n_tty.c

linux 内核源代码

/*
 * 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 <[e-mail]>
 *		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 <[e-mail]>.
 *		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 <linux/audit.h>
#include <linux/file.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);
}

static inline int tty_put_user(struct tty_struct *tty, unsigned char x,
			       unsigned char __user *ptr)
{
	tty_audit_add_data(tty, &x, 1);
	return put_user(x, ptr);
}

/**
 *	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 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.
	 */
	if (left <= 0)
		left = tty->icanon && !tty->canon_data;
	tty->receive_room = left;
}

static void put_tty_queue_nolock(unsigned char c, struct tty_struct *tty)
{
	if (tty->read_cnt < N_TTY_BUF_SIZE) {
		tty->read_buf[tty->read_head] = c;
		tty->read_head = (tty->read_head + 1) & (N_TTY_BUF_SIZE-1);
		tty->read_cnt++;
	}
}

static void put_tty_queue(unsigned char c, struct tty_struct *tty)
{
	unsigned long flags;
	/*
	 *	The problem of stomping on the buffers ends here.
	 *	Why didn't anyone see this one coming? --AJK
	*/
	spin_lock_irqsave(&tty->read_lock, flags);
	put_tty_queue_nolock(c, tty);
	spin_unlock_irqrestore(&tty->read_lock, flags);
}

/**
 *	check_unthrottle	-	allow new receive data
 *	@tty; tty device
 *
 *	Check whether to call the driver.unthrottle function.
 *	We test the TTY_THROTTLED bit first so that it always
 *	indicates the current state. The decision about whether
 *	it is worth allowing more input has been taken by the caller.
 *	Can sleep, may be called under the atomic_read_lock mutex but
 *	this is not guaranteed.
 */
 
static void check_unthrottle(struct tty_struct * tty)
{
	if (tty->count &&
	    test_and_clear_bit(TTY_THROTTLED, &tty->flags) && 
	    tty->driver->unthrottle)
		tty->driver->unthrottle(tty);
}

/**
 *	reset_buffer_flags	-	reset buffer state
 *	@tty: terminal to reset
 *
 *	Reset the read buffer counters, clear the flags, 
 *	and make sure the driver is unthrottled. Called
 *	from n_tty_open() and n_tty_flush_buffer().
 */
static void reset_buffer_flags(struct tty_struct *tty)
{
	unsigned long flags;

	spin_lock_irqsave(&tty->read_lock, flags);
	tty->read_head = tty->read_tail = tty->read_cnt = 0;
	spin_unlock_irqrestore(&tty->read_lock, flags);
	tty->canon_head = tty->canon_data = tty->erasing = 0;
	memset(&tty->read_flags, 0, sizeof tty->read_flags);
	n_tty_set_room(tty);
	check_unthrottle(tty);
}

/**
 *	n_tty_flush_buffer	-	clean input queue
 *	@tty:	terminal device
 *
 *	Flush the input buffer. Called when the line discipline is
 *	being closed, 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).
 *
 *	FIXME: tty->ctrl_status is not spinlocked and relies on
 *	lock_kernel() still.
 */
 
static void n_tty_flush_buffer(struct tty_struct * tty)
{
	/* clear everything and unthrottle the driver */
	reset_buffer_flags(tty);
	
	if (!tty->link)
		return;

	if (tty->link->packet) {
		tty->ctrl_status |= TIOCPKT_FLUSHREAD;
		wake_up_interruptible(&tty->link->read_wait);
	}
}

/**
 *	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. 
 */
 
static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
{
	unsigned long flags;
	ssize_t n = 0;

	spin_lock_irqsave(&tty->read_lock, flags);
	if (!tty->icanon) {
		n = tty->read_cnt;
	} else if (tty->canon_data) {
		n = (tty->canon_head > tty->read_tail) ?
			tty->canon_head - tty->read_tail :
			tty->canon_head + (N_TTY_BUF_SIZE - tty->read_tail);
	}
	spin_unlock_irqrestore(&tty->read_lock, flags);
	return n;
}

/**
 *	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);
}

/**
 *	opost			-	output post processor
 *	@c: character (or partial unicode symbol)
 *	@tty: terminal device
 *
 *	Perform OPOST processing.  Returns -1 when the output device is
 *	full and the character must be retried. 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.
 *
 *	Called from both the receive and transmit sides and can be called
 *	re-entrantly. Relies on lock_kernel() still.
 */
 
static int opost(unsigned char c, struct tty_struct *tty)
{
	int	space, spaces;

	space = tty->driver->write_room(tty);
	if (!space)
		return -1;

	if (O_OPOST(tty)) {
		switch (c) {
		case '\n':
			if (O_ONLRET(tty))
				tty->column = 0;
			if (O_ONLCR(tty)) {
				if (space < 2)
					return -1;
				tty->driver->put_char(tty, '\r');
				tty->column = 0;
			}
			tty->canon_column = tty->column;
			break;
		case '\r':
			if (O_ONOCR(tty) && tty->column == 0)
				return 0;
			if (O_OCRNL(tty)) {
				c = '\n';
				if (O_ONLRET(tty))
					tty->canon_column = tty->column = 0;
				break;
			}
			tty->canon_column = tty->column = 0;
			break;
		case '\t':
			spaces = 8 - (tty->column & 7);
			if (O_TABDLY(tty) == XTABS) {
				if (space < spaces)
					return -1;
				tty->column += spaces;
				tty->driver->write(tty, "        ", spaces);
				return 0;
			}
			tty->column += spaces;
			break;
		case '\b':
			if (tty->column > 0)
				tty->column--;
			break;
		default:
			if (O_OLCUC(tty))
				c = toupper(c);
			if (!iscntrl(c) && !is_continuation(c, tty))
				tty->column++;
			break;
		}
	}
	tty->driver->put_char(tty, c);
	return 0;
}

/**
 *	opost_block		-	block postprocess
 *	@tty: terminal device
 *	@inbuf: user buffer
 *	@nr: number of bytes
 *
 *	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.
 *
 *	Called from write_chan under the tty layer write lock.
 */
 
static ssize_t opost_block(struct tty_struct * tty,
		       const unsigned char * buf, unsigned int nr)
{
	int	space;
	int 	i;
	const unsigned char *cp;

	space = tty->driver->write_room(tty);
	if (!space)
		return 0;
	if (nr > space)
		nr = space;

	for (i = 0, cp = buf; i < nr; i++, cp++) {
		switch (*cp) {
		case '\n':
			if (O_ONLRET(tty))
				tty->column = 0;
			if (O_ONLCR(tty))
				goto break_out;
			tty->canon_column = tty->column;
			break;
		case '\r':
			if (O_ONOCR(tty) && tty->column == 0)
				goto break_out;
			if (O_OCRNL(tty))
				goto break_out;
			tty->canon_column = tty->column = 0;
			break;
		case '\t':
			goto break_out;
		case '\b':
			if (tty->column > 0)
				tty->column--;
			break;
		default:
			if (O_OLCUC(tty))
				goto break_out;
			if (!iscntrl(*cp))
				tty->column++;
			break;
		}
	}
break_out:
	if (tty->driver->flush_chars)
		tty->driver->flush_chars(tty);
	i = tty->driver->write(tty, buf, i);	
	return i;
}


/**
 *	put_char	-	write character to driver
 *	@c: character (or part of unicode symbol)
 *	@tty: terminal device
 *
 *	Queue a byte to the driver layer for output
 */
 
static inline void put_char(unsigned char c, struct tty_struct *tty)
{
	tty->driver->put_char(tty, c);
}

/**
 *	echo_char	-	echo characters
 *	@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.
 */

static void echo_char(unsigned char c, struct tty_struct *tty)
{
	if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t') {
		put_char('^', tty);
		put_char(c ^ 0100, tty);
		tty->column += 2;
	} else
		opost(c, tty);
}

static inline void finish_erasing(struct tty_struct *tty)
{
	if (tty->erasing) {
		put_char('/', tty);
		tty->column++;
		tty->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.
 */
 
static void eraser(unsigned char c, struct tty_struct *tty)
{
	enum { ERASE, WERASE, KILL } kill_type;
	int head, seen_alnums, cnt;
	unsigned long flags;

	if (tty->read_head == tty->canon_head) {
		/* opost('\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)) {
			spin_lock_irqsave(&tty->read_lock, flags);
			tty->read_cnt -= ((tty->read_head - tty->canon_head) &
					  (N_TTY_BUF_SIZE - 1));
			tty->read_head = tty->canon_head;
			spin_unlock_irqrestore(&tty->read_lock, flags);
			return;
		}
		if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
			spin_lock_irqsave(&tty->read_lock, flags);
			tty->read_cnt -= ((tty->read_head - tty->canon_head) &
					  (N_TTY_BUF_SIZE - 1));
			tty->read_head = tty->canon_head;
			spin_unlock_irqrestore(&tty->read_lock, flags);
			finish_erasing(tty);
			echo_char(KILL_CHAR(tty), tty);
			/* Add a newline if ECHOK is on and ECHOKE is off. */
			if (L_ECHOK(tty))
				opost('\n', tty);
			return;
		}
		kill_type = KILL;
	}

	seen_alnums = 0;
	while (tty->read_head != tty->canon_head) {
		head = tty->read_head;

		/* erase a single possibly multibyte character */
		do {
			head = (head - 1) & (N_TTY_BUF_SIZE-1);
			c = tty->read_buf[head];
		} while (is_continuation(c, tty) && head != tty->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 = (tty->read_head - head) & (N_TTY_BUF_SIZE-1);
		spin_lock_irqsave(&tty->read_lock, flags);
		tty->read_head = head;
		tty->read_cnt -= cnt;
		spin_unlock_irqrestore(&tty->read_lock, flags);
		if (L_ECHO(tty)) {
			if (L_ECHOPRT(tty)) {
				if (!tty->erasing) {
					put_char('\\', tty);
					tty->column++;
					tty->erasing = 1;
				}
				/* if cnt > 1, output a multi-byte character */
				echo_char(c, tty);
				while (--cnt > 0) {
					head = (head+1) & (N_TTY_BUF_SIZE-1);
					put_char(tty->read_buf[head], tty);
				}
			} else if (kill_type == ERASE && !L_ECHOE(tty)) {
				echo_char(ERASE_CHAR(tty), tty);
			} else if (c == '\t') {
				unsigned int col = tty->canon_column;