mapsync.c

#include <sys/mman.h>
#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

int
main(int argc, char *argv[])
{
        int fd;
        char *pmaddr;

        if (argc != 2) {
                fprintf(stderr, "Usage: %s filename\n", argv[0]);
                exit(1);
        }

        if ((fd = open(argv[1], O_RDWR|O_CREAT, 0644)) < 0)
                err(1, "open: %s", argv[2]);

        if (ftruncate(fd, (off_t)40960) < 0)
                err(1, "ftruncate: %s", argv[2]);

        if ((pmaddr = (char *)mmap(NULL, 40960, PROT_READ|PROT_WRITE,
                                MAP_SHARED_VALIDATE|MAP_SYNC,
                                fd, 0)) == MAP_FAILED)
                err(1, "mmap(MAP_SYNC): %s", argv[2]);

        close(fd);

        printf("MAP_SYNC successful.\n");
        exit(0);
}