The f_mkdir function creates a new directory.
FRESULT f_mkdir ( const XCHAR* DirName /* Pointer to the directory name */ );
The f_mkdir function creates a new directory.
Available when _FS_READONLY == 0 and _FS_MINIMIZE == 0.
    res = f_mkdir("sub1");
    if (res) die(res);
    res = f_mkdir("sub1/sub2");
    if (res) die(res);
    res = f_mkdir("sub1/sub2/sub3");
    if (res) die(res);