/*
 * hugepage_alloc_test1.c - test the availabilty of hugepages
 *
 * Written by Roland Mainz <roland.mainz@nrubsig.org>
 */

#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>

#include <sys/mman.h>
#include <sys/stat.h>

#include <linux/mman.h>

/*
 * Before using this Linux 5.10.0-13-rt-686-pae requires that "root"
 * reserves hugepages like this:
 *
 * $ printf '128' > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
 * $ cat /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
 * 128
 *
 * Notes:
 * - Terminology: UNIX uses the term "largepages", Linux defiantly uses
 * "hugepages"
 * - the value is the number of MMU (large-/huge-)pages, NOT the number
 * of bytes.
 * - $ /usr/bin/pagesize -a # can inform you which pagesizes are
 * available (i686 usually has { 4k, 2M } pagesizes, SPARCv9 has
 * { 8k, 64k, 4M, 32M, ... } )
 */

ssize_t get_number_of_free_hugepages(void)
{
	int	dirfd;
	int	fd;
	char	buf[256];
	ssize_t	numpages;
	ssize_t	rs; /* read size */
	
	/*
	 * extra step here, since real-world applications likely
	 * want to look at "nr_hugepages" etc, too
	 */
	dirfd = open("/sys/kernel/mm/hugepages/hugepages-2048kB/",
		O_DIRECTORY);
	if (dirfd < 0) {
		perror("open sysfs hugepage dir");
		return -1;
	}
	
	fd = openat(dirfd, "free_hugepages", O_RDONLY);
	if (fd < 0) {
		perror("open sysfs hugepage free pages file");
		(void)close(dirfd);
		return -1;
	}
	rs = read(fd, buf, sizeof(buf));
	if (rs < 0) {
		perror("read error sysfs hugepage free pages file");
		(void)close(dirfd);
		(void)close(fd);
		return -1;
	}

	(void)close(dirfd);
	(void)close(fd);
	
	buf[rs] = '\0';
#if MYDEBUG
	if ((rs > 0) && (buf[rs-1] == '\n'))
		buf[rs-1] = '\0';
	(void)printf("string returned: |%s|\n", buf);
#endif /* MYDEBUG */

	errno = 0;
	numpages = strtol(buf, NULL, 10);
	if (errno != 0) {
		perror("error parsing value of free hugepages");
		return -1;
	}
	
	return numpages;
}


int main(int ac, char *av[])
{
	void *p;
	int saved_errno;
#define TEST_NUM_ALLOC_PAGES (32)
	size_t size = TEST_NUM_ALLOC_PAGES*1024*1024;
	ssize_t free_numpages;

	(void)puts("#start.");
	
	free_numpages = get_number_of_free_hugepages();

	if (free_numpages < (TEST_NUM_ALLOC_PAGES+8)) {
		fprintf(stderr, "not enough hugepages\n");
		return EXIT_FAILURE;
	}
	
	p = mmap(0, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_HUGETLB, -1, 0);
	saved_errno = errno;
	if (p == MAP_FAILED)
		perror("mmap");

	(void)printf("map address = %lx, errno=%d\n",
		(unsigned long)p, (int)saved_errno);

	if (munmap(p, size) == -1)
		perror("munmap");
	
	(void)puts("#done.");

	return EXIT_SUCCESS;
}