xref: /freebsd/sys/vm/vm_map.c (revision 17ee9d00bc1ae1e598c38f25826f861e4bc6c3ce)

/*
 * Copyright (c) 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * The Mach Operating System project at Carnegie-Mellon University.
 *
 * 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.
 *
 *	from: @(#)vm_map.c	8.3 (Berkeley) 1/12/94
 *
 *
 * Copyright (c) 1987, 1990 Carnegie-Mellon University.
 * All rights reserved.
 *
 * Authors: Avadis Tevanian, Jr., Michael Wayne Young
 *
 * 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  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie the
 * rights to redistribute these changes.
 *
 * $Id: vm_map.c,v 1.14 1995/02/14 04:00:17 davidg Exp $
 */

/*
 *	Virtual memory mapping module.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>

#include <vm/vm.h>
#include <vm/vm_page.h>
#include <vm/vm_object.h>
#include <vm/vm_kern.h>

/*
 *	Virtual memory maps provide for the mapping, protection,
 *	and sharing of virtual memory objects.  In addition,
 *	this module provides for an efficient virtual copy of
 *	memory from one map to another.
 *
 *	Synchronization is required prior to most operations.
 *
 *	Maps consist of an ordered doubly-linked list of simple
 *	entries; a single hint is used to speed up lookups.
 *
 *	In order to properly represent the sharing of virtual
 *	memory regions among maps, the map structure is bi-level.
 *	Top-level ("address") maps refer to regions of sharable
 *	virtual memory.  These regions are implemented as
 *	("sharing") maps, which then refer to the actual virtual
 *	memory objects.  When two address maps "share" memory,
 *	their top-level maps both have references to the same
 *	sharing map.  When memory is virtual-copied from one
 *	address map to another, the references in the sharing
 *	maps are actually copied -- no copying occurs at the
 *	virtual memory object level.
 *
 *	Since portions of maps are specified by start/end addreses,
 *	which may not align with existing map entries, all
 *	routines merely "clip" entries to these start/end values.
 *	[That is, an entry is split into two, bordering at a
 *	start or end value.]  Note that these clippings may not
 *	always be necessary (as the two resulting entries are then
 *	not changed); however, the clipping is done for convenience.
 *	No attempt is currently made to "glue back together" two
 *	abutting entries.
 *
 *	As mentioned above, virtual copy operations are performed
 *	by copying VM object references from one sharing map to
 *	another, and then marking both regions as copy-on-write.
 *	It is important to note that only one writeable reference
 *	to a VM object region exists in any map -- this means that
 *	shadow object creation can be delayed until a write operation
 *	occurs.
 */

/*
 *	vm_map_startup:
 *
 *	Initialize the vm_map module.  Must be called before
 *	any other vm_map routines.
 *
 *	Map and entry structures are allocated from the general
 *	purpose memory pool with some exceptions:
 *
 *	- The kernel map and kmem submap are allocated statically.
 *	- Kernel map entries are allocated out of a static pool.
 *
 *	These restrictions are necessary since malloc() uses the
 *	maps and requires map entries.
 */

vm_offset_t kentry_data;
vm_size_t kentry_data_size;
vm_map_entry_t kentry_free;
vm_map_t kmap_free;

int kentry_count;
static vm_offset_t mapvm_start = 0, mapvm = 0, mapvmmax;
static int mapvmpgcnt = 0;

static void _vm_map_clip_end __P((vm_map_t, vm_map_entry_t, vm_offset_t));
static void _vm_map_clip_start __P((vm_map_t, vm_map_entry_t, vm_offset_t));

void
vm_map_startup()
{
	register int i;
	register vm_map_entry_t mep;
	vm_map_t mp;

	/*
	 * Static map structures for allocation before initialization of
	 * kernel map or kmem map.  vm_map_create knows how to deal with them.
	 */
	kmap_free = mp = (vm_map_t) kentry_data;
	i = MAX_KMAP;
	while (--i > 0) {
		mp->header.next = (vm_map_entry_t) (mp + 1);
		mp++;
	}
	mp++->header.next = NULL;

	/*
	 * Form a free list of statically allocated kernel map entries with
	 * the rest.
	 */
	kentry_free = mep = (vm_map_entry_t) mp;
	kentry_count = i = (kentry_data_size - MAX_KMAP * sizeof *mp) / sizeof *mep;
	while (--i > 0) {
		mep->next = mep + 1;
		mep++;
	}
	mep->next = NULL;
}

/*
 * Allocate a vmspace structure, including a vm_map and pmap,
 * and initialize those structures.  The refcnt is set to 1.
 * The remaining fields must be initialized by the caller.
 */
struct vmspace *
vmspace_alloc(min, max, pageable)
	vm_offset_t min, max;
	int pageable;
{
	register struct vmspace *vm;

	if (mapvmpgcnt == 0 && mapvm == 0) {
		int s;

		mapvmpgcnt = (cnt.v_page_count * sizeof(struct vm_map_entry) + PAGE_SIZE - 1) / PAGE_SIZE;
		s = splhigh();
		mapvm_start = mapvm = kmem_alloc_pageable(kmem_map, mapvmpgcnt * PAGE_SIZE);
		mapvmmax = mapvm_start + mapvmpgcnt * PAGE_SIZE;
		splx(s);
		if (!mapvm)
			mapvmpgcnt = 0;
	}
	MALLOC(vm, struct vmspace *, sizeof(struct vmspace), M_VMMAP, M_WAITOK);
	bzero(vm, (caddr_t) &vm->vm_startcopy - (caddr_t) vm);
	vm_map_init(&vm->vm_map, min, max, pageable);
	pmap_pinit(&vm->vm_pmap);
	vm->vm_map.pmap = &vm->vm_pmap;	/* XXX */
	vm->vm_refcnt = 1;
	return (vm);
}

void
vmspace_free(vm)
	register struct vmspace *vm;
{

	if (vm->vm_refcnt == 0)
		panic("vmspace_free: attempt to free already freed vmspace");

	if (--vm->vm_refcnt == 0) {
		/*
		 * Lock the map, to wait out all other references to it.
		 * Delete all of the mappings and pages they hold, then call
		 * the pmap module to reclaim anything left.
		 */
		vm_map_lock(&vm->vm_map);
		(void) vm_map_delete(&vm->vm_map, vm->vm_map.min_offset,
		    vm->vm_map.max_offset);
		vm_map_unlock(&vm->vm_map);
		while( vm->vm_map.ref_count != 1)
			tsleep(&vm->vm_map.ref_count, PVM, "vmsfre", 0);
		--vm->vm_map.ref_count;
		pmap_release(&vm->vm_pmap);
		FREE(vm, M_VMMAP);
	}
}

/*
 *	vm_map_create:
 *
 *	Creates and returns a new empty VM map with
 *	the given physical map structure, and having
 *	the given lower and upper address bounds.
 */
vm_map_t
vm_map_create(pmap, min, max, pageable)
	pmap_t pmap;
	vm_offset_t min, max;
	boolean_t pageable;
{
	register vm_map_t result;

	if (kmem_map == NULL) {
		result = kmap_free;
		kmap_free = (vm_map_t) result->header.next;
		if (result == NULL)
			panic("vm_map_create: out of maps");
	} else
		MALLOC(result, vm_map_t, sizeof(struct vm_map),
		    M_VMMAP, M_WAITOK);

	vm_map_init(result, min, max, pageable);
	result->pmap = pmap;
	return (result);
}

/*
 * Initialize an existing vm_map structure
 * such as that in the vmspace structure.
 * The pmap is set elsewhere.
 */
void
vm_map_init(map, min, max, pageable)
	register struct vm_map *map;
	vm_offset_t min, max;
	boolean_t pageable;
{
	map->header.next = map->header.prev = &map->header;
	map->nentries = 0;
	map->size = 0;
	map->ref_count = 1;
	map->is_main_map = TRUE;
	map->min_offset = min;
	map->max_offset = max;
	map->entries_pageable = pageable;
	map->first_free = &map->header;
	map->hint = &map->header;
	map->timestamp = 0;
	lock_init(&map->lock, TRUE);
	simple_lock_init(&map->ref_lock);
	simple_lock_init(&map->hint_lock);
}

/*
 *	vm_map_entry_create:	[ internal use only ]
 *
 *	Allocates a VM map entry for insertion.
 *	No entry fields are filled in.  This routine is
 */
static struct vm_map_entry *mappool;
static int mappoolcnt;

vm_map_entry_t
vm_map_entry_create(map)
	vm_map_t map;
{
	vm_map_entry_t entry;
	int i;

#define KENTRY_LOW_WATER 64
#define MAPENTRY_LOW_WATER 128

	/*
	 * This is a *very* nasty (and sort of incomplete) hack!!!!
	 */
	if (kentry_count < KENTRY_LOW_WATER) {
		if (mapvmpgcnt && mapvm) {
			vm_page_t m;

			m = vm_page_alloc(kmem_object,
			        mapvm - vm_map_min(kmem_map),
				    (map == kmem_map) ? VM_ALLOC_INTERRUPT : VM_ALLOC_NORMAL);
			if (m) {
				int newentries;

				newentries = (NBPG / sizeof(struct vm_map_entry));
				vm_page_wire(m);
				m->flags &= ~PG_BUSY;
				m->valid = VM_PAGE_BITS_ALL;
				pmap_enter(vm_map_pmap(kmem_map), mapvm,
				    VM_PAGE_TO_PHYS(m), VM_PROT_DEFAULT, 1);

				entry = (vm_map_entry_t) mapvm;
				mapvm += NBPG;
				--mapvmpgcnt;

				for (i = 0; i < newentries; i++) {
					vm_map_entry_dispose(kernel_map, entry);
					entry++;
				}
			}
		}
	}
	if (map == kernel_map || map == kmem_map || map == pager_map) {

		entry = kentry_free;
		if (entry) {
			kentry_free = entry->next;
			--kentry_count;
			return entry;
		}
		entry = mappool;
		if (entry) {
			mappool = entry->next;
			--mappoolcnt;
			return entry;
		}
	} else {
		entry = mappool;
		if (entry) {
			mappool = entry->next;
			--mappoolcnt;
			return entry;
		}
		MALLOC(entry, vm_map_entry_t, sizeof(struct vm_map_entry),
		    M_VMMAPENT, M_WAITOK);
	}
	if (entry == NULL)
		panic("vm_map_entry_create: out of map entries");

	return (entry);
}

/*
 *	vm_map_entry_dispose:	[ internal use only ]
 *
 *	Inverse of vm_map_entry_create.
 */
void
vm_map_entry_dispose(map, entry)
	vm_map_t map;
	vm_map_entry_t entry;
{
	if ((kentry_count < KENTRY_LOW_WATER) ||
	    ((vm_offset_t) entry >= kentry_data && (vm_offset_t) entry < (kentry_data + kentry_data_size)) ||
	    ((vm_offset_t) entry >= mapvm_start && (vm_offset_t) entry < mapvmmax)) {
		entry->next = kentry_free;
		kentry_free = entry;
		++kentry_count;
		return;
	} else {
		if (mappoolcnt < MAPENTRY_LOW_WATER) {
			entry->next = mappool;
			mappool = entry;
			++mappoolcnt;
			return;
		}
		FREE(entry, M_VMMAPENT);
	}
}

/*
 *	vm_map_entry_{un,}link:
 *
 *	Insert/remove entries from maps.
 */
#define	vm_map_entry_link(map, after_where, entry) \
		{ \
		(map)->nentries++; \
		(entry)->prev = (after_where); \
		(entry)->next = (after_where)->next; \
		(entry)->prev->next = (entry); \
		(entry)->next->prev = (entry); \
		}
#define	vm_map_entry_unlink(map, entry) \
		{ \
		(map)->nentries--; \
		(entry)->next->prev = (entry)->prev; \
		(entry)->prev->next = (entry)->next; \
		}

/*
 *	vm_map_reference:
 *
 *	Creates another valid reference to the given map.
 *
 */
void
vm_map_reference(map)
	register vm_map_t map;
{
	if (map == NULL)
		return;

	simple_lock(&map->ref_lock);
	map->ref_count++;
	simple_unlock(&map->ref_lock);
}

/*
 *	vm_map_deallocate:
 *
 *	Removes a reference from the specified map,
 *	destroying it if no references remain.
 *	The map should not be locked.
 */
void
vm_map_deallocate(map)
	register vm_map_t map;
{
	register int c;

	if (map == NULL)
		return;

	simple_lock(&map->ref_lock);
	c = map->ref_count;
	simple_unlock(&map->ref_lock);

	if (c == 0)
		panic("vm_map_deallocate: deallocating already freed map");

	if (c != 1) {
		--map->ref_count;
		wakeup((caddr_t) &map->ref_count);
		return;
	}
	/*
	 * Lock the map, to wait out all other references to it.
	 */

	vm_map_lock(map);
	(void) vm_map_delete(map, map->min_offset, map->max_offset);
	--map->ref_count;
	if( map->ref_count != 0) {
		vm_map_unlock(map);
		return;
	}

	pmap_destroy(map->pmap);
	FREE(map, M_VMMAP);
}

/*
 *	vm_map_insert:
 *
 *	Inserts the given whole VM object into the target
 *	map at the specified address range.  The object's
 *	size should match that of the address range.
 *
 *	Requires that the map be locked, and leaves it so.
 */
int
vm_map_insert(map, object, offset, start, end)
	vm_map_t map;
	vm_object_t object;
	vm_offset_t offset;
	vm_offset_t start;
	vm_offset_t end;
{
	register vm_map_entry_t new_entry;
	register vm_map_entry_t prev_entry;
	vm_map_entry_t temp_entry;

	/*
	 * Check that the start and end points are not bogus.
	 */

	if ((start < map->min_offset) || (end > map->max_offset) ||
	    (start >= end))
		return (KERN_INVALID_ADDRESS);

	/*
	 * Find the entry prior to the proposed starting address; if it's part
	 * of an existing entry, this range is bogus.
	 */

	if (vm_map_lookup_entry(map, start, &temp_entry))
		return (KERN_NO_SPACE);

	prev_entry = temp_entry;

	/*
	 * Assert that the next entry doesn't overlap the end point.
	 */

	if ((prev_entry->next != &map->header) &&
	    (prev_entry->next->start < end))
		return (KERN_NO_SPACE);

	/*
	 * See if we can avoid creating a new entry by extending one of our
	 * neighbors.
	 */

	if (object == NULL) {
		if ((prev_entry != &map->header) &&
		    (prev_entry->end == start) &&
		    (map->is_main_map) &&
		    (prev_entry->is_a_map == FALSE) &&
		    (prev_entry->is_sub_map == FALSE) &&
		    (prev_entry->inheritance == VM_INHERIT_DEFAULT) &&
		    (prev_entry->protection == VM_PROT_DEFAULT) &&
		    (prev_entry->max_protection == VM_PROT_DEFAULT) &&
		    (prev_entry->wired_count == 0)) {

			if (vm_object_coalesce(prev_entry->object.vm_object,
				NULL,
				prev_entry->offset,
				(vm_offset_t) 0,
				(vm_size_t) (prev_entry->end
				    - prev_entry->start),
				(vm_size_t) (end - prev_entry->end))) {
				/*
				 * Coalesced the two objects - can extend the
				 * previous map entry to include the new
				 * range.
				 */
				map->size += (end - prev_entry->end);
				prev_entry->end = end;
				return (KERN_SUCCESS);
			}
		}
	}
	/*
	 * Create a new entry
	 */

	new_entry = vm_map_entry_create(map);
	new_entry->start = start;
	new_entry->end = end;

	new_entry->is_a_map = FALSE;
	new_entry->is_sub_map = FALSE;
	new_entry->object.vm_object = object;
	new_entry->offset = offset;

	new_entry->copy_on_write = FALSE;
	new_entry->needs_copy = FALSE;

	if (map->is_main_map) {
		new_entry->inheritance = VM_INHERIT_DEFAULT;
		new_entry->protection = VM_PROT_DEFAULT;
		new_entry->max_protection = VM_PROT_DEFAULT;
		new_entry->wired_count = 0;
	}
	/*
	 * Insert the new entry into the list
	 */

	vm_map_entry_link(map, prev_entry, new_entry);
	map->size += new_entry->end - new_entry->start;

	/*
	 * Update the free space hint
	 */

	if ((map->first_free == prev_entry) && (prev_entry->end >= new_entry->start))
		map->first_free = new_entry;

	return (KERN_SUCCESS);
}

/*
 *	SAVE_HINT:
 *
 *	Saves the specified entry as the hint for
 *	future lookups.  Performs necessary interlocks.
 */
#define	SAVE_HINT(map,value) \
		simple_lock(&(map)->hint_lock); \
		(map)->hint = (value); \
		simple_unlock(&(map)->hint_lock);

/*
 *	vm_map_lookup_entry:	[ internal use only ]
 *
 *	Finds the map entry containing (or
 *	immediately preceding) the specified address
 *	in the given map; the entry is returned
 *	in the "entry" parameter.  The boolean
 *	result indicates whether the address is
 *	actually contained in the map.
 */
boolean_t
vm_map_lookup_entry(map, address, entry)
	register vm_map_t map;
	register vm_offset_t address;
	vm_map_entry_t *entry;	/* OUT */
{
	register vm_map_entry_t cur;
	register vm_map_entry_t last;

	/*
	 * Start looking either from the head of the list, or from the hint.
	 */

	simple_lock(&map->hint_lock);
	cur = map->hint;
	simple_unlock(&map->hint_lock);

	if (cur == &map->header)
		cur = cur->next;

	if (address >= cur->start) {
		/*
		 * Go from hint to end of list.
		 *
		 * But first, make a quick check to see if we are already looking
		 * at the entry we want (which is usually the case). Note also
		 * that we don't need to save the hint here... it is the same
		 * hint (unless we are at the header, in which case the hint
		 * didn't buy us anything anyway).
		 */
		last = &map->header;
		if ((cur != last) && (cur->end > address)) {
			*entry = cur;
			return (TRUE);
		}
	} else {
		/*
		 * Go from start to hint, *inclusively*
		 */
		last = cur->next;
		cur = map->header.next;
	}

	/*
	 * Search linearly
	 */

	while (cur != last) {
		if (cur->end > address) {
			if (address >= cur->start) {
				/*
				 * Save this lookup for future hints, and
				 * return
				 */

				*entry = cur;
				SAVE_HINT(map, cur);
				return (TRUE);
			}
			break;
		}
		cur = cur->next;
	}
	*entry = cur->prev;
	SAVE_HINT(map, *entry);
	return (FALSE);
}

/*
 * Find sufficient space for `length' bytes in the given map, starting at
 * `start'.  The map must be locked.  Returns 0 on success, 1 on no space.
 */
int
vm_map_findspace(map, start, length, addr)
	register vm_map_t map;
	register vm_offset_t start;
	vm_size_t length;
	vm_offset_t *addr;
{
	register vm_map_entry_t entry, next;
	register vm_offset_t end;

	if (start < map->min_offset)
		start = map->min_offset;
	if (start > map->max_offset)
		return (1);

	/*
	 * Look for the first possible address; if there's already something
	 * at this address, we have to start after it.
	 */
	if (start == map->min_offset) {
		if ((entry = map->first_free) != &map->header)
			start = entry->end;
	} else {
		vm_map_entry_t tmp;

		if (vm_map_lookup_entry(map, start, &tmp))
			start = tmp->end;
		entry = tmp;
	}

	/*
	 * Look through the rest of the map, trying to fit a new region in the
	 * gap between existing regions, or after the very last region.
	 */
	for (;; start = (entry = next)->end) {
		/*
		 * Find the end of the proposed new region.  Be sure we didn't
		 * go beyond the end of the map, or wrap around the address;
		 * if so, we lose.  Otherwise, if this is the last entry, or
		 * if the proposed new region fits before the next entry, we
		 * win.
		 */
		end = start + length;
		if (end > map->max_offset || end < start)
			return (1);
		next = entry->next;
		if (next == &map->header || next->start >= end)
			break;
	}
	SAVE_HINT(map, entry);
	*addr = start;
	if (map == kernel_map && round_page(start + length) > kernel_vm_end)
		pmap_growkernel(round_page(start + length));
	return (0);
}

/*
 *	vm_map_find finds an unallocated region in the target address
 *	map with the given length.  The search is defined to be
 *	first-fit from the specified address; the region found is
 *	returned in the same parameter.
 *
 */
int
vm_map_find(map, object, offset, addr, length, find_space)
	vm_map_t map;
	vm_object_t object;
	vm_offset_t offset;
	vm_offset_t *addr;	/* IN/OUT */
	vm_size_t length;
	boolean_t find_space;
{
	register vm_offset_t start;
	int result, s = 0;

	start = *addr;
	vm_map_lock(map);

	if (map == kmem_map)
		s = splhigh();

	if (find_space) {
		if (vm_map_findspace(map, start, length, addr)) {
			vm_map_unlock(map);
			if (map == kmem_map)
				splx(s);
			return (KERN_NO_SPACE);
		}
		start = *addr;
	}
	result = vm_map_insert(map, object, offset, start, start + length);
	vm_map_unlock(map);

	if (map == kmem_map)
		splx(s);

	return (result);
}

/*
 *	vm_map_simplify_entry:	[ internal use only ]
 *
 *	Simplify the given map entry by:
 *		removing extra sharing maps
 *		[XXX maybe later] merging with a neighbor
 */
void
vm_map_simplify_entry(map, entry)
	vm_map_t map;
	vm_map_entry_t entry;
{
#ifdef	lint
	map++;
#endif

	/*
	 * If this entry corresponds to a sharing map, then see if we can
	 * remove the level of indirection. If it's not a sharing map, then it
	 * points to a VM object, so see if we can merge with either of our
	 * neighbors.
	 */

	if (entry->is_sub_map)
		return;
	if (entry->is_a_map) {
#if	0
		vm_map_t my_share_map;
		int count;

		my_share_map = entry->object.share_map;
		simple_lock(&my_share_map->ref_lock);
		count = my_share_map->ref_count;
		simple_unlock(&my_share_map->ref_lock);

		if (count == 1) {
			/*
			 * Can move the region from entry->start to entry->end
			 * (+ entry->offset) in my_share_map into place of
			 * entry. Later.
			 */
		}
#endif
	} else {
		/*
		 * Try to merge with our neighbors.
		 *
		 * Conditions for merge are:
		 *
		 * 1.  entries are adjacent. 2.  both entries point to objects
		 * with null pagers.
		 *
		 * If a merge is possible, we replace the two entries with a
		 * single entry, then merge the two objects into a single
		 * object.
		 *
		 * Now, all that is left to do is write the code!
		 */
	}
}

/*
 *	vm_map_clip_start:	[ internal use only ]
 *
 *	Asserts that the given entry begins at or after
 *	the specified address; if necessary,
 *	it splits the entry into two.
 */
#define vm_map_clip_start(map, entry, startaddr) \
{ \
	if (startaddr > entry->start) \
		_vm_map_clip_start(map, entry, startaddr); \
}

/*
 *	This routine is called only when it is known that
 *	the entry must be split.
 */
static void
_vm_map_clip_start(map, entry, start)
	register vm_map_t map;
	register vm_map_entry_t entry;
	register vm_offset_t start;
{
	register vm_map_entry_t new_entry;

	/*
	 * See if we can simplify this entry first
	 */

	/* vm_map_simplify_entry(map, entry); */

	/*
	 * Split off the front portion -- note that we must insert the new
	 * entry BEFORE this one, so that this entry has the specified
	 * starting address.
	 */

	new_entry = vm_map_entry_create(map);
	*new_entry = *entry;

	new_entry->end = start;
	entry->offset += (start - entry->start);
	entry->start = start;

	vm_map_entry_link(map, entry->prev, new_entry);

	if (entry->is_a_map || entry->is_sub_map)
		vm_map_reference(new_entry->object.share_map);
	else
		vm_object_reference(new_entry->object.vm_object);
}

/*
 *	vm_map_clip_end:	[ internal use only ]
 *
 *	Asserts that the given entry ends at or before
 *	the specified address; if necessary,
 *	it splits the entry into two.
 */

#define vm_map_clip_end(map, entry, endaddr) \
{ \
	if (endaddr < entry->end) \
		_vm_map_clip_end(map, entry, endaddr); \
}

/*
 *	This routine is called only when it is known that
 *	the entry must be split.
 */
static void
_vm_map_clip_end(map, entry, end)
	register vm_map_t map;
	register vm_map_entry_t entry;
	register vm_offset_t end;
{
	register vm_map_entry_t new_entry;

	/*
	 * Create a new entry and insert it AFTER the specified entry
	 */

	new_entry = vm_map_entry_create(map);
	*new_entry = *entry;

	new_entry->start = entry->end = end;
	new_entry->offset += (end - entry->start);

	vm_map_entry_link(map, entry, new_entry);

	if (entry->is_a_map || entry->is_sub_map)
		vm_map_reference(new_entry->object.share_map);
	else
		vm_object_reference(new_entry->object.vm_object);
}

/*
 *	VM_MAP_RANGE_CHECK:	[ internal use only ]
 *
 *	Asserts that the starting and ending region
 *	addresses fall within the valid range of the map.
 */
#define	VM_MAP_RANGE_CHECK(map, start, end)		\
		{					\
		if (start < vm_map_min(map))		\
			start = vm_map_min(map);	\
		if (end > vm_map_max(map))		\
			end = vm_map_max(map);		\
		if (start > end)			\
			start = end;			\
		}

/*
 *	vm_map_submap:		[ kernel use only ]
 *
 *	Mark the given range as handled by a subordinate map.
 *
 *	This range must have been created with vm_map_find,
 *	and no other operations may have been performed on this
 *	range prior to calling vm_map_submap.
 *
 *	Only a limited number of operations can be performed
 *	within this rage after calling vm_map_submap:
 *		vm_fault
 *	[Don't try vm_map_copy!]
 *
 *	To remove a submapping, one must first remove the
 *	range from the superior map, and then destroy the
 *	submap (if desired).  [Better yet, don't try it.]
 */
int
vm_map_submap(map, start, end, submap)
	register vm_map_t map;
	register vm_offset_t start;
	register vm_offset_t end;
	vm_map_t submap;
{
	vm_map_entry_t entry;
	register int result = KERN_INVALID_ARGUMENT;

	vm_map_lock(map);

	VM_MAP_RANGE_CHECK(map, start, end);

	if (vm_map_lookup_entry(map, start, &entry)) {
		vm_map_clip_start(map, entry, start);
	} else
		entry = entry->next;

	vm_map_clip_end(map, entry, end);

	if ((entry->start == start) && (entry->end == end) &&
	    (!entry->is_a_map) &&
	    (entry->object.vm_object == NULL) &&
	    (!entry->copy_on_write)) {
		entry->is_a_map = FALSE;
		entry->is_sub_map = TRUE;
		vm_map_reference(entry->object.sub_map = submap);
		result = KERN_SUCCESS;
	}
	vm_map_unlock(map);

	return (result);
}

/*
 *	vm_map_protect:
 *
 *	Sets the protection of the specified address
 *	region in the target map.  If "set_max" is
 *	specified, the maximum protection is to be set;
 *	otherwise, only the current protection is affected.
 */
int
vm_map_protect(map, start, end, new_prot, set_max)
	register vm_map_t map;
	register vm_offset_t start;
	register vm_offset_t end;
	register vm_prot_t new_prot;
	register boolean_t set_max;
{
	register vm_map_entry_t current;
	vm_map_entry_t entry;

	vm_map_lock(map);

	VM_MAP_RANGE_CHECK(map, start, end);

	if (vm_map_lookup_entry(map, start, &entry)) {
		vm_map_clip_start(map, entry, start);
	} else
		entry = entry->next;

	/*
	 * Make a first pass to check for protection violations.
	 */

	current = entry;
	while ((current != &map->header) && (current->start < end)) {
		if (current->is_sub_map) {
			vm_map_unlock(map);
			return (KERN_INVALID_ARGUMENT);
		}
		if ((new_prot & current->max_protection) != new_prot) {
			vm_map_unlock(map);
			return (KERN_PROTECTION_FAILURE);
		}
		current = current->next;
	}

	/*
	 * Go back and fix up protections. [Note that clipping is not
	 * necessary the second time.]
	 */

	current = entry;

	while ((current != &map->header) && (current->start < end)) {
		vm_prot_t old_prot;

		vm_map_clip_end(map, current, end);

		old_prot = current->protection;
		if (set_max)
			current->protection =
			    (current->max_protection = new_prot) &
			    old_prot;
		else
			current->protection = new_prot;

		/*
		 * Update physical map if necessary. Worry about copy-on-write
		 * here -- CHECK THIS XXX
		 */

		if (current->protection != old_prot) {

#define MASK(entry)	((entry)->copy_on_write ? ~VM_PROT_WRITE : \
							VM_PROT_ALL)
#define	max(a,b)	((a) > (b) ? (a) : (b))

			if (current->is_a_map) {
				vm_map_entry_t share_entry;
				vm_offset_t share_end;

				vm_map_lock(current->object.share_map);
				(void) vm_map_lookup_entry(
				    current->object.share_map,
				    current->offset,
				    &share_entry);
				share_end = current->offset +
				    (current->end - current->start);
				while ((share_entry !=
					&current->object.share_map->header) &&
				    (share_entry->start < share_end)) {

					pmap_protect(map->pmap,
					    (max(share_entry->start,
						    current->offset) -
						current->offset +
						current->start),
					    min(share_entry->end,
						share_end) -
					    current->offset +
					    current->start,
					    current->protection &
					    MASK(share_entry));

					share_entry = share_entry->next;
				}
				vm_map_unlock(current->object.share_map);
			} else
				pmap_protect(map->pmap, current->start,
				    current->end,
				    current->protection & MASK(entry));
#undef	max
#undef	MASK
		}
		current = current->next;
	}

	vm_map_unlock(map);
	return (KERN_SUCCESS);
}

/*
 *	vm_map_inherit:
 *
 *	Sets the inheritance of the specified address
 *	range in the target map.  Inheritance
 *	affects how the map will be shared with
 *	child maps at the time of vm_map_fork.
 */
int
vm_map_inherit(map, start, end, new_inheritance)
	register vm_map_t map;
	register vm_offset_t start;
	register vm_offset_t end;
	register vm_inherit_t new_inheritance;
{
	register vm_map_entry_t entry;
	vm_map_entry_t temp_entry;

	switch (new_inheritance) {
	case VM_INHERIT_NONE:
	case VM_INHERIT_COPY:
	case VM_INHERIT_SHARE:
		break;
	default:
		return (KERN_INVALID_ARGUMENT);
	}

	vm_map_lock(map);

	VM_MAP_RANGE_CHECK(map, start, end);

	if (vm_map_lookup_entry(map, start, &temp_entry)) {
		entry = temp_entry;
		vm_map_clip_start(map, entry, start);
	} else
		entry = temp_entry->next;

	while ((entry != &map->header) && (entry->start < end)) {
		vm_map_clip_end(map, entry, end);

		entry->inheritance = new_inheritance;

		entry = entry->next;
	}

	vm_map_unlock(map);
	return (KERN_SUCCESS);
}

/*
 *	vm_map_pageable:
 *
 *	Sets the pageability of the specified address
 *	range in the target map.  Regions specified
 *	as not pageable require locked-down physical
 *	memory and physical page maps.
 *
 *	The map must not be locked, but a reference
 *	must remain to the map throughout the call.
 */
int
vm_map_pageable(map, start, end, new_pageable)
	register vm_map_t map;
	register vm_offset_t start;
	register vm_offset_t end;
	register boolean_t new_pageable;
{
	register vm_map_entry_t entry;
	vm_map_entry_t start_entry;
	register vm_offset_t failed = 0;
	int rv;

	vm_map_lock(map);

	VM_MAP_RANGE_CHECK(map, start, end);

	/*
	 * Only one pageability change may take place at one time, since
	 * vm_fault assumes it will be called only once for each
	 * wiring/unwiring.  Therefore, we have to make sure we're actually
	 * changing the pageability for the entire region.  We do so before
	 * making any changes.
	 */

	if (vm_map_lookup_entry(map, start, &start_entry) == FALSE) {
		vm_map_unlock(map);
		return (KERN_INVALID_ADDRESS);
	}
	entry = start_entry;

	/*
	 * Actions are rather different for wiring and unwiring, so we have
	 * two separate cases.
	 */

	if (new_pageable) {

		vm_map_clip_start(map, entry, start);

		/*
		 * Unwiring.  First ensure that the range to be unwired is
		 * really wired down and that there are no holes.
		 */
		while ((entry != &map->header) && (entry->start < end)) {

			if (entry->wired_count == 0 ||
			    (entry->end < end &&
				(entry->next == &map->header ||
				    entry->next->start > entry->end))) {
				vm_map_unlock(map);
				return (KERN_INVALID_ARGUMENT);
			}
			entry = entry->next;
		}

		/*
		 * Now decrement the wiring count for each region. If a region
		 * becomes completely unwired, unwire its physical pages and
		 * mappings.
		 */
		lock_set_recursive(&map->lock);

		entry = start_entry;
		while ((entry != &map->header) && (entry->start < end)) {
			vm_map_clip_end(map, entry, end);

			entry->wired_count--;
			if (entry->wired_count == 0)
				vm_fault_unwire(map, entry->start, entry->end);

			entry = entry->next;
		}
		lock_clear_recursive(&map->lock);
	} else {
		/*
		 * Wiring.  We must do this in two passes:
		 *
		 * 1.  Holding the write lock, we create any shadow or zero-fill
		 * objects that need to be created. Then we clip each map
		 * entry to the region to be wired and increment its wiring
		 * count.  We create objects before clipping the map entries
		 * to avoid object proliferation.
		 *
		 * 2.  We downgrade to a read lock, and call vm_fault_wire to
		 * fault in the pages for any newly wired area (wired_count is
		 * 1).
		 *
		 * Downgrading to a read lock for vm_fault_wire avoids a possible
		 * deadlock with another thread that may have faulted on one
		 * of the pages to be wired (it would mark the page busy,
		 * blocking us, then in turn block on the map lock that we
		 * hold).  Because of problems in the recursive lock package,
		 * we cannot upgrade to a write lock in vm_map_lookup.  Thus,
		 * any actions that require the write lock must be done
		 * beforehand.  Because we keep the read lock on the map, the
		 * copy-on-write status of the entries we modify here cannot
		 * change.
		 */

		/*
		 * Pass 1.
		 */
		while ((entry != &map->header) && (entry->start < end)) {
			if (entry->wired_count == 0) {

				/*
				 * Perform actions of vm_map_lookup that need
				 * the write lock on the map: create a shadow
				 * object for a copy-on-write region, or an
				 * object for a zero-fill region.
				 *
				 * We don't have to do this for entries that
				 * point to sharing maps, because we won't
				 * hold the lock on the sharing map.
				 */
				if (!entry->is_a_map && !entry->is_sub_map) {
					if (entry->needs_copy &&
					    ((entry->protection & VM_PROT_WRITE) != 0)) {

						vm_object_shadow(&entry->object.vm_object,
						    &entry->offset,
						    (vm_size_t) (entry->end
							- entry->start));
						entry->needs_copy = FALSE;
					} else if (entry->object.vm_object == NULL) {
						entry->object.vm_object =
						    vm_object_allocate((vm_size_t) (entry->end
							- entry->start));
						entry->offset = (vm_offset_t) 0;
					}
				}
			}
			vm_map_clip_start(map, entry, start);
			vm_map_clip_end(map, entry, end);
			entry->wired_count++;

			/*
			 * Check for holes
			 */
			if (entry->end < end &&
			    (entry->next == &map->header ||
				entry->next->start > entry->end)) {
				/*
				 * Found one.  Object creation actions do not
				 * need to be undone, but the wired counts
				 * need to be restored.
				 */
				while (entry != &map->header && entry->end > start) {
					entry->wired_count--;
					entry = entry->prev;
				}
				vm_map_unlock(map);
				return (KERN_INVALID_ARGUMENT);
			}
			entry = entry->next;
		}

		/*
		 * Pass 2.
		 */

		/*
		 * HACK HACK HACK HACK
		 *
		 * If we are wiring in the kernel map or a submap of it, unlock
		 * the map to avoid deadlocks.  We trust that the kernel
		 * threads are well-behaved, and therefore will not do
		 * anything destructive to this region of the map while we
		 * have it unlocked.  We cannot trust user threads to do the
		 * same.
		 *
		 * HACK HACK HACK HACK
		 */
		if (vm_map_pmap(map) == kernel_pmap) {
			vm_map_unlock(map);	/* trust me ... */
		} else {
			lock_set_recursive(&map->lock);
			lock_write_to_read(&map->lock);
		}

		rv = 0;
		entry = start_entry;
		while (entry != &map->header && entry->start < end) {
			/*
			 * If vm_fault_wire fails for any page we need to undo
			 * what has been done.  We decrement the wiring count
			 * for those pages which have not yet been wired (now)
			 * and unwire those that have (later).
			 *
			 * XXX this violates the locking protocol on the map,
			 * needs to be fixed.
			 */
			if (rv)
				entry->wired_count--;
			else if (entry->wired_count == 1) {
				rv = vm_fault_wire(map, entry->start, entry->end);
				if (rv) {
					failed = entry->start;
					entry->wired_count--;
				}
			}
			entry = entry->next;
		}

		if (vm_map_pmap(map) == kernel_pmap) {
			vm_map_lock(map);
		} else {
			lock_clear_recursive(&map->lock);
		}
		if (rv) {
			vm_map_unlock(map);
			(void) vm_map_pageable(map, start, failed, TRUE);
			return (rv);
		}
	}

	vm_map_unlock(map);

	return (KERN_SUCCESS);
}

/*
 * vm_map_clean
 *
 * Push any dirty cached pages in the address range to their pager.
 * If syncio is TRUE, dirty pages are written synchronously.
 * If invalidate is TRUE, any cached pages are freed as well.
 *
 * Returns an error if any part of the specified range is not mapped.
 */
int
vm_map_clean(map, start, end, syncio, invalidate)
	vm_map_t map;
	vm_offset_t start;
	vm_offset_t end;
	boolean_t syncio;
	boolean_t invalidate;
{
	register vm_map_entry_t current;
	vm_map_entry_t entry;
	vm_size_t size;
	vm_object_t object;
	vm_offset_t offset;

	vm_map_lock_read(map);
	VM_MAP_RANGE_CHECK(map, start, end);
	if (!vm_map_lookup_entry(map, start, &entry)) {
		vm_map_unlock_read(map);
		return (KERN_INVALID_ADDRESS);
	}
	/*
	 * Make a first pass to check for holes.
	 */
	for (current = entry; current->start < end; current = current->next) {
		if (current->is_sub_map) {
			vm_map_unlock_read(map);
			return (KERN_INVALID_ARGUMENT);
		}
		if (end > current->end &&
		    (current->next == &map->header ||
			current->end != current->next->start)) {
			vm_map_unlock_read(map);
			return (KERN_INVALID_ADDRESS);
		}
	}

	/*
	 * Make a second pass, cleaning/uncaching pages from the indicated
	 * objects as we go.
	 */
	for (current = entry; current->start < end; current = current->next) {
		offset = current->offset + (start - current->start);
		size = (end <= current->end ? end : current->end) - start;
		if (current->is_a_map || current->is_sub_map) {
			register vm_map_t smap;
			vm_map_entry_t tentry;
			vm_size_t tsize;

			smap = current->object.share_map;
			vm_map_lock_read(smap);
			(void) vm_map_lookup_entry(smap, offset, &tentry);
			tsize = tentry->end - offset;
			if (tsize < size)
				size = tsize;
			object = tentry->object.vm_object;
			offset = tentry->offset + (offset - tentry->start);
			vm_map_unlock_read(smap);
		} else {
			object = current->object.vm_object;
		}
		if (object && (object->pager != NULL) &&
		    (object->pager->pg_type == PG_VNODE)) {
			vm_object_lock(object);
			/*
			 * Flush pages if writing is allowed. XXX should we continue
			 * on an error?
			 */
			if ((current->protection & VM_PROT_WRITE) &&
		   	    !vm_object_page_clean(object, offset, offset + size,
			    syncio, FALSE)) {
				vm_object_unlock(object);
				vm_map_unlock_read(map);
				return (KERN_FAILURE);
			}
			if (invalidate)
				vm_object_page_remove(object, offset, offset + size);
			vm_object_unlock(object);
		}
		start += size;
	}

	vm_map_unlock_read(map);
	return (KERN_SUCCESS);
}

/*
 *	vm_map_entry_unwire:	[ internal use only ]
 *
 *	Make the region specified by this entry pageable.
 *
 *	The map in question should be locked.
 *	[This is the reason for this routine's existence.]
 */
void
vm_map_entry_unwire(map, entry)
	vm_map_t map;
	register vm_map_entry_t entry;
{
	vm_fault_unwire(map, entry->start, entry->end);
	entry->wired_count = 0;
}

/*
 *	vm_map_entry_delete:	[ internal use only ]
 *
 *	Deallocate the given entry from the target map.
 */
void
vm_map_entry_delete(map, entry)
	register vm_map_t map;
	register vm_map_entry_t entry;
{
	if (entry->wired_count != 0)
		vm_map_entry_unwire(map, entry);

	vm_map_entry_unlink(map, entry);
	map->size -= entry->end - entry->start;

	if (entry->is_a_map || entry->is_sub_map)
		vm_map_deallocate(entry->object.share_map);
	else
		vm_object_deallocate(entry->object.vm_object);

	vm_map_entry_dispose(map, entry);
}

/*
 *	vm_map_delete:	[ internal use only ]
 *
 *	Deallocates the given address range from the target
 *	map.
 *
 *	When called with a sharing map, removes pages from
 *	that region from all physical maps.
 */
int
vm_map_delete(map, start, end)
	register vm_map_t map;
	vm_offset_t start;
	register vm_offset_t end;
{
	register vm_map_entry_t entry;
	vm_map_entry_t first_entry;

	/*
	 * Find the start of the region, and clip it
	 */

	if (!vm_map_lookup_entry(map, start, &first_entry))
		entry = first_entry->next;
	else {
		entry = first_entry;
		vm_map_clip_start(map, entry, start);

		/*
		 * Fix the lookup hint now, rather than each time though the
		 * loop.
		 */

		SAVE_HINT(map, entry->prev);
	}

	/*
	 * Save the free space hint
	 */

	if (map->first_free->start >= start)
		map->first_free = entry->prev;

	/*
	 * Step through all entries in this region
	 */

	while ((entry != &map->header) && (entry->start < end)) {
		vm_map_entry_t next;
		register vm_offset_t s, e;
		register vm_object_t object;

		vm_map_clip_end(map, entry, end);

		next = entry->next;
		s = entry->start;
		e = entry->end;

		/*
		 * Unwire before removing addresses from the pmap; otherwise,
		 * unwiring will put the entries back in the pmap.
		 */

		object = entry->object.vm_object;
		if (entry->wired_count != 0)
			vm_map_entry_unwire(map, entry);

		/*
		 * If this is a sharing map, we must remove *all* references
		 * to this data, since we can't find all of the physical maps
		 * which are sharing it.
		 */

		if (object == kernel_object || object == kmem_object)
			vm_object_page_remove(object, entry->offset,
			    entry->offset + (e - s));
		else if (!map->is_main_map)
			vm_object_pmap_remove(object,
			    entry->offset,
			    entry->offset + (e - s));
		else
			pmap_remove(map->pmap, s, e);

		/*
		 * Delete the entry (which may delete the object) only after
		 * removing all pmap entries pointing to its pages.
		 * (Otherwise, its page frames may be reallocated, and any
		 * modify bits will be set in the wrong object!)
		 */

		vm_map_entry_delete(map, entry);
		entry = next;
	}
	return (KERN_SUCCESS);
}

/*
 *	vm_map_remove:
 *
 *	Remove the given address range from the target map.
 *	This is the exported form of vm_map_delete.
 */
int
vm_map_remove(map, start, end)
	register vm_map_t map;
	register vm_offset_t start;
	register vm_offset_t end;
{
	register int result, s = 0;

	if (map == kmem_map)
		s = splhigh();

	vm_map_lock(map);
	VM_MAP_RANGE_CHECK(map, start, end);
	result = vm_map_delete(map, start, end);
	vm_map_unlock(map);

	if (map == kmem_map)
		splx(s);

	return (result);
}

/*
 *	vm_map_check_protection:
 *
 *	Assert that the target map allows the specified
 *	privilege on the entire address region given.
 *	The entire region must be allocated.
 */
boolean_t
vm_map_check_protection(map, start, end, protection)
	register vm_map_t map;
	register vm_offset_t start;
	register vm_offset_t end;
	register vm_prot_t protection;
{
	register vm_map_entry_t entry;
	vm_map_entry_t tmp_entry;

	if (!vm_map_lookup_entry(map, start, &tmp_entry)) {
		return (FALSE);
	}
	entry = tmp_entry;

	while (start < end) {
		if (entry == &map->header) {
			return (FALSE);
		}
		/*
		 * No holes allowed!
		 */

		if (start < entry->start) {
			return (FALSE);
		}
		/*
		 * Check protection associated with entry.
		 */

		if ((entry->protection & protection) != protection) {
			return (FALSE);
		}
		/* go to next entry */

		start = entry->end;
		entry = entry->next;
	}
	return (TRUE);
}

/*
 *	vm_map_copy_entry:
 *
 *	Copies the contents of the source entry to the destination
 *	entry.  The entries *must* be aligned properly.
 */
void
vm_map_copy_entry(src_map, dst_map, src_entry, dst_entry)
	vm_map_t src_map, dst_map;
	register vm_map_entry_t src_entry, dst_entry;
{
	vm_object_t temp_object;

	if (src_entry->is_sub_map || dst_entry->is_sub_map)
		return;

	if (dst_entry->object.vm_object != NULL &&
	    (dst_entry->object.vm_object->flags & OBJ_INTERNAL) == 0)
		printf("vm_map_copy_entry: copying over permanent data!\n");

	/*
	 * If our destination map was wired down, unwire it now.
	 */

	if (dst_entry->wired_count != 0)
		vm_map_entry_unwire(dst_map, dst_entry);

	/*
	 * If we're dealing with a sharing map, we must remove the destination
	 * pages from all maps (since we cannot know which maps this sharing
	 * map belongs in).
	 */

	if (dst_map->is_main_map)
		pmap_remove(dst_map->pmap, dst_entry->start, dst_entry->end);
	else
		vm_object_pmap_remove(dst_entry->object.vm_object,
		    dst_entry->offset,
		    dst_entry->offset +
		    (dst_entry->end - dst_entry->start));

	if (src_entry->wired_count == 0) {

		boolean_t src_needs_copy;

		/*
		 * If the source entry is marked needs_copy, it is already
		 * write-protected.
		 */
		if (!src_entry->needs_copy) {

			boolean_t su;

			/*
			 * If the source entry has only one mapping, we can
			 * just protect the virtual address range.
			 */
			if (!(su = src_map->is_main_map)) {
				simple_lock(&src_map->ref_lock);
				su = (src_map->ref_count == 1);
				simple_unlock(&src_map->ref_lock);
			}
			if (su) {
				pmap_protect(src_map->pmap,
				    src_entry->start,
				    src_entry->end,
				    src_entry->protection & ~VM_PROT_WRITE);
			} else {
				vm_object_pmap_copy(src_entry->object.vm_object,
				    src_entry->offset,
				    src_entry->offset + (src_entry->end
					- src_entry->start));
			}
		}
		/*
		 * Make a copy of the object.
		 */
		temp_object = dst_entry->object.vm_object;
		vm_object_copy(src_entry->object.vm_object,
		    src_entry->offset,
		    (vm_size_t) (src_entry->end -
			src_entry->start),
		    &dst_entry->object.vm_object,
		    &dst_entry->offset,
		    &src_needs_copy);
		/*
		 * If we didn't get a copy-object now, mark the source map
		 * entry so that a shadow will be created to hold its changed
		 * pages.
		 */
		if (src_needs_copy)
			src_entry->needs_copy = TRUE;

		/*
		 * The destination always needs to have a shadow created.
		 */
		dst_entry->needs_copy = TRUE;

		/*
		 * Mark the entries copy-on-write, so that write-enabling the
		 * entry won't make copy-on-write pages writable.
		 */
		src_entry->copy_on_write = TRUE;
		dst_entry->copy_on_write = TRUE;
		/*
		 * Get rid of the old object.
		 */
		vm_object_deallocate(temp_object);

		pmap_copy(dst_map->pmap, src_map->pmap, dst_entry->start,
		    dst_entry->end - dst_entry->start, src_entry->start);
	} else {
		/*
		 * Of course, wired down pages can't be set copy-on-write.
		 * Cause wired pages to be copied into the new map by
		 * simulating faults (the new pages are pageable)
		 */
		vm_fault_copy_entry(dst_map, src_map, dst_entry, src_entry);
	}
}

/*
 *	vm_map_copy:
 *
 *	Perform a virtual memory copy from the source
 *	address map/range to the destination map/range.
 *
 *	If src_destroy or dst_alloc is requested,
 *	the source and destination regions should be
 *	disjoint, not only in the top-level map, but
 *	in the sharing maps as well.  [The best way
 *	to guarantee this is to use a new intermediate
 *	map to make copies.  This also reduces map
 *	fragmentation.]
 */
int
vm_map_copy(dst_map, src_map,
    dst_addr, len, src_addr,
    dst_alloc, src_destroy)
	vm_map_t dst_map;
	vm_map_t src_map;
	vm_offset_t dst_addr;
	vm_size_t len;
	vm_offset_t src_addr;
	boolean_t dst_alloc;
	boolean_t src_destroy;
{
	register
	vm_map_entry_t src_entry;
	register
	vm_map_entry_t dst_entry;
	vm_map_entry_t tmp_entry;
	vm_offset_t src_start;
	vm_offset_t src_end;
	vm_offset_t dst_start;
	vm_offset_t dst_end;
	vm_offset_t src_clip;
	vm_offset_t dst_clip;
	int result;
	boolean_t old_src_destroy;

	/*
	 * XXX While we figure out why src_destroy screws up, we'll do it by
	 * explicitly vm_map_delete'ing at the end.
	 */

	old_src_destroy = src_destroy;
	src_destroy = FALSE;

	/*
	 * Compute start and end of region in both maps
	 */

	src_start = src_addr;
	src_end = src_start + len;
	dst_start = dst_addr;
	dst_end = dst_start + len;

	/*
	 * Check that the region can exist in both source and destination.
	 */

	if ((dst_end < dst_start) || (src_end < src_start))
		return (KERN_NO_SPACE);

	/*
	 * Lock the maps in question -- we avoid deadlock by ordering lock
	 * acquisition by map value
	 */

	if (src_map == dst_map) {
		vm_map_lock(src_map);
	} else if ((int) src_map < (int) dst_map) {
		vm_map_lock(src_map);
		vm_map_lock(dst_map);
	} else {
		vm_map_lock(dst_map);
		vm_map_lock(src_map);
	}

	result = KERN_SUCCESS;

	/*
	 * Check protections... source must be completely readable and
	 * destination must be completely writable.  [Note that if we're
	 * allocating the destination region, we don't have to worry about
	 * protection, but instead about whether the region exists.]
	 */

	if (src_map->is_main_map && dst_map->is_main_map) {
		if (!vm_map_check_protection(src_map, src_start, src_end,
			VM_PROT_READ)) {
			result = KERN_PROTECTION_FAILURE;
			goto Return;
		}
		if (dst_alloc) {
			/* XXX Consider making this a vm_map_find instead */
			if ((result = vm_map_insert(dst_map, NULL,
				    (vm_offset_t) 0, dst_start, dst_end)) != KERN_SUCCESS)
				goto Return;
		} else if (!vm_map_check_protection(dst_map, dst_start, dst_end,
			VM_PROT_WRITE)) {
			result = KERN_PROTECTION_FAILURE;
			goto Return;
		}
	}
	/*
	 * Find the start entries and clip.
	 *
	 * Note that checking protection asserts that the lookup cannot fail.
	 *
	 * Also note that we wait to do the second lookup until we have done the
	 * first clip, as the clip may affect which entry we get!
	 */

	(void) vm_map_lookup_entry(src_map, src_addr, &tmp_entry);
	src_entry = tmp_entry;
	vm_map_clip_start(src_map, src_entry, src_start);

	(void) vm_map_lookup_entry(dst_map, dst_addr, &tmp_entry);
	dst_entry = tmp_entry;
	vm_map_clip_start(dst_map, dst_entry, dst_start);

	/*
	 * If both source and destination entries are the same, retry the
	 * first lookup, as it may have changed.
	 */

	if (src_entry == dst_entry) {
		(void) vm_map_lookup_entry(src_map, src_addr, &tmp_entry);
		src_entry = tmp_entry;
	}
	/*
	 * If source and destination entries are still the same, a null copy
	 * is being performed.
	 */

	if (src_entry == dst_entry)
		goto Return;

	/*
	 * Go through entries until we get to the end of the region.
	 */

	while (src_start < src_end) {
		/*
		 * Clip the entries to the endpoint of the entire region.
		 */

		vm_map_clip_end(src_map, src_entry, src_end);
		vm_map_clip_end(dst_map, dst_entry, dst_end);

		/*
		 * Clip each entry to the endpoint of the other entry.
		 */

		src_clip = src_entry->start + (dst_entry->end - dst_entry->start);
		vm_map_clip_end(src_map, src_entry, src_clip);

		dst_clip = dst_entry->start + (src_entry->end - src_entry->start);
		vm_map_clip_end(dst_map, dst_entry, dst_clip);

		/*
		 * Both entries now match in size and relative endpoints.
		 *
		 * If both entries refer to a VM object, we can deal with them
		 * now.
		 */

		if (!src_entry->is_a_map && !dst_entry->is_a_map) {
			vm_map_copy_entry(src_map, dst_map, src_entry,
			    dst_entry);
		} else {
			register vm_map_t new_dst_map;
			vm_offset_t new_dst_start;
			vm_size_t new_size;
			vm_map_t new_src_map;
			vm_offset_t new_src_start;

			/*
			 * We have to follow at least one sharing map.
			 */

			new_size = (dst_entry->end - dst_entry->start);

			if (src_entry->is_a_map) {
				new_src_map = src_entry->object.share_map;
				new_src_start = src_entry->offset;
			} else {
				new_src_map = src_map;
				new_src_start = src_entry->start;
				lock_set_recursive(&src_map->lock);
			}

			if (dst_entry->is_a_map) {
				vm_offset_t new_dst_end;

				new_dst_map = dst_entry->object.share_map;
				new_dst_start = dst_entry->offset;

				/*
				 * Since the destination sharing entries will
				 * be merely deallocated, we can do that now,
				 * and replace the region with a null object.
				 * [This prevents splitting the source map to
				 * match the form of the destination map.]
				 * Note that we can only do so if the source
				 * and destination do not overlap.
				 */

				new_dst_end = new_dst_start + new_size;

				if (new_dst_map != new_src_map) {
					vm_map_lock(new_dst_map);
					(void) vm_map_delete(new_dst_map,
					    new_dst_start,
					    new_dst_end);
					(void) vm_map_insert(new_dst_map,
					    NULL,
					    (vm_offset_t) 0,
					    new_dst_start,
					    new_dst_end);
					vm_map_unlock(new_dst_map);
				}
			} else {
				new_dst_map = dst_map;
				new_dst_start = dst_entry->start;
				lock_set_recursive(&dst_map->lock);
			}

			/*
			 * Recursively copy the sharing map.
			 */

			(void) vm_map_copy(new_dst_map, new_src_map,
			    new_dst_start, new_size, new_src_start,
			    FALSE, FALSE);

			if (dst_map == new_dst_map)
				lock_clear_recursive(&dst_map->lock);
			if (src_map == new_src_map)
				lock_clear_recursive(&src_map->lock);
		}

		/*
		 * Update variables for next pass through the loop.
		 */

		src_start = src_entry->end;
		src_entry = src_entry->next;
		dst_start = dst_entry->end;
		dst_entry = dst_entry->next;

		/*
		 * If the source is to be destroyed, here is the place to do
		 * it.
		 */

		if (src_destroy && src_map->is_main_map &&
		    dst_map->is_main_map)
			vm_map_entry_delete(src_map, src_entry->prev);
	}

	/*
	 * Update the physical maps as appropriate
	 */

	if (src_map->is_main_map && dst_map->is_main_map) {
		if (src_destroy)
			pmap_remove(src_map->pmap, src_addr, src_addr + len);
	}
	/*
	 * Unlock the maps
	 */

Return:;

	if (old_src_destroy)
		vm_map_delete(src_map, src_addr, src_addr + len);

	vm_map_unlock(src_map);
	if (src_map != dst_map)
		vm_map_unlock(dst_map);

	return (result);
}

/*
 * vmspace_fork:
 * Create a new process vmspace structure and vm_map
 * based on those of an existing process.  The new map
 * is based on the old map, according to the inheritance
 * values on the regions in that map.
 *
 * The source map must not be locked.
 */
struct vmspace *
vmspace_fork(vm1)
	register struct vmspace *vm1;
{
	register struct vmspace *vm2;
	vm_map_t old_map = &vm1->vm_map;
	vm_map_t new_map;
	vm_map_entry_t old_entry;
	vm_map_entry_t new_entry;
	pmap_t new_pmap;

	vm_map_lock(old_map);

	vm2 = vmspace_alloc(old_map->min_offset, old_map->max_offset,
	    old_map->entries_pageable);
	bcopy(&vm1->vm_startcopy, &vm2->vm_startcopy,
	    (caddr_t) (vm1 + 1) - (caddr_t) &vm1->vm_startcopy);
	new_pmap = &vm2->vm_pmap;	/* XXX */
	new_map = &vm2->vm_map;	/* XXX */

	old_entry = old_map->header.next;

	while (old_entry != &old_map->header) {
		if (old_entry->is_sub_map)
			panic("vm_map_fork: encountered a submap");

		switch (old_entry->inheritance) {
		case VM_INHERIT_NONE:
			break;

		case VM_INHERIT_SHARE:
			/*
			 * If we don't already have a sharing map:
			 */

			if (!old_entry->is_a_map) {
				vm_map_t new_share_map;
				vm_map_entry_t new_share_entry;

				/*
				 * Create a new sharing map
				 */

				new_share_map = vm_map_create(NULL,
				    old_entry->start,
				    old_entry->end,
				    TRUE);
				new_share_map->is_main_map = FALSE;

				/*
				 * Create the only sharing entry from the old
				 * task map entry.
				 */

				new_share_entry =
				    vm_map_entry_create(new_share_map);
				*new_share_entry = *old_entry;
				new_share_entry->wired_count = 0;

				/*
				 * Insert the entry into the new sharing map
				 */

				vm_map_entry_link(new_share_map,
				    new_share_map->header.prev,
				    new_share_entry);

				/*
				 * Fix up the task map entry to refer to the
				 * sharing map now.
				 */

				old_entry->is_a_map = TRUE;
				old_entry->object.share_map = new_share_map;
				old_entry->offset = old_entry->start;
			}
			/*
			 * Clone the entry, referencing the sharing map.
			 */

			new_entry = vm_map_entry_create(new_map);
			*new_entry = *old_entry;
			new_entry->wired_count = 0;
			vm_map_reference(new_entry->object.share_map);

			/*
			 * Insert the entry into the new map -- we know we're
			 * inserting at the end of the new map.
			 */

			vm_map_entry_link(new_map, new_map->header.prev,
			    new_entry);

			/*
			 * Update the physical map
			 */

			pmap_copy(new_map->pmap, old_map->pmap,
			    new_entry->start,
			    (old_entry->end - old_entry->start),
			    old_entry->start);
			break;

		case VM_INHERIT_COPY:
			/*
			 * Clone the entry and link into the map.
			 */

			new_entry = vm_map_entry_create(new_map);
			*new_entry = *old_entry;
			new_entry->wired_count = 0;
			new_entry->object.vm_object = NULL;
			new_entry->is_a_map = FALSE;
			vm_map_entry_link(new_map, new_map->header.prev,
			    new_entry);
			if (old_entry->is_a_map) {
				int check;

				check = vm_map_copy(new_map,
				    old_entry->object.share_map,
				    new_entry->start,
				    (vm_size_t) (new_entry->end -
					new_entry->start),
				    old_entry->offset,
				    FALSE, FALSE);
				if (check != KERN_SUCCESS)
					printf("vm_map_fork: copy in share_map region failed\n");
			} else {
				vm_map_copy_entry(old_map, new_map, old_entry,
				    new_entry);
			}
			break;
		}
		old_entry = old_entry->next;
	}

	new_map->size = old_map->size;
	vm_map_unlock(old_map);

	return (vm2);
}

/*
 *	vm_map_lookup:
 *
 *	Finds the VM object, offset, and
 *	protection for a given virtual address in the
 *	specified map, assuming a page fault of the
 *	type specified.
 *
 *	Leaves the map in question locked for read; return
 *	values are guaranteed until a vm_map_lookup_done
 *	call is performed.  Note that the map argument
 *	is in/out; the returned map must be used in
 *	the call to vm_map_lookup_done.
 *
 *	A handle (out_entry) is returned for use in
 *	vm_map_lookup_done, to make that fast.
 *
 *	If a lookup is requested with "write protection"
 *	specified, the map may be changed to perform virtual
 *	copying operations, although the data referenced will
 *	remain the same.
 */
int
vm_map_lookup(var_map, vaddr, fault_type, out_entry,
    object, offset, out_prot, wired, single_use)
	vm_map_t *var_map;	/* IN/OUT */
	register vm_offset_t vaddr;
	register vm_prot_t fault_type;

	vm_map_entry_t *out_entry;	/* OUT */
	vm_object_t *object;	/* OUT */
	vm_offset_t *offset;	/* OUT */
	vm_prot_t *out_prot;	/* OUT */
	boolean_t *wired;	/* OUT */
	boolean_t *single_use;	/* OUT */
{
	vm_map_t share_map;
	vm_offset_t share_offset;
	register vm_map_entry_t entry;
	register vm_map_t map = *var_map;
	register vm_prot_t prot;
	register boolean_t su;

RetryLookup:;

	/*
	 * Lookup the faulting address.
	 */

	vm_map_lock_read(map);

#define	RETURN(why) \
		{ \
		vm_map_unlock_read(map); \
		return(why); \
		}

	/*
	 * If the map has an interesting hint, try it before calling full
	 * blown lookup routine.
	 */

	simple_lock(&map->hint_lock);
	entry = map->hint;
	simple_unlock(&map->hint_lock);

	*out_entry = entry;

	if ((entry == &map->header) ||
	    (vaddr < entry->start) || (vaddr >= entry->end)) {
		vm_map_entry_t tmp_entry;

		/*
		 * Entry was either not a valid hint, or the vaddr was not
		 * contained in the entry, so do a full lookup.
		 */
		if (!vm_map_lookup_entry(map, vaddr, &tmp_entry))
			RETURN(KERN_INVALID_ADDRESS);

		entry = tmp_entry;
		*out_entry = entry;
	}
	/*
	 * Handle submaps.
	 */

	if (entry->is_sub_map) {
		vm_map_t old_map = map;

		*var_map = map = entry->object.sub_map;
		vm_map_unlock_read(old_map);
		goto RetryLookup;
	}
	/*
	 * Check whether this task is allowed to have this page.
	 */

	prot = entry->protection;
	if ((fault_type & (prot)) != fault_type)
		RETURN(KERN_PROTECTION_FAILURE);

	/*
	 * If this page is not pageable, we have to get it for all possible
	 * accesses.
	 */

	*wired = (entry->wired_count != 0);
	if (*wired)
		prot = fault_type = entry->protection;

	/*
	 * If we don't already have a VM object, track it down.
	 */

	su = !entry->is_a_map;
	if (su) {
		share_map = map;
		share_offset = vaddr;
	} else {
		vm_map_entry_t share_entry;

		/*
		 * Compute the sharing map, and offset into it.
		 */

		share_map = entry->object.share_map;
		share_offset = (vaddr - entry->start) + entry->offset;

		/*
		 * Look for the backing store object and offset
		 */

		vm_map_lock_read(share_map);

		if (!vm_map_lookup_entry(share_map, share_offset,
			&share_entry)) {
			vm_map_unlock_read(share_map);
			RETURN(KERN_INVALID_ADDRESS);
		}
		entry = share_entry;
	}

	/*
	 * If the entry was copy-on-write, we either ...
	 */

	if (entry->needs_copy) {
		/*
		 * If we want to write the page, we may as well handle that
		 * now since we've got the sharing map locked.
		 *
		 * If we don't need to write the page, we just demote the
		 * permissions allowed.
		 */

		if (fault_type & VM_PROT_WRITE) {
			/*
			 * Make a new object, and place it in the object
			 * chain.  Note that no new references have appeared
			 * -- one just moved from the share map to the new
			 * object.
			 */

			if (lock_read_to_write(&share_map->lock)) {
				if (share_map != map)
					vm_map_unlock_read(map);
				goto RetryLookup;
			}
			vm_object_shadow(
			    &entry->object.vm_object,
			    &entry->offset,
			    (vm_size_t) (entry->end - entry->start));

			entry->needs_copy = FALSE;

			lock_write_to_read(&share_map->lock);
		} else {
			/*
			 * We're attempting to read a copy-on-write page --
			 * don't allow writes.
			 */

			prot &= (~VM_PROT_WRITE);
		}
	}
	/*
	 * Create an object if necessary.
	 */
	if (entry->object.vm_object == NULL) {

		if (lock_read_to_write(&share_map->lock)) {
			if (share_map != map)
				vm_map_unlock_read(map);
			goto RetryLookup;
		}
		entry->object.vm_object = vm_object_allocate(
		    (vm_size_t) (entry->end - entry->start));
		entry->offset = 0;
		lock_write_to_read(&share_map->lock);
	}
	/*
	 * Return the object/offset from this entry.  If the entry was
	 * copy-on-write or empty, it has been fixed up.
	 */

	*offset = (share_offset - entry->start) + entry->offset;
	*object = entry->object.vm_object;

	/*
	 * Return whether this is the only map sharing this data.
	 */

	if (!su) {
		simple_lock(&share_map->ref_lock);
		su = (share_map->ref_count == 1);
		simple_unlock(&share_map->ref_lock);
	}
	*out_prot = prot;
	*single_use = su;

	return (KERN_SUCCESS);

#undef	RETURN
}

/*
 *	vm_map_lookup_done:
 *
 *	Releases locks acquired by a vm_map_lookup
 *	(according to the handle returned by that lookup).
 */

void
vm_map_lookup_done(map, entry)
	register vm_map_t map;
	vm_map_entry_t entry;
{
	/*
	 * If this entry references a map, unlock it first.
	 */

	if (entry->is_a_map)
		vm_map_unlock_read(entry->object.share_map);

	/*
	 * Unlock the main-level map
	 */

	vm_map_unlock_read(map);
}

/*
 *	Routine:	vm_map_simplify
 *	Purpose:
 *		Attempt to simplify the map representation in
 *		the vicinity of the given starting address.
 *	Note:
 *		This routine is intended primarily to keep the
 *		kernel maps more compact -- they generally don't
 *		benefit from the "expand a map entry" technology
 *		at allocation time because the adjacent entry
 *		is often wired down.
 */
void
vm_map_simplify(map, start)
	vm_map_t map;
	vm_offset_t start;
{
	vm_map_entry_t this_entry;
	vm_map_entry_t prev_entry;

	vm_map_lock(map);
	if (
	    (vm_map_lookup_entry(map, start, &this_entry)) &&
	    ((prev_entry = this_entry->prev) != &map->header) &&

	    (prev_entry->end == start) &&
	    (map->is_main_map) &&

	    (prev_entry->is_a_map == FALSE) &&
	    (prev_entry->is_sub_map == FALSE) &&

	    (this_entry->is_a_map == FALSE) &&
	    (this_entry->is_sub_map == FALSE) &&

	    (prev_entry->inheritance == this_entry->inheritance) &&
	    (prev_entry->protection == this_entry->protection) &&
	    (prev_entry->max_protection == this_entry->max_protection) &&
	    (prev_entry->wired_count == this_entry->wired_count) &&

	    (prev_entry->copy_on_write == this_entry->copy_on_write) &&
	    (prev_entry->needs_copy == this_entry->needs_copy) &&

	    (prev_entry->object.vm_object == this_entry->object.vm_object) &&
	    ((prev_entry->offset + (prev_entry->end - prev_entry->start))
		== this_entry->offset)
	    ) {
		if (map->first_free == this_entry)
			map->first_free = prev_entry;

		if (!this_entry->object.vm_object->paging_in_progress) {
			SAVE_HINT(map, prev_entry);
			vm_map_entry_unlink(map, this_entry);
			prev_entry->end = this_entry->end;
			vm_object_deallocate(this_entry->object.vm_object);
			vm_map_entry_dispose(map, this_entry);
		}
	}
	vm_map_unlock(map);
}

/*
 *	vm_map_print:	[ debug ]
 */
void
vm_map_print(map, full)
	register vm_map_t map;
	boolean_t full;
{
	register vm_map_entry_t entry;
	extern int indent;

	iprintf("%s map 0x%x: pmap=0x%x,ref=%d,nentries=%d,version=%d\n",
	    (map->is_main_map ? "Task" : "Share"),
	    (int) map, (int) (map->pmap), map->ref_count, map->nentries,
	    map->timestamp);

	if (!full && indent)
		return;

	indent += 2;
	for (entry = map->header.next; entry != &map->header;
	    entry = entry->next) {
		iprintf("map entry 0x%x: start=0x%x, end=0x%x, ",
		    (int) entry, (int) entry->start, (int) entry->end);
		if (map->is_main_map) {
			static char *inheritance_name[4] =
			{"share", "copy", "none", "donate_copy"};

			printf("prot=%x/%x/%s, ",
			    entry->protection,
			    entry->max_protection,
			    inheritance_name[entry->inheritance]);
			if (entry->wired_count != 0)
				printf("wired, ");
		}
		if (entry->is_a_map || entry->is_sub_map) {
			printf("share=0x%x, offset=0x%x\n",
			    (int) entry->object.share_map,
			    (int) entry->offset);
			if ((entry->prev == &map->header) ||
			    (!entry->prev->is_a_map) ||
			    (entry->prev->object.share_map !=
				entry->object.share_map)) {
				indent += 2;
				vm_map_print(entry->object.share_map, full);
				indent -= 2;
			}
		} else {
			printf("object=0x%x, offset=0x%x",
			    (int) entry->object.vm_object,
			    (int) entry->offset);
			if (entry->copy_on_write)
				printf(", copy (%s)",
				    entry->needs_copy ? "needed" : "done");
			printf("\n");

			if ((entry->prev == &map->header) ||
			    (entry->prev->is_a_map) ||
			    (entry->prev->object.vm_object !=
				entry->object.vm_object)) {
				indent += 2;
				vm_object_print(entry->object.vm_object, full);
				indent -= 2;
			}
		}
	}
	indent -= 2;
}