extern int slip_user_read(int fd, void *buf, int len, struct slip_data *pri);
extern int slip_user_write(int fd, void *buf, int len, struct slip_data *pri);
extern int slip_user_read(int fd, void *buf, int len, struct slip_data *pri);
extern int slip_user_write(int fd, void *buf, int len, struct slip_data *pri);