#ifndef _LINUX_PAGEMAP_H
  #define _LINUX_PAGEMAP_H
  
  /*
   * Copyright 1995 Linus Torvalds
   */
  #include <linux/mm.h>
  #include <linux/fs.h>
  #include <linux/list.h>
  #include <linux/highmem.h>
  #include <linux/compiler.h>
  #include <asm/uaccess.h>
  #include <linux/gfp.h>
  #include <linux/bitops.h>
  #include <linux/hardirq.h> /* for in_interrupt() */
  #include <linux/hugetlb_inline.h>
  
  /*
   * Bits in mapping->flags.  The lower __GFP_BITS_SHIFT bits are the page
   * allocation mode flags.
   */
  enum mapping_flags {
  	AS_EIO		= __GFP_BITS_SHIFT + 0,	/* IO error on async write */
  	AS_ENOSPC	= __GFP_BITS_SHIFT + 1,	/* ENOSPC on async write */
  	AS_MM_ALL_LOCKS	= __GFP_BITS_SHIFT + 2,	/* under mm_take_all_locks() */
  	AS_UNEVICTABLE	= __GFP_BITS_SHIFT + 3,	/* e.g., ramdisk, SHM_LOCK */
  	AS_BALLOON_MAP  = __GFP_BITS_SHIFT + 4, /* balloon page special map */
  };
  
  static inline void mapping_set_error(struct address_space *mapping, int error)
  {
  	if (unlikely(error)) {
  		if (error == -ENOSPC)
  			set_bit(AS_ENOSPC, &mapping->flags);
  		else
  			set_bit(AS_EIO, &mapping->flags);
  	}
  }
  
  static inline void mapping_set_unevictable(struct address_space *mapping)
  {
  	set_bit(AS_UNEVICTABLE, &mapping->flags);
  }
  
  static inline void mapping_clear_unevictable(struct address_space *mapping)
  {
  	clear_bit(AS_UNEVICTABLE, &mapping->flags);
  }
  
  static inline int mapping_unevictable(struct address_space *mapping)
  {
  	if (mapping)
  		return test_bit(AS_UNEVICTABLE, &mapping->flags);
  	return !!mapping;
  }
  
  static inline void mapping_set_balloon(struct address_space *mapping)
  {
  	set_bit(AS_BALLOON_MAP, &mapping->flags);
  }
  
  static inline void mapping_clear_balloon(struct address_space *mapping)
  {
  	clear_bit(AS_BALLOON_MAP, &mapping->flags);
  }
  
  static inline int mapping_balloon(struct address_space *mapping)
  {
  	return mapping && test_bit(AS_BALLOON_MAP, &mapping->flags);
  }
  
  static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
  {
  	return (__force gfp_t)mapping->flags & __GFP_BITS_MASK;
  }
  
  /*
   * This is non-atomic.  Only to be used before the mapping is activated.
   * Probably needs a barrier...
   */
  static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
  {
  	m->flags = (m->flags & ~(__force unsigned long)__GFP_BITS_MASK) |
  				(__force unsigned long)mask;
  }
  
  /*
   * The page cache can done in larger chunks than
   * one page, because it allows for more efficient
   * throughput (it can then be mapped into user
   * space in smaller chunks for same flexibility).
   *
   * Or rather, it _will_ be done in larger chunks.
   */
  #define PAGE_CACHE_SHIFT	PAGE_SHIFT
  #define PAGE_CACHE_SIZE		PAGE_SIZE
  #define PAGE_CACHE_MASK		PAGE_MASK
  #define PAGE_CACHE_ALIGN(addr)	(((addr)+PAGE_CACHE_SIZE-1)&PAGE_CACHE_MASK)
  
  #define page_cache_get(page)		get_page(page)
  #define page_cache_release(page)	put_page(page)
  void release_pages(struct page **pages, int nr, int cold);
  
  /*
   * speculatively take a reference to a page.
   * If the page is free (_count == 0), then _count is untouched, and 0
   * is returned. Otherwise, _count is incremented by 1 and 1 is returned.
   *
   * This function must be called inside the same rcu_read_lock() section as has
   * been used to lookup the page in the pagecache radix-tree (or page table):
   * this allows allocators to use a synchronize_rcu() to stabilize _count.
   *
   * Unless an RCU grace period has passed, the count of all pages coming out
   * of the allocator must be considered unstable. page_count may return higher
   * than expected, and put_page must be able to do the right thing when the
   * page has been finished with, no matter what it is subsequently allocated
   * for (because put_page is what is used here to drop an invalid speculative
   * reference).
   *
   * This is the interesting part of the lockless pagecache (and lockless
   * get_user_pages) locking protocol, where the lookup-side (eg. find_get_page)
   * has the following pattern:
   * 1. find page in radix tree
   * 2. conditionally increment refcount
   * 3. check the page is still in pagecache (if no, goto 1)
   *
   * Remove-side that cares about stability of _count (eg. reclaim) has the
   * following (with tree_lock held for write):
   * A. atomically check refcount is correct and set it to 0 (atomic_cmpxchg)
   * B. remove page from pagecache
   * C. free the page
   *
   * There are 2 critical interleavings that matter:
   * - 2 runs before A: in this case, A sees elevated refcount and bails out
   * - A runs before 2: in this case, 2 sees zero refcount and retries;
   *   subsequently, B will complete and 1 will find no page, causing the
   *   lookup to return NULL.
   *
   * It is possible that between 1 and 2, the page is removed then the exact same
   * page is inserted into the same position in pagecache. That's OK: the
   * old find_get_page using tree_lock could equally have run before or after
   * such a re-insertion, depending on order that locks are granted.
   *
   * Lookups racing against pagecache insertion isn't a big problem: either 1
   * will find the page or it will not. Likewise, the old find_get_page could run
   * either before the insertion or afterwards, depending on timing.
   */
  static inline int page_cache_get_speculative(struct page *page)
  {
  	VM_BUG_ON(in_interrupt());
  
  #ifdef CONFIG_TINY_RCU
  # ifdef CONFIG_PREEMPT_COUNT
  	VM_BUG_ON(!in_atomic());
  # endif
  	/*
  	 * Preempt must be disabled here - we rely on rcu_read_lock doing
  	 * this for us.
  	 *
  	 * Pagecache won't be truncated from interrupt context, so if we have
  	 * found a page in the radix tree here, we have pinned its refcount by
  	 * disabling preempt, and hence no need for the "speculative get" that
  	 * SMP requires.
  	 */
  	VM_BUG_ON_PAGE(page_count(page) == 0, page);
  	atomic_inc(&page->_count);
  
  #else
  	if (unlikely(!get_page_unless_zero(page))) {
  		/*
  		 * Either the page has been freed, or will be freed.
  		 * In either case, retry here and the caller should
  		 * do the right thing (see comments above).
  		 */
  		return 0;
  	}
  #endif
  	VM_BUG_ON_PAGE(PageTail(page), page);
  
  	return 1;
  }
  
  /*
   * Same as above, but add instead of inc (could just be merged)
   */
  static inline int page_cache_add_speculative(struct page *page, int count)
  {
  	VM_BUG_ON(in_interrupt());
  
  #if !defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)
  # ifdef CONFIG_PREEMPT_COUNT
  	VM_BUG_ON(!in_atomic());
  # endif
  	VM_BUG_ON_PAGE(page_count(page) == 0, page);
  	atomic_add(count, &page->_count);
  
  #else
  	if (unlikely(!atomic_add_unless(&page->_count, count, 0)))
  		return 0;
  #endif
  	VM_BUG_ON_PAGE(PageCompound(page) && page != compound_head(page), page);
  
  	return 1;
  }
  
  static inline int page_freeze_refs(struct page *page, int count)
  {
  	return likely(atomic_cmpxchg(&page->_count, count, 0) == count);
  }
  
  static inline void page_unfreeze_refs(struct page *page, int count)
  {
  	VM_BUG_ON_PAGE(page_count(page) != 0, page);
  	VM_BUG_ON(count == 0);
  
  	atomic_set(&page->_count, count);
  }
  
  #ifdef CONFIG_NUMA
  extern struct page *__page_cache_alloc(gfp_t gfp);
  #else
  static inline struct page *__page_cache_alloc(gfp_t gfp)
  {
  	return alloc_pages(gfp, 0);
  }
  #endif
  
  static inline struct page *page_cache_alloc(struct address_space *x)
  {
  	return __page_cache_alloc(mapping_gfp_mask(x));
  }
  
  static inline struct page *page_cache_alloc_cold(struct address_space *x)
  {
  	return __page_cache_alloc(mapping_gfp_mask(x)|__GFP_COLD);
  }
  
  static inline struct page *page_cache_alloc_readahead(struct address_space *x)
  {
  	return __page_cache_alloc(mapping_gfp_mask(x) |
  				  __GFP_COLD | __GFP_NORETRY | __GFP_NOWARN);
  }
  
  typedef int filler_t(void *, struct page *);
  
  pgoff_t page_cache_next_hole(struct address_space *mapping,
  			     pgoff_t index, unsigned long max_scan);
  pgoff_t page_cache_prev_hole(struct address_space *mapping,
  			     pgoff_t index, unsigned long max_scan);
  
  struct page *find_get_entry(struct address_space *mapping, pgoff_t offset);
  struct page *find_get_page(struct address_space *mapping, pgoff_t offset);
  struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset);
  struct page *find_lock_page(struct address_space *mapping, pgoff_t offset);
  struct page *find_or_create_page(struct address_space *mapping, pgoff_t index,
  				 gfp_t gfp_mask);
  unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
  			  unsigned int nr_entries, struct page **entries,
  			  pgoff_t *indices);
  unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
  			unsigned int nr_pages, struct page **pages);
  unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t start,
  			       unsigned int nr_pages, struct page **pages);
  unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
  			int tag, unsigned int nr_pages, struct page **pages);
  
  struct page *grab_cache_page_write_begin(struct address_space *mapping,
  			pgoff_t index, unsigned flags);
  
  /*
   * Returns locked page at given index in given cache, creating it if needed.
   */
  static inline struct page *grab_cache_page(struct address_space *mapping,
  								pgoff_t index)
  {
  	return find_or_create_page(mapping, index, mapping_gfp_mask(mapping));
  }
  
  extern struct page * grab_cache_page_nowait(struct address_space *mapping,
  				pgoff_t index);
  extern struct page * read_cache_page(struct address_space *mapping,
  				pgoff_t index, filler_t *filler, void *data);
  extern struct page * read_cache_page_gfp(struct address_space *mapping,
  				pgoff_t index, gfp_t gfp_mask);
  extern int read_cache_pages(struct address_space *mapping,
  		struct list_head *pages, filler_t *filler, void *data);
  
  static inline struct page *read_mapping_page(struct address_space *mapping,
  				pgoff_t index, void *data)
  {
  	filler_t *filler = (filler_t *)mapping->a_ops->readpage;
  	return read_cache_page(mapping, index, filler, data);
  }
  
  /*
   * Return byte-offset into filesystem object for page.
   */
  static inline loff_t page_offset(struct page *page)
  {
  	return ((loff_t)page->index) << PAGE_CACHE_SHIFT;
  }
  
  static inline loff_t page_file_offset(struct page *page)
  {
  	return ((loff_t)page_file_index(page)) << PAGE_CACHE_SHIFT;
  }
  
  extern pgoff_t linear_hugepage_index(struct vm_area_struct *vma,
  				     unsigned long address);
  
  static inline pgoff_t linear_page_index(struct vm_area_struct *vma,
  					unsigned long address)
  {
  	pgoff_t pgoff;
  	if (unlikely(is_vm_hugetlb_page(vma)))
  		return linear_hugepage_index(vma, address);
  	pgoff = (address - vma->vm_start) >> PAGE_SHIFT;
  	pgoff += vma->vm_pgoff;
  	return pgoff >> (PAGE_CACHE_SHIFT - PAGE_SHIFT);
  }
  
  extern void __lock_page(struct page *page);
  extern int __lock_page_killable(struct page *page);
  extern int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
  				unsigned int flags);
  extern void unlock_page(struct page *page);
  
  static inline void __set_page_locked(struct page *page)
  {
  	__set_bit(PG_locked, &page->flags);
  }
  
  static inline void __clear_page_locked(struct page *page)
  {
  	__clear_bit(PG_locked, &page->flags);
  }
  
  static inline int trylock_page(struct page *page)
  {
  	return (likely(!test_and_set_bit_lock(PG_locked, &page->flags)));
  }
  
  /*
   * lock_page may only be called if we have the page's inode pinned.
   */
  static inline void lock_page(struct page *page)
  {
  	might_sleep();
  	if (!trylock_page(page))
  		__lock_page(page);
  }
  
  /*
   * lock_page_killable is like lock_page but can be interrupted by fatal
   * signals.  It returns 0 if it locked the page and -EINTR if it was
   * killed while waiting.
   */
  static inline int lock_page_killable(struct page *page)
  {
  	might_sleep();
  	if (!trylock_page(page))
  		return __lock_page_killable(page);
  	return 0;
  }
  
  /*
   * lock_page_or_retry - Lock the page, unless this would block and the
   * caller indicated that it can handle a retry.
   */
  static inline int lock_page_or_retry(struct page *page, struct mm_struct *mm,
  				     unsigned int flags)
  {
  	might_sleep();
  	return trylock_page(page) || __lock_page_or_retry(page, mm, flags);
  }
  
  /*
   * This is exported only for wait_on_page_locked/wait_on_page_writeback.
   * Never use this directly!
   */
  extern void wait_on_page_bit(struct page *page, int bit_nr);
  
  extern int wait_on_page_bit_killable(struct page *page, int bit_nr);
  
  static inline int wait_on_page_locked_killable(struct page *page)
  {
  	if (PageLocked(page))
  		return wait_on_page_bit_killable(page, PG_locked);
  	return 0;
  }
  
  /* 
   * Wait for a page to be unlocked.
   *
   * This must be called with the caller "holding" the page,
   * ie with increased "page->count" so that the page won't
   * go away during the wait..
   */
  static inline void wait_on_page_locked(struct page *page)
  {
  	if (PageLocked(page))
  		wait_on_page_bit(page, PG_locked);
  }
  
  /* 
   * Wait for a page to complete writeback
   */
  static inline void wait_on_page_writeback(struct page *page)
  {
  	if (PageWriteback(page))
  		wait_on_page_bit(page, PG_writeback);
  }
  
  extern void end_page_writeback(struct page *page);
  void wait_for_stable_page(struct page *page);
  
  /*
   * Add an arbitrary waiter to a page's wait queue
   */
  extern void add_page_wait_queue(struct page *page, wait_queue_t *waiter);
  
  /*
   * Fault a userspace page into pagetables.  Return non-zero on a fault.
   *
   * This assumes that two userspace pages are always sufficient.  That's
   * not true if PAGE_CACHE_SIZE > PAGE_SIZE.
   */
  static inline int fault_in_pages_writeable(char __user *uaddr, int size)
  {
  	int ret;
  
  	if (unlikely(size == 0))
  		return 0;
  
  	/*
  	 * Writing zeroes into userspace here is OK, because we know that if
  	 * the zero gets there, we'll be overwriting it.
  	 */
  	ret = __put_user(0, uaddr);
  	if (ret == 0) {
  		char __user *end = uaddr + size - 1;
  
  		/*
  		 * If the page was already mapped, this will get a cache miss
  		 * for sure, so try to avoid doing it.
  		 */
  		if (((unsigned long)uaddr & PAGE_MASK) !=
  				((unsigned long)end & PAGE_MASK))
  			ret = __put_user(0, end);
  	}
  	return ret;
  }
  
  static inline int fault_in_pages_readable(const char __user *uaddr, int size)
  {
  	volatile char c;
  	int ret;
  
  	if (unlikely(size == 0))
  		return 0;
  
  	ret = __get_user(c, uaddr);
  	if (ret == 0) {
  		const char __user *end = uaddr + size - 1;
  
  		if (((unsigned long)uaddr & PAGE_MASK) !=
  				((unsigned long)end & PAGE_MASK)) {
  			ret = __get_user(c, end);
  			(void)c;
  		}
  	}
  	return ret;
  }
  
  /*
   * Multipage variants of the above prefault helpers, useful if more than
   * PAGE_SIZE of data needs to be prefaulted. These are separate from the above
   * functions (which only handle up to PAGE_SIZE) to avoid clobbering the
   * filemap.c hotpaths.
   */
  static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
  {
  	int ret = 0;
  	char __user *end = uaddr + size - 1;
  
  	if (unlikely(size == 0))
  		return ret;
  
  	/*
  	 * Writing zeroes into userspace here is OK, because we know that if
  	 * the zero gets there, we'll be overwriting it.
  	 */
  	while (uaddr <= end) {
  		ret = __put_user(0, uaddr);
  		if (ret != 0)
  			return ret;
  		uaddr += PAGE_SIZE;
  	}
  
  	/* Check whether the range spilled into the next page. */
  	if (((unsigned long)uaddr & PAGE_MASK) ==
  			((unsigned long)end & PAGE_MASK))
  		ret = __put_user(0, end);
  
  	return ret;
  }
  
  static inline int fault_in_multipages_readable(const char __user *uaddr,
  					       int size)
  {
  	volatile char c;
  	int ret = 0;
  	const char __user *end = uaddr + size - 1;
  
  	if (unlikely(size == 0))
  		return ret;
  
  	while (uaddr <= end) {
  		ret = __get_user(c, uaddr);
  		if (ret != 0)
  			return ret;
  		uaddr += PAGE_SIZE;
  	}
  
  	/* Check whether the range spilled into the next page. */
  	if (((unsigned long)uaddr & PAGE_MASK) ==
  			((unsigned long)end & PAGE_MASK)) {
  		ret = __get_user(c, end);
  		(void)c;
  	}
  
  	return ret;
  }
  
  int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
  				pgoff_t index, gfp_t gfp_mask);
  int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
  				pgoff_t index, gfp_t gfp_mask);
  extern void delete_from_page_cache(struct page *page);
  extern void __delete_from_page_cache(struct page *page);
  int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask);
  
  /*
   * Like add_to_page_cache_locked, but used to add newly allocated pages:
   * the page is new, so we can just run __set_page_locked() against it.
   */
  static inline int add_to_page_cache(struct page *page,
  		struct address_space *mapping, pgoff_t offset, gfp_t gfp_mask)
  {
  	int error;
  
  	__set_page_locked(page);
  	error = add_to_page_cache_locked(page, mapping, offset, gfp_mask);
  	if (unlikely(error))
  		__clear_page_locked(page);
  	return error;
  }
  
  #endif /* _LINUX_PAGEMAP_H */