TTY Device Driver

原本只是physical或virtual terminal，但現在變成只要是可以連接serial port，都被統稱為tty。

  • tty可分為三種：

    1. Console
    2. Serial port
    3. PTY (pseudo tty)

  • 所有已經跟kernel register的tty，都會在 /sys/class/tty，若kernel知道有真實的device，則kernel會創建device link到真實的node。

    • 可看下方顯示：

  • TTY總共有三層架構，可分為tty core, tty line discipline以及tty driver。

Tiny TTY

TTY device driver透過tty_driver跟TTY core進行register跟unregister。

TTY的主要driver都是由tty_driver這個資料結構提供。

#include <linux/tty_driver.h>
struct tty_driver

創建一個tty device時，需呼叫alloc_tty_driver

#include <linux/tty_driver.h>
static inline struct tty_driver * alloc_tty_driver(unsigned int lines)

lines是要提供tty device driver的device number。

取得了tty_driver後，需要設定適當的初始化。可以先看下方的structure再參考右邊初始化需做哪些設定。

  • 下方的是tty_driver結構，設定後須透過extern void tty_set_operations(struct tty_driver *driver,const struct tty_operations *op);完成初始化。
    • </ul> </div>
    #include <linux/tty_driver.h>
static struct tty_operations serial_ops = {
 .open = tiny_open,
 .close = tiny_close,
 .write = tiny_write,
 .write_room = tiny_write_room,
 .set_termios = tiny_set_termios,
};
...
 /* initialize the tty driver */
 tiny_tty_driver->owner = THIS_MODULE;
 tiny_tty_driver->driver_name = "tiny_tty";
 tiny_tty_driver->name = "ttty";
 tiny_tty_driver->devfs_name = "tts/ttty%d";
 tiny_tty_driver->major = TINY_TTY_MAJOR,
 tiny_tty_driver->type = TTY_DRIVER_TYPE_SERIAL,
 tiny_tty_driver->subtype = SERIAL_TYPE_NORMAL,
 tiny_tty_driver->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_NO_DEVFS,
 tiny_tty_driver->init_termios = tty_std_termios;
 tiny_tty_driver->init_termios.c_cflag = B9600 | CS8 | CREAD | HUPCL | CLOCAL;
 tty_set_operations(tiny_tty_driver, &serial_ops);

    lines是要提供tty device driver的device number。

    </div></div></div>

    struct tty_driver {
    int    magic;        /* magic number for this structure */
    struct kref kref;    /* Reference management */
    struct cdev **cdevs;
    struct module    *owner;
    const char    *driver_name;
    const char    *name;
    int    name_base;    /* offset of printed name */
    int    major;        /* major device number */
    int    minor_start;    /* start of minor device number */
    unsigned int    num;    /* number of devices allocated */
    short    type;        /* type of tty driver */
    short    subtype;    /* subtype of tty driver */
    struct ktermios init_termios; /* Initial termios */
    unsigned long    flags;        /* tty driver flags */
    struct proc_dir_entry *proc_entry; /* /proc fs entry */
    struct tty_driver *other; /* only used for the PTY driver */

    /*
     * Pointer to the tty data structures
     */
    struct tty_struct **ttys;
    struct tty_port **ports;
    struct ktermios **termios;
    void *driver_state;

    /*
     * Driver methods
     */

    const struct tty_operations *ops;
    struct list_head tty_drivers;
};
    • 下方的是tty_operations，設定完後會被tty_set_operations把tty_driver->ops=tty_operations;指派。
      struct tty_operations {
  struct tty_struct * (*lookup)(struct tty_driver *driver,
          struct file *filp, int idx);
  int  (*install)(struct tty_driver *driver, struct tty_struct *tty);
  void (*remove)(struct tty_driver *driver, struct tty_struct *tty);
  int  (*open)(struct tty_struct * tty, struct file * filp);
  void (*close)(struct tty_struct * tty, struct file * filp);
  void (*shutdown)(struct tty_struct *tty);
  void (*cleanup)(struct tty_struct *tty);
  int  (*write)(struct tty_struct * tty,
            const unsigned char *buf, int count);
  int  (*put_char)(struct tty_struct *tty, unsigned char ch);
  void (*flush_chars)(struct tty_struct *tty);
  int  (*write_room)(struct tty_struct *tty);
  int  (*chars_in_buffer)(struct tty_struct *tty);
  int  (*ioctl)(struct tty_struct *tty,
          unsigned int cmd, unsigned long arg);
  long (*compat_ioctl)(struct tty_struct *tty,
               unsigned int cmd, unsigned long arg);
  void (*set_termios)(struct tty_struct *tty, struct ktermios * old);
  void (*throttle)(struct tty_struct * tty);
  void (*unthrottle)(struct tty_struct * tty);
  void (*stop)(struct tty_struct *tty);
  void (*start)(struct tty_struct *tty);
  void (*hangup)(struct tty_struct *tty);
  int (*break_ctl)(struct tty_struct *tty, int state);
  void (*flush_buffer)(struct tty_struct *tty);
  void (*set_ldisc)(struct tty_struct *tty);
  void (*wait_until_sent)(struct tty_struct *tty, int timeout);
  void (*send_xchar)(struct tty_struct *tty, char ch);
  int (*tiocmget)(struct tty_struct *tty);
  int (*tiocmset)(struct tty_struct *tty,
          unsigned int set, unsigned int clear);
  int (*resize)(struct tty_struct *tty, struct winsize *ws);
  int (*set_termiox)(struct tty_struct *tty, struct termiox *tnew);
  int (*get_icount)(struct tty_struct *tty,
              struct serial_icounter_struct *icount);
#ifdef CONFIG_CONSOLE_POLL
  int (*poll_init)(struct tty_driver *driver, int line, char *options);
  int (*poll_get_char)(struct tty_driver *driver, int line);
  void (*poll_put_char)(struct tty_driver *driver, int line, char ch);
#endif
  const struct file_operations *proc_fops;
};

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