bool dir_lookup (const struct dir *, const char *name, struct inode **);
bool dir_add (struct dir *, const char *name, disk_sector_t);
bool dir_remove (struct dir *, const char *name);
bool dir_lookup (const struct dir *, const char *name, struct inode **);
bool dir_add (struct dir *, const char *name, disk_sector_t);
bool dir_remove (struct dir *, const char *name);