Cross-Referenced Linux and Device Driver Code

   /*
    *      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/module.h>
  #include <linux/slab.h>
  #include <linux/compiler.h>
  #include <linux/fs.h>
  #include <linux/uaccess.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/backing-dev.h>
  #include <linux/pagevec.h>
  #include <linux/blkdev.h>
  #include <linux/security.h>
  #include <linux/syscalls.h>
  #include <linux/cpuset.h>
  #include <linux/hardirq.h> /* for BUG_ON(!in_atomic()) only */
  #include <linux/memcontrol.h>
  #include "internal.h"
  
  /*
   * FIXME: remove all knowledge of the buffer layer from the core VM
   */
  #include <linux/buffer_head.h> /* for generic_osync_inode */
  
  #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)
   *
   *  ->i_mutex                   (generic_file_buffered_write)
   *    ->mmap_sem                (fault_in_pages_readable->do_page_fault)
   *
   *  ->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 the mapping's tree_lock.
  */
 void __remove_from_page_cache(struct page *page)
 {
         struct address_space *mapping = page->mapping;
         DEFINE_RADIX_TREE_CONTEXT(ctx, &mapping->page_tree);
 
         mem_cgroup_uncharge_page(page);
 
         radix_tree_lock(&ctx);
         radix_tree_delete(ctx.tree, page->index);
         radix_tree_unlock(&ctx);
 
         page->mapping = NULL;
         mapping_nrpages_dec(mapping);
         __dec_zone_page_state(page, NR_FILE_PAGES);
         BUG_ON(page_mapped(page));
 
         /*
          * Some filesystems seem to re-dirty the page even after
          * the VM has canceled the dirty bit (eg ext3 journaling).
          *
          * Fix it up by doing a final dirty accounting check after
          * having removed the page entirely.
          */
         if (PageDirty(page) && mapping_cap_account_dirty(mapping)) {
                 dec_zone_page_state(page, NR_FILE_DIRTY);
                 dec_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
         }
 }
 
 void remove_from_page_cache(struct page *page)
 {
         BUG_ON(!PageLocked(page));
 
         lock_page_ref_irq(page);
         __remove_from_page_cache(page);
         unlock_page_ref_irq(page);
 }
 
 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;
 }
 
 static int sync_page_killable(void *word)
 {
         sync_page(word);
         return fatal_signal_pending(current) ? -EINTR : 0;
 }
 
 /**
  * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
  * @mapping:    address space structure to write
  * @start:      offset in bytes where the range starts
  * @end:        offset in bytes where the range ends (inclusive)
  * @sync_mode:  enable synchronous operation
  *
  * Start writeback against all of a mapping's dirty pages that lie
  * within the byte offsets <start, end> inclusive.
  *
  * 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.
  */
 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(mapping) * 2,
                 .range_start = start,
                 .range_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, LLONG_MAX, 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);
 }
 
 /**
  * filemap_flush - mostly a non-blocking flush
  * @mapping:    target address_space
  *
  * 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_on_page_writeback_range - wait for writeback to complete
  * @mapping:    target address_space
  * @start:      beginning page index
  * @end:        ending page index
  *
  * Wait for writeback to complete against pages indexed by start->end
  * inclusive
  */
 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;
 }
 
 /**
  * sync_page_range - write and wait on all pages in the passed range
  * @inode:      target inode
  * @mapping:    target address_space
  * @pos:        beginning offset in pages to write
  * @count:      number of bytes to write
  *
  * 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);
 
 /**
  * sync_page_range_nolock - write & wait on all pages in the passed range without locking
  * @inode:      target inode
  * @mapping:    target address_space
  * @pos:        beginning offset in pages to write
  * @count:      number of bytes to write
  *
  * 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 - wait for all under-writeback pages to complete
  * @mapping: address space structure to wait for
  *
  * Walk the list of under-writeback pages of the given address space
  * and wait for all of them.
  */
 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(mapping)) {
                 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);
 
 /**
  * filemap_write_and_wait_range - write out & wait on a file range
  * @mapping:    the address_space for the pages
  * @lstart:     offset in bytes where the range starts
  * @lend:       offset in bytes where the range ends (inclusive)
  *
  * Write out and wait upon file offsets lstart->lend, inclusive.
  *
  * Note that `lend' is inclusive (describes the last byte to be written) so
  * that this function can be used to write to the very end-of-file (end = -1).
  */
 int filemap_write_and_wait_range(struct address_space *mapping,
                                  loff_t lstart, loff_t lend)
 {
         int err = 0;
 
         if (mapping_nrpages(mapping)) {
                 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;
 }
 
 /**
  * add_to_page_cache - add newly allocated pagecache pages
  * @page:       page to add
  * @mapping:    the page's address_space
  * @offset:     page index
  * @gfp_mask:   page allocation mode
  *
  * 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 = mem_cgroup_cache_charge(page, current->mm,
                                         gfp_mask & ~__GFP_HIGHMEM);
         if (error)
                 goto out;
 
         error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
         if (error == 0) {
                 DEFINE_RADIX_TREE_CONTEXT(ctx, &mapping->page_tree);
 
                 lock_page_ref_irq(page);
                 radix_tree_lock(&ctx);
                 error = radix_tree_insert(ctx.tree, offset, page);
                 radix_tree_unlock(&ctx);
                 if (!error) {
                         page_cache_get(page);
                         SetPageLocked(page);
                         page->mapping = mapping;
                         page->index = offset;
                         mapping_nrpages_inc(mapping);
                         __inc_zone_page_state(page, NR_FILE_PAGES);
                 } else
                         mem_cgroup_uncharge_page(page);
 
                 unlock_page_ref_irq(page);
                 radix_tree_preload_end();
         } else
                 mem_cgroup_uncharge_page(page);
 out:
         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;
 }
 
 #ifdef CONFIG_NUMA
 struct page *__page_cache_alloc(gfp_t gfp)
 {
         if (cpuset_do_page_mem_spread()) {
                 int n = cpuset_mem_spread_node();
                 return alloc_pages_node(n, gfp, 0);
         }
         return alloc_pages(gfp, 0);
 }
 EXPORT_SYMBOL(__page_cache_alloc);
 #endif
 
 static int __sleep_on_page_lock(void *word)
 {
         io_schedule();
         return 0;
 }
 
 int __sleep_on_page(void *word)
 {
         schedule();
         return 0;
 }
 
 static inline void wake_up_page(struct page *page, int bit)
 {
         __wake_up_bit(page_waitqueue(page), &page->flags, bit);
 }
 
 void 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 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_page_writeback - end writeback against a page
  * @page: the 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);
 
 /**
  * __lock_page - get a lock on the page, assuming we need to sleep to get it
  * @page: the page to lock
  *
  * 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 __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);
 
 int __lock_page_killable(struct page *page)
 {
         DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
 
         return __wait_on_bit_lock(page_waitqueue(page), &wait,
                                         sync_page_killable, TASK_KILLABLE);
 }
 
 /**
  * __lock_page_nosync - get a lock on the page, without calling sync_page()
  * @page: the page to lock
  *
  * Variant of lock_page that does not require the caller to hold a reference
  * on the page's mapping.
  */
 void __lock_page_nosync(struct page *page)
 {
         DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
         __wait_on_bit_lock(page_waitqueue(page), &wait, __sleep_on_page_lock,
                                                         TASK_UNINTERRUPTIBLE);
 }
 
 /**
  * find_get_page - find and get a page reference
  * @mapping: the address_space to search
  * @offset: the page index
  *
  * Is there a pagecache struct page at the given (mapping, offset) tuple?
  * If yes, increment its refcount and return it; if no, return NULL.
  */
 struct page * find_get_page(struct address_space *mapping, pgoff_t offset)
 {
         void **pagep;
         struct page *page;
 
         rcu_read_lock();
 repeat:
         page = NULL;
         pagep = radix_tree_lookup_slot(&mapping->page_tree, offset);
         if (pagep) {
                 page = radix_tree_deref_slot(pagep);
                 if (unlikely(!page || page == RADIX_TREE_RETRY))
                         goto repeat;
 
                 if (!page_cache_get_speculative(page))
                         goto repeat;
 
                 /*
                  * Has the page moved?
                  * This is part of the lockless pagecache protocol. See
                  * include/linux/pagemap.h for details.
                  */
                 if (unlikely(page != *pagep)) {
                         page_cache_release(page);
                         goto repeat;
                 }
         }
         rcu_read_unlock();
 
         return page;
 }
 EXPORT_SYMBOL(find_get_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,
                                 pgoff_t offset)
 {
         struct page *page;
 
 repeat:
         page = find_get_page(mapping, offset);
         if (page) {
                 lock_page(page);
                 /* Has the page been truncated? */
                 if (unlikely(page->mapping != mapping)) {
                         unlock_page(page);
                         page_cache_release(page);
                         goto repeat;
                 }
         }
         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,
                 pgoff_t index, gfp_t gfp_mask)
 {
         struct page *page;
         int err;
 repeat:
         page = find_lock_page(mapping, index);
         if (!page) {
                 page = __page_cache_alloc(gfp_mask);
                 if (!page)
                         return NULL;
                 err = add_to_page_cache_lru(page, mapping, index, gfp_mask);
                 if (unlikely(err)) {
                         page_cache_release(page);
                         page = NULL;
                         if (err == -EEXIST)
                                 goto repeat;
                 }
         }
         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;
         unsigned int nr_found;
 
         rcu_read_lock();
 restart:
         nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
                                 (void ***)pages, start, nr_pages);
         ret = 0;
         for (i = 0; i < nr_found; i++) {
                 struct page *page;
 repeat:
                 page = radix_tree_deref_slot((void **)pages[i]);
                 if (unlikely(!page))
                         continue;
                 /*
                  * this can only trigger if nr_found == 1, making livelock
                  * a non issue.
                  */
                 if (unlikely(page == RADIX_TREE_RETRY))
                         goto restart;
 
                 if (!page_cache_get_speculative(page))
                         goto repeat;
 
                 /* Has the page moved? */
                 if (unlikely(page != *((void **)pages[i]))) {
                         page_cache_release(page);
                         goto repeat;
                 }
 
                 pages[ret] = page;
                 ret++;
         }
         rcu_read_unlock();
         return ret;
 }
 
 /**
  * find_get_pages_contig - gang contiguous pagecache lookup
  * @mapping:    The address_space to search
  * @index:      The starting page index
  * @nr_pages:   The maximum number of pages
  * @pages:      Where the resulting pages are placed
  *
  * find_get_pages_contig() works exactly like find_get_pages(), except
  * that the returned number of pages are guaranteed to be contiguous.
  *
  * find_get_pages_contig() returns the number of pages which were found.
  */
 unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
                                unsigned int nr_pages, struct page **pages)
 {
         unsigned int i;
         unsigned int ret;
         unsigned int nr_found;
 
         rcu_read_lock();
 restart:
         nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
                                 (void ***)pages, index, nr_pages);
         ret = 0;
         for (i = 0; i < nr_found; i++) {
                 struct page *page;
 repeat:
                 page = radix_tree_deref_slot((void **)pages[i]);
                 if (unlikely(!page))
                         continue;
                 /*
                  * this can only trigger if nr_found == 1, making livelock
                  * a non issue.
                  */
                 if (unlikely(page == RADIX_TREE_RETRY))
                         goto restart;
 
                 if (page->mapping == NULL || page->index != index)
                         break;
 
                 if (!page_cache_get_speculative(page))
                         goto repeat;
 
                 /* Has the page moved? */
                 if (unlikely(page != *((void **)pages[i]))) {
                         page_cache_release(page);
                         goto repeat;
                 }
 
                 pages[ret] = page;
                 ret++;
                 index++;
         }
         rcu_read_unlock();
         return ret;
 }
 EXPORT_SYMBOL(find_get_pages_contig);
 
 /**
  * find_get_pages_tag - find and return pages that match @tag
  * @mapping:    the address_space to search
  * @index:      the starting page index
  * @tag:        the tag index
  * @nr_pages:   the maximum number of pages
  * @pages:      where the resulting pages are placed
  *
  * 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;
         unsigned int nr_found;
 
         rcu_read_lock();
 restart:
         nr_found = radix_tree_gang_lookup_tag_slot(&mapping->page_tree,
                                 (void ***)pages, *index, nr_pages, tag);
         ret = 0;
         for (i = 0; i < nr_found; i++) {
                 struct page *page;
 repeat:
                 page = radix_tree_deref_slot((void **)pages[i]);
                 if (unlikely(!page))
                         continue;
                 /*
                  * this can only trigger if nr_found == 1, making livelock
                  * a non issue.
                  */
                 if (unlikely(page == RADIX_TREE_RETRY))
                         goto restart;
 
                 if (!page_cache_get_speculative(page))
                         goto repeat;
 
                 /* Has the page moved? */
                 if (unlikely(page != *((void **)pages[i]))) {
                         page_cache_release(page);
                         goto repeat;
                 }
 
                 pages[ret] = page;
                 ret++;
         }
         rcu_read_unlock();
 
         if (ret)
                 *index = pages[ret - 1]->index + 1;
 
         return ret;
 }
 EXPORT_SYMBOL(find_get_pages_tag);
 
 /**
  * grab_cache_page_nowait - returns locked page at given index in given cache
  * @mapping: target address_space
  * @index: the page index
  *
  * 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, pgoff_t index)
 {
         struct page *page = find_get_page(mapping, index);
 
         if (page) {
                 if (!TestSetPageLocked(page))
                         return page;
                 page_cache_release(page);
                 return NULL;
         }
         page = __page_cache_alloc(mapping_gfp_mask(mapping) & ~__GFP_FS);
         if (page && add_to_page_cache_lru(page, mapping, index, GFP_KERNEL)) {
                 page_cache_release(page);
                 page = NULL;
         }
         return page;
 }
 EXPORT_SYMBOL(grab_cache_page_nowait);
 
 /*
  * CD/DVDs are error prone. When a medium error occurs, the driver may fail
  * a _large_ part of the i/o request. Imagine the worst scenario:
  *
  *      ---R__________________________________________B__________
  *         ^ reading here                             ^ bad block(assume 4k)
  *
  * read(R) => miss => readahead(R...B) => media error => frustrating retries
  * => failing the whole request => read(R) => read(R+1) =>
  * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
  * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
  * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
  *
  * It is going insane. Fix it by quickly scaling down the readahead size.
  */
 static void shrink_readahead_size_eio(struct file *filp,
                                         struct file_ra_state *ra)
 {
         if (!ra->ra_pages)
                 return;
 
         ra->ra_pages /= 4;
 }
 
 /**
  * do_generic_file_read - generic file read routine
  * @filp:       the file to read
  * @ppos:       current file position
  * @desc:       read_descriptor
  * @actor:      read method
  *
  * 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.
  */
 static void do_generic_file_read(struct file *filp, loff_t *ppos,
                 read_descriptor_t *desc, read_actor_t actor)
 {
         struct address_space *mapping = filp->f_mapping;
         struct inode *inode = mapping->host;
         struct file_ra_state *ra = &filp->f_ra;
         pgoff_t index;
         pgoff_t last_index;
         pgoff_t prev_index;
         unsigned long offset;      /* offset into pagecache page */
         unsigned int prev_offset;
         int error;
 
         index = *ppos >> PAGE_CACHE_SHIFT;
         prev_index = ra->prev_pos >> PAGE_CACHE_SHIFT;
         prev_offset = ra->prev_pos & (PAGE_CACHE_SIZE-1);
         last_index = (*ppos + desc->count + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;
         offset = *ppos & ~PAGE_CACHE_MASK;
 
         for (;;) {
                 struct page *page;
                 pgoff_t end_index;
                 loff_t isize;
                 unsigned long nr, ret;
 
                 cond_resched();
 find_page:
                 page = find_get_page(mapping, index);
                 if (!page) {
                         page_cache_sync_readahead(mapping,
                                         ra, filp,
                                         index, last_index - index);
                         page = find_get_page(mapping, index);
                         if (unlikely(page == NULL))
                                 goto no_cached_page;
                 }
                 if (PageReadahead(page)) {
                         page_cache_async_readahead(mapping,
                                         ra, filp, page,
                                         index, last_index - index);
                 }
                 if (!PageUptodate(page))
                         goto page_not_up_to_date;
 page_ok:
                 /*
                  * i_size must be checked after we know the page is Uptodate.
                  *
                  * Checking i_size after the check 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;
 
                 /* 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 a sequential read accesses a page several times,
                  * only mark it as accessed the first time.
                  */
                 if (prev_index != index || offset != prev_offset)
                         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;
                 prev_offset = offset;
 
                 page_cache_release(page);
                 if (ret == nr && desc->count)
                         continue;
                 goto out;
 
 page_not_up_to_date:
                 /* Get exclusive access to the page ... */
                 if (lock_page_killable(page))
                         goto readpage_eio;
 
                 /* Did it get truncated 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)) {
                         if (lock_page_killable(page))
                                 goto readpage_eio;
                         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);
                                 shrink_readahead_size_eio(filp, ra);
                                 goto readpage_eio;
                         }
                         unlock_page(page);
                 }
 
                 goto page_ok;
 
 readpage_eio:
                 error = -EIO;
 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..
                  */
                 page = page_cache_alloc_cold(mapping);
                 if (!page) {
                         desc->error = -ENOMEM;
                         goto out;
                 }
                 error = add_to_page_cache_lru(page, mapping,
                                                 index, GFP_KERNEL);
                 if (error) {
                         page_cache_release(page);
                         if (error == -EEXIST)
                                 goto find_page;
                         desc->error = error;
                         goto out;
                 }
                 goto readpage;
         }
 
 out:
         ra->prev_pos = prev_index;
         ra->prev_pos <<= PAGE_CACHE_SHIFT;
         ra->prev_pos |= prev_offset;
 
         *ppos = ((loff_t)index << PAGE_CACHE_SHIFT) + offset;
         if (filp)
                 file_accessed(filp);
 }
 
 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;
 }
 
 /*
  * Performs necessary checks before doing a write
  * @iov:        io vector request
  * @nr_segs:    number of segments in the iovec
  * @count:      number of bytes to write
  * @access_flags: type of access: %VERIFY_READ or %VERIFY_WRITE
  *
  * Adjust number of segments and amount of bytes to write (nr_segs should be
  * properly initialized first). Returns appropriate error code that caller
  * should return or zero in case that write should be allowed.
  */
 int generic_segment_checks(const struct iovec *iov,
                         unsigned long *nr_segs, size_t *count, int access_flags)
 {
         unsigned long   seg;
         size_t cnt = 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.
                  */
                 cnt += iv->iov_len;
                 if (unlikely((ssize_t)(cnt|iv->iov_len) < 0))
                         return -EINVAL;
                 if (access_ok(access_flags, iv->iov_base, iv->iov_len))
                         continue;
                 if (seg == 0)
                         return -EFAULT;
                 *nr_segs = seg;
                 cnt -= iv->iov_len;     /* This segment is no good */
                 break;
         }
         *count = cnt;
         return 0;
 }
 EXPORT_SYMBOL(generic_segment_checks);
 
 /**
  * generic_file_aio_read - generic filesystem read routine
  * @iocb:       kernel I/O control block
  * @iov:        io vector request
  * @nr_segs:    number of segments in the iovec
  * @pos:        current file position
  *
  * 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 pos)
 {
         struct file *filp = iocb->ki_filp;
         ssize_t retval;
         unsigned long seg;
         size_t count;
         loff_t *ppos = &iocb->ki_pos;
 
         count = 0;
         retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
         if (retval)
                 return retval;
 
         /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
         if (filp->f_flags & O_DIRECT) {
                 loff_t 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)
                                 *ppos = pos + retval;
                 }
                 if (likely(retval != 0)) {
                         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;
                         }
                         if (desc.count > 0)
                                 break;
                 }
         }
 out:
         return retval;
 }
 EXPORT_SYMBOL(generic_file_aio_read);
 
 static ssize_t
 do_readahead(struct address_space *mapping, struct file *filp,
              pgoff_t 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;
                         pgoff_t start = offset >> PAGE_CACHE_SHIFT;
                         pgoff_t 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
 /**
  * page_cache_read - adds requested page to the page cache if not already there
  * @file:       file to read
  * @offset:     page index
  *
  * 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 page_cache_read(struct file *file, pgoff_t 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_fault - read in file data for page fault handling
  * @vma:        vma in which the fault was taken
  * @vmf:        struct vm_fault containing details of the fault
  *
  * filemap_fault() 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.
  */
 int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
         int error;
         struct file *file = vma->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;
         pgoff_t size;
         int did_readaround = 0;
         int ret = 0;
 
         size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
         if (vmf->pgoff >= size)
                 return VM_FAULT_SIGBUS;
 
         /* If we don't want any read-ahead, don't bother */
         if (VM_RandomReadHint(vma))
                 goto no_cached_page;
 
         /*
          * Do we have something in the page cache already?
          */
 retry_find:
         page = find_lock_page(mapping, vmf->pgoff);
         /*
          * For sequential accesses, we use the generic readahead logic.
          */
         if (VM_SequentialReadHint(vma)) {
                 if (!page) {
                         page_cache_sync_readahead(mapping, ra, file,
                                                            vmf->pgoff, 1);
                         page = find_lock_page(mapping, vmf->pgoff);
                         if (!page)
                                 goto no_cached_page;
                 }
                 if (PageReadahead(page)) {
                         page_cache_async_readahead(mapping, ra, file, page,
                                                            vmf->pgoff, 1);
                 }
         }
 
         if (!page) {
                 unsigned long ra_pages;
 
                 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 > 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) {
                         ret = VM_FAULT_MAJOR;
                         count_vm_event(PGMAJFAULT);
                 }
                 did_readaround = 1;
                 ra_pages = max_sane_readahead(file->f_ra.ra_pages);
                 if (ra_pages) {
                         pgoff_t start = 0;
 
                         if (vmf->pgoff > ra_pages / 2)
                                 start = vmf->pgoff - ra_pages / 2;
                         do_page_cache_readahead(mapping, file, start, ra_pages);
                 }
                 page = find_lock_page(mapping, vmf->pgoff);
                 if (!page)
                         goto no_cached_page;
         }
 
         if (!did_readaround)
                 ra->mmap_miss--;
 
         /*
          * We have a locked page in the page cache, now we need to check
          * that it's up-to-date. If not, it is going to be due to an error.
          */
         if (unlikely(!PageUptodate(page)))
                 goto page_not_uptodate;
 
         /* Must recheck i_size under page lock */
         size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
         if (unlikely(vmf->pgoff >= size)) {
                 unlock_page(page);
                 page_cache_release(page);
                 return VM_FAULT_SIGBUS;
         }
 
         /*
          * Found the page and have a reference on it.
          */
         mark_page_accessed(page);
         ra->prev_pos = (loff_t)page->index << PAGE_CACHE_SHIFT;
         vmf->page = page;
         return ret | VM_FAULT_LOCKED;
 
 no_cached_page:
         /*
          * We're only likely to ever get here if MADV_RANDOM is in
          * effect.
          */
         error = page_cache_read(file, vmf->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.
          */
         if (error == -ENOMEM)
                 return VM_FAULT_OOM;
         return VM_FAULT_SIGBUS;
 
 page_not_uptodate:
         /* IO error path */
         if (!did_readaround) {
                 ret = VM_FAULT_MAJOR;
                 count_vm_event(PGMAJFAULT);
         }
 
         /*
          * 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.
          */
         ClearPageError(page);
         error = mapping->a_ops->readpage(file, page);
         page_cache_release(page);
 
         if (!error || error == AOP_TRUNCATED_PAGE)
                 goto retry_find;
 
         /* Things didn't work out. Return zero to tell the mm layer so. */
         shrink_readahead_size_eio(file, ra);
         return VM_FAULT_SIGBUS;
 }
 EXPORT_SYMBOL(filemap_fault);
 
 struct vm_operations_struct generic_file_vm_ops = {
         .fault          = filemap_fault,
 };
 
 /* 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;
         vma->vm_flags |= VM_CAN_NONLINEAR;
         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 struct page *__read_cache_page(struct address_space *mapping,
                                 pgoff_t index,
                                 int (*filler)(void *,struct page*),
                                 void *data)
 {
         struct page *page;
         int err;
 repeat:
         page = find_get_page(mapping, index);
         if (!page) {
                 page = page_cache_alloc_cold(mapping);
                 if (!page)
                         return ERR_PTR(-ENOMEM);
                 err = add_to_page_cache_lru(page, mapping, index, GFP_KERNEL);
                 if (unlikely(err)) {
                         page_cache_release(page);
                         if (err == -EEXIST)
                                 goto repeat;
                         /* Presumably ENOMEM for radix tree node */
                         return ERR_PTR(err);
                 }
                 err = filler(data, page);
                 if (err < 0) {
                         page_cache_release(page);
                         page = ERR_PTR(err);
                 }
         }
         return page;
 }
 
 /**
  * read_cache_page_async - read into page cache, fill it if needed
  * @mapping:    the page's address_space
  * @index:      the page index
  * @filler:     function to perform the read
  * @data:       destination for read data
  *
  * Same as read_cache_page, but don't wait for page to become unlocked
  * after submitting it to the filler.
  *
  * Read into the page cache. If a page already exists, and PageUptodate() is
  * not set, try to fill the page but don't wait for it to become unlocked.
  *
  * If the page does not get brought uptodate, return -EIO.
  */
 struct page *read_cache_page_async(struct address_space *mapping,
                                 pgoff_t 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))
                 return 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);
                 return ERR_PTR(err);
         }
 out:
         mark_page_accessed(page);
         return page;
 }
 EXPORT_SYMBOL(read_cache_page_async);
 
 /**
  * read_cache_page - read into page cache, fill it if needed
  * @mapping:    the page's address_space
  * @index:      the page index
  * @filler:     function to perform the read
  * @data:       destination for read data
  *
  * Read into the page cache. If a page already exists, and PageUptodate() is
  * not set, try to fill the page then wait for it to become unlocked.
  *
  * If the page does not get brought uptodate, return -EIO.
  */
 struct page *read_cache_page(struct address_space *mapping,
                                 pgoff_t index,
                                 int (*filler)(void *,struct page*),
                                 void *data)
 {
         struct page *page;
 
         page = read_cache_page_async(mapping, index, filler, data);
         if (IS_ERR(page))
                 goto out;
         wait_on_page_locked(page);
         if (!PageUptodate(page)) {
                 page_cache_release(page);
                 page = ERR_PTR(-EIO);
         }
  out:
         return page;
 }
 EXPORT_SYMBOL(read_cache_page);
 
 /*
  * The logic we want is
  *
  *      if suid or (sgid and xgrp)
  *              remove privs
  */
 int should_remove_suid(struct dentry *dentry)
 {
         mode_t mode = dentry->d_inode->i_mode;
         int kill = 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)))
                 return kill;
 
         return 0;
 }
 EXPORT_SYMBOL(should_remove_suid);
 
 int __remove_suid(struct dentry *dentry, int kill)
 {
         struct iattr newattrs;
 
         newattrs.ia_valid = ATTR_FORCE | kill;
         return notify_change(dentry, &newattrs);
 }
 
 int remove_suid(struct dentry *dentry)
 {
         int killsuid = should_remove_suid(dentry);
         int killpriv = security_inode_need_killpriv(dentry);
         int error = 0;
 
         if (killpriv < 0)
                 return killpriv;
         if (killpriv)
                 error = security_inode_killpriv(dentry);
         if (!error && killsuid)
                 error = __remove_suid(dentry, killsuid);
 
         return error;
 }
 EXPORT_SYMBOL(remove_suid);
 
 static size_t __iovec_copy_from_user_inatomic(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_nocache(vaddr, buf, copy);
                 copied += copy;
                 bytes -= copy;
                 vaddr += copy;
                 iov++;
 
                 if (unlikely(left))
                         break;
         }
         return copied - left;
 }
 
 /*
  * Copy as much as we can into the page and return the number of bytes which
  * were sucessfully copied.  If a fault is encountered then return the number of
  * bytes which were copied.
  */
 size_t iov_iter_copy_from_user_atomic(struct page *page,
                 struct iov_iter *i, unsigned long offset, size_t bytes)
 {
         char *kaddr;
         size_t copied;
 
 #ifndef CONFIG_PREEMPT_RT
         BUG_ON(!current->pagefault_disabled);
 #endif
         kaddr = kmap_atomic(page, KM_USER0);
         if (likely(i->nr_segs == 1)) {
                 int left;
                 char __user *buf = i->iov->iov_base + i->iov_offset;
                 left = __copy_from_user_inatomic_nocache(kaddr + offset,
                                                         buf, bytes);
                 copied = bytes - left;
         } else {
                 copied = __iovec_copy_from_user_inatomic(kaddr + offset,
                                                 i->iov, i->iov_offset, bytes);
         }
         kunmap_atomic(kaddr, KM_USER0);
 
         return copied;
 }
 EXPORT_SYMBOL(iov_iter_copy_from_user_atomic);
 
 /*
  * This has the same sideeffects and return value as
  * iov_iter_copy_from_user_atomic().
  * The difference is that it attempts to resolve faults.
  * Page must not be locked.
  */
 size_t iov_iter_copy_from_user(struct page *page,
                 struct iov_iter *i, unsigned long offset, size_t bytes)
 {
         char *kaddr;
         size_t copied;
 
         kaddr = kmap(page);
         if (likely(i->nr_segs == 1)) {
                 int left;
                 char __user *buf = i->iov->iov_base + i->iov_offset;
                 left = __copy_from_user_nocache(kaddr + offset, buf, bytes);
                 copied = bytes - left;
         } else {
                 copied = __iovec_copy_from_user_inatomic(kaddr + offset,
                                                 i->iov, i->iov_offset, bytes);
         }
         kunmap(page);
         return copied;
 }
 EXPORT_SYMBOL(iov_iter_copy_from_user);
 
 void iov_iter_advance(struct iov_iter *i, size_t bytes)
 {
         BUG_ON(i->count < bytes);
 
         if (likely(i->nr_segs == 1)) {
                 i->iov_offset += bytes;
                 i->count -= bytes;
         } else {
                 const struct iovec *iov = i->iov;
                 size_t base = i->iov_offset;
 
                 /*
                  * The !iov->iov_len check ensures we skip over unlikely
                  * zero-length segments (without overruning the iovec).
                  */
                 while (bytes || unlikely(!iov->iov_len && i->count)) {
                         int copy;
 
                         copy = min(bytes, iov->iov_len - base);
                         BUG_ON(!i->count || i->count < copy);
                         i->count -= copy;
                         bytes -= copy;
                         base += copy;
                         if (iov->iov_len == base) {
                                 iov++;
                                 base = 0;
                         }
                 }
                 i->iov = iov;
                 i->iov_offset = base;
         }
 }
 EXPORT_SYMBOL(iov_iter_advance);
 
 /*
  * Fault in the first iovec of the given iov_iter, to a maximum length
  * of bytes. Returns 0 on success, or non-zero if the memory could not be
  * accessed (ie. because it is an invalid address).
  *
  * writev-intensive code may want this to prefault several iovecs -- that
  * would be possible (callers must not rely on the fact that _only_ the
  * first iovec will be faulted with the current implementation).
  */
 int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
 {
         char __user *buf = i->iov->iov_base + i->iov_offset;
         bytes = min(bytes, i->iov->iov_len - i->iov_offset);
         return fault_in_pages_readable(buf, bytes);
 }
 EXPORT_SYMBOL(iov_iter_fault_in_readable);
 
 /*
  * Return the count of just the current iov_iter segment.
  */
 size_t iov_iter_single_seg_count(struct iov_iter *i)
 {
         const struct iovec *iov = i->iov;
         if (i->nr_segs == 1)
                 return i->count;
         else
                 return min(i->count, iov->iov_len - i->iov_offset);
 }
 EXPORT_SYMBOL(iov_iter_single_seg_count);
 
 /*
  * Performs necessary checks before doing a write
  *
  * Can adjust writing position or 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) {
                         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) {
                                 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 {
 #ifdef CONFIG_BLOCK
                 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;
 #else
                 return -EPERM;
 #endif
         }
         return 0;
 }
 EXPORT_SYMBOL(generic_write_checks);
 
 int pagecache_write_begin(struct file *file, struct address_space *mapping,
                                 loff_t pos, unsigned len, unsigned flags,
                                 struct page **pagep, void **fsdata)
 {
         const struct address_space_operations *aops = mapping->a_ops;
 
         if (aops->write_begin) {
                 return aops->write_begin(file, mapping, pos, len, flags,
                                                         pagep, fsdata);
         } else {
                 int ret;
                 pgoff_t index = pos >> PAGE_CACHE_SHIFT;
                 unsigned offset = pos & (PAGE_CACHE_SIZE - 1);
                 struct inode *inode = mapping->host;
                 struct page *page;
 again:
                 page = __grab_cache_page(mapping, index);
                 *pagep = page;
                 if (!page)
                         return -ENOMEM;
 
                 if (flags & AOP_FLAG_UNINTERRUPTIBLE && !PageUptodate(page)) {
                         /*
                          * There is no way to resolve a short write situation
                          * for a !Uptodate page (except by double copying in
                          * the caller done by generic_perform_write_2copy).
                          *
                          * Instead, we have to bring it uptodate here.
                          */
                         ret = aops->readpage(file, page);
                         page_cache_release(page);
                         if (ret) {
                                 if (ret == AOP_TRUNCATED_PAGE)
                                         goto again;
                                 return ret;
                         }
                         goto again;
                 }
 
                 ret = aops->prepare_write(file, page, offset, offset+len);
                 if (ret) {
                         unlock_page(page);
                         page_cache_release(page);
                         if (pos + len > inode->i_size)
                                 vmtruncate(inode, inode->i_size);
                 }
                 return ret;
         }
 }
 EXPORT_SYMBOL(pagecache_write_begin);
 
 int pagecache_write_end(struct file *file, struct address_space *mapping,
                                 loff_t pos, unsigned len, unsigned copied,
                                 struct page *page, void *fsdata)
 {
         const struct address_space_operations *aops = mapping->a_ops;
         int ret;
 
         if (aops->write_end) {
                 mark_page_accessed(page);
                 ret = aops->write_end(file, mapping, pos, len, copied,
                                                         page, fsdata);
         } else {
                 unsigned offset = pos & (PAGE_CACHE_SIZE - 1);
                 struct inode *inode = mapping->host;
 
                 flush_dcache_page(page);
                 ret = aops->commit_write(file, page, offset, offset+len);
                 unlock_page(page);
                 mark_page_accessed(page);
                 page_cache_release(page);
 
                 if (ret < 0) {
                         if (pos + len > inode->i_size)
                                 vmtruncate(inode, inode->i_size);
                 } else if (ret > 0)
                         ret = min_t(size_t, copied, ret);
                 else
                         ret = copied;
         }
 
         return ret;
 }
 EXPORT_SYMBOL(pagecache_write_end);
 
 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.  AIO O_DIRECT ops attempt to sync metadata here.
          */
         if ((written >= 0 || written == -EIOCBQUEUED) &&
             ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
                 int err = generic_osync_inode(inode, mapping, OSYNC_METADATA);
                 if (err < 0)
                         written = err;
         }
         return written;
 }
 EXPORT_SYMBOL(generic_file_direct_write);
 
 /*
  * Find or create a page at the given pagecache position. Return the locked
  * page. This function is specifically for buffered writes.
  */
 struct page *__grab_cache_page(struct address_space *mapping, pgoff_t index)
 {
         int status;
         struct page *page;
 repeat:
         page = find_lock_page(mapping, index);
         if (likely(page))
                 return page;
 
         page = page_cache_alloc(mapping);
         if (!page)
                 return NULL;
         status = add_to_page_cache_lru(page, mapping, index, GFP_KERNEL);
         if (unlikely(status)) {
                 page_cache_release(page);
                 if (status == -EEXIST)
                         goto repeat;
                 return NULL;
         }
         return page;
 }
 EXPORT_SYMBOL(__grab_cache_page);
 
 static ssize_t generic_perform_write_2copy(struct file *file,
                                 struct iov_iter *i, loff_t pos)
 {
         struct address_space *mapping = file->f_mapping;
         const struct address_space_operations *a_ops = mapping->a_ops;
         struct inode *inode = mapping->host;
         long status = 0;
         ssize_t written = 0;
 
         do {
                 struct page *src_page;
                 struct page *page;
                 pgoff_t index;          /* Pagecache index for current page */
                 unsigned long offset;   /* Offset into pagecache page */
                 unsigned long bytes;    /* Bytes to write to page */
                 size_t copied;          /* Bytes copied from user */
 
                 offset = (pos & (PAGE_CACHE_SIZE - 1));
                 index = pos >> PAGE_CACHE_SHIFT;
                 bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
                                                 iov_iter_count(i));
 
                 /*
                  * a non-NULL src_page indicates that we're doing the
                  * copy via get_user_pages and kmap.
                  */
                 src_page = NULL;
 
                 /*
                  * 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.
                  *
                  * Not only is this an optimisation, but it is also required
                  * to check that the address is actually valid, when atomic
                  * usercopies are used, below.
                  */
                 if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
                         status = -EFAULT;
                         break;
                 }
 
                 page = __grab_cache_page(mapping, index);
                 if (!page) {
                         status = -ENOMEM;
                         break;
                 }
 
                 /*
                  * non-uptodate pages cannot cope with short copies, and we
                  * cannot take a pagefault with the destination page locked.
                  * So pin the source page to copy it.
                  */
                 if (!PageUptodate(page) && !segment_eq(get_fs(), KERNEL_DS)) {
                         unlock_page(page);
 
                         src_page = alloc_page(GFP_KERNEL);
                         if (!src_page) {
                                 page_cache_release(page);
                                 status = -ENOMEM;
                                 break;
                         }
 
                         /*
                          * Cannot get_user_pages with a page locked for the
                          * same reason as we can't take a page fault with a
                          * page locked (as explained below).
                          */
                         copied = iov_iter_copy_from_user(src_page, i,
                                                                 offset, bytes);
                         if (unlikely(copied == 0)) {
                                 status = -EFAULT;
                                 page_cache_release(page);
                                 page_cache_release(src_page);
                                 break;
                         }
                         bytes = copied;
 
                         lock_page(page);
                         /*
                          * Can't handle the page going uptodate here, because
                          * that means we would use non-atomic usercopies, which
                          * zero out the tail of the page, which can cause
                          * zeroes to become transiently visible. We could just
                          * use a non-zeroing copy, but the APIs aren't too
                          * consistent.
                          */
                         if (unlikely(!page->mapping || PageUptodate(page))) {
                                 unlock_page(page);
                                 page_cache_release(page);
                                 page_cache_release(src_page);
                                 continue;
                         }
                 }
 
                 status = a_ops->prepare_write(file, page, offset, offset+bytes);
                 if (unlikely(status))
                         goto fs_write_aop_error;
 
                 if (!src_page) {
                         /*
                          * Must not enter the pagefault handler here, because
                          * we hold the page lock, so we might recursively
                          * deadlock on the same lock, or get an ABBA deadlock
                          * against a different lock, or against the mmap_sem
                          * (which nests outside the page lock).  So increment
                          * preempt count, and use _atomic usercopies.
                          *
                          * The page is uptodate so we are OK to encounter a
                          * short copy: if unmodified parts of the page are
                          * marked dirty and written out to disk, it doesn't
                          * really matter.
                          */
                         pagefault_disable();
                         copied = iov_iter_copy_from_user_atomic(page, i,
                                                                 offset, bytes);
                         pagefault_enable();
                 } else {
                         void *src, *dst;
                         src = kmap_atomic(src_page, KM_USER0);
                         dst = kmap_atomic(page, KM_USER1);
                         memcpy(dst + offset, src + offset, bytes);
                         kunmap_atomic(dst, KM_USER1);
                         kunmap_atomic(src, KM_USER0);
                         copied = bytes;
                 }
                 flush_dcache_page(page);
 
                 status = a_ops->commit_write(file, page, offset, offset+bytes);
                 if (unlikely(status < 0))
                         goto fs_write_aop_error;
                 if (unlikely(status > 0)) /* filesystem did partial write */
                         copied = min_t(size_t, copied, status);
 
                 unlock_page(page);
                 mark_page_accessed(page);
                 page_cache_release(page);
                 if (src_page)
                         page_cache_release(src_page);
 
                 iov_iter_advance(i, copied);
                 pos += copied;
                 written += copied;
 
                 balance_dirty_pages_ratelimited(mapping);
                 cond_resched();
                 continue;
 
 fs_write_aop_error:
                 unlock_page(page);
                 page_cache_release(page);
                 if (src_page)
                         page_cache_release(src_page);
 
                 /*
                  * prepare_write() may have instantiated a few blocks
                  * outside i_size.  Trim these off again. Don't need
                  * i_size_read because we hold i_mutex.
                  */
                 if (pos + bytes > inode->i_size)
                         vmtruncate(inode, inode->i_size);
                 break;
         } while (iov_iter_count(i));
 
         return written ? written : status;
 }
 
 static ssize_t generic_perform_write(struct file *file,
                                 struct iov_iter *i, loff_t pos)
 {
         struct address_space *mapping = file->f_mapping;
         const struct address_space_operations *a_ops = mapping->a_ops;
         long status = 0;
         ssize_t written = 0;
         unsigned int flags = 0;
 
         /*
          * Copies from kernel address space cannot fail (NFSD is a big user).
          */
         if (segment_eq(get_fs(), KERNEL_DS))
                 flags |= AOP_FLAG_UNINTERRUPTIBLE;
 
         do {
                 struct page *page;
                 pgoff_t index;          /* Pagecache index for current page */
                 unsigned long offset;   /* Offset into pagecache page */
                 unsigned long bytes;    /* Bytes to write to page */
                 size_t copied;          /* Bytes copied from user */
                 void *fsdata;
 
                 offset = (pos & (PAGE_CACHE_SIZE - 1));
                 index = pos >> PAGE_CACHE_SHIFT;
                 bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
                                                 iov_iter_count(i));
 
 again:
 
                 /*
                  * 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.
                  *
                  * Not only is this an optimisation, but it is also required
                  * to check that the address is actually valid, when atomic
                  * usercopies are used, below.
                  */
                 if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
                         status = -EFAULT;
                         break;
                 }
 
                 status = a_ops->write_begin(file, mapping, pos, bytes, flags,
                                                 &page, &fsdata);
                 if (unlikely(status))
                         break;
 
                 pagefault_disable();
                 copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
                 pagefault_enable();
                 flush_dcache_page(page);
 
                 status = a_ops->write_end(file, mapping, pos, bytes, copied,
                                                 page, fsdata);
                 if (unlikely(status < 0))
                         break;
                 copied = status;
 
                 cond_resched();
 
                 iov_iter_advance(i, copied);
                 if (unlikely(copied == 0)) {
                         /*
                          * If we were unable to copy any data at all, we must
                          * fall back to a single segment length write.
                          *
                          * If we didn't fallback here, we could livelock
                          * because not all segments in the iov can be copied at
                          * once without a pagefault.
                          */
                         bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
                                                 iov_iter_single_seg_count(i));
                         goto again;
                 }
                 pos += copied;
                 written += copied;
 
                 balance_dirty_pages_ratelimited(mapping);
 
         } while (iov_iter_count(i));
 
         return written ? written : status;
 }
 
 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;
         const struct address_space_operations *a_ops = mapping->a_ops;
         struct inode *inode = mapping->host;
         ssize_t status;
         struct iov_iter i;
 
         iov_iter_init(&i, iov, nr_segs, count, written);
         if (a_ops->write_begin)
                 status = generic_perform_write(file, &i, pos);
         else
                 status = generic_perform_write_2copy(file, &i, pos);
 
         if (likely(status >= 0)) {
                 written += status;
                 *ppos = pos + status;
 
                 /*
                  * For now, when the user asks for O_SYNC, we'll actually give
                  * O_DSYNC
                  */
                 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);
 
         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;
         loff_t          pos;
         ssize_t         written;
         ssize_t         err;
 
         ocount = 0;
         err = generic_segment_checks(iov, &nr_segs, &ocount, VERIFY_READ);
         if (err)
                 return err;
 
         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_path.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)) {
                 loff_t endbyte;
                 ssize_t written_buffered;
 
                 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_buffered = generic_file_buffered_write(iocb, iov,
                                                 nr_segs, pos, ppos, count,
                                                 written);
                 /*
                  * If generic_file_buffered_write() retuned a synchronous error
                  * then we want to return the number of bytes which were
                  * direct-written, or the error code if that was zero.  Note
                  * that this differs from normal direct-io semantics, which
                  * will return -EFOO even if some bytes were written.
                  */
                 if (written_buffered < 0) {
                         err = written_buffered;
                         goto out;
                 }
 
                 /*
                  * We need to ensure that the page cache pages are written to
                  * disk and invalidated to preserve the expected O_DIRECT
                  * semantics.
                  */
                 endbyte = pos + written_buffered - written - 1;
                 err = do_sync_mapping_range(file->f_mapping, pos, endbyte,
                                             SYNC_FILE_RANGE_WAIT_BEFORE|
                                             SYNC_FILE_RANGE_WRITE|
                                             SYNC_FILE_RANGE_WAIT_AFTER);
                 if (err == 0) {
                         written = written_buffered;
                         invalidate_mapping_pages(mapping,
                                                  pos >> PAGE_CACHE_SHIFT,
                                                  endbyte >> PAGE_CACHE_SHIFT);
                 } else {
                         /*
                          * We don't know how much we wrote, so just return
                          * the number of bytes which were direct-written
                          */
                 }
         } else {
                 written = generic_file_buffered_write(iocb, iov, nr_segs,
                                 pos, ppos, count, written);
         }
 out:
         current->backing_dev_info = NULL;
         return written ? written : err;
 }
 
 ssize_t generic_file_aio_write_nolock(struct kiocb *iocb,
                 const struct iovec *iov, unsigned long nr_segs, loff_t pos)
 {
         struct file *file = iocb->ki_filp;
         struct address_space *mapping = file->f_mapping;
         struct inode *inode = mapping->host;
         ssize_t ret;
 
         BUG_ON(iocb->ki_pos != pos);
 
         ret = __generic_file_aio_write_nolock(iocb, iov, nr_segs,
                         &iocb->ki_pos);
 
         if (ret > 0 && ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
                 ssize_t err;
 
                 err = sync_page_range_nolock(inode, mapping, pos, ret);
                 if (err < 0)
                         ret = err;
         }
         return ret;
 }
 EXPORT_SYMBOL(generic_file_aio_write_nolock);
 
 ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
                 unsigned long nr_segs, loff_t pos)
 {
         struct file *file = iocb->ki_filp;
         struct address_space *mapping = file->f_mapping;
         struct inode *inode = mapping->host;
         ssize_t ret;
 
         BUG_ON(iocb->ki_pos != pos);
 
         mutex_lock(&inode->i_mutex);
         ret = __generic_file_aio_write_nolock(iocb, iov, nr_segs,
                         &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);
 
 /*
  * 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;
         pgoff_t end = 0; /* silence gcc */
 
         /*
          * 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);
                 end = (offset + write_len - 1) >> PAGE_CACHE_SHIFT;
                 if (mapping_mapped(mapping))
                         unmap_mapping_range(mapping, offset, write_len, 0);
         }
 
         retval = filemap_write_and_wait(mapping);
         if (retval)
                 goto out;
 
         /*
          * After a write we want buffered reads to be sure to go to disk to get
          * the new data.  We invalidate clean cached page from the region we're
          * about to write.  We do this *before* the write so that we can return
          * -EIO without clobbering -EIOCBQUEUED from ->direct_IO().
          */
         if (rw == WRITE && mapping_nrpages(mapping)) {
                 retval = invalidate_inode_pages2_range(mapping,
                                         offset >> PAGE_CACHE_SHIFT, end);
                 if (retval)
                         goto out;
         }
 
         retval = mapping->a_ops->direct_IO(rw, iocb, iov, offset, nr_segs);
 
         /*
          * Finally, try again to invalidate clean pages which might have been
          * cached by non-direct readahead, or faulted in by get_user_pages()
          * if the source of the write was an mmap'ed region of the file
          * we're writing.  Either one is a pretty crazy thing to do,
          * so we don't support it 100%.  If this invalidation
          * fails, tough, the write still worked...
          */
         if (rw == WRITE && mapping_nrpages(mapping)) {
                 invalidate_inode_pages2_range(mapping, offset >> PAGE_CACHE_SHIFT, end);
         }
 out:
         return retval;
 }
 
 /**
  * try_to_release_page() - release old fs-specific metadata on a page
  *
  * @page: the page which the kernel is trying to free
  * @gfp_mask: memory allocation flags (and I/O mode)
  *
  * The address_space is to try to release any data against the page
  * (presumably at page->private).  If the release was successful, return `1'.
  * Otherwise return zero.
  *
  * The @gfp_mask argument specifies whether I/O may be performed to release
  * this page (__GFP_IO), and whether the call may block (__GFP_WAIT).
  *
  * NOTE: @gfp_mask may go away, and this function may become non-blocking.
  */
 int try_to_release_page(struct page *page, gfp_t gfp_mask)
 {
         struct address_space * const mapping = page->mapping;
 
         BUG_ON(!PageLocked(page));
         if (PageWriteback(page))
                 return 0;
 
         if (mapping && mapping->a_ops->releasepage)
                 return mapping->a_ops->releasepage(page, gfp_mask);
         return try_to_free_buffers(page);
 }
 
 EXPORT_SYMBOL(try_to_release_page);