#include <stdio.h>

#define PAGEVEC_SIZE 15

struct pagevec {
	unsigned char nr;
	int vals[PAGEVEC_SIZE];
};

struct pagevec_iter {
	unsigned char idx;
	int last_index;
	struct pagevec pvec;
};

void pagevec_release(struct pagevec *pvec)
{
	int i;

	for (i = 0; i < pvec->nr; i++)
		printf("Freeing val %d\n", pvec->vals[i]);
	pvec->nr = 0;
}

int pagevec_lookup(struct pagevec *pvec, void *mapping, int *start, int end)
{
	int i;

	for (i = 0; i < PAGEVEC_SIZE && *start < 29; i++) {
		pvec->vals[pvec->nr++] = 100 + *start;
		(*start)++;
	}
	return pvec->nr;
}

static inline int get_next_pvec_val(struct pagevec_iter *pvec_i, void *mapping,
				    int end)
{
	if (pvec_i->idx >= pvec_i->pvec.nr) {
		pagevec_release(&pvec_i->pvec);
		if (!pagevec_lookup(&pvec_i->pvec, mapping, &pvec_i->last_index,
				    end))
			return 0;
		pvec_i->idx = 0;
	}
	return pvec_i->pvec.vals[pvec_i->idx++];
}

void pagevec_release_iter(struct pagevec_iter *pvec_i)
{
	pagevec_release(&pvec_i->pvec);
}

#define for_each_page(mapping, page, start, end)			\
	for (struct pagevec_iter pvec_i					\
		__attribute__ ((cleanup (pagevec_release_iter))) = {	\
			.idx = 0, .last_index = start, .pvec = { .nr = 0 } }; \
	     (page = get_next_pvec_val(&pvec_i, mapping, end));)

int main(void)
{
	int page;

	for_each_page(NULL, page, 5, 32) {
		printf("Seeing val %d\n", page);
		if (page > 122)
			break;
	}
	return 0;
}