/*
 * hugepage_alloc_test1.c - test the availabilty of
 * largepages/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, ... } )
 */

/* Linux-specific version */
ssize_t get_number_of_free_hugepages(void)
{
	int	dirfd;
	int	fd;
	/*
	 * |round(log10(18446744073709551615))| is |19| on a 64bit
	 * system, so |128| should be enough (including sign)
	 */
	char	buf[128];
	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)
	const 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)) {
		(void)fprintf(stderr,
			"not enough hugepages, currently free %ld\n",
			(long)free_numpages);
		return EXIT_FAILURE;
	}

	/* get mmap()'ed memory with hugepage attribute */
	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");
		return EXIT_FAILURE;
	}

	(void)printf("map address = 0x%lx, errno=%d\n",
		(unsigned long)p, (int)saved_errno);

	/* use memory */
	volatile unsigned char *c = p;
	for (size_t i = 0 ; i < size ; i++) {
		c[i] = (unsigned char)(i % 255);
	}
	
#if MYDEBUG_USE_PROC_SMAPS
	/*
	 * Wait here so we can check out
	 * $ cat /proc/$mypid/smaps | fgrep -i huge #
	 */
	sleep(1000);
#endif /* MYDEBUG_USE_PROC_SMAPS */

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

	return EXIT_SUCCESS;
}