tty_io.c

unix/linux 编程实践一书的所有源代码

static struct wait_queue *vt_activate_queue = NULL;

/*
 * Sleeps until a vt is activated, or the task is interrupted. Returns
 * 0 if activation, -1 if interrupted.
 */
int vt_waitactive(void)
{
	interruptible_sleep_on(&vt_activate_queue);
	return (current->signal & ~current->blocked) ? -1 : 0;
}

#define vt_wake_waitactive() wake_up(&vt_activate_queue)

void reset_vc(unsigned int new_console)
{
	vt_cons[new_console]->vc_mode = KD_TEXT;
	kbd_table[new_console].kbdmode = VC_XLATE;
	vt_cons[new_console]->vt_mode.mode = VT_AUTO;
	vt_cons[new_console]->vt_mode.waitv = 0;
	vt_cons[new_console]->vt_mode.relsig = 0;
	vt_cons[new_console]->vt_mode.acqsig = 0;
	vt_cons[new_console]->vt_mode.frsig = 0;
	vt_cons[new_console]->vt_pid = -1;
	vt_cons[new_console]->vt_newvt = -1;
	reset_palette (new_console) ;
}

/*
 * Performs the back end of a vt switch
 */
void complete_change_console(unsigned int new_console)
{
	unsigned char old_vc_mode;

        if ((new_console == fg_console) || (vt_dont_switch))
                return;
        if (!vc_cons_allocated(new_console))
                return;
	last_console = fg_console;

	/*
	 * If we're switching, we could be going from KD_GRAPHICS to
	 * KD_TEXT mode or vice versa, which means we need to blank or
	 * unblank the screen later.
	 */
	old_vc_mode = vt_cons[fg_console]->vc_mode;
	update_screen(new_console);

	/*
	 * If this new console is under process control, send it a signal
	 * telling it that it has acquired. Also check if it has died and
	 * clean up (similar to logic employed in change_console())
	 */
	if (vt_cons[new_console]->vt_mode.mode == VT_PROCESS)
	{
		/*
		 * Send the signal as privileged - kill_proc() will
		 * tell us if the process has gone or something else
		 * is awry
		 */
		if (kill_proc(vt_cons[new_console]->vt_pid,
			      vt_cons[new_console]->vt_mode.acqsig,
			      1) != 0)
		{
		/*
		 * The controlling process has died, so we revert back to
		 * normal operation. In this case, we'll also change back
		 * to KD_TEXT mode. I'm not sure if this is strictly correct
		 * but it saves the agony when the X server dies and the screen
		 * remains blanked due to KD_GRAPHICS! It would be nice to do
		 * this outside of VT_PROCESS but there is no single process
		 * to account for and tracking tty count may be undesirable.
		 */
		        reset_vc(new_console);
		}
	}

	/*
	 * We do this here because the controlling process above may have
	 * gone, and so there is now a new vc_mode
	 */
	if (old_vc_mode != vt_cons[new_console]->vc_mode)
	{
		if (vt_cons[new_console]->vc_mode == KD_TEXT)
			do_unblank_screen();
		else
			do_blank_screen(1);
	}

	/* Set the colour palette for this VT */
	if (vt_cons[new_console]->vc_mode == KD_TEXT)
		set_palette() ;
	
	/*
	 * Wake anyone waiting for their VT to activate
	 */
	vt_wake_waitactive();
	return;
}

/*
 * Performs the front-end of a vt switch
 */
void change_console(unsigned int new_console)
{
        if ((new_console == fg_console) || (vt_dont_switch))
                return;
        if (!vc_cons_allocated(new_console))
		return;

	/*
	 * If this vt is in process mode, then we need to handshake with
	 * that process before switching. Essentially, we store where that
	 * vt wants to switch to and wait for it to tell us when it's done
	 * (via VT_RELDISP ioctl).
	 *
	 * We also check to see if the controlling process still exists.
	 * If it doesn't, we reset this vt to auto mode and continue.
	 * This is a cheap way to track process control. The worst thing
	 * that can happen is: we send a signal to a process, it dies, and
	 * the switch gets "lost" waiting for a response; hopefully, the
	 * user will try again, we'll detect the process is gone (unless
	 * the user waits just the right amount of time :-) and revert the
	 * vt to auto control.
	 */
	if (vt_cons[fg_console]->vt_mode.mode == VT_PROCESS)
	{
		/*
		 * Send the signal as privileged - kill_proc() will
		 * tell us if the process has gone or something else
		 * is awry
		 */
		if (kill_proc(vt_cons[fg_console]->vt_pid,
			      vt_cons[fg_console]->vt_mode.relsig,
			      1) == 0)
		{
			/*
			 * It worked. Mark the vt to switch to and
			 * return. The process needs to send us a
			 * VT_RELDISP ioctl to complete the switch.
			 */
			vt_cons[fg_console]->vt_newvt = new_console;
			return;
		}

		/*
		 * The controlling process has died, so we revert back to
		 * normal operation. In this case, we'll also change back
		 * to KD_TEXT mode. I'm not sure if this is strictly correct
		 * but it saves the agony when the X server dies and the screen
		 * remains blanked due to KD_GRAPHICS! It would be nice to do
		 * this outside of VT_PROCESS but there is no single process
		 * to account for and tracking tty count may be undesirable.
		 */
		reset_vc(fg_console);

		/*
		 * Fall through to normal (VT_AUTO) handling of the switch...
		 */
	}

	/*
	 * Ignore all switches in KD_GRAPHICS+VT_AUTO mode
	 */
	if (vt_cons[fg_console]->vc_mode == KD_GRAPHICS)
		return;

	complete_change_console(new_console);
}

void wait_for_keypress(void)
{
	sleep_on(&keypress_wait);
}

void stop_tty(struct tty_struct *tty)
{
	if (tty->stopped)
		return;
	tty->stopped = 1;
	if (tty->link && tty->link->packet) {
		tty->ctrl_status &= ~TIOCPKT_START;
		tty->ctrl_status |= TIOCPKT_STOP;
		wake_up_interruptible(&tty->link->read_wait);
	}
	if (tty->driver.stop)
		(tty->driver.stop)(tty);
}

void start_tty(struct tty_struct *tty)
{
	if (!tty->stopped)
		return;
	tty->stopped = 0;
	if (tty->link && tty->link->packet) {
		tty->ctrl_status &= ~TIOCPKT_STOP;
		tty->ctrl_status |= TIOCPKT_START;
		wake_up_interruptible(&tty->link->read_wait);
	}
	if (tty->driver.start)
		(tty->driver.start)(tty);
	if ((tty->flags & (1 << TTY_DO_WRITE_WAKEUP)) &&
	    tty->ldisc.write_wakeup)
		(tty->ldisc.write_wakeup)(tty);
	wake_up_interruptible(&tty->write_wait);
}

static int tty_read(struct inode * inode, struct file * file, char * buf, int count)
{
	int i;
	struct tty_struct * tty;

	tty = (struct tty_struct *)file->private_data;
	if (tty_paranoia_check(tty, inode->i_rdev, "tty_read"))
		return -EIO;
	if (!tty || (tty->flags & (1 << TTY_IO_ERROR)))
		return -EIO;

	/* This check not only needs to be done before reading, but also
	   whenever read_chan() gets woken up after sleeping, so I've
	   moved it to there.  This should only be done for the N_TTY
	   line discipline, anyway.  Same goes for write_chan(). -- jlc. */
#if 0
	if ((inode->i_rdev != CONSOLE_DEV) && /* don't stop on /dev/console */
	    (tty->pgrp > 0) &&
	    (current->tty == tty) &&
	    (tty->pgrp != current->pgrp))
		if (is_ignored(SIGTTIN) || is_orphaned_pgrp(current->pgrp))
			return -EIO;
		else {
			(void) kill_pg(current->pgrp, SIGTTIN, 1);
			return -ERESTARTSYS;
		}
#endif
	if (tty->ldisc.read)
		/* XXX casts are for what kernel-wide prototypes should be. */
		i = (tty->ldisc.read)(tty,file,(unsigned char *)buf,(unsigned int)count);
	else
		i = -EIO;
	if (i > 0)
		inode->i_atime = CURRENT_TIME;
	return i;
}

/*
 * Split writes up in sane blocksizes to avoid
 * denial-of-service type attacks
 */
static inline int do_tty_write(
	int (*write)(struct tty_struct *, struct file *, const unsigned char *, unsigned int),
	struct inode *inode,
	struct tty_struct *tty,
	struct file *file,
	const unsigned char *buf,
	unsigned int count)
{
	int ret = 0, written = 0;

	for (;;) {
		unsigned int size = PAGE_SIZE*2;
		if (size > count)
			size = count;
		ret = write(tty, file, buf, size);
		if (ret <= 0)
			break;
		written += ret;
		buf += ret;
		count -= ret;
		if (!count)
			break;
		ret = -ERESTARTSYS;
		if (current->signal & ~current->blocked)
			break;
		if (need_resched)
			schedule();
	}
	if (written) {
		inode->i_mtime = CURRENT_TIME;
		ret = written;
	}
	return ret;
}


static int tty_write(struct inode * inode, struct file * file, const char * buf, int count)
{
	int is_console;
	struct tty_struct * tty;

	is_console = (inode->i_rdev == CONSOLE_DEV);

	if (is_console && redirect)
		tty = redirect;
	else
		tty = (struct tty_struct *)file->private_data;
	if (tty_paranoia_check(tty, inode->i_rdev, "tty_write"))
		return -EIO;
	if (!tty || !tty->driver.write || (tty->flags & (1 << TTY_IO_ERROR)))
		return -EIO;
#if 0
	if (!is_console && L_TOSTOP(tty) && (tty->pgrp > 0) &&
	    (current->tty == tty) && (tty->pgrp != current->pgrp)) {
		if (is_orphaned_pgrp(current->pgrp))
			return -EIO;
		if (!is_ignored(SIGTTOU)) {
			(void) kill_pg(current->pgrp, SIGTTOU, 1);
			return -ERESTARTSYS;
		}
	}
#endif
	if (!tty->ldisc.write)
		return -EIO;
	return do_tty_write(tty->ldisc.write,
		inode, tty, file,
		(const unsigned char *)buf,
		(unsigned int)count);
}

/* Semaphore to protect creating and releasing a tty */
static struct semaphore tty_sem = MUTEX;
static void down_tty_sem(int index)
{
	down(&tty_sem);
}
static void up_tty_sem(int index)
{
	up(&tty_sem);
}
static void release_mem(struct tty_struct *tty, int idx);

/*
 * Rewritten to remove races and properly clean up after a failed open.  
 * The new code protects the open with a semaphore, so it's really 
 * quite straightforward.  The semaphore locking can probably be
 * relaxed for the (most common) case of reopening a tty.
 */
static int init_dev(kdev_t device, struct tty_struct **ret_tty)
{
	struct tty_struct *tty, *o_tty;
	struct termios *tp, **tp_loc, *o_tp, **o_tp_loc;
	struct termios *ltp, **ltp_loc, *o_ltp, **o_ltp_loc;
	struct tty_driver *driver;	
	int retval;
	int idx;

	driver = get_tty_driver(device);
	if (!driver)
		return -ENODEV;

	idx = MINOR(device) - driver->minor_start;

	/* 
	 * Check whether we need to acquire the tty semaphore to avoid
	 * race conditions.  For now, play it safe.
	 */
	down_tty_sem(idx);

	/* check whether we're reopening an existing tty */
	tty = driver->table[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.)
	 */

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

	tty = (struct tty_struct*) get_free_page(GFP_KERNEL);
	if(!tty)
		goto fail_no_mem;
	initialize_tty_struct(tty);
	tty->device = device;
	tty->driver = *driver;

	tp_loc = &driver->termios[idx];
	if (!*tp_loc) {
		tp = (struct termios *) kmalloc(sizeof(struct termios),
						GFP_KERNEL);
		if (!tp)
			goto free_mem_out;
		*tp = driver->init_termios;
	}

	ltp_loc = &driver->termios_locked[idx];
	if (!*ltp_loc) {
		ltp = (struct termios *) kmalloc(sizeof(struct termios),
						 GFP_KERNEL);
		if (!ltp)
			goto free_mem_out;
		memset(ltp, 0, sizeof(struct termios));
	}

	if (driver->type == TTY_DRIVER_TYPE_PTY) {
		o_tty = (struct tty_struct *) get_free_page(GFP_KERNEL);
		if (!o_tty)
			goto free_mem_out;
		initialize_tty_struct(o_tty);
		o_tty->device = (kdev_t) MKDEV(driver->other->major,
					driver->other->minor_start + idx);
		o_tty->driver = *driver->other;

		o_tp_loc  = &driver->other->termios[idx];
		if (!*o_tp_loc) {
			o_tp = (struct termios *)
				kmalloc(sizeof(struct termios), GFP_KERNEL);
			if (!o_tp)
				goto free_mem_out;
			*o_tp = driver->other->init_termios;
		}

		o_ltp_loc = &driver->other->termios_locked[idx];
		if (!*o_ltp_loc) {
			o_ltp = (struct termios *)
				kmalloc(sizeof(struct termios), GFP_KERNEL);
			if (!o_ltp)
				goto free_mem_out;
			memset(o_ltp, 0, sizeof(struct termios));
		}

		/*
		 * Everything allocated ... set up the o_tty structure.
		 */
		driver->other->table[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_mem to clean up, so 
	 * there's no need to null out the local pointers.
	 */
	driver->table[idx] = tty;
	if (!*tp_loc)
		*tp_loc = tp;
	if (!*ltp_loc)
		*ltp_loc = ltp;
	tty->termios = *tp_loc;
	tty->termios_locked = *ltp_loc;
	(*driver->refcount)++;
	tty->count++;

	/* 
	 * Structures all installed ... call the ldisc open routines.
	 * If we fail here just call release_mem to clean up.  No need
	 * to decrement the use counts, as release_mem 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;
		}
	}
	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:
	retval = -EIO;
	if (test_bit(TTY_CLOSING, &tty->flags))
		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)
			goto end_init;
		tty->link->count++;
	}
	tty->count++;
	tty->driver = *driver; /* N.B. why do this every time?? */

success:
	retval = 0;
	*ret_tty = tty;
	
	/* All paths come through here to release the semaphore */
end_init:
	up_tty_sem(idx);
	return retval;

	/* Release locally allocated memory ... nothing placed in slots */
free_mem_out:
	if (o_tp)