[PATCH v2 05/19] tty: Remove chars_in_buffer() line discipline method

From: Peter Hurley
Date: Sat Jan 09 2016 - 23:41:59 EST

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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@xxxxxxxxxxxxxxxxxx>
---
Documentation/serial/tty.txt | 3 ---
drivers/tty/amiserial.c | 6 ++----
drivers/tty/cyclades.c | 8 ++++----
drivers/tty/n_gsm.c | 16 ----------------
drivers/tty/n_tty.c | 23 -----------------------
drivers/tty/rocket.c | 6 ++----
drivers/tty/serial/crisv10.c | 12 +++++-------
include/linux/tty_ldisc.h | 7 -------
8 files changed, 13 insertions(+), 68 deletions(-)

diff --git a/Documentation/serial/tty.txt b/Documentation/serial/tty.txt
index bc3842d..798cba8 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 2caaf5a..6ba5681 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 abbed20..a48e7e6 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 c3fe026..e3cc277 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 d9a5fc2..e09fd58 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -384,28 +384,6 @@ 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
*
@@ -2528,7 +2506,6 @@ 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 802eac7..f624b93 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 f13f2eb..e98aef7 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 00c9d68..6101ab8 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,
--
2.7.0

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