int jbd2_journal_invalidatepage(journal_t *journal,
				struct page *page,
				unsigned int offset,
				unsigned int length)
{
	struct buffer_head *head, *bh, *next;
	unsigned int stop = offset + length;
	unsigned int curr_off = 0;
	int partial_page = (offset || length < PAGE_SIZE);
	int may_free = 1;
	int ret = 0;

	if (!PageLocked(page))
		BUG();
	if (!page_has_buffers(page))
		return 0;

	BUG_ON(stop > PAGE_SIZE || stop < length);

	/* We will potentially be playing with lists other than just the
	 * data lists (especially for journaled data mode), so be
	 * cautious in our locking. */

	head = bh = page_buffers(page);
	do {
		unsigned int next_off = curr_off + bh->b_size;
		next = bh->b_this_page;

		if (next_off > stop)
			return 0;

		if (offset <= curr_off) {
			/* This block is wholly outside the truncation point */
			lock_buffer(bh);
			ret = journal_unmap_buffer(journal, bh, partial_page);
			unlock_buffer(bh);
			if (ret < 0)
				return ret;
			may_free &= ret;
		}
		curr_off = next_off;
		bh = next;

	} while (bh != head);

	if (!partial_page) {
		if (may_free && try_to_free_buffers(page))
			J_ASSERT(!page_has_buffers(page));
	}
	return 0;
}
Unknown