/*
* 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.
*
* This file may be redistributed under the terms of the GNU General Public
* License.
*
* 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 write_chan 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 <asm/uaccess.h>
#include <asm/system.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
static inline unsigned char *alloc_buf(void)
{
gfp_t prio = in_interrupt() ? GFP_ATOMIC : GFP_KERNEL;
if (PAGE_SIZE != N_TTY_BUF_SIZE)
return kmalloc(N_TTY_BUF_SIZE, prio);
else
return (unsigned char *)__get_free_page(prio);
}
static inline void free_buf(unsigned char *buf)
{
if (PAGE_SIZE != N_TTY_BUF_SIZE)
kfree(buf);
else
free_page((unsigned long) buf);
}
/**
* n_tty_set__room - receive space
* @tty: terminal
*
* Called by the driver to find out how much data it is
* permitted to feed to the line discipline without any being lost
* and thus to manage flow control. Not serialized. Answers for the
* "instant".
*/
static void n_tty_set_room(struct tty_struct *tty)
{
int left = N_TTY_BUF_SIZE - tty->read_cnt - 1;
/*
* If we are d
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