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>

8 files changed, 13 insertions, 68 deletions

diff --git a/Documentation/serial/tty.txt b/Documentation/serial/tty.txt
index bc3842dc323a..798cba82c762 100644
--- a/Documentation/serial/tty.txt
+++ b/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
diff --git a/drivers/tty/amiserial.c b/drivers/tty/amiserial.c
index 2caaf5a2516d..6ba5681b6385 100644
--- a/drivers/tty/amiserial.c
+++ b/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"))
diff --git a/drivers/tty/cyclades.c b/drivers/tty/cyclades.c
index abbed201dc74..a48e7e66b970 100644
--- a/drivers/tty/cyclades.c
+++ b/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"))
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index c3fe026d3168..e3cc27749344 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2304,21 +2304,6 @@ static void gsmld_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 }
 
 /**
- *      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,
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index b280abaad91b..90eca2605fbf 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -381,28 +381,6 @@ static void n_tty_flush_buffer(struct tty_struct *tty)
 }
 
 /**
- *      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,
diff --git a/drivers/tty/rocket.c b/drivers/tty/rocket.c
index 802eac7e561b..f624b93a237f 100644
--- a/drivers/tty/rocket.c
+++ b/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"))
diff --git a/drivers/tty/serial/crisv10.c b/drivers/tty/serial/crisv10.c
index f13f2ebd215b..e98aef797065 100644
--- a/drivers/tty/serial/crisv10.c
+++ b/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) {
diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h
index 00c9d688d7b7..6101ab8dc148 100644
--- a/include/linux/tty_ldisc.h
+++ b/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,