basic mmap test

a.c

#include <sys/mman.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/types.h>

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <sysexits.h>
#include <unistd.h>

int
main(int argc, char **argv)
{
        struct stat st;
        int fd, err;
        void *p;
        char a;

        if (argc < 2)
                return EX_USAGE;

        fd = open(argv[1], O_RDONLY);
        if (fd < 0)
                return EX_OSERR;

        err = fstat(fd, &st);
        if (err < 0)
                return EX_OSERR;

        if (st.st_size == 0)
                return EX_DATAERR;

        p = mmap(NULL, (st.st_size / PAGE_SIZE) * PAGE_SIZE, PROT_READ, 0, fd,
            0);

        if (p == MAP_FAILED) {
                printf("mmap(2) Fail: %s\n", strerror(errno));
                return EX_SOFTWARE;
        } else
                printf("mmap(2): Success\n");

        a = *(char *)p;
        printf("trap: Success\n");

        return 0;
}