+ /* low level operations */
+ void init_backend();
+ int (*d_open)(const char *pathname, int flags, ...);
+ int (*d_read)(int fd, void *buffer, unsigned int count);
+ int (*d_write)(int fd, const void *buffer, unsigned int count);
+ int (*d_close)(int fd);
+ int (*d_ioctl)(int fd, unsigned long int request, ...);
+