			next = ip_get_destination(base);
			ip_mq_unlock(base);
			base = next;
		}

		ipc_port_send_turnstile_complete(dest);
		return TRUE;
	}

	/*
	 *	The guarantee:  lock port while the entire chain is locked.
	 *	Once port is locked, we can take a reference to dest,
	 *	add port to the chain, and unlock everything.
	 */

	ip_mq_lock(port);
	ipc_port_multiple_unlock();

not_circular:
	require_ip_active(port);
	assert(ip_in_limbo(port));

	/* Clear the watchport boost */
	watchport_elem = ipc_port_clear_watchport_elem_internal(port);

	/* Check if the port is being enqueued as a part of sync bootstrap checkin */
	if (dest->ip_specialreply && dest->ip_sync_bootstrap_checkin) {
		port->ip_sync_bootstrap_checkin = 1;
	}

	ip_reference(dest);

	/* port transitions to IN-TRANSIT state */
	assert(port->ip_receiver_name == MACH_PORT_NULL);
	port->ip_destination = dest;

	/* Setup linkage for source port if it has sync ipc push */
	struct turnstile *send_turnstile = TURNSTILE_NULL;
	if (port_send_turnstile(port)) {
		send_turnstile = turnstile_prepare((uintptr_t)port,
		    port_send_turnstile_address(port),
		    TURNSTILE_NULL, TURNSTILE_SYNC_IPC);

		/*
		 * What ipc_port_adjust_port_locked would do,
		 * but we need to also drop even more locks before
		 * calling turnstile_update_inheritor_complete().
		 */
		ipc_port_adjust_sync_link_state_locked(port, PORT_SYNC_LINK_ANY, NULL);

		turnstile_update_inheritor(send_turnstile, port_send_turnstile(dest),
		    (TURNSTILE_INHERITOR_TURNSTILE | TURNSTILE_IMMEDIATE_UPDATE));

		/* update complete and turnstile complete called after dropping all locks */
	}
	/* now unlock chain */

	ip_mq_unlock(port);

	for (;;) {
		ipc_port_t next;

		if (dest == base) {
			break;
		}

		/* port is IN-TRANSIT */
		require_ip_active(dest);
		assert(ip_in_transit(dest));

		next = ip_get_destination(dest);
		ip_mq_unlock(dest);
		dest = next;
	}

	/* base is not IN-TRANSIT */
	assert(!ip_in_transit(base));

	ip_mq_unlock(base);
	if (took_base_ref) {
		ip_release(base);
	}

	/* All locks dropped, call turnstile_update_inheritor_complete for source port's turnstile */
	if (send_turnstile) {
		turnstile_update_inheritor_complete(send_turnstile, TURNSTILE_INTERLOCK_NOT_HELD);

		/* Take the mq lock to call turnstile complete */
		ip_mq_lock(port);
		turnstile_complete((uintptr_t)port, port_send_turnstile_address(port), NULL, TURNSTILE_SYNC_IPC);
		send_turnstile = TURNSTILE_NULL;
		ip_mq_unlock(port);
		turnstile_cleanup();
	}

	if (watchport_elem) {
		task_watchport_elem_deallocate(watchport_elem);
	}

	return FALSE;
#endif /* !IMPORTANCE_INHERITANCE */
}

/*
 *	Routine:	ipc_port_watchport_elem
 *	Purpose:
 *		Get the port's watchport elem field
 *
 *	Conditions:
 *		port locked
 */
static struct task_watchport_elem *
ipc_port_watchport_elem(ipc_port_t port)
{
	if (port->ip_has_watchport) {
		assert(!port->ip_specialreply);
		return port->ip_twe;
	}
	return NULL;
}

/*
 *	Routine:	ipc_port_update_watchport_elem
 *	Purpose:
 *		Set the port's watchport elem field
 *
 *	Conditions:
 *		port locked and is not a special reply port.
 */
static inline struct task_watchport_elem *
ipc_port_update_watchport_elem(ipc_port_t port, struct task_watchport_elem *we)
{
	struct task_watchport_elem *old_we;
	ipc_port_t pdrequest;

	assert(!port->ip_specialreply);

	/*
	 * Note: ip_pdrequest and ip_twe are unioned.
	 *       and ip_has_watchport controls the union "type"
	 */
	if (port->ip_has_watchport) {
		old_we = port->ip_twe;
		pdrequest = old_we->twe_pdrequest;
		old_we->twe_pdrequest = IP_NULL;
	} else {
		old_we = NULL;
		pdrequest = port->ip_pdrequest;
	}

	if (we) {
		port->ip_has_watchport = true;
		we->twe_pdrequest = pdrequest;
		port->ip_twe = we;
	} else {
		port->ip_has_watchport = false;
		port->ip_pdrequest = pdrequest;
	}

	return old_we;
}

/*
 *	Routine:	ipc_special_reply_stash_pid_locked
 *	Purpose:
 *		Set the pid of process that copied out send once right to special reply port.
 *
 *	Conditions:
 *		port locked
 */
static inline void
ipc_special_reply_stash_pid_locked(ipc_port_t port, int pid)
{
	assert(port->ip_specialreply);
	port->ip_pid = pid;
}

/*
 *	Routine:	ipc_special_reply_get_pid_locked
 *	Purpose:
 *		Get the pid of process that copied out send once right to special reply port.
 *
 *	Conditions:
 *		port locked
 */
int
ipc_special_reply_get_pid_locked(ipc_port_t port)
{
	assert(port->ip_specialreply);
	return port->ip_pid;
}

/*
 * Update the recv turnstile inheritor for a port.
 *
 * Sync IPC through the port receive turnstile only happens for the special
 * reply port case. It has three sub-cases:
 *
 * 1. a send-once right is in transit, and pushes on the send turnstile of its
 *    destination mqueue.
 *
 * 2. a send-once right has been stashed on a knote it was copied out "through",
 *    as the first such copied out port.
 *
 * 3. a send-once right has been stashed on a knote it was copied out "through",
 *    as the second or more copied out port.
 */
void
ipc_port_recv_update_inheritor(
	ipc_port_t port,
	struct turnstile *rcv_turnstile,
	turnstile_update_flags_t flags)
{
	struct turnstile *inheritor = TURNSTILE_NULL;
	struct knote *kn;

	if (ip_active(port) && port->ip_specialreply) {
		ip_mq_lock_held(port);

		switch (port->ip_sync_link_state) {
		case PORT_SYNC_LINK_PORT:
			if (port->ip_sync_inheritor_port != NULL) {
				inheritor = port_send_turnstile(port->ip_sync_inheritor_port);
			}
			break;

		case PORT_SYNC_LINK_WORKLOOP_KNOTE:
			kn = port->ip_sync_inheritor_knote;
			inheritor = filt_ipc_kqueue_turnstile(kn);
			break;

		case PORT_SYNC_LINK_WORKLOOP_STASH:
			inheritor = port->ip_sync_inheritor_ts;
			break;
		}
	}

	turnstile_update_inheritor(rcv_turnstile, inheritor,
	    flags | TURNSTILE_INHERITOR_TURNSTILE);
}

/*
 * Update the send turnstile inheritor for a port.
 *
 * Sync IPC through the port send turnstile has 7 possible reasons to be linked:
 *
 * 1. a special reply port is part of sync ipc for bootstrap checkin and needs
 *    to push on thread doing the sync ipc.
 *
 * 2. a receive right is in transit, and pushes on the send turnstile of its
 *    destination mqueue.
 *
 * 3. port was passed as an exec watchport and port is pushing on main thread
 *    of the task.
 *
 * 4. a receive right has been stashed on a knote it was copied out "through",
 *    as the first such copied out port (same as PORT_SYNC_LINK_WORKLOOP_KNOTE
 *    for the special reply port)
 *
 * 5. a receive right has been stashed on a knote it was copied out "through",
 *    as the second or more copied out port (same as
 *    PORT_SYNC_LINK_WORKLOOP_STASH for the special reply port)
 *
 * 6. a receive right has been copied out as a part of sync bootstrap checkin
 *    and needs to push on thread doing the sync bootstrap checkin.
 *
 * 7. the receive right is monitored by a knote, and pushes on any that is
 *    registered on a workloop. filt_machport makes sure that if such a knote
 *    exists, it is kept as the first item in the knote list, so we never need
 *    to walk.
 */
void
ipc_port_send_update_inheritor(
	ipc_port_t port,
	struct turnstile *send_turnstile,
	turnstile_update_flags_t flags)
{
	ipc_mqueue_t mqueue = &port->ip_messages;
	turnstile_inheritor_t inheritor = TURNSTILE_INHERITOR_NULL;
	struct knote *kn;
	turnstile_update_flags_t inheritor_flags = TURNSTILE_INHERITOR_TURNSTILE;

	ip_mq_lock_held(port);

	if (!ip_active(port)) {
		/* this port is no longer active, it should not push anywhere */
	} else if (port->ip_specialreply) {
		/* Case 1. */
		if (port->ip_sync_bootstrap_checkin && prioritize_launch) {
			inheritor = port->ip_messages.imq_srp_owner_thread;
			inheritor_flags = TURNSTILE_INHERITOR_THREAD;
		}
	} else if (ip_in_transit(port)) {
		/* Case 2. */
		inheritor = port_send_turnstile(ip_get_destination(port));
	} else if (port->ip_has_watchport) {
		/* Case 3. */
		if (prioritize_launch) {
			assert(port->ip_sync_link_state == PORT_SYNC_LINK_ANY);
			inheritor = ipc_port_get_watchport_inheritor(port);
			inheritor_flags = TURNSTILE_INHERITOR_THREAD;
		}
	} else if (port->ip_sync_link_state == PORT_SYNC_LINK_WORKLOOP_KNOTE) {
		/* Case 4. */
		inheritor = filt_ipc_kqueue_turnstile(mqueue->imq_inheritor_knote);
	} else if (port->ip_sync_link_state == PORT_SYNC_LINK_WORKLOOP_STASH) {
		/* Case 5. */
		inheritor = mqueue->imq_inheritor_turnstile;
	} else if (port->ip_sync_link_state == PORT_SYNC_LINK_RCV_THREAD) {
		/* Case 6. */
		if (prioritize_launch) {
			inheritor = port->ip_messages.imq_inheritor_thread_ref;
			inheritor_flags = TURNSTILE_INHERITOR_THREAD;
		}
	} else if ((kn = SLIST_FIRST(&port->ip_klist))) {
		/* Case 7. Push on a workloop that is interested */
		if (filt_machport_kqueue_has_turnstile(kn)) {
			assert(port->ip_sync_link_state == PORT_SYNC_LINK_ANY);
			inheritor = filt_ipc_kqueue_turnstile(kn);
		}
	}

	turnstile_update_inheritor(send_turnstile, inheritor,
	    flags | inheritor_flags);
}

/*
 *	Routine:	ipc_port_send_turnstile_prepare
 *	Purpose:
 *		Get a reference on port's send turnstile, if
 *		port does not have a send turnstile then allocate one.
 *
 *	Conditions:
 *		Nothing is locked.
 */
void
ipc_port_send_turnstile_prepare(ipc_port_t port)
{
	struct turnstile *turnstile = TURNSTILE_NULL;
	struct turnstile *send_turnstile = TURNSTILE_NULL;

retry_alloc:
	ip_mq_lock(port);

	if (port_send_turnstile(port) == NULL ||
	    port_send_turnstile(port)->ts_port_ref == 0) {
		if (turnstile == TURNSTILE_NULL) {
			ip_mq_unlock(port);
			turnstile = turnstile_alloc();
			goto retry_alloc;
		}

		send_turnstile = turnstile_prepare((uintptr_t)port,
		    port_send_turnstile_address(port),
		    turnstile, TURNSTILE_SYNC_IPC);
		turnstile = TURNSTILE_NULL;

		ipc_port_send_update_inheritor(port, send_turnstile,
		    TURNSTILE_IMMEDIATE_UPDATE);

		/* turnstile complete will be called in ipc_port_send_turnstile_complete */
	}

	/* Increment turnstile counter */
	port_send_turnstile(port)->ts_port_ref++;
	ip_mq_unlock(port);

	if (send_turnstile) {
		turnstile_update_inheritor_complete(send_turnstile,
		    TURNSTILE_INTERLOCK_NOT_HELD);
	}
	if (turnstile != TURNSTILE_NULL) {
		turnstile_deallocate(turnstile);
	}
}


/*
 *	Routine:	ipc_port_send_turnstile_complete
 *	Purpose:
 *		Drop a ref on the port's send turnstile, if the
 *		ref becomes zero, deallocate the turnstile.
 *
 *	Conditions:
 *		The space might be locked, use safe deallocate.
 */
void
ipc_port_send_turnstile_complete(ipc_port_t port)
{
	struct turnstile *turnstile = TURNSTILE_NULL;

	/* Drop turnstile count on dest port */
	ip_mq_lock(port);

	port_send_turnstile(port)->ts_port_ref--;
	if (port_send_turnstile(port)->ts_port_ref == 0) {
		turnstile_complete((uintptr_t)port, port_send_turnstile_address(port),
		    &turnstile, TURNSTILE_SYNC_IPC);
		assert(turnstile != TURNSTILE_NULL);
	}
	ip_mq_unlock(port);
	turnstile_cleanup();

	if (turnstile != TURNSTILE_NULL) {
		turnstile_deallocate_safe(turnstile);
		turnstile = TURNSTILE_NULL;
	}
}

/*
 *	Routine:	ipc_port_rcv_turnstile
 *	Purpose:
 *		Get the port's receive turnstile
 *
 *	Conditions:
 *		mqueue locked or thread waiting on turnstile is locked.
 */
static struct turnstile *
ipc_port_rcv_turnstile(ipc_port_t port)
{
	return *port_rcv_turnstile_address(port);
}


/*
 *	Routine:	ipc_port_link_special_reply_port
 *	Purpose:
 *		Link the special reply port with the destination port.
 *              Allocates turnstile to dest port.
 *
 *	Conditions:
 *		Nothing is locked.
 */
void
ipc_port_link_special_reply_port(
	ipc_port_t special_reply_port,
	ipc_port_t dest_port,
	boolean_t sync_bootstrap_checkin)
{
	boolean_t drop_turnstile_ref = FALSE;
	boolean_t special_reply = FALSE;

	/* Check if dest_port needs a turnstile */
	ipc_port_send_turnstile_prepare(dest_port);

	/* Lock the special reply port and establish the linkage */
	ip_mq_lock(special_reply_port);

	special_reply = special_reply_port->ip_specialreply;

	if (sync_bootstrap_checkin && special_reply) {
		special_reply_port->ip_sync_bootstrap_checkin = 1;
	}

	/* Check if we need to drop the acquired turnstile ref on dest port */
	if (!special_reply ||
	    special_reply_port->ip_sync_link_state != PORT_SYNC_LINK_ANY ||
	    special_reply_port->ip_sync_inheritor_port != IPC_PORT_NULL) {
		drop_turnstile_ref = TRUE;
	} else {
		/* take a reference on dest_port */
		ip_reference(dest_port);
		special_reply_port->ip_sync_inheritor_port = dest_port;
		special_reply_port->ip_sync_link_state = PORT_SYNC_LINK_PORT;
	}

	ip_mq_unlock(special_reply_port);

	if (special_reply) {
		/*
		 * For special reply ports, if the destination port is
		 * marked with the thread group blocked tracking flag,
		 * callout to the performance controller.
		 */
		ipc_port_thread_group_blocked(dest_port);
	}

	if (drop_turnstile_ref) {
		ipc_port_send_turnstile_complete(dest_port);
	}

	return;
}

/*
 *	Routine:	ipc_port_thread_group_blocked
 *	Purpose:
 *		Call thread_group_blocked callout if the port
 *	        has ip_tg_block_tracking bit set and the thread
 *	        has not made this callout already.
 *
 *	Conditions:
 *		Nothing is locked.
 */
void
ipc_port_thread_group_blocked(ipc_port_t port __unused)
{
#if CONFIG_THREAD_GROUPS
	bool port_tg_block_tracking = false;
	thread_t self = current_thread();

	if (self->thread_group == NULL ||
	    (self->options & TH_OPT_IPC_TG_BLOCKED)) {
		return;
	}

	port_tg_block_tracking = port->ip_tg_block_tracking;
	if (!port_tg_block_tracking) {
		return;
	}

	machine_thread_group_blocked(self->thread_group, NULL,
	    PERFCONTROL_CALLOUT_BLOCKING_TG_RENDER_SERVER, self);

	self->options |= TH_OPT_IPC_TG_BLOCKED;
#endif
}

/*
 *	Routine:	ipc_port_thread_group_unblocked
 *	Purpose:
 *		Call thread_group_unblocked callout if the
 *		thread had previously made a thread_group_blocked
 *		callout before (indicated by TH_OPT_IPC_TG_BLOCKED
 *		flag on the thread).
 *
 *	Conditions:
 *		Nothing is locked.
 */
void
ipc_port_thread_group_unblocked(void)
{
#if CONFIG_THREAD_GROUPS
	thread_t self = current_thread();

	if (!(self->options & TH_OPT_IPC_TG_BLOCKED)) {
		return;
	}

	machine_thread_group_unblocked(self->thread_group, NULL,
	    PERFCONTROL_CALLOUT_BLOCKING_TG_RENDER_SERVER, self);

	self->options &= ~TH_OPT_IPC_TG_BLOCKED;
#endif
}

#if DEVELOPMENT || DEBUG
inline void
ipc_special_reply_port_bits_reset(ipc_port_t special_reply_port)
{
	special_reply_port->ip_srp_lost_link = 0;
	special_reply_port->ip_srp_msg_sent = 0;
}

static inline void
ipc_special_reply_port_msg_sent_reset(ipc_port_t special_reply_port)
{
	if (special_reply_port->ip_specialreply == 1) {
		special_reply_port->ip_srp_msg_sent = 0;
	}
}

inline void
ipc_special_reply_port_msg_sent(ipc_port_t special_reply_port)
{
	if (special_reply_port->ip_specialreply == 1) {
		special_reply_port->ip_srp_msg_sent = 1;
	}
}

static inline void
ipc_special_reply_port_lost_link(ipc_port_t special_reply_port)
{
	if (special_reply_port->ip_specialreply == 1 && special_reply_port->ip_srp_msg_sent == 0) {
		special_reply_port->ip_srp_lost_link = 1;
	}
}

#else /* DEVELOPMENT || DEBUG */
inline void
ipc_special_reply_port_bits_reset(__unused ipc_port_t special_reply_port)
{
	return;
}

static inline void
ipc_special_reply_port_msg_sent_reset(__unused ipc_port_t special_reply_port)
{
	return;
}

inline void
ipc_special_reply_port_msg_sent(__unused ipc_port_t special_reply_port)
{
	return;
}

static inline void
ipc_special_reply_port_lost_link(__unused ipc_port_t special_reply_port)
{
	return;
}
#endif /* DEVELOPMENT || DEBUG */

/*
 *	Routine:	ipc_port_adjust_special_reply_port_locked
 *	Purpose:
 *		If the special port has a turnstile, update its inheritor.
 *	Condition:
 *		Special reply port locked on entry.
 *		Special reply port unlocked on return.
 *		The passed in port is a special reply port.
 *	Returns:
 *		None.
 */
void
ipc_port_adjust_special_reply_port_locked(
	ipc_port_t special_reply_port,
	struct knote *kn,
	uint8_t flags,
	boolean_t get_turnstile)
{
	ipc_port_t dest_port = IPC_PORT_NULL;
	int sync_link_state = PORT_SYNC_LINK_NO_LINKAGE;
	turnstile_inheritor_t inheritor = TURNSTILE_INHERITOR_NULL;
	struct turnstile *ts = TURNSTILE_NULL;
	struct turnstile *port_stashed_turnstile = TURNSTILE_NULL;

	ip_mq_lock_held(special_reply_port); // ip_sync_link_state is touched

	if (!special_reply_port->ip_specialreply) {
		// only mach_msg_receive_results_complete() calls this with any port
		assert(get_turnstile);
		goto not_special;
	}

	if (flags & IPC_PORT_ADJUST_SR_RECEIVED_MSG) {
		ipc_special_reply_port_msg_sent_reset(special_reply_port);
	}

	if (flags & IPC_PORT_ADJUST_UNLINK_THREAD) {
		special_reply_port->ip_messages.imq_srp_owner_thread = NULL;
	}

	if (flags & IPC_PORT_ADJUST_RESET_BOOSTRAP_CHECKIN) {
		special_reply_port->ip_sync_bootstrap_checkin = 0;
	}

	/* Check if the special reply port is marked non-special */
	if (special_reply_port->ip_sync_link_state == PORT_SYNC_LINK_ANY) {
not_special:
		if (get_turnstile) {
			turnstile_complete((uintptr_t)special_reply_port,
			    port_rcv_turnstile_address(special_reply_port), NULL, TURNSTILE_SYNC_IPC);
		}
		ip_mq_unlock(special_reply_port);
		if (get_turnstile) {
			turnstile_cleanup();
		}
		return;
	}

	if (flags & IPC_PORT_ADJUST_SR_LINK_WORKLOOP) {
		if (ITH_KNOTE_VALID(kn, MACH_MSG_TYPE_PORT_SEND_ONCE)) {
			inheritor = filt_machport_stash_port(kn, special_reply_port,
			    &sync_link_state);
		}
	} else if (flags & IPC_PORT_ADJUST_SR_ALLOW_SYNC_LINKAGE) {
		sync_link_state = PORT_SYNC_LINK_ANY;
	}

	/* Check if need to break linkage */
	if (!get_turnstile && sync_link_state == PORT_SYNC_LINK_NO_LINKAGE &&
	    special_reply_port->ip_sync_link_state == PORT_SYNC_LINK_NO_LINKAGE) {
		ip_mq_unlock(special_reply_port);
		return;
	}

	switch (special_reply_port->ip_sync_link_state) {
	case PORT_SYNC_LINK_PORT:
		dest_port = special_reply_port->ip_sync_inheritor_port;
		special_reply_port->ip_sync_inheritor_port = IPC_PORT_NULL;
		break;
	case PORT_SYNC_LINK_WORKLOOP_KNOTE:
		special_reply_port->ip_sync_inheritor_knote = NULL;
		break;
	case PORT_SYNC_LINK_WORKLOOP_STASH:
		port_stashed_turnstile = special_reply_port->ip_sync_inheritor_ts;
		special_reply_port->ip_sync_inheritor_ts = NULL;
		break;
	}

	/*
	 * Stash (or unstash) the server's PID in the ip_sorights field of the
	 * special reply port, so that stackshot can later retrieve who the client
	 * is blocked on.
	 */
	if (special_reply_port->ip_sync_link_state == PORT_SYNC_LINK_PORT &&
	    sync_link_state == PORT_SYNC_LINK_NO_LINKAGE) {
		ipc_special_reply_stash_pid_locked(special_reply_port, pid_from_task(current_task()));
	} else if (special_reply_port->ip_sync_link_state == PORT_SYNC_LINK_NO_LINKAGE &&
	    sync_link_state == PORT_SYNC_LINK_ANY) {
		/* If we are resetting the special reply port, remove the stashed pid. */
		ipc_special_reply_stash_pid_locked(special_reply_port, 0);
	}

	special_reply_port->ip_sync_link_state = sync_link_state;

	switch (sync_link_state) {
	case PORT_SYNC_LINK_WORKLOOP_KNOTE:
		special_reply_port->ip_sync_inheritor_knote = kn;
		break;
	case PORT_SYNC_LINK_WORKLOOP_STASH:
		turnstile_reference(inheritor);
		special_reply_port->ip_sync_inheritor_ts = inheritor;
		break;
	case PORT_SYNC_LINK_NO_LINKAGE:
		if (flags & IPC_PORT_ADJUST_SR_ENABLE_EVENT) {
			ipc_special_reply_port_lost_link(special_reply_port);
		}
		break;
	}

	/* Get thread's turnstile donated to special reply port */
	if (get_turnstile) {
		turnstile_complete((uintptr_t)special_reply_port,
		    port_rcv_turnstile_address(special_reply_port), NULL, TURNSTILE_SYNC_IPC);
	} else {
		ts = ipc_port_rcv_turnstile(special_reply_port);
		if (ts) {
			turnstile_reference(ts);
			ipc_port_recv_update_inheritor(special_reply_port, ts,
			    TURNSTILE_IMMEDIATE_UPDATE);
		}
	}

	ip_mq_unlock(special_reply_port);

	if (get_turnstile) {
		turnstile_cleanup();
	} else if (ts) {
		/* Call turnstile cleanup after dropping the interlock */
		turnstile_update_inheritor_complete(ts, TURNSTILE_INTERLOCK_NOT_HELD);
		turnstile_deallocate_safe(ts);
	}

	if (port_stashed_turnstile) {
		turnstile_deallocate_safe(port_stashed_turnstile);
	}

	/* Release the ref on the dest port and its turnstile */
	if (dest_port) {
		ipc_port_send_turnstile_complete(dest_port);
		/* release the reference on the dest port, space lock might be held */
		ip_release_safe(dest_port);
	}
}

/*
 *	Routine:	ipc_port_adjust_special_reply_port
 *	Purpose:
 *		If the special port has a turnstile, update its inheritor.
 *	Condition:
 *		Nothing locked.
 *	Returns:
 *		None.
 */
void
ipc_port_adjust_special_reply_port(
	ipc_port_t port,
	uint8_t flags)
{
	if (port->ip_specialreply) {
		ip_mq_lock(port);
		ipc_port_adjust_special_reply_port_locked(port, NULL, flags, FALSE);
	}
}

/*
 *	Routine:	ipc_port_adjust_sync_link_state_locked
 *	Purpose:
 *		Update the sync link state of the port and the
 *		turnstile inheritor.
 *	Condition:
 *		Port locked on entry.
 *		Port locked on return.
 *	Returns:
 *              None.
 */
void
ipc_port_adjust_sync_link_state_locked(
	ipc_port_t port,
	int sync_link_state,
	turnstile_inheritor_t inheritor)
{
	switch (port->ip_sync_link_state) {
	case PORT_SYNC_LINK_RCV_THREAD:
		/* deallocate the thread reference for the inheritor */
		thread_deallocate_safe(port->ip_messages.imq_inheritor_thread_ref);
		break;
	case PORT_SYNC_LINK_WORKLOOP_STASH:
		/* deallocate the turnstile reference for the inheritor */
		turnstile_deallocate_safe(port->ip_messages.imq_inheritor_turnstile);
		break;
	}

	klist_init(&port->ip_klist);

	switch (sync_link_state) {
	case PORT_SYNC_LINK_WORKLOOP_KNOTE:
		port->ip_messages.imq_inheritor_knote = inheritor;
		break;
	case PORT_SYNC_LINK_WORKLOOP_STASH:
		/* knote can be deleted by userspace, take a reference on turnstile */
		turnstile_reference(inheritor);
		port->ip_messages.imq_inheritor_turnstile = inheritor;
		break;
	case PORT_SYNC_LINK_RCV_THREAD:
		/* The thread could exit without clearing port state, take a thread ref */
		thread_reference((thread_t)inheritor);
		port->ip_messages.imq_inheritor_thread_ref = inheritor;
		break;
	default:
		klist_init(&port->ip_klist);
		sync_link_state = PORT_SYNC_LINK_ANY;
	}

	port->ip_sync_link_state = sync_link_state;
}


/*
 *	Routine:	ipc_port_adjust_port_locked
 *	Purpose:
 *		If the port has a turnstile, update its inheritor.
 *	Condition:
 *		Port locked on entry.
 *		Port unlocked on return.
 *	Returns:
 *		None.
 */
void
ipc_port_adjust_port_locked(
	ipc_port_t port,
	struct knote *kn,
	boolean_t sync_bootstrap_checkin)
{
	int sync_link_state = PORT_SYNC_LINK_ANY;
	turnstile_inheritor_t inheritor = TURNSTILE_INHERITOR_NULL;

	ip_mq_lock_held(port); // ip_sync_link_state is touched
	assert(!port->ip_specialreply);

	if (kn) {
		inheritor = filt_machport_stash_port(kn, port, &sync_link_state);
		if (sync_link_state == PORT_SYNC_LINK_WORKLOOP_KNOTE) {
			inheritor = kn;
		}
	} else if (sync_bootstrap_checkin) {
		inheritor = current_thread();
		sync_link_state = PORT_SYNC_LINK_RCV_THREAD;
	}

	ipc_port_adjust_sync_link_state_locked(port, sync_link_state, inheritor);
	port->ip_sync_bootstrap_checkin = 0;

	ipc_port_send_turnstile_recompute_push_locked(port);
	/* port unlocked */
}

/*
 *	Routine:	ipc_port_clear_sync_rcv_thread_boost_locked
 *	Purpose:
 *		If the port is pushing on rcv thread, clear it.
 *	Condition:
 *		Port locked on entry
 *		Port unlocked on return.
 *	Returns:
 *		None.
 */
void
ipc_port_clear_sync_rcv_thread_boost_locked(
	ipc_port_t port)
{
	ip_mq_lock_held(port); // ip_sync_link_state is touched

	if (port->ip_sync_link_state != PORT_SYNC_LINK_RCV_THREAD) {
		ip_mq_unlock(port);
		return;
	}

	ipc_port_adjust_sync_link_state_locked(port, PORT_SYNC_LINK_ANY, NULL);

	ipc_port_send_turnstile_recompute_push_locked(port);
	/* port unlocked */
}

/*
 *	Routine:	ipc_port_has_prdrequest
 *	Purpose:
 *		Returns whether a port has a port-destroyed request armed
 *	Condition:
 *		Port is locked.
 */
bool
ipc_port_has_prdrequest(
	ipc_port_t port)
{
	if (port->ip_specialreply) {
		return false;
	}
	if (port->ip_has_watchport) {
		return port->ip_twe->twe_pdrequest != IP_NULL;
	}
	return port->ip_pdrequest != IP_NULL;
}

/*
 *	Routine:	ipc_port_add_watchport_elem_locked
 *	Purpose:
 *		Transfer the turnstile boost of watchport to task calling exec.
 *	Condition:
 *		Port locked on entry.
 *		Port unlocked on return.
 *	Returns:
 *		KERN_SUCESS on success.
 *		KERN_FAILURE otherwise.
 */
kern_return_t
ipc_port_add_watchport_elem_locked(
	ipc_port_t                 port,
	struct task_watchport_elem *watchport_elem,
	struct task_watchport_elem **old_elem)
{
	ip_mq_lock_held(port);

	/* Watchport boost only works for non-special active ports mapped in an ipc space */
	if (!ip_active(port) || port->ip_specialreply || !ip_in_a_space(port)) {
		ip_mq_unlock(port);
		return KERN_FAILURE;
	}

	if (port->ip_sync_link_state != PORT_SYNC_LINK_ANY) {
		/* Sever the linkage if the port was pushing on knote */
		ipc_port_adjust_sync_link_state_locked(port, PORT_SYNC_LINK_ANY, NULL);
	}

	*old_elem = ipc_port_update_watchport_elem(port, watchport_elem);

	ipc_port_send_turnstile_recompute_push_locked(port);
	/* port unlocked */
	return KERN_SUCCESS;
}

/*
 *	Routine:	ipc_port_clear_watchport_elem_internal_conditional_locked
 *	Purpose:
 *		Remove the turnstile boost of watchport and recompute the push.
 *	Condition:
 *		Port locked on entry.
 *		Port unlocked on return.
 *	Returns:
 *		KERN_SUCESS on success.
 *		KERN_FAILURE otherwise.
 */
kern_return_t
ipc_port_clear_watchport_elem_internal_conditional_locked(
	ipc_port_t                 port,
	struct task_watchport_elem *watchport_elem)
{
	ip_mq_lock_held(port);

	if (ipc_port_watchport_elem(port) != watchport_elem) {
		ip_mq_unlock(port);
		return KERN_FAILURE;
	}

	ipc_port_clear_watchport_elem_internal(port);
	ipc_port_send_turnstile_recompute_push_locked(port);
	/* port unlocked */
	return KERN_SUCCESS;
}

/*
 *	Routine:	ipc_port_replace_watchport_elem_conditional_locked
 *	Purpose:
 *		Replace the turnstile boost of watchport and recompute the push.
 *	Condition:
 *		Port locked on entry.
 *		Port unlocked on return.
 *	Returns:
 *		KERN_SUCESS on success.
 *		KERN_FAILURE otherwise.
 */
kern_return_t
ipc_port_replace_watchport_elem_conditional_locked(
	ipc_port_t                 port,
	struct task_watchport_elem *old_watchport_elem,
	struct task_watchport_elem *new_watchport_elem)
{
	ip_mq_lock_held(port);

	if (port->ip_specialreply ||
	    ipc_port_watchport_elem(port) != old_watchport_elem) {
		ip_mq_unlock(port);
		return KERN_FAILURE;
	}

	ipc_port_update_watchport_elem(port, new_watchport_elem);
	ipc_port_send_turnstile_recompute_push_locked(port);
	/* port unlocked */
	return KERN_SUCCESS;
}

/*
 *	Routine:	ipc_port_clear_watchport_elem_internal
 *	Purpose:
 *		Remove the turnstile boost of watchport.
 *	Condition:
 *		Port locked on entry.
 *		Port locked on return.
 *	Returns:
 *		Old task_watchport_elem returned.
 */
struct task_watchport_elem *
ipc_port_clear_watchport_elem_internal(
	ipc_port_t                 port)
{
	ip_mq_lock_held(port);

	if (!port->ip_has_watchport) {
		return NULL;
	}

	return ipc_port_update_watchport_elem(port, NULL);
}

/*
 *	Routine:	ipc_port_send_turnstile_recompute_push_locked
 *	Purpose:
 *		Update send turnstile inheritor of port and recompute the push.
 *	Condition:
 *		Port locked on entry.
 *		Port unlocked on return.
 *	Returns:
 *		None.
 */
static void
ipc_port_send_turnstile_recompute_push_locked(
	ipc_port_t port)
{
	struct turnstile *send_turnstile = port_send_turnstile(port);
	if (send_turnstile) {
		turnstile_reference(send_turnstile);
		ipc_port_send_update_inheritor(port, send_turnstile,
		    TURNSTILE_IMMEDIATE_UPDATE);
	}
	ip_mq_unlock(port);

	if (send_turnstile) {
		turnstile_update_inheritor_complete(send_turnstile,
		    TURNSTILE_INTERLOCK_NOT_HELD);
		turnstile_deallocate_safe(send_turnstile);
	}
}

/*
 *	Routine:	ipc_port_get_watchport_inheritor
 *	Purpose:
 *		Returns inheritor for watchport.
 *
 *	Conditions:
 *		mqueue locked.
 *	Returns:
 *		watchport inheritor.
 */
static thread_t
ipc_port_get_watchport_inheritor(
	ipc_port_t port)
{
	ip_mq_lock_held(port);
	return ipc_port_watchport_elem(port)->twe_task->watchports->tw_thread;
}

/*
 *	Routine:	ipc_port_get_receiver_task
 *	Purpose:
 *		Returns receiver task pointer and its pid (if any) for port.
 *
 *	Conditions:
 *		Nothing locked. The routine takes port lock.
 */
pid_t
ipc_port_get_receiver_task(ipc_port_t port, uintptr_t *task)
{
	task_t receiver = TASK_NULL;
	pid_t pid = -1;

	if (!port) {
		goto out;
	}

	ip_mq_lock(port);
	if (ip_in_a_space(port) &&
	    !ip_in_space(port, ipc_space_kernel) &&
	    !ip_in_space(port, ipc_space_reply)) {
		receiver = port->ip_receiver->is_task;
		pid = task_pid(receiver);
	}
	ip_mq_unlock(port);

out:
	if (task) {
		*task = (uintptr_t)receiver;
	}
	return pid;
}

/*
 *	Routine:	ipc_port_impcount_delta
 *	Purpose:
 *		Adjust only the importance count associated with a port.
 *		If there are any adjustments to be made to receiver task,
 *		those are handled elsewhere.
 *
 *		For now, be defensive during deductions to make sure the
 *		impcount for the port doesn't underflow zero.  This will
 *		go away when the port boost addition is made atomic (see
 *		note in ipc_port_importance_delta()).
 *	Conditions:
 *		The port is referenced and locked.
 *		Nothing else is locked.
 */
mach_port_delta_t
ipc_port_impcount_delta(
	ipc_port_t        port,
	mach_port_delta_t delta,
	ipc_port_t        __unused base)
{
	mach_port_delta_t absdelta;

	if (!ip_active(port)) {
		return 0;
	}

	/* adding/doing nothing is easy */
	if (delta >= 0) {
		port->ip_impcount += delta;
		return delta;
	}

	absdelta = 0 - delta;
	if (port->ip_impcount >= absdelta) {
		port->ip_impcount -= absdelta;
		return delta;
	}

#if (DEVELOPMENT || DEBUG)
	if (ip_in_a_space(port)) {
		task_t target_task = port->ip_receiver->is_task;
		ipc_importance_task_t target_imp = target_task->task_imp_base;
		const char *target_procname;
		int target_pid;

		if (target_imp != IIT_NULL) {
			target_procname = target_imp->iit_procname;
			target_pid = target_imp->iit_bsd_pid;
		} else {
			target_procname = "unknown";
			target_pid = -1;
		}
		printf("Over-release of importance assertions for port 0x%x receiver pid %d (%s), "
		    "dropping %d assertion(s) but port only has %d remaining.\n",
		    ip_get_receiver_name(port),
		    target_pid, target_procname,
		    absdelta, port->ip_impcount);
	} else if (base != IP_NULL) {
		assert(ip_in_a_space(base));
		task_t target_task = base->ip_receiver->is_task;
		ipc_importance_task_t target_imp = target_task->task_imp_base;
		const char *target_procname;
		int target_pid;

		if (target_imp != IIT_NULL) {
			target_procname = target_imp->iit_procname;
			target_pid = target_imp->iit_bsd_pid;
		} else {
			target_procname = "unknown";
			target_pid = -1;
		}
		printf("Over-release of importance assertions for port 0x%lx "
		    "enqueued on port 0x%x with receiver pid %d (%s), "
		    "dropping %d assertion(s) but port only has %d remaining.\n",
		    (unsigned long)VM_KERNEL_UNSLIDE_OR_PERM((uintptr_t)port),
		    ip_get_receiver_name(base),
		    target_pid, target_procname,
		    absdelta, port->ip_impcount);
	}
#endif

	delta = 0 - port->ip_impcount;
	port->ip_impcount = 0;
	return delta;
}

/*
 *	Routine:	ipc_port_importance_delta_internal
 *	Purpose:
 *		Adjust the importance count through the given port.
 *		If the port is in transit, apply the delta throughout
 *		the chain. Determine if the there is a task at the
 *		base of the chain that wants/needs to be adjusted,
 *		and if so, apply the delta.
 *	Conditions:
 *		The port is referenced and locked on entry.
 *		Importance may be locked.
 *		Nothing else is locked.
 *		The lock may be dropped on exit.
 *		Returns TRUE if lock was dropped.
 */
#if IMPORTANCE_INHERITANCE

boolean_t
ipc_port_importance_delta_internal(
	ipc_port_t              port,
	natural_t               options,
	mach_port_delta_t       *deltap,
	ipc_importance_task_t   *imp_task)
{
	ipc_port_t next, base;
	bool dropped = false;
	bool took_base_ref = false;

	*imp_task = IIT_NULL;

	if (*deltap == 0) {
		return FALSE;
	}

	assert(options == IPID_OPTION_NORMAL || options == IPID_OPTION_SENDPOSSIBLE);

	base = port;

	/* if port is in transit, have to search for end of chain */
	if (ip_in_transit(port)) {
		dropped = true;


		ip_mq_unlock(port);
		ipc_port_multiple_lock(); /* massive serialization */

		took_base_ref = ipc_port_destination_chain_lock(port, &base);
		/* all ports in chain from port to base, inclusive, are locked */

		ipc_port_multiple_unlock();
	}

	/*
	 * If the port lock is dropped b/c the port is in transit, there is a
	 * race window where another thread can drain messages and/or fire a
	 * send possible notification before we get here.
	 *
	 * We solve this race by checking to see if our caller armed the send
	 * possible notification, whether or not it's been fired yet, and
	 * whether or not we've already set the port's ip_spimportant bit. If
	 * we don't need a send-possible boost, then we'll just apply a
	 * harmless 0-boost to the port.
	 */
	if (options & IPID_OPTION_SENDPOSSIBLE) {
		assert(*deltap == 1);
		if (port->ip_sprequests && port->ip_spimportant == 0) {
			port->ip_spimportant = 1;
		} else {
			*deltap = 0;
		}
	}

	/* unlock down to the base, adjusting boost(s) at each level */
	for (;;) {
		*deltap = ipc_port_impcount_delta(port, *deltap, base);

		if (port == base) {
			break;
		}

		/* port is in transit */
		assert(port->ip_tempowner == 0);
		assert(ip_in_transit(port));
		next = ip_get_destination(port);
		ip_mq_unlock(port);
		port = next;
	}

	/* find the task (if any) to boost according to the base */
	if (ip_active(base)) {
		if (base->ip_tempowner != 0) {
			if (IIT_NULL != ip_get_imp_task(base)) {
				*imp_task = ip_get_imp_task(base);
			}
			/* otherwise don't boost */
		} else if (ip_in_a_space(base)) {
			ipc_space_t space = ip_get_receiver(base);

			/* only spaces with boost-accepting tasks */
			if (space->is_task != TASK_NULL &&
			    ipc_importance_task_is_any_receiver_type(space->is_task->task_imp_base)) {
				*imp_task = space->is_task->task_imp_base;
			}
		}
	}

	/*
	 * Only the base is locked.  If we have to hold or drop task
	 * importance assertions, we'll have to drop that lock as well.
	 */
	if (*imp_task != IIT_NULL) {
		/* take a reference before unlocking base */
		ipc_importance_task_reference(*imp_task);
	}

	if (dropped) {
		ip_mq_unlock(base);
		if (took_base_ref) {
			/* importance lock might be held */
			ip_release_safe(base);
		}
	}

	return dropped;
}
#endif /* IMPORTANCE_INHERITANCE */

/*
 *	Routine:	ipc_port_importance_delta
 *	Purpose:
 *		Adjust the importance count through the given port.
 *		If the port is in transit, apply the delta throughout
 *		the chain.
 *
 *		If there is a task at the base of the chain that wants/needs
 *		to be adjusted, apply the delta.
 *	Conditions:
 *		The port is referenced and locked on entry.
 *		Nothing else is locked.
 *		The lock may be dropped on exit.
 *		Returns TRUE if lock was dropped.
 */
#if IMPORTANCE_INHERITANCE

boolean_t
ipc_port_importance_delta(
	ipc_port_t              port,
	natural_t               options,
	mach_port_delta_t       delta)
{
	ipc_importance_task_t imp_task = IIT_NULL;
	boolean_t dropped;

	dropped = ipc_port_importance_delta_internal(port, options, &delta, &imp_task);

	if (IIT_NULL == imp_task || delta == 0) {
		return dropped;
	}

	if (!dropped) {
		ip_mq_unlock(port);
	}

	assert(ipc_importance_task_is_any_receiver_type(imp_task));

	if (delta > 0) {
		ipc_importance_task_hold_internal_assertion(imp_task, delta);
	} else {
		ipc_importance_task_drop_internal_assertion(imp_task, -delta);
	}

	ipc_importance_task_release(imp_task);
	return TRUE;
}
#endif /* IMPORTANCE_INHERITANCE */

/*
 *	Routine:	ipc_port_make_send_locked
 *	Purpose:
 *		Make a naked send right from a receive right.
 *
 *		See ipc_port_make_send for more extensive documentation.
 *
 *	Conditions:
 *		port locked and active.
 */
ipc_port_t
ipc_port_make_send_locked(
	ipc_port_t      port)
{
	require_ip_active(port);
	port->ip_mscount++;
	port->ip_srights++;
	ip_reference(port);
	return port;
}

/*
 *	Routine:	ipc_port_make_send
 *	Purpose:
 *		Make a naked send right from a receive right.
 *
 *		ipc_port_make_send should not be used in any generic IPC
 *		plumbing, as this is an operation that subsystem
 *		owners need to be able to synchronize against
 *		with the make-send-count and no-senders notifications.
 *
 *		It is especially important for kobject types,
 *		and in general MIG upcalls or replies from the kernel
 *		should never use MAKE_SEND dispositions, and prefer
 *		COPY_SEND or MOVE_SEND, so that subsystems can control
 *		where that send right comes from.
 */
ipc_port_t
ipc_port_make_send(
	ipc_port_t      port)
{
	if (!IP_VALID(port)) {
		return port;
	}

	ip_mq_lock(port);
	if (ip_active(port)) {
		ipc_port_make_send_locked(port);
		ip_mq_unlock(port);
		return port;
	}
	ip_mq_unlock(port);
	return IP_DEAD;
}

/*
 *	Routine:	ipc_port_copy_send_locked
 *	Purpose:
 *		Make a naked send right from another naked send right.
 *	Conditions:
 *		port locked.
 */
void
ipc_port_copy_send_locked(
	ipc_port_t      port)
{
	assert(port->ip_srights > 0);
	port->ip_srights++;
	ip_reference(port);
}

/*
 *	Routine:	ipc_port_copy_send
 *	Purpose:
 *		Make a naked send right from another naked send right.
 *			IP_NULL		-> IP_NULL
 *			IP_DEAD		-> IP_DEAD
 *			dead port	-> IP_DEAD
 *			live port	-> port + ref
 *	Conditions:
 *		Nothing locked except possibly a space.
 */

ipc_port_t
ipc_port_copy_send(
	ipc_port_t      port)
{
	ipc_port_t sright;

	if (!IP_VALID(port)) {
		return port;
	}

	ip_mq_lock(port);
	if (ip_active(port)) {
		ipc_port_copy_send_locked(port);
		sright = port;
	} else {
		sright = IP_DEAD;
	}
	ip_mq_unlock(port);

	return sright;
}

/*
 *	Routine:	ipc_port_copyout_send
 *	Purpose:
 *		Copyout a naked send right (possibly null/dead),
 *		or if that fails, destroy the right.
 *	Conditions:
 *		Nothing locked.
 */

static mach_port_name_t
ipc_port_copyout_send_internal(
	ipc_port_t      sright,
	ipc_space_t     space,
	ipc_object_copyout_flags_t flags)
{
	mach_port_name_t name;

	if (IP_VALID(sright)) {
		kern_return_t kr;

		kr = ipc_object_copyout(space, ip_to_object(sright),
		    MACH_MSG_TYPE_PORT_SEND, flags, NULL, NULL, &name);
		if (kr != KERN_SUCCESS) {
			if (kr == KERN_INVALID_CAPABILITY) {
				name = MACH_PORT_DEAD;
			} else {
				name = MACH_PORT_NULL;
			}
		}
	} else {
		name = CAST_MACH_PORT_TO_NAME(sright);
	}

	return name;
}

mach_port_name_t
ipc_port_copyout_send(
	ipc_port_t      sright, /* can be invalid */
	ipc_space_t     space)
{
	return ipc_port_copyout_send_internal(sright, space, IPC_OBJECT_COPYOUT_FLAGS_NONE);
}

/* Used by pthread kext to copyout thread port only */
mach_port_name_t
ipc_port_copyout_send_pinned(
	ipc_port_t      sright, /* can be invalid */
	ipc_space_t     space)
{
	assert(space->is_task != TASK_NULL);

	if (IP_VALID(sright)) {
		assert(ip_kotype(sright) == IKOT_THREAD_CONTROL);
	}

	if (task_is_pinned(space->is_task)) {
		return ipc_port_copyout_send_internal(sright, space, IPC_OBJECT_COPYOUT_FLAGS_PINNED);
	} else {
		return ipc_port_copyout_send_internal(sright, space, IPC_OBJECT_COPYOUT_FLAGS_NONE);
	}
}

/*
 *	Routine:	ipc_port_release_send_and_unlock
 *	Purpose:
 *		Release a naked send right.
 *		Consumes a ref for the port.
 *	Conditions:
 *		Port is valid and locked on entry
 *		Port is unlocked on exit.
 */
void
ipc_port_release_send_and_unlock(
	ipc_port_t      port)
{
	ipc_notify_nsenders_t nsrequest = { };

	if (port->ip_srights == 0) {
		panic("Over-release of port %p send right!", port);
	}
	port->ip_srights--;

	if (ip_active(port) && port->ip_srights == 0) {
		nsrequest = ipc_notify_no_senders_prepare(port);
	}

	ip_mq_unlock(port);
	ip_release(port);

	ipc_notify_no_senders_emit(nsrequest);
}

/*
 *	Routine:	ipc_port_release_send
 *	Purpose:
 *		Release a naked send right.
 *		Consumes a ref for the port.
 *	Conditions:
 *		Nothing locked.
 */

void
ipc_port_release_send(
	ipc_port_t      port)
{
	if (IP_VALID(port)) {
		ip_mq_lock(port);
		ipc_port_release_send_and_unlock(port);
	}
}

/*
 *	Routine:	ipc_port_make_sonce_locked
 *	Purpose:
 *		Make a naked send-once right from a receive right.
 *	Conditions:
 *		The port is locked and active.
 */

ipc_port_t
ipc_port_make_sonce_locked(
	ipc_port_t      port)
{
	require_ip_active(port);
	port->ip_sorights++;
	ip_reference(port);
	return port;
}

/*
 *	Routine:	ipc_port_make_sonce
 *	Purpose:
 *		Make a naked send-once right from a receive right.
 *	Conditions:
 *		The port is not locked.
 */

ipc_port_t
ipc_port_make_sonce(
	ipc_port_t      port)
{
	if (!IP_VALID(port)) {
		return port;
	}

	ip_mq_lock(port);
	if (ip_active(port)) {
		ipc_port_make_sonce_locked(port);
		ip_mq_unlock(port);
		return port;
	}
	ip_mq_unlock(port);
	return IP_DEAD;
}

/*
 *	Routine:	ipc_port_release_sonce
 *	Purpose:
 *		Release a naked send-once right.
 *		Consumes a ref for the port.
 *
 *		In normal situations, this is never used.
 *		Send-once rights are only consumed when
 *		a message (possibly a send-once notification)
 *		is sent to them.
 *	Conditions:
 *		The port is locked, possibly a space too.
 */
void
ipc_port_release_sonce_and_unlock(
	ipc_port_t      port)
{
	ip_mq_lock_held(port);

	if (port->ip_sorights == 0) {
		panic("Over-release of port %p send-once right!", port);
	}

	port->ip_sorights--;

	if (port->ip_specialreply) {
		ipc_port_adjust_special_reply_port_locked(port, NULL,
		    IPC_PORT_ADJUST_RESET_BOOSTRAP_CHECKIN, FALSE);
	} else {
		ip_mq_unlock(port);
	}

	ip_release(port);
}

/*
 *	Routine:	ipc_port_release_sonce
 *	Purpose:
 *		Release a naked send-once right.
 *		Consumes a ref for the port.
 *
 *		In normal situations, this is never used.
 *		Send-once rights are only consumed when
 *		a message (possibly a send-once notification)
 *		is sent to them.
 *	Conditions:
 *		Nothing locked except possibly a space.
 */
void
ipc_port_release_sonce(
	ipc_port_t      port)
{
	if (IP_VALID(port)) {
		ip_mq_lock(port);
		ipc_port_release_sonce_and_unlock(port);
	}
}

/*
 *	Routine:	ipc_port_release_receive
 *	Purpose:
 *		Release a naked (in limbo or in transit) receive right.
 *		Consumes a ref for the port; destroys the port.
 *	Conditions:
 *		Nothing locked.
 */

void
ipc_port_release_receive(
	ipc_port_t      port)
{
	ipc_port_t dest;

	if (!IP_VALID(port)) {
		return;
	}

	ip_mq_lock(port);
	require_ip_active(port);
	assert(!ip_in_a_space(port));
	dest = ip_get_destination(port);

	ipc_port_destroy(port); /* consumes ref, unlocks */

	if (dest != IP_NULL) {
		ipc_port_send_turnstile_complete(dest);
		ip_release(dest);
	}
}

/*
 *	Routine:	ipc_port_alloc_special
 *	Purpose:
 *		Allocate a port in a special space.
 *		The new port is returned with one ref.
 *		If unsuccessful, IP_NULL is returned.
 *	Conditions:
 *		Nothing locked.
 */

ipc_port_t
ipc_port_alloc_special(
	ipc_space_t             space,
	ipc_port_init_flags_t   flags)
{
	ipc_port_t port;

	port = ip_object_to_port(io_alloc(IOT_PORT, Z_WAITOK | Z_ZERO));
	if (port == IP_NULL) {
		return IP_NULL;
	}

	os_atomic_init(&port->ip_object.io_bits, io_makebits(TRUE, IOT_PORT, 0));
	os_atomic_init(&port->ip_object.io_references, 1);

	ipc_port_init(port, space, flags, MACH_PORT_SPECIAL_DEFAULT);
	return port;
}

/*
 *	Routine:	ipc_port_dealloc_special_and_unlock
 *	Purpose:
 *		Deallocate a port in a special space.
 *		Consumes one ref for the port.
 *	Conditions:
 *		Port is locked.
 */

void
ipc_port_dealloc_special_and_unlock(
	ipc_port_t                      port,
	__assert_only ipc_space_t       space)
{
	require_ip_active(port);
//	assert(port->ip_receiver_name != MACH_PORT_NULL);
	assert(ip_in_space(port, space));

	/*
	 *	We clear ip_receiver_name and ip_receiver to simplify
	 *	the ipc_space_kernel check in ipc_mqueue_send.
	 */

	/* port transtions to IN-LIMBO state */
	port->ip_receiver_name = MACH_PORT_NULL;
	port->ip_receiver = IS_NULL;

	/* relevant part of ipc_port_clear_receiver */
	port->ip_mscount = 0;
	port->ip_messages.imq_seqno = 0;

	ipc_port_destroy(port);
}

/*
 *	Routine:	ipc_port_dealloc_special
 *	Purpose:
 *		Deallocate a port in a special space.
 *		Consumes one ref for the port.
 *	Conditions:
 *		Nothing locked.
 */

void
ipc_port_dealloc_special(
	ipc_port_t        port,
	ipc_space_t       space)
{
	ip_mq_lock(port);
	ipc_port_dealloc_special_and_unlock(port, space);
}

/*
 *	Routine:	ipc_port_finalize
 *	Purpose:
 *		Called on last reference deallocate to
 *		free any remaining data associated with the
 *		port.
 *	Conditions:
 *		Nothing locked.
 */
void
ipc_port_finalize(
	ipc_port_t              port)
{
	ipc_port_request_t requests = port->ip_requests;

	assert(port_send_turnstile(port) == TURNSTILE_NULL);
	if (waitq_type(&port->ip_waitq) == WQT_PORT) {
		assert(ipc_port_rcv_turnstile(port) == TURNSTILE_NULL);
	}

	if (ip_active(port)) {
		panic("Trying to free an active port. port %p", port);
	}

	if (requests != IPR_NULL) {
		ipc_table_size_t its = requests->ipr_size;
		it_requests_free(its, requests);
		port->ip_requests = IPR_NULL;
	}

	/*
	 * (81997111) now it is safe to deallocate the prealloc message.
	 * Keep the IP_BIT_PREALLOC bit, it has to be sticky as the turnstile
	 * code looks at it without holding locks.
	 */
	if (IP_PREALLOC(port)) {
		ipc_kmsg_t kmsg = port->ip_premsg;

		if (kmsg == IKM_NULL || ikm_prealloc_inuse_port(kmsg) ||
		    kmsg->ikm_turnstile != TURNSTILE_NULL) {
			panic("port(%p, %p): prealloc message in an invalid state",
			    port, kmsg);
		}

		port->ip_premsg = IKM_NULL;
		ipc_kmsg_free(kmsg);
	}

	waitq_deinit(&port->ip_waitq);
#if MACH_ASSERT
	if (port->ip_made_bt) {
		btref_put(port->ip_made_bt);
	}
#endif
}

/*
 *	Routine:	kdp_mqueue_send_find_owner
 *	Purpose:
 *		Discover the owner of the ipc object that contains the input
 *		waitq object. The thread blocked on the waitq should be
 *		waiting for an IPC_MQUEUE_FULL event.
 *	Conditions:
 *		The 'waitinfo->wait_type' value should already be set to
 *		kThreadWaitPortSend.
 *	Note:
 *		If we find out that the containing port is actually in
 *		transit, we reset the wait_type field to reflect this.
 */
void
kdp_mqueue_send_find_owner(
	struct waitq                   *waitq,
	__assert_only event64_t         event,
	thread_waitinfo_v2_t           *waitinfo,
	struct ipc_service_port_label **isplp)
{
	struct turnstile *turnstile;
	assert(waitinfo->wait_type == kThreadWaitPortSend);
	assert(event == IPC_MQUEUE_FULL);
	assert(waitq_type(waitq) == WQT_TURNSTILE);

	turnstile = waitq_to_turnstile(waitq);
	ipc_port_t port = (ipc_port_t)turnstile->ts_proprietor; /* we are blocking on send */

	zone_id_require(ZONE_ID_IPC_PORT, sizeof(struct ipc_port), port);

	waitinfo->owner = 0;
	waitinfo->context  = VM_KERNEL_UNSLIDE_OR_PERM(port);
	if (ip_mq_lock_held_kdp(port)) {
		/*
		 * someone has the port locked: it may be in an
		 * inconsistent state: bail
		 */
		waitinfo->owner = STACKSHOT_WAITOWNER_PORT_LOCKED;
		return;
	}

	/* now we are the only one accessing the port */
	if (ip_active(port)) {
		/*
		 * In kdp context, port must be left unlocked throughout.
		 * Therefore can't use union field accessor helpers, manually strip PAC
		 * and compare raw pointer.
		 */
		void *raw_ptr = ip_get_receiver_ptr_noauth(port);

		if (port->ip_tempowner) {
			ipc_importance_task_t imp_task = ip_get_imp_task(port);
			if (imp_task != IIT_NULL && imp_task->iit_task != NULL) {
				/* port is held by a tempowner */
				waitinfo->owner = pid_from_task(port->ip_imp_task->iit_task);
			} else {
				waitinfo->owner = STACKSHOT_WAITOWNER_INTRANSIT;
			}
		} else if (ip_in_a_space(port)) { /* no port lock needed */
			if ((ipc_space_t)raw_ptr == ipc_space_kernel) { /* access union field as ip_receiver */
				/*
				 * The kernel pid is 0, make this
				 * distinguishable from no-owner and
				 * inconsistent port state.
				 */
				waitinfo->owner = STACKSHOT_WAITOWNER_KERNEL;
			} else {
				waitinfo->owner = pid_from_task(((ipc_space_t)raw_ptr)->is_task);
			}
		} else if ((ipc_port_t)raw_ptr != IP_NULL) { /* access union field as ip_destination */
			waitinfo->wait_type = kThreadWaitPortSendInTransit;
			waitinfo->owner     = VM_KERNEL_UNSLIDE_OR_PERM((ipc_port_t)raw_ptr);
		}
		if (port->ip_service_port && port->ip_splabel != NULL) {
			*isplp = (struct ipc_service_port_label *)port->ip_splabel;
		}
	}
}

/*
 *	Routine:	kdp_mqueue_recv_find_owner
 *	Purpose:
 *		Discover the "owner" of the ipc object that contains the input
 *		waitq object. The thread blocked on the waitq is trying to
 *		receive on the mqueue.
 *	Conditions:
 *		The 'waitinfo->wait_type' value should already be set to
 *		kThreadWaitPortReceive.
 *	Note:
 *		If we find that we are actualy waiting on a port set, we reset
 *		the wait_type field to reflect this.
 */
void
kdp_mqueue_recv_find_owner(
	struct waitq                   *waitq,
	__assert_only event64_t         event,
	thread_waitinfo_v2_t           *waitinfo,
	struct ipc_service_port_label **isplp)
{
	assert(waitinfo->wait_type == kThreadWaitPortReceive);
	assert(event == IPC_MQUEUE_RECEIVE);

	waitinfo->owner = 0;

	if (waitq_type(waitq) == WQT_PORT_SET) {
		ipc_pset_t set = ips_from_waitq(waitq);

		zone_id_require(ZONE_ID_IPC_PORT_SET, sizeof(struct ipc_pset), set);

		/* Reset wait type to specify waiting on port set receive */
		waitinfo->wait_type = kThreadWaitPortSetReceive;
		waitinfo->context   = VM_KERNEL_UNSLIDE_OR_PERM(set);
		if (ips_mq_lock_held_kdp(set)) {
			waitinfo->owner = STACKSHOT_WAITOWNER_PSET_LOCKED;
		}
		/* There is no specific owner "at the other end" of a port set, so leave unset. */
	} else if (waitq_type(waitq) == WQT_PORT) {
		ipc_port_t port = ip_from_waitq(waitq);

		zone_id_require(ZONE_ID_IPC_PORT, sizeof(struct ipc_port), port);

		waitinfo->context = VM_KERNEL_UNSLIDE_OR_PERM(port);
		if (ip_mq_lock_held_kdp(port)) {
			waitinfo->owner = STACKSHOT_WAITOWNER_PORT_LOCKED;
			return;
		}

		if (ip_active(port)) {
			if (ip_in_a_space(port)) { /* no port lock needed */
				waitinfo->owner = ip_get_receiver_name(port);
			} else {
				waitinfo->owner = STACKSHOT_WAITOWNER_INTRANSIT;
			}
			if (port->ip_specialreply) {
				waitinfo->wait_flags |= STACKSHOT_WAITINFO_FLAGS_SPECIALREPLY;
			}
			if (port->ip_splabel != NULL) {
				*isplp = (struct ipc_service_port_label *)port->ip_splabel;
			}
		}
	}
}

void
ipc_port_set_label(
	ipc_port_t              port,
	ipc_label_t             label)
{
	ipc_kobject_label_t labelp;

	assert(!ip_is_kolabeled(port));

	labelp = zalloc_flags(ipc_kobject_label_zone, Z_WAITOK | Z_ZERO | Z_NOFAIL);
	labelp->ikol_label = label;

	port->ip_kolabel = labelp;
	io_bits_or(ip_to_object(port), IO_BITS_KOLABEL);
}

kern_return_t
ipc_port_reset_thread_attr(
	ipc_port_t port)
{
	uint8_t iotier = THROTTLE_LEVEL_END;
	uint8_t qos = THREAD_QOS_UNSPECIFIED;

	return ipc_port_update_qos_n_iotier(port, qos, iotier);
}

kern_return_t
ipc_port_propagate_thread_attr(
	ipc_port_t port,
	struct thread_attr_for_ipc_propagation attr)
{
	uint8_t iotier = attr.tafip_iotier;
	uint8_t qos = attr.tafip_qos;

	return ipc_port_update_qos_n_iotier(port, qos, iotier);
}

static kern_return_t
ipc_port_update_qos_n_iotier(
	ipc_port_t port,
	uint8_t    qos,
	uint8_t    iotier)
{
	if (port == IPC_PORT_NULL) {
		return KERN_INVALID_ARGUMENT;
	}

	ip_mq_lock(port);

	if (!ip_active(port)) {
		ip_mq_unlock(port);
		return KERN_TERMINATED;
	}

	if (port->ip_specialreply) {
		ip_mq_unlock(port);
		return KERN_INVALID_ARGUMENT;
	}

	port->ip_kernel_iotier_override = iotier;
	port->ip_kernel_qos_override = qos;

	if (ip_in_a_space(port) &&
	    is_active(ip_get_receiver(port)) &&
	    ipc_port_has_klist(port)) {
		KNOTE(&port->ip_klist, 0);
	}

	ip_mq_unlock(port);
	return KERN_SUCCESS;
}

#if MACH_ASSERT
#include <kern/machine.h>

unsigned long   port_count = 0;
unsigned long   port_count_warning = 20000;
unsigned long   port_timestamp = 0;

void            db_port_stack_trace(
	ipc_port_t      port);
void            db_ref(
	int             refs);
int             db_port_walk(
	unsigned int    verbose,
	unsigned int    display,
	unsigned int    ref_search,
	unsigned int    ref_target);

#ifdef MACH_BSD
extern int proc_pid(struct proc*);
#endif /* MACH_BSD */

/*
 *	Initialize all of the debugging state in a port.
 *	Insert the port into a global list of all allocated ports.
 */
void
ipc_port_init_debug(ipc_port_t port, void *fp)
{
	port->ip_timetrack = port_timestamp++;

	if (ipc_portbt) {
		port->ip_made_bt = btref_get(fp, 0);
	}

#ifdef MACH_BSD
	task_t task = current_task_early();
	if (task != TASK_NULL) {
		struct proc *proc = get_bsdtask_info(task);
		if (proc) {
			port->ip_made_pid = proc_pid(proc);
		}
	}
#endif /* MACH_BSD */
}

#endif  /* MACH_ASSERT */