xref: /openbmc/linux/drivers/tty/pty.c (revision 82003e04)
1 /*
2  *  Copyright (C) 1991, 1992  Linus Torvalds
3  *
4  *  Added support for a Unix98-style ptmx device.
5  *    -- C. Scott Ananian <cananian@alumni.princeton.edu>, 14-Jan-1998
6  *
7  */
8 
9 #include <linux/module.h>
10 #include <linux/errno.h>
11 #include <linux/interrupt.h>
12 #include <linux/tty.h>
13 #include <linux/tty_flip.h>
14 #include <linux/fcntl.h>
15 #include <linux/sched.h>
16 #include <linux/string.h>
17 #include <linux/major.h>
18 #include <linux/mm.h>
19 #include <linux/init.h>
20 #include <linux/device.h>
21 #include <linux/uaccess.h>
22 #include <linux/bitops.h>
23 #include <linux/devpts_fs.h>
24 #include <linux/slab.h>
25 #include <linux/mutex.h>
26 #include <linux/poll.h>
27 
28 #undef TTY_DEBUG_HANGUP
29 #ifdef TTY_DEBUG_HANGUP
30 # define tty_debug_hangup(tty, f, args...)	tty_debug(tty, f, ##args)
31 #else
32 # define tty_debug_hangup(tty, f, args...)	do {} while (0)
33 #endif
34 
35 #ifdef CONFIG_UNIX98_PTYS
36 static struct tty_driver *ptm_driver;
37 static struct tty_driver *pts_driver;
38 static DEFINE_MUTEX(devpts_mutex);
39 #endif
40 
41 static void pty_close(struct tty_struct *tty, struct file *filp)
42 {
43 	BUG_ON(!tty);
44 	if (tty->driver->subtype == PTY_TYPE_MASTER)
45 		WARN_ON(tty->count > 1);
46 	else {
47 		if (tty_io_error(tty))
48 			return;
49 		if (tty->count > 2)
50 			return;
51 	}
52 	set_bit(TTY_IO_ERROR, &tty->flags);
53 	wake_up_interruptible(&tty->read_wait);
54 	wake_up_interruptible(&tty->write_wait);
55 	spin_lock_irq(&tty->ctrl_lock);
56 	tty->packet = 0;
57 	spin_unlock_irq(&tty->ctrl_lock);
58 	/* Review - krefs on tty_link ?? */
59 	if (!tty->link)
60 		return;
61 	set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
62 	wake_up_interruptible(&tty->link->read_wait);
63 	wake_up_interruptible(&tty->link->write_wait);
64 	if (tty->driver->subtype == PTY_TYPE_MASTER) {
65 		set_bit(TTY_OTHER_CLOSED, &tty->flags);
66 #ifdef CONFIG_UNIX98_PTYS
67 		if (tty->driver == ptm_driver) {
68 			mutex_lock(&devpts_mutex);
69 			if (tty->link->driver_data)
70 				devpts_pty_kill(tty->link->driver_data);
71 			mutex_unlock(&devpts_mutex);
72 		}
73 #endif
74 		tty_vhangup(tty->link);
75 	}
76 }
77 
78 /*
79  * The unthrottle routine is called by the line discipline to signal
80  * that it can receive more characters.  For PTY's, the TTY_THROTTLED
81  * flag is always set, to force the line discipline to always call the
82  * unthrottle routine when there are fewer than TTY_THRESHOLD_UNTHROTTLE
83  * characters in the queue.  This is necessary since each time this
84  * happens, we need to wake up any sleeping processes that could be
85  * (1) trying to send data to the pty, or (2) waiting in wait_until_sent()
86  * for the pty buffer to be drained.
87  */
88 static void pty_unthrottle(struct tty_struct *tty)
89 {
90 	tty_wakeup(tty->link);
91 	set_bit(TTY_THROTTLED, &tty->flags);
92 }
93 
94 /**
95  *	pty_write		-	write to a pty
96  *	@tty: the tty we write from
97  *	@buf: kernel buffer of data
98  *	@count: bytes to write
99  *
100  *	Our "hardware" write method. Data is coming from the ldisc which
101  *	may be in a non sleeping state. We simply throw this at the other
102  *	end of the link as if we were an IRQ handler receiving stuff for
103  *	the other side of the pty/tty pair.
104  */
105 
106 static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c)
107 {
108 	struct tty_struct *to = tty->link;
109 
110 	if (tty->stopped)
111 		return 0;
112 
113 	if (c > 0) {
114 		/* Stuff the data into the input queue of the other end */
115 		c = tty_insert_flip_string(to->port, buf, c);
116 		/* And shovel */
117 		if (c)
118 			tty_flip_buffer_push(to->port);
119 	}
120 	return c;
121 }
122 
123 /**
124  *	pty_write_room	-	write space
125  *	@tty: tty we are writing from
126  *
127  *	Report how many bytes the ldisc can send into the queue for
128  *	the other device.
129  */
130 
131 static int pty_write_room(struct tty_struct *tty)
132 {
133 	if (tty->stopped)
134 		return 0;
135 	return tty_buffer_space_avail(tty->link->port);
136 }
137 
138 /**
139  *	pty_chars_in_buffer	-	characters currently in our tx queue
140  *	@tty: our tty
141  *
142  *	Report how much we have in the transmit queue. As everything is
143  *	instantly at the other end this is easy to implement.
144  */
145 
146 static int pty_chars_in_buffer(struct tty_struct *tty)
147 {
148 	return 0;
149 }
150 
151 /* Set the lock flag on a pty */
152 static int pty_set_lock(struct tty_struct *tty, int __user *arg)
153 {
154 	int val;
155 	if (get_user(val, arg))
156 		return -EFAULT;
157 	if (val)
158 		set_bit(TTY_PTY_LOCK, &tty->flags);
159 	else
160 		clear_bit(TTY_PTY_LOCK, &tty->flags);
161 	return 0;
162 }
163 
164 static int pty_get_lock(struct tty_struct *tty, int __user *arg)
165 {
166 	int locked = test_bit(TTY_PTY_LOCK, &tty->flags);
167 	return put_user(locked, arg);
168 }
169 
170 /* Set the packet mode on a pty */
171 static int pty_set_pktmode(struct tty_struct *tty, int __user *arg)
172 {
173 	int pktmode;
174 
175 	if (get_user(pktmode, arg))
176 		return -EFAULT;
177 
178 	spin_lock_irq(&tty->ctrl_lock);
179 	if (pktmode) {
180 		if (!tty->packet) {
181 			tty->link->ctrl_status = 0;
182 			smp_mb();
183 			tty->packet = 1;
184 		}
185 	} else
186 		tty->packet = 0;
187 	spin_unlock_irq(&tty->ctrl_lock);
188 
189 	return 0;
190 }
191 
192 /* Get the packet mode of a pty */
193 static int pty_get_pktmode(struct tty_struct *tty, int __user *arg)
194 {
195 	int pktmode = tty->packet;
196 	return put_user(pktmode, arg);
197 }
198 
199 /* Send a signal to the slave */
200 static int pty_signal(struct tty_struct *tty, int sig)
201 {
202 	struct pid *pgrp;
203 
204 	if (sig != SIGINT && sig != SIGQUIT && sig != SIGTSTP)
205 		return -EINVAL;
206 
207 	if (tty->link) {
208 		pgrp = tty_get_pgrp(tty->link);
209 		if (pgrp)
210 			kill_pgrp(pgrp, sig, 1);
211 		put_pid(pgrp);
212 	}
213 	return 0;
214 }
215 
216 static void pty_flush_buffer(struct tty_struct *tty)
217 {
218 	struct tty_struct *to = tty->link;
219 	struct tty_ldisc *ld;
220 
221 	if (!to)
222 		return;
223 
224 	ld = tty_ldisc_ref(to);
225 	tty_buffer_flush(to, ld);
226 	if (ld)
227 		tty_ldisc_deref(ld);
228 
229 	if (to->packet) {
230 		spin_lock_irq(&tty->ctrl_lock);
231 		tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
232 		wake_up_interruptible(&to->read_wait);
233 		spin_unlock_irq(&tty->ctrl_lock);
234 	}
235 }
236 
237 static int pty_open(struct tty_struct *tty, struct file *filp)
238 {
239 	if (!tty || !tty->link)
240 		return -ENODEV;
241 
242 	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
243 		goto out;
244 	if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
245 		goto out;
246 	if (tty->driver->subtype == PTY_TYPE_SLAVE && tty->link->count != 1)
247 		goto out;
248 
249 	clear_bit(TTY_IO_ERROR, &tty->flags);
250 	clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
251 	set_bit(TTY_THROTTLED, &tty->flags);
252 	return 0;
253 
254 out:
255 	set_bit(TTY_IO_ERROR, &tty->flags);
256 	return -EIO;
257 }
258 
259 static void pty_set_termios(struct tty_struct *tty,
260 					struct ktermios *old_termios)
261 {
262 	/* See if packet mode change of state. */
263 	if (tty->link && tty->link->packet) {
264 		int extproc = (old_termios->c_lflag & EXTPROC) | L_EXTPROC(tty);
265 		int old_flow = ((old_termios->c_iflag & IXON) &&
266 				(old_termios->c_cc[VSTOP] == '\023') &&
267 				(old_termios->c_cc[VSTART] == '\021'));
268 		int new_flow = (I_IXON(tty) &&
269 				STOP_CHAR(tty) == '\023' &&
270 				START_CHAR(tty) == '\021');
271 		if ((old_flow != new_flow) || extproc) {
272 			spin_lock_irq(&tty->ctrl_lock);
273 			if (old_flow != new_flow) {
274 				tty->ctrl_status &= ~(TIOCPKT_DOSTOP | TIOCPKT_NOSTOP);
275 				if (new_flow)
276 					tty->ctrl_status |= TIOCPKT_DOSTOP;
277 				else
278 					tty->ctrl_status |= TIOCPKT_NOSTOP;
279 			}
280 			if (extproc)
281 				tty->ctrl_status |= TIOCPKT_IOCTL;
282 			spin_unlock_irq(&tty->ctrl_lock);
283 			wake_up_interruptible(&tty->link->read_wait);
284 		}
285 	}
286 
287 	tty->termios.c_cflag &= ~(CSIZE | PARENB);
288 	tty->termios.c_cflag |= (CS8 | CREAD);
289 }
290 
291 /**
292  *	pty_do_resize		-	resize event
293  *	@tty: tty being resized
294  *	@ws: window size being set.
295  *
296  *	Update the termios variables and send the necessary signals to
297  *	peform a terminal resize correctly
298  */
299 
300 static int pty_resize(struct tty_struct *tty,  struct winsize *ws)
301 {
302 	struct pid *pgrp, *rpgrp;
303 	struct tty_struct *pty = tty->link;
304 
305 	/* For a PTY we need to lock the tty side */
306 	mutex_lock(&tty->winsize_mutex);
307 	if (!memcmp(ws, &tty->winsize, sizeof(*ws)))
308 		goto done;
309 
310 	/* Signal the foreground process group of both ptys */
311 	pgrp = tty_get_pgrp(tty);
312 	rpgrp = tty_get_pgrp(pty);
313 
314 	if (pgrp)
315 		kill_pgrp(pgrp, SIGWINCH, 1);
316 	if (rpgrp != pgrp && rpgrp)
317 		kill_pgrp(rpgrp, SIGWINCH, 1);
318 
319 	put_pid(pgrp);
320 	put_pid(rpgrp);
321 
322 	tty->winsize = *ws;
323 	pty->winsize = *ws;	/* Never used so will go away soon */
324 done:
325 	mutex_unlock(&tty->winsize_mutex);
326 	return 0;
327 }
328 
329 /**
330  *	pty_start - start() handler
331  *	pty_stop  - stop() handler
332  *	@tty: tty being flow-controlled
333  *
334  *	Propagates the TIOCPKT status to the master pty.
335  *
336  *	NB: only the master pty can be in packet mode so only the slave
337  *	    needs start()/stop() handlers
338  */
339 static void pty_start(struct tty_struct *tty)
340 {
341 	unsigned long flags;
342 
343 	if (tty->link && tty->link->packet) {
344 		spin_lock_irqsave(&tty->ctrl_lock, flags);
345 		tty->ctrl_status &= ~TIOCPKT_STOP;
346 		tty->ctrl_status |= TIOCPKT_START;
347 		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
348 		wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);
349 	}
350 }
351 
352 static void pty_stop(struct tty_struct *tty)
353 {
354 	unsigned long flags;
355 
356 	if (tty->link && tty->link->packet) {
357 		spin_lock_irqsave(&tty->ctrl_lock, flags);
358 		tty->ctrl_status &= ~TIOCPKT_START;
359 		tty->ctrl_status |= TIOCPKT_STOP;
360 		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
361 		wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);
362 	}
363 }
364 
365 /**
366  *	pty_common_install		-	set up the pty pair
367  *	@driver: the pty driver
368  *	@tty: the tty being instantiated
369  *	@legacy: true if this is BSD style
370  *
371  *	Perform the initial set up for the tty/pty pair. Called from the
372  *	tty layer when the port is first opened.
373  *
374  *	Locking: the caller must hold the tty_mutex
375  */
376 static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
377 		bool legacy)
378 {
379 	struct tty_struct *o_tty;
380 	struct tty_port *ports[2];
381 	int idx = tty->index;
382 	int retval = -ENOMEM;
383 
384 	/* Opening the slave first has always returned -EIO */
385 	if (driver->subtype != PTY_TYPE_MASTER)
386 		return -EIO;
387 
388 	ports[0] = kmalloc(sizeof **ports, GFP_KERNEL);
389 	ports[1] = kmalloc(sizeof **ports, GFP_KERNEL);
390 	if (!ports[0] || !ports[1])
391 		goto err;
392 	if (!try_module_get(driver->other->owner)) {
393 		/* This cannot in fact currently happen */
394 		goto err;
395 	}
396 	o_tty = alloc_tty_struct(driver->other, idx);
397 	if (!o_tty)
398 		goto err_put_module;
399 
400 	tty_set_lock_subclass(o_tty);
401 	lockdep_set_subclass(&o_tty->termios_rwsem, TTY_LOCK_SLAVE);
402 
403 	if (legacy) {
404 		/* We always use new tty termios data so we can do this
405 		   the easy way .. */
406 		tty_init_termios(tty);
407 		tty_init_termios(o_tty);
408 
409 		driver->other->ttys[idx] = o_tty;
410 		driver->ttys[idx] = tty;
411 	} else {
412 		memset(&tty->termios_locked, 0, sizeof(tty->termios_locked));
413 		tty->termios = driver->init_termios;
414 		memset(&o_tty->termios_locked, 0, sizeof(tty->termios_locked));
415 		o_tty->termios = driver->other->init_termios;
416 	}
417 
418 	/*
419 	 * Everything allocated ... set up the o_tty structure.
420 	 */
421 	tty_driver_kref_get(driver->other);
422 	/* Establish the links in both directions */
423 	tty->link   = o_tty;
424 	o_tty->link = tty;
425 	tty_port_init(ports[0]);
426 	tty_port_init(ports[1]);
427 	tty_buffer_set_limit(ports[0], 8192);
428 	tty_buffer_set_limit(ports[1], 8192);
429 	o_tty->port = ports[0];
430 	tty->port = ports[1];
431 	o_tty->port->itty = o_tty;
432 
433 	tty_buffer_set_lock_subclass(o_tty->port);
434 
435 	tty_driver_kref_get(driver);
436 	tty->count++;
437 	o_tty->count++;
438 	return 0;
439 
440 err_put_module:
441 	module_put(driver->other->owner);
442 err:
443 	kfree(ports[0]);
444 	kfree(ports[1]);
445 	return retval;
446 }
447 
448 static void pty_cleanup(struct tty_struct *tty)
449 {
450 	tty_port_put(tty->port);
451 }
452 
453 /* Traditional BSD devices */
454 #ifdef CONFIG_LEGACY_PTYS
455 
456 static int pty_install(struct tty_driver *driver, struct tty_struct *tty)
457 {
458 	return pty_common_install(driver, tty, true);
459 }
460 
461 static void pty_remove(struct tty_driver *driver, struct tty_struct *tty)
462 {
463 	struct tty_struct *pair = tty->link;
464 	driver->ttys[tty->index] = NULL;
465 	if (pair)
466 		pair->driver->ttys[pair->index] = NULL;
467 }
468 
469 static int pty_bsd_ioctl(struct tty_struct *tty,
470 			 unsigned int cmd, unsigned long arg)
471 {
472 	switch (cmd) {
473 	case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
474 		return pty_set_lock(tty, (int __user *) arg);
475 	case TIOCGPTLCK: /* Get PT Lock status */
476 		return pty_get_lock(tty, (int __user *)arg);
477 	case TIOCPKT: /* Set PT packet mode */
478 		return pty_set_pktmode(tty, (int __user *)arg);
479 	case TIOCGPKT: /* Get PT packet mode */
480 		return pty_get_pktmode(tty, (int __user *)arg);
481 	case TIOCSIG:    /* Send signal to other side of pty */
482 		return pty_signal(tty, (int) arg);
483 	case TIOCGPTN: /* TTY returns ENOTTY, but glibc expects EINVAL here */
484 		return -EINVAL;
485 	}
486 	return -ENOIOCTLCMD;
487 }
488 
489 static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
490 /*
491  * not really modular, but the easiest way to keep compat with existing
492  * bootargs behaviour is to continue using module_param here.
493  */
494 module_param(legacy_count, int, 0);
495 
496 /*
497  * The master side of a pty can do TIOCSPTLCK and thus
498  * has pty_bsd_ioctl.
499  */
500 static const struct tty_operations master_pty_ops_bsd = {
501 	.install = pty_install,
502 	.open = pty_open,
503 	.close = pty_close,
504 	.write = pty_write,
505 	.write_room = pty_write_room,
506 	.flush_buffer = pty_flush_buffer,
507 	.chars_in_buffer = pty_chars_in_buffer,
508 	.unthrottle = pty_unthrottle,
509 	.ioctl = pty_bsd_ioctl,
510 	.cleanup = pty_cleanup,
511 	.resize = pty_resize,
512 	.remove = pty_remove
513 };
514 
515 static const struct tty_operations slave_pty_ops_bsd = {
516 	.install = pty_install,
517 	.open = pty_open,
518 	.close = pty_close,
519 	.write = pty_write,
520 	.write_room = pty_write_room,
521 	.flush_buffer = pty_flush_buffer,
522 	.chars_in_buffer = pty_chars_in_buffer,
523 	.unthrottle = pty_unthrottle,
524 	.set_termios = pty_set_termios,
525 	.cleanup = pty_cleanup,
526 	.resize = pty_resize,
527 	.start = pty_start,
528 	.stop = pty_stop,
529 	.remove = pty_remove
530 };
531 
532 static void __init legacy_pty_init(void)
533 {
534 	struct tty_driver *pty_driver, *pty_slave_driver;
535 
536 	if (legacy_count <= 0)
537 		return;
538 
539 	pty_driver = tty_alloc_driver(legacy_count,
540 			TTY_DRIVER_RESET_TERMIOS |
541 			TTY_DRIVER_REAL_RAW |
542 			TTY_DRIVER_DYNAMIC_ALLOC);
543 	if (IS_ERR(pty_driver))
544 		panic("Couldn't allocate pty driver");
545 
546 	pty_slave_driver = tty_alloc_driver(legacy_count,
547 			TTY_DRIVER_RESET_TERMIOS |
548 			TTY_DRIVER_REAL_RAW |
549 			TTY_DRIVER_DYNAMIC_ALLOC);
550 	if (IS_ERR(pty_slave_driver))
551 		panic("Couldn't allocate pty slave driver");
552 
553 	pty_driver->driver_name = "pty_master";
554 	pty_driver->name = "pty";
555 	pty_driver->major = PTY_MASTER_MAJOR;
556 	pty_driver->minor_start = 0;
557 	pty_driver->type = TTY_DRIVER_TYPE_PTY;
558 	pty_driver->subtype = PTY_TYPE_MASTER;
559 	pty_driver->init_termios = tty_std_termios;
560 	pty_driver->init_termios.c_iflag = 0;
561 	pty_driver->init_termios.c_oflag = 0;
562 	pty_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
563 	pty_driver->init_termios.c_lflag = 0;
564 	pty_driver->init_termios.c_ispeed = 38400;
565 	pty_driver->init_termios.c_ospeed = 38400;
566 	pty_driver->other = pty_slave_driver;
567 	tty_set_operations(pty_driver, &master_pty_ops_bsd);
568 
569 	pty_slave_driver->driver_name = "pty_slave";
570 	pty_slave_driver->name = "ttyp";
571 	pty_slave_driver->major = PTY_SLAVE_MAJOR;
572 	pty_slave_driver->minor_start = 0;
573 	pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
574 	pty_slave_driver->subtype = PTY_TYPE_SLAVE;
575 	pty_slave_driver->init_termios = tty_std_termios;
576 	pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
577 	pty_slave_driver->init_termios.c_ispeed = 38400;
578 	pty_slave_driver->init_termios.c_ospeed = 38400;
579 	pty_slave_driver->other = pty_driver;
580 	tty_set_operations(pty_slave_driver, &slave_pty_ops_bsd);
581 
582 	if (tty_register_driver(pty_driver))
583 		panic("Couldn't register pty driver");
584 	if (tty_register_driver(pty_slave_driver))
585 		panic("Couldn't register pty slave driver");
586 }
587 #else
588 static inline void legacy_pty_init(void) { }
589 #endif
590 
591 /* Unix98 devices */
592 #ifdef CONFIG_UNIX98_PTYS
593 
594 static struct cdev ptmx_cdev;
595 
596 static int pty_unix98_ioctl(struct tty_struct *tty,
597 			    unsigned int cmd, unsigned long arg)
598 {
599 	switch (cmd) {
600 	case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
601 		return pty_set_lock(tty, (int __user *)arg);
602 	case TIOCGPTLCK: /* Get PT Lock status */
603 		return pty_get_lock(tty, (int __user *)arg);
604 	case TIOCPKT: /* Set PT packet mode */
605 		return pty_set_pktmode(tty, (int __user *)arg);
606 	case TIOCGPKT: /* Get PT packet mode */
607 		return pty_get_pktmode(tty, (int __user *)arg);
608 	case TIOCGPTN: /* Get PT Number */
609 		return put_user(tty->index, (unsigned int __user *)arg);
610 	case TIOCSIG:    /* Send signal to other side of pty */
611 		return pty_signal(tty, (int) arg);
612 	}
613 
614 	return -ENOIOCTLCMD;
615 }
616 
617 /**
618  *	ptm_unix98_lookup	-	find a pty master
619  *	@driver: ptm driver
620  *	@idx: tty index
621  *
622  *	Look up a pty master device. Called under the tty_mutex for now.
623  *	This provides our locking.
624  */
625 
626 static struct tty_struct *ptm_unix98_lookup(struct tty_driver *driver,
627 		struct file *file, int idx)
628 {
629 	/* Master must be open via /dev/ptmx */
630 	return ERR_PTR(-EIO);
631 }
632 
633 /**
634  *	pts_unix98_lookup	-	find a pty slave
635  *	@driver: pts driver
636  *	@idx: tty index
637  *
638  *	Look up a pty master device. Called under the tty_mutex for now.
639  *	This provides our locking for the tty pointer.
640  */
641 
642 static struct tty_struct *pts_unix98_lookup(struct tty_driver *driver,
643 		struct file *file, int idx)
644 {
645 	struct tty_struct *tty;
646 
647 	mutex_lock(&devpts_mutex);
648 	tty = devpts_get_priv(file->f_path.dentry);
649 	mutex_unlock(&devpts_mutex);
650 	/* Master must be open before slave */
651 	if (!tty)
652 		return ERR_PTR(-EIO);
653 	return tty;
654 }
655 
656 static int pty_unix98_install(struct tty_driver *driver, struct tty_struct *tty)
657 {
658 	return pty_common_install(driver, tty, false);
659 }
660 
661 /* this is called once with whichever end is closed last */
662 static void pty_unix98_remove(struct tty_driver *driver, struct tty_struct *tty)
663 {
664 	struct pts_fs_info *fsi;
665 
666 	if (tty->driver->subtype == PTY_TYPE_MASTER)
667 		fsi = tty->driver_data;
668 	else
669 		fsi = tty->link->driver_data;
670 
671 	if (fsi) {
672 		devpts_kill_index(fsi, tty->index);
673 		devpts_release(fsi);
674 	}
675 }
676 
677 static const struct tty_operations ptm_unix98_ops = {
678 	.lookup = ptm_unix98_lookup,
679 	.install = pty_unix98_install,
680 	.remove = pty_unix98_remove,
681 	.open = pty_open,
682 	.close = pty_close,
683 	.write = pty_write,
684 	.write_room = pty_write_room,
685 	.flush_buffer = pty_flush_buffer,
686 	.chars_in_buffer = pty_chars_in_buffer,
687 	.unthrottle = pty_unthrottle,
688 	.ioctl = pty_unix98_ioctl,
689 	.resize = pty_resize,
690 	.cleanup = pty_cleanup
691 };
692 
693 static const struct tty_operations pty_unix98_ops = {
694 	.lookup = pts_unix98_lookup,
695 	.install = pty_unix98_install,
696 	.remove = pty_unix98_remove,
697 	.open = pty_open,
698 	.close = pty_close,
699 	.write = pty_write,
700 	.write_room = pty_write_room,
701 	.flush_buffer = pty_flush_buffer,
702 	.chars_in_buffer = pty_chars_in_buffer,
703 	.unthrottle = pty_unthrottle,
704 	.set_termios = pty_set_termios,
705 	.start = pty_start,
706 	.stop = pty_stop,
707 	.cleanup = pty_cleanup,
708 };
709 
710 /**
711  *	ptmx_open		-	open a unix 98 pty master
712  *	@inode: inode of device file
713  *	@filp: file pointer to tty
714  *
715  *	Allocate a unix98 pty master device from the ptmx driver.
716  *
717  *	Locking: tty_mutex protects the init_dev work. tty->count should
718  *		protect the rest.
719  *		allocated_ptys_lock handles the list of free pty numbers
720  */
721 
722 static int ptmx_open(struct inode *inode, struct file *filp)
723 {
724 	struct pts_fs_info *fsi;
725 	struct tty_struct *tty;
726 	struct dentry *dentry;
727 	int retval;
728 	int index;
729 
730 	nonseekable_open(inode, filp);
731 
732 	/* We refuse fsnotify events on ptmx, since it's a shared resource */
733 	filp->f_mode |= FMODE_NONOTIFY;
734 
735 	retval = tty_alloc_file(filp);
736 	if (retval)
737 		return retval;
738 
739 	fsi = devpts_acquire(filp);
740 	if (IS_ERR(fsi)) {
741 		retval = PTR_ERR(fsi);
742 		goto out_free_file;
743 	}
744 
745 	/* find a device that is not in use. */
746 	mutex_lock(&devpts_mutex);
747 	index = devpts_new_index(fsi);
748 	mutex_unlock(&devpts_mutex);
749 
750 	retval = index;
751 	if (index < 0)
752 		goto out_put_fsi;
753 
754 
755 	mutex_lock(&tty_mutex);
756 	tty = tty_init_dev(ptm_driver, index);
757 	/* The tty returned here is locked so we can safely
758 	   drop the mutex */
759 	mutex_unlock(&tty_mutex);
760 
761 	retval = PTR_ERR(tty);
762 	if (IS_ERR(tty))
763 		goto out;
764 
765 	/*
766 	 * From here on out, the tty is "live", and the index and
767 	 * fsi will be killed/put by the tty_release()
768 	 */
769 	set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
770 	tty->driver_data = fsi;
771 
772 	tty_add_file(tty, filp);
773 
774 	dentry = devpts_pty_new(fsi, index, tty->link);
775 	if (IS_ERR(dentry)) {
776 		retval = PTR_ERR(dentry);
777 		goto err_release;
778 	}
779 	tty->link->driver_data = dentry;
780 
781 	retval = ptm_driver->ops->open(tty, filp);
782 	if (retval)
783 		goto err_release;
784 
785 	tty_debug_hangup(tty, "opening (count=%d)\n", tty->count);
786 
787 	tty_unlock(tty);
788 	return 0;
789 err_release:
790 	tty_unlock(tty);
791 	// This will also put-ref the fsi
792 	tty_release(inode, filp);
793 	return retval;
794 out:
795 	devpts_kill_index(fsi, index);
796 out_put_fsi:
797 	devpts_release(fsi);
798 out_free_file:
799 	tty_free_file(filp);
800 	return retval;
801 }
802 
803 static struct file_operations ptmx_fops __ro_after_init;
804 
805 static void __init unix98_pty_init(void)
806 {
807 	ptm_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
808 			TTY_DRIVER_RESET_TERMIOS |
809 			TTY_DRIVER_REAL_RAW |
810 			TTY_DRIVER_DYNAMIC_DEV |
811 			TTY_DRIVER_DEVPTS_MEM |
812 			TTY_DRIVER_DYNAMIC_ALLOC);
813 	if (IS_ERR(ptm_driver))
814 		panic("Couldn't allocate Unix98 ptm driver");
815 	pts_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
816 			TTY_DRIVER_RESET_TERMIOS |
817 			TTY_DRIVER_REAL_RAW |
818 			TTY_DRIVER_DYNAMIC_DEV |
819 			TTY_DRIVER_DEVPTS_MEM |
820 			TTY_DRIVER_DYNAMIC_ALLOC);
821 	if (IS_ERR(pts_driver))
822 		panic("Couldn't allocate Unix98 pts driver");
823 
824 	ptm_driver->driver_name = "pty_master";
825 	ptm_driver->name = "ptm";
826 	ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
827 	ptm_driver->minor_start = 0;
828 	ptm_driver->type = TTY_DRIVER_TYPE_PTY;
829 	ptm_driver->subtype = PTY_TYPE_MASTER;
830 	ptm_driver->init_termios = tty_std_termios;
831 	ptm_driver->init_termios.c_iflag = 0;
832 	ptm_driver->init_termios.c_oflag = 0;
833 	ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
834 	ptm_driver->init_termios.c_lflag = 0;
835 	ptm_driver->init_termios.c_ispeed = 38400;
836 	ptm_driver->init_termios.c_ospeed = 38400;
837 	ptm_driver->other = pts_driver;
838 	tty_set_operations(ptm_driver, &ptm_unix98_ops);
839 
840 	pts_driver->driver_name = "pty_slave";
841 	pts_driver->name = "pts";
842 	pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
843 	pts_driver->minor_start = 0;
844 	pts_driver->type = TTY_DRIVER_TYPE_PTY;
845 	pts_driver->subtype = PTY_TYPE_SLAVE;
846 	pts_driver->init_termios = tty_std_termios;
847 	pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
848 	pts_driver->init_termios.c_ispeed = 38400;
849 	pts_driver->init_termios.c_ospeed = 38400;
850 	pts_driver->other = ptm_driver;
851 	tty_set_operations(pts_driver, &pty_unix98_ops);
852 
853 	if (tty_register_driver(ptm_driver))
854 		panic("Couldn't register Unix98 ptm driver");
855 	if (tty_register_driver(pts_driver))
856 		panic("Couldn't register Unix98 pts driver");
857 
858 	/* Now create the /dev/ptmx special device */
859 	tty_default_fops(&ptmx_fops);
860 	ptmx_fops.open = ptmx_open;
861 
862 	cdev_init(&ptmx_cdev, &ptmx_fops);
863 	if (cdev_add(&ptmx_cdev, MKDEV(TTYAUX_MAJOR, 2), 1) ||
864 	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 2), 1, "/dev/ptmx") < 0)
865 		panic("Couldn't register /dev/ptmx driver");
866 	device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 2), NULL, "ptmx");
867 }
868 
869 #else
870 static inline void unix98_pty_init(void) { }
871 #endif
872 
873 static int __init pty_init(void)
874 {
875 	legacy_pty_init();
876 	unix98_pty_init();
877 	return 0;
878 }
879 device_initcall(pty_init);
880