/*
   * mm/truncate.c - code for taking down pages from address_spaces
   *
   * Copyright (C) 2002, Linus Torvalds
   *

   * 10Sep2002	Andrew Morton

   *		Initial version.
   */
  
  #include <linux/kernel.h>

  #include <linux/backing-dev.h>

  #include <linux/mm.h>

  #include <linux/swap.h>

  #include <linux/module.h>
  #include <linux/pagemap.h>

  #include <linux/highmem.h>

  #include <linux/pagevec.h>

  #include <linux/task_io_accounting_ops.h>

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

  				   do_invalidatepage */

  #include "internal.h"

  /**

   * do_invalidatepage - invalidate part or 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)
  {

  	zero_user_segment(page, partial, PAGE_CACHE_SIZE);

  	if (page_has_private(page))

  		do_invalidatepage(page, partial);
  }

  /*
   * This cancels just the dirty bit on the kernel page itself, it
   * does NOT actually remove dirty bits on any mmap's that may be
   * around. It also leaves the page tagged dirty, so any sync
   * activity will still find it on the dirty lists, and in particular,
   * clear_page_dirty_for_io() will still look at the dirty bits in
   * the VM.
   *
   * Doing this should *normally* only ever be done when a page
   * is truncated, and is not actually mapped anywhere at all. However,
   * fs/buffer.c does this when it notices that somebody has cleaned
   * out all the buffers on a page without actually doing it through
   * the VM. Can you say "ext3 is horribly ugly"? Tought you could.
   */

  void cancel_dirty_page(struct page *page, unsigned int account_size)
  {

  	if (TestClearPageDirty(page)) {
  		struct address_space *mapping = page->mapping;
  		if (mapping && mapping_cap_account_dirty(mapping)) {
  			dec_zone_page_state(page, NR_FILE_DIRTY);

  			dec_bdi_stat(mapping->backing_dev_info,
  					BDI_RECLAIMABLE);

  			if (account_size)
  				task_io_account_cancelled_write(account_size);
  		}

  	}

  }

  EXPORT_SYMBOL(cancel_dirty_page);

  /*
   * If truncate cannot remove the fs-private metadata from the page, the page

   * becomes orphaned.  It will be left on the LRU and may even be mapped into

   * user pagetables if we're racing with filemap_fault().

   *
   * 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_mapping_pages got there first and

   * c) when tmpfs swizzles a page between a tmpfs inode and swapper_space.
   */

  static int

  truncate_complete_page(struct address_space *mapping, struct page *page)
  {
  	if (page->mapping != mapping)

  		return -EIO;

  	if (page_has_private(page))

  		do_invalidatepage(page, 0);

  	cancel_dirty_page(page, PAGE_CACHE_SIZE);

  	clear_page_mlock(page);

  	remove_from_page_cache(page);

  	ClearPageMappedToDisk(page);

  	page_cache_release(page);	/* pagecache ref */

  	return 0;

  }
  
  /*

   * This is for invalidate_mapping_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 (page_has_private(page) && !try_to_release_page(page, 0))

  		return 0;

  	clear_page_mlock(page);

  	ret = remove_mapping(mapping, page);

  
  	return ret;

  }

  int truncate_inode_page(struct address_space *mapping, struct page *page)
  {
  	if (page_mapped(page)) {
  		unmap_mapping_range(mapping,
  				   (loff_t)page->index << PAGE_CACHE_SHIFT,
  				   PAGE_CACHE_SIZE, 0);
  	}
  	return truncate_complete_page(mapping, page);
  }

  /*

   * Used to get rid of pages on hardware memory corruption.
   */
  int generic_error_remove_page(struct address_space *mapping, struct page *page)
  {
  	if (!mapping)
  		return -EINVAL;
  	/*
  	 * Only punch for normal data pages for now.
  	 * Handling other types like directories would need more auditing.
  	 */
  	if (!S_ISREG(mapping->host->i_mode))
  		return -EIO;
  	return truncate_inode_page(mapping, page);
  }
  EXPORT_SYMBOL(generic_error_remove_page);
  
  /*

   * Safely invalidate one page from its pagecache mapping.
   * It only drops clean, unused pages. The page must be locked.
   *
   * Returns 1 if the page is successfully invalidated, otherwise 0.
   */
  int invalidate_inode_page(struct page *page)
  {
  	struct address_space *mapping = page_mapping(page);
  	if (!mapping)
  		return 0;
  	if (PageDirty(page) || PageWriteback(page))
  		return 0;
  	if (page_mapped(page))
  		return 0;
  	return invalidate_complete_page(mapping, page);
  }

  /**

   * truncate_inode_pages - truncate range of pages specified by start & 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 (!trylock_page(page))

  				continue;
  			if (PageWriteback(page)) {
  				unlock_page(page);
  				continue;
  			}

  			truncate_inode_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);

  			truncate_inode_page(mapping, page);

  			if (page->index > next)
  				next = page->index;
  			next++;

  			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 = !trylock_page(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;

  			ret += invalidate_inode_page(page);

  			unlock_page(page);
  			if (next > end)
  				break;
  		}
  		pagevec_release(&pvec);

  		cond_resched();

  	}
  	return ret;
  }

  EXPORT_SYMBOL(invalidate_mapping_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_page_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 (page_has_private(page) && !try_to_release_page(page, GFP_KERNEL))

  		return 0;

  	spin_lock_irq(&mapping->tree_lock);

  	if (PageDirty(page))
  		goto failed;

  	clear_page_mlock(page);

  	BUG_ON(page_has_private(page));

  	__remove_from_page_cache(page);

  	spin_unlock_irq(&mapping->tree_lock);

  	mem_cgroup_uncharge_cache_page(page);

  	page_cache_release(page);	/* pagecache ref */
  	return 1;
  failed:

  	spin_unlock_irq(&mapping->tree_lock);

  	return 0;
  }

  static int do_launder_page(struct address_space *mapping, struct page *page)
  {
  	if (!PageDirty(page))
  		return 0;
  	if (page->mapping != mapping || mapping->a_ops->launder_page == NULL)
  		return 0;
  	return mapping->a_ops->launder_page(page);
  }

  /**
   * 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 -EBUSY 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 ret2 = 0;

  	int did_range_unmap = 0;
  	int wrapped = 0;
  
  	pagevec_init(&pvec, 0);
  	next = start;

  	while (next <= end && !wrapped &&

  		pagevec_lookup(&pvec, mapping, next,
  			min(end - next, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {

  		for (i = 0; i < pagevec_count(&pvec); i++) {

  			struct page *page = pvec.pages[i];
  			pgoff_t page_index;

  
  			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);

  			if (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);
  				}
  			}

  			BUG_ON(page_mapped(page));

  			ret2 = do_launder_page(mapping, page);
  			if (ret2 == 0) {
  				if (!invalidate_complete_page2(mapping, page))

  					ret2 = -EBUSY;

  			}
  			if (ret2 < 0)
  				ret = ret2;

  			unlock_page(page);
  		}
  		pagevec_release(&pvec);
  		cond_resched();
  	}
  	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);

  
  /**
   * truncate_pagecache - unmap and remove pagecache that has been truncated
   * @inode: inode
   * @old: old file offset
   * @new: new file offset
   *
   * inode's new i_size must already be written before truncate_pagecache
   * is called.
   *
   * This function should typically be called before the filesystem
   * releases resources associated with the freed range (eg. deallocates
   * blocks). This way, pagecache will always stay logically coherent
   * with on-disk format, and the filesystem would not have to deal with
   * situations such as writepage being called for a page that has already
   * had its underlying blocks deallocated.
   */
  void truncate_pagecache(struct inode *inode, loff_t old, loff_t new)
  {
  	if (new < old) {
  		struct address_space *mapping = inode->i_mapping;
  
  		/*
  		 * unmap_mapping_range is called twice, first simply for
  		 * efficiency so that truncate_inode_pages does fewer
  		 * single-page unmaps.  However after this first call, and
  		 * before truncate_inode_pages finishes, it is possible for
  		 * private pages to be COWed, which remain after
  		 * truncate_inode_pages finishes, hence the second
  		 * unmap_mapping_range call must be made for correctness.
  		 */
  		unmap_mapping_range(mapping, new + PAGE_SIZE - 1, 0, 1);
  		truncate_inode_pages(mapping, new);
  		unmap_mapping_range(mapping, new + PAGE_SIZE - 1, 0, 1);
  	}
  }
  EXPORT_SYMBOL(truncate_pagecache);
  
  /**
   * vmtruncate - unmap mappings "freed" by truncate() syscall
   * @inode: inode of the file used
   * @offset: file offset to start truncating
   *
   * NOTE! We have to be ready to update the memory sharing
   * between the file and the memory map for a potential last
   * incomplete page.  Ugly, but necessary.
   */
  int vmtruncate(struct inode *inode, loff_t offset)
  {
  	loff_t oldsize;
  	int error;
  
  	error = inode_newsize_ok(inode, offset);
  	if (error)
  		return error;
  	oldsize = inode->i_size;
  	i_size_write(inode, offset);
  	truncate_pagecache(inode, oldsize, offset);
  	if (inode->i_op->truncate)
  		inode->i_op->truncate(inode);
  
  	return error;
  }
  EXPORT_SYMBOL(vmtruncate);