void nilfs_clear_dirty_pages(struct address_space *mapping)
{
	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];
			struct buffer_head *bh, *head;

			lock_page(page);
			ClearPageUptodate(page);
			ClearPageMappedToDisk(page);
			bh = head = page_buffers(page);
			do {
				lock_buffer(bh);
				clear_buffer_dirty(bh);
				clear_buffer_nilfs_volatile(bh);
				clear_buffer_uptodate(bh);
				clear_buffer_mapped(bh);
				unlock_buffer(bh);
				bh = bh->b_this_page;
			} while (bh != head);

			__nilfs_clear_page_dirty(page);
			unlock_page(page);
		}
		pagevec_release(&pvec);
		cond_resched();
	}
}

static int gfs2_write_cache_jdata(struct address_space *mapping,
				  struct writeback_control *wbc)
{
	struct backing_dev_info *bdi = mapping->backing_dev_info;
	int ret = 0;
	int done = 0;
	struct pagevec pvec;
	int nr_pages;
	pgoff_t index;
	pgoff_t end;
	int scanned = 0;
	int range_whole = 0;

	if (wbc->nonblocking && bdi_write_congested(bdi)) {
		wbc->encountered_congestion = 1;
		return 0;
	}

	pagevec_init(&pvec, 0);
	if (wbc->range_cyclic) {
		index = mapping->writeback_index; /* Start from prev offset */
		end = -1;
	} else {
		index = wbc->range_start >> PAGE_CACHE_SHIFT;
		end = wbc->range_end >> PAGE_CACHE_SHIFT;
		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
			range_whole = 1;
		scanned = 1;
	}

retry:
	 while (!done && (index <= end) &&
		(nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
					       PAGECACHE_TAG_DIRTY,
					       min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
		scanned = 1;
		ret = gfs2_write_jdata_pagevec(mapping, wbc, &pvec, nr_pages, end);
		if (ret)
			done = 1;
		if (ret > 0)
			ret = 0;

		pagevec_release(&pvec);
		cond_resched();
	}

	if (!scanned && !done) {
		/*
		 * We hit the last page and there is more work to be done: wrap
		 * back to the start of the file
		 */
		scanned = 1;
		index = 0;
		goto retry;
	}

	if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
		mapping->writeback_index = index;
	return ret;
}

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;
}

/*
 * Radix-tree checker
 */
void nilfs_check_radix_tree(const char *fname, int line,
			    struct address_space *mapping, int tag)
{
	struct pagevec pvec;
	unsigned int i, n;
	pgoff_t index = 0;
	char *page_type;
	int nr_found = 0;

	if (tag == PAGECACHE_TAG_DIRTY)
		page_type = "dirty";
	else if (tag == PAGECACHE_TAG_WRITEBACK)
		page_type = "writeback";
	else
		page_type = "leaking";

	pagevec_init(&pvec, 0);
 repeat:
	if (tag < 0) {
		n = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
		if (n)
			index = pvec.pages[n - 1]->index + 1;
	} else
		n = pagevec_lookup_tag(&pvec, mapping, &index, tag,
				       PAGEVEC_SIZE);
	if (!n) {
		if (nr_found)
			printk(KERN_WARNING "%s: found %d %s pages\n",
			       fname, nr_found, page_type);
		return;
	}

	for (i = 0; i < n; i++) {
		nilfs_page_debug(fname, line, pvec.pages[i], "%s page",
				 page_type);
		nr_found++;
	}
	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);

	while (pagevec_lookup_tag(&pvec, mapping, &index,
					PAGECACHE_TAG_DIRTY)) {
		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();
	}
}

/**
 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
 * @mapping: address space structure to write
 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 * @writepage: function called for each page
 * @data: data passed to writepage function
 *
 * If a page is already under I/O, write_cache_pages() skips it, even
 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 * and msync() need to guarantee that all the data which was dirty at the time
 * the call was made get new I/O started against them.  If wbc->sync_mode is
 * WB_SYNC_ALL then we were called for data integrity and we must wait for
 * existing IO to complete.
 */
int write_cache_pages(struct address_space *mapping,
		      struct writeback_control *wbc, writepage_t writepage,
		      void *data)
{
	struct backing_dev_info *bdi = mapping->backing_dev_info;
	int ret = 0;
	int done = 0;
	struct pagevec pvec;
	int nr_pages;
	pgoff_t uninitialized_var(writeback_index);
	pgoff_t index;
	pgoff_t end;		/* Inclusive */
	pgoff_t done_index;
	int cycled;
	int range_whole = 0;

	if (wbc->nonblocking && bdi_write_congested(bdi)) {
		wbc->encountered_congestion = 1;
		return 0;
	}

	pagevec_init(&pvec, 0);
	if (wbc->range_cyclic) {
		writeback_index = mapping->writeback_index; /* prev offset */
		index = writeback_index;
		if (index == 0)
			cycled = 1;
		else
			cycled = 0;
		end = -1;
	} else {
		index = wbc->range_start >> PAGE_CACHE_SHIFT;
		end = wbc->range_end >> PAGE_CACHE_SHIFT;
		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
			range_whole = 1;
		cycled = 1; /* ignore range_cyclic tests */
	}
retry:
	done_index = index;
	while (!done && (index <= end)) {
		int i;

		nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
			      PAGECACHE_TAG_DIRTY,
			      min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
		if (nr_pages == 0)
			break;

		for (i = 0; i < nr_pages; i++) {
			struct page *page = pvec.pages[i];

			/*
			 * At this point, the page may be truncated or
			 * invalidated (changing page->mapping to NULL), or
			 * even swizzled back from swapper_space to tmpfs file
			 * mapping. However, page->index will not change
			 * because we have a reference on the page.
			 */
			if (page->index > end) {
				/*
				 * can't be range_cyclic (1st pass) because
				 * end == -1 in that case.
				 */
				done = 1;
				break;
			}

			done_index = page->index + 1;

			lock_page(page);

			/*
			 * Page truncated or invalidated. We can freely skip it
			 * then, even for data integrity operations: the page
			 * has disappeared concurrently, so there could be no
			 * real expectation of this data interity operation
			 * even if there is now a new, dirty page at the same
			 * pagecache address.
			 */
			if (unlikely(page->mapping != mapping)) {
continue_unlock:
				unlock_page(page);
				continue;
			}

//.........这里部分代码省略.........

static int gfs2_write_cache_jdata(struct address_space *mapping,
				  struct writeback_control *wbc)
{
	int ret = 0;
	int done = 0;
	struct pagevec pvec;
	int nr_pages;
	pgoff_t uninitialized_var(writeback_index);
	pgoff_t index;
	pgoff_t end;
	pgoff_t done_index;
	int cycled;
	int range_whole = 0;
	int tag;

	pagevec_init(&pvec, 0);
	if (wbc->range_cyclic) {
		writeback_index = mapping->writeback_index; /* prev offset */
		index = writeback_index;
		if (index == 0)
			cycled = 1;
		else
			cycled = 0;
		end = -1;
	} else {
		index = wbc->range_start >> PAGE_CACHE_SHIFT;
		end = wbc->range_end >> PAGE_CACHE_SHIFT;
		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
			range_whole = 1;
		cycled = 1; /* ignore range_cyclic tests */
	}
	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
		tag = PAGECACHE_TAG_TOWRITE;
	else
		tag = PAGECACHE_TAG_DIRTY;

retry:
	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
		tag_pages_for_writeback(mapping, index, end);
	done_index = index;
	while (!done && (index <= end)) {
		nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
			      min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
		if (nr_pages == 0)
			break;

		ret = gfs2_write_jdata_pagevec(mapping, wbc, &pvec, nr_pages, end, &done_index);
		if (ret)
			done = 1;
		if (ret > 0)
			ret = 0;
		pagevec_release(&pvec);
		cond_resched();
	}

	if (!cycled && !done) {
		/*
		 * range_cyclic:
		 * We hit the last page and there is more work to be done: wrap
		 * back to the start of the file
		 */
		cycled = 1;
		index = 0;
		end = writeback_index - 1;
		goto retry;
	}

	if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
		mapping->writeback_index = done_index;

	return ret;
}

//.........这里部分代码省略.........
    int cycled;
    int range_whole = 0;
    int tag;
    int step = 0;

    pagevec_init(&pvec, 0);
next:
    if (wbc->range_cyclic) {
        writeback_index = mapping->writeback_index; /* prev offset */
        index = writeback_index;
        if (index == 0)
            cycled = 1;
        else
            cycled = 0;
        end = -1;
    } else {
        index = wbc->range_start >> PAGE_CACHE_SHIFT;
        end = wbc->range_end >> PAGE_CACHE_SHIFT;
        if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
            range_whole = 1;
        cycled = 1; /* ignore range_cyclic tests */
    }
    if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
        tag = PAGECACHE_TAG_TOWRITE;
    else
        tag = PAGECACHE_TAG_DIRTY;
retry:
    if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
        tag_pages_for_writeback(mapping, index, end);
    done_index = index;
    while (!done && (index <= end)) {
        int i;

        nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
                                      min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1);
        if (nr_pages == 0)
            break;

        for (i = 0; i < nr_pages; i++) {
            struct page *page = pvec.pages[i];

            if (page->index > end) {
                done = 1;
                break;
            }

            done_index = page->index;

            lock_page(page);

            if (unlikely(page->mapping != mapping)) {
continue_unlock:
                unlock_page(page);
                continue;
            }

            if (!PageDirty(page)) {
                /* someone wrote it for us */
                goto continue_unlock;
            }

            if (step == is_cold_data(page))
                goto continue_unlock;

            if (PageWriteback(page)) {
                if (wbc->sync_mode != WB_SYNC_NONE)

//.........这里部分代码省略.........
		mark_inode_dirty_sync(inode);
		f2fs_write_inode(inode, NULL);
		goto sync_nodes;
	}

	ret = wait_on_node_pages_writeback(sbi, ino);
	if (ret)
		goto out;

	/* once recovery info is written, don't need to tack this */
	remove_dirty_inode(sbi, ino, APPEND_INO);
	clear_inode_flag(fi, FI_APPEND_WRITE);
flush_out:
	remove_dirty_inode(sbi, ino, UPDATE_INO);
	clear_inode_flag(fi, FI_UPDATE_WRITE);
	ret = f2fs_issue_flush(sbi);
out:
	trace_f2fs_sync_file_exit(inode, need_cp, datasync, ret);
	f2fs_trace_ios(NULL, 1);
	return ret;
}

static pgoff_t __get_first_dirty_index(struct address_space *mapping,
						pgoff_t pgofs, int whence)
{
	struct pagevec pvec;
	int nr_pages;

	if (whence != SEEK_DATA)
		return 0;

	/* find first dirty page index */
	pagevec_init(&pvec, 0);
	nr_pages = pagevec_lookup_tag(&pvec, mapping, &pgofs,
					PAGECACHE_TAG_DIRTY, 1);
	pgofs = nr_pages ? pvec.pages[0]->index : LONG_MAX;
	pagevec_release(&pvec);
	return pgofs;
}

static bool __found_offset(block_t blkaddr, pgoff_t dirty, pgoff_t pgofs,
							int whence)
{
	switch (whence) {
	case SEEK_DATA:
		if ((blkaddr == NEW_ADDR && dirty == pgofs) ||
			(blkaddr != NEW_ADDR && blkaddr != NULL_ADDR))
			return true;
		break;
	case SEEK_HOLE:
		if (blkaddr == NULL_ADDR)
			return true;
		break;
	}
	return false;
}

static inline int unsigned_offsets(struct file *file)
{
	return file->f_mode & FMODE_UNSIGNED_OFFSET;
}

static loff_t vfs_setpos(struct file *file, loff_t offset, loff_t maxsize)
{
	if (offset < 0 && !unsigned_offsets(file))
		return -EINVAL;

/**ltl
功能:遍历给定地址空间的"脏"页面，写这些页面
参数:
返回值:
说明:
*/
int write_cache_pages(struct address_space *mapping,
		      struct writeback_control *wbc, writepage_t writepage,
		      void *data)
{
	int ret = 0;
	int done = 0;
	struct pagevec pvec;
	int nr_pages;
	pgoff_t uninitialized_var(writeback_index);
	pgoff_t index;/*要冲刷页面的索引*/
	pgoff_t end;		/* Inclusive *//*冲刷最后一个页面的索引，-1表示要循环冲刷*/
	pgoff_t done_index;
	int cycled;/*主要用在回绕需要分成两段进行冲刷的情况下，为1表示前一段冲刷已经完成。*/
	int range_whole = 0;
	int tag;

	pagevec_init(&pvec, 0);
	if (wbc->range_cyclic)
	{//是否要循环进行冲刷
		writeback_index = mapping->writeback_index; /* prev offset */
		index = writeback_index;
		if (index == 0)
			cycled = 1;
		else
			cycled = 0;
		end = -1;
	}
	else 
	{
		index = wbc->range_start >> PAGE_CACHE_SHIFT;
		end = wbc->range_end >> PAGE_CACHE_SHIFT;
		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
			range_whole = 1;
		cycled = 1; /* ignore range_cyclic tests */
	}
	if (wbc->sync_mode == WB_SYNC_ALL)
		tag = PAGECACHE_TAG_TOWRITE;
	else
		tag = PAGECACHE_TAG_DIRTY;
retry:
	if (wbc->sync_mode == WB_SYNC_ALL)
		tag_pages_for_writeback(mapping, index, end);
	done_index = index;
	
	while (!done && (index <= end)) 
	{
		int i;
		/*在地址空间中查找设备了PAGECACHE_TAG_DIRTY标志的页面，将结果保存在pagevec中*/
		nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
			      min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
		if (nr_pages == 0)
			break;
		//对找到的页面进行处理。
		for (i = 0; i < nr_pages; i++) {
			struct page *page = pvec.pages[i];

			/*
			 * At this point, the page may be truncated or
			 * invalidated (changing page->mapping to NULL), or
			 * even swizzled back from swapper_space to tmpfs file
			 * mapping. However, page->index will not change
			 * because we have a reference on the page.
			 */
			if (page->index > end) {
				/*
				 * can't be range_cyclic (1st pass) because
				 * end == -1 in that case.
				 */
				done = 1;
				break;
			}

			done_index = page->index + 1;
			//页面加锁
			lock_page(page);

			/*
			 * Page truncated or invalidated. We can freely skip it
			 * then, even for data integrity operations: the page
			 * has disappeared concurrently, so there could be no
			 * real expectation of this data interity operation
			 * even if there is now a new, dirty page at the same
			 * pagecache address.
			 */
			 /*由于在加锁过程中可能其它进程对页面做过改动，因此要做以下判断*/
			if (unlikely(page->mapping != mapping)) {//页面无效
continue_unlock:
				unlock_page(page);
				continue;
			}

			if (!PageDirty(page)) {//页面回写完成，I_DIRTY标志已经清除。
				/* someone wrote it for us */
				goto continue_unlock;
//.........这里部分代码省略.........

/**
 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
 * @mapping: address space structure to write
 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 * @writepage: function called for each page
 * @data: data passed to writepage function
 *
 * If a page is already under I/O, write_cache_pages() skips it, even
 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 * and msync() need to guarantee that all the data which was dirty at the time
 * the call was made get new I/O started against them.  If wbc->sync_mode is
 * WB_SYNC_ALL then we were called for data integrity and we must wait for
 * existing IO to complete.
 */
int write_cache_pages(struct address_space *mapping,
		      struct writeback_control *wbc, writepage_t writepage,
		      void *data)
{
	struct backing_dev_info *bdi = mapping->backing_dev_info;
	int ret = 0;
	int done = 0;
	struct pagevec pvec;
	int nr_pages;
	pgoff_t index;
	pgoff_t end;		/* Inclusive */
	int scanned = 0;
	int range_whole = 0;
	long nr_to_write = wbc->nr_to_write;

	if (wbc->nonblocking && bdi_write_congested(bdi)) {
		wbc->encountered_congestion = 1;
		return 0;
	}

	pagevec_init(&pvec, 0);
	if (wbc->range_cyclic) {
		index = mapping->writeback_index; /* Start from prev offset */
		end = -1;
	} else {
		index = wbc->range_start >> PAGE_CACHE_SHIFT;
		end = wbc->range_end >> PAGE_CACHE_SHIFT;
		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
			range_whole = 1;
		scanned = 1;
	}
retry:
	while (!done && (index <= end) &&
	       (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
					      PAGECACHE_TAG_DIRTY,
					      min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
		unsigned i;

		scanned = 1;
		for (i = 0; i < nr_pages; i++) {
			struct page *page = pvec.pages[i];

			/*
			 * At this point we hold neither mapping->tree_lock nor
			 * lock on the page itself: the page may be truncated or
			 * invalidated (changing page->mapping to NULL), or even
			 * swizzled back from swapper_space to tmpfs file
			 * mapping
			 */
			lock_page(page);

			if (unlikely(page->mapping != mapping)) {
				unlock_page(page);
				continue;
			}

			if (!wbc->range_cyclic && page->index > end) {
				done = 1;
				unlock_page(page);
				continue;
			}

			if (wbc->sync_mode != WB_SYNC_NONE)
				wait_on_page_writeback(page);

			if (PageWriteback(page) ||
			    !clear_page_dirty_for_io(page)) {
				unlock_page(page);
				continue;
			}

			ret = (*writepage)(page, wbc, data);

			if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE)) {
				unlock_page(page);
				ret = 0;
			}
			if (ret || (--nr_to_write <= 0))
				done = 1;
			if (wbc->nonblocking && bdi_write_congested(bdi)) {
				wbc->encountered_congestion = 1;
				done = 1;
			}
		}
		pagevec_release(&pvec);
//.........这里部分代码省略.........

/*
 * Inspired by write_cache_pages from /mm/page-writeback.c
 */
static int ecryptfs_writepages(struct address_space *mapping,
			       struct writeback_control *wbc)
{
	int ret = 0;
	int done = 0;
	struct pagevec pvec;
	int nr_pages;
	pgoff_t uninitialized_var(writeback_index);
	pgoff_t index;
	pgoff_t end;		/* Inclusive */
	pgoff_t done_index;
	int cycled;
	int range_whole = 0;
	int tag;
	struct page **pgs;
	int pgidx;
	
	/* printk("[g-ecryptfs] Info: call writepages\n"); */

	pgs = kmalloc(sizeof(struct page*)*PAGEVEC_SIZE, GFP_KERNEL);
	if (!pgs) {
		printk("[g-ecryptfs] Error: pgs alloc failed!\n");
		return -EFAULT;
	}

	pagevec_init(&pvec, 0);
	if (wbc->range_cyclic) {
		writeback_index = mapping->writeback_index; /* prev offset */
		index = writeback_index;
		if (index == 0)
			cycled = 1;
		else
			cycled = 0;
		end = -1;
	} else {
		index = wbc->range_start >> PAGE_CACHE_SHIFT;
		end = wbc->range_end >> PAGE_CACHE_SHIFT;
		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
			range_whole = 1;
		cycled = 1; /* ignore range_cyclic tests */
	}
	if (wbc->sync_mode == WB_SYNC_ALL)
		tag = PAGECACHE_TAG_TOWRITE;
	else
		tag = PAGECACHE_TAG_DIRTY;
retry:
	if (wbc->sync_mode == WB_SYNC_ALL)
		tag_pages_for_writeback(mapping, index, end);
	done_index = index;
	while (!done && (index <= end)) {
		int i;
		struct page *page;

		nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
			      min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
		if (nr_pages == 0)
			break;
		pgidx = 0;

		for (i = 0; i < nr_pages; i++) {
			page = pvec.pages[i];

			/*
			 * At this point, the page may be truncated or
			 * invalidated (changing page->mapping to NULL), or
			 * even swizzled back from swapper_space to tmpfs file
			 * mapping. However, page->index will not change
			 * because we have a reference on the page.
			 */
			if (page->index > end) {
				/*
				 * can't be range_cyclic (1st pass) because
				 * end == -1 in that case.
				 */
				done = 1;
				break;
			}

			done_index = page->index + 1;

			lock_page(page);

			/*
			 * Page truncated or invalidated. We can freely skip it
			 * then, even for data integrity operations: the page
			 * has disappeared concurrently, so there could be no
			 * real expectation of this data interity operation
			 * even if there is now a new, dirty page at the same
			 * pagecache address.
			 */
			if (unlikely(page->mapping != mapping)) {
continue_unlock:
				unlock_page(page);
				continue;
			}

			if (!PageDirty(page)) {
//.........这里部分代码省略.........

/**
 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
 * @mapping: address space structure to write
 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 * @writepage: function called for each page
 * @data: data passed to writepage function
 *
 * If a page is already under I/O, write_cache_pages() skips it, even
 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 * and msync() need to guarantee that all the data which was dirty at the time
 * the call was made get new I/O started against them.  If wbc->sync_mode is
 * WB_SYNC_ALL then we were called for data integrity and we must wait for
 * existing IO to complete.
 *
 * To avoid livelocks (when other process dirties new pages), we first tag
 * pages which should be written back with TOWRITE tag and only then start
 * writing them. For data-integrity sync we have to be careful so that we do
 * not miss some pages (e.g., because some other process has cleared TOWRITE
 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
 * by the process clearing the DIRTY tag (and submitting the page for IO).
 */
int write_cache_pages(struct address_space *mapping,
		      struct writeback_control *wbc, writepage_t writepage,
		      void *data)
{
	int ret = 0;
	int done = 0;
	struct pagevec pvec;
	int nr_pages;
	pgoff_t index;
	pgoff_t end;		/* Inclusive */
	pgoff_t done_index;
	int range_whole = 0;
	int tag;

	pagevec_init(&pvec, 0);
	if (wbc->range_cyclic) {
		index = mapping->writeback_index; /* prev offset */
		end = -1;
	} else {
		index = wbc->range_start >> PAGE_CACHE_SHIFT;
		end = wbc->range_end >> PAGE_CACHE_SHIFT;
		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
			range_whole = 1;
	}
	if (wbc->sync_mode == WB_SYNC_ALL)
		tag = PAGECACHE_TAG_TOWRITE;
	else
		tag = PAGECACHE_TAG_DIRTY;

	if (wbc->sync_mode == WB_SYNC_ALL)
		tag_pages_for_writeback(mapping, index, end);

	done_index = index;
	while (!done && (index <= end)) {
		int i;

		nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
			      min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
		if (nr_pages == 0) {
			done_index = 0;
			break;
		}

		for (i = 0; i < nr_pages; i++) {
			struct page *page = pvec.pages[i];

			/*
			 * At this point, the page may be truncated or
			 * invalidated (changing page->mapping to NULL), or
			 * even swizzled back from swapper_space to tmpfs file
			 * mapping. However, page->index will not change
			 * because we have a reference on the page.
			 */
			if (page->index > end) {
				/*
				 * can't be range_cyclic (1st pass) because
				 * end == -1 in that case.
				 */
				done = 1;
				break;
			}

			done_index = page->index + 1;

			lock_page(page);

			/*
			 * Page truncated or invalidated. We can freely skip it
			 * then, even for data integrity operations: the page
			 * has disappeared concurrently, so there could be no
			 * real expectation of this data interity operation
			 * even if there is now a new, dirty page at the same
			 * pagecache address.
			 */
			if (unlikely(page->mapping != mapping)) {
continue_unlock:
				unlock_page(page);
				continue;
//.........这里部分代码省略.........