static int __gfs2_jdata_writepage(struct page *page, struct writeback_control *wbc)
{
	struct inode *inode = page->mapping->host;
	struct gfs2_inode *ip = GFS2_I(inode);
	struct gfs2_sbd *sdp = GFS2_SB(inode);

	if (PageChecked(page)) {
		ClearPageChecked(page);
		if (!page_has_buffers(page)) {
			create_empty_buffers(page, inode->i_sb->s_blocksize,
					     (1 << BH_Dirty)|(1 << BH_Uptodate));
		}
		gfs2_page_add_databufs(ip, page, 0, sdp->sd_vfs->s_blocksize-1);
	}
	return block_write_full_page(page, gfs2_get_block_noalloc, wbc);
}

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;
}

static int gfs2_ordered_writepage(struct page *page,
				  struct writeback_control *wbc)
{
	struct inode *inode = page->mapping->host;
	struct gfs2_inode *ip = GFS2_I(inode);
	int ret;

	ret = gfs2_writepage_common(page, wbc);
	if (ret <= 0)
		return ret;

	if (!page_has_buffers(page)) {
		create_empty_buffers(page, inode->i_sb->s_blocksize,
				     (1 << BH_Dirty)|(1 << BH_Uptodate));
	}
	gfs2_page_add_databufs(ip, page, 0, inode->i_sb->s_blocksize-1);
	return block_write_full_page(page, gfs2_get_block_noalloc, wbc);
}

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_SHIFT - blkbits);
	bh = nilfs_page_get_nth_block(page, block - first_block);

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

struct buffer_head *gfs2_getbuf(struct gfs2_glock *gl, u64 blkno, int create)
{
	struct address_space *mapping = gl->gl_aspace->i_mapping;
	struct gfs2_sbd *sdp = gl->gl_sbd;
	struct page *page;
	struct buffer_head *bh;
	unsigned int shift;
	unsigned long index;
	unsigned int bufnum;

	shift = PAGE_CACHE_SHIFT - sdp->sd_sb.sb_bsize_shift;
	index = blkno >> shift;             /* convert block to page */
	bufnum = blkno - (index << shift);  /* block buf index within page */

	if (create) {
		for (;;) {
			page = grab_cache_page(mapping, index);
			if (page)
				break;
			yield();
		}
	} else {
		page = find_lock_page(mapping, index);
		if (!page)
			return NULL;
	}

	if (!page_has_buffers(page))
		create_empty_buffers(page, sdp->sd_sb.sb_bsize, 0);

	/* Locate header for our buffer within our page */
	for (bh = page_buffers(page); bufnum--; bh = bh->b_this_page)
		/* Do nothing */;
	get_bh(bh);

	if (!buffer_mapped(bh))
		map_bh(bh, sdp->sd_vfs, blkno);

	unlock_page(page);
	mark_page_accessed(page);
	page_cache_release(page);

	return bh;
}

/**
 * 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 |= BIT(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);
}

void
xfs_page_trace(
	int		tag,
	struct inode	*inode,
	struct page	*page,
	int		mask)
{
	xfs_inode_t	*ip;
	bhv_desc_t	*bdp;
	vnode_t		*vp = LINVFS_GET_VP(inode);
	loff_t		isize = i_size_read(inode);
	loff_t		offset = page->index << PAGE_CACHE_SHIFT;
	int		delalloc = -1, unmapped = -1, unwritten = -1;

	if (page_has_buffers(page))
		xfs_count_page_state(page, &delalloc, &unmapped, &unwritten);

	bdp = vn_bhv_lookup(VN_BHV_HEAD(vp), &xfs_vnodeops);
	ip = XFS_BHVTOI(bdp);
	if (!ip->i_rwtrace)
		return;

	ktrace_enter(ip->i_rwtrace,
		(void *)((unsigned long)tag),
		(void *)ip,
		(void *)inode,
		(void *)page,
		(void *)((unsigned long)mask),
		(void *)((unsigned long)((ip->i_d.di_size >> 32) & 0xffffffff)),
		(void *)((unsigned long)(ip->i_d.di_size & 0xffffffff)),
		(void *)((unsigned long)((isize >> 32) & 0xffffffff)),
		(void *)((unsigned long)(isize & 0xffffffff)),
		(void *)((unsigned long)((offset >> 32) & 0xffffffff)),
		(void *)((unsigned long)(offset & 0xffffffff)),
		(void *)((unsigned long)delalloc),
		(void *)((unsigned long)unmapped),
		(void *)((unsigned long)unwritten),
		(void *)NULL,
		(void *)NULL);
}

/**
 * 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;

		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);
			}
			clear_buffer_async_write(bh);
			clear_buffer_dirty(bh);
			clear_buffer_nilfs_volatile(bh);
			clear_buffer_nilfs_checked(bh);
			clear_buffer_nilfs_redirected(bh);
			clear_buffer_uptodate(bh);
			clear_buffer_mapped(bh);
			unlock_buffer(bh);
		} while (bh = bh->b_this_page, bh != head);
	}

	__nilfs_clear_page_dirty(page);
}

static inline void print_buffers(struct page *page, sector_t block)
{
	struct buffer_head *bh, *head;

	if(!page_has_buffers(page)) {
		printk("Warning: page doesn't have buffers, not sure how that happened, allocating buffer !!!\n");
		create_empty_buffers(page, LFS_BSIZE, 0);
		bh = head = page_buffers(page);
		do {
			map_bh(bh, page->mapping->host->i_sb, block++); 
			bh = bh->b_this_page;
		} while(bh != head);
	}

	bh = head = page_buffers(page);
	do {
		if(!buffer_mapped(bh))
			dprintk("The buffer seems to be not mapped ??");
		//dprintk("mapped to blocknr = %Lu\n", bh->b_blocknr);
		bh = bh->b_this_page;
	} while(bh != head);
}

static int tux3_set_page_dirty_assert(struct page *page)
{
	struct buffer_head *head, *buffer;

	/* See comment of tux3_set_page_dirty() */
	ClearPageReclaim(page);

	/* Is there any cases to be called for old page of forked page? */
	WARN_ON(PageForked(page));

	/* This page should be dirty already, otherwise we will lost data. */
	assert(PageDirty(page));
	/* All buffers should be dirty already, otherwise we will lost data. */
	assert(page_has_buffers(page));
	head = buffer = page_buffers(page);
	do {
		assert(buffer_dirty(buffer));
		buffer = buffer->b_this_page;
	} while (buffer != head);

	return 0;
}

/**
 * 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);
}

static void gfs2_invalidatepage(struct page *page, unsigned long offset)
{
	struct gfs2_sbd *sdp = GFS2_SB(page->mapping->host);
	struct buffer_head *bh, *head;
	unsigned long pos = 0;

	BUG_ON(!PageLocked(page));
	if (offset == 0)
		ClearPageChecked(page);
	if (!page_has_buffers(page))
		goto out;

	bh = head = page_buffers(page);
	do {
		if (offset <= pos)
			gfs2_discard(sdp, bh);
		pos += bh->b_size;
		bh = bh->b_this_page;
	} while (bh != head);
out:
	if (offset == 0)
		try_to_release_page(page, 0);
}

/**
 * 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_msg(sb, KERN_WARNING,
			  "discard dirty 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 =
			(BIT(BH_Uptodate) | BIT(BH_Dirty) | BIT(BH_Mapped) |
			 BIT(BH_Async_Write) | BIT(BH_NILFS_Volatile) |
			 BIT(BH_NILFS_Checked) | BIT(BH_NILFS_Redirected));

		bh = head = page_buffers(page);
		do {
			lock_buffer(bh);
			if (!silent)
				nilfs_msg(sb, KERN_WARNING,
					  "discard dirty block: blocknr=%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);
}

/*
 * We have our BIO, so we can now mark the buffers clean.  Make
 * sure to only clean buffers which we know we'll be writing.
 */
static void clean_buffers(struct page *page, unsigned first_unmapped)
{
	unsigned buffer_counter = 0;
	struct buffer_head *bh, *head;
	if (!page_has_buffers(page))
		return;
	head = page_buffers(page);
	bh = head;

	do {
		if (buffer_counter++ == first_unmapped)
			break;
		clear_buffer_dirty(bh);
		bh = bh->b_this_page;
	} while (bh != head);

	/*
	 * we cannot drop the bh if the page is not uptodate or a concurrent
	 * readpage would fail to serialize with the bh and it would read from
	 * disk before we reach the platter.
	 */
	if (buffer_heads_over_limit && PageUptodate(page))
		try_to_free_buffers(page);
}

/**
 * sync_mft_mirror - synchronize an mft record to the mft mirror
 * @ni:		ntfs inode whose mft record to synchronize
 * @m:		mapped, mst protected (extent) mft record to synchronize
 * @sync:	if true, wait for i/o completion
 *
 * Write the mapped, mst protected (extent) mft record @m described by the
 * (regular or extent) ntfs inode @ni to the mft mirror ($MFTMirr).
 *
 * On success return 0.  On error return -errno and set the volume errors flag
 * in the ntfs_volume to which @ni belongs.
 *
 * NOTE:  We always perform synchronous i/o and ignore the @sync parameter.
 *
 * TODO:  If @sync is false, want to do truly asynchronous i/o, i.e. just
 * schedule i/o via ->writepage or do it via kntfsd or whatever.
 */
static int sync_mft_mirror(ntfs_inode *ni, MFT_RECORD *m, int sync)
{
	ntfs_volume *vol = ni->vol;
	struct page *page;
	unsigned int blocksize = vol->sb->s_blocksize;
	int max_bhs = vol->mft_record_size / blocksize;
	struct buffer_head *bhs[max_bhs];
	struct buffer_head *bh, *head;
	u8 *kmirr;
	unsigned int block_start, block_end, m_start, m_end;
	int i_bhs, nr_bhs, err = 0;

	ntfs_debug("Entering for inode 0x%lx.", ni->mft_no);
	BUG_ON(!max_bhs);
	if (unlikely(!vol->mftmirr_ino)) {
		/* This could happen during umount... */
		err = sync_mft_mirror_umount(ni, m);
		if (likely(!err))
			return err;
		goto err_out;
	}
	/* Get the page containing the mirror copy of the mft record @m. */
	page = ntfs_map_page(vol->mftmirr_ino->i_mapping, ni->mft_no >>
			(PAGE_CACHE_SHIFT - vol->mft_record_size_bits));
	if (unlikely(IS_ERR(page))) {
		ntfs_error(vol->sb, "Failed to map mft mirror page.");
		err = PTR_ERR(page);
		goto err_out;
	}
	/*
	 * Exclusion against other writers.   This should never be a problem
	 * since the page in which the mft record @m resides is also locked and
	 * hence any other writers would be held up there but it is better to
	 * make sure no one is writing from elsewhere.
	 */
	lock_page(page);
	/* The address in the page of the mirror copy of the mft record @m. */
	kmirr = page_address(page) + ((ni->mft_no << vol->mft_record_size_bits)
			& ~PAGE_CACHE_MASK);
	/* Copy the mst protected mft record to the mirror. */
	memcpy(kmirr, m, vol->mft_record_size);
	/* Make sure we have mapped buffers. */
	if (!page_has_buffers(page)) {
no_buffers_err_out:
		ntfs_error(vol->sb, "Writing mft mirror records without "
				"existing buffers is not implemented yet.  %s",
				ntfs_please_email);
		err = -EOPNOTSUPP;
		goto unlock_err_out;
	}
	bh = head = page_buffers(page);
	if (!bh)
		goto no_buffers_err_out;
	nr_bhs = 0;
	block_start = 0;
	m_start = kmirr - (u8*)page_address(page);
	m_end = m_start + vol->mft_record_size;
	do {
		block_end = block_start + blocksize;
		/*
		 * If the buffer is outside the mft record, just skip it,
		 * clearing it if it is dirty to make sure it is not written
		 * out.  It should never be marked dirty but better be safe.
		 */
		if ((block_end <= m_start) || (block_start >= m_end)) {
			if (buffer_dirty(bh)) {
				ntfs_warning(vol->sb, "Clearing dirty mft "
						"record page buffer.  %s",
						ntfs_please_email);
				clear_buffer_dirty(bh);
			}
			continue;
		}
		if (!buffer_mapped(bh)) {
			ntfs_error(vol->sb, "Writing mft mirror records "
					"without existing mapped buffers is "
					"not implemented yet.  %s",
					ntfs_please_email);
			err = -EOPNOTSUPP;
			continue;
		}
		if (!buffer_uptodate(bh)) {
			ntfs_error(vol->sb, "Writing mft mirror records "
//.........这里部分代码省略.........

void nilfs_page_debug(const char *fname, int line, struct page *page,
		      const char *m, ...)
{
	struct address_space *mapping;
	struct inode *inode;
	va_list args;
	int len;
	char b[MSIZ];

	/* The page should be locked */
	len = snprintf(b, MSIZ, "PAGE %p ", page);
	va_start(args, m);
	len += vsnprintf(b + len, MSIZ - len, m, args);
	va_end(args);

	if (page == NULL) {
		printk(KERN_DEBUG "%s: page=NULL %s at %d\n", b, fname, line);
		return;
	}
	mapping = page->mapping;
	len += snprintf(b + len, MSIZ - len,
			": cnt=%d index#=%llu mapping=%d lru=%d",
			atomic_read(&page->_count),
			(unsigned long long)page->index, !!mapping,
			!list_empty(&page->lru));
	len += snprintf(b + len, MSIZ - len, " %s(%d) flags=", fname, line);
	len += snprint_page_flags(b + len, MSIZ - len, page);
	if (mapping) {
		if (buffer_nilfs_node(page_buffers(page)))
			inode = NILFS_BTNC_I(mapping);
		else
			inode = NILFS_AS_I(mapping);
		if (inode != NULL)
			len += snprintf(b + len, MSIZ - len, " ino=%lu",
					inode->i_ino);
	}
	printk(KERN_DEBUG "%s\n", b);

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

		bh = head = page_buffers(page);
		if (!bh) {
			printk(KERN_DEBUG "PAGE %p: invalid page buffers\n",
			       page);
			return;
		}
		do {
			len = snprintf(b, MSIZ,
				       "  BH[%d] %p: cnt=%d blk#=%llu state=",
				       i, bh, atomic_read(&bh->b_count),
				       (unsigned long long)bh->b_blocknr);
			len += snprint_bh_state(b + len, MSIZ - len, bh);
			printk(KERN_DEBUG "%s\n", b);
			bh = bh->b_this_page;  i++;
			if (unlikely(!bh)) {
				printk(KERN_DEBUG
				       "PAGE %p: unexpected buffers end\n",
				       page);
				break;
			}
		} while (bh != head);
	}
}

/*
 * This is the worker routine which does all the work of mapping the disk
 * blocks and constructs largest possible bios, submits them for IO if the
 * blocks are not contiguous on the disk.
 *
 * We pass a buffer_head back and forth and use its buffer_mapped() flag to
 * represent the validity of its disk mapping and to decide when to do the next
 * get_block() call.
 */
static struct bio *
do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
		sector_t *last_block_in_bio, struct buffer_head *map_bh,
		  unsigned long *first_logical_block, struct compressed_bio **cb, get_block_t get_block)
{
	struct inode *inode = page->mapping->host;
	const unsigned blkbits = inode->i_blkbits;
	const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits; //SET TO 1
	const unsigned blocksize = 1 << blkbits;
	sector_t block_in_file;
	sector_t last_block;
	sector_t last_block_in_file;
	sector_t blocks[MAX_BUF_PER_PAGE];
	unsigned page_block;                                         //Increments to 1
	unsigned first_hole = blocks_per_page;
	struct block_device *bdev = NULL;
	int fully_mapped = 1;
	unsigned nblocks;
	unsigned relative_block;
	int err;
	/* blkbits = 12 | MAX_BUF_PER_PAGE = 8 */
	
	if (page_has_buffers(page))
		goto confused;

	/* block_in_file : page->index
	 * last_block    : last page->index of requested nr_pages
 	 * last_block_in_file  : always index of last_page_of_file
	 */
	block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
	last_block = block_in_file + nr_pages * blocks_per_page;
	last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
	if (last_block > last_block_in_file)
		last_block = last_block_in_file;
	page_block = 0;

	/*
	 * Map blocks using the result from the previous get_blocks call first.
	 */
	
	/* nblocks : Initially 0 | Later mapped to 1 extent so is mostly 16 */
	nblocks = map_bh->b_size >> blkbits;
	printk(KERN_INFO "\ncurrent_page : %Lu | nblocks_initial : %u", block_in_file, nblocks);

	if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
			block_in_file < (*first_logical_block + nblocks)) {
		unsigned map_offset = block_in_file - *first_logical_block;
		unsigned last = nblocks - map_offset;

		for (relative_block = 0; ; relative_block++) {
			if (relative_block == last) {
				clear_buffer_mapped(map_bh);
				break;
			}
			if (page_block == blocks_per_page)
				break;
			blocks[page_block] = map_bh->b_blocknr + map_offset +
						relative_block;

			page_block++;
			block_in_file++;
		}
		bdev = map_bh->b_bdev;
	}
	
	/*
	 * Then do more get_blocks calls until we are done with this page.
	 */
	map_bh->b_page = page;
	while (page_block < blocks_per_page) {
		map_bh->b_state = 0;
		map_bh->b_size = 0;

		if (block_in_file < last_block) {
			map_bh->b_size = (last_block - block_in_file) << blkbits;
			/* use of get_block => ***needs buffer_head map_bh 
			 * bdev     = map_bh->b_dev
			 * physical = map_bh->b_blocknr
			 * nblocks  = map_bh->b_size (no of logical blocks in extent)
			 * compress_count = map_bh->b_private
			 * first_logical_block
			 */
			if (get_block(inode, block_in_file, map_bh, 0)) //BLOCK_MAPPER
				goto confused;
			*first_logical_block = block_in_file;
		}
		/* generally is mapped.. so FALSE */
		if (!buffer_mapped(map_bh)) {
			fully_mapped = 0;
			if (first_hole == blocks_per_page)
				first_hole = page_block;
//.........这里部分代码省略.........

int ext4_mpage_readpages(struct address_space *mapping,
			 struct list_head *pages, struct page *page,
			 unsigned nr_pages, bool is_readahead)
{
	struct bio *bio = NULL;
	sector_t last_block_in_bio = 0;

	struct inode *inode = mapping->host;
	const unsigned blkbits = inode->i_blkbits;
	const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
	const unsigned blocksize = 1 << blkbits;
	sector_t block_in_file;
	sector_t last_block;
	sector_t last_block_in_file;
	sector_t blocks[MAX_BUF_PER_PAGE];
	unsigned page_block;
	struct block_device *bdev = inode->i_sb->s_bdev;
	int length;
	unsigned relative_block = 0;
	struct ext4_map_blocks map;

	map.m_pblk = 0;
	map.m_lblk = 0;
	map.m_len = 0;
	map.m_flags = 0;

	for (; nr_pages; nr_pages--) {
		int fully_mapped = 1;
		unsigned first_hole = blocks_per_page;

		prefetchw(&page->flags);
		if (pages) {
			page = lru_to_page(pages);
			list_del(&page->lru);
			if (add_to_page_cache_lru(page, mapping, page->index,
				  readahead_gfp_mask(mapping)))
				goto next_page;
		}

		if (page_has_buffers(page))
			goto confused;

		block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
		last_block = block_in_file + nr_pages * blocks_per_page;
		last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
		if (last_block > last_block_in_file)
			last_block = last_block_in_file;
		page_block = 0;

		/*
		 * Map blocks using the previous result first.
		 */
		if ((map.m_flags & EXT4_MAP_MAPPED) &&
		    block_in_file > map.m_lblk &&
		    block_in_file < (map.m_lblk + map.m_len)) {
			unsigned map_offset = block_in_file - map.m_lblk;
			unsigned last = map.m_len - map_offset;

			for (relative_block = 0; ; relative_block++) {
				if (relative_block == last) {
					/* needed? */
					map.m_flags &= ~EXT4_MAP_MAPPED;
					break;
				}
				if (page_block == blocks_per_page)
					break;
				blocks[page_block] = map.m_pblk + map_offset +
					relative_block;
				page_block++;
				block_in_file++;
			}
		}

		/*
		 * Then do more ext4_map_blocks() calls until we are
		 * done with this page.
		 */
		while (page_block < blocks_per_page) {
			if (block_in_file < last_block) {
				map.m_lblk = block_in_file;
				map.m_len = last_block - block_in_file;

				if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
				set_error_page:
					SetPageError(page);
					zero_user_segment(page, 0,
							  PAGE_SIZE);
					unlock_page(page);
					goto next_page;
				}
			}
			if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
				fully_mapped = 0;
				if (first_hole == blocks_per_page)
					first_hole = page_block;
				page_block++;
				block_in_file++;
				continue;
			}
			if (first_hole != blocks_per_page)
//.........这里部分代码省略.........

/*
 * This is the worker routine which does all the work of mapping the disk
 * blocks and constructs largest possible bios, submits them for IO if the
 * blocks are not contiguous on the disk.
 *
 * We pass a buffer_head back and forth and use its buffer_mapped() flag to
 * represent the validity of its disk mapping and to decide when to do the next
 * get_block() call.
 */
static struct bio *
do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
		sector_t *last_block_in_bio, struct buffer_head *map_bh,
		unsigned long *first_logical_block, get_block_t get_block)
{
	struct inode *inode = page->mapping->host;
	const unsigned blkbits = inode->i_blkbits;
	const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
	const unsigned blocksize = 1 << blkbits;
	sector_t block_in_file;
	sector_t last_block;
	sector_t last_block_in_file;
	sector_t blocks[MAX_BUF_PER_PAGE];
	unsigned page_block;
	unsigned first_hole = blocks_per_page;
	struct block_device *bdev = NULL;
	int length;
	int fully_mapped = 1;
	unsigned nblocks;
	unsigned relative_block;

	if (page_has_buffers(page))
		goto confused;

	block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
	last_block = block_in_file + nr_pages * blocks_per_page;
	last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
	if (last_block > last_block_in_file)
		last_block = last_block_in_file;
	page_block = 0;

	/*
	 * Map blocks using the result from the previous get_blocks call first.
	 */
	nblocks = map_bh->b_size >> blkbits;
	if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
			block_in_file < (*first_logical_block + nblocks)) {
		unsigned map_offset = block_in_file - *first_logical_block;
		unsigned last = nblocks - map_offset;

		for (relative_block = 0; ; relative_block++) {
			if (relative_block == last) {
				clear_buffer_mapped(map_bh);
				break;
			}
			if (page_block == blocks_per_page)
				break;
			blocks[page_block] = map_bh->b_blocknr + map_offset +
						relative_block;
			page_block++;
			block_in_file++;
		}
		bdev = map_bh->b_bdev;
	}

	/*
	 * Then do more get_blocks calls until we are done with this page.
	 */
	map_bh->b_page = page;
	while (page_block < blocks_per_page) {
		map_bh->b_state = 0;
		map_bh->b_size = 0;

		if (block_in_file < last_block) {
			map_bh->b_size = (last_block-block_in_file) << blkbits;
			if (get_block(inode, block_in_file, map_bh, 0))
				goto confused;
			*first_logical_block = block_in_file;
		}

		if (!buffer_mapped(map_bh)) {
			fully_mapped = 0;
			if (first_hole == blocks_per_page)
				first_hole = page_block;
			page_block++;
			block_in_file++;
			continue;
		}

		/* some filesystems will copy data into the page during
		 * the get_block call, in which case we don't want to
		 * read it again.  map_buffer_to_page copies the data
		 * we just collected from get_block into the page's buffers
		 * so readpage doesn't have to repeat the get_block call
		 */
		if (buffer_uptodate(map_bh)) {
			map_buffer_to_page(page, map_bh, page_block);
			goto confused;
		}
	
		if (first_hole != blocks_per_page)
//.........这里部分代码省略.........

static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
		      void *data)
{
	struct mpage_data *mpd = data;
	struct bio *bio = mpd->bio;
	struct address_space *mapping = page->mapping;
	struct inode *inode = page->mapping->host;
	const unsigned blkbits = inode->i_blkbits;
	unsigned long end_index;
	const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
	sector_t last_block;
	sector_t block_in_file;
	sector_t blocks[MAX_BUF_PER_PAGE];
	unsigned page_block;
	unsigned first_unmapped = blocks_per_page;
	struct block_device *bdev = NULL;
	int boundary = 0;
	sector_t boundary_block = 0;
	struct block_device *boundary_bdev = NULL;
	int length;
	struct buffer_head map_bh;
	loff_t i_size = i_size_read(inode);
	int ret = 0;
	int wr = (wbc->sync_mode == WB_SYNC_ALL ?  WRITE_SYNC : WRITE);

	if (page_has_buffers(page)) {
		struct buffer_head *head = page_buffers(page);
		struct buffer_head *bh = head;

		/* If they're all mapped and dirty, do it */
		page_block = 0;
		do {
			BUG_ON(buffer_locked(bh));
			if (!buffer_mapped(bh)) {
				/*
				 * unmapped dirty buffers are created by
				 * __set_page_dirty_buffers -> mmapped data
				 */
				if (buffer_dirty(bh))
					goto confused;
				if (first_unmapped == blocks_per_page)
					first_unmapped = page_block;
				continue;
			}

			if (first_unmapped != blocks_per_page)
				goto confused;	/* hole -> non-hole */

			if (!buffer_dirty(bh) || !buffer_uptodate(bh))
				goto confused;
			if (page_block) {
				if (bh->b_blocknr != blocks[page_block-1] + 1)
					goto confused;
			}
			blocks[page_block++] = bh->b_blocknr;
			boundary = buffer_boundary(bh);
			if (boundary) {
				boundary_block = bh->b_blocknr;
				boundary_bdev = bh->b_bdev;
			}
			bdev = bh->b_bdev;
		} while ((bh = bh->b_this_page) != head);

		if (first_unmapped)
			goto page_is_mapped;

		/*
		 * Page has buffers, but they are all unmapped. The page was
		 * created by pagein or read over a hole which was handled by
		 * block_read_full_page().  If this address_space is also
		 * using mpage_readpages then this can rarely happen.
		 */
		goto confused;
	}

	/*
	 * The page has no buffers: map it to disk
	 */
	BUG_ON(!PageUptodate(page));
	block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
	last_block = (i_size - 1) >> blkbits;
	map_bh.b_page = page;
	for (page_block = 0; page_block < blocks_per_page; ) {

		map_bh.b_state = 0;
		map_bh.b_size = 1 << blkbits;
		if (mpd->get_block(inode, block_in_file, &map_bh, 1))
			goto confused;
		if (buffer_new(&map_bh))
			unmap_underlying_metadata(map_bh.b_bdev,
						map_bh.b_blocknr);
		if (buffer_boundary(&map_bh)) {
			boundary_block = map_bh.b_blocknr;
			boundary_bdev = map_bh.b_bdev;
		}
		if (page_block) {
			if (map_bh.b_blocknr != blocks[page_block-1] + 1)
				goto confused;
		}
		blocks[page_block++] = map_bh.b_blocknr;
//.........这里部分代码省略.........