Line Discipline Methods
-----------------------
-TTY side interfaces
-^^^^^^^^^^^^^^^^^^^
-
-======================= =======================================================
-open() Called when the line discipline is attached to
- the terminal. No other call into the line
- discipline for this tty will occur until it
- completes successfully. Should initialize any
- state needed by the ldisc, and set receive_room
- in the tty_struct to the maximum amount of data
- the line discipline is willing to accept from the
- driver with a single call to receive_buf().
- Returning an error will prevent the ldisc from
- being attached. Can sleep.
-
-close() This is called on a terminal when the line
- discipline is being unplugged. At the point of
- execution no further users will enter the
- ldisc code for this tty. Can sleep.
-
-hangup() Called when the tty line is hung up.
- The line discipline should cease I/O to the tty.
- No further calls into the ldisc code will occur.
- Can sleep.
-
-read() (optional) A process requests reading data from
- the line. Multiple read calls may occur in parallel
- and the ldisc must deal with serialization issues.
- If not defined, the process will receive an EIO
- error. May sleep.
-
-write() (optional) A process requests writing data to the
- line. Multiple write calls are serialized by the
- tty layer for the ldisc. If not defined, the
- process will receive an EIO error. May sleep.
-
-flush_buffer() (optional) May be called at any point between
- open and close, and instructs the line discipline
- to empty its input buffer.
-
-set_termios() (optional) Called on termios structure changes.
- The caller passes the old termios data and the
- current data is in the tty. Called under the
- termios semaphore so allowed to sleep. Serialized
- against itself only.
-
-poll() (optional) Check the status for the poll/select
- calls. Multiple poll calls may occur in parallel.
- May sleep.
-
-ioctl() (optional) Called when an ioctl is handed to the
- tty layer that might be for the ldisc. Multiple
- ioctl calls may occur in parallel. May sleep.
-
-compat_ioctl() (optional) Called when a 32 bit ioctl is handed
- to the tty layer that might be for the ldisc.
- Multiple ioctl calls may occur in parallel.
- May sleep.
-======================= =======================================================
-
-Driver Side Interfaces
-^^^^^^^^^^^^^^^^^^^^^^
-
-======================= =======================================================
-receive_buf() (optional) Called by the low-level driver to hand
- a buffer of received bytes to the ldisc for
- processing. The number of bytes is guaranteed not
- to exceed the current value of tty->receive_room.
- All bytes must be processed.
-
-receive_buf2() (optional) Called by the low-level driver to hand
- a buffer of received bytes to the ldisc for
- processing. Returns the number of bytes processed.
-
- If both receive_buf() and receive_buf2() are
- defined, receive_buf2() should be preferred.
-
-write_wakeup() May be called at any point between open and close.
- The TTY_DO_WRITE_WAKEUP flag indicates if a call
- is needed but always races versus calls. Thus the
- ldisc must be careful about setting order and to
- handle unexpected calls. Must not sleep.
-
- The driver is forbidden from calling this directly
- from the ->write call from the ldisc as the ldisc
- is permitted to call the driver write method from
- this function. In such a situation defer it.
-
-dcd_change() Report to the tty line the current DCD pin status
- changes and the relative timestamp. The timestamp
- cannot be NULL.
-======================= =======================================================
-
+.. kernel-doc:: include/linux/tty_ldisc.h
+ :identifiers: tty_ldisc_ops
Driver Access
^^^^^^^^^^^^^
* @name: name of this ldisc rendered in /proc/tty/ldiscs
* @num: ``N_*`` number (%N_TTY, %N_HDLC, ...) reserved to this ldisc
*
- * @open: ``int ()(struct tty_struct *tty)``
+ * @open: [TTY] ``int ()(struct tty_struct *tty)``
*
* This function is called when the line discipline is associated with the
- * @tty. The line discipline can use this as an opportunity to initialize
- * any state needed by the ldisc routines.
+ * @tty. No other call into the line discipline for this tty will occur
+ * until it completes successfully. It should initialize any state needed
+ * by the ldisc, and set @tty->receive_room to the maximum amount of data
+ * the line discipline is willing to accept from the driver with a single
+ * call to @receive_buf(). Returning an error will prevent the ldisc from
+ * being attached.
*
- * @close: ``void ()(struct tty_struct *tty)``
+ * Can sleep.
+ *
+ * @close: [TTY] ``void ()(struct tty_struct *tty)``
*
* This function is called when the line discipline is being shutdown,
* either because the @tty is being closed or because the @tty is being
- * changed to use a new line discipline
+ * changed to use a new line discipline. At the point of execution no
+ * further users will enter the ldisc code for this tty.
+ *
+ * Can sleep.
*
- * @flush_buffer: ``void ()(struct tty_struct *tty)``
+ * @flush_buffer: [TTY] ``void ()(struct tty_struct *tty)``
*
* This function instructs the line discipline to clear its buffers of any
* input characters it may have queued to be delivered to the user mode
- * process.
+ * process. It may be called at any point between open and close.
*
- * @read: ``ssize_t ()(struct tty_struct *tty, struct file *file,
+ * @read: [TTY] ``ssize_t ()(struct tty_struct *tty, struct file *file,
* unsigned char *buf, size_t nr)``
*
* This function is called when the user requests to read from the @tty.
* The line discipline will return whatever characters it has buffered up
* for the user. If this function is not defined, the user will receive
- * an %EIO error.
+ * an %EIO error. Multiple read calls may occur in parallel and the ldisc
+ * must deal with serialization issues.
+ *
+ * Can sleep.
*
- * @write: ``ssize_t ()(struct tty_struct *tty, struct file *file,
+ * @write: [TTY] ``ssize_t ()(struct tty_struct *tty, struct file *file,
* const unsigned char *buf, size_t nr)``
*
* This function is called when the user requests to write to the @tty.
* characters first. If this function is not defined, the user will
* receive an %EIO error.
*
- * @ioctl: ``int ()(struct tty_struct *tty, unsigned int cmd,
+ * Can sleep.
+ *
+ * @ioctl: [TTY] ``int ()(struct tty_struct *tty, unsigned int cmd,
* unsigned long arg)``
*
* This function is called when the user requests an ioctl which is not
* discpline. So a low-level driver can "grab" an ioctl request before
* the line discpline has a chance to see it.
*
- * @compat_ioctl: ``int ()(struct tty_struct *tty, unsigned int cmd,
+ * @compat_ioctl: [TTY] ``int ()(struct tty_struct *tty, unsigned int cmd,
* unsigned long arg)``
*
* Process ioctl calls from 32-bit process on 64-bit system.
* a pointer to wordsize-sensitive structure belongs here, but most of
* ldiscs will happily leave it %NULL.
*
- * @set_termios: ``void ()(struct tty_struct *tty, struct ktermios *old)``
+ * @set_termios: [TTY] ``void ()(struct tty_struct *tty, struct ktermios *old)``
*
* This function notifies the line discpline that a change has been made
* to the termios structure.
*
- * @poll: ``int ()(struct tty_struct *tty, struct file *file,
+ * @poll: [TTY] ``int ()(struct tty_struct *tty, struct file *file,
* struct poll_table_struct *wait)``
*
* This function is called when a user attempts to select/poll on a @tty
* device. It is solely the responsibility of the line discipline to
* handle poll requests.
*
- * @hangup: ``void ()(struct tty_struct *tty)``
+ * @hangup: [TTY] ``void ()(struct tty_struct *tty)``
*
* Called on a hangup. Tells the discipline that it should cease I/O to
- * the tty driver. Can sleep. The driver should seek to perform this
- * action quickly but should wait until any pending driver I/O is
- * completed.
+ * the tty driver. The driver should seek to perform this action quickly
+ * but should wait until any pending driver I/O is completed. No further
+ * calls into the ldisc code will occur.
+ *
+ * Can sleep.
*
- * @receive_buf: ``void ()(struct tty_struct *tty, const unsigned char *cp,
- * const char *fp, int count)``
+ * @receive_buf: [DRV] ``void ()(struct tty_struct *tty,
+ * const unsigned char *cp, const char *fp, int count)``
*
* This function is called by the low-level tty driver to send characters
* received by the hardware to the line discpline for processing. @cp is
* character was received with a parity error, etc. @fp may be %NULL to
* indicate all data received is %TTY_NORMAL.
*
- * @write_wakeup: ``void ()(struct tty_struct *tty)``
+ * @write_wakeup: [DRV] ``void ()(struct tty_struct *tty)``
*
* This function is called by the low-level tty driver to signal that line
* discpline should try to send more characters to the low-level driver
* send, please arise a tasklet or workqueue to do the real data transfer.
* Do not send data in this hook, it may lead to a deadlock.
*
- * @dcd_change: ``void ()(struct tty_struct *tty, unsigned int status)``
+ * @dcd_change: [DRV] ``void ()(struct tty_struct *tty, unsigned int status)``
*
* Tells the discipline that the DCD pin has changed its status. Used
* exclusively by the %N_PPS (Pulse-Per-Second) line discipline.
*
- * @receive_buf2: ``int ()(struct tty_struct *tty, const unsigned char *cp,
- * const char *fp, int count)``
+ * @receive_buf2: [DRV] ``int ()(struct tty_struct *tty,
+ * const unsigned char *cp, const char *fp, int count)``
*
* This function is called by the low-level tty driver to send characters
* received by the hardware to the line discpline for processing. @cp is a
* implementation and the tty routines. The above routines can be defined.
* Unless noted otherwise, they are optional, and can be filled in with a %NULL
* pointer.
+ *
+ * Hooks marked [TTY] are invoked from the TTY core, the [DRV] ones from the
+ * tty_driver side.
*/
struct tty_ldisc_ops {
char *name;
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