testFlush.c

#include <linux/kernel.h>
#include <sys/syscall.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <stdbool.h>
#include <unistd.h>
#include <stdlib.h>
#include <xmmintrin.h>
#include <stdio.h>

/* MMap nvm region. */
static void *
mapFile(const char * pathname, // File name.
        int initSize, // Initial file size.
        bool *isNew) // Is it a new file? [OUT].
{
	*isNew = false;
	void *addr;
	int err;
	int fd;

	if (access(pathname, F_OK) != 0) {
		if ((fd = open(pathname, O_RDWR | O_CREAT | O_EXCL,
						S_IRUSR | S_IWUSR)) < 0)
		{
			printf("create file on NVM error\n");
			return NULL;
		}
		printf("First time file creation\n");
		*isNew = true;

		if ((err = posix_fallocate(fd, 0, initSize)) != 0) {
			printf("failed to allocate space\n");
			close(fd);
			return NULL;
		}

		if ((err = fsync(fd)) != 0) {
			printf("fsync failed\n");
			close(fd);
			return NULL;
		}
	} else {
		if ((fd = open(pathname, O_RDWR)) < 0) {
			printf("open file on NVM error\n");
			return NULL;
		}
		printf("File already exists on NVM\n");
		*isNew = false;
	}

	if ((addr = mmap(NULL, initSize, PROT_READ | PROT_WRITE, MAP_SHARED,
					fd, 0)) == MAP_FAILED)
	{
		printf("failed to mmap\n");
		close(fd);
		return NULL;
	}
	close(fd);
	return addr;
}


int main(int argc, char **argv) {
	bool pmemnew;
	char *pmemaddr = mapFile("/mnt/ext4-pmem0/testflush", 1024, &pmemnew);
	if (pmemaddr == NULL) {
		printf("File mapping failed\n");
		exit(1);
	}

	// write to pmem
	*(pmemaddr) = 47;
	_mm_clflush(pmemaddr);
	_mm_sfence();

	long int ret_status = syscall(333); // 333 is a newly added syscall that causes kernel panic
	printf("syscall ret status = %ld", ret_status);
}