Per-disk current directories

are described by the following structures. These structures can only be 
modified by the FSD during FS_ATTACH and FS_CHDIR operations. 

/* file system independent - current directories */

struct cdfsi {
    unsigned short cdi_hVPB;           /* VPB handle for associated device */
    unsigned short cdi_end;            /* offset to root of path */
    char           cdi_flags;          /* FS independent flags */
    char           cdi_curdir[260];    /* text of current directory */
};

/* file system dependent - current directories */

struct cdfsd {
    char           cdd_work[8];        /* work area */
};