summaryrefslogtreecommitdiff
path: root/drivers/tty/pty.c
blob: 6c7151edd7155d2fda27046467d646e714af00e7 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
// SPDX-License-Identifier: GPL-2.0
/*
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  Added support for a Unix98-style ptmx device.
 *    -- C. Scott Ananian <cananian@alumni.princeton.edu>, 14-Jan-1998
 *
 */

#include <linux/module.h>
#include <linux/errno.h>
#include <linux/interrupt.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <linux/fcntl.h>
#include <linux/sched/signal.h>
#include <linux/string.h>
#include <linux/major.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/uaccess.h>
#include <linux/bitops.h>
#include <linux/devpts_fs.h>
#include <linux/slab.h>
#include <linux/mutex.h>
#include <linux/poll.h>
#include <linux/mount.h>
#include <linux/file.h>
#include <linux/ioctl.h>

#undef TTY_DEBUG_HANGUP
#ifdef TTY_DEBUG_HANGUP
# define tty_debug_hangup(tty, f, args...)	tty_debug(tty, f, ##args)
#else
# define tty_debug_hangup(tty, f, args...)	do {} while (0)
#endif

#ifdef CONFIG_UNIX98_PTYS
static struct tty_driver *ptm_driver;
static struct tty_driver *pts_driver;
static DEFINE_MUTEX(devpts_mutex);
#endif

static void pty_close(struct tty_struct *tty, struct file *filp)
{
	BUG_ON(!tty);
	if (tty->driver->subtype == PTY_TYPE_MASTER)
		WARN_ON(tty->count > 1);
	else {
		if (tty_io_error(tty))
			return;
		if (tty->count > 2)
			return;
	}
	set_bit(TTY_IO_ERROR, &tty->flags);
	wake_up_interruptible(&tty->read_wait);
	wake_up_interruptible(&tty->write_wait);
	spin_lock_irq(&tty->ctrl_lock);
	tty->packet = 0;
	spin_unlock_irq(&tty->ctrl_lock);
	/* Review - krefs on tty_link ?? */
	if (!tty->link)
		return;
	set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
	wake_up_interruptible(&tty->link->read_wait);
	wake_up_interruptible(&tty->link->write_wait);
	if (tty->driver->subtype == PTY_TYPE_MASTER) {
		set_bit(TTY_OTHER_CLOSED, &tty->flags);
#ifdef CONFIG_UNIX98_PTYS
		if (tty->driver == ptm_driver) {
			mutex_lock(&devpts_mutex);
			if (tty->link->driver_data)
				devpts_pty_kill(tty->link->driver_data);
			mutex_unlock(&devpts_mutex);
		}
#endif
		tty_vhangup(tty->link);
	}
}

/*
 * The unthrottle routine is called by the line discipline to signal
 * that it can receive more characters.  For PTY's, the TTY_THROTTLED
 * flag is always set, to force the line discipline to always call the
 * unthrottle routine when there are fewer than TTY_THRESHOLD_UNTHROTTLE
 * characters in the queue.  This is necessary since each time this
 * happens, we need to wake up any sleeping processes that could be
 * (1) trying to send data to the pty, or (2) waiting in wait_until_sent()
 * for the pty buffer to be drained.
 */
static void pty_unthrottle(struct tty_struct *tty)
{
	tty_wakeup(tty->link);
	set_bit(TTY_THROTTLED, &tty->flags);
}

/**
 *	pty_write		-	write to a pty
 *	@tty: the tty we write from
 *	@buf: kernel buffer of data
 *	@count: bytes to write
 *
 *	Our "hardware" write method. Data is coming from the ldisc which
 *	may be in a non sleeping state. We simply throw this at the other
 *	end of the link as if we were an IRQ handler receiving stuff for
 *	the other side of the pty/tty pair.
 */

static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c)
{
	struct tty_struct *to = tty->link;

	if (tty->stopped)
		return 0;

	if (c > 0) {
		/* Stuff the data into the input queue of the other end */
		c = tty_insert_flip_string(to->port, buf, c);
		/* And shovel */
		if (c)
			tty_flip_buffer_push(to->port);
	}
	return c;
}

/**
 *	pty_write_room	-	write space
 *	@tty: tty we are writing from
 *
 *	Report how many bytes the ldisc can send into the queue for
 *	the other device.
 */

static int pty_write_room(struct tty_struct *tty)
{
	if (tty->stopped)
		return 0;
	return tty_buffer_space_avail(tty->link->port);
}

/**
 *	pty_chars_in_buffer	-	characters currently in our tx queue
 *	@tty: our tty
 *
 *	Report how much we have in the transmit queue. As everything is
 *	instantly at the other end this is easy to implement.
 */

static int pty_chars_in_buffer(struct tty_struct *tty)
{
	return 0;
}

/* Set the lock flag on a pty */
static int pty_set_lock(struct tty_struct *tty, int __user *arg)
{
	int val;
	if (get_user(val, arg))
		return -EFAULT;
	if (val)
		set_bit(TTY_PTY_LOCK, &tty->flags);
	else
		clear_bit(TTY_PTY_LOCK, &tty->flags);
	return 0;
}

static int pty_get_lock(struct tty_struct *tty, int __user *arg)
{
	int locked = test_bit(TTY_PTY_LOCK, &tty->flags);
	return put_user(locked, arg);
}

/* Set the packet mode on a pty */
static int pty_set_pktmode(struct tty_struct *tty, int __user *arg)
{
	int pktmode;

	if (get_user(pktmode, arg))
		return -EFAULT;

	spin_lock_irq(&tty->ctrl_lock);
	if (pktmode) {
		if (!tty->packet) {
			tty->link->ctrl_status = 0;
			smp_mb();
			tty->packet = 1;
		}
	} else
		tty->packet = 0;
	spin_unlock_irq(&tty->ctrl_lock);

	return 0;
}

/* Get the packet mode of a pty */
static int pty_get_pktmode(struct tty_struct *tty, int __user *arg)
{
	int pktmode = tty->packet;
	return put_user(pktmode, arg);
}

/* Send a signal to the slave */
static int pty_signal(struct tty_struct *tty, int sig)
{
	struct pid *pgrp;

	if (sig != SIGINT && sig != SIGQUIT && sig != SIGTSTP)
		return -EINVAL;

	if (tty->link) {
		pgrp = tty_get_pgrp(tty->link);
		if (pgrp)
			kill_pgrp(pgrp, sig, 1);
		put_pid(pgrp);
	}
	return 0;
}

static void pty_flush_buffer(struct tty_struct *tty)
{
	struct tty_struct *to = tty->link;

	if (!to)
		return;

	tty_buffer_flush(to, NULL);
	if (to->packet) {
		spin_lock_irq(&tty->ctrl_lock);
		tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
		wake_up_interruptible(&to->read_wait);
		spin_unlock_irq(&tty->ctrl_lock);
	}
}

static int pty_open(struct tty_struct *tty, struct file *filp)
{
	if (!tty || !tty->link)
		return -ENODEV;

	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
		goto out;
	if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
		goto out;
	if (tty->driver->subtype == PTY_TYPE_SLAVE && tty->link->count != 1)
		goto out;

	clear_bit(TTY_IO_ERROR, &tty->flags);
	clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
	set_bit(TTY_THROTTLED, &tty->flags);
	return 0;

out:
	set_bit(TTY_IO_ERROR, &tty->flags);
	return -EIO;
}

static void pty_set_termios(struct tty_struct *tty,
					struct ktermios *old_termios)
{
	/* See if packet mode change of state. */
	if (tty->link && tty->link->packet) {
		int extproc = (old_termios->c_lflag & EXTPROC) | L_EXTPROC(tty);
		int old_flow = ((old_termios->c_iflag & IXON) &&
				(old_termios->c_cc[VSTOP] == '\023') &&
				(old_termios->c_cc[VSTART] == '\021'));
		int new_flow = (I_IXON(tty) &&
				STOP_CHAR(tty) == '\023' &&
				START_CHAR(tty) == '\021');
		if ((old_flow != new_flow) || extproc) {
			spin_lock_irq(&tty->ctrl_lock);
			if (old_flow != new_flow) {
				tty->ctrl_status &= ~(TIOCPKT_DOSTOP | TIOCPKT_NOSTOP);
				if (new_flow)
					tty->ctrl_status |= TIOCPKT_DOSTOP;
				else
					tty->ctrl_status |= TIOCPKT_NOSTOP;
			}
			if (extproc)
				tty->ctrl_status |= TIOCPKT_IOCTL;
			spin_unlock_irq(&tty->ctrl_lock);
			wake_up_interruptible(&tty->link->read_wait);
		}
	}

	tty->termios.c_cflag &= ~(CSIZE | PARENB);
	tty->termios.c_cflag |= (CS8 | CREAD);
}

/**
 *	pty_do_resize		-	resize event
 *	@tty: tty being resized
 *	@ws: window size being set.
 *
 *	Update the termios variables and send the necessary signals to
 *	peform a terminal resize correctly
 */

static int pty_resize(struct tty_struct *tty,  struct winsize *ws)
{
	struct pid *pgrp, *rpgrp;
	struct tty_struct *pty = tty->link;

	/* For a PTY we need to lock the tty side */
	mutex_lock(&tty->winsize_mutex);
	if (!memcmp(ws, &tty->winsize, sizeof(*ws)))
		goto done;

	/* Signal the foreground process group of both ptys */
	pgrp = tty_get_pgrp(tty);
	rpgrp = tty_get_pgrp(pty);

	if (pgrp)
		kill_pgrp(pgrp, SIGWINCH, 1);
	if (rpgrp != pgrp && rpgrp)
		kill_pgrp(rpgrp, SIGWINCH, 1);

	put_pid(pgrp);
	put_pid(rpgrp);

	tty->winsize = *ws;
	pty->winsize = *ws;	/* Never used so will go away soon */
done:
	mutex_unlock(&tty->winsize_mutex);
	return 0;
}

/**
 *	pty_start - start() handler
 *	pty_stop  - stop() handler
 *	@tty: tty being flow-controlled
 *
 *	Propagates the TIOCPKT status to the master pty.
 *
 *	NB: only the master pty can be in packet mode so only the slave
 *	    needs start()/stop() handlers
 */
static void pty_start(struct tty_struct *tty)
{
	unsigned long flags;

	if (tty->link && tty->link->packet) {
		spin_lock_irqsave(&tty->ctrl_lock, flags);
		tty->ctrl_status &= ~TIOCPKT_STOP;
		tty->ctrl_status |= TIOCPKT_START;
		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
		wake_up_interruptible_poll(&tty->link->read_wait, EPOLLIN);
	}
}

static void pty_stop(struct tty_struct *tty)
{
	unsigned long flags;

	if (tty->link && tty->link->packet) {
		spin_lock_irqsave(&tty->ctrl_lock, flags);
		tty->ctrl_status &= ~TIOCPKT_START;
		tty->ctrl_status |= TIOCPKT_STOP;
		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
		wake_up_interruptible_poll(&tty->link->read_wait, EPOLLIN);
	}
}

/**
 *	pty_common_install		-	set up the pty pair
 *	@driver: the pty driver
 *	@tty: the tty being instantiated
 *	@legacy: true if this is BSD style
 *
 *	Perform the initial set up for the tty/pty pair. Called from the
 *	tty layer when the port is first opened.
 *
 *	Locking: the caller must hold the tty_mutex
 */
static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
		bool legacy)
{
	struct tty_struct *o_tty;
	struct tty_port *ports[2];
	int idx = tty->index;
	int retval = -ENOMEM;

	/* Opening the slave first has always returned -EIO */
	if (driver->subtype != PTY_TYPE_MASTER)
		return -EIO;

	ports[0] = kmalloc(sizeof **ports, GFP_KERNEL);
	ports[1] = kmalloc(sizeof **ports, GFP_KERNEL);
	if (!ports[0] || !ports[1])
		goto err;
	if (!try_module_get(driver->other->owner)) {
		/* This cannot in fact currently happen */
		goto err;
	}
	o_tty = alloc_tty_struct(driver->other, idx);
	if (!o_tty)
		goto err_put_module;

	tty_set_lock_subclass(o_tty);
	lockdep_set_subclass(&o_tty->termios_rwsem, TTY_LOCK_SLAVE);

	if (legacy) {
		/* We always use new tty termios data so we can do this
		   the easy way .. */
		tty_init_termios(tty);
		tty_init_termios(o_tty);

		driver->other->ttys[idx] = o_tty;
		driver->ttys[idx] = tty;
	} else {
		memset(&tty->termios_locked, 0, sizeof(tty->termios_locked));
		tty->termios = driver->init_termios;
		memset(&o_tty->termios_locked, 0, sizeof(tty->termios_locked));
		o_tty->termios = driver->other->init_termios;
	}

	/*
	 * Everything allocated ... set up the o_tty structure.
	 */
	tty_driver_kref_get(driver->other);
	/* Establish the links in both directions */
	tty->link   = o_tty;
	o_tty->link = tty;
	tty_port_init(ports[0]);
	tty_port_init(ports[1]);
	tty_buffer_set_limit(ports[0], 8192);
	tty_buffer_set_limit(ports[1], 8192);
	o_tty->port = ports[0];
	tty->port = ports[1];
	o_tty->port->itty = o_tty;

	tty_buffer_set_lock_subclass(o_tty->port);

	tty_driver_kref_get(driver);
	tty->count++;
	o_tty->count++;
	return 0;

err_put_module:
	module_put(driver->other->owner);
err:
	kfree(ports[0]);
	kfree(ports[1]);
	return retval;
}

static void pty_cleanup(struct tty_struct *tty)
{
	tty_port_put(tty->port);
}

/* Traditional BSD devices */
#ifdef CONFIG_LEGACY_PTYS

static int pty_install(struct tty_driver *driver, struct tty_struct *tty)
{
	return pty_common_install(driver, tty, true);
}

static void pty_remove(struct tty_driver *driver, struct tty_struct *tty)
{
	struct tty_struct *pair = tty->link;
	driver->ttys[tty->index] = NULL;
	if (pair)
		pair->driver->ttys[pair->index] = NULL;
}

static int pty_bsd_ioctl(struct tty_struct *tty,
			 unsigned int cmd, unsigned long arg)
{
	switch (cmd) {
	case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
		return pty_set_lock(tty, (int __user *) arg);
	case TIOCGPTLCK: /* Get PT Lock status */
		return pty_get_lock(tty, (int __user *)arg);
	case TIOCPKT: /* Set PT packet mode */
		return pty_set_pktmode(tty, (int __user *)arg);
	case TIOCGPKT: /* Get PT packet mode */
		return pty_get_pktmode(tty, (int __user *)arg);
	case TIOCSIG:    /* Send signal to other side of pty */
		return pty_signal(tty, (int) arg);
	case TIOCGPTN: /* TTY returns ENOTTY, but glibc expects EINVAL here */
		return -EINVAL;
	}
	return -ENOIOCTLCMD;
}

static long pty_bsd_compat_ioctl(struct tty_struct *tty,
				 unsigned int cmd, unsigned long arg)
{
	/*
	 * PTY ioctls don't require any special translation between 32-bit and
	 * 64-bit userspace, they are already compatible.
	 */
	return pty_bsd_ioctl(tty, cmd, arg);
}

static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
/*
 * not really modular, but the easiest way to keep compat with existing
 * bootargs behaviour is to continue using module_param here.
 */
module_param(legacy_count, int, 0);

/*
 * The master side of a pty can do TIOCSPTLCK and thus
 * has pty_bsd_ioctl.
 */
static const struct tty_operations master_pty_ops_bsd = {
	.install = pty_install,
	.open = pty_open,
	.close = pty_close,
	.write = pty_write,
	.write_room = pty_write_room,
	.flush_buffer = pty_flush_buffer,
	.chars_in_buffer = pty_chars_in_buffer,
	.unthrottle = pty_unthrottle,
	.ioctl = pty_bsd_ioctl,
	.compat_ioctl = pty_bsd_compat_ioctl,
	.cleanup = pty_cleanup,
	.resize = pty_resize,
	.remove = pty_remove
};

static const struct tty_operations slave_pty_ops_bsd = {
	.install = pty_install,
	.open = pty_open,
	.close = pty_close,
	.write = pty_write,
	.write_room = pty_write_room,
	.flush_buffer = pty_flush_buffer,
	.chars_in_buffer = pty_chars_in_buffer,
	.unthrottle = pty_unthrottle,
	.set_termios = pty_set_termios,
	.cleanup = pty_cleanup,
	.resize = pty_resize,
	.start = pty_start,
	.stop = pty_stop,
	.remove = pty_remove
};

static void __init legacy_pty_init(void)
{
	struct tty_driver *pty_driver, *pty_slave_driver;

	if (legacy_count <= 0)
		return;

	pty_driver = tty_alloc_driver(legacy_count,
			TTY_DRIVER_RESET_TERMIOS |
			TTY_DRIVER_REAL_RAW |
			TTY_DRIVER_DYNAMIC_ALLOC);
	if (IS_ERR(pty_driver))
		panic("Couldn't allocate pty driver");

	pty_slave_driver = tty_alloc_driver(legacy_count,
			TTY_DRIVER_RESET_TERMIOS |
			TTY_DRIVER_REAL_RAW |
			TTY_DRIVER_DYNAMIC_ALLOC);
	if (IS_ERR(pty_slave_driver))
		panic("Couldn't allocate pty slave driver");

	pty_driver->driver_name = "pty_master";
	pty_driver->name = "pty";
	pty_driver->major = PTY_MASTER_MAJOR;
	pty_driver->minor_start = 0;
	pty_driver->type = TTY_DRIVER_TYPE_PTY;
	pty_driver->subtype = PTY_TYPE_MASTER;
	pty_driver->init_termios = tty_std_termios;
	pty_driver->init_termios.c_iflag = 0;
	pty_driver->init_termios.c_oflag = 0;
	pty_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
	pty_driver->init_termios.c_lflag = 0;
	pty_driver->init_termios.c_ispeed = 38400;
	pty_driver->init_termios.c_ospeed = 38400;
	pty_driver->other = pty_slave_driver;
	tty_set_operations(pty_driver, &master_pty_ops_bsd);

	pty_slave_driver->driver_name = "pty_slave";
	pty_slave_driver->name = "ttyp";
	pty_slave_driver->major = PTY_SLAVE_MAJOR;
	pty_slave_driver->minor_start = 0;
	pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
	pty_slave_driver->subtype = PTY_TYPE_SLAVE;
	pty_slave_driver->init_termios = tty_std_termios;
	pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
	pty_slave_driver->init_termios.c_ispeed = 38400;
	pty_slave_driver->init_termios.c_ospeed = 38400;
	pty_slave_driver->other = pty_driver;
	tty_set_operations(pty_slave_driver, &slave_pty_ops_bsd);

	if (tty_register_driver(pty_driver))
		panic("Couldn't register pty driver");
	if (tty_register_driver(pty_slave_driver))
		panic("Couldn't register pty slave driver");
}
#else
static inline void legacy_pty_init(void) { }
#endif

/* Unix98 devices */
#ifdef CONFIG_UNIX98_PTYS
static struct cdev ptmx_cdev;

/**
 *	ptm_open_peer - open the peer of a pty
 *	@master: the open struct file of the ptmx device node
 *	@tty: the master of the pty being opened
 *	@flags: the flags for open
 *
 *	Provide a race free way for userspace to open the slave end of a pty
 *	(where they have the master fd and cannot access or trust the mount
 *	namespace /dev/pts was mounted inside).
 */
int ptm_open_peer(struct file *master, struct tty_struct *tty, int flags)
{
	int fd = -1;
	struct file *filp;
	int retval = -EINVAL;
	struct path path;

	if (tty->driver != ptm_driver)
		return -EIO;

	fd = get_unused_fd_flags(0);
	if (fd < 0) {
		retval = fd;
		goto err;
	}

	/* Compute the slave's path */
	path.mnt = devpts_mntget(master, tty->driver_data);
	if (IS_ERR(path.mnt)) {
		retval = PTR_ERR(path.mnt);
		goto err_put;
	}
	path.dentry = tty->link->driver_data;

	filp = dentry_open(&path, flags, current_cred());
	mntput(path.mnt);
	if (IS_ERR(filp)) {
		retval = PTR_ERR(filp);
		goto err_put;
	}

	fd_install(fd, filp);
	return fd;

err_put:
	put_unused_fd(fd);
err:
	return retval;
}

static int pty_unix98_ioctl(struct tty_struct *tty,
			    unsigned int cmd, unsigned long arg)
{
	switch (cmd) {
	case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
		return pty_set_lock(tty, (int __user *)arg);
	case TIOCGPTLCK: /* Get PT Lock status */
		return pty_get_lock(tty, (int __user *)arg);
	case TIOCPKT: /* Set PT packet mode */
		return pty_set_pktmode(tty, (int __user *)arg);
	case TIOCGPKT: /* Get PT packet mode */
		return pty_get_pktmode(tty, (int __user *)arg);
	case TIOCGPTN: /* Get PT Number */
		return put_user(tty->index, (unsigned int __user *)arg);
	case TIOCSIG:    /* Send signal to other side of pty */
		return pty_signal(tty, (int) arg);
	}

	return -ENOIOCTLCMD;
}

static long pty_unix98_compat_ioctl(struct tty_struct *tty,
				 unsigned int cmd, unsigned long arg)
{
	/*
	 * PTY ioctls don't require any special translation between 32-bit and
	 * 64-bit userspace, they are already compatible.
	 */
	return pty_unix98_ioctl(tty, cmd, arg);
}

/**
 *	ptm_unix98_lookup	-	find a pty master
 *	@driver: ptm driver
 *	@idx: tty index
 *
 *	Look up a pty master device. Called under the tty_mutex for now.
 *	This provides our locking.
 */

static struct tty_struct *ptm_unix98_lookup(struct tty_driver *driver,
		struct file *file, int idx)
{
	/* Master must be open via /dev/ptmx */
	return ERR_PTR(-EIO);
}

/**
 *	pts_unix98_lookup	-	find a pty slave
 *	@driver: pts driver
 *	@idx: tty index
 *
 *	Look up a pty master device. Called under the tty_mutex for now.
 *	This provides our locking for the tty pointer.
 */

static struct tty_struct *pts_unix98_lookup(struct tty_driver *driver,
		struct file *file, int idx)
{
	struct tty_struct *tty;

	mutex_lock(&devpts_mutex);
	tty = devpts_get_priv(file->f_path.dentry);
	mutex_unlock(&devpts_mutex);
	/* Master must be open before slave */
	if (!tty)
		return ERR_PTR(-EIO);
	return tty;
}

static int pty_unix98_install(struct tty_driver *driver, struct tty_struct *tty)
{
	return pty_common_install(driver, tty, false);
}

/* this is called once with whichever end is closed last */
static void pty_unix98_remove(struct tty_driver *driver, struct tty_struct *tty)
{
	struct pts_fs_info *fsi;

	if (tty->driver->subtype == PTY_TYPE_MASTER)
		fsi = tty->driver_data;
	else
		fsi = tty->link->driver_data;

	if (fsi) {
		devpts_kill_index(fsi, tty->index);
		devpts_release(fsi);
	}
}

static void pty_show_fdinfo(struct tty_struct *tty, struct seq_file *m)
{
	seq_printf(m, "tty-index:\t%d\n", tty->index);
}

static const struct tty_operations ptm_unix98_ops = {
	.lookup = ptm_unix98_lookup,
	.install = pty_unix98_install,
	.remove = pty_unix98_remove,
	.open = pty_open,
	.close = pty_close,
	.write = pty_write,
	.write_room = pty_write_room,
	.flush_buffer = pty_flush_buffer,
	.chars_in_buffer = pty_chars_in_buffer,
	.unthrottle = pty_unthrottle,
	.ioctl = pty_unix98_ioctl,
	.compat_ioctl = pty_unix98_compat_ioctl,
	.resize = pty_resize,
	.cleanup = pty_cleanup,
	.show_fdinfo = pty_show_fdinfo,
};

static const struct tty_operations pty_unix98_ops = {
	.lookup = pts_unix98_lookup,
	.install = pty_unix98_install,
	.remove = pty_unix98_remove,
	.open = pty_open,
	.close = pty_close,
	.write = pty_write,
	.write_room = pty_write_room,
	.flush_buffer = pty_flush_buffer,
	.chars_in_buffer = pty_chars_in_buffer,
	.unthrottle = pty_unthrottle,
	.set_termios = pty_set_termios,
	.start = pty_start,
	.stop = pty_stop,
	.cleanup = pty_cleanup,
};

/**
 *	ptmx_open		-	open a unix 98 pty master
 *	@inode: inode of device file
 *	@filp: file pointer to tty
 *
 *	Allocate a unix98 pty master device from the ptmx driver.
 *
 *	Locking: tty_mutex protects the init_dev work. tty->count should
 *		protect the rest.
 *		allocated_ptys_lock handles the list of free pty numbers
 */

static int ptmx_open(struct inode *inode, struct file *filp)
{
	struct pts_fs_info *fsi;
	struct tty_struct *tty;
	struct dentry *dentry;
	int retval;
	int index;

	nonseekable_open(inode, filp);

	/* We refuse fsnotify events on ptmx, since it's a shared resource */
	filp->f_mode |= FMODE_NONOTIFY;

	retval = tty_alloc_file(filp);
	if (retval)
		return retval;

	fsi = devpts_acquire(filp);
	if (IS_ERR(fsi)) {
		retval = PTR_ERR(fsi);
		goto out_free_file;
	}

	/* find a device that is not in use. */
	mutex_lock(&devpts_mutex);
	index = devpts_new_index(fsi);
	mutex_unlock(&devpts_mutex);

	retval = index;
	if (index < 0)
		goto out_put_fsi;


	mutex_lock(&tty_mutex);
	tty = tty_init_dev(ptm_driver, index);
	/* The tty returned here is locked so we can safely
	   drop the mutex */
	mutex_unlock(&tty_mutex);

	retval = PTR_ERR(tty);
	if (IS_ERR(tty))
		goto out;

	/*
	 * From here on out, the tty is "live", and the index and
	 * fsi will be killed/put by the tty_release()
	 */
	set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
	tty->driver_data = fsi;

	tty_add_file(tty, filp);

	dentry = devpts_pty_new(fsi, index, tty->link);
	if (IS_ERR(dentry)) {
		retval = PTR_ERR(dentry);
		goto err_release;
	}
	tty->link->driver_data = dentry;

	retval = ptm_driver->ops->open(tty, filp);
	if (retval)
		goto err_release;

	tty_debug_hangup(tty, "opening (count=%d)\n", tty->count);

	tty_unlock(tty);
	return 0;
err_release:
	tty_unlock(tty);
	// This will also put-ref the fsi
	tty_release(inode, filp);
	return retval;
out:
	devpts_kill_index(fsi, index);
out_put_fsi:
	devpts_release(fsi);
out_free_file:
	tty_free_file(filp);
	return retval;
}

static struct file_operations ptmx_fops __ro_after_init;

static void __init unix98_pty_init(void)
{
	ptm_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
			TTY_DRIVER_RESET_TERMIOS |
			TTY_DRIVER_REAL_RAW |
			TTY_DRIVER_DYNAMIC_DEV |
			TTY_DRIVER_DEVPTS_MEM |
			TTY_DRIVER_DYNAMIC_ALLOC);
	if (IS_ERR(ptm_driver))
		panic("Couldn't allocate Unix98 ptm driver");
	pts_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
			TTY_DRIVER_RESET_TERMIOS |
			TTY_DRIVER_REAL_RAW |
			TTY_DRIVER_DYNAMIC_DEV |
			TTY_DRIVER_DEVPTS_MEM |
			TTY_DRIVER_DYNAMIC_ALLOC);
	if (IS_ERR(pts_driver))
		panic("Couldn't allocate Unix98 pts driver");

	ptm_driver->driver_name = "pty_master";
	ptm_driver->name = "ptm";
	ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
	ptm_driver->minor_start = 0;
	ptm_driver->type = TTY_DRIVER_TYPE_PTY;
	ptm_driver->subtype = PTY_TYPE_MASTER;
	ptm_driver->init_termios = tty_std_termios;
	ptm_driver->init_termios.c_iflag = 0;
	ptm_driver->init_termios.c_oflag = 0;
	ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
	ptm_driver->init_termios.c_lflag = 0;
	ptm_driver->init_termios.c_ispeed = 38400;
	ptm_driver->init_termios.c_ospeed = 38400;
	ptm_driver->other = pts_driver;
	tty_set_operations(ptm_driver, &ptm_unix98_ops);

	pts_driver->driver_name = "pty_slave";
	pts_driver->name = "pts";
	pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
	pts_driver->minor_start = 0;
	pts_driver->type = TTY_DRIVER_TYPE_PTY;
	pts_driver->subtype = PTY_TYPE_SLAVE;
	pts_driver->init_termios = tty_std_termios;
	pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
	pts_driver->init_termios.c_ispeed = 38400;
	pts_driver->init_termios.c_ospeed = 38400;
	pts_driver->other = ptm_driver;
	tty_set_operations(pts_driver, &pty_unix98_ops);

	if (tty_register_driver(ptm_driver))
		panic("Couldn't register Unix98 ptm driver");
	if (tty_register_driver(pts_driver))
		panic("Couldn't register Unix98 pts driver");

	/* Now create the /dev/ptmx special device */
	tty_default_fops(&ptmx_fops);
	ptmx_fops.open = ptmx_open;

	cdev_init(&ptmx_cdev, &ptmx_fops);
	if (cdev_add(&ptmx_cdev, MKDEV(TTYAUX_MAJOR, 2), 1) ||
	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 2), 1, "/dev/ptmx") < 0)
		panic("Couldn't register /dev/ptmx driver");
	device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 2), NULL, "ptmx");
}

#else
static inline void unix98_pty_init(void) { }
#endif

static int __init pty_init(void)
{
	legacy_pty_init();
	unix98_pty_init();
	return 0;
}
device_initcall(pty_init);