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@xxxxxxxxxx> --- include/linux/tty_ldisc.h | 30 +++++++++++++++++++++++++----- 1 file changed, 25 insertions(+), 5 deletions(-) diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h index 49dc172dedc7..62e089434995 100644 --- a/include/linux/tty_ldisc.h +++ b/include/linux/tty_ldisc.h @@ -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 -- 2.41.0
