/*
   * mm/mmap.c
   *
   * Written by obz.
   *

   * Address space accounting code	<alan@lxorguk.ukuu.org.uk>

   */
  
  #include <linux/slab.h>

  #include <linux/backing-dev.h>

  #include <linux/mm.h>
  #include <linux/shm.h>
  #include <linux/mman.h>
  #include <linux/pagemap.h>
  #include <linux/swap.h>
  #include <linux/syscalls.h>

  #include <linux/capability.h>

  #include <linux/init.h>
  #include <linux/file.h>
  #include <linux/fs.h>
  #include <linux/personality.h>
  #include <linux/security.h>
  #include <linux/hugetlb.h>
  #include <linux/profile.h>
  #include <linux/module.h>
  #include <linux/mount.h>
  #include <linux/mempolicy.h>
  #include <linux/rmap.h>

  #include <linux/mmu_notifier.h>

  #include <linux/perf_event.h>

  
  #include <asm/uaccess.h>
  #include <asm/cacheflush.h>
  #include <asm/tlb.h>

  #include <asm/mmu_context.h>

  #include "internal.h"

  #ifndef arch_mmap_check
  #define arch_mmap_check(addr, len, flags)	(0)
  #endif

  #ifndef arch_rebalance_pgtables
  #define arch_rebalance_pgtables(addr, len)		(addr)
  #endif

  static void unmap_region(struct mm_struct *mm,
  		struct vm_area_struct *vma, struct vm_area_struct *prev,
  		unsigned long start, unsigned long end);

  /*
   * WARNING: the debugging will use recursive algorithms so never enable this
   * unless you know what you are doing.
   */
  #undef DEBUG_MM_RB
  
  /* description of effects of mapping type and prot in current implementation.
   * this is due to the limited x86 page protection hardware.  The expected
   * behavior is in parens:
   *
   * map_type	prot
   *		PROT_NONE	PROT_READ	PROT_WRITE	PROT_EXEC
   * MAP_SHARED	r: (no) no	r: (yes) yes	r: (no) yes	r: (no) yes
   *		w: (no) no	w: (no) no	w: (yes) yes	w: (no) no
   *		x: (no) no	x: (no) yes	x: (no) yes	x: (yes) yes
   *		
   * MAP_PRIVATE	r: (no) no	r: (yes) yes	r: (no) yes	r: (no) yes
   *		w: (no) no	w: (no) no	w: (copy) copy	w: (no) no
   *		x: (no) no	x: (no) yes	x: (no) yes	x: (yes) yes
   *
   */
  pgprot_t protection_map[16] = {
  	__P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,
  	__S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
  };

  pgprot_t vm_get_page_prot(unsigned long vm_flags)
  {

  	return __pgprot(pgprot_val(protection_map[vm_flags &
  				(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
  			pgprot_val(arch_vm_get_page_prot(vm_flags)));

  }
  EXPORT_SYMBOL(vm_get_page_prot);

  int sysctl_overcommit_memory = OVERCOMMIT_GUESS;  /* heuristic overcommit */
  int sysctl_overcommit_ratio = 50;	/* default is 50% */

  int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;

  struct percpu_counter vm_committed_as;

  
  /*
   * Check that a process has enough memory to allocate a new virtual
   * mapping. 0 means there is enough memory for the allocation to
   * succeed and -ENOMEM implies there is not.
   *
   * We currently support three overcommit policies, which are set via the
   * vm.overcommit_memory sysctl.  See Documentation/vm/overcommit-accounting
   *
   * Strict overcommit modes added 2002 Feb 26 by Alan Cox.
   * Additional code 2002 Jul 20 by Robert Love.
   *
   * cap_sys_admin is 1 if the process has admin privileges, 0 otherwise.
   *
   * Note this is a helper function intended to be used by LSMs which
   * wish to use this logic.
   */

  int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)

  {
  	unsigned long free, allowed;
  
  	vm_acct_memory(pages);
  
  	/*
  	 * Sometimes we want to use more memory than we have
  	 */
  	if (sysctl_overcommit_memory == OVERCOMMIT_ALWAYS)
  		return 0;
  
  	if (sysctl_overcommit_memory == OVERCOMMIT_GUESS) {
  		unsigned long n;

  		free = global_page_state(NR_FILE_PAGES);

  		free += nr_swap_pages;
  
  		/*
  		 * Any slabs which are created with the
  		 * SLAB_RECLAIM_ACCOUNT flag claim to have contents
  		 * which are reclaimable, under pressure.  The dentry
  		 * cache and most inode caches should fall into this
  		 */

  		free += global_page_state(NR_SLAB_RECLAIMABLE);

  
  		/*
  		 * Leave the last 3% for root
  		 */
  		if (!cap_sys_admin)
  			free -= free / 32;
  
  		if (free > pages)
  			return 0;
  
  		/*
  		 * nr_free_pages() is very expensive on large systems,
  		 * only call if we're about to fail.
  		 */
  		n = nr_free_pages();

  
  		/*
  		 * Leave reserved pages. The pages are not for anonymous pages.
  		 */
  		if (n <= totalreserve_pages)
  			goto error;
  		else
  			n -= totalreserve_pages;
  
  		/*
  		 * Leave the last 3% for root
  		 */

  		if (!cap_sys_admin)
  			n -= n / 32;
  		free += n;
  
  		if (free > pages)
  			return 0;

  
  		goto error;

  	}
  
  	allowed = (totalram_pages - hugetlb_total_pages())
  	       	* sysctl_overcommit_ratio / 100;
  	/*
  	 * Leave the last 3% for root
  	 */
  	if (!cap_sys_admin)
  		allowed -= allowed / 32;
  	allowed += total_swap_pages;
  
  	/* Don't let a single process grow too big:
  	   leave 3% of the size of this process for other processes */

  	if (mm)
  		allowed -= mm->total_vm / 32;

  	if (percpu_counter_read_positive(&vm_committed_as) < allowed)

  		return 0;

  error:

  	vm_unacct_memory(pages);
  
  	return -ENOMEM;
  }

  /*
   * Requires inode->i_mapping->i_mmap_lock
   */
  static void __remove_shared_vm_struct(struct vm_area_struct *vma,
  		struct file *file, struct address_space *mapping)
  {
  	if (vma->vm_flags & VM_DENYWRITE)

  		atomic_inc(&file->f_path.dentry->d_inode->i_writecount);

  	if (vma->vm_flags & VM_SHARED)
  		mapping->i_mmap_writable--;
  
  	flush_dcache_mmap_lock(mapping);
  	if (unlikely(vma->vm_flags & VM_NONLINEAR))
  		list_del_init(&vma->shared.vm_set.list);
  	else
  		vma_prio_tree_remove(vma, &mapping->i_mmap);
  	flush_dcache_mmap_unlock(mapping);
  }
  
  /*

   * Unlink a file-based vm structure from its prio_tree, to hide
   * vma from rmap and vmtruncate before freeing its page tables.

   */

  void unlink_file_vma(struct vm_area_struct *vma)

  {
  	struct file *file = vma->vm_file;

  	if (file) {
  		struct address_space *mapping = file->f_mapping;
  		spin_lock(&mapping->i_mmap_lock);
  		__remove_shared_vm_struct(vma, file, mapping);
  		spin_unlock(&mapping->i_mmap_lock);
  	}

  }
  
  /*
   * Close a vm structure and free it, returning the next.
   */
  static struct vm_area_struct *remove_vma(struct vm_area_struct *vma)
  {
  	struct vm_area_struct *next = vma->vm_next;

  	might_sleep();

  	if (vma->vm_ops && vma->vm_ops->close)
  		vma->vm_ops->close(vma);

  	if (vma->vm_file) {

  		fput(vma->vm_file);

  		if (vma->vm_flags & VM_EXECUTABLE)
  			removed_exe_file_vma(vma->vm_mm);
  	}

  	mpol_put(vma_policy(vma));

  	kmem_cache_free(vm_area_cachep, vma);

  	return next;

  }

  SYSCALL_DEFINE1(brk, unsigned long, brk)

  {
  	unsigned long rlim, retval;
  	unsigned long newbrk, oldbrk;
  	struct mm_struct *mm = current->mm;

  	unsigned long min_brk;

  
  	down_write(&mm->mmap_sem);

  #ifdef CONFIG_COMPAT_BRK
  	min_brk = mm->end_code;
  #else
  	min_brk = mm->start_brk;
  #endif
  	if (brk < min_brk)

  		goto out;

  
  	/*
  	 * Check against rlimit here. If this check is done later after the test
  	 * of oldbrk with newbrk then it can escape the test and let the data
  	 * segment grow beyond its set limit the in case where the limit is
  	 * not page aligned -Ram Gupta
  	 */

  	rlim = rlimit(RLIMIT_DATA);

  	if (rlim < RLIM_INFINITY && (brk - mm->start_brk) +
  			(mm->end_data - mm->start_data) > rlim)

  		goto out;

  	newbrk = PAGE_ALIGN(brk);
  	oldbrk = PAGE_ALIGN(mm->brk);
  	if (oldbrk == newbrk)
  		goto set_brk;
  
  	/* Always allow shrinking brk. */
  	if (brk <= mm->brk) {
  		if (!do_munmap(mm, newbrk, oldbrk-newbrk))
  			goto set_brk;
  		goto out;
  	}

  	/* Check against existing mmap mappings. */
  	if (find_vma_intersection(mm, oldbrk, newbrk+PAGE_SIZE))
  		goto out;
  
  	/* Ok, looks good - let it rip. */
  	if (do_brk(oldbrk, newbrk-oldbrk) != oldbrk)
  		goto out;
  set_brk:
  	mm->brk = brk;
  out:
  	retval = mm->brk;
  	up_write(&mm->mmap_sem);
  	return retval;
  }
  
  #ifdef DEBUG_MM_RB
  static int browse_rb(struct rb_root *root)
  {
  	int i = 0, j;
  	struct rb_node *nd, *pn = NULL;
  	unsigned long prev = 0, pend = 0;
  
  	for (nd = rb_first(root); nd; nd = rb_next(nd)) {
  		struct vm_area_struct *vma;
  		vma = rb_entry(nd, struct vm_area_struct, vm_rb);
  		if (vma->vm_start < prev)
  			printk("vm_start %lx prev %lx
  ", vma->vm_start, prev), i = -1;
  		if (vma->vm_start < pend)
  			printk("vm_start %lx pend %lx
  ", vma->vm_start, pend);
  		if (vma->vm_start > vma->vm_end)
  			printk("vm_end %lx < vm_start %lx
  ", vma->vm_end, vma->vm_start);
  		i++;
  		pn = nd;

  		prev = vma->vm_start;
  		pend = vma->vm_end;

  	}
  	j = 0;
  	for (nd = pn; nd; nd = rb_prev(nd)) {
  		j++;
  	}
  	if (i != j)
  		printk("backwards %d, forwards %d
  ", j, i), i = 0;
  	return i;
  }
  
  void validate_mm(struct mm_struct *mm)
  {
  	int bug = 0;
  	int i = 0;
  	struct vm_area_struct *tmp = mm->mmap;
  	while (tmp) {
  		tmp = tmp->vm_next;
  		i++;
  	}
  	if (i != mm->map_count)
  		printk("map_count %d vm_next %d
  ", mm->map_count, i), bug = 1;
  	i = browse_rb(&mm->mm_rb);
  	if (i != mm->map_count)
  		printk("map_count %d rb %d
  ", mm->map_count, i), bug = 1;

  	BUG_ON(bug);

  }
  #else
  #define validate_mm(mm) do { } while (0)
  #endif
  
  static struct vm_area_struct *
  find_vma_prepare(struct mm_struct *mm, unsigned long addr,
  		struct vm_area_struct **pprev, struct rb_node ***rb_link,
  		struct rb_node ** rb_parent)
  {
  	struct vm_area_struct * vma;
  	struct rb_node ** __rb_link, * __rb_parent, * rb_prev;
  
  	__rb_link = &mm->mm_rb.rb_node;
  	rb_prev = __rb_parent = NULL;
  	vma = NULL;
  
  	while (*__rb_link) {
  		struct vm_area_struct *vma_tmp;
  
  		__rb_parent = *__rb_link;
  		vma_tmp = rb_entry(__rb_parent, struct vm_area_struct, vm_rb);
  
  		if (vma_tmp->vm_end > addr) {
  			vma = vma_tmp;
  			if (vma_tmp->vm_start <= addr)

  				break;

  			__rb_link = &__rb_parent->rb_left;
  		} else {
  			rb_prev = __rb_parent;
  			__rb_link = &__rb_parent->rb_right;
  		}
  	}
  
  	*pprev = NULL;
  	if (rb_prev)
  		*pprev = rb_entry(rb_prev, struct vm_area_struct, vm_rb);
  	*rb_link = __rb_link;
  	*rb_parent = __rb_parent;
  	return vma;
  }
  
  static inline void
  __vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma,
  		struct vm_area_struct *prev, struct rb_node *rb_parent)
  {

  	struct vm_area_struct *next;
  
  	vma->vm_prev = prev;

  	if (prev) {

  		next = prev->vm_next;

  		prev->vm_next = vma;
  	} else {
  		mm->mmap = vma;
  		if (rb_parent)

  			next = rb_entry(rb_parent,

  					struct vm_area_struct, vm_rb);
  		else

  			next = NULL;

  	}

  	vma->vm_next = next;
  	if (next)
  		next->vm_prev = vma;

  }
  
  void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma,
  		struct rb_node **rb_link, struct rb_node *rb_parent)
  {
  	rb_link_node(&vma->vm_rb, rb_parent, rb_link);
  	rb_insert_color(&vma->vm_rb, &mm->mm_rb);
  }

  static void __vma_link_file(struct vm_area_struct *vma)

  {

  	struct file *file;

  
  	file = vma->vm_file;
  	if (file) {
  		struct address_space *mapping = file->f_mapping;
  
  		if (vma->vm_flags & VM_DENYWRITE)

  			atomic_dec(&file->f_path.dentry->d_inode->i_writecount);

  		if (vma->vm_flags & VM_SHARED)
  			mapping->i_mmap_writable++;
  
  		flush_dcache_mmap_lock(mapping);
  		if (unlikely(vma->vm_flags & VM_NONLINEAR))
  			vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
  		else
  			vma_prio_tree_insert(vma, &mapping->i_mmap);
  		flush_dcache_mmap_unlock(mapping);
  	}
  }
  
  static void
  __vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
  	struct vm_area_struct *prev, struct rb_node **rb_link,
  	struct rb_node *rb_parent)
  {
  	__vma_link_list(mm, vma, prev, rb_parent);
  	__vma_link_rb(mm, vma, rb_link, rb_parent);

  }
  
  static void vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
  			struct vm_area_struct *prev, struct rb_node **rb_link,
  			struct rb_node *rb_parent)
  {
  	struct address_space *mapping = NULL;
  
  	if (vma->vm_file)
  		mapping = vma->vm_file->f_mapping;
  
  	if (mapping) {
  		spin_lock(&mapping->i_mmap_lock);
  		vma->vm_truncate_count = mapping->truncate_count;
  	}

  
  	__vma_link(mm, vma, prev, rb_link, rb_parent);
  	__vma_link_file(vma);

  	if (mapping)
  		spin_unlock(&mapping->i_mmap_lock);
  
  	mm->map_count++;
  	validate_mm(mm);
  }
  
  /*
   * Helper for vma_adjust in the split_vma insert case:
   * insert vm structure into list and rbtree and anon_vma,
   * but it has already been inserted into prio_tree earlier.
   */

  static void __insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)

  {

  	struct vm_area_struct *__vma, *prev;
  	struct rb_node **rb_link, *rb_parent;

  
  	__vma = find_vma_prepare(mm, vma->vm_start,&prev, &rb_link, &rb_parent);

  	BUG_ON(__vma && __vma->vm_start < vma->vm_end);

  	__vma_link(mm, vma, prev, rb_link, rb_parent);
  	mm->map_count++;
  }
  
  static inline void
  __vma_unlink(struct mm_struct *mm, struct vm_area_struct *vma,
  		struct vm_area_struct *prev)
  {

  	struct vm_area_struct *next = vma->vm_next;
  
  	prev->vm_next = next;
  	if (next)
  		next->vm_prev = prev;

  	rb_erase(&vma->vm_rb, &mm->mm_rb);
  	if (mm->mmap_cache == vma)
  		mm->mmap_cache = prev;
  }
  
  /*
   * We cannot adjust vm_start, vm_end, vm_pgoff fields of a vma that
   * is already present in an i_mmap tree without adjusting the tree.
   * The following helper function should be used when such adjustments
   * are necessary.  The "insert" vma (if any) is to be inserted
   * before we drop the necessary locks.
   */

  int vma_adjust(struct vm_area_struct *vma, unsigned long start,

  	unsigned long end, pgoff_t pgoff, struct vm_area_struct *insert)
  {
  	struct mm_struct *mm = vma->vm_mm;
  	struct vm_area_struct *next = vma->vm_next;
  	struct vm_area_struct *importer = NULL;
  	struct address_space *mapping = NULL;
  	struct prio_tree_root *root = NULL;

  	struct anon_vma *anon_vma = NULL;

  	struct file *file = vma->vm_file;

  	long adjust_next = 0;
  	int remove_next = 0;
  
  	if (next && !insert) {

  		struct vm_area_struct *exporter = NULL;

  		if (end >= next->vm_end) {
  			/*
  			 * vma expands, overlapping all the next, and
  			 * perhaps the one after too (mprotect case 6).
  			 */
  again:			remove_next = 1 + (end > next->vm_end);
  			end = next->vm_end;

  			exporter = next;

  			importer = vma;
  		} else if (end > next->vm_start) {
  			/*
  			 * vma expands, overlapping part of the next:
  			 * mprotect case 5 shifting the boundary up.
  			 */
  			adjust_next = (end - next->vm_start) >> PAGE_SHIFT;

  			exporter = next;

  			importer = vma;
  		} else if (end < vma->vm_end) {
  			/*
  			 * vma shrinks, and !insert tells it's not
  			 * split_vma inserting another: so it must be
  			 * mprotect case 4 shifting the boundary down.
  			 */
  			adjust_next = - ((vma->vm_end - end) >> PAGE_SHIFT);

  			exporter = vma;

  			importer = next;
  		}

  		/*
  		 * Easily overlooked: when mprotect shifts the boundary,
  		 * make sure the expanding vma has anon_vma set if the
  		 * shrinking vma had, to cover any anon pages imported.
  		 */

  		if (exporter && exporter->anon_vma && !importer->anon_vma) {
  			if (anon_vma_clone(importer, exporter))

  				return -ENOMEM;

  			importer->anon_vma = exporter->anon_vma;

  		}
  	}

  	if (file) {
  		mapping = file->f_mapping;
  		if (!(vma->vm_flags & VM_NONLINEAR))
  			root = &mapping->i_mmap;
  		spin_lock(&mapping->i_mmap_lock);
  		if (importer &&
  		    vma->vm_truncate_count != next->vm_truncate_count) {
  			/*
  			 * unmap_mapping_range might be in progress:
  			 * ensure that the expanding vma is rescanned.
  			 */
  			importer->vm_truncate_count = 0;
  		}
  		if (insert) {
  			insert->vm_truncate_count = vma->vm_truncate_count;
  			/*
  			 * Put into prio_tree now, so instantiated pages
  			 * are visible to arm/parisc __flush_dcache_page
  			 * throughout; but we cannot insert into address
  			 * space until vma start or end is updated.
  			 */
  			__vma_link_file(insert);
  		}
  	}

  	/*
  	 * When changing only vma->vm_end, we don't really need anon_vma
  	 * lock. This is a fairly rare case by itself, but the anon_vma
  	 * lock may be shared between many sibling processes.  Skipping
  	 * the lock for brk adjustments makes a difference sometimes.
  	 */
  	if (vma->anon_vma && (insert || importer || start != vma->vm_start)) {
  		anon_vma = vma->anon_vma;
  		anon_vma_lock(anon_vma);
  	}

  	if (root) {
  		flush_dcache_mmap_lock(mapping);
  		vma_prio_tree_remove(vma, root);
  		if (adjust_next)
  			vma_prio_tree_remove(next, root);
  	}
  
  	vma->vm_start = start;
  	vma->vm_end = end;
  	vma->vm_pgoff = pgoff;
  	if (adjust_next) {
  		next->vm_start += adjust_next << PAGE_SHIFT;
  		next->vm_pgoff += adjust_next;
  	}
  
  	if (root) {
  		if (adjust_next)
  			vma_prio_tree_insert(next, root);
  		vma_prio_tree_insert(vma, root);
  		flush_dcache_mmap_unlock(mapping);
  	}
  
  	if (remove_next) {
  		/*
  		 * vma_merge has merged next into vma, and needs
  		 * us to remove next before dropping the locks.
  		 */
  		__vma_unlink(mm, next, vma);
  		if (file)
  			__remove_shared_vm_struct(next, file, mapping);

  	} else if (insert) {
  		/*
  		 * split_vma has split insert from vma, and needs
  		 * us to insert it before dropping the locks
  		 * (it may either follow vma or precede it).
  		 */
  		__insert_vm_struct(mm, insert);
  	}

  	if (anon_vma)
  		anon_vma_unlock(anon_vma);

  	if (mapping)
  		spin_unlock(&mapping->i_mmap_lock);
  
  	if (remove_next) {

  		if (file) {

  			fput(file);

  			if (next->vm_flags & VM_EXECUTABLE)
  				removed_exe_file_vma(mm);
  		}

  		if (next->anon_vma)
  			anon_vma_merge(vma, next);

  		mm->map_count--;

  		mpol_put(vma_policy(next));

  		kmem_cache_free(vm_area_cachep, next);
  		/*
  		 * In mprotect's case 6 (see comments on vma_merge),
  		 * we must remove another next too. It would clutter
  		 * up the code too much to do both in one go.
  		 */
  		if (remove_next == 2) {
  			next = vma->vm_next;
  			goto again;
  		}
  	}
  
  	validate_mm(mm);

  
  	return 0;

  }
  
  /*
   * If the vma has a ->close operation then the driver probably needs to release
   * per-vma resources, so we don't attempt to merge those.
   */

  static inline int is_mergeable_vma(struct vm_area_struct *vma,
  			struct file *file, unsigned long vm_flags)
  {

  	/* VM_CAN_NONLINEAR may get set later by f_op->mmap() */
  	if ((vma->vm_flags ^ vm_flags) & ~VM_CAN_NONLINEAR)

  		return 0;
  	if (vma->vm_file != file)
  		return 0;
  	if (vma->vm_ops && vma->vm_ops->close)
  		return 0;
  	return 1;
  }
  
  static inline int is_mergeable_anon_vma(struct anon_vma *anon_vma1,
  					struct anon_vma *anon_vma2)
  {
  	return !anon_vma1 || !anon_vma2 || (anon_vma1 == anon_vma2);
  }
  
  /*
   * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
   * in front of (at a lower virtual address and file offset than) the vma.
   *
   * We cannot merge two vmas if they have differently assigned (non-NULL)
   * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
   *
   * We don't check here for the merged mmap wrapping around the end of pagecache
   * indices (16TB on ia32) because do_mmap_pgoff() does not permit mmap's which
   * wrap, nor mmaps which cover the final page at index -1UL.
   */
  static int
  can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags,
  	struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff)
  {
  	if (is_mergeable_vma(vma, file, vm_flags) &&
  	    is_mergeable_anon_vma(anon_vma, vma->anon_vma)) {
  		if (vma->vm_pgoff == vm_pgoff)
  			return 1;
  	}
  	return 0;
  }
  
  /*
   * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
   * beyond (at a higher virtual address and file offset than) the vma.
   *
   * We cannot merge two vmas if they have differently assigned (non-NULL)
   * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
   */
  static int
  can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
  	struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff)
  {
  	if (is_mergeable_vma(vma, file, vm_flags) &&
  	    is_mergeable_anon_vma(anon_vma, vma->anon_vma)) {
  		pgoff_t vm_pglen;
  		vm_pglen = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
  		if (vma->vm_pgoff + vm_pglen == vm_pgoff)
  			return 1;
  	}
  	return 0;
  }
  
  /*
   * Given a mapping request (addr,end,vm_flags,file,pgoff), figure out
   * whether that can be merged with its predecessor or its successor.
   * Or both (it neatly fills a hole).
   *
   * In most cases - when called for mmap, brk or mremap - [addr,end) is
   * certain not to be mapped by the time vma_merge is called; but when
   * called for mprotect, it is certain to be already mapped (either at
   * an offset within prev, or at the start of next), and the flags of
   * this area are about to be changed to vm_flags - and the no-change
   * case has already been eliminated.
   *
   * The following mprotect cases have to be considered, where AAAA is
   * the area passed down from mprotect_fixup, never extending beyond one
   * vma, PPPPPP is the prev vma specified, and NNNNNN the next vma after:
   *
   *     AAAA             AAAA                AAAA          AAAA
   *    PPPPPPNNNNNN    PPPPPPNNNNNN    PPPPPPNNNNNN    PPPPNNNNXXXX
   *    cannot merge    might become    might become    might become
   *                    PPNNNNNNNNNN    PPPPPPPPPPNN    PPPPPPPPPPPP 6 or
   *    mmap, brk or    case 4 below    case 5 below    PPPPPPPPXXXX 7 or
   *    mremap move:                                    PPPPNNNNNNNN 8
   *        AAAA
   *    PPPP    NNNN    PPPPPPPPPPPP    PPPPPPPPNNNN    PPPPNNNNNNNN
   *    might become    case 1 below    case 2 below    case 3 below
   *
   * Odd one out? Case 8, because it extends NNNN but needs flags of XXXX:
   * mprotect_fixup updates vm_flags & vm_page_prot on successful return.
   */
  struct vm_area_struct *vma_merge(struct mm_struct *mm,
  			struct vm_area_struct *prev, unsigned long addr,
  			unsigned long end, unsigned long vm_flags,
  		     	struct anon_vma *anon_vma, struct file *file,
  			pgoff_t pgoff, struct mempolicy *policy)
  {
  	pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
  	struct vm_area_struct *area, *next;

  	int err;

  
  	/*
  	 * We later require that vma->vm_flags == vm_flags,
  	 * so this tests vma->vm_flags & VM_SPECIAL, too.
  	 */
  	if (vm_flags & VM_SPECIAL)
  		return NULL;
  
  	if (prev)
  		next = prev->vm_next;
  	else
  		next = mm->mmap;
  	area = next;
  	if (next && next->vm_end == end)		/* cases 6, 7, 8 */
  		next = next->vm_next;
  
  	/*
  	 * Can it merge with the predecessor?
  	 */
  	if (prev && prev->vm_end == addr &&
    			mpol_equal(vma_policy(prev), policy) &&
  			can_vma_merge_after(prev, vm_flags,
  						anon_vma, file, pgoff)) {
  		/*
  		 * OK, it can.  Can we now merge in the successor as well?
  		 */
  		if (next && end == next->vm_start &&
  				mpol_equal(policy, vma_policy(next)) &&
  				can_vma_merge_before(next, vm_flags,
  					anon_vma, file, pgoff+pglen) &&
  				is_mergeable_anon_vma(prev->anon_vma,
  						      next->anon_vma)) {
  							/* cases 1, 6 */

  			err = vma_adjust(prev, prev->vm_start,

  				next->vm_end, prev->vm_pgoff, NULL);
  		} else					/* cases 2, 5, 7 */

  			err = vma_adjust(prev, prev->vm_start,

  				end, prev->vm_pgoff, NULL);

  		if (err)
  			return NULL;

  		return prev;
  	}
  
  	/*
  	 * Can this new request be merged in front of next?
  	 */
  	if (next && end == next->vm_start &&
   			mpol_equal(policy, vma_policy(next)) &&
  			can_vma_merge_before(next, vm_flags,
  					anon_vma, file, pgoff+pglen)) {
  		if (prev && addr < prev->vm_end)	/* case 4 */

  			err = vma_adjust(prev, prev->vm_start,

  				addr, prev->vm_pgoff, NULL);
  		else					/* cases 3, 8 */

  			err = vma_adjust(area, addr, next->vm_end,

  				next->vm_pgoff - pglen, NULL);

  		if (err)
  			return NULL;

  		return area;
  	}
  
  	return NULL;
  }
  
  /*

   * Rough compatbility check to quickly see if it's even worth looking
   * at sharing an anon_vma.
   *
   * They need to have the same vm_file, and the flags can only differ
   * in things that mprotect may change.
   *
   * NOTE! The fact that we share an anon_vma doesn't _have_ to mean that
   * we can merge the two vma's. For example, we refuse to merge a vma if
   * there is a vm_ops->close() function, because that indicates that the
   * driver is doing some kind of reference counting. But that doesn't
   * really matter for the anon_vma sharing case.
   */
  static int anon_vma_compatible(struct vm_area_struct *a, struct vm_area_struct *b)
  {
  	return a->vm_end == b->vm_start &&
  		mpol_equal(vma_policy(a), vma_policy(b)) &&
  		a->vm_file == b->vm_file &&
  		!((a->vm_flags ^ b->vm_flags) & ~(VM_READ|VM_WRITE|VM_EXEC)) &&
  		b->vm_pgoff == a->vm_pgoff + ((b->vm_start - a->vm_start) >> PAGE_SHIFT);
  }
  
  /*
   * Do some basic sanity checking to see if we can re-use the anon_vma
   * from 'old'. The 'a'/'b' vma's are in VM order - one of them will be
   * the same as 'old', the other will be the new one that is trying
   * to share the anon_vma.
   *
   * NOTE! This runs with mm_sem held for reading, so it is possible that
   * the anon_vma of 'old' is concurrently in the process of being set up
   * by another page fault trying to merge _that_. But that's ok: if it
   * is being set up, that automatically means that it will be a singleton
   * acceptable for merging, so we can do all of this optimistically. But
   * we do that ACCESS_ONCE() to make sure that we never re-load the pointer.
   *
   * IOW: that the "list_is_singular()" test on the anon_vma_chain only
   * matters for the 'stable anon_vma' case (ie the thing we want to avoid
   * is to return an anon_vma that is "complex" due to having gone through
   * a fork).
   *
   * We also make sure that the two vma's are compatible (adjacent,
   * and with the same memory policies). That's all stable, even with just
   * a read lock on the mm_sem.
   */
  static struct anon_vma *reusable_anon_vma(struct vm_area_struct *old, struct vm_area_struct *a, struct vm_area_struct *b)
  {
  	if (anon_vma_compatible(a, b)) {
  		struct anon_vma *anon_vma = ACCESS_ONCE(old->anon_vma);
  
  		if (anon_vma && list_is_singular(&old->anon_vma_chain))
  			return anon_vma;
  	}
  	return NULL;
  }
  
  /*

   * find_mergeable_anon_vma is used by anon_vma_prepare, to check
   * neighbouring vmas for a suitable anon_vma, before it goes off
   * to allocate a new anon_vma.  It checks because a repetitive
   * sequence of mprotects and faults may otherwise lead to distinct
   * anon_vmas being allocated, preventing vma merge in subsequent
   * mprotect.
   */
  struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
  {

  	struct anon_vma *anon_vma;

  	struct vm_area_struct *near;

  
  	near = vma->vm_next;
  	if (!near)
  		goto try_prev;

  	anon_vma = reusable_anon_vma(near, vma, near);
  	if (anon_vma)
  		return anon_vma;

  try_prev:
  	/*
  	 * It is potentially slow to have to call find_vma_prev here.
  	 * But it's only on the first write fault on the vma, not
  	 * every time, and we could devise a way to avoid it later
  	 * (e.g. stash info in next's anon_vma_node when assigning
  	 * an anon_vma, or when trying vma_merge).  Another time.
  	 */

  	BUG_ON(find_vma_prev(vma->vm_mm, vma->vm_start, &near) != vma);

  	if (!near)
  		goto none;

  	anon_vma = reusable_anon_vma(near, near, vma);
  	if (anon_vma)
  		return anon_vma;

  none:
  	/*
  	 * There's no absolute need to look only at touching neighbours:
  	 * we could search further afield for "compatible" anon_vmas.
  	 * But it would probably just be a waste of time searching,
  	 * or lead to too many vmas hanging off the same anon_vma.
  	 * We're trying to allow mprotect remerging later on,
  	 * not trying to minimize memory used for anon_vmas.
  	 */
  	return NULL;
  }
  
  #ifdef CONFIG_PROC_FS

  void vm_stat_account(struct mm_struct *mm, unsigned long flags,

  						struct file *file, long pages)
  {
  	const unsigned long stack_flags
  		= VM_STACK_FLAGS & (VM_GROWSUP|VM_GROWSDOWN);

  	if (file) {
  		mm->shared_vm += pages;
  		if ((flags & (VM_EXEC|VM_WRITE)) == VM_EXEC)
  			mm->exec_vm += pages;
  	} else if (flags & stack_flags)
  		mm->stack_vm += pages;
  	if (flags & (VM_RESERVED|VM_IO))
  		mm->reserved_vm += pages;
  }
  #endif /* CONFIG_PROC_FS */
  
  /*

   * The caller must hold down_write(&current->mm->mmap_sem).

   */

  unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,

  			unsigned long len, unsigned long prot,
  			unsigned long flags, unsigned long pgoff)
  {
  	struct mm_struct * mm = current->mm;

  	struct inode *inode;
  	unsigned int vm_flags;

  	int error;

  	unsigned long reqprot = prot;

  	/*
  	 * Does the application expect PROT_READ to imply PROT_EXEC?
  	 *
  	 * (the exception is when the underlying filesystem is noexec
  	 *  mounted, in which case we dont add PROT_EXEC.)
  	 */
  	if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))

  		if (!(file && (file->f_path.mnt->mnt_flags & MNT_NOEXEC)))

  			prot |= PROT_EXEC;
  
  	if (!len)
  		return -EINVAL;

  	if (!(flags & MAP_FIXED))
  		addr = round_hint_to_min(addr);

  	/* Careful about overflows.. */
  	len = PAGE_ALIGN(len);

  	if (!len)

  		return -ENOMEM;
  
  	/* offset overflow? */
  	if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
                 return -EOVERFLOW;
  
  	/* Too many mappings? */
  	if (mm->map_count > sysctl_max_map_count)
  		return -ENOMEM;
  
  	/* Obtain the address to map to. we verify (or select) it and ensure
  	 * that it represents a valid section of the address space.
  	 */
  	addr = get_unmapped_area(file, addr, len, pgoff, flags);
  	if (addr & ~PAGE_MASK)
  		return addr;
  
  	/* Do simple checking here so the lower-level routines won't have
  	 * to. we assume access permissions have been handled by the open
  	 * of the memory object, so we don't do any here.
  	 */
  	vm_flags = calc_vm_prot_bits(prot) | calc_vm_flag_bits(flags) |
  			mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;

  	if (flags & MAP_LOCKED)

  		if (!can_do_mlock())
  			return -EPERM;

  	/* mlock MCL_FUTURE? */
  	if (vm_flags & VM_LOCKED) {
  		unsigned long locked, lock_limit;

  		locked = len >> PAGE_SHIFT;
  		locked += mm->locked_vm;

  		lock_limit = rlimit(RLIMIT_MEMLOCK);

  		lock_limit >>= PAGE_SHIFT;

  		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
  			return -EAGAIN;
  	}

  	inode = file ? file->f_path.dentry->d_inode : NULL;

  
  	if (file) {
  		switch (flags & MAP_TYPE) {
  		case MAP_SHARED:
  			if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE))
  				return -EACCES;
  
  			/*
  			 * Make sure we don't allow writing to an append-only
  			 * file..
  			 */
  			if (IS_APPEND(inode) && (file->f_mode & FMODE_WRITE))
  				return -EACCES;
  
  			/*
  			 * Make sure there are no mandatory locks on the file.
  			 */
  			if (locks_verify_locked(inode))
  				return -EAGAIN;
  
  			vm_flags |= VM_SHARED | VM_MAYSHARE;
  			if (!(file->f_mode & FMODE_WRITE))
  				vm_flags &= ~(VM_MAYWRITE | VM_SHARED);
  
  			/* fall through */
  		case MAP_PRIVATE:
  			if (!(file->f_mode & FMODE_READ))
  				return -EACCES;

  			if (file->f_path.mnt->mnt_flags & MNT_NOEXEC) {

  				if (vm_flags & VM_EXEC)
  					return -EPERM;
  				vm_flags &= ~VM_MAYEXEC;
  			}

  
  			if (!file->f_op || !file->f_op->mmap)
  				return -ENODEV;

  			break;
  
  		default:
  			return -EINVAL;
  		}
  	} else {
  		switch (flags & MAP_TYPE) {
  		case MAP_SHARED:

  			/*
  			 * Ignore pgoff.
  			 */
  			pgoff = 0;

  			vm_flags |= VM_SHARED | VM_MAYSHARE;
  			break;
  		case MAP_PRIVATE:
  			/*
  			 * Set pgoff according to addr for anon_vma.
  			 */
  			pgoff = addr >> PAGE_SHIFT;
  			break;
  		default:
  			return -EINVAL;
  		}
  	}

  	error = security_file_mmap(file, reqprot, prot, flags, addr, 0);

  	if (error)
  		return error;

  	return mmap_region(file, addr, len, flags, vm_flags, pgoff);

  }
  EXPORT_SYMBOL(do_mmap_pgoff);

  SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
  		unsigned long, prot, unsigned long, flags,
  		unsigned long, fd, unsigned long, pgoff)
  {
  	struct file *file = NULL;
  	unsigned long retval = -EBADF;
  
  	if (!(flags & MAP_ANONYMOUS)) {
  		if (unlikely(flags & MAP_HUGETLB))
  			return -EINVAL;
  		file = fget(fd);
  		if (!file)
  			goto out;
  	} else if (flags & MAP_HUGETLB) {
  		struct user_struct *user = NULL;
  		/*
  		 * VM_NORESERVE is used because the reservations will be
  		 * taken when vm_ops->mmap() is called
  		 * A dummy user value is used because we are not locking
  		 * memory so no accounting is necessary
  		 */
  		len = ALIGN(len, huge_page_size(&default_hstate));
  		file = hugetlb_file_setup(HUGETLB_ANON_FILE, len, VM_NORESERVE,
  						&user, HUGETLB_ANONHUGE_INODE);
  		if (IS_ERR(file))
  			return PTR_ERR(file);
  	}
  
  	flags &= ~(MAP_EXECUTABLE | MAP_DENYWRITE);
  
  	down_write(&current->mm->mmap_sem);
  	retval = do_mmap_pgoff(file, addr, len, prot, flags, pgoff);
  	up_write(&current->mm->mmap_sem);
  
  	if (file)
  		fput(file);
  out:
  	return retval;
  }

  #ifdef __ARCH_WANT_SYS_OLD_MMAP
  struct mmap_arg_struct {
  	unsigned long addr;
  	unsigned long len;
  	unsigned long prot;
  	unsigned long flags;
  	unsigned long fd;
  	unsigned long offset;
  };
  
  SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg)
  {
  	struct mmap_arg_struct a;
  
  	if (copy_from_user(&a, arg, sizeof(a)))
  		return -EFAULT;
  	if (a.offset & ~PAGE_MASK)
  		return -EINVAL;
  
  	return sys_mmap_pgoff(a.addr, a.len, a.prot, a.flags, a.fd,
  			      a.offset >> PAGE_SHIFT);
  }
  #endif /* __ARCH_WANT_SYS_OLD_MMAP */

  /*
   * Some shared mappigns will want the pages marked read-only
   * to track write events. If so, we'll downgrade vm_page_prot
   * to the private version (using protection_map[] without the
   * VM_SHARED bit).
   */
  int vma_wants_writenotify(struct vm_area_struct *vma)
  {
  	unsigned int vm_flags = vma->vm_flags;
  
  	/* If it was private or non-writable, the write bit is already clear */
  	if ((vm_flags & (VM_WRITE|VM_SHARED)) != ((VM_WRITE|VM_SHARED)))
  		return 0;
  
  	/* The backer wishes to know when pages are first written to? */
  	if (vma->vm_ops && vma->vm_ops->page_mkwrite)
  		return 1;
  
  	/* The open routine did something to the protections already? */
  	if (pgprot_val(vma->vm_page_prot) !=

  	    pgprot_val(vm_get_page_prot(vm_flags)))

  		return 0;
  
  	/* Specialty mapping? */
  	if (vm_flags & (VM_PFNMAP|VM_INSERTPAGE))
  		return 0;
  
  	/* Can the mapping track the dirty pages? */
  	return vma->vm_file && vma->vm_file->f_mapping &&
  		mapping_cap_account_dirty(vma->vm_file->f_mapping);
  }

  /*
   * We account for memory if it's a private writeable mapping,

   * not hugepages and VM_NORESERVE wasn't set.

   */

  static inline int accountable_mapping(struct file *file, unsigned int vm_flags)

  {

  	/*
  	 * hugetlb has its own accounting separate from the core VM
  	 * VM_HUGETLB may not be set yet so we cannot check for that flag.
  	 */
  	if (file && is_file_hugepages(file))
  		return 0;

  	return (vm_flags & (VM_NORESERVE | VM_SHARED | VM_WRITE)) == VM_WRITE;
  }

  unsigned long mmap_region(struct file *file, unsigned long addr,
  			  unsigned long len, unsigned long flags,

  			  unsigned int vm_flags, unsigned long pgoff)

  {
  	struct mm_struct *mm = current->mm;
  	struct vm_area_struct *vma, *prev;
  	int correct_wcount = 0;
  	int error;
  	struct rb_node **rb_link, *rb_parent;
  	unsigned long charged = 0;
  	struct inode *inode =  file ? file->f_path.dentry->d_inode : NULL;

  	/* Clear old maps */
  	error = -ENOMEM;
  munmap_back:
  	vma = find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
  	if (vma && vma->vm_start < addr + len) {
  		if (do_munmap(mm, addr, len))
  			return -ENOMEM;
  		goto munmap_back;
  	}
  
  	/* Check against address space limit. */

  	if (!may_expand_vm(mm, len >> PAGE_SHIFT))

  		return -ENOMEM;

  	/*
  	 * Set 'VM_NORESERVE' if we should not account for the

  	 * memory use of this mapping.

  	 */

  	if ((flags & MAP_NORESERVE)) {
  		/* We honor MAP_NORESERVE if allowed to overcommit */
  		if (sysctl_overcommit_memory != OVERCOMMIT_NEVER)
  			vm_flags |= VM_NORESERVE;
  
  		/* hugetlb applies strict overcommit unless MAP_NORESERVE */
  		if (file && is_file_hugepages(file))
  			vm_flags |= VM_NORESERVE;
  	}

  	/*
  	 * Private writable mapping: check memory availability
  	 */

  	if (accountable_mapping(file, vm_flags)) {

  		charged = len >> PAGE_SHIFT;
  		if (security_vm_enough_memory(charged))
  			return -ENOMEM;
  		vm_flags |= VM_ACCOUNT;

  	}
  
  	/*

  	 * Can we just expand an old mapping?

  	 */

  	vma = vma_merge(mm, prev, addr, addr + len, vm_flags, NULL, file, pgoff, NULL);
  	if (vma)
  		goto out;

  
  	/*
  	 * Determine the object being mapped and call the appropriate
  	 * specific mapper. the address has already been validated, but
  	 * not unmapped, but the maps are removed from the list.
  	 */

  	vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);

  	if (!vma) {
  		error = -ENOMEM;
  		goto unacct_error;
  	}

  
  	vma->vm_mm = mm;
  	vma->vm_start = addr;
  	vma->vm_end = addr + len;
  	vma->vm_flags = vm_flags;

  	vma->vm_page_prot = vm_get_page_prot(vm_flags);

  	vma->vm_pgoff = pgoff;

  	INIT_LIST_HEAD(&vma->anon_vma_chain);

  
  	if (file) {
  		error = -EINVAL;
  		if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
  			goto free_vma;
  		if (vm_flags & VM_DENYWRITE) {
  			error = deny_write_access(file);
  			if (error)
  				goto free_vma;
  			correct_wcount = 1;
  		}
  		vma->vm_file = file;
  		get_file(file);
  		error = file->f_op->mmap(file, vma);
  		if (error)
  			goto unmap_and_free_vma;

  		if (vm_flags & VM_EXECUTABLE)
  			added_exe_file_vma(mm);

  
  		/* Can addr have changed??
  		 *
  		 * Answer: Yes, several device drivers can do it in their
  		 *         f_op->mmap method. -DaveM
  		 */
  		addr = vma->vm_start;
  		pgoff = vma->vm_pgoff;
  		vm_flags = vma->vm_flags;

  	} else if (vm_flags & VM_SHARED) {
  		error = shmem_zero_setup(vma);
  		if (error)
  			goto free_vma;
  	}

  	if (vma_wants_writenotify(vma)) {
  		pgprot_t pprot = vma->vm_page_prot;
  
  		/* Can vma->vm_page_prot have changed??
  		 *
  		 * Answer: Yes, drivers may have changed it in their
  		 *         f_op->mmap method.
  		 *
  		 * Ensures that vmas marked as uncached stay that way.
  		 */

  		vma->vm_page_prot = vm_get_page_prot(vm_flags & ~VM_SHARED);

  		if (pgprot_val(pprot) == pgprot_val(pgprot_noncached(pprot)))
  			vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
  	}

  	vma_link(mm, vma, prev, rb_link, rb_parent);
  	file = vma->vm_file;

  
  	/* Once vma denies write, undo our temporary denial count */
  	if (correct_wcount)
  		atomic_inc(&inode->i_writecount);
  out:

  	perf_event_mmap(vma);

  	mm->total_vm += len >> PAGE_SHIFT;

  	vm_stat_account(mm, vm_flags, file, len >> PAGE_SHIFT);

  	if (vm_flags & VM_LOCKED) {

  		if (!mlock_vma_pages_range(vma, addr, addr + len))
  			mm->locked_vm += (len >> PAGE_SHIFT);

  	} else if ((flags & MAP_POPULATE) && !(flags & MAP_NONBLOCK))

  		make_pages_present(addr, addr + len);

  	return addr;
  
  unmap_and_free_vma:
  	if (correct_wcount)
  		atomic_inc(&inode->i_writecount);
  	vma->vm_file = NULL;
  	fput(file);
  
  	/* Undo any partial mapping done by a device driver. */

  	unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end);
  	charged = 0;

  free_vma:
  	kmem_cache_free(vm_area_cachep, vma);
  unacct_error:
  	if (charged)
  		vm_unacct_memory(charged);
  	return error;
  }

  /* Get an address range which is currently unmapped.
   * For shmat() with addr=0.
   *
   * Ugly calling convention alert:
   * Return value with the low bits set means error value,
   * ie
   *	if (ret & ~PAGE_MASK)
   *		error = ret;
   *
   * This function "knows" that -ENOMEM has the bits set.
   */
  #ifndef HAVE_ARCH_UNMAPPED_AREA
  unsigned long
  arch_get_unmapped_area(struct file *filp, unsigned long addr,
  		unsigned long len, unsigned long pgoff, unsigned long flags)
  {
  	struct mm_struct *mm = current->mm;
  	struct vm_area_struct *vma;
  	unsigned long start_addr;
  
  	if (len > TASK_SIZE)
  		return -ENOMEM;

  	if (flags & MAP_FIXED)
  		return addr;

  	if (addr) {
  		addr = PAGE_ALIGN(addr);
  		vma = find_vma(mm, addr);
  		if (TASK_SIZE - len >= addr &&
  		    (!vma || addr + len <= vma->vm_start))
  			return addr;
  	}

  	if (len > mm->cached_hole_size) {
  	        start_addr = addr = mm->free_area_cache;
  	} else {
  	        start_addr = addr = TASK_UNMAPPED_BASE;
  	        mm->cached_hole_size = 0;
  	}

  
  full_search:
  	for (vma = find_vma(mm, addr); ; vma = vma->vm_next) {
  		/* At this point:  (!vma || addr < vma->vm_end). */
  		if (TASK_SIZE - len < addr) {
  			/*
  			 * Start a new search - just in case we missed
  			 * some holes.
  			 */
  			if (start_addr != TASK_UNMAPPED_BASE) {

  				addr = TASK_UNMAPPED_BASE;
  			        start_addr = addr;
  				mm->cached_hole_size = 0;

  				goto full_search;
  			}
  			return -ENOMEM;
  		}
  		if (!vma || addr + len <= vma->vm_start) {
  			/*
  			 * Remember the place where we stopped the search:
  			 */
  			mm->free_area_cache = addr + len;
  			return addr;
  		}

  		if (addr + mm->cached_hole_size < vma->vm_start)
  		        mm->cached_hole_size = vma->vm_start - addr;

  		addr = vma->vm_end;
  	}
  }
  #endif	

  void arch_unmap_area(struct mm_struct *mm, unsigned long addr)

  {
  	/*
  	 * Is this a new hole at the lowest possible address?
  	 */

  	if (addr >= TASK_UNMAPPED_BASE && addr < mm->free_area_cache) {
  		mm->free_area_cache = addr;
  		mm->cached_hole_size = ~0UL;
  	}

  }
  
  /*
   * This mmap-allocator allocates new areas top-down from below the
   * stack's low limit (the base):
   */
  #ifndef HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
  unsigned long
  arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
  			  const unsigned long len, const unsigned long pgoff,
  			  const unsigned long flags)
  {
  	struct vm_area_struct *vma;
  	struct mm_struct *mm = current->mm;
  	unsigned long addr = addr0;
  
  	/* requested length too big for entire address space */
  	if (len > TASK_SIZE)
  		return -ENOMEM;

  	if (flags & MAP_FIXED)
  		return addr;

  	/* requesting a specific address */
  	if (addr) {
  		addr = PAGE_ALIGN(addr);
  		vma = find_vma(mm, addr);
  		if (TASK_SIZE - len >= addr &&
  				(!vma || addr + len <= vma->vm_start))
  			return addr;
  	}

  	/* check if free_area_cache is useful for us */
  	if (len <= mm->cached_hole_size) {
   	        mm->cached_hole_size = 0;
   		mm->free_area_cache = mm->mmap_base;
   	}

  	/* either no address requested or can't fit in requested address hole */
  	addr = mm->free_area_cache;
  
  	/* make sure it can fit in the remaining address space */

  	if (addr > len) {

  		vma = find_vma(mm, addr-len);
  		if (!vma || addr <= vma->vm_start)
  			/* remember the address as a hint for next time */
  			return (mm->free_area_cache = addr-len);
  	}

  	if (mm->mmap_base < len)
  		goto bottomup;

  	addr = mm->mmap_base-len;
  
  	do {
  		/*
  		 * Lookup failure means no vma is above this address,
  		 * else if new region fits below vma->vm_start,
  		 * return with success:
  		 */
  		vma = find_vma(mm, addr);
  		if (!vma || addr+len <= vma->vm_start)
  			/* remember the address as a hint for next time */
  			return (mm->free_area_cache = addr);

   		/* remember the largest hole we saw so far */
   		if (addr + mm->cached_hole_size < vma->vm_start)
   		        mm->cached_hole_size = vma->vm_start - addr;

  		/* try just below the current vma->vm_start */
  		addr = vma->vm_start-len;

  	} while (len < vma->vm_start);

  bottomup:

  	/*
  	 * A failed mmap() very likely causes application failure,
  	 * so fall back to the bottom-up function here. This scenario
  	 * can happen with large stack limits and large mmap()
  	 * allocations.
  	 */

  	mm->cached_hole_size = ~0UL;
    	mm->free_area_cache = TASK_UNMAPPED_BASE;

  	addr = arch_get_unmapped_area(filp, addr0, len, pgoff, flags);
  	/*
  	 * Restore the topdown base:
  	 */
  	mm->free_area_cache = mm->mmap_base;

  	mm->cached_hole_size = ~0UL;

  
  	return addr;
  }
  #endif

  void arch_unmap_area_topdown(struct mm_struct *mm, unsigned long addr)

  {
  	/*
  	 * Is this a new hole at the highest possible address?
  	 */

  	if (addr > mm->free_area_cache)
  		mm->free_area_cache = addr;

  
  	/* dont allow allocations above current base */

  	if (mm->free_area_cache > mm->mmap_base)
  		mm->free_area_cache = mm->mmap_base;

  }
  
  unsigned long
  get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
  		unsigned long pgoff, unsigned long flags)
  {

  	unsigned long (*get_area)(struct file *, unsigned long,
  				  unsigned long, unsigned long, unsigned long);

  	unsigned long error = arch_mmap_check(addr, len, flags);
  	if (error)
  		return error;
  
  	/* Careful about overflows.. */
  	if (len > TASK_SIZE)
  		return -ENOMEM;

  	get_area = current->mm->get_unmapped_area;
  	if (file && file->f_op && file->f_op->get_unmapped_area)
  		get_area = file->f_op->get_unmapped_area;
  	addr = get_area(file, addr, len, pgoff, flags);
  	if (IS_ERR_VALUE(addr))
  		return addr;

  	if (addr > TASK_SIZE - len)
  		return -ENOMEM;
  	if (addr & ~PAGE_MASK)
  		return -EINVAL;

  	return arch_rebalance_pgtables(addr, len);

  }
  
  EXPORT_SYMBOL(get_unmapped_area);
  
  /* Look up the first VMA which satisfies  addr < vm_end,  NULL if none. */

  struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)

  {
  	struct vm_area_struct *vma = NULL;
  
  	if (mm) {
  		/* Check the cache first. */
  		/* (Cache hit rate is typically around 35%.) */
  		vma = mm->mmap_cache;
  		if (!(vma && vma->vm_end > addr && vma->vm_start <= addr)) {
  			struct rb_node * rb_node;
  
  			rb_node = mm->mm_rb.rb_node;
  			vma = NULL;
  
  			while (rb_node) {
  				struct vm_area_struct * vma_tmp;
  
  				vma_tmp = rb_entry(rb_node,
  						struct vm_area_struct, vm_rb);
  
  				if (vma_tmp->vm_end > addr) {
  					vma = vma_tmp;
  					if (vma_tmp->vm_start <= addr)
  						break;
  					rb_node = rb_node->rb_left;
  				} else
  					rb_node = rb_node->rb_right;
  			}
  			if (vma)
  				mm->mmap_cache = vma;
  		}
  	}
  	return vma;
  }
  
  EXPORT_SYMBOL(find_vma);
  
  /* Same as find_vma, but also return a pointer to the previous VMA in *pprev. */
  struct vm_area_struct *
  find_vma_prev(struct mm_struct *mm, unsigned long addr,
  			struct vm_area_struct **pprev)
  {
  	struct vm_area_struct *vma = NULL, *prev = NULL;

  	struct rb_node *rb_node;

  	if (!mm)
  		goto out;
  
  	/* Guard against addr being lower than the first VMA */
  	vma = mm->mmap;
  
  	/* Go through the RB tree quickly. */
  	rb_node = mm->mm_rb.rb_node;
  
  	while (rb_node) {
  		struct vm_area_struct *vma_tmp;
  		vma_tmp = rb_entry(rb_node, struct vm_area_struct, vm_rb);
  
  		if (addr < vma_tmp->vm_end) {
  			rb_node = rb_node->rb_left;
  		} else {
  			prev = vma_tmp;
  			if (!prev->vm_next || (addr < prev->vm_next->vm_end))
  				break;
  			rb_node = rb_node->rb_right;
  		}
  	}
  
  out:
  	*pprev = prev;
  	return prev ? prev->vm_next : vma;
  }
  
  /*
   * Verify that the stack growth is acceptable and
   * update accounting. This is shared with both the
   * grow-up and grow-down cases.
   */

  static int acct_stack_growth(struct vm_area_struct *vma, unsigned long size, unsigned long grow)

  {
  	struct mm_struct *mm = vma->vm_mm;
  	struct rlimit *rlim = current->signal->rlim;

  	unsigned long new_start;

  
  	/* address space limit tests */

  	if (!may_expand_vm(mm, grow))

  		return -ENOMEM;
  
  	/* Stack limit test */

  	if (size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur))

  		return -ENOMEM;
  
  	/* mlock limit tests */
  	if (vma->vm_flags & VM_LOCKED) {
  		unsigned long locked;
  		unsigned long limit;
  		locked = mm->locked_vm + grow;

  		limit = ACCESS_ONCE(rlim[RLIMIT_MEMLOCK].rlim_cur);
  		limit >>= PAGE_SHIFT;

  		if (locked > limit && !capable(CAP_IPC_LOCK))
  			return -ENOMEM;
  	}

  	/* Check to ensure the stack will not grow into a hugetlb-only region */
  	new_start = (vma->vm_flags & VM_GROWSUP) ? vma->vm_start :
  			vma->vm_end - size;
  	if (is_hugepage_only_range(vma->vm_mm, new_start, size))
  		return -EFAULT;

  	/*
  	 * Overcommit..  This must be the final test, as it will
  	 * update security statistics.
  	 */

  	if (security_vm_enough_memory_mm(mm, grow))

  		return -ENOMEM;
  
  	/* Ok, everything looks good - let it rip */
  	mm->total_vm += grow;
  	if (vma->vm_flags & VM_LOCKED)
  		mm->locked_vm += grow;

  	vm_stat_account(mm, vma->vm_flags, vma->vm_file, grow);

  	return 0;
  }

  #if defined(CONFIG_STACK_GROWSUP) || defined(CONFIG_IA64)

  /*

   * PA-RISC uses this for its stack; IA64 for its Register Backing Store.
   * vma is the last one with address > vma->vm_end.  Have to extend vma.

   */

  int expand_upwards(struct vm_area_struct *vma, unsigned long address)

  {
  	int error;
  
  	if (!(vma->vm_flags & VM_GROWSUP))
  		return -EFAULT;
  
  	/*
  	 * We must make sure the anon_vma is allocated
  	 * so that the anon_vma locking is not a noop.
  	 */
  	if (unlikely(anon_vma_prepare(vma)))
  		return -ENOMEM;

  	vma_lock_anon_vma(vma);

  
  	/*
  	 * vma->vm_start/vm_end cannot change under us because the caller
  	 * is required to hold the mmap_sem in read mode.  We need the
  	 * anon_vma lock to serialize against concurrent expand_stacks.

  	 * Also guard against wrapping around to address 0.

  	 */

  	if (address < PAGE_ALIGN(address+4))
  		address = PAGE_ALIGN(address+4);
  	else {

  		vma_unlock_anon_vma(vma);

  		return -ENOMEM;
  	}

  	error = 0;
  
  	/* Somebody else might have raced and expanded it already */
  	if (address > vma->vm_end) {
  		unsigned long size, grow;
  
  		size = address - vma->vm_start;
  		grow = (address - vma->vm_end) >> PAGE_SHIFT;
  
  		error = acct_stack_growth(vma, size, grow);

  		if (!error) {

  			vma->vm_end = address;

  			perf_event_mmap(vma);
  		}

  	}

  	vma_unlock_anon_vma(vma);

  	return error;
  }

  #endif /* CONFIG_STACK_GROWSUP || CONFIG_IA64 */

  /*
   * vma is the first one with address < vma->vm_start.  Have to extend vma.
   */

  static int expand_downwards(struct vm_area_struct *vma,

  				   unsigned long address)

  {
  	int error;
  
  	/*
  	 * We must make sure the anon_vma is allocated
  	 * so that the anon_vma locking is not a noop.
  	 */
  	if (unlikely(anon_vma_prepare(vma)))
  		return -ENOMEM;

  
  	address &= PAGE_MASK;

  	error = security_file_mmap(NULL, 0, 0, 0, address, 1);

  	if (error)
  		return error;

  	vma_lock_anon_vma(vma);

  
  	/*
  	 * vma->vm_start/vm_end cannot change under us because the caller
  	 * is required to hold the mmap_sem in read mode.  We need the
  	 * anon_vma lock to serialize against concurrent expand_stacks.
  	 */

  
  	/* Somebody else might have raced and expanded it already */
  	if (address < vma->vm_start) {
  		unsigned long size, grow;
  
  		size = vma->vm_end - address;
  		grow = (vma->vm_start - address) >> PAGE_SHIFT;
  
  		error = acct_stack_growth(vma, size, grow);
  		if (!error) {
  			vma->vm_start = address;
  			vma->vm_pgoff -= grow;

  			perf_event_mmap(vma);

  		}
  	}

  	vma_unlock_anon_vma(vma);

  	return error;
  }

  int expand_stack_downwards(struct vm_area_struct *vma, unsigned long address)
  {
  	return expand_downwards(vma, address);
  }
  
  #ifdef CONFIG_STACK_GROWSUP
  int expand_stack(struct vm_area_struct *vma, unsigned long address)
  {
  	return expand_upwards(vma, address);
  }
  
  struct vm_area_struct *
  find_extend_vma(struct mm_struct *mm, unsigned long addr)
  {
  	struct vm_area_struct *vma, *prev;
  
  	addr &= PAGE_MASK;
  	vma = find_vma_prev(mm, addr, &prev);
  	if (vma && (vma->vm_start <= addr))
  		return vma;

  	if (!prev || expand_stack(prev, addr))

  		return NULL;

  	if (prev->vm_flags & VM_LOCKED) {

  		mlock_vma_pages_range(prev, addr, prev->vm_end);

  	}

  	return prev;
  }
  #else
  int expand_stack(struct vm_area_struct *vma, unsigned long address)
  {
  	return expand_downwards(vma, address);
  }

  struct vm_area_struct *
  find_extend_vma(struct mm_struct * mm, unsigned long addr)
  {
  	struct vm_area_struct * vma;
  	unsigned long start;
  
  	addr &= PAGE_MASK;
  	vma = find_vma(mm,addr);
  	if (!vma)
  		return NULL;
  	if (vma->vm_start <= addr)
  		return vma;
  	if (!(vma->vm_flags & VM_GROWSDOWN))
  		return NULL;
  	start = vma->vm_start;
  	if (expand_stack(vma, addr))
  		return NULL;

  	if (vma->vm_flags & VM_LOCKED) {

  		mlock_vma_pages_range(vma, addr, start);

  	}

  	return vma;
  }
  #endif

  /*

   * Ok - we have the memory areas we should free on the vma list,

   * so release them, and do the vma updates.

   *
   * Called with the mm semaphore held.

   */

  static void remove_vma_list(struct mm_struct *mm, struct vm_area_struct *vma)

  {

  	/* Update high watermark before we lower total_vm */
  	update_hiwater_vm(mm);

  	do {

  		long nrpages = vma_pages(vma);
  
  		mm->total_vm -= nrpages;

  		vm_stat_account(mm, vma->vm_flags, vma->vm_file, -nrpages);

  		vma = remove_vma(vma);

  	} while (vma);

  	validate_mm(mm);
  }
  
  /*
   * Get rid of page table information in the indicated region.
   *

   * Called with the mm semaphore held.

   */
  static void unmap_region(struct mm_struct *mm,

  		struct vm_area_struct *vma, struct vm_area_struct *prev,
  		unsigned long start, unsigned long end)

  {

  	struct vm_area_struct *next = prev? prev->vm_next: mm->mmap;

  	struct mmu_gather *tlb;
  	unsigned long nr_accounted = 0;
  
  	lru_add_drain();
  	tlb = tlb_gather_mmu(mm, 0);

  	update_hiwater_rss(mm);

  	unmap_vmas(&tlb, vma, start, end, &nr_accounted, NULL);

  	vm_unacct_memory(nr_accounted);

  	free_pgtables(tlb, vma, prev? prev->vm_end: FIRST_USER_ADDRESS,

  				 next? next->vm_start: 0);

  	tlb_finish_mmu(tlb, start, end);
  }
  
  /*
   * Create a list of vma's touched by the unmap, removing them from the mm's
   * vma list as we go..
   */
  static void
  detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
  	struct vm_area_struct *prev, unsigned long end)
  {
  	struct vm_area_struct **insertion_point;
  	struct vm_area_struct *tail_vma = NULL;

  	unsigned long addr;

  
  	insertion_point = (prev ? &prev->vm_next : &mm->mmap);

  	vma->vm_prev = NULL;

  	do {
  		rb_erase(&vma->vm_rb, &mm->mm_rb);
  		mm->map_count--;
  		tail_vma = vma;
  		vma = vma->vm_next;
  	} while (vma && vma->vm_start < end);
  	*insertion_point = vma;

  	if (vma)
  		vma->vm_prev = prev;

  	tail_vma->vm_next = NULL;

  	if (mm->unmap_area == arch_unmap_area)
  		addr = prev ? prev->vm_end : mm->mmap_base;
  	else
  		addr = vma ?  vma->vm_start : mm->mmap_base;
  	mm->unmap_area(mm, addr);

  	mm->mmap_cache = NULL;		/* Kill the cache. */
  }
  
  /*

   * __split_vma() bypasses sysctl_max_map_count checking.  We use this on the
   * munmap path where it doesn't make sense to fail.

   */

  static int __split_vma(struct mm_struct * mm, struct vm_area_struct * vma,

  	      unsigned long addr, int new_below)
  {
  	struct mempolicy *pol;
  	struct vm_area_struct *new;

  	int err = -ENOMEM;

  	if (is_vm_hugetlb_page(vma) && (addr &
  					~(huge_page_mask(hstate_vma(vma)))))

  		return -EINVAL;

  	new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);

  	if (!new)

  		goto out_err;

  
  	/* most fields are the same, copy all, and then fixup */
  	*new = *vma;

  	INIT_LIST_HEAD(&new->anon_vma_chain);

  	if (new_below)
  		new->vm_end = addr;
  	else {
  		new->vm_start = addr;
  		new->vm_pgoff += ((addr - vma->vm_start) >> PAGE_SHIFT);
  	}

  	pol = mpol_dup(vma_policy(vma));

  	if (IS_ERR(pol)) {

  		err = PTR_ERR(pol);
  		goto out_free_vma;

  	}
  	vma_set_policy(new, pol);

  	if (anon_vma_clone(new, vma))
  		goto out_free_mpol;

  	if (new->vm_file) {

  		get_file(new->vm_file);

  		if (vma->vm_flags & VM_EXECUTABLE)
  			added_exe_file_vma(mm);
  	}

  
  	if (new->vm_ops && new->vm_ops->open)
  		new->vm_ops->open(new);
  
  	if (new_below)

  		err = vma_adjust(vma, addr, vma->vm_end, vma->vm_pgoff +

  			((addr - new->vm_start) >> PAGE_SHIFT), new);
  	else

  		err = vma_adjust(vma, vma->vm_start, addr, vma->vm_pgoff, new);

  	/* Success. */
  	if (!err)
  		return 0;
  
  	/* Clean everything up if vma_adjust failed. */

  	if (new->vm_ops && new->vm_ops->close)
  		new->vm_ops->close(new);

  	if (new->vm_file) {
  		if (vma->vm_flags & VM_EXECUTABLE)
  			removed_exe_file_vma(mm);
  		fput(new->vm_file);
  	}

  	unlink_anon_vmas(new);

   out_free_mpol:
  	mpol_put(pol);
   out_free_vma:
  	kmem_cache_free(vm_area_cachep, new);
   out_err:
  	return err;

  }

  /*
   * Split a vma into two pieces at address 'addr', a new vma is allocated
   * either for the first part or the tail.
   */
  int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
  	      unsigned long addr, int new_below)
  {
  	if (mm->map_count >= sysctl_max_map_count)
  		return -ENOMEM;
  
  	return __split_vma(mm, vma, addr, new_below);
  }

  /* Munmap is split into 2 main parts -- this part which finds
   * what needs doing, and the areas themselves, which do the
   * work.  This now handles partial unmappings.
   * Jeremy Fitzhardinge <jeremy@goop.org>
   */
  int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
  {
  	unsigned long end;

  	struct vm_area_struct *vma, *prev, *last;

  
  	if ((start & ~PAGE_MASK) || start > TASK_SIZE || len > TASK_SIZE-start)
  		return -EINVAL;
  
  	if ((len = PAGE_ALIGN(len)) == 0)
  		return -EINVAL;
  
  	/* Find the first overlapping VMA */

  	vma = find_vma_prev(mm, start, &prev);
  	if (!vma)

  		return 0;

  	/* we have  start < vma->vm_end  */

  
  	/* if it doesn't overlap, we have nothing.. */
  	end = start + len;

  	if (vma->vm_start >= end)

  		return 0;
  
  	/*
  	 * If we need to split any vma, do it now to save pain later.
  	 *
  	 * Note: mremap's move_vma VM_ACCOUNT handling assumes a partially
  	 * unmapped vm_area_struct will remain in use: so lower split_vma
  	 * places tmp vma above, and higher split_vma places tmp vma below.
  	 */

  	if (start > vma->vm_start) {

  		int error;
  
  		/*
  		 * Make sure that map_count on return from munmap() will
  		 * not exceed its limit; but let map_count go just above
  		 * its limit temporarily, to help free resources as expected.
  		 */
  		if (end < vma->vm_end && mm->map_count >= sysctl_max_map_count)
  			return -ENOMEM;
  
  		error = __split_vma(mm, vma, start, 0);

  		if (error)
  			return error;

  		prev = vma;

  	}
  
  	/* Does it split the last one? */
  	last = find_vma(mm, end);
  	if (last && end > last->vm_start) {

  		int error = __split_vma(mm, last, end, 1);

  		if (error)
  			return error;
  	}

  	vma = prev? prev->vm_next: mm->mmap;

  
  	/*

  	 * unlock any mlock()ed ranges before detaching vmas
  	 */
  	if (mm->locked_vm) {
  		struct vm_area_struct *tmp = vma;
  		while (tmp && tmp->vm_start < end) {
  			if (tmp->vm_flags & VM_LOCKED) {
  				mm->locked_vm -= vma_pages(tmp);
  				munlock_vma_pages_all(tmp);
  			}
  			tmp = tmp->vm_next;
  		}
  	}
  
  	/*

  	 * Remove the vma's, and unmap the actual pages
  	 */

  	detach_vmas_to_be_unmapped(mm, vma, prev, end);
  	unmap_region(mm, vma, prev, start, end);

  
  	/* Fix up all other VM information */

  	remove_vma_list(mm, vma);

  
  	return 0;
  }
  
  EXPORT_SYMBOL(do_munmap);

  SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)

  {
  	int ret;
  	struct mm_struct *mm = current->mm;
  
  	profile_munmap(addr);
  
  	down_write(&mm->mmap_sem);
  	ret = do_munmap(mm, addr, len);
  	up_write(&mm->mmap_sem);
  	return ret;
  }
  
  static inline void verify_mm_writelocked(struct mm_struct *mm)
  {

  #ifdef CONFIG_DEBUG_VM

  	if (unlikely(down_read_trylock(&mm->mmap_sem))) {
  		WARN_ON(1);
  		up_read(&mm->mmap_sem);
  	}
  #endif
  }
  
  /*
   *  this is really a simplified "do_mmap".  it only handles
   *  anonymous maps.  eventually we may be able to do some
   *  brk-specific accounting here.
   */
  unsigned long do_brk(unsigned long addr, unsigned long len)
  {
  	struct mm_struct * mm = current->mm;
  	struct vm_area_struct * vma, * prev;
  	unsigned long flags;
  	struct rb_node ** rb_link, * rb_parent;
  	pgoff_t pgoff = addr >> PAGE_SHIFT;

  	int error;

  
  	len = PAGE_ALIGN(len);
  	if (!len)
  		return addr;

  	error = security_file_mmap(NULL, 0, 0, 0, addr, 1);

  	if (error)
  		return error;

  	flags = VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;

  	error = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
  	if (error & ~PAGE_MASK)

  		return error;

  	/*
  	 * mlock MCL_FUTURE?
  	 */
  	if (mm->def_flags & VM_LOCKED) {
  		unsigned long locked, lock_limit;

  		locked = len >> PAGE_SHIFT;
  		locked += mm->locked_vm;

  		lock_limit = rlimit(RLIMIT_MEMLOCK);

  		lock_limit >>= PAGE_SHIFT;

  		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
  			return -EAGAIN;
  	}
  
  	/*
  	 * mm->mmap_sem is required to protect against another thread
  	 * changing the mappings in case we sleep.
  	 */
  	verify_mm_writelocked(mm);
  
  	/*
  	 * Clear old maps.  this also does some error checking for us
  	 */
   munmap_back:
  	vma = find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
  	if (vma && vma->vm_start < addr + len) {
  		if (do_munmap(mm, addr, len))
  			return -ENOMEM;
  		goto munmap_back;
  	}
  
  	/* Check against address space limits *after* clearing old maps... */

  	if (!may_expand_vm(mm, len >> PAGE_SHIFT))

  		return -ENOMEM;
  
  	if (mm->map_count > sysctl_max_map_count)
  		return -ENOMEM;
  
  	if (security_vm_enough_memory(len >> PAGE_SHIFT))
  		return -ENOMEM;

  	/* Can we just expand an old private anonymous mapping? */

  	vma = vma_merge(mm, prev, addr, addr + len, flags,
  					NULL, NULL, pgoff, NULL);
  	if (vma)

  		goto out;
  
  	/*
  	 * create a vma struct for an anonymous mapping
  	 */

  	vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);

  	if (!vma) {
  		vm_unacct_memory(len >> PAGE_SHIFT);
  		return -ENOMEM;
  	}

  	INIT_LIST_HEAD(&vma->anon_vma_chain);

  	vma->vm_mm = mm;
  	vma->vm_start = addr;
  	vma->vm_end = addr + len;
  	vma->vm_pgoff = pgoff;
  	vma->vm_flags = flags;

  	vma->vm_page_prot = vm_get_page_prot(flags);

  	vma_link(mm, vma, prev, rb_link, rb_parent);
  out:

  	perf_event_mmap(vma);

  	mm->total_vm += len >> PAGE_SHIFT;
  	if (flags & VM_LOCKED) {

  		if (!mlock_vma_pages_range(vma, addr, addr + len))
  			mm->locked_vm += (len >> PAGE_SHIFT);

  	}
  	return addr;
  }
  
  EXPORT_SYMBOL(do_brk);
  
  /* Release all mmaps. */
  void exit_mmap(struct mm_struct *mm)
  {
  	struct mmu_gather *tlb;

  	struct vm_area_struct *vma;

  	unsigned long nr_accounted = 0;

  	unsigned long end;

  	/* mm's last user has gone, and its about to be pulled down */

  	mmu_notifier_release(mm);

  	if (mm->locked_vm) {
  		vma = mm->mmap;
  		while (vma) {
  			if (vma->vm_flags & VM_LOCKED)
  				munlock_vma_pages_all(vma);
  			vma = vma->vm_next;
  		}
  	}

  
  	arch_exit_mmap(mm);

  	vma = mm->mmap;

  	if (!vma)	/* Can happen if dup_mmap() received an OOM */
  		return;

  	lru_add_drain();

  	flush_cache_mm(mm);

  	tlb = tlb_gather_mmu(mm, 1);

  	/* update_hiwater_rss(mm) here? but nobody should be looking */

  	/* Use -1 here to ensure all VMAs in the mm are unmapped */

  	end = unmap_vmas(&tlb, vma, 0, -1, &nr_accounted, NULL);

  	vm_unacct_memory(nr_accounted);

  	free_pgtables(tlb, vma, FIRST_USER_ADDRESS, 0);

  	tlb_finish_mmu(tlb, 0, end);

  	/*

  	 * Walk the list again, actually closing and freeing it,
  	 * with preemption enabled, without holding any MM locks.

  	 */

  	while (vma)
  		vma = remove_vma(vma);

  	BUG_ON(mm->nr_ptes > (FIRST_USER_ADDRESS+PMD_SIZE-1)>>PMD_SHIFT);

  }
  
  /* Insert vm structure into process list sorted by address
   * and into the inode's i_mmap tree.  If vm_file is non-NULL
   * then i_mmap_lock is taken here.
   */
  int insert_vm_struct(struct mm_struct * mm, struct vm_area_struct * vma)
  {
  	struct vm_area_struct * __vma, * prev;
  	struct rb_node ** rb_link, * rb_parent;
  
  	/*
  	 * The vm_pgoff of a purely anonymous vma should be irrelevant
  	 * until its first write fault, when page's anon_vma and index
  	 * are set.  But now set the vm_pgoff it will almost certainly
  	 * end up with (unless mremap moves it elsewhere before that
  	 * first wfault), so /proc/pid/maps tells a consistent story.
  	 *
  	 * By setting it to reflect the virtual start address of the
  	 * vma, merges and splits can happen in a seamless way, just
  	 * using the existing file pgoff checks and manipulations.
  	 * Similarly in do_mmap_pgoff and in do_brk.
  	 */
  	if (!vma->vm_file) {
  		BUG_ON(vma->anon_vma);
  		vma->vm_pgoff = vma->vm_start >> PAGE_SHIFT;
  	}
  	__vma = find_vma_prepare(mm,vma->vm_start,&prev,&rb_link,&rb_parent);
  	if (__vma && __vma->vm_start < vma->vm_end)
  		return -ENOMEM;

  	if ((vma->vm_flags & VM_ACCOUNT) &&

  	     security_vm_enough_memory_mm(mm, vma_pages(vma)))

  		return -ENOMEM;

  	vma_link(mm, vma, prev, rb_link, rb_parent);
  	return 0;
  }
  
  /*
   * Copy the vma structure to a new location in the same mm,
   * prior to moving page table entries, to effect an mremap move.
   */
  struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
  	unsigned long addr, unsigned long len, pgoff_t pgoff)
  {
  	struct vm_area_struct *vma = *vmap;
  	unsigned long vma_start = vma->vm_start;
  	struct mm_struct *mm = vma->vm_mm;
  	struct vm_area_struct *new_vma, *prev;
  	struct rb_node **rb_link, *rb_parent;
  	struct mempolicy *pol;
  
  	/*
  	 * If anonymous vma has not yet been faulted, update new pgoff
  	 * to match new location, to increase its chance of merging.
  	 */
  	if (!vma->vm_file && !vma->anon_vma)
  		pgoff = addr >> PAGE_SHIFT;
  
  	find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
  	new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags,
  			vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
  	if (new_vma) {
  		/*
  		 * Source vma may have been merged into new_vma
  		 */
  		if (vma_start >= new_vma->vm_start &&
  		    vma_start < new_vma->vm_end)
  			*vmap = new_vma;
  	} else {

  		new_vma = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);

  		if (new_vma) {
  			*new_vma = *vma;

  			pol = mpol_dup(vma_policy(vma));

  			if (IS_ERR(pol))
  				goto out_free_vma;
  			INIT_LIST_HEAD(&new_vma->anon_vma_chain);
  			if (anon_vma_clone(new_vma, vma))
  				goto out_free_mempol;

  			vma_set_policy(new_vma, pol);
  			new_vma->vm_start = addr;
  			new_vma->vm_end = addr + len;
  			new_vma->vm_pgoff = pgoff;

  			if (new_vma->vm_file) {

  				get_file(new_vma->vm_file);

  				if (vma->vm_flags & VM_EXECUTABLE)
  					added_exe_file_vma(mm);
  			}

  			if (new_vma->vm_ops && new_vma->vm_ops->open)
  				new_vma->vm_ops->open(new_vma);
  			vma_link(mm, new_vma, prev, rb_link, rb_parent);
  		}
  	}
  	return new_vma;

  
   out_free_mempol:
  	mpol_put(pol);
   out_free_vma:
  	kmem_cache_free(vm_area_cachep, new_vma);
  	return NULL;

  }

  
  /*
   * Return true if the calling process may expand its vm space by the passed
   * number of pages
   */
  int may_expand_vm(struct mm_struct *mm, unsigned long npages)
  {
  	unsigned long cur = mm->total_vm;	/* pages */
  	unsigned long lim;

  	lim = rlimit(RLIMIT_AS) >> PAGE_SHIFT;

  
  	if (cur + npages > lim)
  		return 0;
  	return 1;
  }

  static int special_mapping_fault(struct vm_area_struct *vma,
  				struct vm_fault *vmf)

  {

  	pgoff_t pgoff;

  	struct page **pages;

  	/*
  	 * special mappings have no vm_file, and in that case, the mm
  	 * uses vm_pgoff internally. So we have to subtract it from here.
  	 * We are allowed to do this because we are the mm; do not copy
  	 * this code into drivers!
  	 */
  	pgoff = vmf->pgoff - vma->vm_pgoff;

  	for (pages = vma->vm_private_data; pgoff && *pages; ++pages)
  		pgoff--;

  
  	if (*pages) {
  		struct page *page = *pages;
  		get_page(page);

  		vmf->page = page;
  		return 0;

  	}

  	return VM_FAULT_SIGBUS;

  }
  
  /*
   * Having a close hook prevents vma merging regardless of flags.
   */
  static void special_mapping_close(struct vm_area_struct *vma)
  {
  }

  static const struct vm_operations_struct special_mapping_vmops = {

  	.close = special_mapping_close,

  	.fault = special_mapping_fault,

  };
  
  /*
   * Called with mm->mmap_sem held for writing.
   * Insert a new vma covering the given region, with the given flags.
   * Its pages are supplied by the given array of struct page *.
   * The array can be shorter than len >> PAGE_SHIFT if it's null-terminated.
   * The region past the last page supplied will always produce SIGBUS.
   * The array pointer and the pages it points to are assumed to stay alive
   * for as long as this mapping might exist.
   */
  int install_special_mapping(struct mm_struct *mm,
  			    unsigned long addr, unsigned long len,
  			    unsigned long vm_flags, struct page **pages)
  {
  	struct vm_area_struct *vma;
  
  	vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
  	if (unlikely(vma == NULL))
  		return -ENOMEM;

  	INIT_LIST_HEAD(&vma->anon_vma_chain);

  	vma->vm_mm = mm;
  	vma->vm_start = addr;
  	vma->vm_end = addr + len;

  	vma->vm_flags = vm_flags | mm->def_flags | VM_DONTEXPAND;

  	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);

  
  	vma->vm_ops = &special_mapping_vmops;
  	vma->vm_private_data = pages;
  
  	if (unlikely(insert_vm_struct(mm, vma))) {
  		kmem_cache_free(vm_area_cachep, vma);
  		return -ENOMEM;
  	}
  
  	mm->total_vm += len >> PAGE_SHIFT;

  	perf_event_mmap(vma);

  	return 0;
  }

  
  static DEFINE_MUTEX(mm_all_locks_mutex);

  static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma)

  {

  	if (!test_bit(0, (unsigned long *) &anon_vma->root->head.next)) {

  		/*
  		 * The LSB of head.next can't change from under us
  		 * because we hold the mm_all_locks_mutex.
  		 */

  		spin_lock_nest_lock(&anon_vma->root->lock, &mm->mmap_sem);

  		/*
  		 * We can safely modify head.next after taking the

  		 * anon_vma->root->lock. If some other vma in this mm shares

  		 * the same anon_vma we won't take it again.
  		 *
  		 * No need of atomic instructions here, head.next
  		 * can't change from under us thanks to the

  		 * anon_vma->root->lock.

  		 */
  		if (__test_and_set_bit(0, (unsigned long *)

  				       &anon_vma->root->head.next))

  			BUG();
  	}
  }

  static void vm_lock_mapping(struct mm_struct *mm, struct address_space *mapping)

  {
  	if (!test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
  		/*
  		 * AS_MM_ALL_LOCKS can't change from under us because
  		 * we hold the mm_all_locks_mutex.
  		 *
  		 * Operations on ->flags have to be atomic because
  		 * even if AS_MM_ALL_LOCKS is stable thanks to the
  		 * mm_all_locks_mutex, there may be other cpus
  		 * changing other bitflags in parallel to us.
  		 */
  		if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
  			BUG();

  		spin_lock_nest_lock(&mapping->i_mmap_lock, &mm->mmap_sem);

  	}
  }
  
  /*
   * This operation locks against the VM for all pte/vma/mm related
   * operations that could ever happen on a certain mm. This includes
   * vmtruncate, try_to_unmap, and all page faults.
   *
   * The caller must take the mmap_sem in write mode before calling
   * mm_take_all_locks(). The caller isn't allowed to release the
   * mmap_sem until mm_drop_all_locks() returns.
   *
   * mmap_sem in write mode is required in order to block all operations
   * that could modify pagetables and free pages without need of
   * altering the vma layout (for example populate_range() with
   * nonlinear vmas). It's also needed in write mode to avoid new
   * anon_vmas to be associated with existing vmas.
   *
   * A single task can't take more than one mm_take_all_locks() in a row
   * or it would deadlock.
   *
   * The LSB in anon_vma->head.next and the AS_MM_ALL_LOCKS bitflag in
   * mapping->flags avoid to take the same lock twice, if more than one
   * vma in this mm is backed by the same anon_vma or address_space.
   *
   * We can take all the locks in random order because the VM code
   * taking i_mmap_lock or anon_vma->lock outside the mmap_sem never
   * takes more than one of them in a row. Secondly we're protected
   * against a concurrent mm_take_all_locks() by the mm_all_locks_mutex.
   *
   * mm_take_all_locks() and mm_drop_all_locks are expensive operations
   * that may have to take thousand of locks.
   *
   * mm_take_all_locks() can fail if it's interrupted by signals.
   */
  int mm_take_all_locks(struct mm_struct *mm)
  {
  	struct vm_area_struct *vma;

  	struct anon_vma_chain *avc;

  	int ret = -EINTR;
  
  	BUG_ON(down_read_trylock(&mm->mmap_sem));
  
  	mutex_lock(&mm_all_locks_mutex);
  
  	for (vma = mm->mmap; vma; vma = vma->vm_next) {
  		if (signal_pending(current))
  			goto out_unlock;

  		if (vma->vm_file && vma->vm_file->f_mapping)

  			vm_lock_mapping(mm, vma->vm_file->f_mapping);

  	}

  
  	for (vma = mm->mmap; vma; vma = vma->vm_next) {
  		if (signal_pending(current))
  			goto out_unlock;
  		if (vma->anon_vma)

  			list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
  				vm_lock_anon_vma(mm, avc->anon_vma);

  	}

  	ret = 0;
  
  out_unlock:
  	if (ret)
  		mm_drop_all_locks(mm);
  
  	return ret;
  }
  
  static void vm_unlock_anon_vma(struct anon_vma *anon_vma)
  {

  	if (test_bit(0, (unsigned long *) &anon_vma->root->head.next)) {

  		/*
  		 * The LSB of head.next can't change to 0 from under
  		 * us because we hold the mm_all_locks_mutex.
  		 *
  		 * We must however clear the bitflag before unlocking
  		 * the vma so the users using the anon_vma->head will
  		 * never see our bitflag.
  		 *
  		 * No need of atomic instructions here, head.next
  		 * can't change from under us until we release the

  		 * anon_vma->root->lock.

  		 */
  		if (!__test_and_clear_bit(0, (unsigned long *)

  					  &anon_vma->root->head.next))

  			BUG();

  		anon_vma_unlock(anon_vma);

  	}
  }
  
  static void vm_unlock_mapping(struct address_space *mapping)
  {
  	if (test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
  		/*
  		 * AS_MM_ALL_LOCKS can't change to 0 from under us
  		 * because we hold the mm_all_locks_mutex.
  		 */
  		spin_unlock(&mapping->i_mmap_lock);
  		if (!test_and_clear_bit(AS_MM_ALL_LOCKS,
  					&mapping->flags))
  			BUG();
  	}
  }
  
  /*
   * The mmap_sem cannot be released by the caller until
   * mm_drop_all_locks() returns.
   */
  void mm_drop_all_locks(struct mm_struct *mm)
  {
  	struct vm_area_struct *vma;

  	struct anon_vma_chain *avc;

  
  	BUG_ON(down_read_trylock(&mm->mmap_sem));
  	BUG_ON(!mutex_is_locked(&mm_all_locks_mutex));
  
  	for (vma = mm->mmap; vma; vma = vma->vm_next) {
  		if (vma->anon_vma)

  			list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
  				vm_unlock_anon_vma(avc->anon_vma);

  		if (vma->vm_file && vma->vm_file->f_mapping)
  			vm_unlock_mapping(vma->vm_file->f_mapping);
  	}
  
  	mutex_unlock(&mm_all_locks_mutex);
  }

  
  /*
   * initialise the VMA slab
   */
  void __init mmap_init(void)
  {

  	int ret;
  
  	ret = percpu_counter_init(&vm_committed_as, 0);
  	VM_BUG_ON(ret);

  }