// SPDX-License-Identifier: GPL-2.0-only
/*
 * Complete definition from Linux v6.18 mm/filemap.c.
 * Source: https://github.com/torvalds/linux/blob/v6.18/mm/filemap.c
 * Copyright (C) 1994-1999  Linus Torvalds
 * Kernel excerpt; not a standalone user-space program.
 * The book's exact source tag is not asserted.
 */

static struct folio *next_uptodate_folio(struct xa_state *xas,
		struct address_space *mapping, pgoff_t end_pgoff)
{
	struct folio *folio = xas_next_entry(xas, end_pgoff);
	unsigned long max_idx;

	do {
		if (!folio)
			return NULL;
		if (xas_retry(xas, folio))
			continue;
		if (xa_is_value(folio))
			continue;
		if (!folio_try_get(folio))
			continue;
		if (folio_test_locked(folio))
			goto skip;
		/* Has the page moved or been split? */
		if (unlikely(folio != xas_reload(xas)))
			goto skip;
		if (!folio_test_uptodate(folio) || folio_test_readahead(folio))
			goto skip;
		if (!folio_trylock(folio))
			goto skip;
		if (folio->mapping != mapping)
			goto unlock;
		if (!folio_test_uptodate(folio))
			goto unlock;
		max_idx = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
		if (xas->xa_index >= max_idx)
			goto unlock;
		return folio;
unlock:
		folio_unlock(folio);
skip:
		folio_put(folio);
	} while ((folio = xas_next_entry(xas, end_pgoff)) != NULL);

	return NULL;
}