FreeBSD/Linux Kernel Cross Reference
sys/vm/vm_map.c

     /*-
      * 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.
     * 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.
     */
    
    /*
     *      Virtual memory mapping module.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/10.0/sys/vm/vm_map.c 267017 2014-06-03 19:02:52Z delphij $");
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/ktr.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/proc.h>
    #include <sys/vmmeter.h>
    #include <sys/mman.h>
    #include <sys/vnode.h>
    #include <sys/racct.h>
    #include <sys/resourcevar.h>
    #include <sys/rwlock.h>
    #include <sys/file.h>
    #include <sys/sysctl.h>
    #include <sys/sysent.h>
    #include <sys/shm.h>
    
    #include <vm/vm.h>
    #include <vm/vm_param.h>
    #include <vm/pmap.h>
    #include <vm/vm_map.h>
    #include <vm/vm_page.h>
    #include <vm/vm_object.h>
    #include <vm/vm_pager.h>
    #include <vm/vm_kern.h>
    #include <vm/vm_extern.h>
    #include <vm/vnode_pager.h>
    #include <vm/swap_pager.h>
    #include <vm/uma.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 self-adjusting binary search tree of these
    *      entries is used to speed up lookups.
    *
    *      Since portions of maps are specified by start/end addresses,
    *      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.
    *
    *      As mentioned above, virtual copy operations are performed
    *      by copying VM object references from one map to
    *      another, and then marking both regions as copy-on-write.
    */
   
   static struct mtx map_sleep_mtx;
   static uma_zone_t mapentzone;
   static uma_zone_t kmapentzone;
   static uma_zone_t mapzone;
   static uma_zone_t vmspace_zone;
   static int vmspace_zinit(void *mem, int size, int flags);
   static int vm_map_zinit(void *mem, int ize, int flags);
   static void _vm_map_init(vm_map_t map, pmap_t pmap, vm_offset_t min,
       vm_offset_t max);
   static void vm_map_entry_deallocate(vm_map_entry_t entry, boolean_t system_map);
   static void vm_map_entry_dispose(vm_map_t map, vm_map_entry_t entry);
   #ifdef INVARIANTS
   static void vm_map_zdtor(void *mem, int size, void *arg);
   static void vmspace_zdtor(void *mem, int size, void *arg);
   #endif
   
   #define ENTRY_CHARGED(e) ((e)->cred != NULL || \
       ((e)->object.vm_object != NULL && (e)->object.vm_object->cred != NULL && \
        !((e)->eflags & MAP_ENTRY_NEEDS_COPY)))
   
   /* 
    * PROC_VMSPACE_{UN,}LOCK() can be a noop as long as vmspaces are type
    * stable.
    */
   #define PROC_VMSPACE_LOCK(p) do { } while (0)
   #define PROC_VMSPACE_UNLOCK(p) do { } while (0)
   
   /*
    *      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_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.
    */
   
   void
   vm_map_startup(void)
   {
           mtx_init(&map_sleep_mtx, "vm map sleep mutex", NULL, MTX_DEF);
           mapzone = uma_zcreate("MAP", sizeof(struct vm_map), NULL,
   #ifdef INVARIANTS
               vm_map_zdtor,
   #else
               NULL,
   #endif
               vm_map_zinit, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
           uma_prealloc(mapzone, MAX_KMAP);
           kmapentzone = uma_zcreate("KMAP ENTRY", sizeof(struct vm_map_entry),
               NULL, NULL, NULL, NULL, UMA_ALIGN_PTR,
               UMA_ZONE_MTXCLASS | UMA_ZONE_VM);
           mapentzone = uma_zcreate("MAP ENTRY", sizeof(struct vm_map_entry),
               NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
           vmspace_zone = uma_zcreate("VMSPACE", sizeof(struct vmspace), NULL,
   #ifdef INVARIANTS
               vmspace_zdtor,
   #else
               NULL,
   #endif
               vmspace_zinit, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
   }
   
   static int
   vmspace_zinit(void *mem, int size, int flags)
   {
           struct vmspace *vm;
   
           vm = (struct vmspace *)mem;
   
           vm->vm_map.pmap = NULL;
           (void)vm_map_zinit(&vm->vm_map, sizeof(vm->vm_map), flags);
           PMAP_LOCK_INIT(vmspace_pmap(vm));
           return (0);
   }
   
   static int
   vm_map_zinit(void *mem, int size, int flags)
   {
           vm_map_t map;
   
           map = (vm_map_t)mem;
           memset(map, 0, sizeof(*map));
           mtx_init(&map->system_mtx, "vm map (system)", NULL, MTX_DEF | MTX_DUPOK);
           sx_init(&map->lock, "vm map (user)");
           return (0);
   }
   
   #ifdef INVARIANTS
   static void
   vmspace_zdtor(void *mem, int size, void *arg)
   {
           struct vmspace *vm;
   
           vm = (struct vmspace *)mem;
   
           vm_map_zdtor(&vm->vm_map, sizeof(vm->vm_map), arg);
   }
   static void
   vm_map_zdtor(void *mem, int size, void *arg)
   {
           vm_map_t map;
   
           map = (vm_map_t)mem;
           KASSERT(map->nentries == 0,
               ("map %p nentries == %d on free.",
               map, map->nentries));
           KASSERT(map->size == 0,
               ("map %p size == %lu on free.",
               map, (unsigned long)map->size));
   }
   #endif  /* INVARIANTS */
   
   /*
    * Allocate a vmspace structure, including a vm_map and pmap,
    * and initialize those structures.  The refcnt is set to 1.
    *
    * If 'pinit' is NULL then the embedded pmap is initialized via pmap_pinit().
    */
   struct vmspace *
   vmspace_alloc(vm_offset_t min, vm_offset_t max, pmap_pinit_t pinit)
   {
           struct vmspace *vm;
   
           vm = uma_zalloc(vmspace_zone, M_WAITOK);
   
           KASSERT(vm->vm_map.pmap == NULL, ("vm_map.pmap must be NULL"));
   
           if (pinit == NULL)
                   pinit = &pmap_pinit;
   
           if (!pinit(vmspace_pmap(vm))) {
                   uma_zfree(vmspace_zone, vm);
                   return (NULL);
           }
           CTR1(KTR_VM, "vmspace_alloc: %p", vm);
           _vm_map_init(&vm->vm_map, vmspace_pmap(vm), min, max);
           vm->vm_refcnt = 1;
           vm->vm_shm = NULL;
           vm->vm_swrss = 0;
           vm->vm_tsize = 0;
           vm->vm_dsize = 0;
           vm->vm_ssize = 0;
           vm->vm_taddr = 0;
           vm->vm_daddr = 0;
           vm->vm_maxsaddr = 0;
           return (vm);
   }
   
   static void
   vmspace_container_reset(struct proc *p)
   {
   
   #ifdef RACCT
           PROC_LOCK(p);
           racct_set(p, RACCT_DATA, 0);
           racct_set(p, RACCT_STACK, 0);
           racct_set(p, RACCT_RSS, 0);
           racct_set(p, RACCT_MEMLOCK, 0);
           racct_set(p, RACCT_VMEM, 0);
           PROC_UNLOCK(p);
   #endif
   }
   
   static inline void
   vmspace_dofree(struct vmspace *vm)
   {
   
           CTR1(KTR_VM, "vmspace_free: %p", vm);
   
           /*
            * Make sure any SysV shm is freed, it might not have been in
            * exit1().
            */
           shmexit(vm);
   
           /*
            * 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.
            */
           (void)vm_map_remove(&vm->vm_map, vm->vm_map.min_offset,
               vm->vm_map.max_offset);
   
           pmap_release(vmspace_pmap(vm));
           vm->vm_map.pmap = NULL;
           uma_zfree(vmspace_zone, vm);
   }
   
   void
   vmspace_free(struct vmspace *vm)
   {
   
           if (vm->vm_refcnt == 0)
                   panic("vmspace_free: attempt to free already freed vmspace");
   
           if (atomic_fetchadd_int(&vm->vm_refcnt, -1) == 1)
                   vmspace_dofree(vm);
   }
   
   void
   vmspace_exitfree(struct proc *p)
   {
           struct vmspace *vm;
   
           PROC_VMSPACE_LOCK(p);
           vm = p->p_vmspace;
           p->p_vmspace = NULL;
           PROC_VMSPACE_UNLOCK(p);
           KASSERT(vm == &vmspace0, ("vmspace_exitfree: wrong vmspace"));
           vmspace_free(vm);
   }
   
   void
   vmspace_exit(struct thread *td)
   {
           int refcnt;
           struct vmspace *vm;
           struct proc *p;
   
           /*
            * Release user portion of address space.
            * This releases references to vnodes,
            * which could cause I/O if the file has been unlinked.
            * Need to do this early enough that we can still sleep.
            *
            * The last exiting process to reach this point releases as
            * much of the environment as it can. vmspace_dofree() is the
            * slower fallback in case another process had a temporary
            * reference to the vmspace.
            */
   
           p = td->td_proc;
           vm = p->p_vmspace;
           atomic_add_int(&vmspace0.vm_refcnt, 1);
           do {
                   refcnt = vm->vm_refcnt;
                   if (refcnt > 1 && p->p_vmspace != &vmspace0) {
                           /* Switch now since other proc might free vmspace */
                           PROC_VMSPACE_LOCK(p);
                           p->p_vmspace = &vmspace0;
                           PROC_VMSPACE_UNLOCK(p);
                           pmap_activate(td);
                   }
           } while (!atomic_cmpset_int(&vm->vm_refcnt, refcnt, refcnt - 1));
           if (refcnt == 1) {
                   if (p->p_vmspace != vm) {
                           /* vmspace not yet freed, switch back */
                           PROC_VMSPACE_LOCK(p);
                           p->p_vmspace = vm;
                           PROC_VMSPACE_UNLOCK(p);
                           pmap_activate(td);
                   }
                   pmap_remove_pages(vmspace_pmap(vm));
                   /* Switch now since this proc will free vmspace */
                   PROC_VMSPACE_LOCK(p);
                   p->p_vmspace = &vmspace0;
                   PROC_VMSPACE_UNLOCK(p);
                   pmap_activate(td);
                   vmspace_dofree(vm);
           }
           vmspace_container_reset(p);
   }
   
   /* Acquire reference to vmspace owned by another process. */
   
   struct vmspace *
   vmspace_acquire_ref(struct proc *p)
   {
           struct vmspace *vm;
           int refcnt;
   
           PROC_VMSPACE_LOCK(p);
           vm = p->p_vmspace;
           if (vm == NULL) {
                   PROC_VMSPACE_UNLOCK(p);
                   return (NULL);
           }
           do {
                   refcnt = vm->vm_refcnt;
                   if (refcnt <= 0) {      /* Avoid 0->1 transition */
                           PROC_VMSPACE_UNLOCK(p);
                           return (NULL);
                   }
           } while (!atomic_cmpset_int(&vm->vm_refcnt, refcnt, refcnt + 1));
           if (vm != p->p_vmspace) {
                   PROC_VMSPACE_UNLOCK(p);
                   vmspace_free(vm);
                   return (NULL);
           }
           PROC_VMSPACE_UNLOCK(p);
           return (vm);
   }
   
   void
   _vm_map_lock(vm_map_t map, const char *file, int line)
   {
   
           if (map->system_map)
                   mtx_lock_flags_(&map->system_mtx, 0, file, line);
           else
                   sx_xlock_(&map->lock, file, line);
           map->timestamp++;
   }
   
   static void
   vm_map_process_deferred(void)
   {
           struct thread *td;
           vm_map_entry_t entry, next;
           vm_object_t object;
   
           td = curthread;
           entry = td->td_map_def_user;
           td->td_map_def_user = NULL;
           while (entry != NULL) {
                   next = entry->next;
                   if ((entry->eflags & MAP_ENTRY_VN_WRITECNT) != 0) {
                           /*
                            * Decrement the object's writemappings and
                            * possibly the vnode's v_writecount.
                            */
                           KASSERT((entry->eflags & MAP_ENTRY_IS_SUB_MAP) == 0,
                               ("Submap with writecount"));
                           object = entry->object.vm_object;
                           KASSERT(object != NULL, ("No object for writecount"));
                           vnode_pager_release_writecount(object, entry->start,
                               entry->end);
                   }
                   vm_map_entry_deallocate(entry, FALSE);
                   entry = next;
           }
   }
   
   void
   _vm_map_unlock(vm_map_t map, const char *file, int line)
   {
   
           if (map->system_map)
                   mtx_unlock_flags_(&map->system_mtx, 0, file, line);
           else {
                   sx_xunlock_(&map->lock, file, line);
                   vm_map_process_deferred();
           }
   }
   
   void
   _vm_map_lock_read(vm_map_t map, const char *file, int line)
   {
   
           if (map->system_map)
                   mtx_lock_flags_(&map->system_mtx, 0, file, line);
           else
                   sx_slock_(&map->lock, file, line);
   }
   
   void
   _vm_map_unlock_read(vm_map_t map, const char *file, int line)
   {
   
           if (map->system_map)
                   mtx_unlock_flags_(&map->system_mtx, 0, file, line);
           else {
                   sx_sunlock_(&map->lock, file, line);
                   vm_map_process_deferred();
           }
   }
   
   int
   _vm_map_trylock(vm_map_t map, const char *file, int line)
   {
           int error;
   
           error = map->system_map ?
               !mtx_trylock_flags_(&map->system_mtx, 0, file, line) :
               !sx_try_xlock_(&map->lock, file, line);
           if (error == 0)
                   map->timestamp++;
           return (error == 0);
   }
   
   int
   _vm_map_trylock_read(vm_map_t map, const char *file, int line)
   {
           int error;
   
           error = map->system_map ?
               !mtx_trylock_flags_(&map->system_mtx, 0, file, line) :
               !sx_try_slock_(&map->lock, file, line);
           return (error == 0);
   }
   
   /*
    *      _vm_map_lock_upgrade:   [ internal use only ]
    *
    *      Tries to upgrade a read (shared) lock on the specified map to a write
    *      (exclusive) lock.  Returns the value "" if the upgrade succeeds and a
    *      non-zero value if the upgrade fails.  If the upgrade fails, the map is
    *      returned without a read or write lock held.
    *
    *      Requires that the map be read locked.
    */
   int
   _vm_map_lock_upgrade(vm_map_t map, const char *file, int line)
   {
           unsigned int last_timestamp;
   
           if (map->system_map) {
                   mtx_assert_(&map->system_mtx, MA_OWNED, file, line);
           } else {
                   if (!sx_try_upgrade_(&map->lock, file, line)) {
                           last_timestamp = map->timestamp;
                           sx_sunlock_(&map->lock, file, line);
                           vm_map_process_deferred();
                           /*
                            * If the map's timestamp does not change while the
                            * map is unlocked, then the upgrade succeeds.
                            */
                           sx_xlock_(&map->lock, file, line);
                           if (last_timestamp != map->timestamp) {
                                   sx_xunlock_(&map->lock, file, line);
                                   return (1);
                           }
                   }
           }
           map->timestamp++;
           return (0);
   }
   
   void
   _vm_map_lock_downgrade(vm_map_t map, const char *file, int line)
   {
   
           if (map->system_map) {
                   mtx_assert_(&map->system_mtx, MA_OWNED, file, line);
           } else
                   sx_downgrade_(&map->lock, file, line);
   }
   
   /*
    *      vm_map_locked:
    *
    *      Returns a non-zero value if the caller holds a write (exclusive) lock
    *      on the specified map and the value "" otherwise.
    */
   int
   vm_map_locked(vm_map_t map)
   {
   
           if (map->system_map)
                   return (mtx_owned(&map->system_mtx));
           else
                   return (sx_xlocked(&map->lock));
   }
   
   #ifdef INVARIANTS
   static void
   _vm_map_assert_locked(vm_map_t map, const char *file, int line)
   {
   
           if (map->system_map)
                   mtx_assert_(&map->system_mtx, MA_OWNED, file, line);
           else
                   sx_assert_(&map->lock, SA_XLOCKED, file, line);
   }
   
   #define VM_MAP_ASSERT_LOCKED(map) \
       _vm_map_assert_locked(map, LOCK_FILE, LOCK_LINE)
   #else
   #define VM_MAP_ASSERT_LOCKED(map)
   #endif
   
   /*
    *      _vm_map_unlock_and_wait:
    *
    *      Atomically releases the lock on the specified map and puts the calling
    *      thread to sleep.  The calling thread will remain asleep until either
    *      vm_map_wakeup() is performed on the map or the specified timeout is
    *      exceeded.
    *
    *      WARNING!  This function does not perform deferred deallocations of
    *      objects and map entries.  Therefore, the calling thread is expected to
    *      reacquire the map lock after reawakening and later perform an ordinary
    *      unlock operation, such as vm_map_unlock(), before completing its
    *      operation on the map.
    */
   int
   _vm_map_unlock_and_wait(vm_map_t map, int timo, const char *file, int line)
   {
   
           mtx_lock(&map_sleep_mtx);
           if (map->system_map)
                   mtx_unlock_flags_(&map->system_mtx, 0, file, line);
           else
                   sx_xunlock_(&map->lock, file, line);
           return (msleep(&map->root, &map_sleep_mtx, PDROP | PVM, "vmmaps",
               timo));
   }
   
   /*
    *      vm_map_wakeup:
    *
    *      Awaken any threads that have slept on the map using
    *      vm_map_unlock_and_wait().
    */
   void
   vm_map_wakeup(vm_map_t map)
   {
   
           /*
            * Acquire and release map_sleep_mtx to prevent a wakeup()
            * from being performed (and lost) between the map unlock
            * and the msleep() in _vm_map_unlock_and_wait().
            */
           mtx_lock(&map_sleep_mtx);
           mtx_unlock(&map_sleep_mtx);
           wakeup(&map->root);
   }
   
   void
   vm_map_busy(vm_map_t map)
   {
   
           VM_MAP_ASSERT_LOCKED(map);
           map->busy++;
   }
   
   void
   vm_map_unbusy(vm_map_t map)
   {
   
           VM_MAP_ASSERT_LOCKED(map);
           KASSERT(map->busy, ("vm_map_unbusy: not busy"));
           if (--map->busy == 0 && (map->flags & MAP_BUSY_WAKEUP)) {
                   vm_map_modflags(map, 0, MAP_BUSY_WAKEUP);
                   wakeup(&map->busy);
           }
   }
   
   void 
   vm_map_wait_busy(vm_map_t map)
   {
   
           VM_MAP_ASSERT_LOCKED(map);
           while (map->busy) {
                   vm_map_modflags(map, MAP_BUSY_WAKEUP, 0);
                   if (map->system_map)
                           msleep(&map->busy, &map->system_mtx, 0, "mbusy", 0);
                   else
                           sx_sleep(&map->busy, &map->lock, 0, "mbusy", 0);
           }
           map->timestamp++;
   }
   
   long
   vmspace_resident_count(struct vmspace *vmspace)
   {
           return pmap_resident_count(vmspace_pmap(vmspace));
   }
   
   /*
    *      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_t pmap, vm_offset_t min, vm_offset_t max)
   {
           vm_map_t result;
   
           result = uma_zalloc(mapzone, M_WAITOK);
           CTR1(KTR_VM, "vm_map_create: %p", result);
           _vm_map_init(result, pmap, min, max);
           return (result);
   }
   
   /*
    * Initialize an existing vm_map structure
    * such as that in the vmspace structure.
    */
   static void
   _vm_map_init(vm_map_t map, pmap_t pmap, vm_offset_t min, vm_offset_t max)
   {
   
           map->header.next = map->header.prev = &map->header;
           map->needs_wakeup = FALSE;
           map->system_map = 0;
           map->pmap = pmap;
           map->min_offset = min;
           map->max_offset = max;
           map->flags = 0;
           map->root = NULL;
           map->timestamp = 0;
           map->busy = 0;
   }
   
   void
   vm_map_init(vm_map_t map, pmap_t pmap, vm_offset_t min, vm_offset_t max)
   {
   
           _vm_map_init(map, pmap, min, max);
           mtx_init(&map->system_mtx, "system map", NULL, MTX_DEF | MTX_DUPOK);
           sx_init(&map->lock, "user map");
   }
   
   /*
    *      vm_map_entry_dispose:   [ internal use only ]
    *
    *      Inverse of vm_map_entry_create.
    */
   static void
   vm_map_entry_dispose(vm_map_t map, vm_map_entry_t entry)
   {
           uma_zfree(map->system_map ? kmapentzone : mapentzone, entry);
   }
   
   /*
    *      vm_map_entry_create:    [ internal use only ]
    *
    *      Allocates a VM map entry for insertion.
    *      No entry fields are filled in.
    */
   static vm_map_entry_t
   vm_map_entry_create(vm_map_t map)
   {
           vm_map_entry_t new_entry;
   
           if (map->system_map)
                   new_entry = uma_zalloc(kmapentzone, M_NOWAIT);
           else
                   new_entry = uma_zalloc(mapentzone, M_WAITOK);
           if (new_entry == NULL)
                   panic("vm_map_entry_create: kernel resources exhausted");
           return (new_entry);
   }
   
   /*
    *      vm_map_entry_set_behavior:
    *
    *      Set the expected access behavior, either normal, random, or
    *      sequential.
    */
   static inline void
   vm_map_entry_set_behavior(vm_map_entry_t entry, u_char behavior)
   {
           entry->eflags = (entry->eflags & ~MAP_ENTRY_BEHAV_MASK) |
               (behavior & MAP_ENTRY_BEHAV_MASK);
   }
   
   /*
    *      vm_map_entry_set_max_free:
    *
    *      Set the max_free field in a vm_map_entry.
    */
   static inline void
   vm_map_entry_set_max_free(vm_map_entry_t entry)
   {
   
           entry->max_free = entry->adj_free;
           if (entry->left != NULL && entry->left->max_free > entry->max_free)
                   entry->max_free = entry->left->max_free;
           if (entry->right != NULL && entry->right->max_free > entry->max_free)
                   entry->max_free = entry->right->max_free;
   }
   
   /*
    *      vm_map_entry_splay:
    *
    *      The Sleator and Tarjan top-down splay algorithm with the
    *      following variation.  Max_free must be computed bottom-up, so
    *      on the downward pass, maintain the left and right spines in
    *      reverse order.  Then, make a second pass up each side to fix
    *      the pointers and compute max_free.  The time bound is O(log n)
    *      amortized.
    *
    *      The new root is the vm_map_entry containing "addr", or else an
    *      adjacent entry (lower or higher) if addr is not in the tree.
    *
    *      The map must be locked, and leaves it so.
    *
    *      Returns: the new root.
    */
   static vm_map_entry_t
   vm_map_entry_splay(vm_offset_t addr, vm_map_entry_t root)
   {
           vm_map_entry_t llist, rlist;
           vm_map_entry_t ltree, rtree;
           vm_map_entry_t y;
   
           /* Special case of empty tree. */
           if (root == NULL)
                   return (root);
   
           /*
            * Pass One: Splay down the tree until we find addr or a NULL
            * pointer where addr would go.  llist and rlist are the two
            * sides in reverse order (bottom-up), with llist linked by
            * the right pointer and rlist linked by the left pointer in
            * the vm_map_entry.  Wait until Pass Two to set max_free on
            * the two spines.
            */
           llist = NULL;
           rlist = NULL;
           for (;;) {
                   /* root is never NULL in here. */
                   if (addr < root->start) {
                           y = root->left;
                           if (y == NULL)
                                   break;
                           if (addr < y->start && y->left != NULL) {
                                   /* Rotate right and put y on rlist. */
                                   root->left = y->right;
                                   y->right = root;
                                   vm_map_entry_set_max_free(root);
                                   root = y->left;
                                   y->left = rlist;
                                   rlist = y;
                           } else {
                                   /* Put root on rlist. */
                                   root->left = rlist;
                                   rlist = root;
                                   root = y;
                           }
                   } else if (addr >= root->end) {
                           y = root->right;
                           if (y == NULL)
                                   break;
                           if (addr >= y->end && y->right != NULL) {
                                   /* Rotate left and put y on llist. */
                                   root->right = y->left;
                                   y->left = root;
                                   vm_map_entry_set_max_free(root);
                                   root = y->right;
                                   y->right = llist;
                                   llist = y;
                           } else {
                                   /* Put root on llist. */
                                   root->right = llist;
                                   llist = root;
                                   root = y;
                           }
                   } else
                           break;
           }
   
           /*
            * Pass Two: Walk back up the two spines, flip the pointers
            * and set max_free.  The subtrees of the root go at the
            * bottom of llist and rlist.
            */
           ltree = root->left;
           while (llist != NULL) {
                   y = llist->right;
                   llist->right = ltree;
                   vm_map_entry_set_max_free(llist);
                   ltree = llist;
                   llist = y;
           }
           rtree = root->right;
           while (rlist != NULL) {
                   y = rlist->left;
                   rlist->left = rtree;
                   vm_map_entry_set_max_free(rlist);
                   rtree = rlist;
                   rlist = y;
           }
   
           /*
            * Final assembly: add ltree and rtree as subtrees of root.
            */
           root->left = ltree;
           root->right = rtree;
           vm_map_entry_set_max_free(root);
   
           return (root);
   }
   
   /*
    *      vm_map_entry_{un,}link:
    *
    *      Insert/remove entries from maps.
    */
   static void
   vm_map_entry_link(vm_map_t map,
                     vm_map_entry_t after_where,
                     vm_map_entry_t entry)
   {
   
           CTR4(KTR_VM,
               "vm_map_entry_link: map %p, nentries %d, entry %p, after %p", map,
               map->nentries, entry, after_where);
           VM_MAP_ASSERT_LOCKED(map);
           map->nentries++;
           entry->prev = after_where;
           entry->next = after_where->next;
           entry->next->prev = entry;
           after_where->next = entry;
   
           if (after_where != &map->header) {
                   if (after_where != map->root)
                           vm_map_entry_splay(after_where->start, map->root);
                   entry->right = after_where->right;
                   entry->left = after_where;
                   after_where->right = NULL;
                   after_where->adj_free = entry->start - after_where->end;
                   vm_map_entry_set_max_free(after_where);
           } else {
                   entry->right = map->root;
                   entry->left = NULL;
           }
           entry->adj_free = (entry->next == &map->header ? map->max_offset :
               entry->next->start) - entry->end;
           vm_map_entry_set_max_free(entry);
           map->root = entry;
   }
   
   static void
   vm_map_entry_unlink(vm_map_t map,
                       vm_map_entry_t entry)
   {
           vm_map_entry_t next, prev, root;
   
           VM_MAP_ASSERT_LOCKED(map);
           if (entry != map->root)
                   vm_map_entry_splay(entry->start, map->root);
           if (entry->left == NULL)
                   root = entry->right;
           else {
                   root = vm_map_entry_splay(entry->start, entry->left);
                   root->right = entry->right;
                   root->adj_free = (entry->next == &map->header ? map->max_offset :
                       entry->next->start) - root->end;
                   vm_map_entry_set_max_free(root);
           }
           map->root = root;
   
           prev = entry->prev;
           next = entry->next;
           next->prev = prev;
           prev->next = next;
           map->nentries--;
           CTR3(KTR_VM, "vm_map_entry_unlink: map %p, nentries %d, entry %p", map,
               map->nentries, entry);
   }
   
   /*
    *      vm_map_entry_resize_free:
    *
    *      Recompute the amount of free space following a vm_map_entry
    *      and propagate that value up the tree.  Call this function after
    *      resizing a map entry in-place, that is, without a call to
    *      vm_map_entry_link() or _unlink().
   *
   *      The map must be locked, and leaves it so.
   */
  static void
  vm_map_entry_resize_free(vm_map_t map, vm_map_entry_t entry)
  {
  
          /*
           * Using splay trees without parent pointers, propagating
           * max_free up the tree is done by moving the entry to the
           * root and making the change there.
           */
          if (entry != map->root)
                  map->root = vm_map_entry_splay(entry->start, map->root);
  
          entry->adj_free = (entry->next == &map->header ? map->max_offset :
              entry->next->start) - entry->end;
          vm_map_entry_set_max_free(entry);
  }
  
  /*
   *      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(
          vm_map_t map,
          vm_offset_t address,
          vm_map_entry_t *entry)  /* OUT */
  {
          vm_map_entry_t cur;
          boolean_t locked;
  
          /*
           * If the map is empty, then the map entry immediately preceding
           * "address" is the map's header.
           */
          cur = map->root;
          if (cur == NULL)
                  *entry = &map->header;
          else if (address >= cur->start && cur->end > address) {
                  *entry = cur;
                  return (TRUE);
          } else if ((locked = vm_map_locked(map)) ||
              sx_try_upgrade(&map->lock)) {
                  /*
                   * Splay requires a write lock on the map.  However, it only
                   * restructures the binary search tree; it does not otherwise
                   * change the map.  Thus, the map's timestamp need not change
                   * on a temporary upgrade.
                   */
                  map->root = cur = vm_map_entry_splay(address, cur);
                  if (!locked)
                          sx_downgrade(&map->lock);
  
                  /*
                   * If "address" is contained within a map entry, the new root
                   * is that map entry.  Otherwise, the new root is a map entry
                   * immediately before or after "address".
                   */
                  if (address >= cur->start) {
                          *entry = cur;
                          if (cur->end > address)
                                  return (TRUE);
                  } else
                          *entry = cur->prev;
          } else
                  /*
                   * Since the map is only locked for read access, perform a
                   * standard binary search tree lookup for "address".
                   */
                  for (;;) {
                          if (address < cur->start) {
                                  if (cur->left == NULL) {
                                          *entry = cur->prev;
                                          break;
                                  }
                                  cur = cur->left;
                          } else if (cur->end > address) {
                                  *entry = cur;
                                  return (TRUE);
                          } else {
                                  if (cur->right == NULL) {
                                          *entry = cur;
                                          break;
                                  }
                                  cur = cur->right;
                          }
                  }
          return (FALSE);
  }
  
  /*
   *      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.
   *
   *      If object is non-NULL, ref count must be bumped by caller
   *      prior to making call to account for the new entry.
   */
  int
  vm_map_insert(vm_map_t map, vm_object_t object, vm_ooffset_t offset,
                vm_offset_t start, vm_offset_t end, vm_prot_t prot, vm_prot_t max,
                int cow)
  {
          vm_map_entry_t new_entry;
          vm_map_entry_t prev_entry;
          vm_map_entry_t temp_entry;
          vm_eflags_t protoeflags;
          struct ucred *cred;
          vm_inherit_t inheritance;
          boolean_t charge_prev_obj;
  
          VM_MAP_ASSERT_LOCKED(map);
  
          /*
           * 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);
  
          protoeflags = 0;
          charge_prev_obj = FALSE;
  
          if (cow & MAP_COPY_ON_WRITE)
                  protoeflags |= MAP_ENTRY_COW|MAP_ENTRY_NEEDS_COPY;
  
          if (cow & MAP_NOFAULT) {
                  protoeflags |= MAP_ENTRY_NOFAULT;
  
                  KASSERT(object == NULL,
                          ("vm_map_insert: paradoxical MAP_NOFAULT request"));
          }
          if (cow & MAP_DISABLE_SYNCER)
                  protoeflags |= MAP_ENTRY_NOSYNC;
          if (cow & MAP_DISABLE_COREDUMP)
                  protoeflags |= MAP_ENTRY_NOCOREDUMP;
          if (cow & MAP_VN_WRITECOUNT)
                  protoeflags |= MAP_ENTRY_VN_WRITECNT;
          if (cow & MAP_INHERIT_SHARE)
                  inheritance = VM_INHERIT_SHARE;
          else
                  inheritance = VM_INHERIT_DEFAULT;
  
          cred = NULL;
          KASSERT((object != kmem_object && object != kernel_object) ||
              ((object == kmem_object || object == kernel_object) &&
                  !(protoeflags & MAP_ENTRY_NEEDS_COPY)),
              ("kmem or kernel object and cow"));
          if (cow & (MAP_ACC_NO_CHARGE | MAP_NOFAULT))
                  goto charged;
          if ((cow & MAP_ACC_CHARGED) || ((prot & VM_PROT_WRITE) &&
              ((protoeflags & MAP_ENTRY_NEEDS_COPY) || object == NULL))) {
                  if (!(cow & MAP_ACC_CHARGED) && !swap_reserve(end - start))
                          return (KERN_RESOURCE_SHORTAGE);
                  KASSERT(object == NULL || (protoeflags & MAP_ENTRY_NEEDS_COPY) ||
                      object->cred == NULL,
                      ("OVERCOMMIT: vm_map_insert o %p", object));
                  cred = curthread->td_ucred;
                  crhold(cred);
                  if (object == NULL && !(protoeflags & MAP_ENTRY_NEEDS_COPY))
                          charge_prev_obj = TRUE;
          }
  
  charged:
          /* Expand the kernel pmap, if necessary. */
          if (map == kernel_map && end > kernel_vm_end)
                  pmap_growkernel(end);
          if (object != NULL) {
                  /*
                   * OBJ_ONEMAPPING must be cleared unless this mapping
                   * is trivially proven to be the only mapping for any
                   * of the object's pages.  (Object granularity
                   * reference counting is insufficient to recognize
                   * aliases with precision.)
                   */
                  VM_OBJECT_WLOCK(object);
                  if (object->ref_count > 1 || object->shadow_count != 0)
                          vm_object_clear_flag(object, OBJ_ONEMAPPING);
                  VM_OBJECT_WUNLOCK(object);
          }
          else if ((prev_entry != &map->header) &&
                   (prev_entry->eflags == protoeflags) &&
                   (cow & (MAP_ENTRY_GROWS_DOWN | MAP_ENTRY_GROWS_UP)) == 0 &&
                   (prev_entry->end == start) &&
                   (prev_entry->wired_count == 0) &&
                   (prev_entry->cred == cred ||
                    (prev_entry->object.vm_object != NULL &&
                     (prev_entry->object.vm_object->cred == cred))) &&
                     vm_object_coalesce(prev_entry->object.vm_object,
                         prev_entry->offset,
                         (vm_size_t)(prev_entry->end - prev_entry->start),
                         (vm_size_t)(end - prev_entry->end), charge_prev_obj)) {
                  /*
                   * We were able to extend the object.  Determine if we
                   * can extend the previous map entry to include the
                   * new range as well.
                   */
                  if ((prev_entry->inheritance == inheritance) &&
                      (prev_entry->protection == prot) &&
                      (prev_entry->max_protection == max)) {
                          map->size += (end - prev_entry->end);
                          prev_entry->end = end;
                          vm_map_entry_resize_free(map, prev_entry);
                          vm_map_simplify_entry(map, prev_entry);
                          if (cred != NULL)
                                  crfree(cred);
                          return (KERN_SUCCESS);
                  }
  
                  /*
                   * If we can extend the object but cannot extend the
                   * map entry, we have to create a new map entry.  We
                   * must bump the ref count on the extended object to
                   * account for it.  object may be NULL.
                   */
                  object = prev_entry->object.vm_object;
                  offset = prev_entry->offset +
                          (prev_entry->end - prev_entry->start);
                  vm_object_reference(object);
                  if (cred != NULL && object != NULL && object->cred != NULL &&
                      !(prev_entry->eflags & MAP_ENTRY_NEEDS_COPY)) {
                          /* Object already accounts for this uid. */
                          crfree(cred);
                          cred = NULL;
                  }
          }
  
          /*
           * NOTE: if conditionals fail, object can be NULL here.  This occurs
           * in things like the buffer map where we manage kva but do not manage
           * backing objects.
           */
  
          /*
           * Create a new entry
           */
          new_entry = vm_map_entry_create(map);
          new_entry->start = start;
          new_entry->end = end;
          new_entry->cred = NULL;
  
          new_entry->eflags = protoeflags;
          new_entry->object.vm_object = object;
          new_entry->offset = offset;
          new_entry->avail_ssize = 0;
  
          new_entry->inheritance = inheritance;
          new_entry->protection = prot;
          new_entry->max_protection = max;
          new_entry->wired_count = 0;
          new_entry->read_ahead = VM_FAULT_READ_AHEAD_INIT;
          new_entry->next_read = OFF_TO_IDX(offset);
  
          KASSERT(cred == NULL || !ENTRY_CHARGED(new_entry),
              ("OVERCOMMIT: vm_map_insert leaks vm_map %p", new_entry));
          new_entry->cred = cred;
  
          /*
           * Insert the new entry into the list
           */
          vm_map_entry_link(map, prev_entry, new_entry);
          map->size += new_entry->end - new_entry->start;
  
          /*
           * It may be possible to merge the new entry with the next and/or
           * previous entries.  However, due to MAP_STACK_* being a hack, a
           * panic can result from merging such entries.
           */
          if ((cow & (MAP_STACK_GROWS_DOWN | MAP_STACK_GROWS_UP)) == 0)
                  vm_map_simplify_entry(map, new_entry);
  
          if (cow & (MAP_PREFAULT|MAP_PREFAULT_PARTIAL)) {
                  vm_map_pmap_enter(map, start, prot,
                                      object, OFF_TO_IDX(offset), end - start,
                                      cow & MAP_PREFAULT_PARTIAL);
          }
  
          return (KERN_SUCCESS);
  }
  
  /*
   *      vm_map_findspace:
   *
   *      Find the first fit (lowest VM address) for "length" free bytes
   *      beginning at address >= start in the given map.
   *
   *      In a vm_map_entry, "adj_free" is the amount of free space
   *      adjacent (higher address) to this entry, and "max_free" is the
   *      maximum amount of contiguous free space in its subtree.  This
   *      allows finding a free region in one path down the tree, so
   *      O(log n) amortized with splay trees.
   *
   *      The map must be locked, and leaves it so.
   *
   *      Returns: 0 on success, and starting address in *addr,
   *               1 if insufficient space.
   */
  int
  vm_map_findspace(vm_map_t map, vm_offset_t start, vm_size_t length,
      vm_offset_t *addr)  /* OUT */
  {
          vm_map_entry_t entry;
          vm_offset_t st;
  
          /*
           * Request must fit within min/max VM address and must avoid
           * address wrap.
           */
          if (start < map->min_offset)
                  start = map->min_offset;
          if (start + length > map->max_offset || start + length < start)
                  return (1);
  
          /* Empty tree means wide open address space. */
          if (map->root == NULL) {
                  *addr = start;
                  return (0);
          }
  
          /*
           * After splay, if start comes before root node, then there
           * must be a gap from start to the root.
           */
          map->root = vm_map_entry_splay(start, map->root);
          if (start + length <= map->root->start) {
                  *addr = start;
                  return (0);
          }
  
          /*
           * Root is the last node that might begin its gap before
           * start, and this is the last comparison where address
           * wrap might be a problem.
           */
          st = (start > map->root->end) ? start : map->root->end;
          if (length <= map->root->end + map->root->adj_free - st) {
                  *addr = st;
                  return (0);
          }
  
          /* With max_free, can immediately tell if no solution. */
          entry = map->root->right;
          if (entry == NULL || length > entry->max_free)
                  return (1);
  
          /*
           * Search the right subtree in the order: left subtree, root,
           * right subtree (first fit).  The previous splay implies that
           * all regions in the right subtree have addresses > start.
           */
          while (entry != NULL) {
                  if (entry->left != NULL && entry->left->max_free >= length)
                          entry = entry->left;
                  else if (entry->adj_free >= length) {
                          *addr = entry->end;
                          return (0);
                  } else
                          entry = entry->right;
          }
  
          /* Can't get here, so panic if we do. */
          panic("vm_map_findspace: max_free corrupt");
  }
  
  int
  vm_map_fixed(vm_map_t map, vm_object_t object, vm_ooffset_t offset,
      vm_offset_t start, vm_size_t length, vm_prot_t prot,
      vm_prot_t max, int cow)
  {
          vm_offset_t end;
          int result;
  
          end = start + length;
          vm_map_lock(map);
          VM_MAP_RANGE_CHECK(map, start, end);
          (void) vm_map_delete(map, start, end);
          result = vm_map_insert(map, object, offset, start, end, prot,
              max, cow);
          vm_map_unlock(map);
          return (result);
  }
  
  /*
   *      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.
   *
   *      If object is non-NULL, ref count must be bumped by caller
   *      prior to making call to account for the new entry.
   */
  int
  vm_map_find(vm_map_t map, vm_object_t object, vm_ooffset_t offset,
              vm_offset_t *addr,  /* IN/OUT */
              vm_size_t length, vm_offset_t max_addr, int find_space,
              vm_prot_t prot, vm_prot_t max, int cow)
  {
          vm_offset_t alignment, initial_addr, start;
          int result;
  
          if (find_space == VMFS_OPTIMAL_SPACE && (object == NULL ||
              (object->flags & OBJ_COLORED) == 0))
                  find_space = VMFS_ANY_SPACE;
          if (find_space >> 8 != 0) {
                  KASSERT((find_space & 0xff) == 0, ("bad VMFS flags"));
                  alignment = (vm_offset_t)1 << (find_space >> 8);
          } else
                  alignment = 0;
          initial_addr = *addr;
  again:
          start = initial_addr;
          vm_map_lock(map);
          do {
                  if (find_space != VMFS_NO_SPACE) {
                          if (vm_map_findspace(map, start, length, addr) ||
                              (max_addr != 0 && *addr + length > max_addr)) {
                                  vm_map_unlock(map);
                                  if (find_space == VMFS_OPTIMAL_SPACE) {
                                          find_space = VMFS_ANY_SPACE;
                                          goto again;
                                  }
                                  return (KERN_NO_SPACE);
                          }
                          switch (find_space) {
                          case VMFS_SUPER_SPACE:
                          case VMFS_OPTIMAL_SPACE:
                                  pmap_align_superpage(object, offset, addr,
                                      length);
                                  break;
                          case VMFS_ANY_SPACE:
                                  break;
                          default:
                                  if ((*addr & (alignment - 1)) != 0) {
                                          *addr &= ~(alignment - 1);
                                          *addr += alignment;
                                  }
                                  break;
                          }
  
                          start = *addr;
                  }
                  result = vm_map_insert(map, object, offset, start, start +
                      length, prot, max, cow);
          } while (result == KERN_NO_SPACE && find_space != VMFS_NO_SPACE &&
              find_space != VMFS_ANY_SPACE);
          vm_map_unlock(map);
          return (result);
  }
  
  /*
   *      vm_map_simplify_entry:
   *
   *      Simplify the given map entry by merging with either neighbor.  This
   *      routine also has the ability to merge with both neighbors.
   *
   *      The map must be locked.
   *
   *      This routine guarentees that the passed entry remains valid (though
   *      possibly extended).  When merging, this routine may delete one or
   *      both neighbors.
   */
  void
  vm_map_simplify_entry(vm_map_t map, vm_map_entry_t entry)
  {
          vm_map_entry_t next, prev;
          vm_size_t prevsize, esize;
  
          if (entry->eflags & (MAP_ENTRY_IN_TRANSITION | MAP_ENTRY_IS_SUB_MAP))
                  return;
  
          prev = entry->prev;
          if (prev != &map->header) {
                  prevsize = prev->end - prev->start;
                  if ( (prev->end == entry->start) &&
                       (prev->object.vm_object == entry->object.vm_object) &&
                       (!prev->object.vm_object ||
                          (prev->offset + prevsize == entry->offset)) &&
                       (prev->eflags == entry->eflags) &&
                       (prev->protection == entry->protection) &&
                       (prev->max_protection == entry->max_protection) &&
                       (prev->inheritance == entry->inheritance) &&
                       (prev->wired_count == entry->wired_count) &&
                       (prev->cred == entry->cred)) {
                          vm_map_entry_unlink(map, prev);
                          entry->start = prev->start;
                          entry->offset = prev->offset;
                          if (entry->prev != &map->header)
                                  vm_map_entry_resize_free(map, entry->prev);
  
                          /*
                           * If the backing object is a vnode object,
                           * vm_object_deallocate() calls vrele().
                           * However, vrele() does not lock the vnode
                           * because the vnode has additional
                           * references.  Thus, the map lock can be kept
                           * without causing a lock-order reversal with
                           * the vnode lock.
                           *
                           * Since we count the number of virtual page
                           * mappings in object->un_pager.vnp.writemappings,
                           * the writemappings value should not be adjusted
                           * when the entry is disposed of.
                           */
                          if (prev->object.vm_object)
                                  vm_object_deallocate(prev->object.vm_object);
                          if (prev->cred != NULL)
                                  crfree(prev->cred);
                          vm_map_entry_dispose(map, prev);
                  }
          }
  
          next = entry->next;
          if (next != &map->header) {
                  esize = entry->end - entry->start;
                  if ((entry->end == next->start) &&
                      (next->object.vm_object == entry->object.vm_object) &&
                       (!entry->object.vm_object ||
                          (entry->offset + esize == next->offset)) &&
                      (next->eflags == entry->eflags) &&
                      (next->protection == entry->protection) &&
                      (next->max_protection == entry->max_protection) &&
                      (next->inheritance == entry->inheritance) &&
                      (next->wired_count == entry->wired_count) &&
                      (next->cred == entry->cred)) {
                          vm_map_entry_unlink(map, next);
                          entry->end = next->end;
                          vm_map_entry_resize_free(map, entry);
  
                          /*
                           * See comment above.
                           */
                          if (next->object.vm_object)
                                  vm_object_deallocate(next->object.vm_object);
                          if (next->cred != NULL)
                                  crfree(next->cred);
                          vm_map_entry_dispose(map, next);
                  }
          }
  }
  /*
   *      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(vm_map_t map, vm_map_entry_t entry, vm_offset_t start)
  {
          vm_map_entry_t new_entry;
  
          VM_MAP_ASSERT_LOCKED(map);
  
          /*
           * 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.
           */
          vm_map_simplify_entry(map, entry);
  
          /*
           * If there is no object backing this entry, we might as well create
           * one now.  If we defer it, an object can get created after the map
           * is clipped, and individual objects will be created for the split-up
           * map.  This is a bit of a hack, but is also about the best place to
           * put this improvement.
           */
          if (entry->object.vm_object == NULL && !map->system_map) {
                  vm_object_t object;
                  object = vm_object_allocate(OBJT_DEFAULT,
                                  atop(entry->end - entry->start));
                  entry->object.vm_object = object;
                  entry->offset = 0;
                  if (entry->cred != NULL) {
                          object->cred = entry->cred;
                          object->charge = entry->end - entry->start;
                          entry->cred = NULL;
                  }
          } else if (entry->object.vm_object != NULL &&
                     ((entry->eflags & MAP_ENTRY_NEEDS_COPY) == 0) &&
                     entry->cred != NULL) {
                  VM_OBJECT_WLOCK(entry->object.vm_object);
                  KASSERT(entry->object.vm_object->cred == NULL,
                      ("OVERCOMMIT: vm_entry_clip_start: both cred e %p", entry));
                  entry->object.vm_object->cred = entry->cred;
                  entry->object.vm_object->charge = entry->end - entry->start;
                  VM_OBJECT_WUNLOCK(entry->object.vm_object);
                  entry->cred = NULL;
          }
  
          new_entry = vm_map_entry_create(map);
          *new_entry = *entry;
  
          new_entry->end = start;
          entry->offset += (start - entry->start);
          entry->start = start;
          if (new_entry->cred != NULL)
                  crhold(entry->cred);
  
          vm_map_entry_link(map, entry->prev, new_entry);
  
          if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
                  vm_object_reference(new_entry->object.vm_object);
                  /*
                   * The object->un_pager.vnp.writemappings for the
                   * object of MAP_ENTRY_VN_WRITECNT type entry shall be
                   * kept as is here.  The virtual pages are
                   * re-distributed among the clipped entries, so the sum is
                   * left the same.
                   */
          }
  }
  
  /*
   *      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(vm_map_t map, vm_map_entry_t entry, vm_offset_t end)
  {
          vm_map_entry_t new_entry;
  
          VM_MAP_ASSERT_LOCKED(map);
  
          /*
           * If there is no object backing this entry, we might as well create
           * one now.  If we defer it, an object can get created after the map
           * is clipped, and individual objects will be created for the split-up
           * map.  This is a bit of a hack, but is also about the best place to
           * put this improvement.
           */
          if (entry->object.vm_object == NULL && !map->system_map) {
                  vm_object_t object;
                  object = vm_object_allocate(OBJT_DEFAULT,
                                  atop(entry->end - entry->start));
                  entry->object.vm_object = object;
                  entry->offset = 0;
                  if (entry->cred != NULL) {
                          object->cred = entry->cred;
                          object->charge = entry->end - entry->start;
                          entry->cred = NULL;
                  }
          } else if (entry->object.vm_object != NULL &&
                     ((entry->eflags & MAP_ENTRY_NEEDS_COPY) == 0) &&
                     entry->cred != NULL) {
                  VM_OBJECT_WLOCK(entry->object.vm_object);
                  KASSERT(entry->object.vm_object->cred == NULL,
                      ("OVERCOMMIT: vm_entry_clip_end: both cred e %p", entry));
                  entry->object.vm_object->cred = entry->cred;
                  entry->object.vm_object->charge = entry->end - entry->start;
                  VM_OBJECT_WUNLOCK(entry->object.vm_object);
                  entry->cred = NULL;
          }
  
          /*
           * 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);
          if (new_entry->cred != NULL)
                  crhold(entry->cred);
  
          vm_map_entry_link(map, entry, new_entry);
  
          if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
                  vm_object_reference(new_entry->object.vm_object);
          }
  }
  
  /*
   *      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(
          vm_map_t map,
          vm_offset_t start,
          vm_offset_t end,
          vm_map_t submap)
  {
          vm_map_entry_t entry;
          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->eflags & MAP_ENTRY_COW) == 0) &&
              (entry->object.vm_object == NULL)) {
                  entry->object.sub_map = submap;
                  entry->eflags |= MAP_ENTRY_IS_SUB_MAP;
                  result = KERN_SUCCESS;
          }
          vm_map_unlock(map);
  
          return (result);
  }
  
  /*
   * The maximum number of pages to map
   */
  #define MAX_INIT_PT     96
  
  /*
   *      vm_map_pmap_enter:
   *
   *      Preload read-only mappings for the specified object's resident pages
   *      into the target map.  If "flags" is MAP_PREFAULT_PARTIAL, then only
   *      the resident pages within the address range [addr, addr + ulmin(size,
   *      ptoa(MAX_INIT_PT))) are mapped.  Otherwise, all resident pages within
   *      the specified address range are mapped.  This eliminates many soft
   *      faults on process startup and immediately after an mmap(2).  Because
   *      these are speculative mappings, cached pages are not reactivated and
   *      mapped.
   */
  void
  vm_map_pmap_enter(vm_map_t map, vm_offset_t addr, vm_prot_t prot,
      vm_object_t object, vm_pindex_t pindex, vm_size_t size, int flags)
  {
          vm_offset_t start;
          vm_page_t p, p_start;
          vm_pindex_t psize, tmpidx;
  
          if ((prot & (VM_PROT_READ | VM_PROT_EXECUTE)) == 0 || object == NULL)
                  return;
          VM_OBJECT_RLOCK(object);
          if (object->type == OBJT_DEVICE || object->type == OBJT_SG) {
                  VM_OBJECT_RUNLOCK(object);
                  VM_OBJECT_WLOCK(object);
                  if (object->type == OBJT_DEVICE || object->type == OBJT_SG) {
                          pmap_object_init_pt(map->pmap, addr, object, pindex,
                              size);
                          VM_OBJECT_WUNLOCK(object);
                          return;
                  }
                  VM_OBJECT_LOCK_DOWNGRADE(object);
          }
  
          psize = atop(size);
          if (psize > MAX_INIT_PT && (flags & MAP_PREFAULT_PARTIAL) != 0)
                  psize = MAX_INIT_PT;
          if (psize + pindex > object->size) {
                  if (object->size < pindex) {
                          VM_OBJECT_RUNLOCK(object);
                          return;
                  }
                  psize = object->size - pindex;
          }
  
          start = 0;
          p_start = NULL;
  
          p = vm_page_find_least(object, pindex);
          /*
           * Assert: the variable p is either (1) the page with the
           * least pindex greater than or equal to the parameter pindex
           * or (2) NULL.
           */
          for (;
               p != NULL && (tmpidx = p->pindex - pindex) < psize;
               p = TAILQ_NEXT(p, listq)) {
                  /*
                   * don't allow an madvise to blow away our really
                   * free pages allocating pv entries.
                   */
                  if ((flags & MAP_PREFAULT_MADVISE) &&
                      cnt.v_free_count < cnt.v_free_reserved) {
                          psize = tmpidx;
                          break;
                  }
                  if (p->valid == VM_PAGE_BITS_ALL) {
                          if (p_start == NULL) {
                                  start = addr + ptoa(tmpidx);
                                  p_start = p;
                          }
                  } else if (p_start != NULL) {
                          pmap_enter_object(map->pmap, start, addr +
                              ptoa(tmpidx), p_start, prot);
                          p_start = NULL;
                  }
          }
          if (p_start != NULL)
                  pmap_enter_object(map->pmap, start, addr + ptoa(psize),
                      p_start, prot);
          VM_OBJECT_RUNLOCK(object);
  }
  
  /*
   *      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(vm_map_t map, vm_offset_t start, vm_offset_t end,
                 vm_prot_t new_prot, boolean_t set_max)
  {
          vm_map_entry_t current, entry;
          vm_object_t obj;
          struct ucred *cred;
          vm_prot_t old_prot;
  
          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->eflags & MAP_ENTRY_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;
          }
  
  
          /*
           * Do an accounting pass for private read-only mappings that
           * now will do cow due to allowed write (e.g. debugger sets
           * breakpoint on text segment)
           */
          for (current = entry; (current != &map->header) &&
               (current->start < end); current = current->next) {
  
                  vm_map_clip_end(map, current, end);
  
                  if (set_max ||
                      ((new_prot & ~(current->protection)) & VM_PROT_WRITE) == 0 ||
                      ENTRY_CHARGED(current)) {
                          continue;
                  }
  
                  cred = curthread->td_ucred;
                  obj = current->object.vm_object;
  
                  if (obj == NULL || (current->eflags & MAP_ENTRY_NEEDS_COPY)) {
                          if (!swap_reserve(current->end - current->start)) {
                                  vm_map_unlock(map);
                                  return (KERN_RESOURCE_SHORTAGE);
                          }
                          crhold(cred);
                          current->cred = cred;
                          continue;
                  }
  
                  VM_OBJECT_WLOCK(obj);
                  if (obj->type != OBJT_DEFAULT && obj->type != OBJT_SWAP) {
                          VM_OBJECT_WUNLOCK(obj);
                          continue;
                  }
  
                  /*
                   * Charge for the whole object allocation now, since
                   * we cannot distinguish between non-charged and
                   * charged clipped mapping of the same object later.
                   */
                  KASSERT(obj->charge == 0,
                      ("vm_map_protect: object %p overcharged\n", obj));
                  if (!swap_reserve(ptoa(obj->size))) {
                          VM_OBJECT_WUNLOCK(obj);
                          vm_map_unlock(map);
                          return (KERN_RESOURCE_SHORTAGE);
                  }
  
                  crhold(cred);
                  obj->cred = cred;
                  obj->charge = ptoa(obj->size);
                  VM_OBJECT_WUNLOCK(obj);
          }
  
          /*
           * Go back and fix up protections. [Note that clipping is not
           * necessary the second time.]
           */
          current = entry;
          while ((current != &map->header) && (current->start < end)) {
                  old_prot = current->protection;
  
                  if (set_max)
                          current->protection =
                              (current->max_protection = new_prot) &
                              old_prot;
                  else
                          current->protection = new_prot;
  
                  if ((current->eflags & (MAP_ENTRY_COW | MAP_ENTRY_USER_WIRED))
                       == (MAP_ENTRY_COW | MAP_ENTRY_USER_WIRED) &&
                      (current->protection & VM_PROT_WRITE) != 0 &&
                      (old_prot & VM_PROT_WRITE) == 0) {
                          vm_fault_copy_entry(map, map, current, current, NULL);
                  }
  
                  /*
                   * When restricting access, update the physical map.  Worry
                   * about copy-on-write here.
                   */
                  if ((old_prot & ~current->protection) != 0) {
  #define MASK(entry)     (((entry)->eflags & MAP_ENTRY_COW) ? ~VM_PROT_WRITE : \
                                                          VM_PROT_ALL)
                          pmap_protect(map->pmap, current->start,
                              current->end,
                              current->protection & MASK(current));
  #undef  MASK
                  }
                  vm_map_simplify_entry(map, current);
                  current = current->next;
          }
          vm_map_unlock(map);
          return (KERN_SUCCESS);
  }
  
  /*
   *      vm_map_madvise:
   *
   *      This routine traverses a processes map handling the madvise
   *      system call.  Advisories are classified as either those effecting
   *      the vm_map_entry structure, or those effecting the underlying
   *      objects.
   */
  int
  vm_map_madvise(
          vm_map_t map,
          vm_offset_t start,
          vm_offset_t end,
          int behav)
  {
          vm_map_entry_t current, entry;
          int modify_map = 0;
  
          /*
           * Some madvise calls directly modify the vm_map_entry, in which case
           * we need to use an exclusive lock on the map and we need to perform
           * various clipping operations.  Otherwise we only need a read-lock
           * on the map.
           */
          switch(behav) {
          case MADV_NORMAL:
          case MADV_SEQUENTIAL:
          case MADV_RANDOM:
          case MADV_NOSYNC:
          case MADV_AUTOSYNC:
          case MADV_NOCORE:
          case MADV_CORE:
                  modify_map = 1;
                  vm_map_lock(map);
                  break;
          case MADV_WILLNEED:
          case MADV_DONTNEED:
          case MADV_FREE:
                  vm_map_lock_read(map);
                  break;
          default:
                  return (KERN_INVALID_ARGUMENT);
          }
  
          /*
           * Locate starting entry and clip if necessary.
           */
          VM_MAP_RANGE_CHECK(map, start, end);
  
          if (vm_map_lookup_entry(map, start, &entry)) {
                  if (modify_map)
                          vm_map_clip_start(map, entry, start);
          } else {
                  entry = entry->next;
          }
  
          if (modify_map) {
                  /*
                   * madvise behaviors that are implemented in the vm_map_entry.
                   *
                   * We clip the vm_map_entry so that behavioral changes are
                   * limited to the specified address range.
                   */
                  for (current = entry;
                       (current != &map->header) && (current->start < end);
                       current = current->next
                  ) {
                          if (current->eflags & MAP_ENTRY_IS_SUB_MAP)
                                  continue;
  
                          vm_map_clip_end(map, current, end);
  
                          switch (behav) {
                          case MADV_NORMAL:
                                  vm_map_entry_set_behavior(current, MAP_ENTRY_BEHAV_NORMAL);
                                  break;
                          case MADV_SEQUENTIAL:
                                  vm_map_entry_set_behavior(current, MAP_ENTRY_BEHAV_SEQUENTIAL);
                                  break;
                          case MADV_RANDOM:
                                  vm_map_entry_set_behavior(current, MAP_ENTRY_BEHAV_RANDOM);
                                  break;
                          case MADV_NOSYNC:
                                  current->eflags |= MAP_ENTRY_NOSYNC;
                                  break;
                          case MADV_AUTOSYNC:
                                  current->eflags &= ~MAP_ENTRY_NOSYNC;
                                  break;
                          case MADV_NOCORE:
                                  current->eflags |= MAP_ENTRY_NOCOREDUMP;
                                  break;
                          case MADV_CORE:
                                  current->eflags &= ~MAP_ENTRY_NOCOREDUMP;
                                  break;
                          default:
                                  break;
                          }
                          vm_map_simplify_entry(map, current);
                  }
                  vm_map_unlock(map);
          } else {
                  vm_pindex_t pstart, pend;
  
                  /*
                   * madvise behaviors that are implemented in the underlying
                   * vm_object.
                   *
                   * Since we don't clip the vm_map_entry, we have to clip
                   * the vm_object pindex and count.
                   */
                  for (current = entry;
                       (current != &map->header) && (current->start < end);
                       current = current->next
                  ) {
                          vm_offset_t useEnd, useStart;
  
                          if (current->eflags & MAP_ENTRY_IS_SUB_MAP)
                                  continue;
  
                          pstart = OFF_TO_IDX(current->offset);
                          pend = pstart + atop(current->end - current->start);
                          useStart = current->start;
                          useEnd = current->end;
  
                          if (current->start < start) {
                                  pstart += atop(start - current->start);
                                  useStart = start;
                          }
                          if (current->end > end) {
                                  pend -= atop(current->end - end);
                                  useEnd = end;
                          }
  
                          if (pstart >= pend)
                                  continue;
  
                          /*
                           * Perform the pmap_advise() before clearing
                           * PGA_REFERENCED in vm_page_advise().  Otherwise, a
                           * concurrent pmap operation, such as pmap_remove(),
                           * could clear a reference in the pmap and set
                           * PGA_REFERENCED on the page before the pmap_advise()
                           * had completed.  Consequently, the page would appear
                           * referenced based upon an old reference that
                           * occurred before this pmap_advise() ran.
                           */
                          if (behav == MADV_DONTNEED || behav == MADV_FREE)
                                  pmap_advise(map->pmap, useStart, useEnd,
                                      behav);
  
                          vm_object_madvise(current->object.vm_object, pstart,
                              pend, behav);
                          if (behav == MADV_WILLNEED) {
                                  vm_map_pmap_enter(map,
                                      useStart,
                                      current->protection,
                                      current->object.vm_object,
                                      pstart,
                                      ptoa(pend - pstart),
                                      MAP_PREFAULT_MADVISE
                                  );
                          }
                  }
                  vm_map_unlock_read(map);
          }
          return (0);
  }
  
  
  /*
   *      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 vmspace_fork.
   */
  int
  vm_map_inherit(vm_map_t map, vm_offset_t start, vm_offset_t end,
                 vm_inherit_t new_inheritance)
  {
          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;
                  vm_map_simplify_entry(map, entry);
                  entry = entry->next;
          }
          vm_map_unlock(map);
          return (KERN_SUCCESS);
  }
  
  /*
   *      vm_map_unwire:
   *
   *      Implements both kernel and user unwiring.
   */
  int
  vm_map_unwire(vm_map_t map, vm_offset_t start, vm_offset_t end,
      int flags)
  {
          vm_map_entry_t entry, first_entry, tmp_entry;
          vm_offset_t saved_start;
          unsigned int last_timestamp;
          int rv;
          boolean_t need_wakeup, result, user_unwire;
  
          user_unwire = (flags & VM_MAP_WIRE_USER) ? TRUE : FALSE;
          vm_map_lock(map);
          VM_MAP_RANGE_CHECK(map, start, end);
          if (!vm_map_lookup_entry(map, start, &first_entry)) {
                  if (flags & VM_MAP_WIRE_HOLESOK)
                          first_entry = first_entry->next;
                  else {
                          vm_map_unlock(map);
                          return (KERN_INVALID_ADDRESS);
                  }
          }
          last_timestamp = map->timestamp;
          entry = first_entry;
          while (entry != &map->header && entry->start < end) {
                  if (entry->eflags & MAP_ENTRY_IN_TRANSITION) {
                          /*
                           * We have not yet clipped the entry.
                           */
                          saved_start = (start >= entry->start) ? start :
                              entry->start;
                          entry->eflags |= MAP_ENTRY_NEEDS_WAKEUP;
                          if (vm_map_unlock_and_wait(map, 0)) {
                                  /*
                                   * Allow interruption of user unwiring?
                                   */
                          }
                          vm_map_lock(map);
                          if (last_timestamp+1 != map->timestamp) {
                                  /*
                                   * Look again for the entry because the map was
                                   * modified while it was unlocked.
                                   * Specifically, the entry may have been
                                   * clipped, merged, or deleted.
                                   */
                                  if (!vm_map_lookup_entry(map, saved_start,
                                      &tmp_entry)) {
                                          if (flags & VM_MAP_WIRE_HOLESOK)
                                                  tmp_entry = tmp_entry->next;
                                          else {
                                                  if (saved_start == start) {
                                                          /*
                                                           * First_entry has been deleted.
                                                           */
                                                          vm_map_unlock(map);
                                                          return (KERN_INVALID_ADDRESS);
                                                  }
                                                  end = saved_start;
                                                  rv = KERN_INVALID_ADDRESS;
                                                  goto done;
                                          }
                                  }
                                  if (entry == first_entry)
                                          first_entry = tmp_entry;
                                  else
                                          first_entry = NULL;
                                  entry = tmp_entry;
                          }
                          last_timestamp = map->timestamp;
                          continue;
                  }
                  vm_map_clip_start(map, entry, start);
                  vm_map_clip_end(map, entry, end);
                  /*
                   * Mark the entry in case the map lock is released.  (See
                   * above.)
                   */
                  entry->eflags |= MAP_ENTRY_IN_TRANSITION;
                  entry->wiring_thread = curthread;
                  /*
                   * Check the map for holes in the specified region.
                   * If VM_MAP_WIRE_HOLESOK was specified, skip this check.
                   */
                  if (((flags & VM_MAP_WIRE_HOLESOK) == 0) &&
                      (entry->end < end && (entry->next == &map->header ||
                      entry->next->start > entry->end))) {
                          end = entry->end;
                          rv = KERN_INVALID_ADDRESS;
                          goto done;
                  }
                  /*
                   * If system unwiring, require that the entry is system wired.
                   */
                  if (!user_unwire &&
                      vm_map_entry_system_wired_count(entry) == 0) {
                          end = entry->end;
                          rv = KERN_INVALID_ARGUMENT;
                          goto done;
                  }
                  entry = entry->next;
          }
          rv = KERN_SUCCESS;
  done:
          need_wakeup = FALSE;
          if (first_entry == NULL) {
                  result = vm_map_lookup_entry(map, start, &first_entry);
                  if (!result && (flags & VM_MAP_WIRE_HOLESOK))
                          first_entry = first_entry->next;
                  else
                          KASSERT(result, ("vm_map_unwire: lookup failed"));
          }
          for (entry = first_entry; entry != &map->header && entry->start < end;
              entry = entry->next) {
                  /*
                   * If VM_MAP_WIRE_HOLESOK was specified, an empty
                   * space in the unwired region could have been mapped
                   * while the map lock was dropped for draining
                   * MAP_ENTRY_IN_TRANSITION.  Moreover, another thread
                   * could be simultaneously wiring this new mapping
                   * entry.  Detect these cases and skip any entries
                   * marked as in transition by us.
                   */
                  if ((entry->eflags & MAP_ENTRY_IN_TRANSITION) == 0 ||
                      entry->wiring_thread != curthread) {
                          KASSERT((flags & VM_MAP_WIRE_HOLESOK) != 0,
                              ("vm_map_unwire: !HOLESOK and new/changed entry"));
                          continue;
                  }
  
                  if (rv == KERN_SUCCESS && (!user_unwire ||
                      (entry->eflags & MAP_ENTRY_USER_WIRED))) {
                          if (user_unwire)
                                  entry->eflags &= ~MAP_ENTRY_USER_WIRED;
                          entry->wired_count--;
                          if (entry->wired_count == 0) {
                                  /*
                                   * Retain the map lock.
                                   */
                                  vm_fault_unwire(map, entry->start, entry->end,
                                      entry->object.vm_object != NULL &&
                                      (entry->object.vm_object->flags &
                                      OBJ_FICTITIOUS) != 0);
                          }
                  }
                  KASSERT((entry->eflags & MAP_ENTRY_IN_TRANSITION) != 0,
                      ("vm_map_unwire: in-transition flag missing"));
                  entry->eflags &= ~MAP_ENTRY_IN_TRANSITION;
                  entry->wiring_thread = NULL;
                  if (entry->eflags & MAP_ENTRY_NEEDS_WAKEUP) {
                          entry->eflags &= ~MAP_ENTRY_NEEDS_WAKEUP;
                          need_wakeup = TRUE;
                  }
                  vm_map_simplify_entry(map, entry);
          }
          vm_map_unlock(map);
          if (need_wakeup)
                  vm_map_wakeup(map);
          return (rv);
  }
  
  /*
   *      vm_map_wire:
   *
   *      Implements both kernel and user wiring.
   */
  int
  vm_map_wire(vm_map_t map, vm_offset_t start, vm_offset_t end,
      int flags)
  {
          vm_map_entry_t entry, first_entry, tmp_entry;
          vm_offset_t saved_end, saved_start;
          unsigned int last_timestamp;
          int rv;
          boolean_t fictitious, need_wakeup, result, user_wire;
          vm_prot_t prot;
  
          prot = 0;
          if (flags & VM_MAP_WIRE_WRITE)
                  prot |= VM_PROT_WRITE;
          user_wire = (flags & VM_MAP_WIRE_USER) ? TRUE : FALSE;
          vm_map_lock(map);
          VM_MAP_RANGE_CHECK(map, start, end);
          if (!vm_map_lookup_entry(map, start, &first_entry)) {
                  if (flags & VM_MAP_WIRE_HOLESOK)
                          first_entry = first_entry->next;
                  else {
                          vm_map_unlock(map);
                          return (KERN_INVALID_ADDRESS);
                  }
          }
          last_timestamp = map->timestamp;
          entry = first_entry;
          while (entry != &map->header && entry->start < end) {
                  if (entry->eflags & MAP_ENTRY_IN_TRANSITION) {
                          /*
                           * We have not yet clipped the entry.
                           */
                          saved_start = (start >= entry->start) ? start :
                              entry->start;
                          entry->eflags |= MAP_ENTRY_NEEDS_WAKEUP;
                          if (vm_map_unlock_and_wait(map, 0)) {
                                  /*
                                   * Allow interruption of user wiring?
                                   */
                          }
                          vm_map_lock(map);
                          if (last_timestamp + 1 != map->timestamp) {
                                  /*
                                   * Look again for the entry because the map was
                                   * modified while it was unlocked.
                                   * Specifically, the entry may have been
                                   * clipped, merged, or deleted.
                                   */
                                  if (!vm_map_lookup_entry(map, saved_start,
                                      &tmp_entry)) {
                                          if (flags & VM_MAP_WIRE_HOLESOK)
                                                  tmp_entry = tmp_entry->next;
                                          else {
                                                  if (saved_start == start) {
                                                          /*
                                                           * first_entry has been deleted.
                                                           */
                                                          vm_map_unlock(map);
                                                          return (KERN_INVALID_ADDRESS);
                                                  }
                                                  end = saved_start;
                                                  rv = KERN_INVALID_ADDRESS;
                                                  goto done;
                                          }
                                  }
                                  if (entry == first_entry)
                                          first_entry = tmp_entry;
                                  else
                                          first_entry = NULL;
                                  entry = tmp_entry;
                          }
                          last_timestamp = map->timestamp;
                          continue;
                  }
                  vm_map_clip_start(map, entry, start);
                  vm_map_clip_end(map, entry, end);
                  /*
                   * Mark the entry in case the map lock is released.  (See
                   * above.)
                   */
                  entry->eflags |= MAP_ENTRY_IN_TRANSITION;
                  entry->wiring_thread = curthread;
                  if ((entry->protection & (VM_PROT_READ | VM_PROT_EXECUTE)) == 0
                      || (entry->protection & prot) != prot) {
                          entry->eflags |= MAP_ENTRY_WIRE_SKIPPED;
                          if ((flags & VM_MAP_WIRE_HOLESOK) == 0) {
                                  end = entry->end;
                                  rv = KERN_INVALID_ADDRESS;
                                  goto done;
                          }
                          goto next_entry;
                  }
                  if (entry->wired_count == 0) {
                          entry->wired_count++;
                          saved_start = entry->start;
                          saved_end = entry->end;
                          fictitious = entry->object.vm_object != NULL &&
                              (entry->object.vm_object->flags &
                              OBJ_FICTITIOUS) != 0;
                          /*
                           * Release the map lock, relying on the in-transition
                           * mark.  Mark the map busy for fork.
                           */
                          vm_map_busy(map);
                          vm_map_unlock(map);
                          rv = vm_fault_wire(map, saved_start, saved_end,
                              fictitious);
                          vm_map_lock(map);
                          vm_map_unbusy(map);
                          if (last_timestamp + 1 != map->timestamp) {
                                  /*
                                   * Look again for the entry because the map was
                                   * modified while it was unlocked.  The entry
                                   * may have been clipped, but NOT merged or
                                   * deleted.
                                   */
                                  result = vm_map_lookup_entry(map, saved_start,
                                      &tmp_entry);
                                  KASSERT(result, ("vm_map_wire: lookup failed"));
                                  if (entry == first_entry)
                                          first_entry = tmp_entry;
                                  else
                                          first_entry = NULL;
                                  entry = tmp_entry;
                                  while (entry->end < saved_end) {
                                          if (rv != KERN_SUCCESS) {
                                                  KASSERT(entry->wired_count == 1,
                                                      ("vm_map_wire: bad count"));
                                                  entry->wired_count = -1;
                                          }
                                          entry = entry->next;
                                  }
                          }
                          last_timestamp = map->timestamp;
                          if (rv != KERN_SUCCESS) {
                                  KASSERT(entry->wired_count == 1,
                                      ("vm_map_wire: bad count"));
                                  /*
                                   * Assign an out-of-range value to represent
                                   * the failure to wire this entry.
                                   */
                                  entry->wired_count = -1;
                                  end = entry->end;
                                  goto done;
                          }
                  } else if (!user_wire ||
                             (entry->eflags & MAP_ENTRY_USER_WIRED) == 0) {
                          entry->wired_count++;
                  }
                  /*
                   * Check the map for holes in the specified region.
                   * If VM_MAP_WIRE_HOLESOK was specified, skip this check.
                   */
          next_entry:
                  if (((flags & VM_MAP_WIRE_HOLESOK) == 0) &&
                      (entry->end < end && (entry->next == &map->header ||
                      entry->next->start > entry->end))) {
                          end = entry->end;
                          rv = KERN_INVALID_ADDRESS;
                          goto done;
                  }
                  entry = entry->next;
          }
          rv = KERN_SUCCESS;
  done:
          need_wakeup = FALSE;
          if (first_entry == NULL) {
                  result = vm_map_lookup_entry(map, start, &first_entry);
                  if (!result && (flags & VM_MAP_WIRE_HOLESOK))
                          first_entry = first_entry->next;
                  else
                          KASSERT(result, ("vm_map_wire: lookup failed"));
          }
          for (entry = first_entry; entry != &map->header && entry->start < end;
              entry = entry->next) {
                  if ((entry->eflags & MAP_ENTRY_WIRE_SKIPPED) != 0)
                          goto next_entry_done;
  
                  /*
                   * If VM_MAP_WIRE_HOLESOK was specified, an empty
                   * space in the unwired region could have been mapped
                   * while the map lock was dropped for faulting in the
                   * pages or draining MAP_ENTRY_IN_TRANSITION.
                   * Moreover, another thread could be simultaneously
                   * wiring this new mapping entry.  Detect these cases
                   * and skip any entries marked as in transition by us.
                   */
                  if ((entry->eflags & MAP_ENTRY_IN_TRANSITION) == 0 ||
                      entry->wiring_thread != curthread) {
                          KASSERT((flags & VM_MAP_WIRE_HOLESOK) != 0,
                              ("vm_map_wire: !HOLESOK and new/changed entry"));
                          continue;
                  }
  
                  if (rv == KERN_SUCCESS) {
                          if (user_wire)
                                  entry->eflags |= MAP_ENTRY_USER_WIRED;
                  } else if (entry->wired_count == -1) {
                          /*
                           * Wiring failed on this entry.  Thus, unwiring is
                           * unnecessary.
                           */
                          entry->wired_count = 0;
                  } else {
                          if (!user_wire ||
                              (entry->eflags & MAP_ENTRY_USER_WIRED) == 0)
                                  entry->wired_count--;
                          if (entry->wired_count == 0) {
                                  /*
                                   * Retain the map lock.
                                   */
                                  vm_fault_unwire(map, entry->start, entry->end,
                                      entry->object.vm_object != NULL &&
                                      (entry->object.vm_object->flags &
                                      OBJ_FICTITIOUS) != 0);
                          }
                  }
          next_entry_done:
                  KASSERT((entry->eflags & MAP_ENTRY_IN_TRANSITION) != 0,
                      ("vm_map_wire: in-transition flag missing %p", entry));
                  KASSERT(entry->wiring_thread == curthread,
                      ("vm_map_wire: alien wire %p", entry));
                  entry->eflags &= ~(MAP_ENTRY_IN_TRANSITION |
                      MAP_ENTRY_WIRE_SKIPPED);
                  entry->wiring_thread = NULL;
                  if (entry->eflags & MAP_ENTRY_NEEDS_WAKEUP) {
                          entry->eflags &= ~MAP_ENTRY_NEEDS_WAKEUP;
                          need_wakeup = TRUE;
                  }
                  vm_map_simplify_entry(map, entry);
          }
          vm_map_unlock(map);
          if (need_wakeup)
                  vm_map_wakeup(map);
          return (rv);
  }
  
  /*
   * vm_map_sync
   *
   * 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.
   *
   * If the size of the region from start to end is zero, we are
   * supposed to flush all modified pages within the region containing
   * start.  Unfortunately, a region can be split or coalesced with
   * neighboring regions, making it difficult to determine what the
   * original region was.  Therefore, we approximate this requirement by
   * flushing the current region containing start.
   *
   * Returns an error if any part of the specified range is not mapped.
   */
  int
  vm_map_sync(
          vm_map_t map,
          vm_offset_t start,
          vm_offset_t end,
          boolean_t syncio,
          boolean_t invalidate)
  {
          vm_map_entry_t current;
          vm_map_entry_t entry;
          vm_size_t size;
          vm_object_t object;
          vm_ooffset_t offset;
          unsigned int last_timestamp;
          boolean_t failed;
  
          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);
          } else if (start == end) {
                  start = entry->start;
                  end = entry->end;
          }
          /*
           * Make a first pass to check for user-wired memory and holes.
           */
          for (current = entry; current != &map->header && current->start < end;
              current = current->next) {
                  if (invalidate && (current->eflags & MAP_ENTRY_USER_WIRED)) {
                          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);
                  }
          }
  
          if (invalidate)
                  pmap_remove(map->pmap, start, end);
          failed = FALSE;
  
          /*
           * Make a second pass, cleaning/uncaching pages from the indicated
           * objects as we go.
           */
          for (current = entry; current != &map->header && current->start < end;) {
                  offset = current->offset + (start - current->start);
                  size = (end <= current->end ? end : current->end) - start;
                  if (current->eflags & MAP_ENTRY_IS_SUB_MAP) {
                          vm_map_t smap;
                          vm_map_entry_t tentry;
                          vm_size_t tsize;
  
                          smap = current->object.sub_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;
                  }
                  vm_object_reference(object);
                  last_timestamp = map->timestamp;
                  vm_map_unlock_read(map);
                  if (!vm_object_sync(object, offset, size, syncio, invalidate))
                          failed = TRUE;
                  start += size;
                  vm_object_deallocate(object);
                  vm_map_lock_read(map);
                  if (last_timestamp == map->timestamp ||
                      !vm_map_lookup_entry(map, start, &current))
                          current = current->next;
          }
  
          vm_map_unlock_read(map);
          return (failed ? KERN_FAILURE : 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.]
   */
  static void
  vm_map_entry_unwire(vm_map_t map, vm_map_entry_t entry)
  {
          vm_fault_unwire(map, entry->start, entry->end,
              entry->object.vm_object != NULL &&
              (entry->object.vm_object->flags & OBJ_FICTITIOUS) != 0);
          entry->wired_count = 0;
  }
  
  static void
  vm_map_entry_deallocate(vm_map_entry_t entry, boolean_t system_map)
  {
  
          if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) == 0)
                  vm_object_deallocate(entry->object.vm_object);
          uma_zfree(system_map ? kmapentzone : mapentzone, entry);
  }
  
  /*
   *      vm_map_entry_delete:    [ internal use only ]
   *
   *      Deallocate the given entry from the target map.
   */
  static void
  vm_map_entry_delete(vm_map_t map, vm_map_entry_t entry)
  {
          vm_object_t object;
          vm_pindex_t offidxstart, offidxend, count, size1;
          vm_ooffset_t size;
  
          vm_map_entry_unlink(map, entry);
          object = entry->object.vm_object;
          size = entry->end - entry->start;
          map->size -= size;
  
          if (entry->cred != NULL) {
                  swap_release_by_cred(size, entry->cred);
                  crfree(entry->cred);
          }
  
          if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) == 0 &&
              (object != NULL)) {
                  KASSERT(entry->cred == NULL || object->cred == NULL ||
                      (entry->eflags & MAP_ENTRY_NEEDS_COPY),
                      ("OVERCOMMIT vm_map_entry_delete: both cred %p", entry));
                  count = OFF_TO_IDX(size);
                  offidxstart = OFF_TO_IDX(entry->offset);
                  offidxend = offidxstart + count;
                  VM_OBJECT_WLOCK(object);
                  if (object->ref_count != 1 &&
                      ((object->flags & (OBJ_NOSPLIT|OBJ_ONEMAPPING)) == OBJ_ONEMAPPING ||
                      object == kernel_object || object == kmem_object)) {
                          vm_object_collapse(object);
  
                          /*
                           * The option OBJPR_NOTMAPPED can be passed here
                           * because vm_map_delete() already performed
                           * pmap_remove() on the only mapping to this range
                           * of pages. 
                           */
                          vm_object_page_remove(object, offidxstart, offidxend,
                              OBJPR_NOTMAPPED);
                          if (object->type == OBJT_SWAP)
                                  swap_pager_freespace(object, offidxstart, count);
                          if (offidxend >= object->size &&
                              offidxstart < object->size) {
                                  size1 = object->size;
                                  object->size = offidxstart;
                                  if (object->cred != NULL) {
                                          size1 -= object->size;
                                          KASSERT(object->charge >= ptoa(size1),
                                              ("vm_map_entry_delete: object->charge < 0"));
                                          swap_release_by_cred(ptoa(size1), object->cred);
                                          object->charge -= ptoa(size1);
                                  }
                          }
                  }
                  VM_OBJECT_WUNLOCK(object);
          } else
                  entry->object.vm_object = NULL;
          if (map->system_map)
                  vm_map_entry_deallocate(entry, TRUE);
          else {
                  entry->next = curthread->td_map_def_user;
                  curthread->td_map_def_user = entry;
          }
  }
  
  /*
   *      vm_map_delete:  [ internal use only ]
   *
   *      Deallocates the given address range from the target
   *      map.
   */
  int
  vm_map_delete(vm_map_t map, vm_offset_t start, vm_offset_t end)
  {
          vm_map_entry_t entry;
          vm_map_entry_t first_entry;
  
          VM_MAP_ASSERT_LOCKED(map);
  
          /*
           * 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);
          }
  
          /*
           * Step through all entries in this region
           */
          while ((entry != &map->header) && (entry->start < end)) {
                  vm_map_entry_t next;
  
                  /*
                   * Wait for wiring or unwiring of an entry to complete.
                   * Also wait for any system wirings to disappear on
                   * user maps.
                   */
                  if ((entry->eflags & MAP_ENTRY_IN_TRANSITION) != 0 ||
                      (vm_map_pmap(map) != kernel_pmap &&
                      vm_map_entry_system_wired_count(entry) != 0)) {
                          unsigned int last_timestamp;
                          vm_offset_t saved_start;
                          vm_map_entry_t tmp_entry;
  
                          saved_start = entry->start;
                          entry->eflags |= MAP_ENTRY_NEEDS_WAKEUP;
                          last_timestamp = map->timestamp;
                          (void) vm_map_unlock_and_wait(map, 0);
                          vm_map_lock(map);
                          if (last_timestamp + 1 != map->timestamp) {
                                  /*
                                   * Look again for the entry because the map was
                                   * modified while it was unlocked.
                                   * Specifically, the entry may have been
                                   * clipped, merged, or deleted.
                                   */
                                  if (!vm_map_lookup_entry(map, saved_start,
                                                           &tmp_entry))
                                          entry = tmp_entry->next;
                                  else {
                                          entry = tmp_entry;
                                          vm_map_clip_start(map, entry,
                                                            saved_start);
                                  }
                          }
                          continue;
                  }
                  vm_map_clip_end(map, entry, end);
  
                  next = entry->next;
  
                  /*
                   * Unwire before removing addresses from the pmap; otherwise,
                   * unwiring will put the entries back in the pmap.
                   */
                  if (entry->wired_count != 0) {
                          vm_map_entry_unwire(map, entry);
                  }
  
                  pmap_remove(map->pmap, entry->start, entry->end);
  
                  /*
                   * Delete the entry 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(vm_map_t map, vm_offset_t start, vm_offset_t end)
  {
          int result;
  
          vm_map_lock(map);
          VM_MAP_RANGE_CHECK(map, start, end);
          result = vm_map_delete(map, start, end);
          vm_map_unlock(map);
          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.
   *
   *      WARNING!  This code does not and should not check whether the
   *      contents of the region is accessible.  For example a smaller file
   *      might be mapped into a larger address space.
   *
   *      NOTE!  This code is also called by munmap().
   *
   *      The map must be locked.  A read lock is sufficient.
   */
  boolean_t
  vm_map_check_protection(vm_map_t map, vm_offset_t start, vm_offset_t end,
                          vm_prot_t protection)
  {
          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.
   */
  static void
  vm_map_copy_entry(
          vm_map_t src_map,
          vm_map_t dst_map,
          vm_map_entry_t src_entry,
          vm_map_entry_t dst_entry,
          vm_ooffset_t *fork_charge)
  {
          vm_object_t src_object;
          vm_map_entry_t fake_entry;
          vm_offset_t size;
          struct ucred *cred;
          int charged;
  
          VM_MAP_ASSERT_LOCKED(dst_map);
  
          if ((dst_entry->eflags|src_entry->eflags) & MAP_ENTRY_IS_SUB_MAP)
                  return;
  
          if (src_entry->wired_count == 0) {
  
                  /*
                   * If the source entry is marked needs_copy, it is already
                   * write-protected.
                   */
                  if ((src_entry->eflags & MAP_ENTRY_NEEDS_COPY) == 0) {
                          pmap_protect(src_map->pmap,
                              src_entry->start,
                              src_entry->end,
                              src_entry->protection & ~VM_PROT_WRITE);
                  }
  
                  /*
                   * Make a copy of the object.
                   */
                  size = src_entry->end - src_entry->start;
                  if ((src_object = src_entry->object.vm_object) != NULL) {
                          VM_OBJECT_WLOCK(src_object);
                          charged = ENTRY_CHARGED(src_entry);
                          if ((src_object->handle == NULL) &&
                                  (src_object->type == OBJT_DEFAULT ||
                                   src_object->type == OBJT_SWAP)) {
                                  vm_object_collapse(src_object);
                                  if ((src_object->flags & (OBJ_NOSPLIT|OBJ_ONEMAPPING)) == OBJ_ONEMAPPING) {
                                          vm_object_split(src_entry);
                                          src_object = src_entry->object.vm_object;
                                  }
                          }
                          vm_object_reference_locked(src_object);
                          vm_object_clear_flag(src_object, OBJ_ONEMAPPING);
                          if (src_entry->cred != NULL &&
                              !(src_entry->eflags & MAP_ENTRY_NEEDS_COPY)) {
                                  KASSERT(src_object->cred == NULL,
                                      ("OVERCOMMIT: vm_map_copy_entry: cred %p",
                                       src_object));
                                  src_object->cred = src_entry->cred;
                                  src_object->charge = size;
                          }
                          VM_OBJECT_WUNLOCK(src_object);
                          dst_entry->object.vm_object = src_object;
                          if (charged) {
                                  cred = curthread->td_ucred;
                                  crhold(cred);
                                  dst_entry->cred = cred;
                                  *fork_charge += size;
                                  if (!(src_entry->eflags &
                                        MAP_ENTRY_NEEDS_COPY)) {
                                          crhold(cred);
                                          src_entry->cred = cred;
                                          *fork_charge += size;
                                  }
                          }
                          src_entry->eflags |= (MAP_ENTRY_COW|MAP_ENTRY_NEEDS_COPY);
                          dst_entry->eflags |= (MAP_ENTRY_COW|MAP_ENTRY_NEEDS_COPY);
                          dst_entry->offset = src_entry->offset;
                          if (src_entry->eflags & MAP_ENTRY_VN_WRITECNT) {
                                  /*
                                   * MAP_ENTRY_VN_WRITECNT cannot
                                   * indicate write reference from
                                   * src_entry, since the entry is
                                   * marked as needs copy.  Allocate a
                                   * fake entry that is used to
                                   * decrement object->un_pager.vnp.writecount
                                   * at the appropriate time.  Attach
                                   * fake_entry to the deferred list.
                                   */
                                  fake_entry = vm_map_entry_create(dst_map);
                                  fake_entry->eflags = MAP_ENTRY_VN_WRITECNT;
                                  src_entry->eflags &= ~MAP_ENTRY_VN_WRITECNT;
                                  vm_object_reference(src_object);
                                  fake_entry->object.vm_object = src_object;
                                  fake_entry->start = src_entry->start;
                                  fake_entry->end = src_entry->end;
                                  fake_entry->next = curthread->td_map_def_user;
                                  curthread->td_map_def_user = fake_entry;
                          }
                  } else {
                          dst_entry->object.vm_object = NULL;
                          dst_entry->offset = 0;
                          if (src_entry->cred != NULL) {
                                  dst_entry->cred = curthread->td_ucred;
                                  crhold(dst_entry->cred);
                                  *fork_charge += size;
                          }
                  }
  
                  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,
                      fork_charge);
          }
  }
  
  /*
   * vmspace_map_entry_forked:
   * Update the newly-forked vmspace each time a map entry is inherited
   * or copied.  The values for vm_dsize and vm_tsize are approximate
   * (and mostly-obsolete ideas in the face of mmap(2) et al.)
   */
  static void
  vmspace_map_entry_forked(const struct vmspace *vm1, struct vmspace *vm2,
      vm_map_entry_t entry)
  {
          vm_size_t entrysize;
          vm_offset_t newend;
  
          entrysize = entry->end - entry->start;
          vm2->vm_map.size += entrysize;
          if (entry->eflags & (MAP_ENTRY_GROWS_DOWN | MAP_ENTRY_GROWS_UP)) {
                  vm2->vm_ssize += btoc(entrysize);
          } else if (entry->start >= (vm_offset_t)vm1->vm_daddr &&
              entry->start < (vm_offset_t)vm1->vm_daddr + ctob(vm1->vm_dsize)) {
                  newend = MIN(entry->end,
                      (vm_offset_t)vm1->vm_daddr + ctob(vm1->vm_dsize));
                  vm2->vm_dsize += btoc(newend - entry->start);
          } else if (entry->start >= (vm_offset_t)vm1->vm_taddr &&
              entry->start < (vm_offset_t)vm1->vm_taddr + ctob(vm1->vm_tsize)) {
                  newend = MIN(entry->end,
                      (vm_offset_t)vm1->vm_taddr + ctob(vm1->vm_tsize));
                  vm2->vm_tsize += btoc(newend - entry->start);
          }
  }
  
  /*
   * 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.
   *
   * XXX It might be worth coalescing the entries added to the new vmspace.
   *
   * The source map must not be locked.
   */
  struct vmspace *
  vmspace_fork(struct vmspace *vm1, vm_ooffset_t *fork_charge)
  {
          struct vmspace *vm2;
          vm_map_t new_map, old_map;
          vm_map_entry_t new_entry, old_entry;
          vm_object_t object;
          int locked;
  
          old_map = &vm1->vm_map;
          /* Copy immutable fields of vm1 to vm2. */
          vm2 = vmspace_alloc(old_map->min_offset, old_map->max_offset, NULL);
          if (vm2 == NULL)
                  return (NULL);
          vm2->vm_taddr = vm1->vm_taddr;
          vm2->vm_daddr = vm1->vm_daddr;
          vm2->vm_maxsaddr = vm1->vm_maxsaddr;
          vm_map_lock(old_map);
          if (old_map->busy)
                  vm_map_wait_busy(old_map);
          new_map = &vm2->vm_map;
          locked = vm_map_trylock(new_map); /* trylock to silence WITNESS */
          KASSERT(locked, ("vmspace_fork: lock failed"));
  
          old_entry = old_map->header.next;
  
          while (old_entry != &old_map->header) {
                  if (old_entry->eflags & MAP_ENTRY_IS_SUB_MAP)
                          panic("vm_map_fork: encountered a submap");
  
                  switch (old_entry->inheritance) {
                  case VM_INHERIT_NONE:
                          break;
  
                  case VM_INHERIT_SHARE:
                          /*
                           * Clone the entry, creating the shared object if necessary.
                           */
                          object = old_entry->object.vm_object;
                          if (object == NULL) {
                                  object = vm_object_allocate(OBJT_DEFAULT,
                                          atop(old_entry->end - old_entry->start));
                                  old_entry->object.vm_object = object;
                                  old_entry->offset = 0;
                                  if (old_entry->cred != NULL) {
                                          object->cred = old_entry->cred;
                                          object->charge = old_entry->end -
                                              old_entry->start;
                                          old_entry->cred = NULL;
                                  }
                          }
  
                          /*
                           * Add the reference before calling vm_object_shadow
                           * to insure that a shadow object is created.
                           */
                          vm_object_reference(object);
                          if (old_entry->eflags & MAP_ENTRY_NEEDS_COPY) {
                                  vm_object_shadow(&old_entry->object.vm_object,
                                      &old_entry->offset,
                                      old_entry->end - old_entry->start);
                                  old_entry->eflags &= ~MAP_ENTRY_NEEDS_COPY;
                                  /* Transfer the second reference too. */
                                  vm_object_reference(
                                      old_entry->object.vm_object);
  
                                  /*
                                   * As in vm_map_simplify_entry(), the
                                   * vnode lock will not be acquired in
                                   * this call to vm_object_deallocate().
                                   */
                                  vm_object_deallocate(object);
                                  object = old_entry->object.vm_object;
                          }
                          VM_OBJECT_WLOCK(object);
                          vm_object_clear_flag(object, OBJ_ONEMAPPING);
                          if (old_entry->cred != NULL) {
                                  KASSERT(object->cred == NULL, ("vmspace_fork both cred"));
                                  object->cred = old_entry->cred;
                                  object->charge = old_entry->end - old_entry->start;
                                  old_entry->cred = NULL;
                          }
  
                          /*
                           * Assert the correct state of the vnode
                           * v_writecount while the object is locked, to
                           * not relock it later for the assertion
                           * correctness.
                           */
                          if (old_entry->eflags & MAP_ENTRY_VN_WRITECNT &&
                              object->type == OBJT_VNODE) {
                                  KASSERT(((struct vnode *)object->handle)->
                                      v_writecount > 0,
                                      ("vmspace_fork: v_writecount %p", object));
                                  KASSERT(object->un_pager.vnp.writemappings > 0,
                                      ("vmspace_fork: vnp.writecount %p",
                                      object));
                          }
                          VM_OBJECT_WUNLOCK(object);
  
                          /*
                           * Clone the entry, referencing the shared object.
                           */
                          new_entry = vm_map_entry_create(new_map);
                          *new_entry = *old_entry;
                          new_entry->eflags &= ~(MAP_ENTRY_USER_WIRED |
                              MAP_ENTRY_IN_TRANSITION);
                          new_entry->wiring_thread = NULL;
                          new_entry->wired_count = 0;
                          if (new_entry->eflags & MAP_ENTRY_VN_WRITECNT) {
                                  vnode_pager_update_writecount(object,
                                      new_entry->start, new_entry->end);
                          }
  
                          /*
                           * 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);
                          vmspace_map_entry_forked(vm1, vm2, 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;
                          /*
                           * Copied entry is COW over the old object.
                           */
                          new_entry->eflags &= ~(MAP_ENTRY_USER_WIRED |
                              MAP_ENTRY_IN_TRANSITION | MAP_ENTRY_VN_WRITECNT);
                          new_entry->wiring_thread = NULL;
                          new_entry->wired_count = 0;
                          new_entry->object.vm_object = NULL;
                          new_entry->cred = NULL;
                          vm_map_entry_link(new_map, new_map->header.prev,
                              new_entry);
                          vmspace_map_entry_forked(vm1, vm2, new_entry);
                          vm_map_copy_entry(old_map, new_map, old_entry,
                              new_entry, fork_charge);
                          break;
                  }
                  old_entry = old_entry->next;
          }
          /*
           * Use inlined vm_map_unlock() to postpone handling the deferred
           * map entries, which cannot be done until both old_map and
           * new_map locks are released.
           */
          sx_xunlock(&old_map->lock);
          sx_xunlock(&new_map->lock);
          vm_map_process_deferred();
  
          return (vm2);
  }
  
  int
  vm_map_stack(vm_map_t map, vm_offset_t addrbos, vm_size_t max_ssize,
      vm_prot_t prot, vm_prot_t max, int cow)
  {
          vm_map_entry_t new_entry, prev_entry;
          vm_offset_t bot, top;
          vm_size_t growsize, init_ssize;
          int orient, rv;
          rlim_t lmemlim, vmemlim;
  
          /*
           * The stack orientation is piggybacked with the cow argument.
           * Extract it into orient and mask the cow argument so that we
           * don't pass it around further.
           * NOTE: We explicitly allow bi-directional stacks.
           */
          orient = cow & (MAP_STACK_GROWS_DOWN|MAP_STACK_GROWS_UP);
          KASSERT(orient != 0, ("No stack grow direction"));
  
          if (addrbos < vm_map_min(map) ||
              addrbos > vm_map_max(map) ||
              addrbos + max_ssize < addrbos)
                  return (KERN_NO_SPACE);
  
          growsize = sgrowsiz;
          init_ssize = (max_ssize < growsize) ? max_ssize : growsize;
  
          PROC_LOCK(curproc);
          lmemlim = lim_cur(curproc, RLIMIT_MEMLOCK);
          vmemlim = lim_cur(curproc, RLIMIT_VMEM);
          PROC_UNLOCK(curproc);
  
          vm_map_lock(map);
  
          /* If addr is already mapped, no go */
          if (vm_map_lookup_entry(map, addrbos, &prev_entry)) {
                  vm_map_unlock(map);
                  return (KERN_NO_SPACE);
          }
  
          if (!old_mlock && map->flags & MAP_WIREFUTURE) {
                  if (ptoa(pmap_wired_count(map->pmap)) + init_ssize > lmemlim) {
                          vm_map_unlock(map);
                          return (KERN_NO_SPACE);
                  }
          }
  
          /* If we would blow our VMEM resource limit, no go */
          if (map->size + init_ssize > vmemlim) {
                  vm_map_unlock(map);
                  return (KERN_NO_SPACE);
          }
  
          /*
           * If we can't accomodate max_ssize in the current mapping, no go.
           * However, we need to be aware that subsequent user mappings might
           * map into the space we have reserved for stack, and currently this
           * space is not protected.
           *
           * Hopefully we will at least detect this condition when we try to
           * grow the stack.
           */
          if ((prev_entry->next != &map->header) &&
              (prev_entry->next->start < addrbos + max_ssize)) {
                  vm_map_unlock(map);
                  return (KERN_NO_SPACE);
          }
  
          /*
           * We initially map a stack of only init_ssize.  We will grow as
           * needed later.  Depending on the orientation of the stack (i.e.
           * the grow direction) we either map at the top of the range, the
           * bottom of the range or in the middle.
           *
           * Note: we would normally expect prot and max to be VM_PROT_ALL,
           * and cow to be 0.  Possibly we should eliminate these as input
           * parameters, and just pass these values here in the insert call.
           */
          if (orient == MAP_STACK_GROWS_DOWN)
                  bot = addrbos + max_ssize - init_ssize;
          else if (orient == MAP_STACK_GROWS_UP)
                  bot = addrbos;
          else
                  bot = round_page(addrbos + max_ssize/2 - init_ssize/2);
          top = bot + init_ssize;
          rv = vm_map_insert(map, NULL, 0, bot, top, prot, max, cow);
  
          /* Now set the avail_ssize amount. */
          if (rv == KERN_SUCCESS) {
                  if (prev_entry != &map->header)
                          vm_map_clip_end(map, prev_entry, bot);
                  new_entry = prev_entry->next;
                  if (new_entry->end != top || new_entry->start != bot)
                          panic("Bad entry start/end for new stack entry");
  
                  new_entry->avail_ssize = max_ssize - init_ssize;
                  if (orient & MAP_STACK_GROWS_DOWN)
                          new_entry->eflags |= MAP_ENTRY_GROWS_DOWN;
                  if (orient & MAP_STACK_GROWS_UP)
                          new_entry->eflags |= MAP_ENTRY_GROWS_UP;
          }
  
          vm_map_unlock(map);
          return (rv);
  }
  
  static int stack_guard_page = 0;
  TUNABLE_INT("security.bsd.stack_guard_page", &stack_guard_page);
  SYSCTL_INT(_security_bsd, OID_AUTO, stack_guard_page, CTLFLAG_RW,
      &stack_guard_page, 0,
      "Insert stack guard page ahead of the growable segments.");
  
  /* Attempts to grow a vm stack entry.  Returns KERN_SUCCESS if the
   * desired address is already mapped, or if we successfully grow
   * the stack.  Also returns KERN_SUCCESS if addr is outside the
   * stack range (this is strange, but preserves compatibility with
   * the grow function in vm_machdep.c).
   */
  int
  vm_map_growstack(struct proc *p, vm_offset_t addr)
  {
          vm_map_entry_t next_entry, prev_entry;
          vm_map_entry_t new_entry, stack_entry;
          struct vmspace *vm = p->p_vmspace;
          vm_map_t map = &vm->vm_map;
          vm_offset_t end;
          vm_size_t growsize;
          size_t grow_amount, max_grow;
          rlim_t lmemlim, stacklim, vmemlim;
          int is_procstack, rv;
          struct ucred *cred;
  #ifdef notyet
          uint64_t limit;
  #endif
  #ifdef RACCT
          int error;
  #endif
  
  Retry:
          PROC_LOCK(p);
          lmemlim = lim_cur(p, RLIMIT_MEMLOCK);
          stacklim = lim_cur(p, RLIMIT_STACK);
          vmemlim = lim_cur(p, RLIMIT_VMEM);
          PROC_UNLOCK(p);
  
          vm_map_lock_read(map);
  
          /* If addr is already in the entry range, no need to grow.*/
          if (vm_map_lookup_entry(map, addr, &prev_entry)) {
                  vm_map_unlock_read(map);
                  return (KERN_SUCCESS);
          }
  
          next_entry = prev_entry->next;
          if (!(prev_entry->eflags & MAP_ENTRY_GROWS_UP)) {
                  /*
                   * This entry does not grow upwards. Since the address lies
                   * beyond this entry, the next entry (if one exists) has to
                   * be a downward growable entry. The entry list header is
                   * never a growable entry, so it suffices to check the flags.
                   */
                  if (!(next_entry->eflags & MAP_ENTRY_GROWS_DOWN)) {
                          vm_map_unlock_read(map);
                          return (KERN_SUCCESS);
                  }
                  stack_entry = next_entry;
          } else {
                  /*
                   * This entry grows upward. If the next entry does not at
                   * least grow downwards, this is the entry we need to grow.
                   * otherwise we have two possible choices and we have to
                   * select one.
                   */
                  if (next_entry->eflags & MAP_ENTRY_GROWS_DOWN) {
                          /*
                           * We have two choices; grow the entry closest to
                           * the address to minimize the amount of growth.
                           */
                          if (addr - prev_entry->end <= next_entry->start - addr)
                                  stack_entry = prev_entry;
                          else
                                  stack_entry = next_entry;
                  } else
                          stack_entry = prev_entry;
          }
  
          if (stack_entry == next_entry) {
                  KASSERT(stack_entry->eflags & MAP_ENTRY_GROWS_DOWN, ("foo"));
                  KASSERT(addr < stack_entry->start, ("foo"));
                  end = (prev_entry != &map->header) ? prev_entry->end :
                      stack_entry->start - stack_entry->avail_ssize;
                  grow_amount = roundup(stack_entry->start - addr, PAGE_SIZE);
                  max_grow = stack_entry->start - end;
          } else {
                  KASSERT(stack_entry->eflags & MAP_ENTRY_GROWS_UP, ("foo"));
                  KASSERT(addr >= stack_entry->end, ("foo"));
                  end = (next_entry != &map->header) ? next_entry->start :
                      stack_entry->end + stack_entry->avail_ssize;
                  grow_amount = roundup(addr + 1 - stack_entry->end, PAGE_SIZE);
                  max_grow = end - stack_entry->end;
          }
  
          if (grow_amount > stack_entry->avail_ssize) {
                  vm_map_unlock_read(map);
                  return (KERN_NO_SPACE);
          }
  
          /*
           * If there is no longer enough space between the entries nogo, and
           * adjust the available space.  Note: this  should only happen if the
           * user has mapped into the stack area after the stack was created,
           * and is probably an error.
           *
           * This also effectively destroys any guard page the user might have
           * intended by limiting the stack size.
           */
          if (grow_amount + (stack_guard_page ? PAGE_SIZE : 0) > max_grow) {
                  if (vm_map_lock_upgrade(map))
                          goto Retry;
  
                  stack_entry->avail_ssize = max_grow;
  
                  vm_map_unlock(map);
                  return (KERN_NO_SPACE);
          }
  
          is_procstack = (addr >= (vm_offset_t)vm->vm_maxsaddr) ? 1 : 0;
  
          /*
           * If this is the main process stack, see if we're over the stack
           * limit.
           */
          if (is_procstack && (ctob(vm->vm_ssize) + grow_amount > stacklim)) {
                  vm_map_unlock_read(map);
                  return (KERN_NO_SPACE);
          }
  #ifdef RACCT
          PROC_LOCK(p);
          if (is_procstack &&
              racct_set(p, RACCT_STACK, ctob(vm->vm_ssize) + grow_amount)) {
                  PROC_UNLOCK(p);
                  vm_map_unlock_read(map);
                  return (KERN_NO_SPACE);
          }
          PROC_UNLOCK(p);
  #endif
  
          /* Round up the grow amount modulo sgrowsiz */
          growsize = sgrowsiz;
          grow_amount = roundup(grow_amount, growsize);
          if (grow_amount > stack_entry->avail_ssize)
                  grow_amount = stack_entry->avail_ssize;
          if (is_procstack && (ctob(vm->vm_ssize) + grow_amount > stacklim)) {
                  grow_amount = trunc_page((vm_size_t)stacklim) -
                      ctob(vm->vm_ssize);
          }
  #ifdef notyet
          PROC_LOCK(p);
          limit = racct_get_available(p, RACCT_STACK);
          PROC_UNLOCK(p);
          if (is_procstack && (ctob(vm->vm_ssize) + grow_amount > limit))
                  grow_amount = limit - ctob(vm->vm_ssize);
  #endif
          if (!old_mlock && map->flags & MAP_WIREFUTURE) {
                  if (ptoa(pmap_wired_count(map->pmap)) + grow_amount > lmemlim) {
                          vm_map_unlock_read(map);
                          rv = KERN_NO_SPACE;
                          goto out;
                  }
  #ifdef RACCT
                  PROC_LOCK(p);
                  if (racct_set(p, RACCT_MEMLOCK,
                      ptoa(pmap_wired_count(map->pmap)) + grow_amount)) {
                          PROC_UNLOCK(p);
                          vm_map_unlock_read(map);
                          rv = KERN_NO_SPACE;
                          goto out;
                  }
                  PROC_UNLOCK(p);
  #endif
          }
          /* If we would blow our VMEM resource limit, no go */
          if (map->size + grow_amount > vmemlim) {
                  vm_map_unlock_read(map);
                  rv = KERN_NO_SPACE;
                  goto out;
          }
  #ifdef RACCT
          PROC_LOCK(p);
          if (racct_set(p, RACCT_VMEM, map->size + grow_amount)) {
                  PROC_UNLOCK(p);
                  vm_map_unlock_read(map);
                  rv = KERN_NO_SPACE;
                  goto out;
          }
          PROC_UNLOCK(p);
  #endif
  
          if (vm_map_lock_upgrade(map))
                  goto Retry;
  
          if (stack_entry == next_entry) {
                  /*
                   * Growing downward.
                   */
                  /* Get the preliminary new entry start value */
                  addr = stack_entry->start - grow_amount;
  
                  /*
                   * If this puts us into the previous entry, cut back our
                   * growth to the available space. Also, see the note above.
                   */
                  if (addr < end) {
                          stack_entry->avail_ssize = max_grow;
                          addr = end;
                          if (stack_guard_page)
                                  addr += PAGE_SIZE;
                  }
  
                  rv = vm_map_insert(map, NULL, 0, addr, stack_entry->start,
                      next_entry->protection, next_entry->max_protection, 0);
  
                  /* Adjust the available stack space by the amount we grew. */
                  if (rv == KERN_SUCCESS) {
                          if (prev_entry != &map->header)
                                  vm_map_clip_end(map, prev_entry, addr);
                          new_entry = prev_entry->next;
                          KASSERT(new_entry == stack_entry->prev, ("foo"));
                          KASSERT(new_entry->end == stack_entry->start, ("foo"));
                          KASSERT(new_entry->start == addr, ("foo"));
                          grow_amount = new_entry->end - new_entry->start;
                          new_entry->avail_ssize = stack_entry->avail_ssize -
                              grow_amount;
                          stack_entry->eflags &= ~MAP_ENTRY_GROWS_DOWN;
                          new_entry->eflags |= MAP_ENTRY_GROWS_DOWN;
                  }
          } else {
                  /*
                   * Growing upward.
                   */
                  addr = stack_entry->end + grow_amount;
  
                  /*
                   * If this puts us into the next entry, cut back our growth
                   * to the available space. Also, see the note above.
                   */
                  if (addr > end) {
                          stack_entry->avail_ssize = end - stack_entry->end;
                          addr = end;
                          if (stack_guard_page)
                                  addr -= PAGE_SIZE;
                  }
  
                  grow_amount = addr - stack_entry->end;
                  cred = stack_entry->cred;
                  if (cred == NULL && stack_entry->object.vm_object != NULL)
                          cred = stack_entry->object.vm_object->cred;
                  if (cred != NULL && !swap_reserve_by_cred(grow_amount, cred))
                          rv = KERN_NO_SPACE;
                  /* Grow the underlying object if applicable. */
                  else if (stack_entry->object.vm_object == NULL ||
                           vm_object_coalesce(stack_entry->object.vm_object,
                           stack_entry->offset,
                           (vm_size_t)(stack_entry->end - stack_entry->start),
                           (vm_size_t)grow_amount, cred != NULL)) {
                          map->size += (addr - stack_entry->end);
                          /* Update the current entry. */
                          stack_entry->end = addr;
                          stack_entry->avail_ssize -= grow_amount;
                          vm_map_entry_resize_free(map, stack_entry);
                          rv = KERN_SUCCESS;
  
                          if (next_entry != &map->header)
                                  vm_map_clip_start(map, next_entry, addr);
                  } else
                          rv = KERN_FAILURE;
          }
  
          if (rv == KERN_SUCCESS && is_procstack)
                  vm->vm_ssize += btoc(grow_amount);
  
          vm_map_unlock(map);
  
          /*
           * Heed the MAP_WIREFUTURE flag if it was set for this process.
           */
          if (rv == KERN_SUCCESS && (map->flags & MAP_WIREFUTURE)) {
                  vm_map_wire(map,
                      (stack_entry == next_entry) ? addr : addr - grow_amount,
                      (stack_entry == next_entry) ? stack_entry->start : addr,
                      (p->p_flag & P_SYSTEM)
                      ? VM_MAP_WIRE_SYSTEM|VM_MAP_WIRE_NOHOLES
                      : VM_MAP_WIRE_USER|VM_MAP_WIRE_NOHOLES);
          }
  
  out:
  #ifdef RACCT
          if (rv != KERN_SUCCESS) {
                  PROC_LOCK(p);
                  error = racct_set(p, RACCT_VMEM, map->size);
                  KASSERT(error == 0, ("decreasing RACCT_VMEM failed"));
                  if (!old_mlock) {
                          error = racct_set(p, RACCT_MEMLOCK,
                              ptoa(pmap_wired_count(map->pmap)));
                          KASSERT(error == 0, ("decreasing RACCT_MEMLOCK failed"));
                  }
                  error = racct_set(p, RACCT_STACK, ctob(vm->vm_ssize));
                  KASSERT(error == 0, ("decreasing RACCT_STACK failed"));
                  PROC_UNLOCK(p);
          }
  #endif
  
          return (rv);
  }
  
  /*
   * Unshare the specified VM space for exec.  If other processes are
   * mapped to it, then create a new one.  The new vmspace is null.
   */
  int
  vmspace_exec(struct proc *p, vm_offset_t minuser, vm_offset_t maxuser)
  {
          struct vmspace *oldvmspace = p->p_vmspace;
          struct vmspace *newvmspace;
  
          KASSERT((curthread->td_pflags & TDP_EXECVMSPC) == 0,
              ("vmspace_exec recursed"));
          newvmspace = vmspace_alloc(minuser, maxuser, NULL);
          if (newvmspace == NULL)
                  return (ENOMEM);
          newvmspace->vm_swrss = oldvmspace->vm_swrss;
          /*
           * This code is written like this for prototype purposes.  The
           * goal is to avoid running down the vmspace here, but let the
           * other process's that are still using the vmspace to finally
           * run it down.  Even though there is little or no chance of blocking
           * here, it is a good idea to keep this form for future mods.
           */
          PROC_VMSPACE_LOCK(p);
          p->p_vmspace = newvmspace;
          PROC_VMSPACE_UNLOCK(p);
          if (p == curthread->td_proc)
                  pmap_activate(curthread);
          curthread->td_pflags |= TDP_EXECVMSPC;
          return (0);
  }
  
  /*
   * Unshare the specified VM space for forcing COW.  This
   * is called by rfork, for the (RFMEM|RFPROC) == 0 case.
   */
  int
  vmspace_unshare(struct proc *p)
  {
          struct vmspace *oldvmspace = p->p_vmspace;
          struct vmspace *newvmspace;
          vm_ooffset_t fork_charge;
  
          if (oldvmspace->vm_refcnt == 1)
                  return (0);
          fork_charge = 0;
          newvmspace = vmspace_fork(oldvmspace, &fork_charge);
          if (newvmspace == NULL)
                  return (ENOMEM);
          if (!swap_reserve_by_cred(fork_charge, p->p_ucred)) {
                  vmspace_free(newvmspace);
                  return (ENOMEM);
          }
          PROC_VMSPACE_LOCK(p);
          p->p_vmspace = newvmspace;
          PROC_VMSPACE_UNLOCK(p);
          if (p == curthread->td_proc)
                  pmap_activate(curthread);
          vmspace_free(oldvmspace);
          return (0);
  }
  
  /*
   *      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(vm_map_t *var_map,                /* IN/OUT */
                vm_offset_t vaddr,
                vm_prot_t fault_typea,
                vm_map_entry_t *out_entry,        /* OUT */
                vm_object_t *object,              /* OUT */
                vm_pindex_t *pindex,              /* OUT */
                vm_prot_t *out_prot,              /* OUT */
                boolean_t *wired)                 /* OUT */
  {
          vm_map_entry_t entry;
          vm_map_t map = *var_map;
          vm_prot_t prot;
          vm_prot_t fault_type = fault_typea;
          vm_object_t eobject;
          vm_size_t size;
          struct ucred *cred;
  
  RetryLookup:;
  
          vm_map_lock_read(map);
  
          /*
           * Lookup the faulting address.
           */
          if (!vm_map_lookup_entry(map, vaddr, out_entry)) {
                  vm_map_unlock_read(map);
                  return (KERN_INVALID_ADDRESS);
          }
  
          entry = *out_entry;
  
          /*
           * Handle submaps.
           */
          if (entry->eflags & MAP_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;
          fault_type &= (VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE);
          if ((fault_type & prot) != fault_type || prot == VM_PROT_NONE) {
                  vm_map_unlock_read(map);
                  return (KERN_PROTECTION_FAILURE);
          }
          if ((entry->eflags & MAP_ENTRY_USER_WIRED) &&
              (entry->eflags & MAP_ENTRY_COW) &&
              (fault_type & VM_PROT_WRITE)) {
                  vm_map_unlock_read(map);
                  return (KERN_PROTECTION_FAILURE);
          }
          if ((fault_typea & VM_PROT_COPY) != 0 &&
              (entry->max_protection & VM_PROT_WRITE) == 0 &&
              (entry->eflags & MAP_ENTRY_COW) == 0) {
                  vm_map_unlock_read(map);
                  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)
                  fault_type = entry->protection;
          size = entry->end - entry->start;
          /*
           * If the entry was copy-on-write, we either ...
           */
          if (entry->eflags & MAP_ENTRY_NEEDS_COPY) {
                  /*
                   * If we want to write the page, we may as well handle that
                   * now since we've got the map locked.
                   *
                   * If we don't need to write the page, we just demote the
                   * permissions allowed.
                   */
                  if ((fault_type & VM_PROT_WRITE) != 0 ||
                      (fault_typea & VM_PROT_COPY) != 0) {
                          /*
                           * Make a new object, and place it in the object
                           * chain.  Note that no new references have appeared
                           * -- one just moved from the map to the new
                           * object.
                           */
                          if (vm_map_lock_upgrade(map))
                                  goto RetryLookup;
  
                          if (entry->cred == NULL) {
                                  /*
                                   * The debugger owner is charged for
                                   * the memory.
                                   */
                                  cred = curthread->td_ucred;
                                  crhold(cred);
                                  if (!swap_reserve_by_cred(size, cred)) {
                                          crfree(cred);
                                          vm_map_unlock(map);
                                          return (KERN_RESOURCE_SHORTAGE);
                                  }
                                  entry->cred = cred;
                          }
                          vm_object_shadow(&entry->object.vm_object,
                              &entry->offset, size);
                          entry->eflags &= ~MAP_ENTRY_NEEDS_COPY;
                          eobject = entry->object.vm_object;
                          if (eobject->cred != NULL) {
                                  /*
                                   * The object was not shadowed.
                                   */
                                  swap_release_by_cred(size, entry->cred);
                                  crfree(entry->cred);
                                  entry->cred = NULL;
                          } else if (entry->cred != NULL) {
                                  VM_OBJECT_WLOCK(eobject);
                                  eobject->cred = entry->cred;
                                  eobject->charge = size;
                                  VM_OBJECT_WUNLOCK(eobject);
                                  entry->cred = NULL;
                          }
  
                          vm_map_lock_downgrade(map);
                  } 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 &&
              !map->system_map) {
                  if (vm_map_lock_upgrade(map))
                          goto RetryLookup;
                  entry->object.vm_object = vm_object_allocate(OBJT_DEFAULT,
                      atop(size));
                  entry->offset = 0;
                  if (entry->cred != NULL) {
                          VM_OBJECT_WLOCK(entry->object.vm_object);
                          entry->object.vm_object->cred = entry->cred;
                          entry->object.vm_object->charge = size;
                          VM_OBJECT_WUNLOCK(entry->object.vm_object);
                          entry->cred = NULL;
                  }
                  vm_map_lock_downgrade(map);
          }
  
          /*
           * Return the object/offset from this entry.  If the entry was
           * copy-on-write or empty, it has been fixed up.
           */
          *pindex = OFF_TO_IDX((vaddr - entry->start) + entry->offset);
          *object = entry->object.vm_object;
  
          *out_prot = prot;
          return (KERN_SUCCESS);
  }
  
  /*
   *      vm_map_lookup_locked:
   *
   *      Lookup the faulting address.  A version of vm_map_lookup that returns 
   *      KERN_FAILURE instead of blocking on map lock or memory allocation.
   */
  int
  vm_map_lookup_locked(vm_map_t *var_map,         /* IN/OUT */
                       vm_offset_t vaddr,
                       vm_prot_t fault_typea,
                       vm_map_entry_t *out_entry, /* OUT */
                       vm_object_t *object,       /* OUT */
                       vm_pindex_t *pindex,       /* OUT */
                       vm_prot_t *out_prot,       /* OUT */
                       boolean_t *wired)          /* OUT */
  {
          vm_map_entry_t entry;
          vm_map_t map = *var_map;
          vm_prot_t prot;
          vm_prot_t fault_type = fault_typea;
  
          /*
           * Lookup the faulting address.
           */
          if (!vm_map_lookup_entry(map, vaddr, out_entry))
                  return (KERN_INVALID_ADDRESS);
  
          entry = *out_entry;
  
          /*
           * Fail if the entry refers to a submap.
           */
          if (entry->eflags & MAP_ENTRY_IS_SUB_MAP)
                  return (KERN_FAILURE);
  
          /*
           * Check whether this task is allowed to have this page.
           */
          prot = entry->protection;
          fault_type &= VM_PROT_READ | VM_PROT_WRITE | VM_PROT_EXECUTE;
          if ((fault_type & prot) != fault_type)
                  return (KERN_PROTECTION_FAILURE);
          if ((entry->eflags & MAP_ENTRY_USER_WIRED) &&
              (entry->eflags & MAP_ENTRY_COW) &&
              (fault_type & VM_PROT_WRITE))
                  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)
                  fault_type = entry->protection;
  
          if (entry->eflags & MAP_ENTRY_NEEDS_COPY) {
                  /*
                   * Fail if the entry was copy-on-write for a write fault.
                   */
                  if (fault_type & VM_PROT_WRITE)
                          return (KERN_FAILURE);
                  /*
                   * We're attempting to read a copy-on-write page --
                   * don't allow writes.
                   */
                  prot &= ~VM_PROT_WRITE;
          }
  
          /*
           * Fail if an object should be created.
           */
          if (entry->object.vm_object == NULL && !map->system_map)
                  return (KERN_FAILURE);
  
          /*
           * Return the object/offset from this entry.  If the entry was
           * copy-on-write or empty, it has been fixed up.
           */
          *pindex = OFF_TO_IDX((vaddr - entry->start) + entry->offset);
          *object = entry->object.vm_object;
  
          *out_prot = prot;
          return (KERN_SUCCESS);
  }
  
  /*
   *      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(vm_map_t map, vm_map_entry_t entry)
  {
          /*
           * Unlock the main-level map
           */
          vm_map_unlock_read(map);
  }
  
  #include "opt_ddb.h"
  #ifdef DDB
  #include <sys/kernel.h>
  
  #include <ddb/ddb.h>
  
  static void
  vm_map_print(vm_map_t map)
  {
          vm_map_entry_t entry;
  
          db_iprintf("Task map %p: pmap=%p, nentries=%d, version=%u\n",
              (void *)map,
              (void *)map->pmap, map->nentries, map->timestamp);
  
          db_indent += 2;
          for (entry = map->header.next; entry != &map->header;
              entry = entry->next) {
                  db_iprintf("map entry %p: start=%p, end=%p\n",
                      (void *)entry, (void *)entry->start, (void *)entry->end);
                  {
                          static char *inheritance_name[4] =
                          {"share", "copy", "none", "donate_copy"};
  
                          db_iprintf(" prot=%x/%x/%s",
                              entry->protection,
                              entry->max_protection,
                              inheritance_name[(int)(unsigned char)entry->inheritance]);
                          if (entry->wired_count != 0)
                                  db_printf(", wired");
                  }
                  if (entry->eflags & MAP_ENTRY_IS_SUB_MAP) {
                          db_printf(", share=%p, offset=0x%jx\n",
                              (void *)entry->object.sub_map,
                              (uintmax_t)entry->offset);
                          if ((entry->prev == &map->header) ||
                              (entry->prev->object.sub_map !=
                                  entry->object.sub_map)) {
                                  db_indent += 2;
                                  vm_map_print((vm_map_t)entry->object.sub_map);
                                  db_indent -= 2;
                          }
                  } else {
                          if (entry->cred != NULL)
                                  db_printf(", ruid %d", entry->cred->cr_ruid);
                          db_printf(", object=%p, offset=0x%jx",
                              (void *)entry->object.vm_object,
                              (uintmax_t)entry->offset);
                          if (entry->object.vm_object && entry->object.vm_object->cred)
                                  db_printf(", obj ruid %d charge %jx",
                                      entry->object.vm_object->cred->cr_ruid,
                                      (uintmax_t)entry->object.vm_object->charge);
                          if (entry->eflags & MAP_ENTRY_COW)
                                  db_printf(", copy (%s)",
                                      (entry->eflags & MAP_ENTRY_NEEDS_COPY) ? "needed" : "done");
                          db_printf("\n");
  
                          if ((entry->prev == &map->header) ||
                              (entry->prev->object.vm_object !=
                                  entry->object.vm_object)) {
                                  db_indent += 2;
                                  vm_object_print((db_expr_t)(intptr_t)
                                                  entry->object.vm_object,
                                                  1, 0, (char *)0);
                                  db_indent -= 2;
                          }
                  }
          }
          db_indent -= 2;
  }
  
  DB_SHOW_COMMAND(map, map)
  {
  
          if (!have_addr) {
                  db_printf("usage: show map <addr>\n");
                  return;
          }
          vm_map_print((vm_map_t)addr);
  }
  
  DB_SHOW_COMMAND(procvm, procvm)
  {
          struct proc *p;
  
          if (have_addr) {
                  p = (struct proc *) addr;
          } else {
                  p = curproc;
          }
  
          db_printf("p = %p, vmspace = %p, map = %p, pmap = %p\n",
              (void *)p, (void *)p->p_vmspace, (void *)&p->p_vmspace->vm_map,
              (void *)vmspace_pmap(p->p_vmspace));
  
          vm_map_print((vm_map_t)&p->p_vmspace->vm_map);
  }
  
  #endif /* DDB */