FreeBSD/Linux Kernel Cross Reference
sys/uvm/uvm_map.c

     /*      $NetBSD: uvm_map.c,v 1.164.2.3 2004/05/09 09:01:32 jdc Exp $    */
     
     /*
      * Copyright (c) 1997 Charles D. Cranor and Washington University.
      * Copyright (c) 1991, 1993, The Regents of the University of California.
      *
      * All rights reserved.
      *
      * This code is derived from software contributed to Berkeley by
     * The Mach Operating System project at Carnegie-Mellon University.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by Charles D. Cranor,
     *      Washington University, the University of California, Berkeley and
     *      its contributors.
     * 4. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)vm_map.c    8.3 (Berkeley) 1/12/94
     * from: Id: uvm_map.c,v 1.1.2.27 1998/02/07 01:16:54 chs Exp
     *
     *
     * Copyright (c) 1987, 1990 Carnegie-Mellon University.
     * All rights reserved.
     *
     * Permission to use, copy, modify and distribute this software and
     * its documentation is hereby granted, provided that both the copyright
     * notice and this permission notice appear in all copies of the
     * software, derivative works or modified versions, and any portions
     * thereof, and that both notices appear in supporting documentation.
     *
     * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
     * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
     * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
     *
     * Carnegie Mellon requests users of this software to return to
     *
     *  Software Distribution Coordinator  or  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.
     */
    
    /*
     * uvm_map.c: uvm map operations
     */
    
    #include <sys/cdefs.h>
    __KERNEL_RCSID(0, "$NetBSD: uvm_map.c,v 1.164.2.3 2004/05/09 09:01:32 jdc Exp $");
    
    #include "opt_ddb.h"
    #include "opt_uvmhist.h"
    #include "opt_uvm.h"
    #include "opt_sysv.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/mman.h>
    #include <sys/proc.h>
    #include <sys/malloc.h>
    #include <sys/pool.h>
    #include <sys/kernel.h>
    #include <sys/mount.h>
    #include <sys/vnode.h>
    
    #ifdef SYSVSHM
    #include <sys/shm.h>
    #endif
    
    #define UVM_MAP
    #include <uvm/uvm.h>
    #undef RB_AUGMENT
    #define RB_AUGMENT(x)   uvm_rb_augment(x)
    
   #ifdef DDB
   #include <uvm/uvm_ddb.h>
   #endif
   
   extern struct vm_map *pager_map;
   
   #ifndef UVMMAP_NOCOUNTERS
   #include <sys/device.h>
   struct evcnt map_ubackmerge = EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL,
       "uvmmap", "ubackmerge");
   struct evcnt map_uforwmerge = EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL,
       "uvmmap", "uforwmerge");
   struct evcnt map_ubimerge = EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL,
       "uvmmap", "ubimerge");
   struct evcnt map_unomerge = EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL,
       "uvmmap", "unomerge");
   struct evcnt map_kbackmerge = EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL,
       "uvmmap", "kbackmerge");
   struct evcnt map_kforwmerge = EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL,
       "uvmmap", "kforwmerge");
   struct evcnt map_kbimerge = EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL,
       "uvmmap", "kbimerge");
   struct evcnt map_knomerge = EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL,
       "uvmmap", "knomerge");
   struct evcnt uvm_map_call = EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL,
       "uvmmap", "map_call");
   struct evcnt uvm_mlk_call = EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL,
       "uvmmap", "mlk_call");
   struct evcnt uvm_mlk_hint = EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL,
       "uvmmap", "mlk_hint");
   
   EVCNT_ATTACH_STATIC(map_ubackmerge);
   EVCNT_ATTACH_STATIC(map_uforwmerge);
   EVCNT_ATTACH_STATIC(map_ubimerge);
   EVCNT_ATTACH_STATIC(map_unomerge);
   EVCNT_ATTACH_STATIC(map_kbackmerge);
   EVCNT_ATTACH_STATIC(map_kforwmerge);
   EVCNT_ATTACH_STATIC(map_kbimerge);
   EVCNT_ATTACH_STATIC(map_knomerge);
   EVCNT_ATTACH_STATIC(uvm_map_call);
   EVCNT_ATTACH_STATIC(uvm_mlk_call);
   EVCNT_ATTACH_STATIC(uvm_mlk_hint);
   
   #define UVMCNT_INCR(ev)         ev.ev_count++
   #define UVMCNT_DECR(ev)         ev.ev_count--
   #else
   #define UVMCNT_INCR(ev)
   #define UVMCNT_DECR(ev)
   #endif
   
   const char vmmapbsy[] = "vmmapbsy";
   
   /*
    * pool for vmspace structures.
    */
   
   struct pool uvm_vmspace_pool;
   
   /*
    * pool for dynamically-allocated map entries.
    */
   
   struct pool uvm_map_entry_pool;
   struct pool uvm_map_entry_kmem_pool;
   
   MALLOC_DEFINE(M_VMMAP, "VM map", "VM map structures");
   MALLOC_DEFINE(M_VMPMAP, "VM pmap", "VM pmap");
   
   #ifdef PMAP_GROWKERNEL
   /*
    * This global represents the end of the kernel virtual address
    * space.  If we want to exceed this, we must grow the kernel
    * virtual address space dynamically.
    *
    * Note, this variable is locked by kernel_map's lock.
    */
   vaddr_t uvm_maxkaddr;
   #endif
   
   /*
    * macros
    */
   
   /*
    * uvm_map_entry_link: insert entry into a map
    *
    * => map must be locked
    */
   #define uvm_map_entry_link(map, after_where, entry) do { \
           KASSERT(entry->start < entry->end); \
           (map)->nentries++; \
           (entry)->prev = (after_where); \
           (entry)->next = (after_where)->next; \
           (entry)->prev->next = (entry); \
           (entry)->next->prev = (entry); \
           uvm_rb_insert((map), (entry)); \
   } while (/*CONSTCOND*/ 0)
   
   /*
    * uvm_map_entry_unlink: remove entry from a map
    *
    * => map must be locked
    */
   #define uvm_map_entry_unlink(map, entry) do { \
           (map)->nentries--; \
           (entry)->next->prev = (entry)->prev; \
           (entry)->prev->next = (entry)->next; \
           uvm_rb_remove((map), (entry)); \
   } while (/*CONSTCOND*/ 0)
   
   /*
    * SAVE_HINT: saves the specified entry as the hint for future lookups.
    *
    * => map need not be locked (protected by hint_lock).
    */
   #define SAVE_HINT(map,check,value) do { \
           simple_lock(&(map)->hint_lock); \
           if ((map)->hint == (check)) \
                   (map)->hint = (value); \
           simple_unlock(&(map)->hint_lock); \
   } while (/*CONSTCOND*/ 0)
   
   /*
    * VM_MAP_RANGE_CHECK: check and correct range
    *
    * => map must at least be read locked
    */
   
   #define VM_MAP_RANGE_CHECK(map, start, end) do { \
           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;                    \
   } while (/*CONSTCOND*/ 0)
   
   /*
    * local prototypes
    */
   
   static struct vm_map_entry *
                   uvm_mapent_alloc(struct vm_map *, int);
   static void     uvm_mapent_copy(struct vm_map_entry *, struct vm_map_entry *);
   static void     uvm_mapent_free(struct vm_map_entry *);
   static void     uvm_map_entry_unwire(struct vm_map *, struct vm_map_entry *);
   static void     uvm_map_reference_amap(struct vm_map_entry *, int);
   static int      uvm_map_space_avail(vaddr_t *, vsize_t, voff_t, vsize_t, int,
                       struct vm_map_entry *);
   static void     uvm_map_unreference_amap(struct vm_map_entry *, int);
   
   int _uvm_tree_sanity(struct vm_map *, const char *);
   static vsize_t uvm_rb_subtree_space(const struct vm_map_entry *);
   
   static __inline int
   uvm_compare(const struct vm_map_entry *a, const struct vm_map_entry *b)
   {
   
           if (a->start < b->start)
                   return (-1);
           else if (a->start > b->start)
                   return (1);
   
           return (0);
   }
   
   static __inline void
   uvm_rb_augment(struct vm_map_entry *entry)
   {
   
           entry->space = uvm_rb_subtree_space(entry);
   }
   
   RB_PROTOTYPE(uvm_tree, vm_map_entry, rb_entry, uvm_compare);
   
   RB_GENERATE(uvm_tree, vm_map_entry, rb_entry, uvm_compare);
   
   static __inline vsize_t
   uvm_rb_space(const struct vm_map *map, const struct vm_map_entry *entry)
   {
           /* XXX map is not used */
   
           KASSERT(entry->next != NULL);
           return entry->next->start - entry->end;
   }
   
   static vsize_t
   uvm_rb_subtree_space(const struct vm_map_entry *entry)
   {
           vaddr_t space, tmp;
   
           space = entry->ownspace;
           if (RB_LEFT(entry, rb_entry)) {
                   tmp = RB_LEFT(entry, rb_entry)->space;
                   if (tmp > space)
                           space = tmp;
           }
   
           if (RB_RIGHT(entry, rb_entry)) {
                   tmp = RB_RIGHT(entry, rb_entry)->space;
                   if (tmp > space)
                           space = tmp;
           }
   
           return (space);
   }
   
   static __inline void
   uvm_rb_fixup(struct vm_map *map, struct vm_map_entry *entry)
   {
           /* We need to traverse to the very top */
           do {
                   entry->ownspace = uvm_rb_space(map, entry);
                   entry->space = uvm_rb_subtree_space(entry);
           } while ((entry = RB_PARENT(entry, rb_entry)) != NULL);
   }
   
   static __inline void
   uvm_rb_insert(struct vm_map *map, struct vm_map_entry *entry)
   {
           vaddr_t space = uvm_rb_space(map, entry);
           struct vm_map_entry *tmp;
   
           entry->ownspace = entry->space = space;
           tmp = RB_INSERT(uvm_tree, &(map)->rbhead, entry);
   #ifdef DIAGNOSTIC
           if (tmp != NULL)
                   panic("uvm_rb_insert: duplicate entry?");
   #endif
           uvm_rb_fixup(map, entry);
           if (entry->prev != &map->header)
                   uvm_rb_fixup(map, entry->prev);
   }
   
   static __inline void
   uvm_rb_remove(struct vm_map *map, struct vm_map_entry *entry)
   {
           struct vm_map_entry *parent;
   
           parent = RB_PARENT(entry, rb_entry);
           RB_REMOVE(uvm_tree, &(map)->rbhead, entry);
           if (entry->prev != &map->header)
                   uvm_rb_fixup(map, entry->prev);
           if (parent)
                   uvm_rb_fixup(map, parent);
   }
   
   #ifdef DEBUG
   int uvm_debug_check_rbtree = 0;
   #define uvm_tree_sanity(x,y)            \
           if (uvm_debug_check_rbtree)     \
                   _uvm_tree_sanity(x,y)
   #else
   #define uvm_tree_sanity(x,y)
   #endif
   
   int
   _uvm_tree_sanity(struct vm_map *map, const char *name)
   {
           struct vm_map_entry *tmp, *trtmp;
           int n = 0, i = 1;
   
           RB_FOREACH(tmp, uvm_tree, &map->rbhead) {
                   if (tmp->ownspace != uvm_rb_space(map, tmp)) {
                           printf("%s: %d/%d ownspace %lx != %lx %s\n",
                               name, n + 1, map->nentries,
                               (ulong)tmp->ownspace, (ulong)uvm_rb_space(map, tmp),
                               tmp->next == &map->header ? "(last)" : "");
                           goto error;
                   }
           }
           trtmp = NULL;
           RB_FOREACH(tmp, uvm_tree, &map->rbhead) {
                   if (tmp->space != uvm_rb_subtree_space(tmp)) {
                           printf("%s: space %lx != %lx\n",
                               name, (ulong)tmp->space,
                               (ulong)uvm_rb_subtree_space(tmp));
                           goto error;
                   }
                   if (trtmp != NULL && trtmp->start >= tmp->start) {
                           printf("%s: corrupt: 0x%lx >= 0x%lx\n",
                               name, trtmp->start, tmp->start);
                           goto error;
                   }
                   n++;
   
                   trtmp = tmp;
           }
   
           if (n != map->nentries) {
                   printf("%s: nentries: %d vs %d\n",
                       name, n, map->nentries);
                   goto error;
           }
   
           for (tmp = map->header.next; tmp && tmp != &map->header;
               tmp = tmp->next, i++) {
                   trtmp = RB_FIND(uvm_tree, &map->rbhead, tmp);
                   if (trtmp != tmp) {
                           printf("%s: lookup: %d: %p - %p: %p\n",
                               name, i, tmp, trtmp,
                               RB_PARENT(tmp, rb_entry));
                           goto error;
                   }
           }
   
           return (0);
    error:
   #ifdef  DDB
           /* handy breakpoint location for error case */
           __asm(".globl treesanity_label\ntreesanity_label:");
   #endif
           return (-1);
   }
   
   /*
    * local inlines
    */
   
   /*
    * uvm_mapent_alloc: allocate a map entry
    */
   
   static __inline struct vm_map_entry *
   uvm_mapent_alloc(struct vm_map *map, int flags)
   {
           struct vm_map_entry *me;
           int s;
           int pflags = (flags & UVM_FLAG_NOWAIT) ? PR_NOWAIT : PR_WAITOK;
           UVMHIST_FUNC("uvm_mapent_alloc"); UVMHIST_CALLED(maphist);
   
           if (map->flags & VM_MAP_INTRSAFE || cold) {
                   s = splvm();
                   simple_lock(&uvm.kentry_lock);
                   me = uvm.kentry_free;
                   if (me)
                           uvm.kentry_free = me->next;
                   simple_unlock(&uvm.kentry_lock);
                   splx(s);
                   if (__predict_false(me == NULL)) {
                           panic("uvm_mapent_alloc: out of static map entries, "
                               "check MAX_KMAPENT (currently %d)",
                               MAX_KMAPENT);
                   }
                   me->flags = UVM_MAP_STATIC;
           } else if (map == kernel_map) {
                   me = pool_get(&uvm_map_entry_kmem_pool, pflags);
                   if (__predict_false(me == NULL))
                           return NULL;
                   me->flags = UVM_MAP_KMEM;
           } else {
                   me = pool_get(&uvm_map_entry_pool, pflags);
                   if (__predict_false(me == NULL))
                           return NULL;
                   me->flags = 0;
           }
   
           UVMHIST_LOG(maphist, "<- new entry=0x%x [kentry=%d]", me,
               ((map->flags & VM_MAP_INTRSAFE) != 0 || map == kernel_map), 0, 0);
           return (me);
   }
   
   /*
    * uvm_mapent_free: free map entry
    */
   
   static __inline void
   uvm_mapent_free(struct vm_map_entry *me)
   {
           int s;
           UVMHIST_FUNC("uvm_mapent_free"); UVMHIST_CALLED(maphist);
   
           UVMHIST_LOG(maphist,"<- freeing map entry=0x%x [flags=%d]",
                   me, me->flags, 0, 0);
           if (me->flags & UVM_MAP_STATIC) {
                   s = splvm();
                   simple_lock(&uvm.kentry_lock);
                   me->next = uvm.kentry_free;
                   uvm.kentry_free = me;
                   simple_unlock(&uvm.kentry_lock);
                   splx(s);
           } else if (me->flags & UVM_MAP_KMEM) {
                   pool_put(&uvm_map_entry_kmem_pool, me);
           } else {
                   pool_put(&uvm_map_entry_pool, me);
           }
   }
   
   /*
    * uvm_mapent_copy: copy a map entry, preserving flags
    */
   
   static __inline void
   uvm_mapent_copy(struct vm_map_entry *src, struct vm_map_entry *dst)
   {
   
           memcpy(dst, src, ((char *)&src->uvm_map_entry_stop_copy) -
               ((char *)src));
   }
   
   /*
    * uvm_map_entry_unwire: unwire a map entry
    *
    * => map should be locked by caller
    */
   
   static __inline void
   uvm_map_entry_unwire(struct vm_map *map, struct vm_map_entry *entry)
   {
   
           entry->wired_count = 0;
           uvm_fault_unwire_locked(map, entry->start, entry->end);
   }
   
   
   /*
    * wrapper for calling amap_ref()
    */
   static __inline void
   uvm_map_reference_amap(struct vm_map_entry *entry, int flags)
   {
   
           amap_ref(entry->aref.ar_amap, entry->aref.ar_pageoff,
               (entry->end - entry->start) >> PAGE_SHIFT, flags);
   }
   
   
   /*
    * wrapper for calling amap_unref()
    */
   static __inline void
   uvm_map_unreference_amap(struct vm_map_entry *entry, int flags)
   {
   
           amap_unref(entry->aref.ar_amap, entry->aref.ar_pageoff,
               (entry->end - entry->start) >> PAGE_SHIFT, flags);
   }
   
   
   /*
    * uvm_map_init: init mapping system at boot time.   note that we allocate
    * and init the static pool of struct vm_map_entry *'s for the kernel here.
    */
   
   void
   uvm_map_init(void)
   {
           static struct vm_map_entry kernel_map_entry[MAX_KMAPENT];
   #if defined(UVMHIST)
           static struct uvm_history_ent maphistbuf[100];
           static struct uvm_history_ent pdhistbuf[100];
   #endif
           int lcv;
   
           /*
            * first, init logging system.
            */
   
           UVMHIST_FUNC("uvm_map_init");
           UVMHIST_INIT_STATIC(maphist, maphistbuf);
           UVMHIST_INIT_STATIC(pdhist, pdhistbuf);
           UVMHIST_CALLED(maphist);
           UVMHIST_LOG(maphist,"<starting uvm map system>", 0, 0, 0, 0);
   
           /*
            * now set up static pool of kernel map entrys ...
            */
   
           simple_lock_init(&uvm.kentry_lock);
           uvm.kentry_free = NULL;
           for (lcv = 0 ; lcv < MAX_KMAPENT ; lcv++) {
                   kernel_map_entry[lcv].next = uvm.kentry_free;
                   uvm.kentry_free = &kernel_map_entry[lcv];
           }
   
           /*
            * initialize the map-related pools.
            */
           pool_init(&uvm_vmspace_pool, sizeof(struct vmspace),
               0, 0, 0, "vmsppl", &pool_allocator_nointr);
           pool_init(&uvm_map_entry_pool, sizeof(struct vm_map_entry),
               0, 0, 0, "vmmpepl", &pool_allocator_nointr);
           pool_init(&uvm_map_entry_kmem_pool, sizeof(struct vm_map_entry),
               0, 0, 0, "vmmpekpl", NULL);
   }
   
   /*
    * clippers
    */
   
   /*
    * uvm_map_clip_start: ensure that the entry begins at or after
    *      the starting address, if it doesn't we split the entry.
    *
    * => caller should use UVM_MAP_CLIP_START macro rather than calling
    *    this directly
    * => map must be locked by caller
    */
   
   void
   uvm_map_clip_start(struct vm_map *map, struct vm_map_entry *entry,
       vaddr_t start)
   {
           struct vm_map_entry *new_entry;
           vaddr_t new_adj;
   
           /* uvm_map_simplify_entry(map, entry); */ /* XXX */
   
           uvm_tree_sanity(map, "clip_start entry");
   
           /*
            * Split off the front portion.  note that we must insert the new
            * entry BEFORE this one, so that this entry has the specified
            * starting address.
            */
   
           new_entry = uvm_mapent_alloc(map, 0);
           uvm_mapent_copy(entry, new_entry); /* entry -> new_entry */
   
           new_entry->end = start;
           new_adj = start - new_entry->start;
           if (entry->object.uvm_obj)
                   entry->offset += new_adj;       /* shift start over */
   
           /* Does not change order for the RB tree */
           entry->start = start;
   
           if (new_entry->aref.ar_amap) {
                   amap_splitref(&new_entry->aref, &entry->aref, new_adj);
           }
   
           uvm_map_entry_link(map, entry->prev, new_entry);
   
           if (UVM_ET_ISSUBMAP(entry)) {
                   /* ... unlikely to happen, but play it safe */
                    uvm_map_reference(new_entry->object.sub_map);
           } else {
                   if (UVM_ET_ISOBJ(entry) &&
                       entry->object.uvm_obj->pgops &&
                       entry->object.uvm_obj->pgops->pgo_reference)
                           entry->object.uvm_obj->pgops->pgo_reference(
                               entry->object.uvm_obj);
           }
   
           uvm_tree_sanity(map, "clip_start leave");
   }
   
   /*
    * uvm_map_clip_end: ensure that the entry ends at or before
    *      the ending address, if it does't we split the reference
    *
    * => caller should use UVM_MAP_CLIP_END macro rather than calling
    *    this directly
    * => map must be locked by caller
    */
   
   void
   uvm_map_clip_end(struct vm_map *map, struct vm_map_entry *entry, vaddr_t end)
   {
           struct vm_map_entry *   new_entry;
           vaddr_t new_adj; /* #bytes we move start forward */
   
           uvm_tree_sanity(map, "clip_end entry");
           /*
            *      Create a new entry and insert it
            *      AFTER the specified entry
            */
   
           new_entry = uvm_mapent_alloc(map, 0);
           uvm_mapent_copy(entry, new_entry); /* entry -> new_entry */
   
           new_entry->start = entry->end = end;
           new_adj = end - entry->start;
           if (new_entry->object.uvm_obj)
                   new_entry->offset += new_adj;
   
           if (entry->aref.ar_amap)
                   amap_splitref(&entry->aref, &new_entry->aref, new_adj);
   
           uvm_rb_fixup(map, entry);
   
           uvm_map_entry_link(map, entry, new_entry);
   
           if (UVM_ET_ISSUBMAP(entry)) {
                   /* ... unlikely to happen, but play it safe */
                   uvm_map_reference(new_entry->object.sub_map);
           } else {
                   if (UVM_ET_ISOBJ(entry) &&
                       entry->object.uvm_obj->pgops &&
                       entry->object.uvm_obj->pgops->pgo_reference)
                           entry->object.uvm_obj->pgops->pgo_reference(
                               entry->object.uvm_obj);
           }
   
           uvm_tree_sanity(map, "clip_end leave");
   }
   
   
   /*
    *   M A P   -   m a i n   e n t r y   p o i n t
    */
   /*
    * uvm_map: establish a valid mapping in a map
    *
    * => assume startp is page aligned.
    * => assume size is a multiple of PAGE_SIZE.
    * => assume sys_mmap provides enough of a "hint" to have us skip
    *      over text/data/bss area.
    * => map must be unlocked (we will lock it)
    * => <uobj,uoffset> value meanings (4 cases):
    *       [1] <NULL,uoffset>             == uoffset is a hint for PMAP_PREFER
    *       [2] <NULL,UVM_UNKNOWN_OFFSET>  == don't PMAP_PREFER
    *       [3] <uobj,uoffset>             == normal mapping
    *       [4] <uobj,UVM_UNKNOWN_OFFSET>  == uvm_map finds offset based on VA
    *
    *    case [4] is for kernel mappings where we don't know the offset until
    *    we've found a virtual address.   note that kernel object offsets are
    *    always relative to vm_map_min(kernel_map).
    *
    * => if `align' is non-zero, we align the virtual address to the specified
    *      alignment.
    *      this is provided as a mechanism for large pages.
    *
    * => XXXCDC: need way to map in external amap?
    */
   
   int
   uvm_map(struct vm_map *map, vaddr_t *startp /* IN/OUT */, vsize_t size,
       struct uvm_object *uobj, voff_t uoffset, vsize_t align, uvm_flag_t flags)
   {
           struct vm_map_entry *prev_entry, *new_entry;
           const int amapwaitflag = (flags & UVM_FLAG_NOWAIT) ?
               AMAP_EXTEND_NOWAIT : 0;
           vm_prot_t prot = UVM_PROTECTION(flags), maxprot =
               UVM_MAXPROTECTION(flags);
           vm_inherit_t inherit = UVM_INHERIT(flags);
           int advice = UVM_ADVICE(flags);
           int error, merged = 0, kmap = (vm_map_pmap(map) == pmap_kernel());
           UVMHIST_FUNC("uvm_map");
           UVMHIST_CALLED(maphist);
   
           UVMHIST_LOG(maphist, "(map=0x%x, *startp=0x%x, size=%d, flags=0x%x)",
               map, *startp, size, flags);
           UVMHIST_LOG(maphist, "  uobj/offset 0x%x/%d", uobj, uoffset,0,0);
   
           /*
            * detect a popular device driver bug.
            */
   
           KASSERT(doing_shutdown || curlwp != NULL ||
               (map->flags & VM_MAP_INTRSAFE));
   
           /*
            * zero-sized mapping doesn't make any sense.
            */
           KASSERT(size > 0);
   
           uvm_tree_sanity(map, "map entry");
   
           /*
            * check sanity of protection code
            */
   
           if ((prot & maxprot) != prot) {
                   UVMHIST_LOG(maphist, "<- prot. failure:  prot=0x%x, max=0x%x",
                   prot, maxprot,0,0);
                   return EACCES;
           }
   
           /*
            * for pager_map, allocate the new entry first to avoid sleeping
            * for memory while we have the map locked.
            */
   
           new_entry = NULL;
           if (map == pager_map) {
                   new_entry = uvm_mapent_alloc(map, (flags & UVM_FLAG_NOWAIT));
                   if (__predict_false(new_entry == NULL))
                           return ENOMEM;
           }
   
           /*
            * figure out where to put new VM range
            */
   
           if (vm_map_lock_try(map) == FALSE) {
                   if (flags & UVM_FLAG_TRYLOCK) {
                           if (new_entry) {
                                   uvm_mapent_free(new_entry);
                           }
                           return EAGAIN;
                   }
                   vm_map_lock(map); /* could sleep here */
           }
           if ((prev_entry = uvm_map_findspace(map, *startp, size, startp,
               uobj, uoffset, align, flags)) == NULL) {
                   UVMHIST_LOG(maphist,"<- uvm_map_findspace failed!",0,0,0,0);
                   vm_map_unlock(map);
                   if (new_entry) {
                           uvm_mapent_free(new_entry);
                   }
                   return ENOMEM;
           }
   
   #ifdef PMAP_GROWKERNEL
           /*
            * If the kernel pmap can't map the requested space,
            * then allocate more resources for it.
            */
           if (map == kernel_map && uvm_maxkaddr < (*startp + size))
                   uvm_maxkaddr = pmap_growkernel(*startp + size);
   #endif
   
           UVMCNT_INCR(uvm_map_call);
   
           /*
            * if uobj is null, then uoffset is either a VAC hint for PMAP_PREFER
            * [typically from uvm_map_reserve] or it is UVM_UNKNOWN_OFFSET.   in
            * either case we want to zero it  before storing it in the map entry
            * (because it looks strange and confusing when debugging...)
            *
            * if uobj is not null
            *   if uoffset is not UVM_UNKNOWN_OFFSET then we have a normal mapping
            *      and we do not need to change uoffset.
            *   if uoffset is UVM_UNKNOWN_OFFSET then we need to find the offset
            *      now (based on the starting address of the map).   this case is
            *      for kernel object mappings where we don't know the offset until
            *      the virtual address is found (with uvm_map_findspace).   the
            *      offset is the distance we are from the start of the map.
            */
   
           if (uobj == NULL) {
                   uoffset = 0;
           } else {
                   if (uoffset == UVM_UNKNOWN_OFFSET) {
                           KASSERT(UVM_OBJ_IS_KERN_OBJECT(uobj));
                           uoffset = *startp - vm_map_min(kernel_map);
                   }
           }
   
           /*
            * try and insert in map by extending previous entry, if possible.
            * XXX: we don't try and pull back the next entry.   might be useful
            * for a stack, but we are currently allocating our stack in advance.
            */
   
           if (flags & UVM_FLAG_NOMERGE)
                   goto nomerge;
   
           if (prev_entry->end == *startp &&
               prev_entry != &map->header &&
               prev_entry->object.uvm_obj == uobj) {
   
                   if (prev_entry->flags & UVM_MAP_NOMERGE)
                           goto forwardmerge;
   
                   if (uobj && prev_entry->offset +
                       (prev_entry->end - prev_entry->start) != uoffset)
                           goto forwardmerge;
   
                   if (UVM_ET_ISSUBMAP(prev_entry))
                           goto forwardmerge;
   
                   if (prev_entry->protection != prot ||
                       prev_entry->max_protection != maxprot)
                           goto forwardmerge;
   
                   if (prev_entry->inheritance != inherit ||
                       prev_entry->advice != advice)
                           goto forwardmerge;
   
                   /* wiring status must match (new area is unwired) */
                   if (VM_MAPENT_ISWIRED(prev_entry))
                           goto forwardmerge;
   
                   /*
                    * can't extend a shared amap.  note: no need to lock amap to
                    * look at refs since we don't care about its exact value.
                    * if it is one (i.e. we have only reference) it will stay there
                    */
   
                   if (prev_entry->aref.ar_amap &&
                       amap_refs(prev_entry->aref.ar_amap) != 1) {
                           goto forwardmerge;
                   }
   
                   if (prev_entry->aref.ar_amap) {
                           error = amap_extend(prev_entry, size,
                               amapwaitflag | AMAP_EXTEND_FORWARDS);
                           if (error) {
                                   vm_map_unlock(map);
                                   if (new_entry) {
                                           uvm_mapent_free(new_entry);
                                   }
                                   return error;
                           }
                   }
   
                   if (kmap)
                           UVMCNT_INCR(map_kbackmerge);
                   else
                           UVMCNT_INCR(map_ubackmerge);
                   UVMHIST_LOG(maphist,"  starting back merge", 0, 0, 0, 0);
   
                   /*
                    * drop our reference to uobj since we are extending a reference
                    * that we already have (the ref count can not drop to zero).
                    */
   
                   if (uobj && uobj->pgops->pgo_detach)
                           uobj->pgops->pgo_detach(uobj);
   
                   prev_entry->end += size;
                   uvm_rb_fixup(map, prev_entry);
   
                   uvm_tree_sanity(map, "map backmerged");
   
                   UVMHIST_LOG(maphist,"<- done (via backmerge)!", 0, 0, 0, 0);
                   if (new_entry) {
                           uvm_mapent_free(new_entry);
                           new_entry = NULL;
                   }
                   merged++;
           }
   
   forwardmerge:
           if (prev_entry->next->start == (*startp + size) &&
               prev_entry->next != &map->header &&
               prev_entry->next->object.uvm_obj == uobj) {
   
                   if (prev_entry->next->flags & UVM_MAP_NOMERGE)
                           goto nomerge;
   
                   if (uobj && prev_entry->next->offset != uoffset + size)
                           goto nomerge;
   
                   if (UVM_ET_ISSUBMAP(prev_entry->next))
                           goto nomerge;
   
                   if (prev_entry->next->protection != prot ||
                       prev_entry->next->max_protection != maxprot)
                           goto nomerge;
   
                   if (prev_entry->next->inheritance != inherit ||
                       prev_entry->next->advice != advice)
                           goto nomerge;
   
                   /* wiring status must match (new area is unwired) */
                   if (VM_MAPENT_ISWIRED(prev_entry->next))
                           goto nomerge;
   
                   /*
                    * can't extend a shared amap.  note: no need to lock amap to
                    * look at refs since we don't care about its exact value.
                    * if it is one (i.e. we have only reference) it will stay there.
                    *
                    * note that we also can't merge two amaps, so if we
                    * merged with the previous entry which has an amap,
                    * and the next entry also has an amap, we give up.
                    *
                    * Interesting cases:
                    * amap, new, amap -> give up second merge (single fwd extend)
                    * amap, new, none -> double forward extend (extend again here)
                    * none, new, amap -> double backward extend (done here)
                    * uobj, new, amap -> single backward extend (done here)
                    *
                    * XXX should we attempt to deal with someone refilling
                    * the deallocated region between two entries that are
                    * backed by the same amap (ie, arefs is 2, "prev" and
                    * "next" refer to it, and adding this allocation will
                    * close the hole, thus restoring arefs to 1 and
                    * deallocating the "next" vm_map_entry)?  -- @@@
                    */
   
                   if (prev_entry->next->aref.ar_amap &&
                       (amap_refs(prev_entry->next->aref.ar_amap) != 1 ||
                        (merged && prev_entry->aref.ar_amap))) {
                           goto nomerge;
                   }
   
                   if (merged) {
                           /*
                            * Try to extend the amap of the previous entry to
                            * cover the next entry as well.  If it doesn't work
                            * just skip on, don't actually give up, since we've
                            * already completed the back merge.
                            */
                           if (prev_entry->aref.ar_amap) {
                                   if (amap_extend(prev_entry,
                                       prev_entry->next->end -
                                       prev_entry->next->start,
                                       amapwaitflag | AMAP_EXTEND_FORWARDS))
                                           goto nomerge;
                           }
   
                           /*
                            * Try to extend the amap of the *next* entry
                            * back to cover the new allocation *and* the
                            * previous entry as well (the previous merge
                            * didn't have an amap already otherwise we
                           * wouldn't be checking here for an amap).  If
                           * it doesn't work just skip on, again, don't
                           * actually give up, since we've already
                           * completed the back merge.
                           */
                          else if (prev_entry->next->aref.ar_amap) {
                                  if (amap_extend(prev_entry->next,
                                      prev_entry->end -
                                      prev_entry->start,
                                      amapwaitflag | AMAP_EXTEND_BACKWARDS))
                                          goto nomerge;
                          }
                  } else {
                          /*
                           * Pull the next entry's amap backwards to cover this
                           * new allocation.
                           */
                          if (prev_entry->next->aref.ar_amap) {
                                  error = amap_extend(prev_entry->next, size,
                                      amapwaitflag | AMAP_EXTEND_BACKWARDS);
                                  if (error) {
                                          vm_map_unlock(map);
                                          if (new_entry) {
                                                  uvm_mapent_free(new_entry);
                                          }
                                          return error;
                                  }
                          }
                  }
  
                  if (merged) {
                          if (kmap) {
                                  UVMCNT_DECR(map_kbackmerge);
                                  UVMCNT_INCR(map_kbimerge);
                          } else {
                                  UVMCNT_DECR(map_ubackmerge);
                                  UVMCNT_INCR(map_ubimerge);
                          }
                  } else {
                          if (kmap)
                                  UVMCNT_INCR(map_kforwmerge);
                          else
                                  UVMCNT_INCR(map_uforwmerge);
                  }
                  UVMHIST_LOG(maphist,"  starting forward merge", 0, 0, 0, 0);
  
                  /*
                   * drop our reference to uobj since we are extending a reference
                   * that we already have (the ref count can not drop to zero).
                   * (if merged, we've already detached)
                   */
                  if (uobj && uobj->pgops->pgo_detach && !merged)
                          uobj->pgops->pgo_detach(uobj);
  
                  if (merged) {
                          struct vm_map_entry *dead = prev_entry->next;
                          prev_entry->end = dead->end;
                          uvm_map_entry_unlink(map, dead);
                          if (dead->aref.ar_amap != NULL) {
                                  prev_entry->aref = dead->aref;
                                  dead->aref.ar_amap = NULL;
                          }
                          uvm_mapent_free(dead);
                  } else {
                          prev_entry->next->start -= size;
                          if (prev_entry != &map->header)
                                  uvm_rb_fixup(map, prev_entry);
                          if (uobj)
                                  prev_entry->next->offset = uoffset;
                  }
  
                  uvm_tree_sanity(map, "map forwardmerged");
  
                  UVMHIST_LOG(maphist,"<- done forwardmerge", 0, 0, 0, 0);
                  if (new_entry) {
                          uvm_mapent_free(new_entry);
                          new_entry = NULL;
                  }
                  merged++;
          }
  
  nomerge:
          if (!merged) {
                  UVMHIST_LOG(maphist,"  allocating new map entry", 0, 0, 0, 0);
                  if (kmap)
                          UVMCNT_INCR(map_knomerge);
                  else
                          UVMCNT_INCR(map_unomerge);
  
                  /*
                   * allocate new entry and link it in.
                   */
  
                  if (new_entry == NULL) {
                          new_entry = uvm_mapent_alloc(map,
                                  (flags & UVM_FLAG_NOWAIT));
                          if (__predict_false(new_entry == NULL)) {
                                  vm_map_unlock(map);
                                  return ENOMEM;
                          }
                  }
                  new_entry->start = *startp;
                  new_entry->end = new_entry->start + size;
                  new_entry->object.uvm_obj = uobj;
                  new_entry->offset = uoffset;
  
                  if (uobj)
                          new_entry->etype = UVM_ET_OBJ;
                  else
                          new_entry->etype = 0;
  
                  if (flags & UVM_FLAG_COPYONW) {
                          new_entry->etype |= UVM_ET_COPYONWRITE;
                          if ((flags & UVM_FLAG_OVERLAY) == 0)
                                  new_entry->etype |= UVM_ET_NEEDSCOPY;
                  }
                  if (flags & UVM_FLAG_NOMERGE) {
                          new_entry->flags |= UVM_MAP_NOMERGE;
                  }
  
                  new_entry->protection = prot;
                  new_entry->max_protection = maxprot;
                  new_entry->inheritance = inherit;
                  new_entry->wired_count = 0;
                  new_entry->advice = advice;
                  if (flags & UVM_FLAG_OVERLAY) {
  
                          /*
                           * to_add: for BSS we overallocate a little since we
                           * are likely to extend
                           */
  
                          vaddr_t to_add = (flags & UVM_FLAG_AMAPPAD) ?
                                  UVM_AMAP_CHUNK << PAGE_SHIFT : 0;
                          struct vm_amap *amap = amap_alloc(size, to_add,
                              (flags & UVM_FLAG_NOWAIT) ? M_NOWAIT : M_WAITOK);
                          if (__predict_false(amap == NULL)) {
                                  vm_map_unlock(map);
                                  uvm_mapent_free(new_entry);
                                  return ENOMEM;
                          }
                          new_entry->aref.ar_pageoff = 0;
                          new_entry->aref.ar_amap = amap;
                  } else {
                          new_entry->aref.ar_pageoff = 0;
                          new_entry->aref.ar_amap = NULL;
                  }
                  uvm_map_entry_link(map, prev_entry, new_entry);
  
                  /*
                   * Update the free space hint
                   */
  
                  if ((map->first_free == prev_entry) &&
                      (prev_entry->end >= new_entry->start))
                          map->first_free = new_entry;
          }
  
          map->size += size;
  
          UVMHIST_LOG(maphist,"<- done!", 0, 0, 0, 0);
          vm_map_unlock(map);
          return 0;
  }
  
  /*
   * uvm_map_lookup_entry: find map entry at or before an address
   *
   * => map must at least be read-locked by caller
   * => entry is returned in "entry"
   * => return value is true if address is in the returned entry
   */
  
  boolean_t
  uvm_map_lookup_entry(struct vm_map *map, vaddr_t address,
      struct vm_map_entry **entry /* OUT */)
  {
          struct vm_map_entry *cur;
          boolean_t use_tree = FALSE;
          UVMHIST_FUNC("uvm_map_lookup_entry");
          UVMHIST_CALLED(maphist);
  
          UVMHIST_LOG(maphist,"(map=0x%x,addr=0x%x,ent=0x%x)",
              map, address, entry, 0);
  
          /*
           * start looking either from the head of the
           * list, or from the hint.
           */
  
          simple_lock(&map->hint_lock);
          cur = map->hint;
          simple_unlock(&map->hint_lock);
  
          if (cur == &map->header)
                  cur = cur->next;
  
          UVMCNT_INCR(uvm_mlk_call);
          if (address >= cur->start) {
  
                  /*
                   * go from hint to end of list.
                   *
                   * but first, make a quick check to see if
                   * we are already looking at the entry we
                   * want (which is usually the case).
                   * note also that we don't need to save the hint
                   * here... it is the same hint (unless we are
                   * at the header, in which case the hint didn't
                   * buy us anything anyway).
                   */
  
                  if (cur != &map->header && cur->end > address) {
                          UVMCNT_INCR(uvm_mlk_hint);
                          *entry = cur;
                          UVMHIST_LOG(maphist,"<- got it via hint (0x%x)",
                              cur, 0, 0, 0);
                          return (TRUE);
                  }
  
                  if (map->nentries > 30)
                          use_tree = TRUE;
          } else {
  
                  /*
                   * invalid hint.  use tree.
                   */
                  use_tree = TRUE;
          }
  
          uvm_tree_sanity(map, __func__);
  
          if (use_tree) {
                  struct vm_map_entry *prev = &map->header;
                  cur = RB_ROOT(&map->rbhead);
  
                  /*
                   * Simple lookup in the tree.  Happens when the hint is
                   * invalid, or nentries reach a threshold.
                   */
                  while (cur) {
                          if (address >= cur->start) {
                                  if (address < cur->end) {
                                          *entry = cur;
                                          goto got;
                                  }
                                  prev = cur;
                                  cur = RB_RIGHT(cur, rb_entry);
                          } else
                                  cur = RB_LEFT(cur, rb_entry);
                  }
                  *entry = prev;
                  goto failed;
          }
  
          /*
           * search linearly
           */
  
          while (cur != &map->header) {
                  if (cur->end > address) {
                          if (address >= cur->start) {
                                  /*
                                   * save this lookup for future
                                   * hints, and return
                                   */
  
                                  *entry = cur;
  got:
                                  SAVE_HINT(map, map->hint, *entry);
                                  UVMHIST_LOG(maphist,"<- search got it (0x%x)",
                                          cur, 0, 0, 0);
                                  KDASSERT((*entry)->start <= address);
                                  KDASSERT(address < (*entry)->end);
                                  return (TRUE);
                          }
                          break;
                  }
                  cur = cur->next;
          }
          *entry = cur->prev;
  failed:
          SAVE_HINT(map, map->hint, *entry);
          UVMHIST_LOG(maphist,"<- failed!",0,0,0,0);
          KDASSERT((*entry) == &map->header || (*entry)->end <= address);
          KDASSERT((*entry)->next == &map->header ||
              address < (*entry)->next->start);
          return (FALSE);
  }
  
  /*
   * See if the range between start and start + length fits in the gap
   * entry->next->start and entry->end.  Returns 1 if fits, 0 if doesn't
   * fit, and -1 address wraps around.
   */
  static __inline int
  uvm_map_space_avail(vaddr_t *start, vsize_t length, voff_t uoffset,
      vsize_t align, int topdown, struct vm_map_entry *entry)
  {
          vaddr_t end;
  
  #ifdef PMAP_PREFER
          /*
           * push start address forward as needed to avoid VAC alias problems.
           * we only do this if a valid offset is specified.
           */
  
          if (uoffset != UVM_UNKNOWN_OFFSET)
                  PMAP_PREFER(uoffset, start);
  #endif
          if (align != 0) {
                  if ((*start & (align - 1)) != 0) {
                          if (topdown)
                                  *start &= ~(align - 1);
                          else
                                  *start = roundup(*start, align);
                  }
                  /*
                   * XXX Should we PMAP_PREFER() here again?
                   */
          }
  
          /*
           * Find the end of the proposed new region.  Be sure we didn't
           * wrap around the address; if so, we lose.  Otherwise, if the
           * proposed new region fits before the next entry, we win.
           */
  
          end = *start + length;
          if (end < *start)
                  return (-1);
  
          if (entry->next->start >= end && *start >= entry->end)
                  return (1);
  
          return (0);
  }
  
  /*
   * uvm_map_findspace: find "length" sized space in "map".
   *
   * => "hint" is a hint about where we want it, unless FINDSPACE_FIXED is
   *      set (in which case we insist on using "hint").
   * => "result" is VA returned
   * => uobj/uoffset are to be used to handle VAC alignment, if required
   * => if `align' is non-zero, we attempt to align to that value.
   * => caller must at least have read-locked map
   * => returns NULL on failure, or pointer to prev. map entry if success
   * => note this is a cross between the old vm_map_findspace and vm_map_find
   */
  
  struct vm_map_entry *
  uvm_map_findspace(struct vm_map *map, vaddr_t hint, vsize_t length,
      vaddr_t *result /* OUT */, struct uvm_object *uobj, voff_t uoffset,
      vsize_t align, int flags)
  {
          struct vm_map_entry *entry;
          struct vm_map_entry *child, *prev, *tmp;
          vaddr_t orig_hint;
          const int topdown = map->flags & VM_MAP_TOPDOWN;
          UVMHIST_FUNC("uvm_map_findspace");
          UVMHIST_CALLED(maphist);
  
          UVMHIST_LOG(maphist, "(map=0x%x, hint=0x%x, len=%d, flags=0x%x)",
              map, hint, length, flags);
          KASSERT((align & (align - 1)) == 0);
          KASSERT((flags & UVM_FLAG_FIXED) == 0 || align == 0);
  
          uvm_tree_sanity(map, "map_findspace entry");
  
          /*
           * remember the original hint.  if we are aligning, then we
           * may have to try again with no alignment constraint if
           * we fail the first time.
           */
  
          orig_hint = hint;
          if (hint < map->min_offset) {   /* check ranges ... */
                  if (flags & UVM_FLAG_FIXED) {
                          UVMHIST_LOG(maphist,"<- VA below map range",0,0,0,0);
                          return (NULL);
                  }
                  hint = map->min_offset;
          }
          if (hint > map->max_offset) {
                  UVMHIST_LOG(maphist,"<- VA 0x%x > range [0x%x->0x%x]",
                      hint, map->min_offset, map->max_offset, 0);
                  return (NULL);
          }
  
          /*
           * Look for the first possible address; if there's already
           * something at this address, we have to start after it.
           */
  
          /*
           * @@@: there are four, no, eight cases to consider.
           *
           * 0: found,     fixed,     bottom up -> fail
           * 1: found,     fixed,     top down  -> fail
           * 2: found,     not fixed, bottom up -> start after entry->end,
           *                                       loop up
           * 3: found,     not fixed, top down  -> start before entry->start,
           *                                       loop down
           * 4: not found, fixed,     bottom up -> check entry->next->start, fail
           * 5: not found, fixed,     top down  -> check entry->next->start, fail
           * 6: not found, not fixed, bottom up -> check entry->next->start,
           *                                       loop up
           * 7: not found, not fixed, top down  -> check entry->next->start,
           *                                       loop down
           *
           * as you can see, it reduces to roughly five cases, and that
           * adding top down mapping only adds one unique case (without
           * it, there would be four cases).
           */
  
          if ((flags & UVM_FLAG_FIXED) == 0 && hint == map->min_offset) {
                  entry = map->first_free;
          } else {
                  if (uvm_map_lookup_entry(map, hint, &entry)) {
                          /* "hint" address already in use ... */
                          if (flags & UVM_FLAG_FIXED) {
                                  UVMHIST_LOG(maphist, "<- fixed & VA in use",
                                      0, 0, 0, 0);
                                  return (NULL);
                          }
                          if (topdown)
                                  /* Start from lower gap. */
                                  entry = entry->prev;
                  } else if (flags & UVM_FLAG_FIXED) {
                          if (entry->next->start >= hint + length &&
                              hint + length > hint)
                                  goto found;
  
                          /* "hint" address is gap but too small */
                          UVMHIST_LOG(maphist, "<- fixed mapping failed",
                              0, 0, 0, 0);
                          return (NULL); /* only one shot at it ... */
                  } else {
                          /*
                           * See if given hint fits in this gap.
                           */
                          switch (uvm_map_space_avail(&hint, length,
                              uoffset, align, topdown, entry)) {
                          case 1:
                                  goto found;
                          case -1:
                                  goto wraparound;
                          }
  
                          if (topdown) {
                                  /*
                                   * Still there is a chance to fit
                                   * if hint > entry->end.
                                   */
                          } else {
                                  /* Start from higer gap. */
                                  entry = entry->next;
                                  if (entry == &map->header)
                                          goto notfound;
                                  goto nextgap;
                          }
                  }
          }
  
          /*
           * Note that all UVM_FLAGS_FIXED case is already handled.
           */
          KDASSERT((flags & UVM_FLAG_FIXED) == 0);
  
          /* Try to find the space in the red-black tree */
  
          /* Check slot before any entry */
          hint = topdown ? entry->next->start - length : entry->end;
          switch (uvm_map_space_avail(&hint, length, uoffset, align,
              topdown, entry)) {
          case 1:
                  goto found;
          case -1:
                  goto wraparound;
          }
  
  nextgap:
          KDASSERT((flags & UVM_FLAG_FIXED) == 0);
          /* If there is not enough space in the whole tree, we fail */
          tmp = RB_ROOT(&map->rbhead);
          if (tmp == NULL || tmp->space < length)
                  goto notfound;
  
          prev = NULL; /* previous candidate */
  
          /* Find an entry close to hint that has enough space */
          for (; tmp;) {
                  KASSERT(tmp->next->start == tmp->end + tmp->ownspace);
                  if (topdown) {
                          if (tmp->next->start < hint + length &&
                              (prev == NULL || tmp->end > prev->end)) {
                                  if (tmp->ownspace >= length)
                                          prev = tmp;
                                  else if ((child = RB_LEFT(tmp, rb_entry))
                                      != NULL && child->space >= length)
                                          prev = tmp;
                          }
                  } else {
                          if (tmp->end >= hint &&
                              (prev == NULL || tmp->end < prev->end)) {
                                  if (tmp->ownspace >= length)
                                          prev = tmp;
                                  else if ((child = RB_RIGHT(tmp, rb_entry))
                                      != NULL && child->space >= length)
                                          prev = tmp;
                          }
                  }
                  if (tmp->next->start < hint + length)
                          child = RB_RIGHT(tmp, rb_entry);
                  else if (tmp->end > hint)
                          child = RB_LEFT(tmp, rb_entry);
                  else {
                          if (tmp->ownspace >= length)
                                  break;
                          if (topdown)
                                  child = RB_LEFT(tmp, rb_entry);
                          else
                                  child = RB_RIGHT(tmp, rb_entry);
                  }
                  if (child == NULL || child->space < length)
                          break;
                  tmp = child;
          }
  
          if (tmp != NULL && tmp->start < hint && hint < tmp->next->start) {
                  /*
                   * Check if the entry that we found satifies the
                   * space requirement
                   */
                  if (topdown) {
                          if (hint > tmp->next->start - length)
                                  hint = tmp->next->start - length;
                  } else {
                          if (hint < tmp->end)
                                  hint = tmp->end;
                  }
                  switch (uvm_map_space_avail(&hint, length, uoffset, align,
                      topdown, tmp)) {
                  case 1:
                          entry = tmp;
                          goto found;
                  case -1:
                          goto wraparound;
                  }
                  if (tmp->ownspace >= length)
                          goto listsearch;
          }
          if (prev == NULL)
                  goto notfound;
  
          if (topdown) {
                  KASSERT(orig_hint >= prev->next->start - length ||
                      prev->next->start - length > prev->next->start);
                  hint = prev->next->start - length;
          } else {
                  KASSERT(orig_hint <= prev->end);
                  hint = prev->end;
          }
          switch (uvm_map_space_avail(&hint, length, uoffset, align,
              topdown, prev)) {
          case 1:
                  entry = prev;
                  goto found;
          case -1:
                  goto wraparound;
          }
          if (prev->ownspace >= length)
                  goto listsearch;
  
          if (topdown)
                  tmp = RB_LEFT(prev, rb_entry);
          else
                  tmp = RB_RIGHT(prev, rb_entry);
          for (;;) {
                  KASSERT(tmp && tmp->space >= length);
                  if (topdown)
                          child = RB_RIGHT(tmp, rb_entry);
                  else
                          child = RB_LEFT(tmp, rb_entry);
                  if (child && child->space >= length) {
                          tmp = child;
                          continue;
                  }
                  if (tmp->ownspace >= length)
                          break;
                  if (topdown)
                          tmp = RB_LEFT(tmp, rb_entry);
                  else
                          tmp = RB_RIGHT(tmp, rb_entry);
          }
  
          if (topdown) {
                  KASSERT(orig_hint >= tmp->next->start - length ||
                      tmp->next->start - length > tmp->next->start);
                  hint = tmp->next->start - length;
          } else {
                  KASSERT(orig_hint <= tmp->end);
                  hint = tmp->end;
          }
          switch (uvm_map_space_avail(&hint, length, uoffset, align,
              topdown, tmp)) {
          case 1:
                  entry = tmp;
                  goto found;
          case -1:
                  goto wraparound;
          }
  
          /*
           * The tree fails to find an entry because of offset or alignment
           * restrictions.  Search the list instead.
           */
   listsearch:
          /*
           * Look through the rest of the map, trying to fit a new region in
           * the gap between existing regions, or after the very last region.
           * note: entry->end = base VA of current gap,
           *       entry->next->start = VA of end of current gap
           */
  
          for (;;) {
                  /* Update hint for current gap. */
                  hint = topdown ? entry->next->start - length : entry->end;
  
                  /* See if it fits. */
                  switch (uvm_map_space_avail(&hint, length, uoffset, align,
                      topdown, entry)) {
                  case 1:
                          goto found;
                  case -1:
                          goto wraparound;
                  }
  
                  /* Advance to next/previous gap */
                  if (topdown) {
                          if (entry == &map->header) {
                                  UVMHIST_LOG(maphist, "<- failed (off start)",
                                      0,0,0,0);
                                  goto notfound;
                          }
                          entry = entry->prev;
                  } else {
                          entry = entry->next;
                          if (entry == &map->header) {
                                  UVMHIST_LOG(maphist, "<- failed (off end)",
                                      0,0,0,0);
                                  goto notfound;
                          }
                  }
          }
  
   found:
          SAVE_HINT(map, map->hint, entry);
          *result = hint;
          UVMHIST_LOG(maphist,"<- got it!  (result=0x%x)", hint, 0,0,0);
          KASSERT( topdown || hint >= orig_hint);
          KASSERT(!topdown || hint <= orig_hint);
          KASSERT(entry->end <= hint);
          KASSERT(hint + length <= entry->next->start);
          return (entry);
  
   wraparound:
          UVMHIST_LOG(maphist, "<- failed (wrap around)", 0,0,0,0);
  
          return (NULL);
  
   notfound:
          UVMHIST_LOG(maphist, "<- failed (notfound)", 0,0,0,0);
  
          return (NULL);
  }
  
  /*
   *   U N M A P   -   m a i n   h e l p e r   f u n c t i o n s
   */
  
  /*
   * uvm_unmap_remove: remove mappings from a vm_map (from "start" up to "stop")
   *
   * => caller must check alignment and size
   * => map must be locked by caller
   * => we return a list of map entries that we've remove from the map
   *    in "entry_list"
   */
  
  void
  uvm_unmap_remove(struct vm_map *map, vaddr_t start, vaddr_t end,
      struct vm_map_entry **entry_list /* OUT */)
  {
          struct vm_map_entry *entry, *first_entry, *next;
          vaddr_t len;
          UVMHIST_FUNC("uvm_unmap_remove"); UVMHIST_CALLED(maphist);
  
          UVMHIST_LOG(maphist,"(map=0x%x, start=0x%x, end=0x%x)",
              map, start, end, 0);
          VM_MAP_RANGE_CHECK(map, start, end);
  
          uvm_tree_sanity(map, "unmap_remove entry");
  
          /*
           * find first entry
           */
  
          if (uvm_map_lookup_entry(map, start, &first_entry) == TRUE) {
                  /* clip and go... */
                  entry = first_entry;
                  UVM_MAP_CLIP_START(map, entry, start);
                  /* critical!  prevents stale hint */
                  SAVE_HINT(map, entry, entry->prev);
          } else {
                  entry = first_entry->next;
          }
  
          /*
           * Save the free space hint
           */
  
          if (map->first_free->start >= start)
                  map->first_free = entry->prev;
  
          /*
           * note: we now re-use first_entry for a different task.  we remove
           * a number of map entries from the map and save them in a linked
           * list headed by "first_entry".  once we remove them from the map
           * the caller should unlock the map and drop the references to the
           * backing objects [c.f. uvm_unmap_detach].  the object is to
           * separate unmapping from reference dropping.  why?
           *   [1] the map has to be locked for unmapping
           *   [2] the map need not be locked for reference dropping
           *   [3] dropping references may trigger pager I/O, and if we hit
           *       a pager that does synchronous I/O we may have to wait for it.
           *   [4] we would like all waiting for I/O to occur with maps unlocked
           *       so that we don't block other threads.
           */
  
          first_entry = NULL;
          *entry_list = NULL;
  
          /*
           * break up the area into map entry sized regions and unmap.  note
           * that all mappings have to be removed before we can even consider
           * dropping references to amaps or VM objects (otherwise we could end
           * up with a mapping to a page on the free list which would be very bad)
           */
  
          while ((entry != &map->header) && (entry->start < end)) {
                  UVM_MAP_CLIP_END(map, entry, end);
                  next = entry->next;
                  len = entry->end - entry->start;
  
                  /*
                   * unwire before removing addresses from the pmap; otherwise
                   * unwiring will put the entries back into the pmap (XXX).
                   */
  
                  if (VM_MAPENT_ISWIRED(entry)) {
                          uvm_map_entry_unwire(map, entry);
                  }
                  if ((map->flags & VM_MAP_PAGEABLE) == 0) {
  
                          /*
                           * if the map is non-pageable, any pages mapped there
                           * must be wired and entered with pmap_kenter_pa(),
                           * and we should free any such pages immediately.
                           * this is mostly used for kmem_map and mb_map.
                           */
  
                          uvm_km_pgremove_intrsafe(entry->start, entry->end);
                          pmap_kremove(entry->start, len);
                  } else if (UVM_ET_ISOBJ(entry) &&
                             UVM_OBJ_IS_KERN_OBJECT(entry->object.uvm_obj)) {
                          KASSERT(vm_map_pmap(map) == pmap_kernel());
  
                          /*
                           * note: kernel object mappings are currently used in
                           * two ways:
                           *  [1] "normal" mappings of pages in the kernel object
                           *  [2] uvm_km_valloc'd allocations in which we
                           *      pmap_enter in some non-kernel-object page
                           *      (e.g. vmapbuf).
                           *
                           * for case [1], we need to remove the mapping from
                           * the pmap and then remove the page from the kernel
                           * object (because, once pages in a kernel object are
                           * unmapped they are no longer needed, unlike, say,
                           * a vnode where you might want the data to persist
                           * until flushed out of a queue).
                           *
                           * for case [2], we need to remove the mapping from
                           * the pmap.  there shouldn't be any pages at the
                           * specified offset in the kernel object [but it
                           * doesn't hurt to call uvm_km_pgremove just to be
                           * safe?]
                           *
                           * uvm_km_pgremove currently does the following:
                           *   for pages in the kernel object in range:
                           *     - drops the swap slot
                           *     - uvm_pagefree the page
                           */
  
                          /*
                           * remove mappings from pmap and drop the pages
                           * from the object.  offsets are always relative
                           * to vm_map_min(kernel_map).
                           */
  
                          pmap_remove(pmap_kernel(), entry->start,
                              entry->start + len);
                          uvm_km_pgremove(entry->object.uvm_obj,
                              entry->start - vm_map_min(kernel_map),
                              entry->end - vm_map_min(kernel_map));
  
                          /*
                           * null out kernel_object reference, we've just
                           * dropped it
                           */
  
                          entry->etype &= ~UVM_ET_OBJ;
                          entry->object.uvm_obj = NULL;
                  } else if (UVM_ET_ISOBJ(entry) || entry->aref.ar_amap) {
  
                          /*
                           * remove mappings the standard way.
                           */
  
                          pmap_remove(map->pmap, entry->start, entry->end);
                  }
  
                  /*
                   * remove entry from map and put it on our list of entries
                   * that we've nuked.  then go to next entry.
                   */
  
                  UVMHIST_LOG(maphist, "  removed map entry 0x%x", entry, 0, 0,0);
  
                  /* critical!  prevents stale hint */
                  SAVE_HINT(map, entry, entry->prev);
  
                  uvm_map_entry_unlink(map, entry);
                  KASSERT(map->size >= len);
                  map->size -= len;
                  entry->prev = NULL;
                  entry->next = first_entry;
                  first_entry = entry;
                  entry = next;
          }
          if ((map->flags & VM_MAP_DYING) == 0) {
                  pmap_update(vm_map_pmap(map));
          }
  
          uvm_tree_sanity(map, "unmap_remove leave");
  
          /*
           * now we've cleaned up the map and are ready for the caller to drop
           * references to the mapped objects.
           */
  
          *entry_list = first_entry;
          UVMHIST_LOG(maphist,"<- done!", 0, 0, 0, 0);
  }
  
  /*
   * uvm_unmap_detach: drop references in a chain of map entries
   *
   * => we will free the map entries as we traverse the list.
   */
  
  void
  uvm_unmap_detach(struct vm_map_entry *first_entry, int flags)
  {
          struct vm_map_entry *next_entry;
          UVMHIST_FUNC("uvm_unmap_detach"); UVMHIST_CALLED(maphist);
  
          while (first_entry) {
                  KASSERT(!VM_MAPENT_ISWIRED(first_entry));
                  UVMHIST_LOG(maphist,
                      "  detach 0x%x: amap=0x%x, obj=0x%x, submap?=%d",
                      first_entry, first_entry->aref.ar_amap,
                      first_entry->object.uvm_obj,
                      UVM_ET_ISSUBMAP(first_entry));
  
                  /*
                   * drop reference to amap, if we've got one
                   */
  
                  if (first_entry->aref.ar_amap)
                          uvm_map_unreference_amap(first_entry, flags);
  
                  /*
                   * drop reference to our backing object, if we've got one
                   */
  
                  KASSERT(!UVM_ET_ISSUBMAP(first_entry));
                  if (UVM_ET_ISOBJ(first_entry) &&
                      first_entry->object.uvm_obj->pgops->pgo_detach) {
                          (*first_entry->object.uvm_obj->pgops->pgo_detach)
                                  (first_entry->object.uvm_obj);
                  }
                  next_entry = first_entry->next;
                  uvm_mapent_free(first_entry);
                  first_entry = next_entry;
          }
          UVMHIST_LOG(maphist, "<- done", 0,0,0,0);
  }
  
  /*
   *   E X T R A C T I O N   F U N C T I O N S
   */
  
  /*
   * uvm_map_reserve: reserve space in a vm_map for future use.
   *
   * => we reserve space in a map by putting a dummy map entry in the
   *    map (dummy means obj=NULL, amap=NULL, prot=VM_PROT_NONE)
   * => map should be unlocked (we will write lock it)
   * => we return true if we were able to reserve space
   * => XXXCDC: should be inline?
   */
  
  int
  uvm_map_reserve(struct vm_map *map, vsize_t size,
      vaddr_t offset      /* hint for pmap_prefer */,
      vsize_t align       /* alignment hint */,
      vaddr_t *raddr      /* IN:hint, OUT: reserved VA */)
  {
          UVMHIST_FUNC("uvm_map_reserve"); UVMHIST_CALLED(maphist);
  
          UVMHIST_LOG(maphist, "(map=0x%x, size=0x%x, offset=0x%x,addr=0x%x)",
              map,size,offset,raddr);
  
          size = round_page(size);
          if (*raddr < vm_map_min(map))
                  *raddr = vm_map_min(map);               /* hint */
  
          /*
           * reserve some virtual space.
           */
  
          if (uvm_map(map, raddr, size, NULL, offset, 0,
              UVM_MAPFLAG(UVM_PROT_NONE, UVM_PROT_NONE, UVM_INH_NONE,
              UVM_ADV_RANDOM, UVM_FLAG_NOMERGE)) != 0) {
              UVMHIST_LOG(maphist, "<- done (no VM)", 0,0,0,0);
                  return (FALSE);
          }
  
          UVMHIST_LOG(maphist, "<- done (*raddr=0x%x)", *raddr,0,0,0);
          return (TRUE);
  }
  
  /*
   * uvm_map_replace: replace a reserved (blank) area of memory with
   * real mappings.
   *
   * => caller must WRITE-LOCK the map
   * => we return TRUE if replacement was a success
   * => we expect the newents chain to have nnewents entrys on it and
   *    we expect newents->prev to point to the last entry on the list
   * => note newents is allowed to be NULL
   */
  
  int
  uvm_map_replace(struct vm_map *map, vaddr_t start, vaddr_t end,
      struct vm_map_entry *newents, int nnewents)
  {
          struct vm_map_entry *oldent, *last;
  
          uvm_tree_sanity(map, "map_replace entry");
  
          /*
           * first find the blank map entry at the specified address
           */
  
          if (!uvm_map_lookup_entry(map, start, &oldent)) {
                  return (FALSE);
          }
  
          /*
           * check to make sure we have a proper blank entry
           */
  
          if (oldent->start != start || oldent->end != end ||
              oldent->object.uvm_obj != NULL || oldent->aref.ar_amap != NULL) {
                  return (FALSE);
          }
  
  #ifdef DIAGNOSTIC
  
          /*
           * sanity check the newents chain
           */
  
          {
                  struct vm_map_entry *tmpent = newents;
                  int nent = 0;
                  vaddr_t cur = start;
  
                  while (tmpent) {
                          nent++;
                          if (tmpent->start < cur)
                                  panic("uvm_map_replace1");
                          if (tmpent->start > tmpent->end || tmpent->end > end) {
                  printf("tmpent->start=0x%lx, tmpent->end=0x%lx, end=0x%lx\n",
                              tmpent->start, tmpent->end, end);
                                  panic("uvm_map_replace2");
                          }
                          cur = tmpent->end;
                          if (tmpent->next) {
                                  if (tmpent->next->prev != tmpent)
                                          panic("uvm_map_replace3");
                          } else {
                                  if (newents->prev != tmpent)
                                          panic("uvm_map_replace4");
                          }
                          tmpent = tmpent->next;
                  }
                  if (nent != nnewents)
                          panic("uvm_map_replace5");
          }
  #endif
  
          /*
           * map entry is a valid blank!   replace it.   (this does all the
           * work of map entry link/unlink...).
           */
  
          if (newents) {
                  last = newents->prev;
  
                  /* critical: flush stale hints out of map */
                  SAVE_HINT(map, map->hint, newents);
                  if (map->first_free == oldent)
                          map->first_free = last;
  
                  last->next = oldent->next;
                  last->next->prev = last;
  
                  /* Fix RB tree */
                  uvm_rb_remove(map, oldent);
  
                  newents->prev = oldent->prev;
                  newents->prev->next = newents;
                  map->nentries = map->nentries + (nnewents - 1);
  
                  /* Fixup the RB tree */
                  {
                          int i;
                          struct vm_map_entry *tmp;
  
                          tmp = newents;
                          for (i = 0; i < nnewents && tmp; i++) {
                                  uvm_rb_insert(map, tmp);
                                  tmp = tmp->next;
                          }
                  }
          } else {
  
                  /* critical: flush stale hints out of map */
                  SAVE_HINT(map, map->hint, oldent->prev);
                  if (map->first_free == oldent)
                          map->first_free = oldent->prev;
  
                  /* NULL list of new entries: just remove the old one */
                  uvm_map_entry_unlink(map, oldent);
          }
  
          uvm_tree_sanity(map, "map_replace leave");
  
          /*
           * now we can free the old blank entry, unlock the map and return.
           */
  
          uvm_mapent_free(oldent);
          return (TRUE);
  }
  
  /*
   * uvm_map_extract: extract a mapping from a map and put it somewhere
   *      (maybe removing the old mapping)
   *
   * => maps should be unlocked (we will write lock them)
   * => returns 0 on success, error code otherwise
   * => start must be page aligned
   * => len must be page sized
   * => flags:
   *      UVM_EXTRACT_REMOVE: remove mappings from srcmap
   *      UVM_EXTRACT_CONTIG: abort if unmapped area (advisory only)
   *      UVM_EXTRACT_QREF: for a temporary extraction do quick obj refs
   *      UVM_EXTRACT_FIXPROT: set prot to maxprot as we go
   *    >>>NOTE: if you set REMOVE, you are not allowed to use CONTIG or QREF!<<<
   *    >>>NOTE: QREF's must be unmapped via the QREF path, thus should only
   *             be used from within the kernel in a kernel level map <<<
   */
  
  int
  uvm_map_extract(struct vm_map *srcmap, vaddr_t start, vsize_t len,
      struct vm_map *dstmap, vaddr_t *dstaddrp, int flags)
  {
          vaddr_t dstaddr, end, newend, oldoffset, fudge, orig_fudge;
          struct vm_map_entry *chain, *endchain, *entry, *orig_entry, *newentry,
              *deadentry, *oldentry;
          vsize_t elen;
          int nchain, error, copy_ok;
          UVMHIST_FUNC("uvm_map_extract"); UVMHIST_CALLED(maphist);
  
          UVMHIST_LOG(maphist,"(srcmap=0x%x,start=0x%x, len=0x%x", srcmap, start,
              len,0);
          UVMHIST_LOG(maphist," ...,dstmap=0x%x, flags=0x%x)", dstmap,flags,0,0);
  
          uvm_tree_sanity(srcmap, "map_extract src enter");
          uvm_tree_sanity(dstmap, "map_extract dst enter");
  
          /*
           * step 0: sanity check: start must be on a page boundary, length
           * must be page sized.  can't ask for CONTIG/QREF if you asked for
           * REMOVE.
           */
  
          KASSERT((start & PAGE_MASK) == 0 && (len & PAGE_MASK) == 0);
          KASSERT((flags & UVM_EXTRACT_REMOVE) == 0 ||
                  (flags & (UVM_EXTRACT_CONTIG|UVM_EXTRACT_QREF)) == 0);
  
          /*
           * step 1: reserve space in the target map for the extracted area
           */
  
          dstaddr = vm_map_min(dstmap);
          if (uvm_map_reserve(dstmap, len, start, 0, &dstaddr) == FALSE)
                  return (ENOMEM);
          *dstaddrp = dstaddr;    /* pass address back to caller */
          UVMHIST_LOG(maphist, "  dstaddr=0x%x", dstaddr,0,0,0);
  
          /*
           * step 2: setup for the extraction process loop by init'ing the
           * map entry chain, locking src map, and looking up the first useful
           * entry in the map.
           */
  
          end = start + len;
          newend = dstaddr + len;
          chain = endchain = NULL;
          nchain = 0;
          vm_map_lock(srcmap);
  
          if (uvm_map_lookup_entry(srcmap, start, &entry)) {
  
                  /* "start" is within an entry */
                  if (flags & UVM_EXTRACT_QREF) {
  
                          /*
                           * for quick references we don't clip the entry, so
                           * the entry may map space "before" the starting
                           * virtual address... this is the "fudge" factor
                           * (which can be non-zero only the first time
                           * through the "while" loop in step 3).
                           */
  
                          fudge = start - entry->start;
                  } else {
  
                          /*
                           * normal reference: we clip the map to fit (thus
                           * fudge is zero)
                           */
  
                          UVM_MAP_CLIP_START(srcmap, entry, start);
                          SAVE_HINT(srcmap, srcmap->hint, entry->prev);
                          fudge = 0;
                  }
          } else {
  
                  /* "start" is not within an entry ... skip to next entry */
                  if (flags & UVM_EXTRACT_CONTIG) {
                          error = EINVAL;
                          goto bad;    /* definite hole here ... */
                  }
  
                  entry = entry->next;
                  fudge = 0;
          }
  
          /* save values from srcmap for step 6 */
          orig_entry = entry;
          orig_fudge = fudge;
  
          /*
           * step 3: now start looping through the map entries, extracting
           * as we go.
           */
  
          while (entry->start < end && entry != &srcmap->header) {
  
                  /* if we are not doing a quick reference, clip it */
                  if ((flags & UVM_EXTRACT_QREF) == 0)
                          UVM_MAP_CLIP_END(srcmap, entry, end);
  
                  /* clear needs_copy (allow chunking) */
                  if (UVM_ET_ISNEEDSCOPY(entry)) {
                          amap_copy(srcmap, entry, M_NOWAIT, TRUE, start, end);
                          if (UVM_ET_ISNEEDSCOPY(entry)) {  /* failed? */
                                  error = ENOMEM;
                                  goto bad;
                          }
  
                          /* amap_copy could clip (during chunk)!  update fudge */
                          if (fudge) {
                                  fudge = start - entry->start;
                                  orig_fudge = fudge;
                          }
                  }
  
                  /* calculate the offset of this from "start" */
                  oldoffset = (entry->start + fudge) - start;
  
                  /* allocate a new map entry */
                  newentry = uvm_mapent_alloc(dstmap, 0);
                  if (newentry == NULL) {
                          error = ENOMEM;
                          goto bad;
                  }
  
                  /* set up new map entry */
                  newentry->next = NULL;
                  newentry->prev = endchain;
                  newentry->start = dstaddr + oldoffset;
                  newentry->end =
                      newentry->start + (entry->end - (entry->start + fudge));
                  if (newentry->end > newend || newentry->end < newentry->start)
                          newentry->end = newend;
                  newentry->object.uvm_obj = entry->object.uvm_obj;
                  if (newentry->object.uvm_obj) {
                          if (newentry->object.uvm_obj->pgops->pgo_reference)
                                  newentry->object.uvm_obj->pgops->
                                      pgo_reference(newentry->object.uvm_obj);
                                  newentry->offset = entry->offset + fudge;
                  } else {
                          newentry->offset = 0;
                  }
                  newentry->etype = entry->etype;
                  newentry->protection = (flags & UVM_EXTRACT_FIXPROT) ?
                          entry->max_protection : entry->protection;
                  newentry->max_protection = entry->max_protection;
                  newentry->inheritance = entry->inheritance;
                  newentry->wired_count = 0;
                  newentry->aref.ar_amap = entry->aref.ar_amap;
                  if (newentry->aref.ar_amap) {
                          newentry->aref.ar_pageoff =
                              entry->aref.ar_pageoff + (fudge >> PAGE_SHIFT);
                          uvm_map_reference_amap(newentry, AMAP_SHARED |
                              ((flags & UVM_EXTRACT_QREF) ? AMAP_REFALL : 0));
                  } else {
                          newentry->aref.ar_pageoff = 0;
                  }
                  newentry->advice = entry->advice;
  
                  /* now link it on the chain */
                  nchain++;
                  if (endchain == NULL) {
                          chain = endchain = newentry;
                  } else {
                          endchain->next = newentry;
                          endchain = newentry;
                  }
  
                  /* end of 'while' loop! */
                  if ((flags & UVM_EXTRACT_CONTIG) && entry->end < end &&
                      (entry->next == &srcmap->header ||
                      entry->next->start != entry->end)) {
                          error = EINVAL;
                          goto bad;
                  }
                  entry = entry->next;
                  fudge = 0;
          }
  
          /*
           * step 4: close off chain (in format expected by uvm_map_replace)
           */
  
          if (chain)
                  chain->prev = endchain;
  
          /*
           * step 5: attempt to lock the dest map so we can pmap_copy.
           * note usage of copy_ok:
           *   1 => dstmap locked, pmap_copy ok, and we "replace" here (step 5)
           *   0 => dstmap unlocked, NO pmap_copy, and we will "replace" in step 7
           */
  
          if (srcmap == dstmap || vm_map_lock_try(dstmap) == TRUE) {
                  copy_ok = 1;
                  if (!uvm_map_replace(dstmap, dstaddr, dstaddr+len, chain,
                      nchain)) {
                          if (srcmap != dstmap)
                                  vm_map_unlock(dstmap);
                          error = EIO;
                          goto bad;
                  }
          } else {
                  copy_ok = 0;
                  /* replace defered until step 7 */
          }
  
          /*
           * step 6: traverse the srcmap a second time to do the following:
           *  - if we got a lock on the dstmap do pmap_copy
           *  - if UVM_EXTRACT_REMOVE remove the entries
           * we make use of orig_entry and orig_fudge (saved in step 2)
           */
  
          if (copy_ok || (flags & UVM_EXTRACT_REMOVE)) {
  
                  /* purge possible stale hints from srcmap */
                  if (flags & UVM_EXTRACT_REMOVE) {
                          SAVE_HINT(srcmap, srcmap->hint, orig_entry->prev);
                          if (srcmap->first_free->start >= start)
                                  srcmap->first_free = orig_entry->prev;
                  }
  
                  entry = orig_entry;
                  fudge = orig_fudge;
                  deadentry = NULL;       /* for UVM_EXTRACT_REMOVE */
  
                  while (entry->start < end && entry != &srcmap->header) {
                          if (copy_ok) {
                                  oldoffset = (entry->start + fudge) - start;
                                  elen = MIN(end, entry->end) -
                                      (entry->start + fudge);
                                  pmap_copy(dstmap->pmap, srcmap->pmap,
                                      dstaddr + oldoffset, elen,
                                      entry->start + fudge);
                          }
  
                          /* we advance "entry" in the following if statement */
                          if (flags & UVM_EXTRACT_REMOVE) {
                                  pmap_remove(srcmap->pmap, entry->start,
                                                  entry->end);
                                  oldentry = entry;       /* save entry */
                                  entry = entry->next;    /* advance */
                                  uvm_map_entry_unlink(srcmap, oldentry);
                                                          /* add to dead list */
                                  oldentry->next = deadentry;
                                  deadentry = oldentry;
                          } else {
                                  entry = entry->next;            /* advance */
                          }
  
                          /* end of 'while' loop */
                          fudge = 0;
                  }
                  pmap_update(srcmap->pmap);
  
                  /*
                   * unlock dstmap.  we will dispose of deadentry in
                   * step 7 if needed
                   */
  
                  if (copy_ok && srcmap != dstmap)
                          vm_map_unlock(dstmap);
  
          } else {
                  deadentry = NULL;
          }
  
          /*
           * step 7: we are done with the source map, unlock.   if copy_ok
           * is 0 then we have not replaced the dummy mapping in dstmap yet
           * and we need to do so now.
           */
  
          vm_map_unlock(srcmap);
          if ((flags & UVM_EXTRACT_REMOVE) && deadentry)
                  uvm_unmap_detach(deadentry, 0);   /* dispose of old entries */
  
          /* now do the replacement if we didn't do it in step 5 */
          if (copy_ok == 0) {
                  vm_map_lock(dstmap);
                  error = uvm_map_replace(dstmap, dstaddr, dstaddr+len, chain,
                      nchain);
                  vm_map_unlock(dstmap);
  
                  if (error == FALSE) {
                          error = EIO;
                          goto bad2;
                  }
          }
  
          uvm_tree_sanity(srcmap, "map_extract src leave");
          uvm_tree_sanity(dstmap, "map_extract dst leave");
  
          return (0);
  
          /*
           * bad: failure recovery
           */
  bad:
          vm_map_unlock(srcmap);
  bad2:                   /* src already unlocked */
          if (chain)
                  uvm_unmap_detach(chain,
                      (flags & UVM_EXTRACT_QREF) ? AMAP_REFALL : 0);
  
          uvm_tree_sanity(srcmap, "map_extract src err leave");
          uvm_tree_sanity(dstmap, "map_extract dst err leave");
  
          uvm_unmap(dstmap, dstaddr, dstaddr+len);   /* ??? */
          return (error);
  }
  
  /* end of extraction functions */
  
  /*
   * uvm_map_submap: punch down part of a map into a submap
   *
   * => only the kernel_map is allowed to be submapped
   * => the purpose of submapping is to break up the locking granularity
   *      of a larger map
   * => the range specified must have been mapped previously with a uvm_map()
   *      call [with uobj==NULL] to create a blank map entry in the main map.
   *      [And it had better still be blank!]
   * => maps which contain submaps should never be copied or forked.
   * => to remove a submap, use uvm_unmap() on the main map
   *      and then uvm_map_deallocate() the submap.
   * => main map must be unlocked.
   * => submap must have been init'd and have a zero reference count.
   *      [need not be locked as we don't actually reference it]
   */
  
  int
  uvm_map_submap(struct vm_map *map, vaddr_t start, vaddr_t end,
      struct vm_map *submap)
  {
          struct vm_map_entry *entry;
          int error;
  
          vm_map_lock(map);
          VM_MAP_RANGE_CHECK(map, start, end);
  
          if (uvm_map_lookup_entry(map, start, &entry)) {
                  UVM_MAP_CLIP_START(map, entry, start);
                  UVM_MAP_CLIP_END(map, entry, end);              /* to be safe */
          } else {
                  entry = NULL;
          }
  
          if (entry != NULL &&
              entry->start == start && entry->end == end &&
              entry->object.uvm_obj == NULL && entry->aref.ar_amap == NULL &&
              !UVM_ET_ISCOPYONWRITE(entry) && !UVM_ET_ISNEEDSCOPY(entry)) {
                  entry->etype |= UVM_ET_SUBMAP;
                  entry->object.sub_map = submap;
                  entry->offset = 0;
                  uvm_map_reference(submap);
                  error = 0;
          } else {
                  error = EINVAL;
          }
          vm_map_unlock(map);
          return error;
  }
  
  
  /*
   * uvm_map_protect: change map protection
   *
   * => set_max means set max_protection.
   * => map must be unlocked.
   */
  
  #define MASK(entry)     (UVM_ET_ISCOPYONWRITE(entry) ? \
                           ~VM_PROT_WRITE : VM_PROT_ALL)
  
  int
  uvm_map_protect(struct vm_map *map, vaddr_t start, vaddr_t end,
      vm_prot_t new_prot, boolean_t set_max)
  {
          struct vm_map_entry *current, *entry;
          int error = 0;
          UVMHIST_FUNC("uvm_map_protect"); UVMHIST_CALLED(maphist);
          UVMHIST_LOG(maphist,"(map=0x%x,start=0x%x,end=0x%x,new_prot=0x%x)",
                      map, start, end, new_prot);
  
          vm_map_lock(map);
          VM_MAP_RANGE_CHECK(map, start, end);
          if (uvm_map_lookup_entry(map, start, &entry)) {
                  UVM_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 (UVM_ET_ISSUBMAP(current)) {
                          error = EINVAL;
                          goto out;
                  }
                  if ((new_prot & current->max_protection) != new_prot) {
                          error = EACCES;
                          goto out;
                  }
                  /*
                   * Don't allow VM_PROT_EXECUTE to be set on entries that
                   * point to vnodes that are associated with a NOEXEC file
                   * system.
                   */
                  if (UVM_ET_ISOBJ(current) &&
                      UVM_OBJ_IS_VNODE(current->object.uvm_obj)) {
                          struct vnode *vp =
                              (struct vnode *) current->object.uvm_obj;
  
                          if ((new_prot & VM_PROT_EXECUTE) != 0 &&
                              (vp->v_mount->mnt_flag & MNT_NOEXEC) != 0) {
                                  error = EACCES;
                                  goto out;
                          }
                  }
                  current = current->next;
          }
  
          /* go back and fix up protections (no need to clip this time). */
  
          current = entry;
          while ((current != &map->header) && (current->start < end)) {
                  vm_prot_t old_prot;
  
                  UVM_MAP_CLIP_END(map, current, end);
                  old_prot = current->protection;
                  if (set_max)
                          current->protection =
                              (current->max_protection = new_prot) & old_prot;
                  else
                          current->protection = new_prot;
  
                  /*
                   * update physical map if necessary.  worry about copy-on-write
                   * here -- CHECK THIS XXX
                   */
  
                  if (current->protection != old_prot) {
                          /* update pmap! */
                          pmap_protect(map->pmap, current->start, current->end,
                              current->protection & MASK(entry));
  
                          /*
                           * If this entry points at a vnode, and the
                           * protection includes VM_PROT_EXECUTE, mark
                           * the vnode as VEXECMAP.
                           */
                          if (UVM_ET_ISOBJ(current)) {
                                  struct uvm_object *uobj =
                                      current->object.uvm_obj;
  
                                  if (UVM_OBJ_IS_VNODE(uobj) &&
                                      (current->protection & VM_PROT_EXECUTE))
                                          vn_markexec((struct vnode *) uobj);
                          }
                  }
  
                  /*
                   * If the map is configured to lock any future mappings,
                   * wire this entry now if the old protection was VM_PROT_NONE
                   * and the new protection is not VM_PROT_NONE.
                   */
  
                  if ((map->flags & VM_MAP_WIREFUTURE) != 0 &&
                      VM_MAPENT_ISWIRED(entry) == 0 &&
                      old_prot == VM_PROT_NONE &&
                      new_prot != VM_PROT_NONE) {
                          if (uvm_map_pageable(map, entry->start,
                              entry->end, FALSE,
                              UVM_LK_ENTER|UVM_LK_EXIT) != 0) {
  
                                  /*
                                   * If locking the entry fails, remember the
                                   * error if it's the first one.  Note we
                                   * still continue setting the protection in
                                   * the map, but will return the error
                                   * condition regardless.
                                   *
                                   * XXX Ignore what the actual error is,
                                   * XXX just call it a resource shortage
                                   * XXX so that it doesn't get confused
                                   * XXX what uvm_map_protect() itself would
                                   * XXX normally return.
                                   */
  
                                  error = ENOMEM;
                          }
                  }
                  current = current->next;
          }
          pmap_update(map->pmap);
  
   out:
          vm_map_unlock(map);
          UVMHIST_LOG(maphist, "<- done, error=%d",error,0,0,0);
          return error;
  }
  
  #undef  MASK
  
  /*
   * uvm_map_inherit: set inheritance code for range of addrs in map.
   *
   * => map must be unlocked
   * => note that the inherit code is used during a "fork".  see fork
   *      code for details.
   */
  
  int
  uvm_map_inherit(struct vm_map *map, vaddr_t start, vaddr_t end,
      vm_inherit_t new_inheritance)
  {
          struct vm_map_entry *entry, *temp_entry;
          UVMHIST_FUNC("uvm_map_inherit"); UVMHIST_CALLED(maphist);
          UVMHIST_LOG(maphist,"(map=0x%x,start=0x%x,end=0x%x,new_inh=0x%x)",
              map, start, end, new_inheritance);
  
          switch (new_inheritance) {
          case MAP_INHERIT_NONE:
          case MAP_INHERIT_COPY:
          case MAP_INHERIT_SHARE:
                  break;
          default:
                  UVMHIST_LOG(maphist,"<- done (INVALID ARG)",0,0,0,0);
                  return EINVAL;
          }
  
          vm_map_lock(map);
          VM_MAP_RANGE_CHECK(map, start, end);
          if (uvm_map_lookup_entry(map, start, &temp_entry)) {
                  entry = temp_entry;
                  UVM_MAP_CLIP_START(map, entry, start);
          }  else {
                  entry = temp_entry->next;
          }
          while ((entry != &map->header) && (entry->start < end)) {
                  UVM_MAP_CLIP_END(map, entry, end);
                  entry->inheritance = new_inheritance;
                  entry = entry->next;
          }
          vm_map_unlock(map);
          UVMHIST_LOG(maphist,"<- done (OK)",0,0,0,0);
          return 0;
  }
  
  /*
   * uvm_map_advice: set advice code for range of addrs in map.
   *
   * => map must be unlocked
   */
  
  int
  uvm_map_advice(struct vm_map *map, vaddr_t start, vaddr_t end, int new_advice)
  {
          struct vm_map_entry *entry, *temp_entry;
          UVMHIST_FUNC("uvm_map_advice"); UVMHIST_CALLED(maphist);
          UVMHIST_LOG(maphist,"(map=0x%x,start=0x%x,end=0x%x,new_adv=0x%x)",
              map, start, end, new_advice);
  
          vm_map_lock(map);
          VM_MAP_RANGE_CHECK(map, start, end);
          if (uvm_map_lookup_entry(map, start, &temp_entry)) {
                  entry = temp_entry;
                  UVM_MAP_CLIP_START(map, entry, start);
          } else {
                  entry = temp_entry->next;
          }
  
          /*
           * XXXJRT: disallow holes?
           */
  
          while ((entry != &map->header) && (entry->start < end)) {
                  UVM_MAP_CLIP_END(map, entry, end);
  
                  switch (new_advice) {
                  case MADV_NORMAL:
                  case MADV_RANDOM:
                  case MADV_SEQUENTIAL:
                          /* nothing special here */
                          break;
  
                  default:
                          vm_map_unlock(map);
                          UVMHIST_LOG(maphist,"<- done (INVALID ARG)",0,0,0,0);
                          return EINVAL;
                  }
                  entry->advice = new_advice;
                  entry = entry->next;
          }
  
          vm_map_unlock(map);
          UVMHIST_LOG(maphist,"<- done (OK)",0,0,0,0);
          return 0;
  }
  
  /*
   * uvm_map_pageable: sets the pageability of a range in a map.
   *
   * => wires map entries.  should not be used for transient page locking.
   *      for that, use uvm_fault_wire()/uvm_fault_unwire() (see uvm_vslock()).
   * => regions sepcified as not pageable require lock-down (wired) memory
   *      and page tables.
   * => map must never be read-locked
   * => if islocked is TRUE, map is already write-locked
   * => we always unlock the map, since we must downgrade to a read-lock
   *      to call uvm_fault_wire()
   * => XXXCDC: check this and try and clean it up.
   */
  
  int
  uvm_map_pageable(struct vm_map *map, vaddr_t start, vaddr_t end,
      boolean_t new_pageable, int lockflags)
  {
          struct vm_map_entry *entry, *start_entry, *failed_entry;
          int rv;
  #ifdef DIAGNOSTIC
          u_int timestamp_save;
  #endif
          UVMHIST_FUNC("uvm_map_pageable"); UVMHIST_CALLED(maphist);
          UVMHIST_LOG(maphist,"(map=0x%x,start=0x%x,end=0x%x,new_pageable=0x%x)",
                      map, start, end, new_pageable);
          KASSERT(map->flags & VM_MAP_PAGEABLE);
  
          if ((lockflags & UVM_LK_ENTER) == 0)
                  vm_map_lock(map);
          VM_MAP_RANGE_CHECK(map, start, end);
  
          /*
           * only one pageability change may take place at one time, since
           * uvm_fault_wire assumes it will be called only once for each
           * wiring/unwiring.  therefore, we have to make sure we're actually
           * changing the pageability for the entire region.  we do so before
           * making any changes.
           */
  
          if (uvm_map_lookup_entry(map, start, &start_entry) == FALSE) {
                  if ((lockflags & UVM_LK_EXIT) == 0)
                          vm_map_unlock(map);
  
                  UVMHIST_LOG(maphist,"<- done (fault)",0,0,0,0);
                  return EFAULT;
          }
          entry = start_entry;
  
          /*
           * handle wiring and unwiring separately.
           */
  
          if (new_pageable) {             /* unwire */
                  UVM_MAP_CLIP_START(map, entry, start);
  
                  /*
                   * unwiring.  first ensure that the range to be unwired is
                   * really wired down and that there are no holes.
                   */
  
                  while ((entry != &map->header) && (entry->start < end)) {
                          if (entry->wired_count == 0 ||
                              (entry->end < end &&
                               (entry->next == &map->header ||
                                entry->next->start > entry->end))) {
                                  if ((lockflags & UVM_LK_EXIT) == 0)
                                          vm_map_unlock(map);
                                  UVMHIST_LOG(maphist, "<- done (INVAL)",0,0,0,0);
                                  return EINVAL;
                          }
                          entry = entry->next;
                  }
  
                  /*
                   * POSIX 1003.1b - a single munlock call unlocks a region,
                   * regardless of the number of mlock calls made on that
                   * region.
                   */
  
                  entry = start_entry;
                  while ((entry != &map->header) && (entry->start < end)) {
                          UVM_MAP_CLIP_END(map, entry, end);
                          if (VM_MAPENT_ISWIRED(entry))
                                  uvm_map_entry_unwire(map, entry);
                          entry = entry->next;
                  }
                  if ((lockflags & UVM_LK_EXIT) == 0)
                          vm_map_unlock(map);
                  UVMHIST_LOG(maphist,"<- done (OK UNWIRE)",0,0,0,0);
                  return 0;
          }
  
          /*
           * wire case: in two passes [XXXCDC: ugly block of code here]
           *
           * 1: holding the write lock, we create any anonymous maps that need
           *    to be created.  then we clip each map entry to the region to
           *    be wired and increment its wiring count.
           *
           * 2: we downgrade to a read lock, and call uvm_fault_wire to fault
           *    in the pages for any newly wired area (wired_count == 1).
           *
           *    downgrading to a read lock for uvm_fault_wire avoids a possible
           *    deadlock with another thread that may have faulted on one of
           *    the pages to be wired (it would mark the page busy, blocking
           *    us, then in turn block on the map lock that we hold).  because
           *    of problems in the recursive lock package, we cannot upgrade
           *    to a write lock in vm_map_lookup.  thus, any actions that
           *    require the write lock must be done beforehand.  because we
           *    keep the read lock on the map, the copy-on-write status of the
           *    entries we modify here cannot change.
           */
  
          while ((entry != &map->header) && (entry->start < end)) {
                  if (VM_MAPENT_ISWIRED(entry) == 0) { /* not already wired? */
  
                          /*
                           * perform actions of vm_map_lookup that need the
                           * write lock on the map: create an anonymous map
                           * for a copy-on-write region, or an anonymous map
                           * for a zero-fill region.  (XXXCDC: submap case
                           * ok?)
                           */
  
                          if (!UVM_ET_ISSUBMAP(entry)) {  /* not submap */
                                  if (UVM_ET_ISNEEDSCOPY(entry) &&
                                      ((entry->max_protection & VM_PROT_WRITE) ||
                                       (entry->object.uvm_obj == NULL))) {
                                          amap_copy(map, entry, M_WAITOK, TRUE,
                                              start, end);
                                          /* XXXCDC: wait OK? */
                                  }
                          }
                  }
                  UVM_MAP_CLIP_START(map, entry, start);
                  UVM_MAP_CLIP_END(map, entry, end);
                  entry->wired_count++;
  
                  /*
                   * Check for holes
                   */
  
                  if (entry->protection == VM_PROT_NONE ||
                      (entry->end < end &&
                       (entry->next == &map->header ||
                        entry->next->start > entry->end))) {
  
                          /*
                           * found one.  amap creation actions do not need to
                           * be undone, but the wired counts need to be restored.
                           */
  
                          while (entry != &map->header && entry->end > start) {
                                  entry->wired_count--;
                                  entry = entry->prev;
                          }
                          if ((lockflags & UVM_LK_EXIT) == 0)
                                  vm_map_unlock(map);
                          UVMHIST_LOG(maphist,"<- done (INVALID WIRE)",0,0,0,0);
                          return EINVAL;
                  }
                  entry = entry->next;
          }
  
          /*
           * Pass 2.
           */
  
  #ifdef DIAGNOSTIC
          timestamp_save = map->timestamp;
  #endif
          vm_map_busy(map);
          vm_map_downgrade(map);
  
          rv = 0;
          entry = start_entry;
          while (entry != &map->header && entry->start < end) {
                  if (entry->wired_count == 1) {
                          rv = uvm_fault_wire(map, entry->start, entry->end,
                              VM_FAULT_WIREMAX, entry->max_protection);
                          if (rv) {
  
                                  /*
                                   * wiring failed.  break out of the loop.
                                   * we'll clean up the map below, once we
                                   * have a write lock again.
                                   */
  
                                  break;
                          }
                  }
                  entry = entry->next;
          }
  
          if (rv) {       /* failed? */
  
                  /*
                   * Get back to an exclusive (write) lock.
                   */
  
                  vm_map_upgrade(map);
                  vm_map_unbusy(map);
  
  #ifdef DIAGNOSTIC
                  if (timestamp_save != map->timestamp)
                          panic("uvm_map_pageable: stale map");
  #endif
  
                  /*
                   * first drop the wiring count on all the entries
                   * which haven't actually been wired yet.
                   */
  
                  failed_entry = entry;
                  while (entry != &map->header && entry->start < end) {
                          entry->wired_count--;
                          entry = entry->next;
                  }
  
                  /*
                   * now, unwire all the entries that were successfully
                   * wired above.
                   */
  
                  entry = start_entry;
                  while (entry != failed_entry) {
                          entry->wired_count--;
                          if (VM_MAPENT_ISWIRED(entry) == 0)
                                  uvm_map_entry_unwire(map, entry);
                          entry = entry->next;
                  }
                  if ((lockflags & UVM_LK_EXIT) == 0)
                          vm_map_unlock(map);
                  UVMHIST_LOG(maphist, "<- done (RV=%d)", rv,0,0,0);
                  return (rv);
          }
  
          /* We are holding a read lock here. */
          if ((lockflags & UVM_LK_EXIT) == 0) {
                  vm_map_unbusy(map);
                  vm_map_unlock_read(map);
          } else {
  
                  /*
                   * Get back to an exclusive (write) lock.
                   */
  
                  vm_map_upgrade(map);
                  vm_map_unbusy(map);
          }
  
          UVMHIST_LOG(maphist,"<- done (OK WIRE)",0,0,0,0);
          return 0;
  }
  
  /*
   * uvm_map_pageable_all: special case of uvm_map_pageable - affects
   * all mapped regions.
   *
   * => map must not be locked.
   * => if no flags are specified, all regions are unwired.
   * => XXXJRT: has some of the same problems as uvm_map_pageable() above.
   */
  
  int
  uvm_map_pageable_all(struct vm_map *map, int flags, vsize_t limit)
  {
          struct vm_map_entry *entry, *failed_entry;
          vsize_t size;
          int rv;
  #ifdef DIAGNOSTIC
          u_int timestamp_save;
  #endif
          UVMHIST_FUNC("uvm_map_pageable_all"); UVMHIST_CALLED(maphist);
          UVMHIST_LOG(maphist,"(map=0x%x,flags=0x%x)", map, flags, 0, 0);
  
          KASSERT(map->flags & VM_MAP_PAGEABLE);
  
          vm_map_lock(map);
  
          /*
           * handle wiring and unwiring separately.
           */
  
          if (flags == 0) {                       /* unwire */
  
                  /*
                   * POSIX 1003.1b -- munlockall unlocks all regions,
                   * regardless of how many times mlockall has been called.
                   */
  
                  for (entry = map->header.next; entry != &map->header;
                       entry = entry->next) {
                          if (VM_MAPENT_ISWIRED(entry))
                                  uvm_map_entry_unwire(map, entry);
                  }
                  vm_map_modflags(map, 0, VM_MAP_WIREFUTURE);
                  vm_map_unlock(map);
                  UVMHIST_LOG(maphist,"<- done (OK UNWIRE)",0,0,0,0);
                  return 0;
          }
  
          if (flags & MCL_FUTURE) {
  
                  /*
                   * must wire all future mappings; remember this.
                   */
  
                  vm_map_modflags(map, VM_MAP_WIREFUTURE, 0);
          }
  
          if ((flags & MCL_CURRENT) == 0) {
  
                  /*
                   * no more work to do!
                   */
  
                  UVMHIST_LOG(maphist,"<- done (OK no wire)",0,0,0,0);
                  vm_map_unlock(map);
                  return 0;
          }
  
          /*
           * wire case: in three passes [XXXCDC: ugly block of code here]
           *
           * 1: holding the write lock, count all pages mapped by non-wired
           *    entries.  if this would cause us to go over our limit, we fail.
           *
           * 2: still holding the write lock, we create any anonymous maps that
           *    need to be created.  then we increment its wiring count.
           *
           * 3: we downgrade to a read lock, and call uvm_fault_wire to fault
           *    in the pages for any newly wired area (wired_count == 1).
           *
           *    downgrading to a read lock for uvm_fault_wire avoids a possible
           *    deadlock with another thread that may have faulted on one of
           *    the pages to be wired (it would mark the page busy, blocking
           *    us, then in turn block on the map lock that we hold).  because
           *    of problems in the recursive lock package, we cannot upgrade
           *    to a write lock in vm_map_lookup.  thus, any actions that
           *    require the write lock must be done beforehand.  because we
           *    keep the read lock on the map, the copy-on-write status of the
           *    entries we modify here cannot change.
           */
  
          for (size = 0, entry = map->header.next; entry != &map->header;
               entry = entry->next) {
                  if (entry->protection != VM_PROT_NONE &&
                      VM_MAPENT_ISWIRED(entry) == 0) { /* not already wired? */
                          size += entry->end - entry->start;
                  }
          }
  
          if (atop(size) + uvmexp.wired > uvmexp.wiredmax) {
                  vm_map_unlock(map);
                  return ENOMEM;
          }
  
          /* XXX non-pmap_wired_count case must be handled by caller */
  #ifdef pmap_wired_count
          if (limit != 0 &&
              (size + ptoa(pmap_wired_count(vm_map_pmap(map))) > limit)) {
                  vm_map_unlock(map);
                  return ENOMEM;
          }
  #endif
  
          /*
           * Pass 2.
           */
  
          for (entry = map->header.next; entry != &map->header;
               entry = entry->next) {
                  if (entry->protection == VM_PROT_NONE)
                          continue;
                  if (VM_MAPENT_ISWIRED(entry) == 0) { /* not already wired? */
  
                          /*
                           * perform actions of vm_map_lookup that need the
                           * write lock on the map: create an anonymous map
                           * for a copy-on-write region, or an anonymous map
                           * for a zero-fill region.  (XXXCDC: submap case
                           * ok?)
                           */
  
                          if (!UVM_ET_ISSUBMAP(entry)) {  /* not submap */
                                  if (UVM_ET_ISNEEDSCOPY(entry) &&
                                      ((entry->max_protection & VM_PROT_WRITE) ||
                                       (entry->object.uvm_obj == NULL))) {
                                          amap_copy(map, entry, M_WAITOK, TRUE,
                                              entry->start, entry->end);
                                          /* XXXCDC: wait OK? */
                                  }
                          }
                  }
                  entry->wired_count++;
          }
  
          /*
           * Pass 3.
           */
  
  #ifdef DIAGNOSTIC
          timestamp_save = map->timestamp;
  #endif
          vm_map_busy(map);
          vm_map_downgrade(map);
  
          rv = 0;
          for (entry = map->header.next; entry != &map->header;
               entry = entry->next) {
                  if (entry->wired_count == 1) {
                          rv = uvm_fault_wire(map, entry->start, entry->end,
                              VM_FAULT_WIREMAX, entry->max_protection);
                          if (rv) {
  
                                  /*
                                   * wiring failed.  break out of the loop.
                                   * we'll clean up the map below, once we
                                   * have a write lock again.
                                   */
  
                                  break;
                          }
                  }
          }
  
          if (rv) {
  
                  /*
                   * Get back an exclusive (write) lock.
                   */
  
                  vm_map_upgrade(map);
                  vm_map_unbusy(map);
  
  #ifdef DIAGNOSTIC
                  if (timestamp_save != map->timestamp)
                          panic("uvm_map_pageable_all: stale map");
  #endif
  
                  /*
                   * first drop the wiring count on all the entries
                   * which haven't actually been wired yet.
                   *
                   * Skip VM_PROT_NONE entries like we did above.
                   */
  
                  failed_entry = entry;
                  for (/* nothing */; entry != &map->header;
                       entry = entry->next) {
                          if (entry->protection == VM_PROT_NONE)
                                  continue;
                          entry->wired_count--;
                  }
  
                  /*
                   * now, unwire all the entries that were successfully
                   * wired above.
                   *
                   * Skip VM_PROT_NONE entries like we did above.
                   */
  
                  for (entry = map->header.next; entry != failed_entry;
                       entry = entry->next) {
                          if (entry->protection == VM_PROT_NONE)
                                  continue;
                          entry->wired_count--;
                          if (VM_MAPENT_ISWIRED(entry))
                                  uvm_map_entry_unwire(map, entry);
                  }
                  vm_map_unlock(map);
                  UVMHIST_LOG(maphist,"<- done (RV=%d)", rv,0,0,0);
                  return (rv);
          }
  
          /* We are holding a read lock here. */
          vm_map_unbusy(map);
          vm_map_unlock_read(map);
  
          UVMHIST_LOG(maphist,"<- done (OK WIRE)",0,0,0,0);
          return 0;
  }
  
  /*
   * uvm_map_clean: clean out a map range
   *
   * => valid flags:
   *   if (flags & PGO_CLEANIT): dirty pages are cleaned first
   *   if (flags & PGO_SYNCIO): dirty pages are written synchronously
   *   if (flags & PGO_DEACTIVATE): any cached pages are deactivated after clean
   *   if (flags & PGO_FREE): any cached pages are freed after clean
   * => returns an error if any part of the specified range isn't mapped
   * => never a need to flush amap layer since the anonymous memory has
   *      no permanent home, but may deactivate pages there
   * => called from sys_msync() and sys_madvise()
   * => caller must not write-lock map (read OK).
   * => we may sleep while cleaning if SYNCIO [with map read-locked]
   */
  
  int
  uvm_map_clean(struct vm_map *map, vaddr_t start, vaddr_t end, int flags)
  {
          struct vm_map_entry *current, *entry;
          struct uvm_object *uobj;
          struct vm_amap *amap;
          struct vm_anon *anon;
          struct vm_page *pg;
          vaddr_t offset;
          vsize_t size;
          int error, refs;
          UVMHIST_FUNC("uvm_map_clean"); UVMHIST_CALLED(maphist);
  
          UVMHIST_LOG(maphist,"(map=0x%x,start=0x%x,end=0x%x,flags=0x%x)",
                      map, start, end, flags);
          KASSERT((flags & (PGO_FREE|PGO_DEACTIVATE)) !=
                  (PGO_FREE|PGO_DEACTIVATE));
  
          vm_map_lock_read(map);
          VM_MAP_RANGE_CHECK(map, start, end);
          if (uvm_map_lookup_entry(map, start, &entry) == FALSE) {
                  vm_map_unlock_read(map);
                  return EFAULT;
          }
  
          /*
           * Make a first pass to check for holes.
           */
  
          for (current = entry; current->start < end; current = current->next) {
                  if (UVM_ET_ISSUBMAP(current)) {
                          vm_map_unlock_read(map);
                          return EINVAL;
                  }
                  if (end <= current->end) {
                          break;
                  }
                  if (current->end != current->next->start) {
                          vm_map_unlock_read(map);
                          return EFAULT;
                  }
          }
  
          error = 0;
          for (current = entry; start < end; current = current->next) {
                  amap = current->aref.ar_amap;   /* top layer */
                  uobj = current->object.uvm_obj; /* bottom layer */
                  KASSERT(start >= current->start);
  
                  /*
                   * No amap cleaning necessary if:
                   *
                   *      (1) There's no amap.
                   *
                   *      (2) We're not deactivating or freeing pages.
                   */
  
                  if (amap == NULL || (flags & (PGO_DEACTIVATE|PGO_FREE)) == 0)
                          goto flush_object;
  
                  amap_lock(amap);
                  offset = start - current->start;
                  size = MIN(end, current->end) - start;
                  for ( ; size != 0; size -= PAGE_SIZE, offset += PAGE_SIZE) {
                          anon = amap_lookup(&current->aref, offset);
                          if (anon == NULL)
                                  continue;
  
                          simple_lock(&anon->an_lock);
                          pg = anon->u.an_page;
                          if (pg == NULL) {
                                  simple_unlock(&anon->an_lock);
                                  continue;
                          }
  
                          switch (flags & (PGO_CLEANIT|PGO_FREE|PGO_DEACTIVATE)) {
  
                          /*
                           * In these first 3 cases, we just deactivate the page.
                           */
  
                          case PGO_CLEANIT|PGO_FREE:
                          case PGO_CLEANIT|PGO_DEACTIVATE:
                          case PGO_DEACTIVATE:
   deactivate_it:
                                  /*
                                   * skip the page if it's loaned or wired,
                                   * since it shouldn't be on a paging queue
                                   * at all in these cases.
                                   */
  
                                  uvm_lock_pageq();
                                  if (pg->loan_count != 0 ||
                                      pg->wire_count != 0) {
                                          uvm_unlock_pageq();
                                          simple_unlock(&anon->an_lock);
                                          continue;
                                  }
                                  KASSERT(pg->uanon == anon);
                                  pmap_clear_reference(pg);
                                  uvm_pagedeactivate(pg);
                                  uvm_unlock_pageq();
                                  simple_unlock(&anon->an_lock);
                                  continue;
  
                          case PGO_FREE:
  
                                  /*
                                   * If there are multiple references to
                                   * the amap, just deactivate the page.
                                   */
  
                                  if (amap_refs(amap) > 1)
                                          goto deactivate_it;
  
                                  /* skip the page if it's wired */
                                  if (pg->wire_count != 0) {
                                          simple_unlock(&anon->an_lock);
                                          continue;
                                  }
                                  amap_unadd(&current->aref, offset);
                                  refs = --anon->an_ref;
                                  simple_unlock(&anon->an_lock);
                                  if (refs == 0)
                                          uvm_anfree(anon);
                                  continue;
                          }
                  }
                  amap_unlock(amap);
  
   flush_object:
                  /*
                   * flush pages if we've got a valid backing object.
                   * note that we must always clean object pages before
                   * freeing them since otherwise we could reveal stale
                   * data from files.
                   */
  
                  offset = current->offset + (start - current->start);
                  size = MIN(end, current->end) - start;
                  if (uobj != NULL) {
                          simple_lock(&uobj->vmobjlock);
                          if (uobj->pgops->pgo_put != NULL)
                                  error = (uobj->pgops->pgo_put)(uobj, offset,
                                      offset + size, flags | PGO_CLEANIT);
                          else
                                  error = 0;
                  }
                  start += size;
          }
          vm_map_unlock_read(map);
          return (error);
  }
  
  
  /*
   * uvm_map_checkprot: check protection in map
   *
   * => must allow specified protection in a fully allocated region.
   * => map must be read or write locked by caller.
   */
  
  boolean_t
  uvm_map_checkprot(struct vm_map *map, vaddr_t start, vaddr_t end,
      vm_prot_t protection)
  {
          struct vm_map_entry *entry;
          struct vm_map_entry *tmp_entry;
  
          if (!uvm_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);
                  }
                  start = entry->end;
                  entry = entry->next;
          }
          return (TRUE);
  }
  
  /*
   * uvmspace_alloc: allocate a vmspace structure.
   *
   * - structure includes vm_map and pmap
   * - XXX: no locking on this structure
   * - refcnt set to 1, rest must be init'd by caller
   */
  struct vmspace *
  uvmspace_alloc(vaddr_t min, vaddr_t max)
  {
          struct vmspace *vm;
          UVMHIST_FUNC("uvmspace_alloc"); UVMHIST_CALLED(maphist);
  
          vm = pool_get(&uvm_vmspace_pool, PR_WAITOK);
          uvmspace_init(vm, NULL, min, max);
          UVMHIST_LOG(maphist,"<- done (vm=0x%x)", vm,0,0,0);
          return (vm);
  }
  
  /*
   * uvmspace_init: initialize a vmspace structure.
   *
   * - XXX: no locking on this structure
   * - refcnt set to 1, rest must be init'd by caller
   */
  void
  uvmspace_init(struct vmspace *vm, struct pmap *pmap, vaddr_t min, vaddr_t max)
  {
          UVMHIST_FUNC("uvmspace_init"); UVMHIST_CALLED(maphist);
  
          memset(vm, 0, sizeof(*vm));
          uvm_map_setup(&vm->vm_map, min, max, VM_MAP_PAGEABLE
  #ifdef __USING_TOPDOWN_VM
              | VM_MAP_TOPDOWN
  #endif
              );
          if (pmap)
                  pmap_reference(pmap);
          else
                  pmap = pmap_create();
          vm->vm_map.pmap = pmap;
          vm->vm_refcnt = 1;
          UVMHIST_LOG(maphist,"<- done",0,0,0,0);
  }
  
  /*
   * uvmspace_share: share a vmspace between two proceses
   *
   * - XXX: no locking on vmspace
   * - used for vfork, threads(?)
   */
  
  void
  uvmspace_share(struct proc *p1, struct proc *p2)
  {
  
          p2->p_vmspace = p1->p_vmspace;
          p1->p_vmspace->vm_refcnt++;
  }
  
  /*
   * uvmspace_unshare: ensure that process "p" has its own, unshared, vmspace
   *
   * - XXX: no locking on vmspace
   */
  
  void
  uvmspace_unshare(struct lwp *l)
  {
          struct proc *p = l->l_proc;
          struct vmspace *nvm, *ovm = p->p_vmspace;
  
          if (ovm->vm_refcnt == 1)
                  /* nothing to do: vmspace isn't shared in the first place */
                  return;
  
          /* make a new vmspace, still holding old one */
          nvm = uvmspace_fork(ovm);
  
          pmap_deactivate(l);             /* unbind old vmspace */
          p->p_vmspace = nvm;
          pmap_activate(l);               /* switch to new vmspace */
  
          uvmspace_free(ovm);             /* drop reference to old vmspace */
  }
  
  /*
   * uvmspace_exec: the process wants to exec a new program
   *
   * - XXX: no locking on vmspace
   */
  
  void
  uvmspace_exec(struct lwp *l, vaddr_t start, vaddr_t end)
  {
          struct proc *p = l->l_proc;
          struct vmspace *nvm, *ovm = p->p_vmspace;
          struct vm_map *map = &ovm->vm_map;
  
  #ifdef __sparc__
          /* XXX cgd 960926: the sparc #ifdef should be a MD hook */
          kill_user_windows(l);   /* before stack addresses go away */
  #endif
  
          /*
           * see if more than one process is using this vmspace...
           */
  
          if (ovm->vm_refcnt == 1) {
  
                  /*
                   * if p is the only process using its vmspace then we can safely
                   * recycle that vmspace for the program that is being exec'd.
                   */
  
  #ifdef SYSVSHM
                  /*
                   * SYSV SHM semantics require us to kill all segments on an exec
                   */
  
                  if (ovm->vm_shm)
                          shmexit(ovm);
  #endif
  
                  /*
                   * POSIX 1003.1b -- "lock future mappings" is revoked
                   * when a process execs another program image.
                   */
  
                  vm_map_modflags(map, 0, VM_MAP_WIREFUTURE);
  
                  /*
                   * now unmap the old program
                   */
  
                  pmap_remove_all(map->pmap);
                  uvm_unmap(map, map->min_offset, map->max_offset);
                  KASSERT(map->header.prev == &map->header);
                  KASSERT(map->nentries == 0);
  
                  /*
                   * resize the map
                   */
  
                  map->min_offset = start;
                  map->max_offset = end;
          } else {
  
                  /*
                   * p's vmspace is being shared, so we can't reuse it for p since
                   * it is still being used for others.   allocate a new vmspace
                   * for p
                   */
  
                  nvm = uvmspace_alloc(start, end);
  
                  /*
                   * install new vmspace and drop our ref to the old one.
                   */
  
                  pmap_deactivate(l);
                  p->p_vmspace = nvm;
                  pmap_activate(l);
  
                  uvmspace_free(ovm);
          }
  }
  
  /*
   * uvmspace_free: free a vmspace data structure
   *
   * - XXX: no locking on vmspace
   */
  
  void
  uvmspace_free(struct vmspace *vm)
  {
          struct vm_map_entry *dead_entries;
          struct vm_map *map;
          UVMHIST_FUNC("uvmspace_free"); UVMHIST_CALLED(maphist);
  
          UVMHIST_LOG(maphist,"(vm=0x%x) ref=%d", vm, vm->vm_refcnt,0,0);
          if (--vm->vm_refcnt > 0) {
                  return;
          }
  
          /*
           * at this point, there should be no other references to the map.
           * delete all of the mappings, then destroy the pmap.
           */
  
          map = &vm->vm_map;
          map->flags |= VM_MAP_DYING;
          pmap_remove_all(map->pmap);
  #ifdef SYSVSHM
          /* Get rid of any SYSV shared memory segments. */
          if (vm->vm_shm != NULL)
                  shmexit(vm);
  #endif
          if (map->nentries) {
                  uvm_unmap_remove(map, map->min_offset, map->max_offset,
                      &dead_entries);
                  if (dead_entries != NULL)
                          uvm_unmap_detach(dead_entries, 0);
          }
          KASSERT(map->nentries == 0);
          KASSERT(map->size == 0);
          pmap_destroy(map->pmap);
          pool_put(&uvm_vmspace_pool, vm);
  }
  
  /*
   *   F O R K   -   m a i n   e n t r y   p o i n t
   */
  /*
   * uvmspace_fork: fork a process' main map
   *
   * => create a new vmspace for child process from parent.
   * => parent's map must not be locked.
   */
  
  struct vmspace *
  uvmspace_fork(struct vmspace *vm1)
  {
          struct vmspace *vm2;
          struct vm_map *old_map = &vm1->vm_map;
          struct vm_map *new_map;
          struct vm_map_entry *old_entry;
          struct vm_map_entry *new_entry;
          UVMHIST_FUNC("uvmspace_fork"); UVMHIST_CALLED(maphist);
  
          vm_map_lock(old_map);
  
          vm2 = uvmspace_alloc(old_map->min_offset, old_map->max_offset);
          memcpy(&vm2->vm_startcopy, &vm1->vm_startcopy,
              (caddr_t) (vm1 + 1) - (caddr_t) &vm1->vm_startcopy);
          new_map = &vm2->vm_map;           /* XXX */
  
          old_entry = old_map->header.next;
          new_map->size = old_map->size;
  
          /*
           * go entry-by-entry
           */
  
          while (old_entry != &old_map->header) {
  
                  /*
                   * first, some sanity checks on the old entry
                   */
  
                  KASSERT(!UVM_ET_ISSUBMAP(old_entry));
                  KASSERT(UVM_ET_ISCOPYONWRITE(old_entry) ||
                          !UVM_ET_ISNEEDSCOPY(old_entry));
  
                  switch (old_entry->inheritance) {
                  case MAP_INHERIT_NONE:
  
                          /*
                           * drop the mapping, modify size
                           */
                          new_map->size -= old_entry->end - old_entry->start;
                          break;
  
                  case MAP_INHERIT_SHARE:
  
                          /*
                           * share the mapping: this means we want the old and
                           * new entries to share amaps and backing objects.
                           */
                          /*
                           * if the old_entry needs a new amap (due to prev fork)
                           * then we need to allocate it now so that we have
                           * something we own to share with the new_entry.   [in
                           * other words, we need to clear needs_copy]
                           */
  
                          if (UVM_ET_ISNEEDSCOPY(old_entry)) {
                                  /* get our own amap, clears needs_copy */
                                  amap_copy(old_map, old_entry, M_WAITOK, FALSE,
                                      0, 0);
                                  /* XXXCDC: WAITOK??? */
                          }
  
                          new_entry = uvm_mapent_alloc(new_map, 0);
                          /* old_entry -> new_entry */
                          uvm_mapent_copy(old_entry, new_entry);
  
                          /* new pmap has nothing wired in it */
                          new_entry->wired_count = 0;
  
                          /*
                           * gain reference to object backing the map (can't
                           * be a submap, already checked this case).
                           */
  
                          if (new_entry->aref.ar_amap)
                                  uvm_map_reference_amap(new_entry, AMAP_SHARED);
  
                          if (new_entry->object.uvm_obj &&
                              new_entry->object.uvm_obj->pgops->pgo_reference)
                                  new_entry->object.uvm_obj->
                                      pgops->pgo_reference(
                                          new_entry->object.uvm_obj);
  
                          /* insert entry at end of new_map's entry list */
                          uvm_map_entry_link(new_map, new_map->header.prev,
                              new_entry);
  
                          break;
  
                  case MAP_INHERIT_COPY:
  
                          /*
                           * copy-on-write the mapping (using mmap's
                           * MAP_PRIVATE semantics)
                           *
                           * allocate new_entry, adjust reference counts.
                           * (note that new references are read-only).
                           */
  
                          new_entry = uvm_mapent_alloc(new_map, 0);
                          /* old_entry -> new_entry */
                          uvm_mapent_copy(old_entry, new_entry);
  
                          if (new_entry->aref.ar_amap)
                                  uvm_map_reference_amap(new_entry, 0);
  
                          if (new_entry->object.uvm_obj &&
                              new_entry->object.uvm_obj->pgops->pgo_reference)
                                  new_entry->object.uvm_obj->pgops->pgo_reference
                                      (new_entry->object.uvm_obj);
  
                          /* new pmap has nothing wired in it */
                          new_entry->wired_count = 0;
  
                          new_entry->etype |=
                              (UVM_ET_COPYONWRITE|UVM_ET_NEEDSCOPY);
                          uvm_map_entry_link(new_map, new_map->header.prev,
                              new_entry);
  
                          /*
                           * the new entry will need an amap.  it will either
                           * need to be copied from the old entry or created
                           * from scratch (if the old entry does not have an
                           * amap).  can we defer this process until later
                           * (by setting "needs_copy") or do we need to copy
                           * the amap now?
                           *
                           * we must copy the amap now if any of the following
                           * conditions hold:
                           * 1. the old entry has an amap and that amap is
                           *    being shared.  this means that the old (parent)
                           *    process is sharing the amap with another
                           *    process.  if we do not clear needs_copy here
                           *    we will end up in a situation where both the
                           *    parent and child process are refering to the
                           *    same amap with "needs_copy" set.  if the
                           *    parent write-faults, the fault routine will
                           *    clear "needs_copy" in the parent by allocating
                           *    a new amap.   this is wrong because the
                           *    parent is supposed to be sharing the old amap
                           *    and the new amap will break that.
                           *
                           * 2. if the old entry has an amap and a non-zero
                           *    wire count then we are going to have to call
                           *    amap_cow_now to avoid page faults in the
                           *    parent process.   since amap_cow_now requires
                           *    "needs_copy" to be clear we might as well
                           *    clear it here as well.
                           *
                           */
  
                          if (old_entry->aref.ar_amap != NULL) {
                                  if ((amap_flags(old_entry->aref.ar_amap) &
                                       AMAP_SHARED) != 0 ||
                                      VM_MAPENT_ISWIRED(old_entry)) {
  
                                          amap_copy(new_map, new_entry, M_WAITOK,
                                              FALSE, 0, 0);
                                          /* XXXCDC: M_WAITOK ... ok? */
                                  }
                          }
  
                          /*
                           * if the parent's entry is wired down, then the
                           * parent process does not want page faults on
                           * access to that memory.  this means that we
                           * cannot do copy-on-write because we can't write
                           * protect the old entry.   in this case we
                           * resolve all copy-on-write faults now, using
                           * amap_cow_now.   note that we have already
                           * allocated any needed amap (above).
                           */
  
                          if (VM_MAPENT_ISWIRED(old_entry)) {
  
                            /*
                             * resolve all copy-on-write faults now
                             * (note that there is nothing to do if
                             * the old mapping does not have an amap).
                             */
                            if (old_entry->aref.ar_amap)
                              amap_cow_now(new_map, new_entry);
  
                          } else {
  
                            /*
                             * setup mappings to trigger copy-on-write faults
                             * we must write-protect the parent if it has
                             * an amap and it is not already "needs_copy"...
                             * if it is already "needs_copy" then the parent
                             * has already been write-protected by a previous
                             * fork operation.
                             */
  
                            if (old_entry->aref.ar_amap &&
                                !UVM_ET_ISNEEDSCOPY(old_entry)) {
                                if (old_entry->max_protection & VM_PROT_WRITE) {
                                  pmap_protect(old_map->pmap,
                                               old_entry->start,
                                               old_entry->end,
                                               old_entry->protection &
                                               ~VM_PROT_WRITE);
                                  pmap_update(old_map->pmap);
                                }
                                old_entry->etype |= UVM_ET_NEEDSCOPY;
                            }
                          }
                          break;
                  }  /* end of switch statement */
                  old_entry = old_entry->next;
          }
  
          vm_map_unlock(old_map);
  
  #ifdef SYSVSHM
          if (vm1->vm_shm)
                  shmfork(vm1, vm2);
  #endif
  
  #ifdef PMAP_FORK
          pmap_fork(vm1->vm_map.pmap, vm2->vm_map.pmap);
  #endif
  
          UVMHIST_LOG(maphist,"<- done",0,0,0,0);
          return (vm2);
  }
  
  
  #if defined(DDB)
  
  /*
   * DDB hooks
   */
  
  /*
   * uvm_map_printit: actually prints the map
   */
  
  void
  uvm_map_printit(struct vm_map *map, boolean_t full,
      void (*pr)(const char *, ...))
  {
          struct vm_map_entry *entry;
  
          (*pr)("MAP %p: [0x%lx->0x%lx]\n", map, map->min_offset,map->max_offset);
          (*pr)("\t#ent=%d, sz=%d, ref=%d, version=%d, flags=0x%x\n",
              map->nentries, map->size, map->ref_count, map->timestamp,
              map->flags);
          (*pr)("\tpmap=%p(resident=%d)\n", map->pmap,
              pmap_resident_count(map->pmap));
          if (!full)
                  return;
          for (entry = map->header.next; entry != &map->header;
              entry = entry->next) {
                  (*pr)(" - %p: 0x%lx->0x%lx: obj=%p/0x%llx, amap=%p/%d\n",
                      entry, entry->start, entry->end, entry->object.uvm_obj,
                      (long long)entry->offset, entry->aref.ar_amap,
                      entry->aref.ar_pageoff);
                  (*pr)(
                      "\tsubmap=%c, cow=%c, nc=%c, prot(max)=%d/%d, inh=%d, "
                      "wc=%d, adv=%d\n",
                      (entry->etype & UVM_ET_SUBMAP) ? 'T' : 'F',
                      (entry->etype & UVM_ET_COPYONWRITE) ? 'T' : 'F',
                      (entry->etype & UVM_ET_NEEDSCOPY) ? 'T' : 'F',
                      entry->protection, entry->max_protection,
                      entry->inheritance, entry->wired_count, entry->advice);
          }
  }
  
  /*
   * uvm_object_printit: actually prints the object
   */
  
  void
  uvm_object_printit(struct uvm_object *uobj, boolean_t full,
      void (*pr)(const char *, ...))
  {
          struct vm_page *pg;
          int cnt = 0;
  
          (*pr)("OBJECT %p: locked=%d, pgops=%p, npages=%d, ",
              uobj, uobj->vmobjlock.lock_data, uobj->pgops, uobj->uo_npages);
          if (UVM_OBJ_IS_KERN_OBJECT(uobj))
                  (*pr)("refs=<SYSTEM>\n");
          else
                  (*pr)("refs=%d\n", uobj->uo_refs);
  
          if (!full) {
                  return;
          }
          (*pr)("  PAGES <pg,offset>:\n  ");
          TAILQ_FOREACH(pg, &uobj->memq, listq) {
                  cnt++;
                  (*pr)("<%p,0x%llx> ", pg, (long long)pg->offset);
                  if ((cnt % 3) == 0) {
                          (*pr)("\n  ");
                  }
          }
          if ((cnt % 3) != 0) {
                  (*pr)("\n");
          }
  }
  
  /*
   * uvm_page_printit: actually print the page
   */
  
  static const char page_flagbits[] =
          "\2\1BUSY\2WANTED\3TABLED\4CLEAN\5PAGEOUT\6RELEASED\7FAKE\10RDONLY"
          "\11ZERO\15PAGER1";
  static const char page_pqflagbits[] =
          "\2\1FREE\2INACTIVE\3ACTIVE\5ANON\6AOBJ";
  
  void
  uvm_page_printit(struct vm_page *pg, boolean_t full,
      void (*pr)(const char *, ...))
  {
          struct vm_page *tpg;
          struct uvm_object *uobj;
          struct pglist *pgl;
          char pgbuf[128];
          char pqbuf[128];
  
          (*pr)("PAGE %p:\n", pg);
          bitmask_snprintf(pg->flags, page_flagbits, pgbuf, sizeof(pgbuf));
          bitmask_snprintf(pg->pqflags, page_pqflagbits, pqbuf, sizeof(pqbuf));
          (*pr)("  flags=%s, pqflags=%s, wire_count=%d, pa=0x%lx\n",
              pgbuf, pqbuf, pg->wire_count, (long)VM_PAGE_TO_PHYS(pg));
          (*pr)("  uobject=%p, uanon=%p, offset=0x%llx loan_count=%d\n",
              pg->uobject, pg->uanon, (long long)pg->offset, pg->loan_count);
  #if defined(UVM_PAGE_TRKOWN)
          if (pg->flags & PG_BUSY)
                  (*pr)("  owning process = %d, tag=%s\n",
                      pg->owner, pg->owner_tag);
          else
                  (*pr)("  page not busy, no owner\n");
  #else
          (*pr)("  [page ownership tracking disabled]\n");
  #endif
  
          if (!full)
                  return;
  
          /* cross-verify object/anon */
          if ((pg->pqflags & PQ_FREE) == 0) {
                  if (pg->pqflags & PQ_ANON) {
                          if (pg->uanon == NULL || pg->uanon->u.an_page != pg)
                              (*pr)("  >>> ANON DOES NOT POINT HERE <<< (%p)\n",
                                  (pg->uanon) ? pg->uanon->u.an_page : NULL);
                          else
                                  (*pr)("  anon backpointer is OK\n");
                  } else {
                          uobj = pg->uobject;
                          if (uobj) {
                                  (*pr)("  checking object list\n");
                                  TAILQ_FOREACH(tpg, &uobj->memq, listq) {
                                          if (tpg == pg) {
                                                  break;
                                          }
                                  }
                                  if (tpg)
                                          (*pr)("  page found on object list\n");
                                  else
                          (*pr)("  >>> PAGE NOT FOUND ON OBJECT LIST! <<<\n");
                          }
                  }
          }
  
          /* cross-verify page queue */
          if (pg->pqflags & PQ_FREE) {
                  int fl = uvm_page_lookup_freelist(pg);
                  int color = VM_PGCOLOR_BUCKET(pg);
                  pgl = &uvm.page_free[fl].pgfl_buckets[color].pgfl_queues[
                      ((pg)->flags & PG_ZERO) ? PGFL_ZEROS : PGFL_UNKNOWN];
          } else if (pg->pqflags & PQ_INACTIVE) {
                  pgl = &uvm.page_inactive;
          } else if (pg->pqflags & PQ_ACTIVE) {
                  pgl = &uvm.page_active;
          } else {
                  pgl = NULL;
          }
  
          if (pgl) {
                  (*pr)("  checking pageq list\n");
                  TAILQ_FOREACH(tpg, pgl, pageq) {
                          if (tpg == pg) {
                                  break;
                          }
                  }
                  if (tpg)
                          (*pr)("  page found on pageq list\n");
                  else
                          (*pr)("  >>> PAGE NOT FOUND ON PAGEQ LIST! <<<\n");
          }
  }
  #endif