mmap errno 22 in c reading openmpi datatype decription

Question

I'm using mmap to read from a file.
The mmap returns errno 22, invalid argument.
The stat.st_size in this case is 400 which I don't think it is "too large".
I don't think I'm encountering "we dont like addr, length or offset".
I'm running this program on Intel Xeon E5(which I dont think its relevant).
What am I missing here?

if( argc > 1 ) {
    struct stat stat;

    for( int i = 1; i < argc; i++ ) {
        if( access(argv[i], R_OK) == -1 ) {
            printf("\n Cannot access datatype description file %s\n", argv[i]);
            continue;
        }
        int fd = open(argv[i], O_RDONLY);
        if( fd == -1 ) {
            printf("\n Cannot open datatype description from file %s\n", argv[i]);
            continue;
        }
        if( fstat(fd, &stat) == -1 ) {
            printf("\n Cannot stat the %s file\n", argv[i]);
            continue;
        }

        void* addr = mmap(NULL, stat.st_size, PROT_READ, MAP_FILE, fd, 0);

        if( MAP_FAILED == addr ) {
            printf("\nCannot map the datatype description file %s\n", argv[i]);
            printf("%s %d stat.st_size %d\n", strerror(errno), errno, stat.st_size );
            perror("mmap");
            close(fd);
            continue;
        }

        munmap(addr, stat.st_size);
        free(addr);
        close(fd);
    }
}

Answer 1

From man 2 mmap:

       MAP_FILE
              Compatibility flag.  Ignored.
...
       EINVAL flags  contained neither MAP_PRIVATE or MAP_SHARED, or contained
              both of these values.

You need to pass one of MAP_PRIVATE or MAP_SHARED, and you should stop passing MAP_FILE. (What did you even think it did?)