page cache: Convert filemap_range_has_page to XArray

bool filemap_range_has_page(struct address_space *mapping,

			   loff_t start_byte, loff_t end_byte)

{

	pgoff_t index = start_byte >> PAGE_SHIFT;

	pgoff_t end = end_byte >> PAGE_SHIFT;

	struct page *page;

	XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);

	pgoff_t max = end_byte >> PAGE_SHIFT;

	if (end_byte < start_byte)

		return false;

	if (mapping->nrpages == 0)

		return false;

	rcu_read_lock();

	for (;;) {

		page = xas_find(&xas, max);

		if (xas_retry(&xas, page))

			continue;

		/* Shadow entries don't count */

		if (xa_is_value(page))

			continue;

		/*

		 * We don't need to try to pin this page; we're about to

		 * release the RCU lock anyway.  It is enough to know that

		 * there was a page here recently.

		 */

		break;

	}

	rcu_read_unlock();

	if (!find_get_pages_range(mapping, &index, end, 1, &page))

		return false;

	put_page(page);

	return true;

	return page != NULL;

}

EXPORT_SYMBOL(filemap_range_has_page);