msync.c

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

static const size_t FILE_SIZE = 512;

int main(int argc, char** argv)
{
	const char* name = (argc >= 1) ? argv[0] : "msync";

	if (argc < 2)
	{
		fprintf(stderr, "usage: %s <file>\n", name);
		return EXIT_FAILURE;
	}

	const char* path = argv[1];

	int fd = open(path, O_RDWR | O_CREAT, 0777);
	if (fd == -1)
	{
		perror(name);
		return EXIT_FAILURE;
	}

	void* mapping = mmap(NULL, FILE_SIZE, PROT_WRITE, MAP_SHARED, fd, 0);
	if (mapping == MAP_FAILED)
	{
		perror(name);
		return EXIT_FAILURE;
	}

	for (size_t pos = 0; pos < FILE_SIZE; ++pos)
		((uint8_t*)mapping)[pos] = 0xff;

	if (msync(mapping, FILE_SIZE, MS_SYNC) != 0)
	{
		perror(name);
		return EXIT_FAILURE;
	}

	return EXIT_SUCCESS;
}