/*
   * mm/truncate.c - code for taking down pages from address_spaces
   *
   * Copyright (C) 2002, Linus Torvalds
   *
   * 10Sep2002	akpm@zip.com.au
   *		Initial version.
   */
  
  #include <linux/kernel.h>
  #include <linux/mm.h>

  #include <linux/swap.h>

  #include <linux/module.h>
  #include <linux/pagemap.h>
  #include <linux/pagevec.h>
  #include <linux/buffer_head.h>	/* grr. try_to_release_page,

  				   do_invalidatepage */

  /**
   * do_invalidatepage - invalidate part of all of a page
   * @page: the page which is affected
   * @offset: the index of the truncation point
   *
   * do_invalidatepage() is called when all or part of the page has become
   * invalidated by a truncate operation.
   *
   * do_invalidatepage() does not have to release all buffers, but it must
   * ensure that no dirty buffer is left outside @offset and that no I/O
   * is underway against any of the blocks which are outside the truncation
   * point.  Because the caller is about to free (and possibly reuse) those
   * blocks on-disk.
   */
  void do_invalidatepage(struct page *page, unsigned long offset)
  {
  	void (*invalidatepage)(struct page *, unsigned long);
  	invalidatepage = page->mapping->a_ops->invalidatepage;

  #ifdef CONFIG_BLOCK

  	if (!invalidatepage)
  		invalidatepage = block_invalidatepage;

  #endif

  	if (invalidatepage)
  		(*invalidatepage)(page, offset);
  }

  static inline void truncate_partial_page(struct page *page, unsigned partial)
  {
  	memclear_highpage_flush(page, partial, PAGE_CACHE_SIZE-partial);
  	if (PagePrivate(page))
  		do_invalidatepage(page, partial);
  }
  
  /*
   * If truncate cannot remove the fs-private metadata from the page, the page
   * becomes anonymous.  It will be left on the LRU and may even be mapped into
   * user pagetables if we're racing with filemap_nopage().
   *
   * We need to bale out if page->mapping is no longer equal to the original
   * mapping.  This happens a) when the VM reclaimed the page while we waited on
   * its lock, b) when a concurrent invalidate_inode_pages got there first and
   * c) when tmpfs swizzles a page between a tmpfs inode and swapper_space.
   */
  static void
  truncate_complete_page(struct address_space *mapping, struct page *page)
  {
  	if (page->mapping != mapping)
  		return;
  
  	if (PagePrivate(page))
  		do_invalidatepage(page, 0);
  
  	clear_page_dirty(page);
  	ClearPageUptodate(page);
  	ClearPageMappedToDisk(page);
  	remove_from_page_cache(page);
  	page_cache_release(page);	/* pagecache ref */
  }
  
  /*
   * This is for invalidate_inode_pages().  That function can be called at
   * any time, and is not supposed to throw away dirty pages.  But pages can

   * be marked dirty at any time too, so use remove_mapping which safely
   * discards clean, unused pages.

   *
   * Returns non-zero if the page was successfully invalidated.
   */
  static int
  invalidate_complete_page(struct address_space *mapping, struct page *page)
  {

  	int ret;

  	if (page->mapping != mapping)
  		return 0;
  
  	if (PagePrivate(page) && !try_to_release_page(page, 0))
  		return 0;

  	ret = remove_mapping(mapping, page);

  
  	return ret;

  }
  
  /**

   * truncate_inode_pages - truncate range of pages specified by start and
   * end byte offsets

   * @mapping: mapping to truncate
   * @lstart: offset from which to truncate

   * @lend: offset to which to truncate

   *

   * Truncate the page cache, removing the pages that are between
   * specified offsets (and zeroing out partial page
   * (if lstart is not page aligned)).

   *
   * Truncate takes two passes - the first pass is nonblocking.  It will not
   * block on page locks and it will not block on writeback.  The second pass
   * will wait.  This is to prevent as much IO as possible in the affected region.
   * The first pass will remove most pages, so the search cost of the second pass
   * is low.
   *
   * When looking at page->index outside the page lock we need to be careful to
   * copy it into a local to avoid races (it could change at any time).
   *
   * We pass down the cache-hot hint to the page freeing code.  Even if the
   * mapping is large, it is probably the case that the final pages are the most
   * recently touched, and freeing happens in ascending file offset order.

   */

  void truncate_inode_pages_range(struct address_space *mapping,
  				loff_t lstart, loff_t lend)

  {
  	const pgoff_t start = (lstart + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;

  	pgoff_t end;

  	const unsigned partial = lstart & (PAGE_CACHE_SIZE - 1);
  	struct pagevec pvec;
  	pgoff_t next;
  	int i;
  
  	if (mapping->nrpages == 0)
  		return;

  	BUG_ON((lend & (PAGE_CACHE_SIZE - 1)) != (PAGE_CACHE_SIZE - 1));
  	end = (lend >> PAGE_CACHE_SHIFT);

  	pagevec_init(&pvec, 0);
  	next = start;

  	while (next <= end &&
  	       pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {

  		for (i = 0; i < pagevec_count(&pvec); i++) {
  			struct page *page = pvec.pages[i];
  			pgoff_t page_index = page->index;

  			if (page_index > end) {
  				next = page_index;
  				break;
  			}

  			if (page_index > next)
  				next = page_index;
  			next++;
  			if (TestSetPageLocked(page))
  				continue;
  			if (PageWriteback(page)) {
  				unlock_page(page);
  				continue;
  			}
  			truncate_complete_page(mapping, page);
  			unlock_page(page);
  		}
  		pagevec_release(&pvec);
  		cond_resched();
  	}
  
  	if (partial) {
  		struct page *page = find_lock_page(mapping, start - 1);
  		if (page) {
  			wait_on_page_writeback(page);
  			truncate_partial_page(page, partial);
  			unlock_page(page);
  			page_cache_release(page);
  		}
  	}
  
  	next = start;
  	for ( ; ; ) {
  		cond_resched();
  		if (!pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
  			if (next == start)
  				break;
  			next = start;
  			continue;
  		}

  		if (pvec.pages[0]->index > end) {
  			pagevec_release(&pvec);
  			break;
  		}

  		for (i = 0; i < pagevec_count(&pvec); i++) {
  			struct page *page = pvec.pages[i];

  			if (page->index > end)
  				break;

  			lock_page(page);
  			wait_on_page_writeback(page);
  			if (page->index > next)
  				next = page->index;
  			next++;
  			truncate_complete_page(mapping, page);
  			unlock_page(page);
  		}
  		pagevec_release(&pvec);
  	}
  }

  EXPORT_SYMBOL(truncate_inode_pages_range);

  /**
   * truncate_inode_pages - truncate *all* the pages from an offset
   * @mapping: mapping to truncate
   * @lstart: offset from which to truncate
   *

   * Called under (and serialised by) inode->i_mutex.

   */
  void truncate_inode_pages(struct address_space *mapping, loff_t lstart)
  {
  	truncate_inode_pages_range(mapping, lstart, (loff_t)-1);
  }

  EXPORT_SYMBOL(truncate_inode_pages);
  
  /**
   * invalidate_mapping_pages - Invalidate all the unlocked pages of one inode
   * @mapping: the address_space which holds the pages to invalidate
   * @start: the offset 'from' which to invalidate
   * @end: the offset 'to' which to invalidate (inclusive)
   *
   * This function only removes the unlocked pages, if you want to
   * remove all the pages of one inode, you must call truncate_inode_pages.
   *
   * invalidate_mapping_pages() will not block on IO activity. It will not
   * invalidate pages which are dirty, locked, under writeback or mapped into
   * pagetables.
   */
  unsigned long invalidate_mapping_pages(struct address_space *mapping,
  				pgoff_t start, pgoff_t end)
  {
  	struct pagevec pvec;
  	pgoff_t next = start;
  	unsigned long ret = 0;
  	int i;
  
  	pagevec_init(&pvec, 0);
  	while (next <= end &&
  			pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
  		for (i = 0; i < pagevec_count(&pvec); i++) {
  			struct page *page = pvec.pages[i];

  			pgoff_t index;
  			int lock_failed;

  			lock_failed = TestSetPageLocked(page);
  
  			/*
  			 * We really shouldn't be looking at the ->index of an
  			 * unlocked page.  But we're not allowed to lock these
  			 * pages.  So we rely upon nobody altering the ->index
  			 * of this (pinned-by-us) page.
  			 */
  			index = page->index;
  			if (index > next)
  				next = index;

  			next++;

  			if (lock_failed)
  				continue;

  			if (PageDirty(page) || PageWriteback(page))
  				goto unlock;
  			if (page_mapped(page))
  				goto unlock;
  			ret += invalidate_complete_page(mapping, page);
  unlock:
  			unlock_page(page);
  			if (next > end)
  				break;
  		}
  		pagevec_release(&pvec);

  	}
  	return ret;
  }
  
  unsigned long invalidate_inode_pages(struct address_space *mapping)
  {
  	return invalidate_mapping_pages(mapping, 0, ~0UL);
  }

  EXPORT_SYMBOL(invalidate_inode_pages);

  /*
   * This is like invalidate_complete_page(), except it ignores the page's
   * refcount.  We do this because invalidate_inode_pages2() needs stronger
   * invalidation guarantees, and cannot afford to leave pages behind because
   * shrink_list() has a temp ref on them, or because they're transiently sitting
   * in the lru_cache_add() pagevecs.
   */
  static int
  invalidate_complete_page2(struct address_space *mapping, struct page *page)
  {
  	if (page->mapping != mapping)
  		return 0;

  	if (PagePrivate(page) && !try_to_release_page(page, GFP_KERNEL))

  		return 0;
  
  	write_lock_irq(&mapping->tree_lock);
  	if (PageDirty(page))
  		goto failed;
  
  	BUG_ON(PagePrivate(page));
  	__remove_from_page_cache(page);
  	write_unlock_irq(&mapping->tree_lock);
  	ClearPageUptodate(page);
  	page_cache_release(page);	/* pagecache ref */
  	return 1;
  failed:
  	write_unlock_irq(&mapping->tree_lock);
  	return 0;
  }

  /**
   * invalidate_inode_pages2_range - remove range of pages from an address_space

   * @mapping: the address_space

   * @start: the page offset 'from' which to invalidate
   * @end: the page offset 'to' which to invalidate (inclusive)
   *
   * Any pages which are found to be mapped into pagetables are unmapped prior to
   * invalidation.
   *
   * Returns -EIO if any pages could not be invalidated.
   */
  int invalidate_inode_pages2_range(struct address_space *mapping,
  				  pgoff_t start, pgoff_t end)
  {
  	struct pagevec pvec;
  	pgoff_t next;
  	int i;
  	int ret = 0;
  	int did_range_unmap = 0;
  	int wrapped = 0;
  
  	pagevec_init(&pvec, 0);
  	next = start;
  	while (next <= end && !ret && !wrapped &&
  		pagevec_lookup(&pvec, mapping, next,
  			min(end - next, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
  		for (i = 0; !ret && i < pagevec_count(&pvec); i++) {
  			struct page *page = pvec.pages[i];
  			pgoff_t page_index;
  			int was_dirty;
  
  			lock_page(page);
  			if (page->mapping != mapping) {
  				unlock_page(page);
  				continue;
  			}
  			page_index = page->index;
  			next = page_index + 1;
  			if (next == 0)
  				wrapped = 1;
  			if (page_index > end) {
  				unlock_page(page);
  				break;
  			}
  			wait_on_page_writeback(page);
  			while (page_mapped(page)) {
  				if (!did_range_unmap) {
  					/*
  					 * Zap the rest of the file in one hit.
  					 */
  					unmap_mapping_range(mapping,

  					   (loff_t)page_index<<PAGE_CACHE_SHIFT,
  					   (loff_t)(end - page_index + 1)

  							<< PAGE_CACHE_SHIFT,
  					    0);
  					did_range_unmap = 1;
  				} else {
  					/*
  					 * Just zap this page
  					 */
  					unmap_mapping_range(mapping,

  					  (loff_t)page_index<<PAGE_CACHE_SHIFT,

  					  PAGE_CACHE_SIZE, 0);
  				}
  			}
  			was_dirty = test_clear_page_dirty(page);

  			if (!invalidate_complete_page2(mapping, page)) {

  				if (was_dirty)
  					set_page_dirty(page);
  				ret = -EIO;
  			}
  			unlock_page(page);
  		}
  		pagevec_release(&pvec);
  		cond_resched();
  	}

  	WARN_ON_ONCE(ret);

  	return ret;
  }
  EXPORT_SYMBOL_GPL(invalidate_inode_pages2_range);
  
  /**
   * invalidate_inode_pages2 - remove all pages from an address_space

   * @mapping: the address_space

   *
   * Any pages which are found to be mapped into pagetables are unmapped prior to
   * invalidation.
   *
   * Returns -EIO if any pages could not be invalidated.
   */
  int invalidate_inode_pages2(struct address_space *mapping)
  {
  	return invalidate_inode_pages2_range(mapping, 0, -1);
  }
  EXPORT_SYMBOL_GPL(invalidate_inode_pages2);