@@ -71,7 +71,7 @@ int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
* call to @receive_buf(). Returning an error will prevent the ldisc from
* being attached.
*
- * Can sleep.
+ * Optional. Can sleep.
*
* @close: [TTY] ``void ()(struct tty_struct *tty)``
*
@@ -80,7 +80,7 @@ int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
* 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.
+ * Optional. Can sleep.
*
* @flush_buffer: [TTY] ``void ()(struct tty_struct *tty)``
*
@@ -88,6 +88,8 @@ int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
* input characters it may have queued to be delivered to the user mode
* process. It may be called at any point between open and close.
*
+ * Optional.
+ *
* @read: [TTY] ``ssize_t ()(struct tty_struct *tty, struct file *file,
* unsigned char *buf, size_t nr)``
*
@@ -97,7 +99,7 @@ int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
* an %EIO error. Multiple read calls may occur in parallel and the ldisc
* must deal with serialization issues.
*
- * Can sleep.
+ * Optional: %EIO unless provided. Can sleep.
*
* @write: [TTY] ``ssize_t ()(struct tty_struct *tty, struct file *file,
* const unsigned char *buf, size_t nr)``
@@ -108,7 +110,7 @@ int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
* characters first. If this function is not defined, the user will
* receive an %EIO error.
*
- * Can sleep.
+ * Optional: %EIO unless provided. Can sleep.
*
* @ioctl: [TTY] ``int ()(struct tty_struct *tty, unsigned int cmd,
* unsigned long arg)``
@@ -120,6 +122,8 @@ int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
* discpline. So a low-level driver can "grab" an ioctl request before
* the line discpline has a chance to see it.
*
+ * Optional.
+ *
* @compat_ioctl: [TTY] ``int ()(struct tty_struct *tty, unsigned int cmd,
* unsigned long arg)``
*
@@ -130,11 +134,15 @@ int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
* a pointer to wordsize-sensitive structure belongs here, but most of
* ldiscs will happily leave it %NULL.
*
+ * Optional.
+ *
* @set_termios: [TTY] ``void ()(struct tty_struct *tty, const struct ktermios *old)``
*
* This function notifies the line discpline that a change has been made
* to the termios structure.
*
+ * Optional.
+ *
* @poll: [TTY] ``int ()(struct tty_struct *tty, struct file *file,
* struct poll_table_struct *wait)``
*
@@ -142,6 +150,8 @@ int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
* device. It is solely the responsibility of the line discipline to
* handle poll requests.
*
+ * Optional.
+ *
* @hangup: [TTY] ``void ()(struct tty_struct *tty)``
*
* Called on a hangup. Tells the discipline that it should cease I/O to
@@ -149,7 +159,7 @@ int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
* but should wait until any pending driver I/O is completed. No further
* calls into the ldisc code will occur.
*
- * Can sleep.
+ * Optional. Can sleep.
*
* @receive_buf: [DRV] ``void ()(struct tty_struct *tty,
* const unsigned char *cp, const char *fp, int count)``
@@ -161,6 +171,8 @@ int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
* character was received with a parity error, etc. @fp may be %NULL to
* indicate all data received is %TTY_NORMAL.
*
+ * Optional.
+ *
* @write_wakeup: [DRV] ``void ()(struct tty_struct *tty)``
*
* This function is called by the low-level tty driver to signal that line
@@ -170,11 +182,15 @@ int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
* 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.
*
+ * Optional.
+ *
* @dcd_change: [DRV] ``void ()(struct tty_struct *tty, bool active)``
*
* Tells the discipline that the DCD pin has changed its status. Used
* exclusively by the %N_PPS (Pulse-Per-Second) line discipline.
*
+ * Optional.
+ *
* @receive_buf2: [DRV] ``int ()(struct tty_struct *tty,
* const unsigned char *cp, const char *fp, int count)``
*
@@ -186,6 +202,8 @@ int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
* indicate all data received is %TTY_NORMAL. If assigned, prefer this
* function for automatic flow control.
*
+ * Optional.
+ *
* @lookahead_buf: [DRV] ``void ()(struct tty_struct *tty,
* const unsigned char *cp, const char *fp, int count)``
*
@@ -198,6 +216,8 @@ int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
* same characters (e.g. by skipping the actions for high-priority
* characters already handled by ->lookahead_buf()).
*
+ * Optional.
+ *
* @owner: module containting this ldisc (for reference counting)
*
* This structure defines the interface between the tty line discipline
There is no need to provide any hook in struct tty_ldisc_ops. Document that and write down that read/write return EIO in that case. The rest is simply ignored. Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org> --- include/linux/tty_ldisc.h | 30 +++++++++++++++++++++++++----- 1 file changed, 25 insertions(+), 5 deletions(-)