#define _GNU_SOURCE
#include <assert.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

// compile: gcc ./tmp.c
//
// run: rm -f ./tmp && strace -Te fdatasync ./a.out <0|1>
//
// if the fdatasync time is higher when run with 0 vs with 1, sync_file_range
// probably works on your filesystem.

int main(int argc, char** argv) {
        assert(argc == 2);
        bool use_sync_file_range = atoi(argv[1]) > 0;
        int fd = open("./tmp", O_CREAT | O_WRONLY);
        assert(fd != -1);
        char buf[1048576];
        for (int i = 0; i < 1024; ++i) {
                size_t rem = 1048576;
                while (rem > 0) {
                        ssize_t ret = write(fd, &buf[1048576 - rem], rem);
                        assert(ret > 0);
                        rem -= (size_t)ret;
                }
                if (use_sync_file_range) {
                        int ret = sync_file_range(fd, 0, 1048576 * (i + 1), SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE);
                        assert(ret == 0);
                }
        }
        int ret = fdatasync(fd);
        assert(ret == 0);
}