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32 results

amdgpu_kms.c

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  • filemap.c 68.23 KiB
    /*
     *	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/backing-dev.h>
    #include <linux/security.h>
    #include <linux/syscalls.h>
    #include <linux/cpuset.h>
    #include <linux/hardirq.h> /* for BUG_ON(!in_atomic()) only */
    #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
     *          ->zone.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 a write_lock on the mapping's tree_lock.
     */
    void __remove_from_page_cache(struct page *page)
    {
    	struct address_space *mapping = page->mapping;
    
    	radix_tree_delete(&mapping->page_tree, page->index);
    	page->mapping = NULL;
    	mapping->nrpages--;
    	__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)
    {
    	struct address_space *mapping = page->mapping;
    
    	BUG_ON(!PageLocked(page));
    
    	write_lock_irq(&mapping->tree_lock);
    	__remove_from_page_cache(page);
    	write_unlock_irq(&mapping->tree_lock);
    }
    
    static int sync_page(void *word)
    {
    	struct address_space *mapping;
    	struct page *page;
    
    	page = container_of((unsigned long *)word, struct page, flags);
    
    	/*
    	 * page_mapping() is being called without PG_locked held.
    	 * Some knowledge of the state and use of the page is used to
    	 * reduce the requirements down to a memory barrier.
    	 * The danger here is of a stale page_mapping() return value
    	 * indicating a struct address_space different from the one it's
    	 * associated with when it is associated with one.
    	 * After smp_mb(), it's either the correct page_mapping() for
    	 * the page, or an old page_mapping() and the page's own
    	 * page_mapping() has gone NULL.
    	 * The ->sync_page() address_space operation must tolerate
    	 * page_mapping() going NULL. By an amazing coincidence,
    	 * this comes about because none of the users of the page
    	 * in the ->sync_page() methods make essential use of the
    	 * page_mapping(), merely passing the page down to the backing
    	 * device's unplug functions when it's non-NULL, which in turn
    	 * ignore it for all cases but swap, where only page_private(page) is
    	 * of interest. When page_mapping() does go NULL, the entire
    	 * call stack gracefully ignores the page and returns.
    	 * -- wli
    	 */
    	smp_mb();
    	mapping = page_mapping(page);
    	if (mapping && mapping->a_ops && mapping->a_ops->sync_page)
    		mapping->a_ops->sync_page(page);
    	io_schedule();
    	return 0;
    }
    
    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 * 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
     * @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) {
    		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) {
    		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 = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
    
    	if (error == 0) {
    		write_lock_irq(&mapping->tree_lock);
    		error = radix_tree_insert(&mapping->page_tree, offset, page);
    		if (!error) {
    			page_cache_get(page);
    			SetPageLocked(page);
    			page->mapping = mapping;
    			page->index = offset;
    			mapping->nrpages++;
    			__inc_zone_page_state(page, NR_FILE_PAGES);
    		}
    		write_unlock_irq(&mapping->tree_lock);
    		radix_tree_preload_end();
    	}
    	return error;
    }
    EXPORT_SYMBOL(add_to_page_cache);
    
    int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
    				pgoff_t offset, gfp_t gfp_mask)
    {
    	int ret = add_to_page_cache(page, mapping, offset, gfp_mask);
    	if (ret == 0)
    		lru_cache_add(page);
    	return ret;
    }
    
    #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;
    }
    
    /*
     * In order to wait for pages to become available there must be
     * waitqueues associated with pages. By using a hash table of
     * waitqueues where the bucket discipline is to maintain all
     * waiters on the same queue and wake all when any of the pages
     * become available, and for the woken contexts to check to be
     * sure the appropriate page became available, this saves space
     * at a cost of "thundering herd" phenomena during rare hash
     * collisions.
     */
    static wait_queue_head_t *page_waitqueue(struct page *page)
    {
    	const struct zone *zone = page_zone(page);
    
    	return &zone->wait_table[hash_ptr(page, zone->wait_table_bits)];
    }
    
    static inline void wake_up_page(struct page *page, int bit)
    {
    	__wake_up_bit(page_waitqueue(page), &page->flags, bit);
    }
    
    void fastcall wait_on_page_bit(struct page *page, int bit_nr)
    {
    	DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
    
    	if (test_bit(bit_nr, &page->flags))
    		__wait_on_bit(page_waitqueue(page), &wait, sync_page,
    							TASK_UNINTERRUPTIBLE);
    }
    EXPORT_SYMBOL(wait_on_page_bit);
    
    /**
     * unlock_page - unlock a locked page
     * @page: the page
     *
     * Unlocks the page and wakes up sleepers in ___wait_on_page_locked().
     * Also wakes sleepers in wait_on_page_writeback() because the wakeup
     * mechananism between PageLocked pages and PageWriteback pages is shared.
     * But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
     *
     * The first mb is necessary to safely close the critical section opened by the
     * TestSetPageLocked(), the second mb is necessary to enforce ordering between
     * the clear_bit and the read of the waitqueue (to avoid SMP races with a
     * parallel wait_on_page_locked()).
     */
    void fastcall unlock_page(struct page *page)
    {
    	smp_mb__before_clear_bit();
    	if (!TestClearPageLocked(page))
    		BUG();
    	smp_mb__after_clear_bit(); 
    	wake_up_page(page, PG_locked);
    }
    EXPORT_SYMBOL(unlock_page);
    
    /**
     * end_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 fastcall __lock_page(struct page *page)
    {
    	DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
    
    	__wait_on_bit_lock(page_waitqueue(page), &wait, sync_page,
    							TASK_UNINTERRUPTIBLE);
    }
    EXPORT_SYMBOL(__lock_page);
    
    int fastcall __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);
    }
    
    /*
     * Variant of lock_page that does not require the caller to hold a reference
     * on the page's mapping.
     */
    void fastcall __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)
    {
    	struct page *page;
    
    	read_lock_irq(&mapping->tree_lock);
    	page = radix_tree_lookup(&mapping->page_tree, offset);
    	if (page)
    		page_cache_get(page);
    	read_unlock_irq(&mapping->tree_lock);
    	return page;
    }
    EXPORT_SYMBOL(find_get_page);
    
    /**
     * 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:
    	read_lock_irq(&mapping->tree_lock);
    	page = radix_tree_lookup(&mapping->page_tree, offset);
    	if (page) {
    		page_cache_get(page);
    		if (TestSetPageLocked(page)) {
    			read_unlock_irq(&mapping->tree_lock);
    			__lock_page(page);
    
    			/* Has the page been truncated while we slept? */
    			if (unlikely(page->mapping != mapping)) {
    				unlock_page(page);
    				page_cache_release(page);
    				goto repeat;
    			}
    			VM_BUG_ON(page->index != offset);
    			goto out;
    		}
    	}
    	read_unlock_irq(&mapping->tree_lock);
    out:
    	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;
    
    	read_lock_irq(&mapping->tree_lock);
    	ret = radix_tree_gang_lookup(&mapping->page_tree,
    				(void **)pages, start, nr_pages);
    	for (i = 0; i < ret; i++)
    		page_cache_get(pages[i]);
    	read_unlock_irq(&mapping->tree_lock);
    	return ret;
    }
    
    /**
     * 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;
    
    	read_lock_irq(&mapping->tree_lock);
    	ret = radix_tree_gang_lookup(&mapping->page_tree,
    				(void **)pages, index, nr_pages);
    	for (i = 0; i < ret; i++) {
    		if (pages[i]->mapping == NULL || pages[i]->index != index)
    			break;
    
    		page_cache_get(pages[i]);
    		index++;
    	}
    	read_unlock_irq(&mapping->tree_lock);
    	return i;
    }
    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;
    
    	read_lock_irq(&mapping->tree_lock);
    	ret = radix_tree_gang_lookup_tag(&mapping->page_tree,
    				(void **)pages, *index, nr_pages, tag);
    	for (i = 0; i < ret; i++)
    		page_cache_get(pages[i]);
    	if (ret)
    		*index = pages[ret - 1]->index + 1;
    	read_unlock_irq(&mapping->tree_lock);
    	return ret;
    }
    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_mapping_read - generic file read routine
     * @mapping:	address_space to be read
     * @ra:		file's readahead state
     * @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.
     *
     * Note the struct file* is only passed for the use of readpage.
     * It may be NULL.
     */
    void do_generic_mapping_read(struct address_space *mapping,
    			     struct file_ra_state *ra,
    			     struct file *filp,
    			     loff_t *ppos,
    			     read_descriptor_t *desc,
    			     read_actor_t actor)
    {
    	struct inode *inode = mapping->host;
    	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);
    }
    EXPORT_SYMBOL(do_generic_mapping_read);
    
    int file_read_actor(read_descriptor_t *desc, struct page *page,
    			unsigned long offset, unsigned long size)
    {
    	char *kaddr;
    	unsigned long left, count = desc->count;
    
    	if (size > count)
    		size = count;
    
    	/*
    	 * Faults on the destination of a read are common, so do it before
    	 * taking the kmap.
    	 */
    	if (!fault_in_pages_writeable(desc->arg.buf, size)) {
    		kaddr = kmap_atomic(page, KM_USER0);
    		left = __copy_to_user_inatomic(desc->arg.buf,
    						kaddr + offset, size);
    		kunmap_atomic(kaddr, KM_USER0);
    		if (left == 0)
    			goto success;
    	}
    
    	/* Do it the slow way */
    	kaddr = kmap(page);
    	left = __copy_to_user(desc->arg.buf, kaddr + offset, size);
    	kunmap(page);
    
    	if (left) {
    		size -= left;
    		desc->error = -EFAULT;
    	}
    success:
    	desc->count = count - size;
    	desc->written += size;
    	desc->arg.buf += size;
    	return size;
    }
    
    /*
     * 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 fastcall 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;
    	unsigned long 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;
    }
    
    /*
     * Same as read_cache_page, but don't wait for page to become unlocked
     * after submitting it to the filler.
     */
    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;
    
    	BUG_ON(!in_atomic());
    	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);
    
    static void __iov_iter_advance_iov(struct iov_iter *i, size_t bytes)
    {
    	if (likely(i->nr_segs == 1)) {
    		i->iov_offset += 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.
    		 */
    		while (bytes || !iov->iov_len) {
    			int copy = min(bytes, iov->iov_len - base);
    
    			bytes -= copy;
    			base += copy;
    			if (iov->iov_len == base) {
    				iov++;
    				base = 0;
    			}
    		}
    		i->iov = iov;
    		i->iov_offset = base;
    	}
    }
    
    void iov_iter_advance(struct iov_iter *i, size_t bytes)
    {
    	BUG_ON(i->count < bytes);
    
    	__iov_iter_advance_iov(i, bytes);
    	i->count -= bytes;
    }
    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) {
    		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) {
    		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);