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linux-next/drivers/tty/n_tty.c
Tejun Heo 28b0f8a696 tty: make n_tty_read() always abort if hangup is in progress 
A tty is hung up by __tty_hangup() setting file->f_op to
hung_up_tty_fops, which is skipped on ttys whose write operation isn't
tty_write().  This means that, for example, /dev/console whose write
op is redirected_tty_write() is never actually marked hung up.

Because n_tty_read() uses the hung up status to decide whether to
abort the waiting readers, the lack of hung-up marking can lead to the
following scenario.

 1. A session contains two processes.  The leader and its child.  The
    child ignores SIGHUP.

 2. The leader exits and starts disassociating from the controlling
    terminal (/dev/console).

 3. __tty_hangup() skips setting f_op to hung_up_tty_fops.

 4. SIGHUP is delivered and ignored.

 5. tty_ldisc_hangup() is invoked.  It wakes up the waits which should
    clear the read lockers of tty->ldisc_sem.

 6. The reader wakes up but because tty_hung_up_p() is false, it
    doesn't abort and goes back to sleep while read-holding
    tty->ldisc_sem.

 7. The leader progresses to tty_ldisc_lock() in tty_ldisc_hangup()
    and is now stuck in D sleep indefinitely waiting for
    tty->ldisc_sem.

The following is Alan's explanation on why some ttys aren't hung up.

 http://lkml.kernel.org/r/20171101170908.6ad08580@alans-desktop

 1. It broke the serial consoles because they would hang up and close
    down the hardware. With tty_port that *should* be fixable properly
    for any cases remaining.

 2. The console layer was (and still is) completely broken and doens't
    refcount properly. So if you turn on console hangups it breaks (as
    indeed does freeing consoles and half a dozen other things).

As neither can be fixed quickly, this patch works around the problem
by introducing a new flag, TTY_HUPPING, which is used solely to tell
n_tty_read() that hang-up is in progress for the console and the
readers should be aborted regardless of the hung-up status of the
device.

The following is a sample hung task warning caused by this issue.

  INFO: task agetty:2662 blocked for more than 120 seconds.
        Not tainted 4.11.3-dbg-tty-lockup-02478-gfd6c7ee-dirty #28
  "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
      0  2662      1 0x00000086
  Call Trace:
   __schedule+0x267/0x890
   schedule+0x36/0x80
   schedule_timeout+0x23c/0x2e0
   ldsem_down_write+0xce/0x1f6
   tty_ldisc_lock+0x16/0x30
   tty_ldisc_hangup+0xb3/0x1b0
   __tty_hangup+0x300/0x410
   disassociate_ctty+0x6c/0x290
   do_exit+0x7ef/0xb00
   do_group_exit+0x3f/0xa0
   get_signal+0x1b3/0x5d0
   do_signal+0x28/0x660
   exit_to_usermode_loop+0x46/0x86
   do_syscall_64+0x9c/0xb0
   entry_SYSCALL64_slow_path+0x25/0x25

The following is the repro.  Run "$PROG /dev/console".  The parent
process hangs in D state.

  #include <sys/types.h>
  #include <sys/stat.h>
  #include <sys/wait.h>
  #include <sys/ioctl.h>
  #include <fcntl.h>
  #include <unistd.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <errno.h>
  #include <signal.h>
  #include <time.h>
  #include <termios.h>

  int main(int argc, char **argv)
  {
	  struct sigaction sact = { .sa_handler = SIG_IGN };
	  struct timespec ts1s = { .tv_sec = 1 };
	  pid_t pid;
	  int fd;

	  if (argc < 2) {
		  fprintf(stderr, "test-hung-tty /dev/$TTY\n");
		  return 1;
	  }

	  /* fork a child to ensure that it isn't already the session leader */
	  pid = fork();
	  if (pid < 0) {
		  perror("fork");
		  return 1;
	  }

	  if (pid > 0) {
		  /* top parent, wait for everyone */
		  while (waitpid(-1, NULL, 0) >= 0)
			  ;
		  if (errno != ECHILD)
			  perror("waitpid");
		  return 0;
	  }

	  /* new session, start a new session and set the controlling tty */
	  if (setsid() < 0) {
		  perror("setsid");
		  return 1;
	  }

	  fd = open(argv[1], O_RDWR);
	  if (fd < 0) {
		  perror("open");
		  return 1;
	  }

	  if (ioctl(fd, TIOCSCTTY, 1) < 0) {
		  perror("ioctl");
		  return 1;
	  }

	  /* fork a child, sleep a bit and exit */
	  pid = fork();
	  if (pid < 0) {
		  perror("fork");
		  return 1;
	  }

	  if (pid > 0) {
		  nanosleep(&ts1s, NULL);
		  printf("Session leader exiting\n");
		  exit(0);
	  }

	  /*
	   * The child ignores SIGHUP and keeps reading from the controlling
	   * tty.  Because SIGHUP is ignored, the child doesn't get killed on
	   * parent exit and the bug in n_tty makes the read(2) block the
	   * parent's control terminal hangup attempt.  The parent ends up in
	   * D sleep until the child is explicitly killed.
	   */
	  sigaction(SIGHUP, &sact, NULL);
	  printf("Child reading tty\n");
	  while (1) {
		  char buf[1024];

		  if (read(fd, buf, sizeof(buf)) < 0) {
			  perror("read");
			  return 1;
		  }
	  }

	  return 0;
  }

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Alan Cox <alan@llwyncelyn.cymru>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2018-02-28 13:21:10 +01:00

2480 lines
61 KiB
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// SPDX-License-Identifier: GPL-1.0+
/*
* n_tty.c --- implements the N_TTY line discipline.
*
* This code used to be in tty_io.c, but things are getting hairy
* enough that it made sense to split things off. (The N_TTY
* processing has changed so much that it's hardly recognizable,
* anyway...)
*
* Note that the open routine for N_TTY is guaranteed never to return
* an error. This is because Linux will fall back to setting a line
* to N_TTY if it can not switch to any other line discipline.
*
* Written by Theodore Ts'o, Copyright 1994.
*
* This file also contains code originally written by Linus Torvalds,
* Copyright 1991, 1992, 1993, and by Julian Cowley, Copyright 1994.
*
* Reduced memory usage for older ARM systems - Russell King.
*
* 2000/01/20 Fixed SMP locking on put_tty_queue using bits of
* the patch by Andrew J. Kroll <ag784@freenet.buffalo.edu>
* who actually finally proved there really was a race.
*
* 2002/03/18 Implemented n_tty_wakeup to send SIGIO POLL_OUTs to
* waiting writing processes-Sapan Bhatia <sapan@corewars.org>.
* Also fixed a bug in BLOCKING mode where n_tty_write returns
* EAGAIN
*/
#include <linux/types.h>
#include <linux/major.h>
#include <linux/errno.h>
#include <linux/signal.h>
#include <linux/fcntl.h>
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/tty.h>
#include <linux/timer.h>
#include <linux/ctype.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/bitops.h>
#include <linux/audit.h>
#include <linux/file.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/ratelimit.h>
#include <linux/vmalloc.h>
/* number of characters left in xmit buffer before select has we have room */
#define WAKEUP_CHARS 256
/*
* This defines the low- and high-watermarks for throttling and
* unthrottling the TTY driver. These watermarks are used for
* controlling the space in the read buffer.
*/
#define TTY_THRESHOLD_THROTTLE 128 /* now based on remaining room */
#define TTY_THRESHOLD_UNTHROTTLE 128
/*
* Special byte codes used in the echo buffer to represent operations
* or special handling of characters. Bytes in the echo buffer that
* are not part of such special blocks are treated as normal character
* codes.
*/
#define ECHO_OP_START 0xff
#define ECHO_OP_MOVE_BACK_COL 0x80
#define ECHO_OP_SET_CANON_COL 0x81
#define ECHO_OP_ERASE_TAB 0x82
#define ECHO_COMMIT_WATERMARK 256
#define ECHO_BLOCK 256
#define ECHO_DISCARD_WATERMARK N_TTY_BUF_SIZE - (ECHO_BLOCK + 32)
#undef N_TTY_TRACE
#ifdef N_TTY_TRACE
# define n_tty_trace(f, args...) trace_printk(f, ##args)
#else
# define n_tty_trace(f, args...)
#endif
struct n_tty_data {
/* producer-published */
size_t read_head;
size_t commit_head;
size_t canon_head;
size_t echo_head;
size_t echo_commit;
size_t echo_mark;
DECLARE_BITMAP(char_map, 256);
/* private to n_tty_receive_overrun (single-threaded) */
unsigned long overrun_time;
int num_overrun;
/* non-atomic */
bool no_room;
/* must hold exclusive termios_rwsem to reset these */
unsigned char lnext:1, erasing:1, raw:1, real_raw:1, icanon:1;
unsigned char push:1;
/* shared by producer and consumer */
char read_buf[N_TTY_BUF_SIZE];
DECLARE_BITMAP(read_flags, N_TTY_BUF_SIZE);
unsigned char echo_buf[N_TTY_BUF_SIZE];
/* consumer-published */
size_t read_tail;
size_t line_start;
/* protected by output lock */
unsigned int column;
unsigned int canon_column;
size_t echo_tail;
struct mutex atomic_read_lock;
struct mutex output_lock;
};
static inline size_t read_cnt(struct n_tty_data *ldata)
{
return ldata->read_head - ldata->read_tail;
}
static inline unsigned char read_buf(struct n_tty_data *ldata, size_t i)
{
return ldata->read_buf[i & (N_TTY_BUF_SIZE - 1)];
}
static inline unsigned char *read_buf_addr(struct n_tty_data *ldata, size_t i)
{
return &ldata->read_buf[i & (N_TTY_BUF_SIZE - 1)];
}
static inline unsigned char echo_buf(struct n_tty_data *ldata, size_t i)
{
return ldata->echo_buf[i & (N_TTY_BUF_SIZE - 1)];
}
static inline unsigned char *echo_buf_addr(struct n_tty_data *ldata, size_t i)
{
return &ldata->echo_buf[i & (N_TTY_BUF_SIZE - 1)];
}
static int tty_copy_to_user(struct tty_struct *tty, void __user *to,
size_t tail, size_t n)
{
struct n_tty_data *ldata = tty->disc_data;
size_t size = N_TTY_BUF_SIZE - tail;
const void *from = read_buf_addr(ldata, tail);
int uncopied;
if (n > size) {
tty_audit_add_data(tty, from, size);
uncopied = copy_to_user(to, from, size);
if (uncopied)
return uncopied;
to += size;
n -= size;
from = ldata->read_buf;
}
tty_audit_add_data(tty, from, n);
return copy_to_user(to, from, n);
}
/**
* n_tty_kick_worker - start input worker (if required)
* @tty: terminal
*
* Re-schedules the flip buffer work if it may have stopped
*
* Caller holds exclusive termios_rwsem
* or
* n_tty_read()/consumer path:
* holds non-exclusive termios_rwsem
*/
static void n_tty_kick_worker(struct tty_struct *tty)
{
struct n_tty_data *ldata = tty->disc_data;
/* Did the input worker stop? Restart it */
if (unlikely(ldata->no_room)) {
ldata->no_room = 0;
WARN_RATELIMIT(tty->port->itty == NULL,
"scheduling with invalid itty\n");
/* see if ldisc has been killed - if so, this means that
* even though the ldisc has been halted and ->buf.work
* cancelled, ->buf.work is about to be rescheduled
*/
WARN_RATELIMIT(test_bit(TTY_LDISC_HALTED, &tty->flags),
"scheduling buffer work for halted ldisc\n");
tty_buffer_restart_work(tty->port);
}
}
static ssize_t chars_in_buffer(struct tty_struct *tty)
{
struct n_tty_data *ldata = tty->disc_data;
ssize_t n = 0;
if (!ldata->icanon)
n = ldata->commit_head - ldata->read_tail;
else
n = ldata->canon_head - ldata->read_tail;
return n;
}
/**
* n_tty_write_wakeup - asynchronous I/O notifier
* @tty: tty device
*
* Required for the ptys, serial driver etc. since processes
* that attach themselves to the master and rely on ASYNC
* IO must be woken up
*/
static void n_tty_write_wakeup(struct tty_struct *tty)
{
clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
}
static void n_tty_check_throttle(struct tty_struct *tty)
{
struct n_tty_data *ldata = tty->disc_data;
/*
* Check the remaining room for the input canonicalization
* mode. We don't want to throttle the driver if we're in
* canonical mode and don't have a newline yet!
*/
if (ldata->icanon && ldata->canon_head == ldata->read_tail)
return;
while (1) {
int throttled;
tty_set_flow_change(tty, TTY_THROTTLE_SAFE);
if (N_TTY_BUF_SIZE - read_cnt(ldata) >= TTY_THRESHOLD_THROTTLE)
break;
throttled = tty_throttle_safe(tty);
if (!throttled)
break;
}
__tty_set_flow_change(tty, 0);
}
static void n_tty_check_unthrottle(struct tty_struct *tty)
{
if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
return;
n_tty_kick_worker(tty);
tty_wakeup(tty->link);
return;
}
/* If there is enough space in the read buffer now, let the
* low-level driver know. We use chars_in_buffer() to
* check the buffer, as it now knows about canonical mode.
* Otherwise, if the driver is throttled and the line is
* longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
* we won't get any more characters.
*/
while (1) {
int unthrottled;
tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
break;
n_tty_kick_worker(tty);
unthrottled = tty_unthrottle_safe(tty);
if (!unthrottled)
break;
}
__tty_set_flow_change(tty, 0);
}
/**
* put_tty_queue - add character to tty
* @c: character
* @ldata: n_tty data
*
* Add a character to the tty read_buf queue.
*
* n_tty_receive_buf()/producer path:
* caller holds non-exclusive termios_rwsem
*/
static inline void put_tty_queue(unsigned char c, struct n_tty_data *ldata)
{
*read_buf_addr(ldata, ldata->read_head) = c;
ldata->read_head++;
}
/**
* reset_buffer_flags - reset buffer state
* @tty: terminal to reset
*
* Reset the read buffer counters and clear the flags.
* Called from n_tty_open() and n_tty_flush_buffer().
*
* Locking: caller holds exclusive termios_rwsem
* (or locking is not required)
*/
static void reset_buffer_flags(struct n_tty_data *ldata)
{
ldata->read_head = ldata->canon_head = ldata->read_tail = 0;
ldata->echo_head = ldata->echo_tail = ldata->echo_commit = 0;
ldata->commit_head = 0;
ldata->echo_mark = 0;
ldata->line_start = 0;
ldata->erasing = 0;
bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
ldata->push = 0;
}
static void n_tty_packet_mode_flush(struct tty_struct *tty)
{
unsigned long flags;
if (tty->link->packet) {
spin_lock_irqsave(&tty->ctrl_lock, flags);
tty->ctrl_status |= TIOCPKT_FLUSHREAD;
spin_unlock_irqrestore(&tty->ctrl_lock, flags);
wake_up_interruptible(&tty->link->read_wait);
}
}
/**
* n_tty_flush_buffer - clean input queue
* @tty: terminal device
*
* Flush the input buffer. Called when the tty layer wants the
* buffer flushed (eg at hangup) or when the N_TTY line discipline
* internally has to clean the pending queue (for example some signals).
*
* Holds termios_rwsem to exclude producer/consumer while
* buffer indices are reset.
*
* Locking: ctrl_lock, exclusive termios_rwsem
*/
static void n_tty_flush_buffer(struct tty_struct *tty)
{
down_write(&tty->termios_rwsem);
reset_buffer_flags(tty->disc_data);
n_tty_kick_worker(tty);
if (tty->link)
n_tty_packet_mode_flush(tty);
up_write(&tty->termios_rwsem);
}
/**
* is_utf8_continuation - utf8 multibyte check
* @c: byte to check
*
* Returns true if the utf8 character 'c' is a multibyte continuation
* character. We use this to correctly compute the on screen size
* of the character when printing
*/
static inline int is_utf8_continuation(unsigned char c)
{
return (c & 0xc0) == 0x80;
}
/**
* is_continuation - multibyte check
* @c: byte to check
*
* Returns true if the utf8 character 'c' is a multibyte continuation
* character and the terminal is in unicode mode.
*/
static inline int is_continuation(unsigned char c, struct tty_struct *tty)
{
return I_IUTF8(tty) && is_utf8_continuation(c);
}
/**
* do_output_char - output one character
* @c: character (or partial unicode symbol)
* @tty: terminal device
* @space: space available in tty driver write buffer
*
* This is a helper function that handles one output character
* (including special characters like TAB, CR, LF, etc.),
* doing OPOST processing and putting the results in the
* tty driver's write buffer.
*
* Note that Linux currently ignores TABDLY, CRDLY, VTDLY, FFDLY
* and NLDLY. They simply aren't relevant in the world today.
* If you ever need them, add them here.
*
* Returns the number of bytes of buffer space used or -1 if
* no space left.
*
* Locking: should be called under the output_lock to protect
* the column state and space left in the buffer
*/
static int do_output_char(unsigned char c, struct tty_struct *tty, int space)
{
struct n_tty_data *ldata = tty->disc_data;
int spaces;
if (!space)
return -1;
switch (c) {
case '\n':
if (O_ONLRET(tty))
ldata->column = 0;
if (O_ONLCR(tty)) {
if (space < 2)
return -1;
ldata->canon_column = ldata->column = 0;
tty->ops->write(tty, "\r\n", 2);
return 2;
}
ldata->canon_column = ldata->column;
break;
case '\r':
if (O_ONOCR(tty) && ldata->column == 0)
return 0;
if (O_OCRNL(tty)) {
c = '\n';
if (O_ONLRET(tty))
ldata->canon_column = ldata->column = 0;
break;
}
ldata->canon_column = ldata->column = 0;
break;
case '\t':
spaces = 8 - (ldata->column & 7);
if (O_TABDLY(tty) == XTABS) {
if (space < spaces)
return -1;
ldata->column += spaces;
tty->ops->write(tty, " ", spaces);
return spaces;
}
ldata->column += spaces;
break;
case '\b':
if (ldata->column > 0)
ldata->column--;
break;
default:
if (!iscntrl(c)) {
if (O_OLCUC(tty))
c = toupper(c);
if (!is_continuation(c, tty))
ldata->column++;
}
break;
}
tty_put_char(tty, c);
return 1;
}
/**
* process_output - output post processor
* @c: character (or partial unicode symbol)
* @tty: terminal device
*
* Output one character with OPOST processing.
* Returns -1 when the output device is full and the character
* must be retried.
*
* Locking: output_lock to protect column state and space left
* (also, this is called from n_tty_write under the
* tty layer write lock)
*/
static int process_output(unsigned char c, struct tty_struct *tty)
{
struct n_tty_data *ldata = tty->disc_data;
int space, retval;
mutex_lock(&ldata->output_lock);
space = tty_write_room(tty);
retval = do_output_char(c, tty, space);
mutex_unlock(&ldata->output_lock);
if (retval < 0)
return -1;
else
return 0;
}
/**
* process_output_block - block post processor
* @tty: terminal device
* @buf: character buffer
* @nr: number of bytes to output
*
* Output a block of characters with OPOST processing.
* Returns the number of characters output.
*
* This path is used to speed up block console writes, among other
* things when processing blocks of output data. It handles only
* the simple cases normally found and helps to generate blocks of
* symbols for the console driver and thus improve performance.
*
* Locking: output_lock to protect column state and space left
* (also, this is called from n_tty_write under the
* tty layer write lock)
*/
static ssize_t process_output_block(struct tty_struct *tty,
const unsigned char *buf, unsigned int nr)
{
struct n_tty_data *ldata = tty->disc_data;
int space;
int i;
const unsigned char *cp;
mutex_lock(&ldata->output_lock);
space = tty_write_room(tty);
if (!space) {
mutex_unlock(&ldata->output_lock);
return 0;
}
if (nr > space)
nr = space;
for (i = 0, cp = buf; i < nr; i++, cp++) {
unsigned char c = *cp;
switch (c) {
case '\n':
if (O_ONLRET(tty))
ldata->column = 0;
if (O_ONLCR(tty))
goto break_out;
ldata->canon_column = ldata->column;
break;
case '\r':
if (O_ONOCR(tty) && ldata->column == 0)
goto break_out;
if (O_OCRNL(tty))
goto break_out;
ldata->canon_column = ldata->column = 0;
break;
case '\t':
goto break_out;
case '\b':
if (ldata->column > 0)
ldata->column--;
break;
default:
if (!iscntrl(c)) {
if (O_OLCUC(tty))
goto break_out;
if (!is_continuation(c, tty))
ldata->column++;
}
break;
}
}
break_out:
i = tty->ops->write(tty, buf, i);
mutex_unlock(&ldata->output_lock);
return i;
}
/**
* process_echoes - write pending echo characters
* @tty: terminal device
*
* Write previously buffered echo (and other ldisc-generated)
* characters to the tty.
*
* Characters generated by the ldisc (including echoes) need to
* be buffered because the driver's write buffer can fill during
* heavy program output. Echoing straight to the driver will
* often fail under these conditions, causing lost characters and
* resulting mismatches of ldisc state information.
*
* Since the ldisc state must represent the characters actually sent
* to the driver at the time of the write, operations like certain
* changes in column state are also saved in the buffer and executed
* here.
*
* A circular fifo buffer is used so that the most recent characters
* are prioritized. Also, when control characters are echoed with a
* prefixed "^", the pair is treated atomically and thus not separated.
*
* Locking: callers must hold output_lock
*/
static size_t __process_echoes(struct tty_struct *tty)
{
struct n_tty_data *ldata = tty->disc_data;
int space, old_space;
size_t tail;
unsigned char c;
old_space = space = tty_write_room(tty);
tail = ldata->echo_tail;
while (ldata->echo_commit != tail) {
c = echo_buf(ldata, tail);
if (c == ECHO_OP_START) {
unsigned char op;
int no_space_left = 0;
/*
* If the buffer byte is the start of a multi-byte
* operation, get the next byte, which is either the
* op code or a control character value.
*/
op = echo_buf(ldata, tail + 1);
switch (op) {
unsigned int num_chars, num_bs;
case ECHO_OP_ERASE_TAB:
num_chars = echo_buf(ldata, tail + 2);
/*
* Determine how many columns to go back
* in order to erase the tab.
* This depends on the number of columns
* used by other characters within the tab
* area. If this (modulo 8) count is from
* the start of input rather than from a
* previous tab, we offset by canon column.
* Otherwise, tab spacing is normal.
*/
if (!(num_chars & 0x80))
num_chars += ldata->canon_column;
num_bs = 8 - (num_chars & 7);
if (num_bs > space) {
no_space_left = 1;
break;
}
space -= num_bs;
while (num_bs--) {
tty_put_char(tty, '\b');
if (ldata->column > 0)
ldata->column--;
}
tail += 3;
break;
case ECHO_OP_SET_CANON_COL:
ldata->canon_column = ldata->column;
tail += 2;
break;
case ECHO_OP_MOVE_BACK_COL:
if (ldata->column > 0)
ldata->column--;
tail += 2;
break;
case ECHO_OP_START:
/* This is an escaped echo op start code */
if (!space) {
no_space_left = 1;
break;
}
tty_put_char(tty, ECHO_OP_START);
ldata->column++;
space--;
tail += 2;
break;
default:
/*
* If the op is not a special byte code,
* it is a ctrl char tagged to be echoed
* as "^X" (where X is the letter
* representing the control char).
* Note that we must ensure there is
* enough space for the whole ctrl pair.
*
*/
if (space < 2) {
no_space_left = 1;
break;
}
tty_put_char(tty, '^');
tty_put_char(tty, op ^ 0100);
ldata->column += 2;
space -= 2;
tail += 2;
}
if (no_space_left)
break;
} else {
if (O_OPOST(tty)) {
int retval = do_output_char(c, tty, space);
if (retval < 0)
break;
space -= retval;
} else {
if (!space)
break;
tty_put_char(tty, c);
space -= 1;
}
tail += 1;
}
}
/* If the echo buffer is nearly full (so that the possibility exists
* of echo overrun before the next commit), then discard enough
* data at the tail to prevent a subsequent overrun */
while (ldata->echo_commit - tail >= ECHO_DISCARD_WATERMARK) {
if (echo_buf(ldata, tail) == ECHO_OP_START) {
if (echo_buf(ldata, tail + 1) == ECHO_OP_ERASE_TAB)
tail += 3;
else
tail += 2;
} else
tail++;
}
ldata->echo_tail = tail;
return old_space - space;
}
static void commit_echoes(struct tty_struct *tty)
{
struct n_tty_data *ldata = tty->disc_data;
size_t nr, old, echoed;
size_t head;
head = ldata->echo_head;
ldata->echo_mark = head;
old = ldata->echo_commit - ldata->echo_tail;
/* Process committed echoes if the accumulated # of bytes
* is over the threshold (and try again each time another
* block is accumulated) */
nr = head - ldata->echo_tail;
if (nr < ECHO_COMMIT_WATERMARK || (nr % ECHO_BLOCK > old % ECHO_BLOCK))
return;
mutex_lock(&ldata->output_lock);
ldata->echo_commit = head;
echoed = __process_echoes(tty);
mutex_unlock(&ldata->output_lock);
if (echoed && tty->ops->flush_chars)
tty->ops->flush_chars(tty);
}
static void process_echoes(struct tty_struct *tty)
{
struct n_tty_data *ldata = tty->disc_data;
size_t echoed;
if (ldata->echo_mark == ldata->echo_tail)
return;
mutex_lock(&ldata->output_lock);
ldata->echo_commit = ldata->echo_mark;
echoed = __process_echoes(tty);
mutex_unlock(&ldata->output_lock);
if (echoed && tty->ops->flush_chars)
tty->ops->flush_chars(tty);
}
/* NB: echo_mark and echo_head should be equivalent here */
static void flush_echoes(struct tty_struct *tty)
{
struct n_tty_data *ldata = tty->disc_data;
if ((!L_ECHO(tty) && !L_ECHONL(tty)) ||
ldata->echo_commit == ldata->echo_head)
return;
mutex_lock(&ldata->output_lock);
ldata->echo_commit = ldata->echo_head;
__process_echoes(tty);
mutex_unlock(&ldata->output_lock);
}
/**
* add_echo_byte - add a byte to the echo buffer
* @c: unicode byte to echo
* @ldata: n_tty data
*
* Add a character or operation byte to the echo buffer.
*/
static inline void add_echo_byte(unsigned char c, struct n_tty_data *ldata)
{
*echo_buf_addr(ldata, ldata->echo_head++) = c;
}
/**
* echo_move_back_col - add operation to move back a column
* @ldata: n_tty data
*
* Add an operation to the echo buffer to move back one column.
*/
static void echo_move_back_col(struct n_tty_data *ldata)
{
add_echo_byte(ECHO_OP_START, ldata);
add_echo_byte(ECHO_OP_MOVE_BACK_COL, ldata);
}
/**
* echo_set_canon_col - add operation to set the canon column
* @ldata: n_tty data
*
* Add an operation to the echo buffer to set the canon column
* to the current column.
*/
static void echo_set_canon_col(struct n_tty_data *ldata)
{
add_echo_byte(ECHO_OP_START, ldata);
add_echo_byte(ECHO_OP_SET_CANON_COL, ldata);
}
/**
* echo_erase_tab - add operation to erase a tab
* @num_chars: number of character columns already used
* @after_tab: true if num_chars starts after a previous tab
* @ldata: n_tty data
*
* Add an operation to the echo buffer to erase a tab.
*
* Called by the eraser function, which knows how many character
* columns have been used since either a previous tab or the start
* of input. This information will be used later, along with
* canon column (if applicable), to go back the correct number
* of columns.
*/
static void echo_erase_tab(unsigned int num_chars, int after_tab,
struct n_tty_data *ldata)
{
add_echo_byte(ECHO_OP_START, ldata);
add_echo_byte(ECHO_OP_ERASE_TAB, ldata);
/* We only need to know this modulo 8 (tab spacing) */
num_chars &= 7;
/* Set the high bit as a flag if num_chars is after a previous tab */
if (after_tab)
num_chars |= 0x80;
add_echo_byte(num_chars, ldata);
}
/**
* echo_char_raw - echo a character raw
* @c: unicode byte to echo
* @tty: terminal device
*
* Echo user input back onto the screen. This must be called only when
* L_ECHO(tty) is true. Called from the driver receive_buf path.
*
* This variant does not treat control characters specially.
*/
static void echo_char_raw(unsigned char c, struct n_tty_data *ldata)
{
if (c == ECHO_OP_START) {
add_echo_byte(ECHO_OP_START, ldata);
add_echo_byte(ECHO_OP_START, ldata);
} else {
add_echo_byte(c, ldata);
}
}
/**
* echo_char - echo a character
* @c: unicode byte to echo
* @tty: terminal device
*
* Echo user input back onto the screen. This must be called only when
* L_ECHO(tty) is true. Called from the driver receive_buf path.
*
* This variant tags control characters to be echoed as "^X"
* (where X is the letter representing the control char).
*/
static void echo_char(unsigned char c, struct tty_struct *tty)
{
struct n_tty_data *ldata = tty->disc_data;
if (c == ECHO_OP_START) {
add_echo_byte(ECHO_OP_START, ldata);
add_echo_byte(ECHO_OP_START, ldata);
} else {
if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t')
add_echo_byte(ECHO_OP_START, ldata);
add_echo_byte(c, ldata);
}
}
/**
* finish_erasing - complete erase
* @ldata: n_tty data
*/
static inline void finish_erasing(struct n_tty_data *ldata)
{
if (ldata->erasing) {
echo_char_raw('/', ldata);
ldata->erasing = 0;
}
}
/**
* eraser - handle erase function
* @c: character input
* @tty: terminal device
*
* Perform erase and necessary output when an erase character is
* present in the stream from the driver layer. Handles the complexities
* of UTF-8 multibyte symbols.
*
* n_tty_receive_buf()/producer path:
* caller holds non-exclusive termios_rwsem
*/
static void eraser(unsigned char c, struct tty_struct *tty)
{
struct n_tty_data *ldata = tty->disc_data;
enum { ERASE, WERASE, KILL } kill_type;
size_t head;
size_t cnt;
int seen_alnums;
if (ldata->read_head == ldata->canon_head) {
/* process_output('\a', tty); */ /* what do you think? */
return;
}
if (c == ERASE_CHAR(tty))
kill_type = ERASE;
else if (c == WERASE_CHAR(tty))
kill_type = WERASE;
else {
if (!L_ECHO(tty)) {
ldata->read_head = ldata->canon_head;
return;
}
if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
ldata->read_head = ldata->canon_head;
finish_erasing(ldata);
echo_char(KILL_CHAR(tty), tty);
/* Add a newline if ECHOK is on and ECHOKE is off. */
if (L_ECHOK(tty))
echo_char_raw('\n', ldata);
return;
}
kill_type = KILL;
}
seen_alnums = 0;
while (ldata->read_head != ldata->canon_head) {
head = ldata->read_head;
/* erase a single possibly multibyte character */
do {
head--;
c = read_buf(ldata, head);
} while (is_continuation(c, tty) && head != ldata->canon_head);
/* do not partially erase */
if (is_continuation(c, tty))
break;
if (kill_type == WERASE) {
/* Equivalent to BSD's ALTWERASE. */
if (isalnum(c) || c == '_')
seen_alnums++;
else if (seen_alnums)
break;
}
cnt = ldata->read_head - head;
ldata->read_head = head;
if (L_ECHO(tty)) {
if (L_ECHOPRT(tty)) {
if (!ldata->erasing) {
echo_char_raw('\\', ldata);
ldata->erasing = 1;
}
/* if cnt > 1, output a multi-byte character */
echo_char(c, tty);
while (--cnt > 0) {
head++;
echo_char_raw(read_buf(ldata, head), ldata);
echo_move_back_col(ldata);
}
} else if (kill_type == ERASE && !L_ECHOE(tty)) {
echo_char(ERASE_CHAR(tty), tty);
} else if (c == '\t') {
unsigned int num_chars = 0;
int after_tab = 0;
size_t tail = ldata->read_head;
/*
* Count the columns used for characters
* since the start of input or after a
* previous tab.
* This info is used to go back the correct
* number of columns.
*/
while (tail != ldata->canon_head) {
tail--;
c = read_buf(ldata, tail);
if (c == '\t') {
after_tab = 1;
break;
} else if (iscntrl(c)) {
if (L_ECHOCTL(tty))
num_chars += 2;
} else if (!is_continuation(c, tty)) {
num_chars++;
}
}
echo_erase_tab(num_chars, after_tab, ldata);
} else {
if (iscntrl(c) && L_ECHOCTL(tty)) {
echo_char_raw('\b', ldata);
echo_char_raw(' ', ldata);
echo_char_raw('\b', ldata);
}
if (!iscntrl(c) || L_ECHOCTL(tty)) {
echo_char_raw('\b', ldata);
echo_char_raw(' ', ldata);
echo_char_raw('\b', ldata);
}
}
}
if (kill_type == ERASE)
break;
}
if (ldata->read_head == ldata->canon_head && L_ECHO(tty))
finish_erasing(ldata);
}
/**
* isig - handle the ISIG optio
* @sig: signal
* @tty: terminal
*
* Called when a signal is being sent due to terminal input.
* Called from the driver receive_buf path so serialized.
*
* Performs input and output flush if !NOFLSH. In this context, the echo
* buffer is 'output'. The signal is processed first to alert any current
* readers or writers to discontinue and exit their i/o loops.
*
* Locking: ctrl_lock
*/
static void __isig(int sig, struct tty_struct *tty)
{
struct pid *tty_pgrp = tty_get_pgrp(tty);
if (tty_pgrp) {
kill_pgrp(tty_pgrp, sig, 1);
put_pid(tty_pgrp);
}
}
static void isig(int sig, struct tty_struct *tty)
{
struct n_tty_data *ldata = tty->disc_data;
if (L_NOFLSH(tty)) {
/* signal only */
__isig(sig, tty);
} else { /* signal and flush */
up_read(&tty->termios_rwsem);
down_write(&tty->termios_rwsem);
__isig(sig, tty);
/* clear echo buffer */
mutex_lock(&ldata->output_lock);
ldata->echo_head = ldata->echo_tail = 0;
ldata->echo_mark = ldata->echo_commit = 0;
mutex_unlock(&ldata->output_lock);
/* clear output buffer */
tty_driver_flush_buffer(tty);
/* clear input buffer */
reset_buffer_flags(tty->disc_data);
/* notify pty master of flush */
if (tty->link)
n_tty_packet_mode_flush(tty);
up_write(&tty->termios_rwsem);
down_read(&tty->termios_rwsem);
}
}
/**
* n_tty_receive_break - handle break
* @tty: terminal
*
* An RS232 break event has been hit in the incoming bitstream. This
* can cause a variety of events depending upon the termios settings.
*
* n_tty_receive_buf()/producer path:
* caller holds non-exclusive termios_rwsem
*
* Note: may get exclusive termios_rwsem if flushing input buffer
*/
static void n_tty_receive_break(struct tty_struct *tty)
{
struct n_tty_data *ldata = tty->disc_data;
if (I_IGNBRK(tty))
return;
if (I_BRKINT(tty)) {
isig(SIGINT, tty);
return;
}
if (I_PARMRK(tty)) {
put_tty_queue('\377', ldata);
put_tty_queue('\0', ldata);
}
put_tty_queue('\0', ldata);
}
/**
* n_tty_receive_overrun - handle overrun reporting
* @tty: terminal
*
* Data arrived faster than we could process it. While the tty
* driver has flagged this the bits that were missed are gone
* forever.
*
* Called from the receive_buf path so single threaded. Does not
* need locking as num_overrun and overrun_time are function
* private.
*/
static void n_tty_receive_overrun(struct tty_struct *tty)
{
struct n_tty_data *ldata = tty->disc_data;
ldata->num_overrun++;
if (time_after(jiffies, ldata->overrun_time + HZ) ||
time_after(ldata->overrun_time, jiffies)) {
tty_warn(tty, "%d input overrun(s)\n", ldata->num_overrun);
ldata->overrun_time = jiffies;
ldata->num_overrun = 0;
}
}
/**
* n_tty_receive_parity_error - error notifier
* @tty: terminal device
* @c: character
*
* Process a parity error and queue the right data to indicate
* the error case if necessary.
*
* n_tty_receive_buf()/producer path:
* caller holds non-exclusive termios_rwsem
*/
static void n_tty_receive_parity_error(struct tty_struct *tty, unsigned char c)
{
struct n_tty_data *ldata = tty->disc_data;
if (I_INPCK(tty)) {
if (I_IGNPAR(tty))
return;
if (I_PARMRK(tty)) {
put_tty_queue('\377', ldata);
put_tty_queue('\0', ldata);
put_tty_queue(c, ldata);
} else
put_tty_queue('\0', ldata);
} else
put_tty_queue(c, ldata);
}
static void
n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c)
{
isig(signal, tty);
if (I_IXON(tty))
start_tty(tty);
if (L_ECHO(tty)) {
echo_char(c, tty);
commit_echoes(tty);
} else
process_echoes(tty);
return;
}
/**
* n_tty_receive_char - perform processing
* @tty: terminal device
* @c: character
*
* Process an individual character of input received from the driver.
* This is serialized with respect to itself by the rules for the
* driver above.
*
* n_tty_receive_buf()/producer path:
* caller holds non-exclusive termios_rwsem
* publishes canon_head if canonical mode is active
*
* Returns 1 if LNEXT was received, else returns 0
*/
static int
n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)
{
struct n_tty_data *ldata = tty->disc_data;
if (I_IXON(tty)) {
if (c == START_CHAR(tty)) {
start_tty(tty);
process_echoes(tty);
return 0;
}
if (c == STOP_CHAR(tty)) {
stop_tty(tty);
return 0;
}
}
if (L_ISIG(tty)) {
if (c == INTR_CHAR(tty)) {
n_tty_receive_signal_char(tty, SIGINT, c);
return 0;
} else if (c == QUIT_CHAR(tty)) {
n_tty_receive_signal_char(tty, SIGQUIT, c);
return 0;
} else if (c == SUSP_CHAR(tty)) {
n_tty_receive_signal_char(tty, SIGTSTP, c);
return 0;
}
}
if (tty->stopped && !tty->flow_stopped && I_IXON(tty) && I_IXANY(tty)) {
start_tty(tty);
process_echoes(tty);
}
if (c == '\r') {
if (I_IGNCR(tty))
return 0;
if (I_ICRNL(tty))
c = '\n';
} else if (c == '\n' && I_INLCR(tty))
c = '\r';
if (ldata->icanon) {
if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
(c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
eraser(c, tty);
commit_echoes(tty);
return 0;
}
if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
ldata->lnext = 1;
if (L_ECHO(tty)) {
finish_erasing(ldata);
if (L_ECHOCTL(tty)) {
echo_char_raw('^', ldata);
echo_char_raw('\b', ldata);
commit_echoes(tty);
}
}
return 1;
}
if (c == REPRINT_CHAR(tty) && L_ECHO(tty) && L_IEXTEN(tty)) {
size_t tail = ldata->canon_head;
finish_erasing(ldata);
echo_char(c, tty);
echo_char_raw('\n', ldata);
while (tail != ldata->read_head) {
echo_char(read_buf(ldata, tail), tty);
tail++;
}
commit_echoes(tty);
return 0;
}
if (c == '\n') {
if (L_ECHO(tty) || L_ECHONL(tty)) {
echo_char_raw('\n', ldata);
commit_echoes(tty);
}
goto handle_newline;
}
if (c == EOF_CHAR(tty)) {
c = __DISABLED_CHAR;
goto handle_newline;
}
if ((c == EOL_CHAR(tty)) ||
(c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
/*
* XXX are EOL_CHAR and EOL2_CHAR echoed?!?
*/
if (L_ECHO(tty)) {
/* Record the column of first canon char. */
if (ldata->canon_head == ldata->read_head)
echo_set_canon_col(ldata);
echo_char(c, tty);
commit_echoes(tty);
}
/*
* XXX does PARMRK doubling happen for
* EOL_CHAR and EOL2_CHAR?
*/
if (c == (unsigned char) '\377' && I_PARMRK(tty))
put_tty_queue(c, ldata);
handle_newline:
set_bit(ldata->read_head & (N_TTY_BUF_SIZE - 1), ldata->read_flags);
put_tty_queue(c, ldata);
smp_store_release(&ldata->canon_head, ldata->read_head);
kill_fasync(&tty->fasync, SIGIO, POLL_IN);
wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
return 0;
}
}
if (L_ECHO(tty)) {
finish_erasing(ldata);
if (c == '\n')
echo_char_raw('\n', ldata);
else {
/* Record the column of first canon char. */
if (ldata->canon_head == ldata->read_head)
echo_set_canon_col(ldata);
echo_char(c, tty);
}
commit_echoes(tty);
}
/* PARMRK doubling check */
if (c == (unsigned char) '\377' && I_PARMRK(tty))
put_tty_queue(c, ldata);
put_tty_queue(c, ldata);
return 0;
}
static inline void
n_tty_receive_char_inline(struct tty_struct *tty, unsigned char c)
{
struct n_tty_data *ldata = tty->disc_data;
if (tty->stopped && !tty->flow_stopped && I_IXON(tty) && I_IXANY(tty)) {
start_tty(tty);
process_echoes(tty);
}
if (L_ECHO(tty)) {
finish_erasing(ldata);
/* Record the column of first canon char. */
if (ldata->canon_head == ldata->read_head)
echo_set_canon_col(ldata);
echo_char(c, tty);
commit_echoes(tty);
}
/* PARMRK doubling check */
if (c == (unsigned char) '\377' && I_PARMRK(tty))
put_tty_queue(c, ldata);
put_tty_queue(c, ldata);
}
static void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
{
n_tty_receive_char_inline(tty, c);
}
static inline void
n_tty_receive_char_fast(struct tty_struct *tty, unsigned char c)
{
struct n_tty_data *ldata = tty->disc_data;
if (tty->stopped && !tty->flow_stopped && I_IXON(tty) && I_IXANY(tty)) {
start_tty(tty);
process_echoes(tty);
}
if (L_ECHO(tty)) {
finish_erasing(ldata);
/* Record the column of first canon char. */
if (ldata->canon_head == ldata->read_head)
echo_set_canon_col(ldata);
echo_char(c, tty);
commit_echoes(tty);
}
put_tty_queue(c, ldata);
}
static void n_tty_receive_char_closing(struct tty_struct *tty, unsigned char c)
{
if (I_ISTRIP(tty))
c &= 0x7f;
if (I_IUCLC(tty) && L_IEXTEN(tty))
c = tolower(c);
if (I_IXON(tty)) {
if (c == STOP_CHAR(tty))
stop_tty(tty);
else if (c == START_CHAR(tty) ||
(tty->stopped && !tty->flow_stopped && I_IXANY(tty) &&
c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) &&
c != SUSP_CHAR(tty))) {
start_tty(tty);
process_echoes(tty);
}
}
}
static void
n_tty_receive_char_flagged(struct tty_struct *tty, unsigned char c, char flag)
{
switch (flag) {
case TTY_BREAK:
n_tty_receive_break(tty);
break;
case TTY_PARITY:
case TTY_FRAME:
n_tty_receive_parity_error(tty, c);
break;
case TTY_OVERRUN:
n_tty_receive_overrun(tty);
break;
default:
tty_err(tty, "unknown flag %d\n", flag);
break;
}
}
static void
n_tty_receive_char_lnext(struct tty_struct *tty, unsigned char c, char flag)
{
struct n_tty_data *ldata = tty->disc_data;
ldata->lnext = 0;
if (likely(flag == TTY_NORMAL)) {
if (I_ISTRIP(tty))
c &= 0x7f;
if (I_IUCLC(tty) && L_IEXTEN(tty))
c = tolower(c);
n_tty_receive_char(tty, c);
} else
n_tty_receive_char_flagged(tty, c, flag);
}
static void
n_tty_receive_buf_real_raw(struct tty_struct *tty, const unsigned char *cp,
char *fp, int count)
{
struct n_tty_data *ldata = tty->disc_data;
size_t n, head;
head = ldata->read_head & (N_TTY_BUF_SIZE - 1);
n = min_t(size_t, count, N_TTY_BUF_SIZE - head);
memcpy(read_buf_addr(ldata, head), cp, n);
ldata->read_head += n;
cp += n;
count -= n;
head = ldata->read_head & (N_TTY_BUF_SIZE - 1);
n = min_t(size_t, count, N_TTY_BUF_SIZE - head);
memcpy(read_buf_addr(ldata, head), cp, n);
ldata->read_head += n;
}
static void
n_tty_receive_buf_raw(struct tty_struct *tty, const unsigned char *cp,
char *fp, int count)
{
struct n_tty_data *ldata = tty->disc_data;
char flag = TTY_NORMAL;
while (count--) {
if (fp)
flag = *fp++;
if (likely(flag == TTY_NORMAL))
put_tty_queue(*cp++, ldata);
else
n_tty_receive_char_flagged(tty, *cp++, flag);
}
}
static void
n_tty_receive_buf_closing(struct tty_struct *tty, const unsigned char *cp,
char *fp, int count)
{
char flag = TTY_NORMAL;
while (count--) {
if (fp)
flag = *fp++;
if (likely(flag == TTY_NORMAL))
n_tty_receive_char_closing(tty, *cp++);
}
}
static void
n_tty_receive_buf_standard(struct tty_struct *tty, const unsigned char *cp,
char *fp, int count)
{
struct n_tty_data *ldata = tty->disc_data;
char flag = TTY_NORMAL;
while (count--) {
if (fp)
flag = *fp++;
if (likely(flag == TTY_NORMAL)) {
unsigned char c = *cp++;
if (I_ISTRIP(tty))
c &= 0x7f;
if (I_IUCLC(tty) && L_IEXTEN(tty))
c = tolower(c);
if (L_EXTPROC(tty)) {
put_tty_queue(c, ldata);
continue;
}
if (!test_bit(c, ldata->char_map))
n_tty_receive_char_inline(tty, c);
else if (n_tty_receive_char_special(tty, c) && count) {
if (fp)
flag = *fp++;
n_tty_receive_char_lnext(tty, *cp++, flag);
count--;
}
} else
n_tty_receive_char_flagged(tty, *cp++, flag);
}
}
static void
n_tty_receive_buf_fast(struct tty_struct *tty, const unsigned char *cp,
char *fp, int count)
{
struct n_tty_data *ldata = tty->disc_data;
char flag = TTY_NORMAL;
while (count--) {
if (fp)
flag = *fp++;
if (likely(flag == TTY_NORMAL)) {
unsigned char c = *cp++;
if (!test_bit(c, ldata->char_map))
n_tty_receive_char_fast(tty, c);
else if (n_tty_receive_char_special(tty, c) && count) {
if (fp)
flag = *fp++;
n_tty_receive_char_lnext(tty, *cp++, flag);
count--;
}
} else
n_tty_receive_char_flagged(tty, *cp++, flag);
}
}
static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
char *fp, int count)
{
struct n_tty_data *ldata = tty->disc_data;
bool preops = I_ISTRIP(tty) || (I_IUCLC(tty) && L_IEXTEN(tty));
if (ldata->real_raw)
n_tty_receive_buf_real_raw(tty, cp, fp, count);
else if (ldata->raw || (L_EXTPROC(tty) && !preops))
n_tty_receive_buf_raw(tty, cp, fp, count);
else if (tty->closing && !L_EXTPROC(tty))
n_tty_receive_buf_closing(tty, cp, fp, count);
else {
if (ldata->lnext) {
char flag = TTY_NORMAL;
if (fp)
flag = *fp++;
n_tty_receive_char_lnext(tty, *cp++, flag);
count--;
}
if (!preops && !I_PARMRK(tty))
n_tty_receive_buf_fast(tty, cp, fp, count);
else
n_tty_receive_buf_standard(tty, cp, fp, count);
flush_echoes(tty);
if (tty->ops->flush_chars)
tty->ops->flush_chars(tty);
}
if (ldata->icanon && !L_EXTPROC(tty))
return;
/* publish read_head to consumer */
smp_store_release(&ldata->commit_head, ldata->read_head);
if (read_cnt(ldata)) {
kill_fasync(&tty->fasync, SIGIO, POLL_IN);
wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
}
}
/**
* n_tty_receive_buf_common - process input
* @tty: device to receive input
* @cp: input chars
* @fp: flags for each char (if NULL, all chars are TTY_NORMAL)
* @count: number of input chars in @cp
*
* Called by the terminal driver when a block of characters has
* been received. This function must be called from soft contexts
* not from interrupt context. The driver is responsible for making
* calls one at a time and in order (or using flush_to_ldisc)
*
* Returns the # of input chars from @cp which were processed.
*
* In canonical mode, the maximum line length is 4096 chars (including
* the line termination char); lines longer than 4096 chars are
* truncated. After 4095 chars, input data is still processed but
* not stored. Overflow processing ensures the tty can always
* receive more input until at least one line can be read.
*
* In non-canonical mode, the read buffer will only accept 4095 chars;
* this provides the necessary space for a newline char if the input
* mode is switched to canonical.
*
* Note it is possible for the read buffer to _contain_ 4096 chars
* in non-canonical mode: the read buffer could already contain the
* maximum canon line of 4096 chars when the mode is switched to
* non-canonical.
*
* n_tty_receive_buf()/producer path:
* claims non-exclusive termios_rwsem
* publishes commit_head or canon_head
*/
static int
n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp,
char *fp, int count, int flow)
{
struct n_tty_data *ldata = tty->disc_data;
int room, n, rcvd = 0, overflow;
down_read(&tty->termios_rwsem);
while (1) {
/*
* When PARMRK is set, each input char may take up to 3 chars
* in the read buf; reduce the buffer space avail by 3x
*
* If we are doing input canonicalization, and there are no
* pending newlines, let characters through without limit, so
* that erase characters will be handled. Other excess
* characters will be beeped.
*
* paired with store in *_copy_from_read_buf() -- guarantees
* the consumer has loaded the data in read_buf up to the new
* read_tail (so this producer will not overwrite unread data)
*/
size_t tail = smp_load_acquire(&ldata->read_tail);
room = N_TTY_BUF_SIZE - (ldata->read_head - tail);
if (I_PARMRK(tty))
room = (room + 2) / 3;
room--;
if (room <= 0) {
overflow = ldata->icanon && ldata->canon_head == tail;
if (overflow && room < 0)
ldata->read_head--;
room = overflow;
ldata->no_room = flow && !room;
} else
overflow = 0;
n = min(count, room);
if (!n)
break;
/* ignore parity errors if handling overflow */
if (!overflow || !fp || *fp != TTY_PARITY)
__receive_buf(tty, cp, fp, n);
cp += n;
if (fp)
fp += n;
count -= n;
rcvd += n;
}
tty->receive_room = room;
/* Unthrottle if handling overflow on pty */
if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
if (overflow) {
tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
tty_unthrottle_safe(tty);
__tty_set_flow_change(tty, 0);
}
} else
n_tty_check_throttle(tty);
up_read(&tty->termios_rwsem);
return rcvd;
}
static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
char *fp, int count)
{
n_tty_receive_buf_common(tty, cp, fp, count, 0);
}
static int n_tty_receive_buf2(struct tty_struct *tty, const unsigned char *cp,
char *fp, int count)
{
return n_tty_receive_buf_common(tty, cp, fp, count, 1);
}
/**
* n_tty_set_termios - termios data changed
* @tty: terminal
* @old: previous data
*
* Called by the tty layer when the user changes termios flags so
* that the line discipline can plan ahead. This function cannot sleep
* and is protected from re-entry by the tty layer. The user is
* guaranteed that this function will not be re-entered or in progress
* when the ldisc is closed.
*
* Locking: Caller holds tty->termios_rwsem
*/
static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
{
struct n_tty_data *ldata = tty->disc_data;
if (!old || (old->c_lflag ^ tty->termios.c_lflag) & (ICANON | EXTPROC)) {
bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
ldata->line_start = ldata->read_tail;
if (!L_ICANON(tty) || !read_cnt(ldata)) {
ldata->canon_head = ldata->read_tail;
ldata->push = 0;
} else {
set_bit((ldata->read_head - 1) & (N_TTY_BUF_SIZE - 1),
ldata->read_flags);
ldata->canon_head = ldata->read_head;
ldata->push = 1;
}
ldata->commit_head = ldata->read_head;
ldata->erasing = 0;
ldata->lnext = 0;
}
ldata->icanon = (L_ICANON(tty) != 0);
if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
I_PARMRK(tty)) {
bitmap_zero(ldata->char_map, 256);
if (I_IGNCR(tty) || I_ICRNL(tty))
set_bit('\r', ldata->char_map);
if (I_INLCR(tty))
set_bit('\n', ldata->char_map);
if (L_ICANON(tty)) {
set_bit(ERASE_CHAR(tty), ldata->char_map);
set_bit(KILL_CHAR(tty), ldata->char_map);
set_bit(EOF_CHAR(tty), ldata->char_map);
set_bit('\n', ldata->char_map);
set_bit(EOL_CHAR(tty), ldata->char_map);
if (L_IEXTEN(tty)) {
set_bit(WERASE_CHAR(tty), ldata->char_map);
set_bit(LNEXT_CHAR(tty), ldata->char_map);
set_bit(EOL2_CHAR(tty), ldata->char_map);
if (L_ECHO(tty))
set_bit(REPRINT_CHAR(tty),
ldata->char_map);
}
}
if (I_IXON(tty)) {
set_bit(START_CHAR(tty), ldata->char_map);
set_bit(STOP_CHAR(tty), ldata->char_map);
}
if (L_ISIG(tty)) {
set_bit(INTR_CHAR(tty), ldata->char_map);
set_bit(QUIT_CHAR(tty), ldata->char_map);
set_bit(SUSP_CHAR(tty), ldata->char_map);
}
clear_bit(__DISABLED_CHAR, ldata->char_map);
ldata->raw = 0;
ldata->real_raw = 0;
} else {
ldata->raw = 1;
if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
(I_IGNPAR(tty) || !I_INPCK(tty)) &&
(tty->driver->flags & TTY_DRIVER_REAL_RAW))
ldata->real_raw = 1;
else
ldata->real_raw = 0;
}
/*
* Fix tty hang when I_IXON(tty) is cleared, but the tty
* been stopped by STOP_CHAR(tty) before it.
*/
if (!I_IXON(tty) && old && (old->c_iflag & IXON) && !tty->flow_stopped) {
start_tty(tty);
process_echoes(tty);
}
/* The termios change make the tty ready for I/O */
wake_up_interruptible(&tty->write_wait);
wake_up_interruptible(&tty->read_wait);
}
/**
* n_tty_close - close the ldisc for this tty
* @tty: device
*
* Called from the terminal layer when this line discipline is
* being shut down, either because of a close or becsuse of a
* discipline change. The function will not be called while other
* ldisc methods are in progress.
*/
static void n_tty_close(struct tty_struct *tty)
{
struct n_tty_data *ldata = tty->disc_data;
if (tty->link)
n_tty_packet_mode_flush(tty);
vfree(ldata);
tty->disc_data = NULL;
}
/**
* n_tty_open - open an ldisc
* @tty: terminal to open
*
* Called when this line discipline is being attached to the
* terminal device. Can sleep. Called serialized so that no
* other events will occur in parallel. No further open will occur
* until a close.
*/
static int n_tty_open(struct tty_struct *tty)
{
struct n_tty_data *ldata;
/* Currently a malloc failure here can panic */
ldata = vmalloc(sizeof(*ldata));
if (!ldata)
goto err;
ldata->overrun_time = jiffies;
mutex_init(&ldata->atomic_read_lock);
mutex_init(&ldata->output_lock);
tty->disc_data = ldata;
reset_buffer_flags(tty->disc_data);
ldata->column = 0;
ldata->canon_column = 0;
ldata->num_overrun = 0;
ldata->no_room = 0;
ldata->lnext = 0;
tty->closing = 0;
/* indicate buffer work may resume */
clear_bit(TTY_LDISC_HALTED, &tty->flags);
n_tty_set_termios(tty, NULL);
tty_unthrottle(tty);
return 0;
err:
return -ENOMEM;
}
static inline int input_available_p(struct tty_struct *tty, int poll)
{
struct n_tty_data *ldata = tty->disc_data;
int amt = poll && !TIME_CHAR(tty) && MIN_CHAR(tty) ? MIN_CHAR(tty) : 1;
if (ldata->icanon && !L_EXTPROC(tty))
return ldata->canon_head != ldata->read_tail;
else
return ldata->commit_head - ldata->read_tail >= amt;
}
/**
* copy_from_read_buf - copy read data directly
* @tty: terminal device
* @b: user data
* @nr: size of data
*
* Helper function to speed up n_tty_read. It is only called when
* ICANON is off; it copies characters straight from the tty queue to
* user space directly. It can be profitably called twice; once to
* drain the space from the tail pointer to the (physical) end of the
* buffer, and once to drain the space from the (physical) beginning of
* the buffer to head pointer.
*
* Called under the ldata->atomic_read_lock sem
*
* n_tty_read()/consumer path:
* caller holds non-exclusive termios_rwsem
* read_tail published
*/
static int copy_from_read_buf(struct tty_struct *tty,
unsigned char __user **b,
size_t *nr)
{
struct n_tty_data *ldata = tty->disc_data;
int retval;
size_t n;
bool is_eof;
size_t head = smp_load_acquire(&ldata->commit_head);
size_t tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1);
retval = 0;
n = min(head - ldata->read_tail, N_TTY_BUF_SIZE - tail);
n = min(*nr, n);
if (n) {
const unsigned char *from = read_buf_addr(ldata, tail);
retval = copy_to_user(*b, from, n);
n -= retval;
is_eof = n == 1 && *from == EOF_CHAR(tty);
tty_audit_add_data(tty, from, n);
smp_store_release(&ldata->read_tail, ldata->read_tail + n);
/* Turn single EOF into zero-length read */
if (L_EXTPROC(tty) && ldata->icanon && is_eof &&
(head == ldata->read_tail))
n = 0;
*b += n;
*nr -= n;
}
return retval;
}
/**
* canon_copy_from_read_buf - copy read data in canonical mode
* @tty: terminal device
* @b: user data
* @nr: size of data
*
* Helper function for n_tty_read. It is only called when ICANON is on;
* it copies one line of input up to and including the line-delimiting
* character into the user-space buffer.
*
* NB: When termios is changed from non-canonical to canonical mode and
* the read buffer contains data, n_tty_set_termios() simulates an EOF
* push (as if C-d were input) _without_ the DISABLED_CHAR in the buffer.
* This causes data already processed as input to be immediately available
* as input although a newline has not been received.
*
* Called under the atomic_read_lock mutex
*
* n_tty_read()/consumer path:
* caller holds non-exclusive termios_rwsem
* read_tail published
*/
static int canon_copy_from_read_buf(struct tty_struct *tty,
unsigned char __user **b,
size_t *nr)
{
struct n_tty_data *ldata = tty->disc_data;
size_t n, size, more, c;
size_t eol;
size_t tail;
int ret, found = 0;
/* N.B. avoid overrun if nr == 0 */
if (!*nr)
return 0;
n = min(*nr + 1, smp_load_acquire(&ldata->canon_head) - ldata->read_tail);
tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1);
size = min_t(size_t, tail + n, N_TTY_BUF_SIZE);
n_tty_trace("%s: nr:%zu tail:%zu n:%zu size:%zu\n",
__func__, *nr, tail, n, size);
eol = find_next_bit(ldata->read_flags, size, tail);
more = n - (size - tail);
if (eol == N_TTY_BUF_SIZE && more) {
/* scan wrapped without finding set bit */
eol = find_next_bit(ldata->read_flags, more, 0);
found = eol != more;
} else
found = eol != size;
n = eol - tail;
if (n > N_TTY_BUF_SIZE)
n += N_TTY_BUF_SIZE;
c = n + found;
if (!found || read_buf(ldata, eol) != __DISABLED_CHAR) {
c = min(*nr, c);
n = c;
}
n_tty_trace("%s: eol:%zu found:%d n:%zu c:%zu tail:%zu more:%zu\n",
__func__, eol, found, n, c, tail, more);
ret = tty_copy_to_user(tty, *b, tail, n);
if (ret)
return -EFAULT;
*b += n;
*nr -= n;
if (found)
clear_bit(eol, ldata->read_flags);
smp_store_release(&ldata->read_tail, ldata->read_tail + c);
if (found) {
if (!ldata->push)
ldata->line_start = ldata->read_tail;
else
ldata->push = 0;
tty_audit_push();
}
return 0;
}
extern ssize_t redirected_tty_write(struct file *, const char __user *,
size_t, loff_t *);
/**
* job_control - check job control
* @tty: tty
* @file: file handle
*
* Perform job control management checks on this file/tty descriptor
* and if appropriate send any needed signals and return a negative
* error code if action should be taken.
*
* Locking: redirected write test is safe
* current->signal->tty check is safe
* ctrl_lock to safely reference tty->pgrp
*/
static int job_control(struct tty_struct *tty, struct file *file)
{
/* Job control check -- must be done at start and after
every sleep (POSIX.1 7.1.1.4). */
/* NOTE: not yet done after every sleep pending a thorough
check of the logic of this change. -- jlc */
/* don't stop on /dev/console */
if (file->f_op->write == redirected_tty_write)
return 0;
return __tty_check_change(tty, SIGTTIN);
}
/**
* n_tty_read - read function for tty
* @tty: tty device
* @file: file object
* @buf: userspace buffer pointer
* @nr: size of I/O
*
* Perform reads for the line discipline. We are guaranteed that the
* line discipline will not be closed under us but we may get multiple
* parallel readers and must handle this ourselves. We may also get
* a hangup. Always called in user context, may sleep.
*
* This code must be sure never to sleep through a hangup.
*
* n_tty_read()/consumer path:
* claims non-exclusive termios_rwsem
* publishes read_tail
*/
static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
unsigned char __user *buf, size_t nr)
{
struct n_tty_data *ldata = tty->disc_data;
unsigned char __user *b = buf;
DEFINE_WAIT_FUNC(wait, woken_wake_function);
int c;
int minimum, time;
ssize_t retval = 0;
long timeout;
int packet;
size_t tail;
c = job_control(tty, file);
if (c < 0)
return c;
/*
* Internal serialization of reads.
*/
if (file->f_flags & O_NONBLOCK) {
if (!mutex_trylock(&ldata->atomic_read_lock))
return -EAGAIN;
} else {
if (mutex_lock_interruptible(&ldata->atomic_read_lock))
return -ERESTARTSYS;
}
down_read(&tty->termios_rwsem);
minimum = time = 0;
timeout = MAX_SCHEDULE_TIMEOUT;
if (!ldata->icanon) {
minimum = MIN_CHAR(tty);
if (minimum) {
time = (HZ / 10) * TIME_CHAR(tty);
} else {
timeout = (HZ / 10) * TIME_CHAR(tty);
minimum = 1;
}
}
packet = tty->packet;
tail = ldata->read_tail;
add_wait_queue(&tty->read_wait, &wait);
while (nr) {
/* First test for status change. */
if (packet && tty->link->ctrl_status) {
unsigned char cs;
if (b != buf)
break;
spin_lock_irq(&tty->link->ctrl_lock);
cs = tty->link->ctrl_status;
tty->link->ctrl_status = 0;
spin_unlock_irq(&tty->link->ctrl_lock);
if (put_user(cs, b)) {
retval = -EFAULT;
break;
}
b++;
nr--;
break;
}
if (!input_available_p(tty, 0)) {
up_read(&tty->termios_rwsem);
tty_buffer_flush_work(tty->port);
down_read(&tty->termios_rwsem);
if (!input_available_p(tty, 0)) {
if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
retval = -EIO;
break;
}
if (tty_hung_up_p(file))
break;
/*
* Abort readers for ttys which never actually
* get hung up. See __tty_hangup().
*/
if (test_bit(TTY_HUPPING, &tty->flags))
break;
if (!timeout)
break;
if (file->f_flags & O_NONBLOCK) {
retval = -EAGAIN;
break;
}
if (signal_pending(current)) {
retval = -ERESTARTSYS;
break;
}
up_read(&tty->termios_rwsem);
timeout = wait_woken(&wait, TASK_INTERRUPTIBLE,
timeout);
down_read(&tty->termios_rwsem);
continue;
}
}
if (ldata->icanon && !L_EXTPROC(tty)) {
retval = canon_copy_from_read_buf(tty, &b, &nr);
if (retval)
break;
} else {
int uncopied;
/* Deal with packet mode. */
if (packet && b == buf) {
if (put_user(TIOCPKT_DATA, b)) {
retval = -EFAULT;
break;
}
b++;
nr--;
}
uncopied = copy_from_read_buf(tty, &b, &nr);
uncopied += copy_from_read_buf(tty, &b, &nr);
if (uncopied) {
retval = -EFAULT;
break;
}
}
n_tty_check_unthrottle(tty);
if (b - buf >= minimum)
break;
if (time)
timeout = time;
}
if (tail != ldata->read_tail)
n_tty_kick_worker(tty);
up_read(&tty->termios_rwsem);
remove_wait_queue(&tty->read_wait, &wait);
mutex_unlock(&ldata->atomic_read_lock);
if (b - buf)
retval = b - buf;
return retval;
}
/**
* n_tty_write - write function for tty
* @tty: tty device
* @file: file object
* @buf: userspace buffer pointer
* @nr: size of I/O
*
* Write function of the terminal device. This is serialized with
* respect to other write callers but not to termios changes, reads
* and other such events. Since the receive code will echo characters,
* thus calling driver write methods, the output_lock is used in
* the output processing functions called here as well as in the
* echo processing function to protect the column state and space
* left in the buffer.
*
* This code must be sure never to sleep through a hangup.
*
* Locking: output_lock to protect column state and space left
* (note that the process_output*() functions take this
* lock themselves)
*/
static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
const unsigned char *buf, size_t nr)
{
const unsigned char *b = buf;
DEFINE_WAIT_FUNC(wait, woken_wake_function);
int c;
ssize_t retval = 0;
/* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
if (L_TOSTOP(tty) && file->f_op->write != redirected_tty_write) {
retval = tty_check_change(tty);
if (retval)
return retval;
}
down_read(&tty->termios_rwsem);
/* Write out any echoed characters that are still pending */
process_echoes(tty);
add_wait_queue(&tty->write_wait, &wait);
while (1) {
if (signal_pending(current)) {
retval = -ERESTARTSYS;
break;
}
if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
retval = -EIO;
break;
}
if (O_OPOST(tty)) {
while (nr > 0) {
ssize_t num = process_output_block(tty, b, nr);
if (num < 0) {
if (num == -EAGAIN)
break;
retval = num;
goto break_out;
}
b += num;
nr -= num;
if (nr == 0)
break;
c = *b;
if (process_output(c, tty) < 0)
break;
b++; nr--;
}
if (tty->ops->flush_chars)
tty->ops->flush_chars(tty);
} else {
struct n_tty_data *ldata = tty->disc_data;
while (nr > 0) {
mutex_lock(&ldata->output_lock);
c = tty->ops->write(tty, b, nr);
mutex_unlock(&ldata->output_lock);
if (c < 0) {
retval = c;
goto break_out;
}
if (!c)
break;
b += c;
nr -= c;
}
}
if (!nr)
break;
if (file->f_flags & O_NONBLOCK) {
retval = -EAGAIN;
break;
}
up_read(&tty->termios_rwsem);
wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
down_read(&tty->termios_rwsem);
}
break_out:
remove_wait_queue(&tty->write_wait, &wait);
if (nr && tty->fasync)
set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
up_read(&tty->termios_rwsem);
return (b - buf) ? b - buf : retval;
}
/**
* n_tty_poll - poll method for N_TTY
* @tty: terminal device
* @file: file accessing it
* @wait: poll table
*
* Called when the line discipline is asked to poll() for data or
* for special events. This code is not serialized with respect to
* other events save open/close.
*
* This code must be sure never to sleep through a hangup.
* Called without the kernel lock held - fine
*/
static __poll_t n_tty_poll(struct tty_struct *tty, struct file *file,
poll_table *wait)
{
__poll_t mask = 0;
poll_wait(file, &tty->read_wait, wait);
poll_wait(file, &tty->write_wait, wait);
if (input_available_p(tty, 1))
mask |= EPOLLIN | EPOLLRDNORM;
else {
tty_buffer_flush_work(tty->port);
if (input_available_p(tty, 1))
mask |= EPOLLIN | EPOLLRDNORM;
}
if (tty->packet && tty->link->ctrl_status)
mask |= EPOLLPRI | EPOLLIN | EPOLLRDNORM;
if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
mask |= EPOLLHUP;
if (tty_hung_up_p(file))
mask |= EPOLLHUP;
if (tty->ops->write && !tty_is_writelocked(tty) &&
tty_chars_in_buffer(tty) < WAKEUP_CHARS &&
tty_write_room(tty) > 0)
mask |= EPOLLOUT | EPOLLWRNORM;
return mask;
}
static unsigned long inq_canon(struct n_tty_data *ldata)
{
size_t nr, head, tail;
if (ldata->canon_head == ldata->read_tail)
return 0;
head = ldata->canon_head;
tail = ldata->read_tail;
nr = head - tail;
/* Skip EOF-chars.. */
while (head != tail) {
if (test_bit(tail & (N_TTY_BUF_SIZE - 1), ldata->read_flags) &&
read_buf(ldata, tail) == __DISABLED_CHAR)
nr--;
tail++;
}
return nr;
}
static int n_tty_ioctl(struct tty_struct *tty, struct file *file,
unsigned int cmd, unsigned long arg)
{
struct n_tty_data *ldata = tty->disc_data;
int retval;
switch (cmd) {
case TIOCOUTQ:
return put_user(tty_chars_in_buffer(tty), (int __user *) arg);
case TIOCINQ:
down_write(&tty->termios_rwsem);
if (L_ICANON(tty) && !L_EXTPROC(tty))
retval = inq_canon(ldata);
else
retval = read_cnt(ldata);
up_write(&tty->termios_rwsem);
return put_user(retval, (unsigned int __user *) arg);
default:
return n_tty_ioctl_helper(tty, file, cmd, arg);
}
}
static struct tty_ldisc_ops n_tty_ops = {
.magic = TTY_LDISC_MAGIC,
.name = "n_tty",
.open = n_tty_open,
.close = n_tty_close,
.flush_buffer = n_tty_flush_buffer,
.read = n_tty_read,
.write = n_tty_write,
.ioctl = n_tty_ioctl,
.set_termios = n_tty_set_termios,
.poll = n_tty_poll,
.receive_buf = n_tty_receive_buf,
.write_wakeup = n_tty_write_wakeup,
.receive_buf2 = n_tty_receive_buf2,
};
/**
* n_tty_inherit_ops - inherit N_TTY methods
* @ops: struct tty_ldisc_ops where to save N_TTY methods
*
* Enables a 'subclass' line discipline to 'inherit' N_TTY methods.
*/
void n_tty_inherit_ops(struct tty_ldisc_ops *ops)
{
*ops = n_tty_ops;
ops->owner = NULL;
ops->refcount = ops->flags = 0;
}
EXPORT_SYMBOL_GPL(n_tty_inherit_ops);
void __init n_tty_init(void)
{
tty_register_ldisc(N_TTY, &n_tty_ops);
}
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