text: /*
   *	linux/mm/filemap.c
   *
   * Copyright (C) 1994-1999  Linus Torvalds
   */
  
  /*
   * This file handles the generic file mmap semantics used by
   * most "normal" filesystems (but you don't /have/ to use this:
   * the NFS filesystem used to do this differently, for example)
   */
  #include <linux/config.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/compiler.h>
  #include <linux/fs.h>
  #include <linux/aio.h>
  #include <linux/capability.h>
  #include <linux/kernel_stat.h>
  #include <linux/mm.h>
  #include <linux/swap.h>
  #include <linux/mman.h>
  #include <linux/pagemap.h>
  #include <linux/file.h>
  #include <linux/uio.h>
  #include <linux/hash.h>
  #include <linux/writeback.h>
  #include <linux/pagevec.h>
  #include <linux/blkdev.h>
  #include <linux/security.h>
  #include <linux/syscalls.h>
  #include "filemap.h"
  /*
   * FIXME: remove all knowledge of the buffer layer from the core VM
   */
  #include <linux/buffer_head.h> /* for generic_osync_inode */
  
  #include <asm/uaccess.h>
  #include <asm/mman.h>
  
  static ssize_t
  generic_file_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
  	loff_t offset, unsigned long nr_segs);
  
  /*
   * Shared mappings implemented 30.11.1994. It's not fully working yet,
   * though.
   *
   * Shared mappings now work. 15.8.1995  Bruno.
   *
   * finished 'unifying' the page and buffer cache and SMP-threaded the
   * page-cache, 21.05.1999, Ingo Molnar <mingo@redhat.com>
   *
   * SMP-threaded pagemap-LRU 1999, Andrea Arcangeli <andrea@suse.de>
   */
  
  /*
   * Lock ordering:
   *
   *  ->i_mmap_lock		(vmtruncate)
   *    ->private_lock		(__free_pte->__set_page_dirty_buffers)
   *      ->swap_lock		(exclusive_swap_page, others)
   *        ->mapping->tree_lock
   *
   *  ->i_mutex
   *    ->i_mmap_lock		(truncate->unmap_mapping_range)
   *
   *  ->mmap_sem
   *    ->i_mmap_lock
   *      ->page_table_lock or pte_lock	(various, mainly in memory.c)
   *        ->mapping->tree_lock	(arch-dependent flush_dcache_mmap_lock)
   *
   *  ->mmap_sem
   *    ->lock_page		(access_process_vm)
   *
   *  ->mmap_sem
   *    ->i_mutex			(msync)
   *
   *  ->i_mutex
   *    ->i_alloc_sem             (various)
   *
   *  ->inode_lock
   *    ->sb_lock			(fs/fs-writeback.c)
   *    ->mapping->tree_lock	(__sync_single_inode)
   *
   *  ->i_mmap_lock
   *    ->anon_vma.lock		(vma_adjust)
   *
   *  ->anon_vma.lock
   *    ->page_table_lock or pte_lock	(anon_vma_prepare and various)
   *
   *  ->page_table_lock or pte_lock
   *    ->swap_lock		(try_to_unmap_one)
   *    ->private_lock		(try_to_unmap_one)
   *    ->tree_lock		(try_to_unmap_one)
   *    ->zone.lru_lock		(follow_page->mark_page_accessed)
   *    ->zone.lru_lock		(check_pte_range->isolate_lru_page)
   *    ->private_lock		(page_remove_rmap->set_page_dirty)
   *    ->tree_lock		(page_remove_rmap->set_page_dirty)
   *    ->inode_lock		(page_remove_rmap->set_page_dirty)
   *    ->inode_lock		(zap_pte_range->set_page_dirty)
   *    ->private_lock		(zap_pte_range->__set_page_dirty_buffers)
   *
   *  ->task->proc_lock
   *    ->dcache_lock		(proc_pid_lookup)
   */
  
  /*
   * Remove a page from the page cache and free it. Caller has to make
   * sure the page is locked and that nobody else uses it - or that usage
   * is safe.  The caller must hold a write_lock on the mapping's tree_lock.
   */
  void __remove_from_page_cache(struct page *page)
  {
  	struct address_space *mapping = page->mapping;
  
  	radix_tree_delete(&mapping->page_tree, page->index);
  	page->mapping = NULL;
  	mapping->nrpages--;
  	pagecache_acct(-1);
  }
  
  void remove_from_page_cache(struct page *page)
  {
  	struct address_space *mapping = page->mapping;
  
  	BUG_ON(!PageLocked(page));
  
  	write_lock_irq(&mapping->tree_lock);
  	__remove_from_page_cache(page);
  	write_unlock_irq(&mapping->tree_lock);
  }
  
  static int sync_page(void *word)
  {
  	struct address_space *mapping;
  	struct page *page;
  
  	page = container_of((unsigned long *)word, struct page, flags);
  
  	/*
  	 * page_mapping() is being called without PG_locked held.
  	 * Some knowledge of the state and use of the page is used to
  	 * reduce the requirements down to a memory barrier.
  	 * The danger here is of a stale page_mapping() return value
  	 * indicating a struct address_space different from the one it's
  	 * associated with when it is associated with one.
  	 * After smp_mb(), it's either the correct page_mapping() for
  	 * the page, or an old page_mapping() and the page's own
  	 * page_mapping() has gone NULL.
  	 * The ->sync_page() address_space operation must tolerate
  	 * page_mapping() going NULL. By an amazing coincidence,
  	 * this comes about because none of the users of the page
  	 * in the ->sync_page() methods make essential use of the
  	 * page_mapping(), merely passing the page down to the backing
  	 * device's unplug functions when it's non-NULL, which in turn
  	 * ignore it for all cases but swap, where only page_private(page) is
  	 * of interest. When page_mapping() does go NULL, the entire
  	 * call stack gracefully ignores the page and returns.
  	 * -- wli
  	 */
  	smp_mb();
  	mapping = page_mapping(page);
  	if (mapping && mapping->a_ops && mapping->a_ops->sync_page)
  		mapping->a_ops->sync_page(page);
  	io_schedule();
  	return 0;
  }
  
  /**
   * filemap_fdatawrite_range - start writeback against all of a mapping's
   * dirty pages that lie within the byte offsets <start, end>
   * @mapping:	address space structure to write
   * @start:	offset in bytes where the range starts
   * @end:	offset in bytes where the range ends
   * @sync_mode:	enable synchronous operation
   *
   * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
   * opposed to a regular memory * cleansing writeback.  The difference between
   * these two operations is that if a dirty page/buffer is encountered, it must
   * be waited upon, and not just skipped over.
   */
  static int __filemap_fdatawrite_range(struct address_space *mapping,
  	loff_t start, loff_t end, int sync_mode)
  {
  	int ret;
  	struct writeback_control wbc = {
  		.sync_mode = sync_mode,
  		.nr_to_write = mapping->nrpages * 2,
  		.start = start,
  		.end = end,
  	};
  
  	if (!mapping_cap_writeback_dirty(mapping))
  		return 0;
  
  	ret = do_writepages(mapping, &wbc);
  	return ret;
  }
  
  static inline int __filemap_fdatawrite(struct address_space *mapping,
  	int sync_mode)
  {
  	return __filemap_fdatawrite_range(mapping, 0, 0, sync_mode);
  }
  
  int filemap_fdatawrite(struct address_space *mapping)
  {
  	return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
  }
  EXPORT_SYMBOL(filemap_fdatawrite);
  
  static int filemap_fdatawrite_range(struct address_space *mapping,
  	loff_t start, loff_t end)
  {
  	return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_ALL);
  }
  
  /*
   * This is a mostly non-blocking flush.  Not suitable for data-integrity
   * purposes - I/O may not be started against all dirty pages.
   */
  int filemap_flush(struct address_space *mapping)
  {
  	return __filemap_fdatawrite(mapping, WB_SYNC_NONE);
  }
  EXPORT_SYMBOL(filemap_flush);
  
  /*
   * Wait for writeback to complete against pages indexed by start->end
   * inclusive
   */
  static int wait_on_page_writeback_range(struct address_space *mapping,
  				pgoff_t start, pgoff_t end)
  {
  	struct pagevec pvec;
  	int nr_pages;
  	int ret = 0;
  	pgoff_t index;
  
  	if (end < start)
  		return 0;
  
  	pagevec_init(&pvec, 0);
  	index = start;
  	while ((index <= end) &&
  			(nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
  			PAGECACHE_TAG_WRITEBACK,
  			min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1)) != 0) {
  		unsigned i;
  
  		for (i = 0; i < nr_pages; i++) {
  			struct page *page = pvec.pages[i];
  
  			/* until radix tree lookup accepts end_index */
  			if (page->index > end)
  				continue;
  
  			wait_on_page_writeback(page);
  			if (PageError(page))
  				ret = -EIO;
  		}
  		pagevec_release(&pvec);
  		cond_resched();
  	}
  
  	/* Check for outstanding write errors */
  	if (test_and_clear_bit(AS_ENOSPC, &mapping->flags))
  		ret = -ENOSPC;
  	if (test_and_clear_bit(AS_EIO, &mapping->flags))
  		ret = -EIO;
  
  	return ret;
  }
  
  /*
   * Write and wait upon all the pages in the passed range.  This is a "data
   * integrity" operation.  It waits upon in-flight writeout before starting and
   * waiting upon new writeout.  If there was an IO error, return it.
   *
   * We need to re-take i_mutex during the generic_osync_inode list walk because
   * it is otherwise livelockable.
   */
  int sync_page_range(struct inode *inode, struct address_space *mapping,
  			loff_t pos, loff_t count)
  {
  	pgoff_t start = pos >> PAGE_CACHE_SHIFT;
  	pgoff_t end = (pos + count - 1) >> PAGE_CACHE_SHIFT;
  	int ret;
  
  	if (!mapping_cap_writeback_dirty(mapping) || !count)
  		return 0;
  	ret = filemap_fdatawrite_range(mapping, pos, pos + count - 1);
  	if (ret == 0) {
  		mutex_lock(&inode->i_mutex);
  		ret = generic_osync_inode(inode, mapping, OSYNC_METADATA);
  		mutex_unlock(&inode->i_mutex);
  	}
  	if (ret == 0)
  		ret = wait_on_page_writeback_range(mapping, start, end);
  	return ret;
  }
  EXPORT_SYMBOL(sync_page_range);
  
  /*
   * Note: Holding i_mutex across sync_page_range_nolock is not a good idea
   * as it forces O_SYNC writers to different parts of the same file
   * to be serialised right until io completion.
   */
  int sync_page_range_nolock(struct inode *inode, struct address_space *mapping,
  			   loff_t pos, loff_t count)
  {
  	pgoff_t start = pos >> PAGE_CACHE_SHIFT;
  	pgoff_t end = (pos + count - 1) >> PAGE_CACHE_SHIFT;
  	int ret;
  
  	if (!mapping_cap_writeback_dirty(mapping) || !count)
  		return 0;
  	ret = filemap_fdatawrite_range(mapping, pos, pos + count - 1);
  	if (ret == 0)
  		ret = generic_osync_inode(inode, mapping, OSYNC_METADATA);
  	if (ret == 0)
  		ret = wait_on_page_writeback_range(mapping, start, end);
  	return ret;
  }
  EXPORT_SYMBOL(sync_page_range_nolock);
  
  /**
   * filemap_fdatawait - walk the list of under-writeback pages of the given
   *     address space and wait for all of them.
   *
   * @mapping: address space structure to wait for
   */
  int filemap_fdatawait(struct address_space *mapping)
  {
  	loff_t i_size = i_size_read(mapping->host);
  
  	if (i_size == 0)
  		return 0;
  
  	return wait_on_page_writeback_range(mapping, 0,
  				(i_size - 1) >> PAGE_CACHE_SHIFT);
  }
  EXPORT_SYMBOL(filemap_fdatawait);
  
  int filemap_write_and_wait(struct address_space *mapping)
  {
  	int err = 0;
  
  	if (mapping->nrpages) {
  		err = filemap_fdatawrite(mapping);
  		/*
  		 * Even if the above returned error, the pages may be
  		 * written partially (e.g. -ENOSPC), so we wait for it.
  		 * But the -EIO is special case, it may indicate the worst
  		 * thing (e.g. bug) happened, so we avoid waiting for it.
  		 */
  		if (err != -EIO) {
  			int err2 = filemap_fdatawait(mapping);
  			if (!err)
  				err = err2;
  		}
  	}
  	return err;
  }
  EXPORT_SYMBOL(filemap_write_and_wait);
  
  int filemap_write_and_wait_range(struct address_space *mapping,
  				 loff_t lstart, loff_t lend)
  {
  	int err = 0;
  
  	if (mapping->nrpages) {
  		err = __filemap_fdatawrite_range(mapping, lstart, lend,
  						 WB_SYNC_ALL);
  		/* See comment of filemap_write_and_wait() */
  		if (err != -EIO) {
  			int err2 = wait_on_page_writeback_range(mapping,
  						lstart >> PAGE_CACHE_SHIFT,
  						lend >> PAGE_CACHE_SHIFT);
  			if (!err)
  				err = err2;
  		}
  	}
  	return err;
  }
  
  /*
   * This function is used to add newly allocated pagecache pages:
   * the page is new, so we can just run SetPageLocked() against it.
   * The other page state flags were set by rmqueue().
   *
   * This function does not add the page to the LRU.  The caller must do that.
   */
  int add_to_page_cache(struct page *page, struct address_space *mapping,
  		pgoff_t offset, gfp_t gfp_mask)
  {
  	int error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
  
  	if (error == 0) {
  		write_lock_irq(&mapping->tree_lock);
  		error = radix_tree_insert(&mapping->page_tree, offset, page);
  		if (!error) {
  			page_cache_get(page);
  			SetPageLocked(page);
  			page->mapping = mapping;
  			page->index = offset;
  			mapping->nrpages++;
  			pagecache_acct(1);
  		}
  		write_unlock_irq(&mapping->tree_lock);
  		radix_tree_preload_end();
  	}
  	return error;
  }
  
  EXPORT_SYMBOL(add_to_page_cache);
  
  int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
  				pgoff_t offset, gfp_t gfp_mask)
  {
  	int ret = add_to_page_cache(page, mapping, offset, gfp_mask);
  	if (ret == 0)
  		lru_cache_add(page);
  	return ret;
  }
  
  /*
   * In order to wait for pages to become available there must be
   * waitqueues associated with pages. By using a hash table of
   * waitqueues where the bucket discipline is to maintain all
   * waiters on the same queue and wake all when any of the pages
   * become available, and for the woken contexts to check to be
   * sure the appropriate page became available, this saves space
   * at a cost of "thundering herd" phenomena during rare hash
   * collisions.
   */
  static wait_queue_head_t *page_waitqueue(struct page *page)
  {
  	const struct zone *zone = page_zone(page);
  
  	return &zone->wait_table[hash_ptr(page, zone->wait_table_bits)];
  }
  
  static inline void wake_up_page(struct page *page, int bit)
  {
  	__wake_up_bit(page_waitqueue(page), &page->flags, bit);
  }
  
  void fastcall wait_on_page_bit(struct page *page, int bit_nr)
  {
  	DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
  
  	if (test_bit(bit_nr, &page->flags))
  		__wait_on_bit(page_waitqueue(page), &wait, sync_page,
  							TASK_UNINTERRUPTIBLE);
  }
  EXPORT_SYMBOL(wait_on_page_bit);
  
  /**
   * unlock_page() - unlock a locked page
   *
   * @page: the page
   *
   * Unlocks the page and wakes up sleepers in ___wait_on_page_locked().
   * Also wakes sleepers in wait_on_page_writeback() because the wakeup
   * mechananism between PageLocked pages and PageWriteback pages is shared.
   * But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
   *
   * The first mb is necessary to safely close the critical section opened by the
   * TestSetPageLocked(), the second mb is necessary to enforce ordering between
   * the clear_bit and the read of the waitqueue (to avoid SMP races with a
   * parallel wait_on_page_locked()).
   */
  void fastcall unlock_page(struct page *page)
  {
  	smp_mb__before_clear_bit();
  	if (!TestClearPageLocked(page))
  		BUG();
  	smp_mb__after_clear_bit(); 
  	wake_up_page(page, PG_locked);
  }
  EXPORT_SYMBOL(unlock_page);
  
  /*
   * End writeback against a page.
   */
  void end_page_writeback(struct page *page)
  {
  	if (!TestClearPageReclaim(page) || rotate_reclaimable_page(page)) {
  		if (!test_clear_page_writeback(page))
  			BUG();
  	}
  	smp_mb__after_clear_bit();
  	wake_up_page(page, PG_writeback);
  }
  EXPORT_SYMBOL(end_page_writeback);
  
  /*
   * Get a lock on the page, assuming we need to sleep to get it.
   *
   * Ugly: running sync_page() in state TASK_UNINTERRUPTIBLE is scary.  If some
   * random driver's requestfn sets TASK_RUNNING, we could busywait.  However
   * chances are that on the second loop, the block layer's plug list is empty,
   * so sync_page() will then return in state TASK_UNINTERRUPTIBLE.
   */
  void fastcall __lock_page(struct page *page)
  {
  	DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
  
  	__wait_on_bit_lock(page_waitqueue(page), &wait, sync_page,
  							TASK_UNINTERRUPTIBLE);
  }
  EXPORT_SYMBOL(__lock_page);
  
  /*
   * a rather lightweight function, finding and getting a reference to a
   * hashed page atomically.
   */
  struct page * find_get_page(struct address_space *mapping, unsigned long offset)
  {
  	struct page *page;
  
  	read_lock_irq(&mapping->tree_lock);
  	page = radix_tree_lookup(&mapping->page_tree, offset);
  	if (page)
  		page_cache_get(page);
  	read_unlock_irq(&mapping->tree_lock);
  	return page;
  }
  
  EXPORT_SYMBOL(find_get_page);
  
  /*
   * Same as above, but trylock it instead of incrementing the count.
   */
  struct page *find_trylock_page(struct address_space *mapping, unsigned long offset)
  {
  	struct page *page;
  
  	read_lock_irq(&mapping->tree_lock);
  	page = radix_tree_lookup(&mapping->page_tree, offset);
  	if (page && TestSetPageLocked(page))
  		page = NULL;
  	read_unlock_irq(&mapping->tree_lock);
  	return page;
  }
  
  EXPORT_SYMBOL(find_trylock_page);
  
  /**
   * find_lock_page - locate, pin and lock a pagecache page
   *
   * @mapping: the address_space to search
   * @offset: the page index
   *
   * Locates the desired pagecache page, locks it, increments its reference
   * count and returns its address.
   *
   * Returns zero if the page was not present. find_lock_page() may sleep.
   */
  struct page *find_lock_page(struct address_space *mapping,
  				unsigned long offset)
  {
  	struct page *page;
  
  	read_lock_irq(&mapping->tree_lock);
  repeat:
  	page = radix_tree_lookup(&mapping->page_tree, offset);
  	if (page) {
  		page_cache_get(page);
  		if (TestSetPageLocked(page)) {
  			read_unlock_irq(&mapping->tree_lock);
  			__lock_page(page);
  			read_lock_irq(&mapping->tree_lock);
  
  			/* Has the page been truncated while we slept? */
  			if (unlikely(page->mapping != mapping ||
  				     page->index != offset)) {
  				unlock_page(page);
  				page_cache_release(page);
  				goto repeat;
  			}
  		}
  	}
  	read_unlock_irq(&mapping->tree_lock);
  	return page;
  }
  
  EXPORT_SYMBOL(find_lock_page);
  
  /**
   * find_or_create_page - locate or add a pagecache page
   *
   * @mapping: the page's address_space
   * @index: the page's index into the mapping
   * @gfp_mask: page allocation mode
   *
   * Locates a page in the pagecache.  If the page is not present, a new page
   * is allocated using @gfp_mask and is added to the pagecache and to the VM's
   * LRU list.  The returned page is locked and has its reference count
   * incremented.
   *
   * find_or_create_page() may sleep, even if @gfp_flags specifies an atomic
   * allocation!
   *
   * find_or_create_page() returns the desired page's address, or zero on
   * memory exhaustion.
   */
  struct page *find_or_create_page(struct address_space *mapping,
  		unsigned long index, gfp_t gfp_mask)
  {
  	struct page *page, *cached_page = NULL;
  	int err;
  repeat:
  	page = find_lock_page(mapping, index);
  	if (!page) {
  		if (!cached_page) {
  			cached_page = alloc_page(gfp_mask);
  			if (!cached_page)
  				return NULL;
  		}
  		err = add_to_page_cache_lru(cached_page, mapping,
  					index, gfp_mask);
  		if (!err) {
  			page = cached_page;
  			cached_page = NULL;
  		} else if (err == -EEXIST)
  			goto repeat;
  	}
  	if (cached_page)
  		page_cache_release(cached_page);
  	return page;
  }
  
  EXPORT_SYMBOL(find_or_create_page);
  
  /**
   * find_get_pages - gang pagecache lookup
   * @mapping:	The address_space to search
   * @start:	The starting page index
   * @nr_pages:	The maximum number of pages
   * @pages:	Where the resulting pages are placed
   *
   * find_get_pages() will search for and return a group of up to
   * @nr_pages pages in the mapping.  The pages are placed at @pages.
   * find_get_pages() takes a reference against the returned pages.
   *
   * The search returns a group of mapping-contiguous pages with ascending
   * indexes.  There may be holes in the indices due to not-present pages.
   *
   * find_get_pages() returns the number of pages which were found.
   */
  unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
  			    unsigned int nr_pages, struct page **pages)
  {
  	unsigned int i;
  	unsigned int ret;
  
  	read_lock_irq(&mapping->tree_lock);
  	ret = radix_tree_gang_lookup(&mapping->page_tree,
  				(void **)pages, start, nr_pages);
  	for (i = 0; i < ret; i++)
  		page_cache_get(pages[i]);
  	read_unlock_irq(&mapping->tree_lock);
  	return ret;
  }
  
  /*
   * Like find_get_pages, except we only return pages which are tagged with
   * `tag'.   We update *index to index the next page for the traversal.
   */
  unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
  			int tag, unsigned int nr_pages, struct page **pages)
  {
  	unsigned int i;
  	unsigned int ret;
  
  	read_lock_irq(&mapping->tree_lock);
  	ret = radix_tree_gang_lookup_tag(&mapping->page_tree,
  				(void **)pages, *index, nr_pages, tag);
  	for (i = 0; i < ret; i++)
  		page_cache_get(pages[i]);
  	if (ret)
  		*index = pages[ret - 1]->index + 1;
  	read_unlock_irq(&mapping->tree_lock);
  	return ret;
  }
  
  /*
   * Same as grab_cache_page, but do not wait if the page is unavailable.
   * This is intended for speculative data generators, where the data can
   * be regenerated if the page couldn't be grabbed.  This routine should
   * be safe to call while holding the lock for another page.
   *
   * Clear __GFP_FS when allocating the page to avoid recursion into the fs
   * and deadlock against the caller's locked page.
   */
  struct page *
  grab_cache_page_nowait(struct address_space *mapping, unsigned long index)
  {
  	struct page *page = find_get_page(mapping, index);
  	gfp_t gfp_mask;
  
  	if (page) {
  		if (!TestSetPageLocked(page))
  			return page;
  		page_cache_release(page);
  		return NULL;
  	}
  	gfp_mask = mapping_gfp_mask(mapping) & ~__GFP_FS;
  	page = alloc_pages(gfp_mask, 0);
  	if (page && add_to_page_cache_lru(page, mapping, index, gfp_mask)) {
  		page_cache_release(page);
  		page = NULL;
  	}
  	return page;
  }
  
  EXPORT_SYMBOL(grab_cache_page_nowait);
  
  /*
   * This is a generic file read routine, and uses the
   * mapping->a_ops->readpage() function for the actual low-level
   * stuff.
   *
   * This is really ugly. But the goto's actually try to clarify some
   * of the logic when it comes to error handling etc.
   *
   * Note the struct file* is only passed for the use of readpage.  It may be
   * NULL.
   */
  void do_generic_mapping_read(struct address_space *mapping,
  			     struct file_ra_state *_ra,
  			     struct file *filp,
  			     loff_t *ppos,
  			     read_descriptor_t *desc,
  			     read_actor_t actor)
  {
  	struct inode *inode = mapping->host;
  	unsigned long index;
  	unsigned long end_index;
  	unsigned long offset;
  	unsigned long last_index;
  	unsigned long next_index;
  	unsigned long prev_index;
  	loff_t isize;
  	struct page *cached_page;
  	int error;
  	struct file_ra_state ra = *_ra;
  
  	cached_page = NULL;
  	index = *ppos >> PAGE_CACHE_SHIFT;
  	next_index = index;
  	prev_index = ra.prev_page;
  	last_index = (*ppos + desc->count + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;
  	offset = *ppos & ~PAGE_CACHE_MASK;
  
  	isize = i_size_read(inode);
  	if (!isize)
  		goto out;
  
  	end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
  	for (;;) {
  		struct page *page;
  		unsigned long nr, ret;
  
  		/* nr is the maximum number of bytes to copy from this page */
  		nr = PAGE_CACHE_SIZE;
  		if (index >= end_index) {
  			if (index > end_index)
  				goto out;
  			nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
  			if (nr <= offset) {
  				goto out;
  			}
  		}
  		nr = nr - offset;
  
  		cond_resched();
  		if (index == next_index)
  			next_index = page_cache_readahead(mapping, &ra, filp,
  					index, last_index - index);
  
  find_page:
  		page = find_get_page(mapping, index);
  		if (unlikely(page == NULL)) {
  			handle_ra_miss(mapping, &ra, index);
  			goto no_cached_page;
  		}
  		if (!PageUptodate(page))
  			goto page_not_up_to_date;
  page_ok:
  
  		/* If users can be writing to this page using arbitrary
  		 * virtual addresses, take care about potential aliasing
  		 * before reading the page on the kernel side.
  		 */
  		if (mapping_writably_mapped(mapping))
  			flush_dcache_page(page);
  
  		/*
  		 * When (part of) the same page is read multiple times
  		 * in succession, only mark it as accessed the first time.
  		 */
  		if (prev_index != index)
  			mark_page_accessed(page);
  		prev_index = index;
  
  		/*
  		 * Ok, we have the page, and it's up-to-date, so
  		 * now we can copy it to user space...
  		 *
  		 * The actor routine returns how many bytes were actually used..
  		 * NOTE! This may not be the same as how much of a user buffer
  		 * we filled up (we may be padding etc), so we can only update
  		 * "pos" here (the actor routine has to update the user buffer
  		 * pointers and the remaining count).
  		 */
  		ret = actor(desc, page, offset, nr);
  		offset += ret;
  		index += offset >> PAGE_CACHE_SHIFT;
  		offset &= ~PAGE_CACHE_MASK;
  
  		page_cache_release(page);
  		if (ret == nr && desc->count)
  			continue;
  		goto out;
  
  page_not_up_to_date:
  		/* Get exclusive access to the page ... */
  		lock_page(page);
  
  		/* Did it get unhashed before we got the lock? */
  		if (!page->mapping) {
  			unlock_page(page);
  			page_cache_release(page);
  			continue;
  		}
  
  		/* Did somebody else fill it already? */
  		if (PageUptodate(page)) {
  			unlock_page(page);
  			goto page_ok;
  		}
  
  readpage:
  		/* Start the actual read. The read will unlock the page. */
  		error = mapping->a_ops->readpage(filp, page);
  
  		if (unlikely(error)) {
  			if (error == AOP_TRUNCATED_PAGE) {
  				page_cache_release(page);
  				goto find_page;
  			}
  			goto readpage_error;
  		}
  
  		if (!PageUptodate(page)) {
  			lock_page(page);
  			if (!PageUptodate(page)) {
  				if (page->mapping == NULL) {
  					/*
  					 * invalidate_inode_pages got it
  					 */
  					unlock_page(page);
  					page_cache_release(page);
  					goto find_page;
  				}
  				unlock_page(page);
  				error = -EIO;
  				goto readpage_error;
  			}
  			unlock_page(page);
  		}
  
  		/*
  		 * i_size must be checked after we have done ->readpage.
  		 *
  		 * Checking i_size after the readpage allows us to calculate
  		 * the correct value for "nr", which means the zero-filled
  		 * part of the page is not copied back to userspace (unless
  		 * another truncate extends the file - this is desired though).
  		 */
  		isize = i_size_read(inode);
  		end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
  		if (unlikely(!isize || index > end_index)) {
  			page_cache_release(page);
  			goto out;
  		}
  
  		/* nr is the maximum number of bytes to copy from this page */
  		nr = PAGE_CACHE_SIZE;
  		if (index == end_index) {
  			nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
  			if (nr <= offset) {
  				page_cache_release(page);
  				goto out;
  			}
  		}
  		nr = nr - offset;
  		goto page_ok;
  
  readpage_error:
  		/* UHHUH! A synchronous read error occurred. Report it */
  		desc->error = error;
  		page_cache_release(page);
  		goto out;
  
  no_cached_page:
  		/*
  		 * Ok, it wasn't cached, so we need to create a new
  		 * page..
  		 */
  		if (!cached_page) {
  			cached_page = page_cache_alloc_cold(mapping);
  			if (!cached_page) {
  				desc->error = -ENOMEM;
  				goto out;
  			}
  		}
  		error = add_to_page_cache_lru(cached_page, mapping,
  						index, GFP_KERNEL);
  		if (error) {
  			if (error == -EEXIST)
  				goto find_page;
  			desc->error = error;
  			goto out;
  		}
  		page = cached_page;
  		cached_page = NULL;
  		goto readpage;
  	}
  
  out:
  	*_ra = ra;
  
  	*ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
  	if (cached_page)
  		page_cache_release(cached_page);
  	if (filp)
  		file_accessed(filp);
  }
  
  EXPORT_SYMBOL(do_generic_mapping_read);
  
  int file_read_actor(read_descriptor_t *desc, struct page *page,
  			unsigned long offset, unsigned long size)
  {
  	char *kaddr;
  	unsigned long left, count = desc->count;
  
  	if (size > count)
  		size = count;
  
  	/*
  	 * Faults on the destination of a read are common, so do it before
  	 * taking the kmap.
  	 */
  	if (!fault_in_pages_writeable(desc->arg.buf, size)) {
  		kaddr = kmap_atomic(page, KM_USER0);
  		left = __copy_to_user_inatomic(desc->arg.buf,
  						kaddr + offset, size);
  		kunmap_atomic(kaddr, KM_USER0);
  		if (left == 0)
  			goto success;
  	}
  
  	/* Do it the slow way */
  	kaddr = kmap(page);
  	left = __copy_to_user(desc->arg.buf, kaddr + offset, size);
  	kunmap(page);
  
  	if (left) {
  		size -= left;
  		desc->error = -EFAULT;
  	}
  success:
  	desc->count = count - size;
  	desc->written += size;
  	desc->arg.buf += size;
  	return size;
  }
  
  /*
   * This is the "read()" routine for all filesystems
   * that can use the page cache directly.
   */
  ssize_t
  __generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
  		unsigned long nr_segs, loff_t *ppos)
  {
  	struct file *filp = iocb->ki_filp;
  	ssize_t retval;
  	unsigned long seg;
  	size_t count;
  
  	count = 0;
  	for (seg = 0; seg < nr_segs; seg++) {
  		const struct iovec *iv = &iov[seg];
  
  		/*
  		 * If any segment has a negative length, or the cumulative
  		 * length ever wraps negative then return -EINVAL.
  		 */
  		count += iv->iov_len;
  		if (unlikely((ssize_t)(count|iv->iov_len) < 0))
  			return -EINVAL;
  		if (access_ok(VERIFY_WRITE, iv->iov_base, iv->iov_len))
  			continue;
  		if (seg == 0)
  			return -EFAULT;
  		nr_segs = seg;
  		count -= iv->iov_len;	/* This segment is no good */
  		break;
  	}
  
  	/* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
  	if (filp->f_flags & O_DIRECT) {
  		loff_t pos = *ppos, size;
  		struct address_space *mapping;
  		struct inode *inode;
  
  		mapping = filp->f_mapping;
  		inode = mapping->host;
  		retval = 0;
  		if (!count)
  			goto out; /* skip atime */
  		size = i_size_read(inode);
  		if (pos < size) {
  			retval = generic_file_direct_IO(READ, iocb,
  						iov, pos, nr_segs);
  			if (retval > 0 && !is_sync_kiocb(iocb))
  				retval = -EIOCBQUEUED;
  			if (retval > 0)
  				*ppos = pos + retval;
  		}
  		file_accessed(filp);
  		goto out;
  	}
  
  	retval = 0;
  	if (count) {
  		for (seg = 0; seg < nr_segs; seg++) {
  			read_descriptor_t desc;
  
  			desc.written = 0;
  			desc.arg.buf = iov[seg].iov_base;
  			desc.count = iov[seg].iov_len;
  			if (desc.count == 0)
  				continue;
  			desc.error = 0;
  			do_generic_file_read(filp,ppos,&desc,file_read_actor);
  			retval += desc.written;
  			if (desc.error) {
  				retval = retval ?: desc.error;
  				break;
  			}
  		}
  	}
  out:
  	return retval;
  }
  
  EXPORT_SYMBOL(__generic_file_aio_read);
  
  ssize_t
  generic_file_aio_read(struct kiocb *iocb, char __user *buf, size_t count, loff_t pos)
  {
  	struct iovec local_iov = { .iov_base = buf, .iov_len = count };
  
  	BUG_ON(iocb->ki_pos != pos);
  	return __generic_file_aio_read(iocb, &local_iov, 1, &iocb->ki_pos);
  }
  
  EXPORT_SYMBOL(generic_file_aio_read);
  
  ssize_t
  generic_file_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
  {
  	struct iovec local_iov = { .iov_base = buf, .iov_len = count };
  	struct kiocb kiocb;
  	ssize_t ret;
  
  	init_sync_kiocb(&kiocb, filp);
  	ret = __generic_file_aio_read(&kiocb, &local_iov, 1, ppos);
  	if (-EIOCBQUEUED == ret)
  		ret = wait_on_sync_kiocb(&kiocb);
  	return ret;
  }
  
  EXPORT_SYMBOL(generic_file_read);
  
  int file_send_actor(read_descriptor_t * desc, struct page *page, unsigned long offset, unsigned long size)
  {
  	ssize_t written;
  	unsigned long count = desc->count;
  	struct file *file = desc->arg.data;
  
  	if (size > count)
  		size = count;
  
  	written = file->f_op->sendpage(file, page, offset,
  				       size, &file->f_pos, size<count);
  	if (written < 0) {
  		desc->error = written;
  		written = 0;
  	}
  	desc->count = count - written;
  	desc->written += written;
  	return written;
  }
  
  ssize_t generic_file_sendfile(struct file *in_file, loff_t *ppos,
  			 size_t count, read_actor_t actor, void *target)
  {
  	read_descriptor_t desc;
  
  	if (!count)
  		return 0;
  
  	desc.written = 0;
  	desc.count = count;
  	desc.arg.data = target;
  	desc.error = 0;
  
  	do_generic_file_read(in_file, ppos, &desc, actor);
  	if (desc.written)
  		return desc.written;
  	return desc.error;
  }
  
  EXPORT_SYMBOL(generic_file_sendfile);
  
  static ssize_t
  do_readahead(struct address_space *mapping, struct file *filp,
  	     unsigned long index, unsigned long nr)
  {
  	if (!mapping || !mapping->a_ops || !mapping->a_ops->readpage)
  		return -EINVAL;
  
  	force_page_cache_readahead(mapping, filp, index,
  					max_sane_readahead(nr));
  	return 0;
  }
  
  asmlinkage ssize_t sys_readahead(int fd, loff_t offset, size_t count)
  {
  	ssize_t ret;
  	struct file *file;
  
  	ret = -EBADF;
  	file = fget(fd);
  	if (file) {
  		if (file->f_mode & FMODE_READ) {
  			struct address_space *mapping = file->f_mapping;
  			unsigned long start = offset >> PAGE_CACHE_SHIFT;
  			unsigned long end = (offset + count - 1) >> PAGE_CACHE_SHIFT;
  			unsigned long len = end - start + 1;
  			ret = do_readahead(mapping, file, start, len);
  		}
  		fput(file);
  	}
  	return ret;
  }
  
  #ifdef CONFIG_MMU
  /*
   * This adds the requested page to the page cache if it isn't already there,
   * and schedules an I/O to read in its contents from disk.
   */
  static int FASTCALL(page_cache_read(struct file * file, unsigned long offset));
  static int fastcall page_cache_read(struct file * file, unsigned long offset)
  {
  	struct address_space *mapping = file->f_mapping;
  	struct page *page; 
  	int ret;
  
  	do {
  		page = page_cache_alloc_cold(mapping);
  		if (!page)
  			return -ENOMEM;
  
  		ret = add_to_page_cache_lru(page, mapping, offset, GFP_KERNEL);
  		if (ret == 0)
  			ret = mapping->a_ops->readpage(file, page);
  		else if (ret == -EEXIST)
  			ret = 0; /* losing race to add is OK */
  
  		page_cache_release(page);
  
  	} while (ret == AOP_TRUNCATED_PAGE);
  		
  	return ret;
  }
  
  #define MMAP_LOTSAMISS  (100)
  
  /*
   * filemap_nopage() is invoked via the vma operations vector for a
   * mapped memory region to read in file data during a page fault.
   *
   * The goto's are kind of ugly, but this streamlines the normal case of having
   * it in the page cache, and handles the special cases reasonably without
   * having a lot of duplicated code.
   */
  struct page *filemap_nopage(struct vm_area_struct *area,
  				unsigned long address, int *type)
  {
  	int error;
  	struct file *file = area->vm_file;
  	struct address_space *mapping = file->f_mapping;
  	struct file_ra_state *ra = &file->f_ra;
  	struct inode *inode = mapping->host;
  	struct page *page;
  	unsigned long size, pgoff;
  	int did_readaround = 0, majmin = VM_FAULT_MINOR;
  
  	pgoff = ((address-area->vm_start) >> PAGE_CACHE_SHIFT) + area->vm_pgoff;
  
  retry_all:
  	size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
  	if (pgoff >= size)
  		goto outside_data_content;
  
  	/* If we don't want any read-ahead, don't bother */
  	if (VM_RandomReadHint(area))
  		goto no_cached_page;
  
  	/*
  	 * The readahead code wants to be told about each and every page
  	 * so it can build and shrink its windows appropriately
  	 *
  	 * For sequential accesses, we use the generic readahead logic.
  	 */
  	if (VM_SequentialReadHint(area))
  		page_cache_readahead(mapping, ra, file, pgoff, 1);
  
  	/*
  	 * Do we have something in the page cache already?
  	 */
  retry_find:
  	page = find_get_page(mapping, pgoff);
  	if (!page) {
  		unsigned long ra_pages;
  
  		if (VM_SequentialReadHint(area)) {
  			handle_ra_miss(mapping, ra, pgoff);
  			goto no_cached_page;
  		}
  		ra->mmap_miss++;
  
  		/*
  		 * Do we miss much more than hit in this file? If so,
  		 * stop bothering with read-ahead. It will only hurt.
  		 */
  		if (ra->mmap_miss > ra->mmap_hit + MMAP_LOTSAMISS)
  			goto no_cached_page;
  
  		/*
  		 * To keep the pgmajfault counter straight, we need to
  		 * check did_readaround, as this is an inner loop.
  		 */
  		if (!did_readaround) {
  			majmin = VM_FAULT_MAJOR;
  			inc_page_state(pgmajfault);
  		}
  		did_readaround = 1;
  		ra_pages = max_sane_readahead(file->f_ra.ra_pages);
  		if (ra_pages) {
  			pgoff_t start = 0;
  
  			if (pgoff > ra_pages / 2)
  				start = pgoff - ra_pages / 2;
  			do_page_cache_readahead(mapping, file, start, ra_pages);
  		}
  		page = find_get_page(mapping, pgoff);
  		if (!page)
  			goto no_cached_page;
  	}
  
  	if (!did_readaround)
  		ra->mmap_hit++;
  
  	/*
  	 * Ok, found a page in the page cache, now we need to check
  	 * that it's up-to-date.
  	 */
  	if (!PageUptodate(page))
  		goto page_not_uptodate;
  
  success:
  	/*
  	 * Found the page and have a reference on it.
  	 */
  	mark_page_accessed(page);
  	if (type)
  		*type = majmin;
  	return page;
  
  outside_data_content:
  	/*
  	 * An external ptracer can access pages that normally aren't
  	 * accessible..
  	 */
  	if (area->vm_mm == current->mm)
  		return NULL;
  	/* Fall through to the non-read-ahead case */
  no_cached_page:
  	/*
  	 * We're only likely to ever get here if MADV_RANDOM is in
  	 * effect.
  	 */
  	error = page_cache_read(file, pgoff);
  	grab_swap_token();
  
  	/*
  	 * The page we want has now been added to the page cache.
  	 * In the unlikely event that someone removed it in the
  	 * meantime, we'll just come back here and read it again.
  	 */
  	if (error >= 0)
  		goto retry_find;
  
  	/*
  	 * An error return from page_cache_read can result if the
  	 * system is low on memory, or a problem occurs while trying
  	 * to schedule I/O.
  	 */
  	if (error == -ENOMEM)
  		return NOPAGE_OOM;
  	return NULL;
  
  page_not_uptodate:
  	if (!did_readaround) {
  		majmin = VM_FAULT_MAJOR;
  		inc_page_state(pgmajfault);
  	}
  	lock_page(page);
  
  	/* Did it get unhashed while we waited for it? */
  	if (!page->mapping) {
  		unlock_page(page);
  		page_cache_release(page);
  		goto retry_all;
  	}
  
  	/* Did somebody else get it up-to-date? */
  	if (PageUptodate(page)) {
  		unlock_page(page);
  		goto success;
  	}
  
  	error = mapping->a_ops->readpage(file, page);
  	if (!error) {
  		wait_on_page_locked(page);
  		if (PageUptodate(page))
  			goto success;
  	} else if (error == AOP_TRUNCATED_PAGE) {
  		page_cache_release(page);
  		goto retry_find;
  	}
  
  	/*
  	 * Umm, take care of errors if the page isn't up-to-date.
  	 * Try to re-read it _once_. We do this synchronously,
  	 * because there really aren't any performance issues here
  	 * and we need to check for errors.
  	 */
  	lock_page(page);
  
  	/* Somebody truncated the page on us? */
  	if (!page->mapping) {
  		unlock_page(page);
  		page_cache_release(page);
  		goto retry_all;
  	}
  
  	/* Somebody else successfully read it in? */
  	if (PageUptodate(page)) {
  		unlock_page(page);
  		goto success;
  	}
  	ClearPageError(page);
  	error = mapping->a_ops->readpage(file, page);
  	if (!error) {
  		wait_on_page_locked(page);
  		if (PageUptodate(page))
  			goto success;
  	} else if (error == AOP_TRUNCATED_PAGE) {
  		page_cache_release(page);
  		goto retry_find;
  	}
  
  	/*
  	 * Things didn't work out. Return zero to tell the
  	 * mm layer so, possibly freeing the page cache page first.
  	 */
  	page_cache_release(page);
  	return NULL;
  }
  
  EXPORT_SYMBOL(filemap_nopage);
  
  static struct page * filemap_getpage(struct file *file, unsigned long pgoff,
  					int nonblock)
  {
  	struct address_space *mapping = file->f_mapping;
  	struct page *page;
  	int error;
  
  	/*
  	 * Do we have something in the page cache already?
  	 */
  retry_find:
  	page = find_get_page(mapping, pgoff);
  	if (!page) {
  		if (nonblock)
  			return NULL;
  		goto no_cached_page;
  	}
  
  	/*
  	 * Ok, found a page in the page cache, now we need to check
  	 * that it's up-to-date.
  	 */
  	if (!PageUptodate(page)) {
  		if (nonblock) {
  			page_cache_release(page);
  			return NULL;
  		}
  		goto page_not_uptodate;
  	}
  
  success:
  	/*
  	 * Found the page and have a reference on it.
  	 */
  	mark_page_accessed(page);
  	return page;
  
  no_cached_page:
  	error = page_cache_read(file, pgoff);
  
  	/*
  	 * The page we want has now been added to the page cache.
  	 * In the unlikely event that someone removed it in the
  	 * meantime, we'll just come back here and read it again.
  	 */
  	if (error >= 0)
  		goto retry_find;
  
  	/*
  	 * An error return from page_cache_read can result if the
  	 * system is low on memory, or a problem occurs while trying
  	 * to schedule I/O.
  	 */
  	return NULL;
  
  page_not_uptodate:
  	lock_page(page);
  
  	/* Did it get unhashed while we waited for it? */
  	if (!page->mapping) {
  		unlock_page(page);
  		goto err;
  	}
  
  	/* Did somebody else get it up-to-date? */
  	if (PageUptodate(page)) {
  		unlock_page(page);
  		goto success;
  	}
  
  	error = mapping->a_ops->readpage(file, page);
  	if (!error) {
  		wait_on_page_locked(page);
  		if (PageUptodate(page))
  			goto success;
  	} else if (error == AOP_TRUNCATED_PAGE) {
  		page_cache_release(page);
  		goto retry_find;
  	}
  
  	/*
  	 * Umm, take care of errors if the page isn't up-to-date.
  	 * Try to re-read it _once_. We do this synchronously,
  	 * because there really aren't any performance issues here
  	 * and we need to check for errors.
  	 */
  	lock_page(page);
  
  	/* Somebody truncated the page on us? */
  	if (!page->mapping) {
  		unlock_page(page);
  		goto err;
  	}
  	/* Somebody else successfully read it in? */
  	if (PageUptodate(page)) {
  		unlock_page(page);
  		goto success;
  	}
  
  	ClearPageError(page);
  	error = mapping->a_ops->readpage(file, page);
  	if (!error) {
  		wait_on_page_locked(page);
  		if (PageUptodate(page))
  			goto success;
  	} else if (error == AOP_TRUNCATED_PAGE) {
  		page_cache_release(page);
  		goto retry_find;
  	}
  
  	/*
  	 * Things didn't work out. Return zero to tell the
  	 * mm layer so, possibly freeing the page cache page first.
  	 */
  err:
  	page_cache_release(page);
  
  	return NULL;
  }
  
  int filemap_populate(struct vm_area_struct *vma, unsigned long addr,
  		unsigned long len, pgprot_t prot, unsigned long pgoff,
  		int nonblock)
  {
  	struct file *file = vma->vm_file;
  	struct address_space *mapping = file->f_mapping;
  	struct inode *inode = mapping->host;
  	unsigned long size;
  	struct mm_struct *mm = vma->vm_mm;
  	struct page *page;
  	int err;
  
  	if (!nonblock)
  		force_page_cache_readahead(mapping, vma->vm_file,
  					pgoff, len >> PAGE_CACHE_SHIFT);
  
  repeat:
  	size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
  	if (pgoff + (len >> PAGE_CACHE_SHIFT) > size)
  		return -EINVAL;
  
  	page = filemap_getpage(file, pgoff, nonblock);
  
  	/* XXX: This is wrong, a filesystem I/O error may have happened. Fix that as
  	 * done in shmem_populate calling shmem_getpage */
  	if (!page && !nonblock)
  		return -ENOMEM;
  
  	if (page) {
  		err = install_page(mm, vma, addr, page, prot);
  		if (err) {
  			page_cache_release(page);
  			return err;
  		}
  	} else if (vma->vm_flags & VM_NONLINEAR) {
  		/* No page was found just because we can't read it in now (being
  		 * here implies nonblock != 0), but the page may exist, so set
  		 * the PTE to fault it in later. */
  		err = install_file_pte(mm, vma, addr, pgoff, prot);
  		if (err)
  			return err;
  	}
  
  	len -= PAGE_SIZE;
  	addr += PAGE_SIZE;
  	pgoff++;
  	if (len)
  		goto repeat;
  
  	return 0;
  }
  EXPORT_SYMBOL(filemap_populate);
  
  struct vm_operations_struct generic_file_vm_ops = {
  	.nopage		= filemap_nopage,
  	.populate	= filemap_populate,
  };
  
  /* This is used for a general mmap of a disk file */
  
  int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
  {
  	struct address_space *mapping = file->f_mapping;
  
  	if (!mapping->a_ops->readpage)
  		return -ENOEXEC;
  	file_accessed(file);
  	vma->vm_ops = &generic_file_vm_ops;
  	return 0;
  }
  
  /*
   * This is for filesystems which do not implement ->writepage.
   */
  int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
  {
  	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
  		return -EINVAL;
  	return generic_file_mmap(file, vma);
  }
  #else
  int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
  {
  	return -ENOSYS;
  }
  int generic_file_readonly_mmap(struct file * file, struct vm_area_struct * vma)
  {
  	return -ENOSYS;
  }
  #endif /* CONFIG_MMU */
  
  EXPORT_SYMBOL(generic_file_mmap);
  EXPORT_SYMBOL(generic_file_readonly_mmap);
  
  static inline struct page *__read_cache_page(struct address_space *mapping,
  				unsigned long index,
  				int (*filler)(void *,struct page*),
  				void *data)
  {
  	struct page *page, *cached_page = NULL;
  	int err;
  repeat:
  	page = find_get_page(mapping, index);
  	if (!page) {
  		if (!cached_page) {
  			cached_page = page_cache_alloc_cold(mapping);
  			if (!cached_page)
  				return ERR_PTR(-ENOMEM);
  		}
  		err = add_to_page_cache_lru(cached_page, mapping,
  					index, GFP_KERNEL);
  		if (err == -EEXIST)
  			goto repeat;
  		if (err < 0) {
  			/* Presumably ENOMEM for radix tree node */
  			page_cache_release(cached_page);
  			return ERR_PTR(err);
  		}
  		page = cached_page;
  		cached_page = NULL;
  		err = filler(data, page);
  		if (err < 0) {
  			page_cache_release(page);
  			page = ERR_PTR(err);
  		}
  	}
  	if (cached_page)
  		page_cache_release(cached_page);
  	return page;
  }
  
  /*
   * Read into the page cache. If a page already exists,
   * and PageUptodate() is not set, try to fill the page.
   */
  struct page *read_cache_page(struct address_space *mapping,
  				unsigned long index,
  				int (*filler)(void *,struct page*),
  				void *data)
  {
  	struct page *page;
  	int err;
  
  retry:
  	page = __read_cache_page(mapping, index, filler, data);
  	if (IS_ERR(page))
  		goto out;
  	mark_page_accessed(page);
  	if (PageUptodate(page))
  		goto out;
  
  	lock_page(page);
  	if (!page->mapping) {
  		unlock_page(page);
  		page_cache_release(page);
  		goto retry;
  	}
  	if (PageUptodate(page)) {
  		unlock_page(page);
  		goto out;
  	}
  	err = filler(data, page);
  	if (err < 0) {
  		page_cache_release(page);
  		page = ERR_PTR(err);
  	}
   out:
  	return page;
  }
  
  EXPORT_SYMBOL(read_cache_page);
  
  /*
   * If the page was newly created, increment its refcount and add it to the
   * caller's lru-buffering pagevec.  This function is specifically for
   * generic_file_write().
   */
  static inline struct page *
  __grab_cache_page(struct address_space *mapping, unsigned long index,
  			struct page **cached_page, struct pagevec *lru_pvec)
  {
  	int err;
  	struct page *page;
  repeat:
  	page = find_lock_page(mapping, index);
  	if (!page) {
  		if (!*cached_page) {
  			*cached_page = page_cache_alloc(mapping);
  			if (!*cached_page)
  				return NULL;
  		}
  		err = add_to_page_cache(*cached_page, mapping,
  					index, GFP_KERNEL);
  		if (err == -EEXIST)
  			goto repeat;
  		if (err == 0) {
  			page = *cached_page;
  			page_cache_get(page);
  			if (!pagevec_add(lru_pvec, page))
  				__pagevec_lru_add(lru_pvec);
  			*cached_page = NULL;
  		}
  	}
  	return page;
  }
  
  /*
   * The logic we want is
   *
   *	if suid or (sgid and xgrp)
   *		remove privs
   */
  int remove_suid(struct dentry *dentry)
  {
  	mode_t mode = dentry->d_inode->i_mode;
  	int kill = 0;
  	int result = 0;
  
  	/* suid always must be killed */
  	if (unlikely(mode & S_ISUID))
  		kill = ATTR_KILL_SUID;
  
  	/*
  	 * sgid without any exec bits is just a mandatory locking mark; leave
  	 * it alone.  If some exec bits are set, it's a real sgid; kill it.
  	 */
  	if (unlikely((mode & S_ISGID) && (mode & S_IXGRP)))
  		kill |= ATTR_KILL_SGID;
  
  	if (unlikely(kill && !capable(CAP_FSETID))) {
  		struct iattr newattrs;
  
  		newattrs.ia_valid = ATTR_FORCE | kill;
  		result = notify_change(dentry, &newattrs);
  	}
  	return result;
  }
  EXPORT_SYMBOL(remove_suid);
  
  size_t
  __filemap_copy_from_user_iovec(char *vaddr, 
  			const struct iovec *iov, size_t base, size_t bytes)
  {
  	size_t copied = 0, left = 0;
  
  	while (bytes) {
  		char __user *buf = iov->iov_base + base;
  		int copy = min(bytes, iov->iov_len - base);
  
  		base = 0;
  		left = __copy_from_user_inatomic(vaddr, buf, copy);
  		copied += copy;
  		bytes -= copy;
  		vaddr += copy;
  		iov++;
  
  		if (unlikely(left)) {
  			/* zero the rest of the target like __copy_from_user */
  			if (bytes)
  				memset(vaddr, 0, bytes);
  			break;
  		}
  	}
  	return copied - left;
  }
  
  /*
   * Performs necessary checks before doing a write
   *
   * Can adjust writing position aor amount of bytes to write.
   * Returns appropriate error code that caller should return or
   * zero in case that write should be allowed.
   */
  inline int generic_write_checks(struct file *file, loff_t *pos, size_t *count, int isblk)
  {
  	struct inode *inode = file->f_mapping->host;
  	unsigned long limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
  
          if (unlikely(*pos < 0))
                  return -EINVAL;
  
  	if (!isblk) {
  		/* FIXME: this is for backwards compatibility with 2.4 */
  		if (file->f_flags & O_APPEND)
                          *pos = i_size_read(inode);
  
  		if (limit != RLIM_INFINITY) {
  			if (*pos >= limit) {
  				send_sig(SIGXFSZ, current, 0);
  				return -EFBIG;
  			}
  			if (*count > limit - (typeof(limit))*pos) {
  				*count = limit - (typeof(limit))*pos;
  			}
  		}
  	}
  
  	/*
  	 * LFS rule
  	 */
  	if (unlikely(*pos + *count > MAX_NON_LFS &&
  				!(file->f_flags & O_LARGEFILE))) {
  		if (*pos >= MAX_NON_LFS) {
  			send_sig(SIGXFSZ, current, 0);
  			return -EFBIG;
  		}
  		if (*count > MAX_NON_LFS - (unsigned long)*pos) {
  			*count = MAX_NON_LFS - (unsigned long)*pos;
  		}
  	}
  
  	/*
  	 * Are we about to exceed the fs block limit ?
  	 *
  	 * If we have written data it becomes a short write.  If we have
  	 * exceeded without writing data we send a signal and return EFBIG.
  	 * Linus frestrict idea will clean these up nicely..
  	 */
  	if (likely(!isblk)) {
  		if (unlikely(*pos >= inode->i_sb->s_maxbytes)) {
  			if (*count || *pos > inode->i_sb->s_maxbytes) {
  				send_sig(SIGXFSZ, current, 0);
  				return -EFBIG;
  			}
  			/* zero-length writes at ->s_maxbytes are OK */
  		}
  
  		if (unlikely(*pos + *count > inode->i_sb->s_maxbytes))
  			*count = inode->i_sb->s_maxbytes - *pos;
  	} else {
  		loff_t isize;
  		if (bdev_read_only(I_BDEV(inode)))
  			return -EPERM;
  		isize = i_size_read(inode);
  		if (*pos >= isize) {
  			if (*count || *pos > isize)
  				return -ENOSPC;
  		}
  
  		if (*pos + *count > isize)
  			*count = isize - *pos;
  	}
  	return 0;
  }
  EXPORT_SYMBOL(generic_write_checks);
  
  ssize_t
  generic_file_direct_write(struct kiocb *iocb, const struct iovec *iov,
  		unsigned long *nr_segs, loff_t pos, loff_t *ppos,
  		size_t count, size_t ocount)
  {
  	struct file	*file = iocb->ki_filp;
  	struct address_space *mapping = file->f_mapping;
  	struct inode	*inode = mapping->host;
  	ssize_t		written;
  
  	if (count != ocount)
  		*nr_segs = iov_shorten((struct iovec *)iov, *nr_segs, count);
  
  	written = generic_file_direct_IO(WRITE, iocb, iov, pos, *nr_segs);
  	if (written > 0) {
  		loff_t end = pos + written;
  		if (end > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
  			i_size_write(inode,  end);
  			mark_inode_dirty(inode);
  		}
  		*ppos = end;
  	}
  
  	/*
  	 * Sync the fs metadata but not the minor inode changes and
  	 * of course not the data as we did direct DMA for the IO.
  	 * i_mutex is held, which protects generic_osync_inode() from
  	 * livelocking.
  	 */
  	if (written >= 0 && ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
  		int err = generic_osync_inode(inode, mapping, OSYNC_METADATA);
  		if (err < 0)
  			written = err;
  	}
  	if (written == count && !is_sync_kiocb(iocb))
  		written = -EIOCBQUEUED;
  	return written;
  }
  EXPORT_SYMBOL(generic_file_direct_write);
  
  ssize_t
  generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
  		unsigned long nr_segs, loff_t pos, loff_t *ppos,
  		size_t count, ssize_t written)
  {
  	struct file *file = iocb->ki_filp;
  	struct address_space * mapping = file->f_mapping;
  	struct address_space_operations *a_ops = mapping->a_ops;
  	struct inode 	*inode = mapping->host;
  	long		status = 0;
  	struct page	*page;
  	struct page	*cached_page = NULL;
  	size_t		bytes;
  	struct pagevec	lru_pvec;
  	const struct iovec *cur_iov = iov; /* current iovec */
  	size_t		iov_base = 0;	   /* offset in the current iovec */
  	char __user	*buf;
  
  	pagevec_init(&lru_pvec, 0);
  
  	/*
  	 * handle partial DIO write.  Adjust cur_iov if needed.
  	 */
  	if (likely(nr_segs == 1))
  		buf = iov->iov_base + written;
  	else {
  		filemap_set_next_iovec(&cur_iov, &iov_base, written);
  		buf = cur_iov->iov_base + iov_base;
  	}
  
  	do {
  		unsigned long index;
  		unsigned long offset;
  		unsigned long maxlen;
  		size_t copied;
  
  		offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
  		index = pos >> PAGE_CACHE_SHIFT;
  		bytes = PAGE_CACHE_SIZE - offset;
  		if (bytes > count)
  			bytes = count;
  
  		/*
  		 * Bring in the user page that we will copy from _first_.
  		 * Otherwise there's a nasty deadlock on copying from the
  		 * same page as we're writing to, without it being marked
  		 * up-to-date.
  		 */
  		maxlen = cur_iov->iov_len - iov_base;
  		if (maxlen > bytes)
  			maxlen = bytes;
  		fault_in_pages_readable(buf, maxlen);
  
  		page = __grab_cache_page(mapping,index,&cached_page,&lru_pvec);
  		if (!page) {
  			status = -ENOMEM;
  			break;
  		}
  
  		status = a_ops->prepare_write(file, page, offset, offset+bytes);
  		if (unlikely(status)) {
  			loff_t isize = i_size_read(inode);
  
  			if (status != AOP_TRUNCATED_PAGE)
  				unlock_page(page);
  			page_cache_release(page);
  			if (status == AOP_TRUNCATED_PAGE)
  				continue;
  			/*
  			 * prepare_write() may have instantiated a few blocks
  			 * outside i_size.  Trim these off again.
  			 */
  			if (pos + bytes > isize)
  				vmtruncate(inode, isize);
  			break;
  		}
  		if (likely(nr_segs == 1))
  			copied = filemap_copy_from_user(page, offset,
  							buf, bytes);
  		else
  			copied = filemap_copy_from_user_iovec(page, offset,
  						cur_iov, iov_base, bytes);
  		flush_dcache_page(page);
  		status = a_ops->commit_write(file, page, offset, offset+bytes);
  		if (status == AOP_TRUNCATED_PAGE) {
  			page_cache_release(page);
  			continue;
  		}
  		if (likely(copied > 0)) {
  			if (!status)
  				status = copied;
  
  			if (status >= 0) {
  				written += status;
  				count -= status;
  				pos += status;
  				buf += status;
  				if (unlikely(nr_segs > 1)) {
  					filemap_set_next_iovec(&cur_iov,
  							&iov_base, status);
  					if (count)
  						buf = cur_iov->iov_base +
  							iov_base;
  				} else {
  					iov_base += status;
  				}
  			}
  		}
  		if (unlikely(copied != bytes))
  			if (status >= 0)
  				status = -EFAULT;
  		unlock_page(page);
  		mark_page_accessed(page);
  		page_cache_release(page);
  		if (status < 0)
  			break;
  		balance_dirty_pages_ratelimited(mapping);
  		cond_resched();
  	} while (count);
  	*ppos = pos;
  
  	if (cached_page)
  		page_cache_release(cached_page);
  
  	/*
  	 * For now, when the user asks for O_SYNC, we'll actually give O_DSYNC
  	 */
  	if (likely(status >= 0)) {
  		if (unlikely((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
  			if (!a_ops->writepage || !is_sync_kiocb(iocb))
  				status = generic_osync_inode(inode, mapping,
  						OSYNC_METADATA|OSYNC_DATA);
  		}
    	}
  	
  	/*
  	 * If we get here for O_DIRECT writes then we must have fallen through
  	 * to buffered writes (block instantiation inside i_size).  So we sync
  	 * the file data here, to try to honour O_DIRECT expectations.
  	 */
  	if (unlikely(file->f_flags & O_DIRECT) && written)
  		status = filemap_write_and_wait(mapping);
  
  	pagevec_lru_add(&lru_pvec);
  	return written ? written : status;
  }
  EXPORT_SYMBOL(generic_file_buffered_write);
  
  static ssize_t
  __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
  				unsigned long nr_segs, loff_t *ppos)
  {
  	struct file *file = iocb->ki_filp;
  	struct address_space * mapping = file->f_mapping;
  	size_t ocount;		/* original count */
  	size_t count;		/* after file limit checks */
  	struct inode 	*inode = mapping->host;
  	unsigned long	seg;
  	loff_t		pos;
  	ssize_t		written;
  	ssize_t		err;
  
  	ocount = 0;
  	for (seg = 0; seg < nr_segs; seg++) {
  		const struct iovec *iv = &iov[seg];
  
  		/*
  		 * If any segment has a negative length, or the cumulative
  		 * length ever wraps negative then return -EINVAL.
  		 */
  		ocount += iv->iov_len;
  		if (unlikely((ssize_t)(ocount|iv->iov_len) < 0))
  			return -EINVAL;
  		if (access_ok(VERIFY_READ, iv->iov_base, iv->iov_len))
  			continue;
  		if (seg == 0)
  			return -EFAULT;
  		nr_segs = seg;
  		ocount -= iv->iov_len;	/* This segment is no good */
  		break;
  	}
  
  	count = ocount;
  	pos = *ppos;
  
  	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
  
  	/* We can write back this queue in page reclaim */
  	current->backing_dev_info = mapping->backing_dev_info;
  	written = 0;
  
  	err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
  	if (err)
  		goto out;
  
  	if (count == 0)
  		goto out;
  
  	err = remove_suid(file->f_dentry);
  	if (err)
  		goto out;
  
  	file_update_time(file);
  
  	/* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
  	if (unlikely(file->f_flags & O_DIRECT)) {
  		written = generic_file_direct_write(iocb, iov,
  				&nr_segs, pos, ppos, count, ocount);
  		if (written < 0 || written == count)
  			goto out;
  		/*
  		 * direct-io write to a hole: fall through to buffered I/O
  		 * for completing the rest of the request.
  		 */
  		pos += written;
  		count -= written;
  	}
  
  	written = generic_file_buffered_write(iocb, iov, nr_segs,
  			pos, ppos, count, written);
  out:
  	current->backing_dev_info = NULL;
  	return written ? written : err;
  }
  EXPORT_SYMBOL(generic_file_aio_write_nolock);
  
  ssize_t
  generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
  				unsigned long nr_segs, loff_t *ppos)
  {
  	struct file *file = iocb->ki_filp;
  	struct address_space *mapping = file->f_mapping;
  	struct inode *inode = mapping->host;
  	ssize_t ret;
  	loff_t pos = *ppos;
  
  	ret = __generic_file_aio_write_nolock(iocb, iov, nr_segs, ppos);
  
  	if (ret > 0 && ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
  		int err;
  
  		err = sync_page_range_nolock(inode, mapping, pos, ret);
  		if (err < 0)
  			ret = err;
  	}
  	return ret;
  }
  
  static ssize_t
  __generic_file_write_nolock(struct file *file, const struct iovec *iov,
  				unsigned long nr_segs, loff_t *ppos)
  {
  	struct kiocb kiocb;
  	ssize_t ret;
  
  	init_sync_kiocb(&kiocb, file);
  	ret = __generic_file_aio_write_nolock(&kiocb, iov, nr_segs, ppos);
  	if (ret == -EIOCBQUEUED)
  		ret = wait_on_sync_kiocb(&kiocb);
  	return ret;
  }
  
  ssize_t
  generic_file_write_nolock(struct file *file, const struct iovec *iov,
  				unsigned long nr_segs, loff_t *ppos)
  {
  	struct kiocb kiocb;
  	ssize_t ret;
  
  	init_sync_kiocb(&kiocb, file);
  	ret = generic_file_aio_write_nolock(&kiocb, iov, nr_segs, ppos);
  	if (-EIOCBQUEUED == ret)
  		ret = wait_on_sync_kiocb(&kiocb);
  	return ret;
  }
  EXPORT_SYMBOL(generic_file_write_nolock);
  
  ssize_t generic_file_aio_write(struct kiocb *iocb, const char __user *buf,
  			       size_t count, loff_t pos)
  {
  	struct file *file = iocb->ki_filp;
  	struct address_space *mapping = file->f_mapping;
  	struct inode *inode = mapping->host;
  	ssize_t ret;
  	struct iovec local_iov = { .iov_base = (void __user *)buf,
  					.iov_len = count };
  
  	BUG_ON(iocb->ki_pos != pos);
  
  	mutex_lock(&inode->i_mutex);
  	ret = __generic_file_aio_write_nolock(iocb, &local_iov, 1,
  						&iocb->ki_pos);
  	mutex_unlock(&inode->i_mutex);
  
  	if (ret > 0 && ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
  		ssize_t err;
  
  		err = sync_page_range(inode, mapping, pos, ret);
  		if (err < 0)
  			ret = err;
  	}
  	return ret;
  }
  EXPORT_SYMBOL(generic_file_aio_write);
  
  ssize_t generic_file_write(struct file *file, const char __user *buf,
  			   size_t count, loff_t *ppos)
  {
  	struct address_space *mapping = file->f_mapping;
  	struct inode *inode = mapping->host;
  	ssize_t	ret;
  	struct iovec local_iov = { .iov_base = (void __user *)buf,
  					.iov_len = count };
  
  	mutex_lock(&inode->i_mutex);
  	ret = __generic_file_write_nolock(file, &local_iov, 1, ppos);
  	mutex_unlock(&inode->i_mutex);
  
  	if (ret > 0 && ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
  		ssize_t err;
  
  		err = sync_page_range(inode, mapping, *ppos - ret, ret);
  		if (err < 0)
  			ret = err;
  	}
  	return ret;
  }
  EXPORT_SYMBOL(generic_file_write);
  
  ssize_t generic_file_readv(struct file *filp, const struct iovec *iov,
  			unsigned long nr_segs, loff_t *ppos)
  {
  	struct kiocb kiocb;
  	ssize_t ret;
  
  	init_sync_kiocb(&kiocb, filp);
  	ret = __generic_file_aio_read(&kiocb, iov, nr_segs, ppos);
  	if (-EIOCBQUEUED == ret)
  		ret = wait_on_sync_kiocb(&kiocb);
  	return ret;
  }
  EXPORT_SYMBOL(generic_file_readv);
  
  ssize_t generic_file_writev(struct file *file, const struct iovec *iov,
  			unsigned long nr_segs, loff_t *ppos)
  {
  	struct address_space *mapping = file->f_mapping;
  	struct inode *inode = mapping->host;
  	ssize_t ret;
  
  	mutex_lock(&inode->i_mutex);
  	ret = __generic_file_write_nolock(file, iov, nr_segs, ppos);
  	mutex_unlock(&inode->i_mutex);
  
  	if (ret > 0 && ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
  		int err;
  
  		err = sync_page_range(inode, mapping, *ppos - ret, ret);
  		if (err < 0)
  			ret = err;
  	}
  	return ret;
  }
  EXPORT_SYMBOL(generic_file_writev);
  
  /*
   * Called under i_mutex for writes to S_ISREG files.   Returns -EIO if something
   * went wrong during pagecache shootdown.
   */
  static ssize_t
  generic_file_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
  	loff_t offset, unsigned long nr_segs)
  {
  	struct file *file = iocb->ki_filp;
  	struct address_space *mapping = file->f_mapping;
  	ssize_t retval;
  	size_t write_len = 0;
  
  	/*
  	 * If it's a write, unmap all mmappings of the file up-front.  This
  	 * will cause any pte dirty bits to be propagated into the pageframes
  	 * for the subsequent filemap_write_and_wait().
  	 */
  	if (rw == WRITE) {
  		write_len = iov_length(iov, nr_segs);
  	       	if (mapping_mapped(mapping))
  			unmap_mapping_range(mapping, offset, write_len, 0);
  	}
  
  	retval = filemap_write_and_wait(mapping);
  	if (retval == 0) {
  		retval = mapping->a_ops->direct_IO(rw, iocb, iov,
  						offset, nr_segs);
  		if (rw == WRITE && mapping->nrpages) {
  			pgoff_t end = (offset + write_len - 1)
  						>> PAGE_CACHE_SHIFT;
  			int err = invalidate_inode_pages2_range(mapping,
  					offset >> PAGE_CACHE_SHIFT, end);
  			if (err)
  				retval = err;
  		}
  	}
  	return retval;
  }
  