#define _POSIX_C_SOURCE 200809L
#include <sys/mman.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>

#ifndef PAGE_SIZE
#define PAGE_SIZE sysconf(_SC_PAGE_SIZE)
#endif

#define BLOCK (128*PAGE_SIZE)

void *alloc_huge(size_t n, int c)
{
	char *vm;
	size_t i;
	int fd;
	FILE *f;

	f = tmpfile();
	if (!f) return 0;
	fd = fileno(f);

	if (n & (BLOCK-1)) n = (n & -BLOCK) + BLOCK;

	vm = mmap(0, n, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
	if (vm == MAP_FAILED) goto fail1;

	if (ftruncate(fd, 128*PAGE_SIZE) < 0)
		goto fail2;
	for (i=0; i<n; i+=BLOCK)
		if (mmap(vm+i, BLOCK, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_FIXED, fd, 0) == MAP_FAILED)
			goto fail2;
	if (mmap(vm, BLOCK, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED, -1, 0) == MAP_FAILED)
		goto fail2;
	if (n>BLOCK && mmap(vm+n-2*BLOCK, 2*BLOCK, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED, -1, 0) == MAP_FAILED)
		goto fail2;

	memset(vm, c, BLOCK);
	if (n > BLOCK) {
		memset(vm+BLOCK, c, BLOCK);
		memset(vm+n-2*BLOCK, c, 2*BLOCK);
	}

	return vm;

fail2:
	munmap(vm, n);
fail1:
	fclose(f);
	return 0;
}