tty_io.c

来自「linux 内核源代码」· C语言 代码 · 共 2,498 行 · 第 1/5 页

static int init_dev(struct tty_driver *driver, int idx,
	struct tty_struct **ret_tty)
{
	struct tty_struct *tty, *o_tty;
	struct ktermios *tp, **tp_loc, *o_tp, **o_tp_loc;
	struct ktermios *ltp, **ltp_loc, *o_ltp, **o_ltp_loc;
	int retval = 0;

	/* check whether we're reopening an existing tty */
	if (driver->flags & TTY_DRIVER_DEVPTS_MEM) {
		tty = devpts_get_tty(idx);
		/*
		 * If we don't have a tty here on a slave open, it's because
		 * the master already started the close process and there's
		 * no relation between devpts file and tty anymore.
		 */
		if (!tty && driver->subtype == PTY_TYPE_SLAVE) {
			retval = -EIO;
			goto end_init;
		}
		/*
		 * It's safe from now on because init_dev() is called with
		 * tty_mutex held and release_dev() won't change tty->count
		 * or tty->flags without having to grab tty_mutex
		 */
		if (tty && driver->subtype == PTY_TYPE_MASTER)
			tty = tty->link;
	} else {
		tty = driver->ttys[idx];
	}
	if (tty) goto fast_track;

	/*
	 * First time open is complex, especially for PTY devices.
	 * This code guarantees that either everything succeeds and the
	 * TTY is ready for operation, or else the table slots are vacated
	 * and the allocated memory released.  (Except that the termios 
	 * and locked termios may be retained.)
	 */

	if (!try_module_get(driver->owner)) {
		retval = -ENODEV;
		goto end_init;
	}

	o_tty = NULL;
	tp = o_tp = NULL;
	ltp = o_ltp = NULL;

	tty = alloc_tty_struct();
	if(!tty)
		goto fail_no_mem;
	initialize_tty_struct(tty);
	tty->driver = driver;
	tty->index = idx;
	tty_line_name(driver, idx, tty->name);

	if (driver->flags & TTY_DRIVER_DEVPTS_MEM) {
		tp_loc = &tty->termios;
		ltp_loc = &tty->termios_locked;
	} else {
		tp_loc = &driver->termios[idx];
		ltp_loc = &driver->termios_locked[idx];
	}

	if (!*tp_loc) {
		tp = kmalloc(sizeof(struct ktermios), GFP_KERNEL);
		if (!tp)
			goto free_mem_out;
		*tp = driver->init_termios;
	}

	if (!*ltp_loc) {
		ltp = kzalloc(sizeof(struct ktermios), GFP_KERNEL);
		if (!ltp)
			goto free_mem_out;
	}

	if (driver->type == TTY_DRIVER_TYPE_PTY) {
		o_tty = alloc_tty_struct();
		if (!o_tty)
			goto free_mem_out;
		initialize_tty_struct(o_tty);
		o_tty->driver = driver->other;
		o_tty->index = idx;
		tty_line_name(driver->other, idx, o_tty->name);

		if (driver->flags & TTY_DRIVER_DEVPTS_MEM) {
			o_tp_loc = &o_tty->termios;
			o_ltp_loc = &o_tty->termios_locked;
		} else {
			o_tp_loc = &driver->other->termios[idx];
			o_ltp_loc = &driver->other->termios_locked[idx];
		}

		if (!*o_tp_loc) {
			o_tp = kmalloc(sizeof(struct ktermios), GFP_KERNEL);
			if (!o_tp)
				goto free_mem_out;
			*o_tp = driver->other->init_termios;
		}

		if (!*o_ltp_loc) {
			o_ltp = kzalloc(sizeof(struct ktermios), GFP_KERNEL);
			if (!o_ltp)
				goto free_mem_out;
		}

		/*
		 * Everything allocated ... set up the o_tty structure.
		 */
		if (!(driver->other->flags & TTY_DRIVER_DEVPTS_MEM)) {
			driver->other->ttys[idx] = o_tty;
		}
		if (!*o_tp_loc)
			*o_tp_loc = o_tp;
		if (!*o_ltp_loc)
			*o_ltp_loc = o_ltp;
		o_tty->termios = *o_tp_loc;
		o_tty->termios_locked = *o_ltp_loc;
		driver->other->refcount++;
		if (driver->subtype == PTY_TYPE_MASTER)
			o_tty->count++;

		/* Establish the links in both directions */
		tty->link   = o_tty;
		o_tty->link = tty;
	}

	/* 
	 * All structures have been allocated, so now we install them.
	 * Failures after this point use release_tty to clean up, so
	 * there's no need to null out the local pointers.
	 */
	if (!(driver->flags & TTY_DRIVER_DEVPTS_MEM)) {
		driver->ttys[idx] = tty;
	}
	
	if (!*tp_loc)
		*tp_loc = tp;
	if (!*ltp_loc)
		*ltp_loc = ltp;
	tty->termios = *tp_loc;
	tty->termios_locked = *ltp_loc;
	/* Compatibility until drivers always set this */
	tty->termios->c_ispeed = tty_termios_input_baud_rate(tty->termios);
	tty->termios->c_ospeed = tty_termios_baud_rate(tty->termios);
	driver->refcount++;
	tty->count++;

	/* 
	 * Structures all installed ... call the ldisc open routines.
	 * If we fail here just call release_tty to clean up.  No need
	 * to decrement the use counts, as release_tty doesn't care.
	 */

	if (tty->ldisc.open) {
		retval = (tty->ldisc.open)(tty);
		if (retval)
			goto release_mem_out;
	}
	if (o_tty && o_tty->ldisc.open) {
		retval = (o_tty->ldisc.open)(o_tty);
		if (retval) {
			if (tty->ldisc.close)
				(tty->ldisc.close)(tty);
			goto release_mem_out;
		}
		tty_ldisc_enable(o_tty);
	}
	tty_ldisc_enable(tty);
	goto success;

	/*
	 * This fast open can be used if the tty is already open.
	 * No memory is allocated, and the only failures are from
	 * attempting to open a closing tty or attempting multiple
	 * opens on a pty master.
	 */
fast_track:
	if (test_bit(TTY_CLOSING, &tty->flags)) {
		retval = -EIO;
		goto end_init;
	}
	if (driver->type == TTY_DRIVER_TYPE_PTY &&
	    driver->subtype == PTY_TYPE_MASTER) {
		/*
		 * special case for PTY masters: only one open permitted, 
		 * and the slave side open count is incremented as well.
		 */
		if (tty->count) {
			retval = -EIO;
			goto end_init;
		}
		tty->link->count++;
	}
	tty->count++;
	tty->driver = driver; /* N.B. why do this every time?? */

	/* FIXME */
	if(!test_bit(TTY_LDISC, &tty->flags))
		printk(KERN_ERR "init_dev but no ldisc\n");
success:
	*ret_tty = tty;
	
	/* All paths come through here to release the mutex */
end_init:
	return retval;

	/* Release locally allocated memory ... nothing placed in slots */
free_mem_out:
	kfree(o_tp);
	if (o_tty)
		free_tty_struct(o_tty);
	kfree(ltp);
	kfree(tp);
	free_tty_struct(tty);

fail_no_mem:
	module_put(driver->owner);
	retval = -ENOMEM;
	goto end_init;

	/* call the tty release_tty routine to clean out this slot */
release_mem_out:
	if (printk_ratelimit())
		printk(KERN_INFO "init_dev: ldisc open failed, "
				 "clearing slot %d\n", idx);
	release_tty(tty, idx);
	goto end_init;
}

/**
 *	release_one_tty		-	release tty structure memory
 *
 *	Releases memory associated with a tty structure, and clears out the
 *	driver table slots. This function is called when a device is no longer
 *	in use. It also gets called when setup of a device fails.
 *
 *	Locking:
 *		tty_mutex - sometimes only
 *		takes the file list lock internally when working on the list
 *	of ttys that the driver keeps.
 *		FIXME: should we require tty_mutex is held here ??
 */
static void release_one_tty(struct tty_struct *tty, int idx)
{
	int devpts = tty->driver->flags & TTY_DRIVER_DEVPTS_MEM;
	struct ktermios *tp;

	if (!devpts)
		tty->driver->ttys[idx] = NULL;

	if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) {
		tp = tty->termios;
		if (!devpts)
			tty->driver->termios[idx] = NULL;
		kfree(tp);

		tp = tty->termios_locked;
		if (!devpts)
			tty->driver->termios_locked[idx] = NULL;
		kfree(tp);
	}


	tty->magic = 0;
	tty->driver->refcount--;

	file_list_lock();
	list_del_init(&tty->tty_files);
	file_list_unlock();

	free_tty_struct(tty);
}

/**
 *	release_tty		-	release tty structure memory
 *
 *	Release both @tty and a possible linked partner (think pty pair),
 *	and decrement the refcount of the backing module.
 *
 *	Locking:
 *		tty_mutex - sometimes only
 *		takes the file list lock internally when working on the list
 *	of ttys that the driver keeps.
 *		FIXME: should we require tty_mutex is held here ??
 */
static void release_tty(struct tty_struct *tty, int idx)
{
	struct tty_driver *driver = tty->driver;

	if (tty->link)
		release_one_tty(tty->link, idx);
	release_one_tty(tty, idx);
	module_put(driver->owner);
}

/*
 * Even releasing the tty structures is a tricky business.. We have
 * to be very careful that the structures are all released at the
 * same time, as interrupts might otherwise get the wrong pointers.
 *
 * WSH 09/09/97: rewritten to avoid some nasty race conditions that could
 * lead to double frees or releasing memory still in use.
 */
static void release_dev(struct file * filp)
{
	struct tty_struct *tty, *o_tty;
	int	pty_master, tty_closing, o_tty_closing, do_sleep;
	int	devpts;
	int	idx;
	char	buf[64];
	unsigned long flags;
	
	tty = (struct tty_struct *)filp->private_data;
	if (tty_paranoia_check(tty, filp->f_path.dentry->d_inode, "release_dev"))
		return;

	check_tty_count(tty, "release_dev");

	tty_fasync(-1, filp, 0);

	idx = tty->index;
	pty_master = (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
		      tty->driver->subtype == PTY_TYPE_MASTER);
	devpts = (tty->driver->flags & TTY_DRIVER_DEVPTS_MEM) != 0;
	o_tty = tty->link;

#ifdef TTY_PARANOIA_CHECK
	if (idx < 0 || idx >= tty->driver->num) {
		printk(KERN_DEBUG "release_dev: bad idx when trying to "
				  "free (%s)\n", tty->name);
		return;
	}
	if (!(tty->driver->flags & TTY_DRIVER_DEVPTS_MEM)) {
		if (tty != tty->driver->ttys[idx]) {
			printk(KERN_DEBUG "release_dev: driver.table[%d] not tty "
			       "for (%s)\n", idx, tty->name);
			return;
		}
		if (tty->termios != tty->driver->termios[idx]) {
			printk(KERN_DEBUG "release_dev: driver.termios[%d] not termios "
			       "for (%s)\n",
			       idx, tty->name);
			return;
		}
		if (tty->termios_locked != tty->driver->termios_locked[idx]) {
			printk(KERN_DEBUG "release_dev: driver.termios_locked[%d] not "
			       "termios_locked for (%s)\n",
			       idx, tty->name);
			return;
		}
	}
#endif

#ifdef TTY_DEBUG_HANGUP
	printk(KERN_DEBUG "release_dev of %s (tty count=%d)...",
	       tty_name(tty, buf), tty->count);
#endif

#ifdef TTY_PARANOIA_CHECK
	if (tty->driver->other &&
	     !(tty->driver->flags & TTY_DRIVER_DEVPTS_MEM)) {
		if (o_tty != tty->driver->other->ttys[idx]) {
			printk(KERN_DEBUG "release_dev: other->table[%d] "
					  "not o_tty for (%s)\n",
			       idx, tty->name);
			return;
		}
		if (o_tty->termios != tty->driver->other->termios[idx]) {
			printk(KERN_DEBUG "release_dev: other->termios[%d] "
					  "not o_termios for (%s)\n",
			       idx, tty->name);
			return;
		}
		if (o_tty->termios_locked != 
		      tty->driver->other->termios_locked[idx]) {
			printk(KERN_DEBUG "release_dev: other->termios_locked["
					  "%d] not o_termios_locked for (%s)\n",
			       idx, tty->name);
			return;
		}
		if (o_tty->link != tty) {
			printk(KERN_DEBUG "release_dev: bad pty pointers\n");
			return;
		}
	}
#endif
	if (tty->driver->close)
		tty->driver->close(tty, filp);

	/*
	 * Sanity check: if tty->count is going to zero, there shouldn't be
	 * any waiters on tty->read_wait or tty->write_wait.  We test the
	 * wait queues and kick everyone out _before_ actually starting to
	 * close.  This ensures that we won't block while releasing the tty
	 * structure.
	 *
	 * The test for the o_tty closing is necessary, since the master and
	 * slave sides may close in any order.  If the slave side closes out
	 * first, its count will be one, since the master side holds an open.
	 * Thus this test wouldn't be triggered at the time the slave closes,
	 * so we do it now.
	 *
	 * Note that it's possible for the tty to be opened again while we're
	 * flushing out waiters.  By recalculating the closing flags before
	 * each iteration we avoid any problems.
	 */
	while (1) {
		/* Guard against races with tty->count changes elsewhere and
		   opens on /dev/tty */
		   
		mutex_lock(&tty_mutex);
		tty_closing = tty->count <= 1;
		o_tty_closing = o_tty &&
			(o_tty->count <= (pty_master ? 1 : 0));
		do_sleep = 0;

		if (tty_closing) {
			if (waitqueue_active(&tty->read_wait)) {
				wake_up(&tty->read_wait);
				do_sleep++;
			}
			if (waitqueue_active(&tty->write_wait)) {
				wake_up(&tty->write_wait);
				do_sleep++;
			}
		}
		if (o_tty_closing) {
			if (waitqueue_active(&o_tty->read_wait)) {
				wake_up(&o_tty->read_wait);
				do_sleep++;
			}
			if (waitqueue_active(&o_tty->write_wait)) {
				wake_up(&o_tty->write_wait);
				do_sleep++;
			}
		}
		if (!do_sleep)
			break;

		printk(KERN_WARNING "release_dev: %s: read/write wait queue "
				    "active!\n", tty_name(tty, buf));
		mutex_unlock(&tty_mutex);
		schedule();
	}	

	/*
	 * The closing flags are now consistent with the open counts on 
	 * both sides, and we've completed the last operation that could 
	 * block, so it's safe to proceed with closing.
	 */
	if (pty_master) {
		if (--o_tty->count < 0) {
			printk(KERN_WARNING "release_dev: bad pty slave count "
					    "(%d) for %s\n",
			       o_tty->count, tty_name(o_tty, buf));
			o_tty->count = 0;
		}
	}
	if (--tty->count < 0) {
		printk(KERN_WARNING "release_dev: bad tty->count (%d) for %s\n",
		       tty->count, tty_name(tty, buf));
		tty->count = 0;
	}
	
	/*
	 * We've decremented tty->count, so we need to remove this file
	 * descriptor off the tty->tty_files list; this serves two
	 * purposes:
	 *  - check_tty_count sees the correct number of file descriptors
	 *    associated with this tty.
	 *  - do_tty_hangup no longer sees this file descriptor as
	 *    something that needs to be handled for hangups.
	 */
	file_kill(filp);
	filp->private_data = NULL;

	/*
	 * Perform some housekeeping before deciding whether to return.
	 *
	 * Set the TTY_CLOSING flag if this was the last open.  In the
	 * case of a pty we may have to wait around for the other side
	 * to close, and TTY_CLOSING makes sure we can't be reopened.
	 */
	if(tty_closing)
		set_bit(TTY_CLOSING, &tty->flags);
	if(o_tty_closing)
		set_bit(TTY_CLOSING, &o_tty->flags);

	/*
	 * If _either_ side is closing, make sure there aren't any
	 * processes that still think tty or o_tty is their controlling
	 * tty.
	 */
	if (tty_closing || o_tty_closing) {
		rea