fs/nilfs2/page.c - kernel/msm-4.9 - Gitiles

 /*
  * page.c - buffer/page management specific to NILFS
  *
  * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or
  * (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  *
  * Written by Ryusuke Konishi <ryusuke@osrg.net>,
  *            Seiji Kihara <kihara@osrg.net>.
  */

 #include <linux/pagemap.h>
 #include <linux/writeback.h>
 #include <linux/swap.h>
 #include <linux/bitops.h>
 #include <linux/page-flags.h>
 #include <linux/list.h>
 #include <linux/highmem.h>
 #include <linux/pagevec.h>
 #include <linux/gfp.h>
 #include "nilfs.h"
 #include "page.h"
 #include "mdt.h"


 #define NILFS_BUFFER_INHERENT_BITS  \
 	((1UL << BH_Uptodate) | (1UL << BH_Mapped) | (1UL << BH_NILFS_Node) | \
 	 (1UL << BH_NILFS_Volatile) | (1UL << BH_NILFS_Checked))

 static struct buffer_head *
 __nilfs_get_page_block(struct page *page, unsigned long block, pgoff_t index,
 		       int blkbits, unsigned long b_state)

 {
 	unsigned long first_block;
 	struct buffer_head *bh;

 	if (!page_has_buffers(page))
 		create_empty_buffers(page, 1 << blkbits, b_state);

 	first_block = (unsigned long)index << (PAGE_CACHE_SHIFT - blkbits);
 	bh = nilfs_page_get_nth_block(page, block - first_block);

 	touch_buffer(bh);
 	wait_on_buffer(bh);
 	return bh;
 }

 struct buffer_head *nilfs_grab_buffer(struct inode *inode,
 				      struct address_space *mapping,
 				      unsigned long blkoff,
 				      unsigned long b_state)
 {
 	int blkbits = inode->i_blkbits;
 	pgoff_t index = blkoff >> (PAGE_CACHE_SHIFT - blkbits);
 	struct page *page;
 	struct buffer_head *bh;

 	page = grab_cache_page(mapping, index);
 	if (unlikely(!page))
 		return NULL;

 	bh = __nilfs_get_page_block(page, blkoff, index, blkbits, b_state);
 	if (unlikely(!bh)) {
 		unlock_page(page);
 		page_cache_release(page);
 		return NULL;
 	}
 	return bh;
 }

 /**
  * nilfs_forget_buffer - discard dirty state
  * @inode: owner inode of the buffer
  * @bh: buffer head of the buffer to be discarded
  */
 void nilfs_forget_buffer(struct buffer_head *bh)
 {
 	struct page *page = bh->b_page;
 	const unsigned long clear_bits =
 		(1 << BH_Uptodate | 1 << BH_Dirty | 1 << BH_Mapped |
 		 1 << BH_Async_Write | 1 << BH_NILFS_Volatile |
 		 1 << BH_NILFS_Checked | 1 << BH_NILFS_Redirected);

 	lock_buffer(bh);
 	set_mask_bits(&bh->b_state, clear_bits, 0);
 	if (nilfs_page_buffers_clean(page))
 		__nilfs_clear_page_dirty(page);

 	bh->b_blocknr = -1;
 	ClearPageUptodate(page);
 	ClearPageMappedToDisk(page);
 	unlock_buffer(bh);
 	brelse(bh);
 }

 /**
  * nilfs_copy_buffer -- copy buffer data and flags
  * @dbh: destination buffer
  * @sbh: source buffer
  */
 void nilfs_copy_buffer(struct buffer_head *dbh, struct buffer_head *sbh)
 {
 	void *kaddr0, *kaddr1;
 	unsigned long bits;
 	struct page *spage = sbh->b_page, *dpage = dbh->b_page;
 	struct buffer_head *bh;

 	kaddr0 = kmap_atomic(spage);
 	kaddr1 = kmap_atomic(dpage);
 	memcpy(kaddr1 + bh_offset(dbh), kaddr0 + bh_offset(sbh), sbh->b_size);
 	kunmap_atomic(kaddr1);
 	kunmap_atomic(kaddr0);

 	dbh->b_state = sbh->b_state & NILFS_BUFFER_INHERENT_BITS;
 	dbh->b_blocknr = sbh->b_blocknr;
 	dbh->b_bdev = sbh->b_bdev;

 	bh = dbh;
 	bits = sbh->b_state & ((1UL << BH_Uptodate) | (1UL << BH_Mapped));
 	while ((bh = bh->b_this_page) != dbh) {
 		lock_buffer(bh);
 		bits &= bh->b_state;
 		unlock_buffer(bh);
 	}
 	if (bits & (1UL << BH_Uptodate))
 		SetPageUptodate(dpage);
 	else
 		ClearPageUptodate(dpage);
 	if (bits & (1UL << BH_Mapped))
 		SetPageMappedToDisk(dpage);
 	else
 		ClearPageMappedToDisk(dpage);
 }

 /**
  * nilfs_page_buffers_clean - check if a page has dirty buffers or not.
  * @page: page to be checked
  *
  * nilfs_page_buffers_clean() returns zero if the page has dirty buffers.
  * Otherwise, it returns non-zero value.
  */
 int nilfs_page_buffers_clean(struct page *page)
 {
 	struct buffer_head *bh, *head;

 	bh = head = page_buffers(page);
 	do {
 		if (buffer_dirty(bh))
 			return 0;
 		bh = bh->b_this_page;
 	} while (bh != head);
 	return 1;
 }

 void nilfs_page_bug(struct page *page)
 {
 	struct address_space *m;
 	unsigned long ino;

 	if (unlikely(!page)) {
 		printk(KERN_CRIT "NILFS_PAGE_BUG(NULL)\n");
 		return;
 	}

 	m = page->mapping;
 	ino = m ? m->host->i_ino : 0;

 	printk(KERN_CRIT "NILFS_PAGE_BUG(%p): cnt=%d index#=%llu flags=0x%lx "
 	       "mapping=%p ino=%lu\n",
 	       page, page_ref_count(page),
 	       (unsigned long long)page->index, page->flags, m, ino);

 	if (page_has_buffers(page)) {
 		struct buffer_head *bh, *head;
 		int i = 0;

 		bh = head = page_buffers(page);
 		do {
 			printk(KERN_CRIT
 			       " BH[%d] %p: cnt=%d block#=%llu state=0x%lx\n",
 			       i++, bh, atomic_read(&bh->b_count),
 			       (unsigned long long)bh->b_blocknr, bh->b_state);
 			bh = bh->b_this_page;
 		} while (bh != head);
 	}
 }

 /**
  * nilfs_copy_page -- copy the page with buffers
  * @dst: destination page
  * @src: source page
  * @copy_dirty: flag whether to copy dirty states on the page's buffer heads.
  *
  * This function is for both data pages and btnode pages.  The dirty flag
  * should be treated by caller.  The page must not be under i/o.
  * Both src and dst page must be locked
  */
 static void nilfs_copy_page(struct page *dst, struct page *src, int copy_dirty)
 {
 	struct buffer_head *dbh, *dbufs, *sbh, *sbufs;
 	unsigned long mask = NILFS_BUFFER_INHERENT_BITS;

 	BUG_ON(PageWriteback(dst));

 	sbh = sbufs = page_buffers(src);
 	if (!page_has_buffers(dst))
 		create_empty_buffers(dst, sbh->b_size, 0);

 	if (copy_dirty)
 		mask |= (1UL << BH_Dirty);

 	dbh = dbufs = page_buffers(dst);
 	do {
 		lock_buffer(sbh);
 		lock_buffer(dbh);
 		dbh->b_state = sbh->b_state & mask;
 		dbh->b_blocknr = sbh->b_blocknr;
 		dbh->b_bdev = sbh->b_bdev;
 		sbh = sbh->b_this_page;
 		dbh = dbh->b_this_page;
 	} while (dbh != dbufs);

 	copy_highpage(dst, src);

 	if (PageUptodate(src) && !PageUptodate(dst))
 		SetPageUptodate(dst);
 	else if (!PageUptodate(src) && PageUptodate(dst))
 		ClearPageUptodate(dst);
 	if (PageMappedToDisk(src) && !PageMappedToDisk(dst))
 		SetPageMappedToDisk(dst);
 	else if (!PageMappedToDisk(src) && PageMappedToDisk(dst))
 		ClearPageMappedToDisk(dst);

 	do {
 		unlock_buffer(sbh);
 		unlock_buffer(dbh);
 		sbh = sbh->b_this_page;
 		dbh = dbh->b_this_page;
 	} while (dbh != dbufs);
 }

 int nilfs_copy_dirty_pages(struct address_space *dmap,
 			   struct address_space *smap)
 {
 	struct pagevec pvec;
 	unsigned int i;
 	pgoff_t index = 0;
 	int err = 0;

 	pagevec_init(&pvec, 0);
 repeat:
 	if (!pagevec_lookup_tag(&pvec, smap, &index, PAGECACHE_TAG_DIRTY,
 				PAGEVEC_SIZE))
 		return 0;

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

 		lock_page(page);
 		if (unlikely(!PageDirty(page)))
 			NILFS_PAGE_BUG(page, "inconsistent dirty state");

 		dpage = grab_cache_page(dmap, page->index);
 		if (unlikely(!dpage)) {
 			/* No empty page is added to the page cache */
 			err = -ENOMEM;
 			unlock_page(page);
 			break;
 		}
 		if (unlikely(!page_has_buffers(page)))
 			NILFS_PAGE_BUG(page,
 				       "found empty page in dat page cache");

 		nilfs_copy_page(dpage, page, 1);
 		__set_page_dirty_nobuffers(dpage);

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

 	if (likely(!err))
 		goto repeat;
 	return err;
 }

 /**
  * nilfs_copy_back_pages -- copy back pages to original cache from shadow cache
  * @dmap: destination page cache
  * @smap: source page cache
  *
  * No pages must no be added to the cache during this process.
  * This must be ensured by the caller.
  */
 void nilfs_copy_back_pages(struct address_space *dmap,
 			   struct address_space *smap)
 {
 	struct pagevec pvec;
 	unsigned int i, n;
 	pgoff_t index = 0;
 	int err;

 	pagevec_init(&pvec, 0);
 repeat:
 	n = pagevec_lookup(&pvec, smap, index, PAGEVEC_SIZE);
 	if (!n)
 		return;
 	index = pvec.pages[n - 1]->index + 1;

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

 		lock_page(page);
 		dpage = find_lock_page(dmap, offset);
 		if (dpage) {
 			/* override existing page on the destination cache */
 			WARN_ON(PageDirty(dpage));
 			nilfs_copy_page(dpage, page, 0);
 			unlock_page(dpage);
 			page_cache_release(dpage);
 		} else {
 			struct page *page2;

 			/* move the page to the destination cache */
 			spin_lock_irq(&smap->tree_lock);
 			page2 = radix_tree_delete(&smap->page_tree, offset);
 			WARN_ON(page2 != page);

 			smap->nrpages--;
 			spin_unlock_irq(&smap->tree_lock);

 			spin_lock_irq(&dmap->tree_lock);
 			err = radix_tree_insert(&dmap->page_tree, offset, page);
 			if (unlikely(err < 0)) {
 				WARN_ON(err == -EEXIST);
 				page->mapping = NULL;
 				page_cache_release(page); /* for cache */
 			} else {
 				page->mapping = dmap;
 				dmap->nrpages++;
 				if (PageDirty(page))
 					radix_tree_tag_set(&dmap->page_tree,
 							   offset,
 							   PAGECACHE_TAG_DIRTY);
 			}
 			spin_unlock_irq(&dmap->tree_lock);
 		}
 		unlock_page(page);
 	}
 	pagevec_release(&pvec);
 	cond_resched();

 	goto repeat;
 }

 /**
  * nilfs_clear_dirty_pages - discard dirty pages in address space
  * @mapping: address space with dirty pages for discarding
  * @silent: suppress [true] or print [false] warning messages
  */
 void nilfs_clear_dirty_pages(struct address_space *mapping, bool silent)
 {
 	struct pagevec pvec;
 	unsigned int i;
 	pgoff_t index = 0;

 	pagevec_init(&pvec, 0);

 	while (pagevec_lookup_tag(&pvec, mapping, &index, PAGECACHE_TAG_DIRTY,
 				  PAGEVEC_SIZE)) {
 		for (i = 0; i < pagevec_count(&pvec); i++) {
 			struct page *page = pvec.pages[i];

 			lock_page(page);
 			nilfs_clear_dirty_page(page, silent);
 			unlock_page(page);
 		}
 		pagevec_release(&pvec);
 		cond_resched();
 	}
 }

 /**
  * nilfs_clear_dirty_page - discard dirty page
  * @page: dirty page that will be discarded
  * @silent: suppress [true] or print [false] warning messages
  */
 void nilfs_clear_dirty_page(struct page *page, bool silent)
 {
 	struct inode *inode = page->mapping->host;
 	struct super_block *sb = inode->i_sb;

 	BUG_ON(!PageLocked(page));

 	if (!silent) {
 		nilfs_warning(sb, __func__,
 				"discard page: offset %lld, ino %lu",
 				page_offset(page), inode->i_ino);
 	}

 	ClearPageUptodate(page);
 	ClearPageMappedToDisk(page);

 	if (page_has_buffers(page)) {
 		struct buffer_head *bh, *head;
 		const unsigned long clear_bits =
 			(1 << BH_Uptodate | 1 << BH_Dirty | 1 << BH_Mapped |
 			 1 << BH_Async_Write | 1 << BH_NILFS_Volatile |
 			 1 << BH_NILFS_Checked | 1 << BH_NILFS_Redirected);

 		bh = head = page_buffers(page);
 		do {
 			lock_buffer(bh);
 			if (!silent) {
 				nilfs_warning(sb, __func__,
 					"discard block %llu, size %zu",
 					(u64)bh->b_blocknr, bh->b_size);
 			}
 			set_mask_bits(&bh->b_state, clear_bits, 0);
 			unlock_buffer(bh);
 		} while (bh = bh->b_this_page, bh != head);
 	}

 	__nilfs_clear_page_dirty(page);
 }

 unsigned nilfs_page_count_clean_buffers(struct page *page,
 					unsigned from, unsigned to)
 {
 	unsigned block_start, block_end;
 	struct buffer_head *bh, *head;
 	unsigned nc = 0;

 	for (bh = head = page_buffers(page), block_start = 0;
 	     bh != head || !block_start;
 	     block_start = block_end, bh = bh->b_this_page) {
 		block_end = block_start + bh->b_size;
 		if (block_end > from && block_start < to && !buffer_dirty(bh))
 			nc++;
 	}
 	return nc;
 }

 void nilfs_mapping_init(struct address_space *mapping, struct inode *inode)
 {
 	mapping->host = inode;
 	mapping->flags = 0;
 	mapping_set_gfp_mask(mapping, GFP_NOFS);
 	mapping->private_data = NULL;
 	mapping->a_ops = &empty_aops;
 }

 /*
  * NILFS2 needs clear_page_dirty() in the following two cases:
  *
  * 1) For B-tree node pages and data pages of the dat/gcdat, NILFS2 clears
  *    page dirty flags when it copies back pages from the shadow cache
  *    (gcdat->{i_mapping,i_btnode_cache}) to its original cache
  *    (dat->{i_mapping,i_btnode_cache}).
  *
  * 2) Some B-tree operations like insertion or deletion may dispose buffers
  *    in dirty state, and this needs to cancel the dirty state of their pages.
  */
 int __nilfs_clear_page_dirty(struct page *page)
 {
 	struct address_space *mapping = page->mapping;

 	if (mapping) {
 		spin_lock_irq(&mapping->tree_lock);
 		if (test_bit(PG_dirty, &page->flags)) {
 			radix_tree_tag_clear(&mapping->page_tree,
 					     page_index(page),
 					     PAGECACHE_TAG_DIRTY);
 			spin_unlock_irq(&mapping->tree_lock);
 			return clear_page_dirty_for_io(page);
 		}
 		spin_unlock_irq(&mapping->tree_lock);
 		return 0;
 	}
 	return TestClearPageDirty(page);
 }

 /**
  * nilfs_find_uncommitted_extent - find extent of uncommitted data
  * @inode: inode
  * @start_blk: start block offset (in)
  * @blkoff: start offset of the found extent (out)
  *
  * This function searches an extent of buffers marked "delayed" which
  * starts from a block offset equal to or larger than @start_blk.  If
  * such an extent was found, this will store the start offset in
  * @blkoff and return its length in blocks.  Otherwise, zero is
  * returned.
  */
 unsigned long nilfs_find_uncommitted_extent(struct inode *inode,
 					    sector_t start_blk,
 					    sector_t *blkoff)
 {
 	unsigned int i;
 	pgoff_t index;
 	unsigned int nblocks_in_page;
 	unsigned long length = 0;
 	sector_t b;
 	struct pagevec pvec;
 	struct page *page;

 	if (inode->i_mapping->nrpages == 0)
 		return 0;

 	index = start_blk >> (PAGE_CACHE_SHIFT - inode->i_blkbits);
 	nblocks_in_page = 1U << (PAGE_CACHE_SHIFT - inode->i_blkbits);

 	pagevec_init(&pvec, 0);

 repeat:
 	pvec.nr = find_get_pages_contig(inode->i_mapping, index, PAGEVEC_SIZE,
 					pvec.pages);
 	if (pvec.nr == 0)
 		return length;

 	if (length > 0 && pvec.pages[0]->index > index)
 		goto out;

 	b = pvec.pages[0]->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
 	i = 0;
 	do {
 		page = pvec.pages[i];

 		lock_page(page);
 		if (page_has_buffers(page)) {
 			struct buffer_head *bh, *head;

 			bh = head = page_buffers(page);
 			do {
 				if (b < start_blk)
 					continue;
 				if (buffer_delay(bh)) {
 					if (length == 0)
 						*blkoff = b;
 					length++;
 				} else if (length > 0) {
 					goto out_locked;
 				}
 			} while (++b, bh = bh->b_this_page, bh != head);
 		} else {
 			if (length > 0)
 				goto out_locked;

 			b += nblocks_in_page;
 		}
 		unlock_page(page);

 	} while (++i < pagevec_count(&pvec));

 	index = page->index + 1;
 	pagevec_release(&pvec);
 	cond_resched();
 	goto repeat;

 out_locked:
 	unlock_page(page);
 out:
 	pagevec_release(&pvec);
 	return length;
 }
	/*
	* page.c - buffer/page management specific to NILFS
	*
	* Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write to the Free Software
	* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
	*
	* Written by Ryusuke Konishi <ryusuke@osrg.net>,
	* Seiji Kihara <kihara@osrg.net>.
	*/

	#include <linux/pagemap.h>
	#include <linux/writeback.h>
	#include <linux/swap.h>
	#include <linux/bitops.h>
	#include <linux/page-flags.h>
	#include <linux/list.h>
	#include <linux/highmem.h>
	#include <linux/pagevec.h>
	#include <linux/gfp.h>
	#include "nilfs.h"
	#include "page.h"
	#include "mdt.h"


	#define NILFS_BUFFER_INHERENT_BITS \
	((1UL << BH_Uptodate) \| (1UL << BH_Mapped) \| (1UL << BH_NILFS_Node) \| \
	(1UL << BH_NILFS_Volatile) \| (1UL << BH_NILFS_Checked))

	static struct buffer_head *
	__nilfs_get_page_block(struct page *page, unsigned long block, pgoff_t index,
	int blkbits, unsigned long b_state)

	{
	unsigned long first_block;
	struct buffer_head *bh;

	if (!page_has_buffers(page))
	create_empty_buffers(page, 1 << blkbits, b_state);

	first_block = (unsigned long)index << (PAGE_CACHE_SHIFT - blkbits);
	bh = nilfs_page_get_nth_block(page, block - first_block);

	touch_buffer(bh);
	wait_on_buffer(bh);
	return bh;
	}

	struct buffer_head nilfs_grab_buffer(struct inode inode,
	struct address_space *mapping,
	unsigned long blkoff,
	unsigned long b_state)
	{
	int blkbits = inode->i_blkbits;
	pgoff_t index = blkoff >> (PAGE_CACHE_SHIFT - blkbits);
	struct page *page;
	struct buffer_head *bh;

	page = grab_cache_page(mapping, index);
	if (unlikely(!page))
	return NULL;

	bh = __nilfs_get_page_block(page, blkoff, index, blkbits, b_state);
	if (unlikely(!bh)) {
	unlock_page(page);
	page_cache_release(page);
	return NULL;
	}
	return bh;
	}

	/**
	* nilfs_forget_buffer - discard dirty state
	* @inode: owner inode of the buffer
	* @bh: buffer head of the buffer to be discarded
	*/
	void nilfs_forget_buffer(struct buffer_head *bh)
	{
	struct page *page = bh->b_page;
	const unsigned long clear_bits =
	(1 << BH_Uptodate \| 1 << BH_Dirty \| 1 << BH_Mapped \|
	1 << BH_Async_Write \| 1 << BH_NILFS_Volatile \|
	1 << BH_NILFS_Checked \| 1 << BH_NILFS_Redirected);

	lock_buffer(bh);
	set_mask_bits(&bh->b_state, clear_bits, 0);
	if (nilfs_page_buffers_clean(page))
	__nilfs_clear_page_dirty(page);

	bh->b_blocknr = -1;
	ClearPageUptodate(page);
	ClearPageMappedToDisk(page);
	unlock_buffer(bh);
	brelse(bh);
	}

	/**
	* nilfs_copy_buffer -- copy buffer data and flags
	* @dbh: destination buffer
	* @sbh: source buffer
	*/
	void nilfs_copy_buffer(struct buffer_head dbh, struct buffer_head sbh)
	{
	void kaddr0, kaddr1;
	unsigned long bits;
	struct page spage = sbh->b_page, dpage = dbh->b_page;
	struct buffer_head *bh;

	kaddr0 = kmap_atomic(spage);
	kaddr1 = kmap_atomic(dpage);
	memcpy(kaddr1 + bh_offset(dbh), kaddr0 + bh_offset(sbh), sbh->b_size);
	kunmap_atomic(kaddr1);
	kunmap_atomic(kaddr0);

	dbh->b_state = sbh->b_state & NILFS_BUFFER_INHERENT_BITS;
	dbh->b_blocknr = sbh->b_blocknr;
	dbh->b_bdev = sbh->b_bdev;

	bh = dbh;
	bits = sbh->b_state & ((1UL << BH_Uptodate) \| (1UL << BH_Mapped));
	while ((bh = bh->b_this_page) != dbh) {
	lock_buffer(bh);
	bits &= bh->b_state;
	unlock_buffer(bh);
	}
	if (bits & (1UL << BH_Uptodate))
	SetPageUptodate(dpage);
	else
	ClearPageUptodate(dpage);
	if (bits & (1UL << BH_Mapped))
	SetPageMappedToDisk(dpage);
	else
	ClearPageMappedToDisk(dpage);
	}

	/**
	* nilfs_page_buffers_clean - check if a page has dirty buffers or not.
	* @page: page to be checked
	*
	* nilfs_page_buffers_clean() returns zero if the page has dirty buffers.
	* Otherwise, it returns non-zero value.
	*/
	int nilfs_page_buffers_clean(struct page *page)
	{
	struct buffer_head bh, head;

	bh = head = page_buffers(page);
	do {
	if (buffer_dirty(bh))
	return 0;
	bh = bh->b_this_page;
	} while (bh != head);
	return 1;
	}

	void nilfs_page_bug(struct page *page)
	{
	struct address_space *m;
	unsigned long ino;

	if (unlikely(!page)) {
	printk(KERN_CRIT "NILFS_PAGE_BUG(NULL)\n");
	return;
	}

	m = page->mapping;
	ino = m ? m->host->i_ino : 0;

	printk(KERN_CRIT "NILFS_PAGE_BUG(%p): cnt=%d index#=%llu flags=0x%lx "
	"mapping=%p ino=%lu\n",
	page, page_ref_count(page),
	(unsigned long long)page->index, page->flags, m, ino);

	if (page_has_buffers(page)) {
	struct buffer_head bh, head;
	int i = 0;

	bh = head = page_buffers(page);
	do {
	printk(KERN_CRIT
	" BH[%d] %p: cnt=%d block#=%llu state=0x%lx\n",
	i++, bh, atomic_read(&bh->b_count),
	(unsigned long long)bh->b_blocknr, bh->b_state);
	bh = bh->b_this_page;
	} while (bh != head);
	}
	}

	/**
	* nilfs_copy_page -- copy the page with buffers
	* @dst: destination page
	* @src: source page
	* @copy_dirty: flag whether to copy dirty states on the page's buffer heads.
	*
	* This function is for both data pages and btnode pages. The dirty flag
	* should be treated by caller. The page must not be under i/o.
	* Both src and dst page must be locked
	*/
	static void nilfs_copy_page(struct page dst, struct page src, int copy_dirty)
	{
	struct buffer_head dbh, dbufs, sbh, sbufs;
	unsigned long mask = NILFS_BUFFER_INHERENT_BITS;

	BUG_ON(PageWriteback(dst));

	sbh = sbufs = page_buffers(src);
	if (!page_has_buffers(dst))
	create_empty_buffers(dst, sbh->b_size, 0);

	if (copy_dirty)
	mask \|= (1UL << BH_Dirty);

	dbh = dbufs = page_buffers(dst);
	do {
	lock_buffer(sbh);
	lock_buffer(dbh);
	dbh->b_state = sbh->b_state & mask;
	dbh->b_blocknr = sbh->b_blocknr;
	dbh->b_bdev = sbh->b_bdev;
	sbh = sbh->b_this_page;
	dbh = dbh->b_this_page;
	} while (dbh != dbufs);

	copy_highpage(dst, src);

	if (PageUptodate(src) && !PageUptodate(dst))
	SetPageUptodate(dst);
	else if (!PageUptodate(src) && PageUptodate(dst))
	ClearPageUptodate(dst);
	if (PageMappedToDisk(src) && !PageMappedToDisk(dst))
	SetPageMappedToDisk(dst);
	else if (!PageMappedToDisk(src) && PageMappedToDisk(dst))
	ClearPageMappedToDisk(dst);

	do {
	unlock_buffer(sbh);
	unlock_buffer(dbh);
	sbh = sbh->b_this_page;
	dbh = dbh->b_this_page;
	} while (dbh != dbufs);
	}

	int nilfs_copy_dirty_pages(struct address_space *dmap,
	struct address_space *smap)
	{
	struct pagevec pvec;
	unsigned int i;
	pgoff_t index = 0;
	int err = 0;

	pagevec_init(&pvec, 0);
	repeat:
	if (!pagevec_lookup_tag(&pvec, smap, &index, PAGECACHE_TAG_DIRTY,
	PAGEVEC_SIZE))
	return 0;

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

	lock_page(page);
	if (unlikely(!PageDirty(page)))
	NILFS_PAGE_BUG(page, "inconsistent dirty state");

	dpage = grab_cache_page(dmap, page->index);
	if (unlikely(!dpage)) {
	/* No empty page is added to the page cache */
	err = -ENOMEM;
	unlock_page(page);
	break;
	}
	if (unlikely(!page_has_buffers(page)))
	NILFS_PAGE_BUG(page,
	"found empty page in dat page cache");

	nilfs_copy_page(dpage, page, 1);
	__set_page_dirty_nobuffers(dpage);

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

	if (likely(!err))
	goto repeat;
	return err;
	}

	/**
	* nilfs_copy_back_pages -- copy back pages to original cache from shadow cache
	* @dmap: destination page cache
	* @smap: source page cache
	*
	* No pages must no be added to the cache during this process.
	* This must be ensured by the caller.
	*/
	void nilfs_copy_back_pages(struct address_space *dmap,
	struct address_space *smap)
	{
	struct pagevec pvec;
	unsigned int i, n;
	pgoff_t index = 0;
	int err;

	pagevec_init(&pvec, 0);
	repeat:
	n = pagevec_lookup(&pvec, smap, index, PAGEVEC_SIZE);
	if (!n)
	return;
	index = pvec.pages[n - 1]->index + 1;

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

	lock_page(page);
	dpage = find_lock_page(dmap, offset);
	if (dpage) {
	/* override existing page on the destination cache */
	WARN_ON(PageDirty(dpage));
	nilfs_copy_page(dpage, page, 0);
	unlock_page(dpage);
	page_cache_release(dpage);
	} else {
	struct page *page2;

	/* move the page to the destination cache */
	spin_lock_irq(&smap->tree_lock);
	page2 = radix_tree_delete(&smap->page_tree, offset);
	WARN_ON(page2 != page);

	smap->nrpages--;
	spin_unlock_irq(&smap->tree_lock);

	spin_lock_irq(&dmap->tree_lock);
	err = radix_tree_insert(&dmap->page_tree, offset, page);
	if (unlikely(err < 0)) {
	WARN_ON(err == -EEXIST);
	page->mapping = NULL;
	page_cache_release(page); /* for cache */
	} else {
	page->mapping = dmap;
	dmap->nrpages++;
	if (PageDirty(page))
	radix_tree_tag_set(&dmap->page_tree,
	offset,
	PAGECACHE_TAG_DIRTY);
	}
	spin_unlock_irq(&dmap->tree_lock);
	}
	unlock_page(page);
	}
	pagevec_release(&pvec);
	cond_resched();

	goto repeat;
	}

	/**
	* nilfs_clear_dirty_pages - discard dirty pages in address space
	* @mapping: address space with dirty pages for discarding
	* @silent: suppress [true] or print [false] warning messages
	*/
	void nilfs_clear_dirty_pages(struct address_space *mapping, bool silent)
	{
	struct pagevec pvec;
	unsigned int i;
	pgoff_t index = 0;

	pagevec_init(&pvec, 0);

	while (pagevec_lookup_tag(&pvec, mapping, &index, PAGECACHE_TAG_DIRTY,
	PAGEVEC_SIZE)) {
	for (i = 0; i < pagevec_count(&pvec); i++) {
	struct page *page = pvec.pages[i];

	lock_page(page);
	nilfs_clear_dirty_page(page, silent);
	unlock_page(page);
	}
	pagevec_release(&pvec);
	cond_resched();
	}
	}

	/**
	* nilfs_clear_dirty_page - discard dirty page
	* @page: dirty page that will be discarded
	* @silent: suppress [true] or print [false] warning messages
	*/
	void nilfs_clear_dirty_page(struct page *page, bool silent)
	{
	struct inode *inode = page->mapping->host;
	struct super_block *sb = inode->i_sb;

	BUG_ON(!PageLocked(page));

	if (!silent) {
	nilfs_warning(sb, __func__,
	"discard page: offset %lld, ino %lu",
	page_offset(page), inode->i_ino);
	}

	ClearPageUptodate(page);
	ClearPageMappedToDisk(page);

	if (page_has_buffers(page)) {
	struct buffer_head bh, head;
	const unsigned long clear_bits =
	(1 << BH_Uptodate \| 1 << BH_Dirty \| 1 << BH_Mapped \|
	1 << BH_Async_Write \| 1 << BH_NILFS_Volatile \|
	1 << BH_NILFS_Checked \| 1 << BH_NILFS_Redirected);

	bh = head = page_buffers(page);
	do {
	lock_buffer(bh);
	if (!silent) {
	nilfs_warning(sb, __func__,
	"discard block %llu, size %zu",
	(u64)bh->b_blocknr, bh->b_size);
	}
	set_mask_bits(&bh->b_state, clear_bits, 0);
	unlock_buffer(bh);
	} while (bh = bh->b_this_page, bh != head);
	}

	__nilfs_clear_page_dirty(page);
	}

	unsigned nilfs_page_count_clean_buffers(struct page *page,
	unsigned from, unsigned to)
	{
	unsigned block_start, block_end;
	struct buffer_head bh, head;
	unsigned nc = 0;

	for (bh = head = page_buffers(page), block_start = 0;
	bh != head \|\| !block_start;
	block_start = block_end, bh = bh->b_this_page) {
	block_end = block_start + bh->b_size;
	if (block_end > from && block_start < to && !buffer_dirty(bh))
	nc++;
	}
	return nc;
	}

	void nilfs_mapping_init(struct address_space mapping, struct inode inode)
	{
	mapping->host = inode;
	mapping->flags = 0;
	mapping_set_gfp_mask(mapping, GFP_NOFS);
	mapping->private_data = NULL;
	mapping->a_ops = &empty_aops;
	}

	/*
	* NILFS2 needs clear_page_dirty() in the following two cases:
	*
	* 1) For B-tree node pages and data pages of the dat/gcdat, NILFS2 clears
	* page dirty flags when it copies back pages from the shadow cache
	* (gcdat->{i_mapping,i_btnode_cache}) to its original cache
	* (dat->{i_mapping,i_btnode_cache}).
	*
	* 2) Some B-tree operations like insertion or deletion may dispose buffers
	* in dirty state, and this needs to cancel the dirty state of their pages.
	*/
	int __nilfs_clear_page_dirty(struct page *page)
	{
	struct address_space *mapping = page->mapping;

	if (mapping) {
	spin_lock_irq(&mapping->tree_lock);
	if (test_bit(PG_dirty, &page->flags)) {
	radix_tree_tag_clear(&mapping->page_tree,
	page_index(page),
	PAGECACHE_TAG_DIRTY);
	spin_unlock_irq(&mapping->tree_lock);
	return clear_page_dirty_for_io(page);
	}
	spin_unlock_irq(&mapping->tree_lock);
	return 0;
	}
	return TestClearPageDirty(page);
	}

	/**
	* nilfs_find_uncommitted_extent - find extent of uncommitted data
	* @inode: inode
	* @start_blk: start block offset (in)
	* @blkoff: start offset of the found extent (out)
	*
	* This function searches an extent of buffers marked "delayed" which
	* starts from a block offset equal to or larger than @start_blk. If
	* such an extent was found, this will store the start offset in
	* @blkoff and return its length in blocks. Otherwise, zero is
	* returned.
	*/
	unsigned long nilfs_find_uncommitted_extent(struct inode *inode,
	sector_t start_blk,
	sector_t *blkoff)
	{
	unsigned int i;
	pgoff_t index;
	unsigned int nblocks_in_page;
	unsigned long length = 0;
	sector_t b;
	struct pagevec pvec;
	struct page *page;

	if (inode->i_mapping->nrpages == 0)
	return 0;

	index = start_blk >> (PAGE_CACHE_SHIFT - inode->i_blkbits);
	nblocks_in_page = 1U << (PAGE_CACHE_SHIFT - inode->i_blkbits);

	pagevec_init(&pvec, 0);

	repeat:
	pvec.nr = find_get_pages_contig(inode->i_mapping, index, PAGEVEC_SIZE,
	pvec.pages);
	if (pvec.nr == 0)
	return length;

	if (length > 0 && pvec.pages[0]->index > index)
	goto out;

	b = pvec.pages[0]->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
	i = 0;
	do {
	page = pvec.pages[i];

	lock_page(page);
	if (page_has_buffers(page)) {
	struct buffer_head bh, head;

	bh = head = page_buffers(page);
	do {
	if (b < start_blk)
	continue;
	if (buffer_delay(bh)) {
	if (length == 0)
	*blkoff = b;
	length++;
	} else if (length > 0) {
	goto out_locked;
	}
	} while (++b, bh = bh->b_this_page, bh != head);
	} else {
	if (length > 0)
	goto out_locked;

	b += nblocks_in_page;
	}
	unlock_page(page);

	} while (++i < pagevec_count(&pvec));

	index = page->index + 1;
	pagevec_release(&pvec);
	cond_resched();
	goto repeat;

	out_locked:
	unlock_page(page);
	out:
	pagevec_release(&pvec);
	return length;
	}