tty: Remove chars_in_buffer() line discipline method

The chars_in_buffer() line discipline method serves no functional
purpose, other than as a (dubious) debugging aid for mostly bit-rotting
drivers. Despite being documented as an optional method, every caller
is unconditionally executed (although conditionally compiled).
Furthermore, direct tty->ldisc access without an ldisc ref is unsafe.
Lastly, N_TTY's chars_in_buffer() has warned of removal since 3.12.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/serial/tty.txt

@@ -72,9 +72,6 @@ flush_buffer()	-	(optional) May be called at any point between
 			open and close, and instructs the line discipline
 			to empty its input buffer.
 
-chars_in_buffer() -	(optional) Report the number of bytes in the 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

drivers/tty/amiserial.c

@@ -965,8 +965,7 @@ static void rs_throttle(struct tty_struct * tty)
 	struct serial_state *info = tty->driver_data;
 	unsigned long flags;
 #ifdef SERIAL_DEBUG_THROTTLE
-	printk("throttle %s: %d....\n", tty_name(tty),
-	       tty->ldisc.chars_in_buffer(tty));
+	printk("throttle %s ....\n", tty_name(tty));
 #endif
 
 	if (serial_paranoia_check(info, tty->name, "rs_throttle"))
@@ -988,8 +987,7 @@ static void rs_unthrottle(struct tty_struct * tty)
 	struct serial_state *info = tty->driver_data;
 	unsigned long flags;
 #ifdef SERIAL_DEBUG_THROTTLE
-	printk("unthrottle %s: %d....\n", tty_name(tty),
-	       tty->ldisc.chars_in_buffer(tty));
+	printk("unthrottle %s ....\n", tty_name(tty));
 #endif
 
 	if (serial_paranoia_check(info, tty->name, "rs_unthrottle"))

drivers/tty/cyclades.c

@@ -2852,8 +2852,8 @@ static void cy_throttle(struct tty_struct *tty)
 	unsigned long flags;
 
 #ifdef CY_DEBUG_THROTTLE
-	printk(KERN_DEBUG "cyc:throttle %s: %ld...ttyC%d\n", tty_name(tty),
-			tty->ldisc.chars_in_buffer(tty), info->line);
+	printk(KERN_DEBUG "cyc:throttle %s ...ttyC%d\n", tty_name(tty),
+			 info->line);
 #endif
 
 	if (serial_paranoia_check(info, tty->name, "cy_throttle"))
@@ -2891,8 +2891,8 @@ static void cy_unthrottle(struct tty_struct *tty)
 	unsigned long flags;
 
 #ifdef CY_DEBUG_THROTTLE
-	printk(KERN_DEBUG "cyc:unthrottle %s: %ld...ttyC%d\n",
-		tty_name(tty), tty_chars_in_buffer(tty), info->line);
+	printk(KERN_DEBUG "cyc:unthrottle %s ...ttyC%d\n",
+		tty_name(tty), info->line);
 #endif
 
 	if (serial_paranoia_check(info, tty->name, "cy_unthrottle"))

drivers/tty/n_gsm.c

@@ -2303,21 +2303,6 @@ static void gsmld_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 	/* If clogged call tty_throttle(tty); */
 }
 
-/**
- *	gsmld_chars_in_buffer	-	report available bytes
- *	@tty: tty device
- *
- *	Report the number of characters buffered to be delivered to user
- *	at this instant in time.
- *
- *	Locking: gsm lock
- */
-
-static ssize_t gsmld_chars_in_buffer(struct tty_struct *tty)
-{
-	return 0;
-}
-
 /**
  *	gsmld_flush_buffer	-	clean input queue
  *	@tty:	terminal device
@@ -2830,7 +2815,6 @@ static struct tty_ldisc_ops tty_ldisc_packet = {
 	.open            = gsmld_open,
 	.close           = gsmld_close,
 	.flush_buffer    = gsmld_flush_buffer,
-	.chars_in_buffer = gsmld_chars_in_buffer,
 	.read            = gsmld_read,
 	.write           = gsmld_write,
 	.ioctl           = gsmld_ioctl,

drivers/tty/n_tty.c

@@ -380,28 +380,6 @@ static void n_tty_flush_buffer(struct tty_struct *tty)
 	up_write(&tty->termios_rwsem);
 }
 
-/**
- *	n_tty_chars_in_buffer	-	report available bytes
- *	@tty: tty device
- *
- *	Report the number of characters buffered to be delivered to user
- *	at this instant in time.
- *
- *	Locking: exclusive termios_rwsem
- */
-
-static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
-{
-	ssize_t n;
-
-	WARN_ONCE(1, "%s is deprecated and scheduled for removal.", __func__);
-
-	down_write(&tty->termios_rwsem);
-	n = chars_in_buffer(tty);
-	up_write(&tty->termios_rwsem);
-	return n;
-}
-
 /**
  *	is_utf8_continuation	-	utf8 multibyte check
  *	@c: byte to check
@@ -2525,7 +2503,6 @@ struct tty_ldisc_ops tty_ldisc_N_TTY = {
 	.open            = n_tty_open,
 	.close           = n_tty_close,
 	.flush_buffer    = n_tty_flush_buffer,
-	.chars_in_buffer = n_tty_chars_in_buffer,
 	.read            = n_tty_read,
 	.write           = n_tty_write,
 	.ioctl           = n_tty_ioctl,

drivers/tty/rocket.c

@@ -1360,8 +1360,7 @@ static void rp_throttle(struct tty_struct *tty)
 	struct r_port *info = tty->driver_data;
 
 #ifdef ROCKET_DEBUG_THROTTLE
-	printk(KERN_INFO "throttle %s: %d....\n", tty->name,
-	       tty->ldisc.chars_in_buffer(tty));
+	printk(KERN_INFO "throttle %s ....\n", tty->name);
 #endif
 
 	if (rocket_paranoia_check(info, "rp_throttle"))
@@ -1377,8 +1376,7 @@ static void rp_unthrottle(struct tty_struct *tty)
 {
 	struct r_port *info = tty->driver_data;
 #ifdef ROCKET_DEBUG_THROTTLE
-	printk(KERN_INFO "unthrottle %s: %d....\n", tty->name,
-	       tty->ldisc.chars_in_buffer(tty));
+	printk(KERN_INFO "unthrottle %s ....\n", tty->name);
 #endif
 
 	if (rocket_paranoia_check(info, "rp_unthrottle"))

drivers/tty/serial/crisv10.c

@@ -2968,7 +2968,7 @@ static int rs_raw_write(struct tty_struct *tty,
 
 	local_save_flags(flags);
 	DFLOW(DEBUG_LOG(info->line, "write count %i ", count));
-	DFLOW(DEBUG_LOG(info->line, "ldisc %i\n", tty->ldisc.chars_in_buffer(tty)));
+	DFLOW(DEBUG_LOG(info->line, "ldisc\n"));
 
 
 	/* The local_irq_disable/restore_flags pairs below are needed
@@ -3161,10 +3161,9 @@ rs_throttle(struct tty_struct * tty)
 {
 	struct e100_serial *info = (struct e100_serial *)tty->driver_data;
 #ifdef SERIAL_DEBUG_THROTTLE
-	printk("throttle %s: %lu....\n", tty_name(tty),
-	       (unsigned long)tty->ldisc.chars_in_buffer(tty));
+	printk("throttle %s ....\n", tty_name(tty));
 #endif
-	DFLOW(DEBUG_LOG(info->line,"rs_throttle %lu\n", tty->ldisc.chars_in_buffer(tty)));
+	DFLOW(DEBUG_LOG(info->line,"rs_throttle\n"));
 
 	/* Do RTS before XOFF since XOFF might take some time */
 	if (tty->termios.c_cflag & CRTSCTS) {
@@ -3181,10 +3180,9 @@ rs_unthrottle(struct tty_struct * tty)
 {
 	struct e100_serial *info = (struct e100_serial *)tty->driver_data;
 #ifdef SERIAL_DEBUG_THROTTLE
-	printk("unthrottle %s: %lu....\n", tty_name(tty),
-	       (unsigned long)tty->ldisc.chars_in_buffer(tty));
+	printk("unthrottle %s ....\n", tty_name(tty));
 #endif
-	DFLOW(DEBUG_LOG(info->line,"rs_unthrottle ldisc %d\n", tty->ldisc.chars_in_buffer(tty)));
+	DFLOW(DEBUG_LOG(info->line,"rs_unthrottle ldisc\n"));
 	DFLOW(DEBUG_LOG(info->line,"rs_unthrottle flip.count: %i\n", tty->flip.count));
 	/* Do RTS before XOFF since XOFF might take some time */
 	if (tty->termios.c_cflag & CRTSCTS) {

include/linux/tty_ldisc.h

@@ -25,12 +25,6 @@
  *	buffers of any input characters it may have queued to be
  *	delivered to the user mode process.
  *
- * ssize_t (*chars_in_buffer)(struct tty_struct *tty);
- *
- *	This function returns the number of input characters the line
- *	discipline may have queued up to be delivered to the user mode
- *	process.
- *
  * ssize_t (*read)(struct tty_struct * tty, struct file * file,
  *		   unsigned char * buf, size_t nr);
  *
@@ -188,7 +182,6 @@ struct tty_ldisc_ops {
 	int	(*open)(struct tty_struct *);
 	void	(*close)(struct tty_struct *);
 	void	(*flush_buffer)(struct tty_struct *tty);
-	ssize_t	(*chars_in_buffer)(struct tty_struct *tty);
 	ssize_t	(*read)(struct tty_struct *tty, struct file *file,
 			unsigned char __user *buf, size_t nr);
 	ssize_t	(*write)(struct tty_struct *tty, struct file *file,