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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Tty buffer allocation management
4 */
5
6#include <linux/types.h>
7#include <linux/errno.h>
8#include <linux/minmax.h>
9#include <linux/tty.h>
10#include <linux/tty_driver.h>
11#include <linux/tty_flip.h>
12#include <linux/timer.h>
13#include <linux/string.h>
14#include <linux/slab.h>
15#include <linux/sched.h>
16#include <linux/wait.h>
17#include <linux/bitops.h>
18#include <linux/delay.h>
19#include <linux/module.h>
20#include <linux/ratelimit.h>
21#include "tty.h"
22
23#define MIN_TTYB_SIZE 256
24#define TTYB_ALIGN_MASK 0xff
25
26/*
27 * Byte threshold to limit memory consumption for flip buffers.
28 * The actual memory limit is > 2x this amount.
29 */
30#define TTYB_DEFAULT_MEM_LIMIT (640 * 1024UL)
31
32/*
33 * We default to dicing tty buffer allocations to this many characters
34 * in order to avoid multiple page allocations. We know the size of
35 * tty_buffer itself but it must also be taken into account that the
36 * buffer is 256 byte aligned. See tty_buffer_find for the allocation
37 * logic this must match.
38 */
39
40#define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~TTYB_ALIGN_MASK)
41
42/**
43 * tty_buffer_lock_exclusive - gain exclusive access to buffer
44 * @port: tty port owning the flip buffer
45 *
46 * Guarantees safe use of the &tty_ldisc_ops.receive_buf() method by excluding
47 * the buffer work and any pending flush from using the flip buffer. Data can
48 * continue to be added concurrently to the flip buffer from the driver side.
49 *
50 * See also tty_buffer_unlock_exclusive().
51 */
52void tty_buffer_lock_exclusive(struct tty_port *port)
53{
54 struct tty_bufhead *buf = &port->buf;
55
56 atomic_inc(&buf->priority);
57 mutex_lock(&buf->lock);
58}
59EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
60
61/**
62 * tty_buffer_unlock_exclusive - release exclusive access
63 * @port: tty port owning the flip buffer
64 *
65 * The buffer work is restarted if there is data in the flip buffer.
66 *
67 * See also tty_buffer_lock_exclusive().
68 */
69void tty_buffer_unlock_exclusive(struct tty_port *port)
70{
71 struct tty_bufhead *buf = &port->buf;
72 int restart;
73
74 restart = buf->head->commit != buf->head->read;
75
76 atomic_dec(&buf->priority);
77 mutex_unlock(&buf->lock);
78 if (restart)
79 queue_work(system_unbound_wq, &buf->work);
80}
81EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
82
83/**
84 * tty_buffer_space_avail - return unused buffer space
85 * @port: tty port owning the flip buffer
86 *
87 * Returns: the # of bytes which can be written by the driver without reaching
88 * the buffer limit.
89 *
90 * Note: this does not guarantee that memory is available to write the returned
91 * # of bytes (use tty_prepare_flip_string() to pre-allocate if memory
92 * guarantee is required).
93 */
94unsigned int tty_buffer_space_avail(struct tty_port *port)
95{
96 int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
97
98 return max(space, 0);
99}
100EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
101
102static void tty_buffer_reset(struct tty_buffer *p, size_t size)
103{
104 p->used = 0;
105 p->size = size;
106 p->next = NULL;
107 p->commit = 0;
108 p->lookahead = 0;
109 p->read = 0;
110 p->flags = true;
111}
112
113/**
114 * tty_buffer_free_all - free buffers used by a tty
115 * @port: tty port to free from
116 *
117 * Remove all the buffers pending on a tty whether queued with data or in the
118 * free ring. Must be called when the tty is no longer in use.
119 */
120void tty_buffer_free_all(struct tty_port *port)
121{
122 struct tty_bufhead *buf = &port->buf;
123 struct tty_buffer *p, *next;
124 struct llist_node *llist;
125 unsigned int freed = 0;
126 int still_used;
127
128 while ((p = buf->head) != NULL) {
129 buf->head = p->next;
130 freed += p->size;
131 if (p->size > 0)
132 kfree(p);
133 }
134 llist = llist_del_all(&buf->free);
135 llist_for_each_entry_safe(p, next, llist, free)
136 kfree(p);
137
138 tty_buffer_reset(&buf->sentinel, 0);
139 buf->head = &buf->sentinel;
140 buf->tail = &buf->sentinel;
141
142 still_used = atomic_xchg(&buf->mem_used, 0);
143 WARN(still_used != freed, "we still have not freed %d bytes!",
144 still_used - freed);
145}
146
147/**
148 * tty_buffer_alloc - allocate a tty buffer
149 * @port: tty port
150 * @size: desired size (characters)
151 *
152 * Allocate a new tty buffer to hold the desired number of characters. We
153 * round our buffers off in 256 character chunks to get better allocation
154 * behaviour.
155 *
156 * Returns: %NULL if out of memory or the allocation would exceed the per
157 * device queue.
158 */
159static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
160{
161 struct llist_node *free;
162 struct tty_buffer *p;
163
164 /* Round the buffer size out */
165 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
166
167 if (size <= MIN_TTYB_SIZE) {
168 free = llist_del_first(&port->buf.free);
169 if (free) {
170 p = llist_entry(free, struct tty_buffer, free);
171 goto found;
172 }
173 }
174
175 /* Should possibly check if this fails for the largest buffer we
176 * have queued and recycle that ?
177 */
178 if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
179 return NULL;
180 p = kmalloc(sizeof(struct tty_buffer) + 2 * size,
181 GFP_ATOMIC | __GFP_NOWARN);
182 if (p == NULL)
183 return NULL;
184
185found:
186 tty_buffer_reset(p, size);
187 atomic_add(size, &port->buf.mem_used);
188 return p;
189}
190
191/**
192 * tty_buffer_free - free a tty buffer
193 * @port: tty port owning the buffer
194 * @b: the buffer to free
195 *
196 * Free a tty buffer, or add it to the free list according to our internal
197 * strategy.
198 */
199static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
200{
201 struct tty_bufhead *buf = &port->buf;
202
203 /* Dumb strategy for now - should keep some stats */
204 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
205
206 if (b->size > MIN_TTYB_SIZE)
207 kfree(b);
208 else if (b->size > 0)
209 llist_add(&b->free, &buf->free);
210}
211
212/**
213 * tty_buffer_flush - flush full tty buffers
214 * @tty: tty to flush
215 * @ld: optional ldisc ptr (must be referenced)
216 *
217 * Flush all the buffers containing receive data. If @ld != %NULL, flush the
218 * ldisc input buffer.
219 *
220 * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
221 */
222void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
223{
224 struct tty_port *port = tty->port;
225 struct tty_bufhead *buf = &port->buf;
226 struct tty_buffer *next;
227
228 atomic_inc(&buf->priority);
229
230 mutex_lock(&buf->lock);
231 /* paired w/ release in __tty_buffer_request_room; ensures there are
232 * no pending memory accesses to the freed buffer
233 */
234 while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
235 tty_buffer_free(port, buf->head);
236 buf->head = next;
237 }
238 buf->head->read = buf->head->commit;
239 buf->head->lookahead = buf->head->read;
240
241 if (ld && ld->ops->flush_buffer)
242 ld->ops->flush_buffer(tty);
243
244 atomic_dec(&buf->priority);
245 mutex_unlock(&buf->lock);
246}
247
248/**
249 * __tty_buffer_request_room - grow tty buffer if needed
250 * @port: tty port
251 * @size: size desired
252 * @flags: buffer has to store flags along character data
253 *
254 * Make at least @size bytes of linear space available for the tty buffer.
255 *
256 * Will change over to a new buffer if the current buffer is encoded as
257 * %TTY_NORMAL (so has no flags buffer) and the new buffer requires a flags
258 * buffer.
259 *
260 * Returns: the size we managed to find.
261 */
262static int __tty_buffer_request_room(struct tty_port *port, size_t size,
263 bool flags)
264{
265 struct tty_bufhead *buf = &port->buf;
266 struct tty_buffer *b, *n;
267 int left, change;
268
269 b = buf->tail;
270 if (!b->flags)
271 left = 2 * b->size - b->used;
272 else
273 left = b->size - b->used;
274
275 change = !b->flags && flags;
276 if (change || left < size) {
277 /* This is the slow path - looking for new buffers to use */
278 n = tty_buffer_alloc(port, size);
279 if (n != NULL) {
280 n->flags = flags;
281 buf->tail = n;
282 /*
283 * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
284 * ensures they see all buffer data.
285 */
286 smp_store_release(&b->commit, b->used);
287 /*
288 * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
289 * ensures the latest commit value can be read before the head
290 * is advanced to the next buffer.
291 */
292 smp_store_release(&b->next, n);
293 } else if (change)
294 size = 0;
295 else
296 size = left;
297 }
298 return size;
299}
300
301int tty_buffer_request_room(struct tty_port *port, size_t size)
302{
303 return __tty_buffer_request_room(port, size, true);
304}
305EXPORT_SYMBOL_GPL(tty_buffer_request_room);
306
307/**
308 * tty_insert_flip_string_fixed_flag - add characters to the tty buffer
309 * @port: tty port
310 * @chars: characters
311 * @flag: flag value for each character
312 * @size: size
313 *
314 * Queue a series of bytes to the tty buffering. All the characters passed are
315 * marked with the supplied flag.
316 *
317 * Returns: the number added.
318 */
319int tty_insert_flip_string_fixed_flag(struct tty_port *port,
320 const unsigned char *chars, char flag, size_t size)
321{
322 int copied = 0;
323 bool flags = flag != TTY_NORMAL;
324
325 do {
326 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
327 int space = __tty_buffer_request_room(port, goal, flags);
328 struct tty_buffer *tb = port->buf.tail;
329
330 if (unlikely(space == 0))
331 break;
332 memcpy(char_buf_ptr(tb, tb->used), chars, space);
333 if (tb->flags)
334 memset(flag_buf_ptr(tb, tb->used), flag, space);
335 tb->used += space;
336 copied += space;
337 chars += space;
338 /* There is a small chance that we need to split the data over
339 * several buffers. If this is the case we must loop.
340 */
341 } while (unlikely(size > copied));
342 return copied;
343}
344EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
345
346/**
347 * tty_insert_flip_string_flags - add characters to the tty buffer
348 * @port: tty port
349 * @chars: characters
350 * @flags: flag bytes
351 * @size: size
352 *
353 * Queue a series of bytes to the tty buffering. For each character the flags
354 * array indicates the status of the character.
355 *
356 * Returns: the number added.
357 */
358int tty_insert_flip_string_flags(struct tty_port *port,
359 const unsigned char *chars, const char *flags, size_t size)
360{
361 int copied = 0;
362
363 do {
364 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
365 int space = tty_buffer_request_room(port, goal);
366 struct tty_buffer *tb = port->buf.tail;
367
368 if (unlikely(space == 0))
369 break;
370 memcpy(char_buf_ptr(tb, tb->used), chars, space);
371 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
372 tb->used += space;
373 copied += space;
374 chars += space;
375 flags += space;
376 /* There is a small chance that we need to split the data over
377 * several buffers. If this is the case we must loop.
378 */
379 } while (unlikely(size > copied));
380 return copied;
381}
382EXPORT_SYMBOL(tty_insert_flip_string_flags);
383
384/**
385 * __tty_insert_flip_char - add one character to the tty buffer
386 * @port: tty port
387 * @ch: character
388 * @flag: flag byte
389 *
390 * Queue a single byte @ch to the tty buffering, with an optional flag. This is
391 * the slow path of tty_insert_flip_char().
392 */
393int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag)
394{
395 struct tty_buffer *tb;
396 bool flags = flag != TTY_NORMAL;
397
398 if (!__tty_buffer_request_room(port, 1, flags))
399 return 0;
400
401 tb = port->buf.tail;
402 if (tb->flags)
403 *flag_buf_ptr(tb, tb->used) = flag;
404 *char_buf_ptr(tb, tb->used++) = ch;
405
406 return 1;
407}
408EXPORT_SYMBOL(__tty_insert_flip_char);
409
410/**
411 * tty_prepare_flip_string - make room for characters
412 * @port: tty port
413 * @chars: return pointer for character write area
414 * @size: desired size
415 *
416 * Prepare a block of space in the buffer for data.
417 *
418 * This is used for drivers that need their own block copy routines into the
419 * buffer. There is no guarantee the buffer is a DMA target!
420 *
421 * Returns: the length available and buffer pointer (@chars) to the space which
422 * is now allocated and accounted for as ready for normal characters.
423 */
424int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
425 size_t size)
426{
427 int space = __tty_buffer_request_room(port, size, false);
428
429 if (likely(space)) {
430 struct tty_buffer *tb = port->buf.tail;
431
432 *chars = char_buf_ptr(tb, tb->used);
433 if (tb->flags)
434 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
435 tb->used += space;
436 }
437 return space;
438}
439EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
440
441/**
442 * tty_ldisc_receive_buf - forward data to line discipline
443 * @ld: line discipline to process input
444 * @p: char buffer
445 * @f: %TTY_NORMAL, %TTY_BREAK, etc. flags buffer
446 * @count: number of bytes to process
447 *
448 * Callers other than flush_to_ldisc() need to exclude the kworker from
449 * concurrent use of the line discipline, see paste_selection().
450 *
451 * Returns: the number of bytes processed.
452 */
453int tty_ldisc_receive_buf(struct tty_ldisc *ld, const unsigned char *p,
454 const char *f, int count)
455{
456 if (ld->ops->receive_buf2)
457 count = ld->ops->receive_buf2(ld->tty, p, f, count);
458 else {
459 count = min_t(int, count, ld->tty->receive_room);
460 if (count && ld->ops->receive_buf)
461 ld->ops->receive_buf(ld->tty, p, f, count);
462 }
463 return count;
464}
465EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
466
467static void lookahead_bufs(struct tty_port *port, struct tty_buffer *head)
468{
469 head->lookahead = max(head->lookahead, head->read);
470
471 while (head) {
472 struct tty_buffer *next;
473 unsigned int count;
474
475 /*
476 * Paired w/ release in __tty_buffer_request_room();
477 * ensures commit value read is not stale if the head
478 * is advancing to the next buffer.
479 */
480 next = smp_load_acquire(&head->next);
481 /*
482 * Paired w/ release in __tty_buffer_request_room() or in
483 * tty_buffer_flush(); ensures we see the committed buffer data.
484 */
485 count = smp_load_acquire(&head->commit) - head->lookahead;
486 if (!count) {
487 head = next;
488 continue;
489 }
490
491 if (port->client_ops->lookahead_buf) {
492 unsigned char *p, *f = NULL;
493
494 p = char_buf_ptr(head, head->lookahead);
495 if (head->flags)
496 f = flag_buf_ptr(head, head->lookahead);
497
498 port->client_ops->lookahead_buf(port, p, f, count);
499 }
500
501 head->lookahead += count;
502 }
503}
504
505static int
506receive_buf(struct tty_port *port, struct tty_buffer *head, int count)
507{
508 unsigned char *p = char_buf_ptr(head, head->read);
509 const char *f = NULL;
510 int n;
511
512 if (head->flags)
513 f = flag_buf_ptr(head, head->read);
514
515 n = port->client_ops->receive_buf(port, p, f, count);
516 if (n > 0)
517 memset(p, 0, n);
518 return n;
519}
520
521/**
522 * flush_to_ldisc - flush data from buffer to ldisc
523 * @work: tty structure passed from work queue.
524 *
525 * This routine is called out of the software interrupt to flush data from the
526 * buffer chain to the line discipline.
527 *
528 * The receive_buf() method is single threaded for each tty instance.
529 *
530 * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
531 */
532static void flush_to_ldisc(struct work_struct *work)
533{
534 struct tty_port *port = container_of(work, struct tty_port, buf.work);
535 struct tty_bufhead *buf = &port->buf;
536
537 mutex_lock(&buf->lock);
538
539 while (1) {
540 struct tty_buffer *head = buf->head;
541 struct tty_buffer *next;
542 int count, rcvd;
543
544 /* Ldisc or user is trying to gain exclusive access */
545 if (atomic_read(&buf->priority))
546 break;
547
548 /* paired w/ release in __tty_buffer_request_room();
549 * ensures commit value read is not stale if the head
550 * is advancing to the next buffer
551 */
552 next = smp_load_acquire(&head->next);
553 /* paired w/ release in __tty_buffer_request_room() or in
554 * tty_buffer_flush(); ensures we see the committed buffer data
555 */
556 count = smp_load_acquire(&head->commit) - head->read;
557 if (!count) {
558 if (next == NULL)
559 break;
560 buf->head = next;
561 tty_buffer_free(port, head);
562 continue;
563 }
564
565 rcvd = receive_buf(port, head, count);
566 head->read += rcvd;
567 if (rcvd < count)
568 lookahead_bufs(port, head);
569 if (!rcvd)
570 break;
571
572 if (need_resched())
573 cond_resched();
574 }
575
576 mutex_unlock(&buf->lock);
577
578}
579
580static inline void tty_flip_buffer_commit(struct tty_buffer *tail)
581{
582 /*
583 * Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
584 * buffer data.
585 */
586 smp_store_release(&tail->commit, tail->used);
587}
588
589/**
590 * tty_flip_buffer_push - push terminal buffers
591 * @port: tty port to push
592 *
593 * Queue a push of the terminal flip buffers to the line discipline. Can be
594 * called from IRQ/atomic context.
595 *
596 * In the event of the queue being busy for flipping the work will be held off
597 * and retried later.
598 */
599void tty_flip_buffer_push(struct tty_port *port)
600{
601 struct tty_bufhead *buf = &port->buf;
602
603 tty_flip_buffer_commit(buf->tail);
604 queue_work(system_unbound_wq, &buf->work);
605}
606EXPORT_SYMBOL(tty_flip_buffer_push);
607
608/**
609 * tty_insert_flip_string_and_push_buffer - add characters to the tty buffer and
610 * push
611 * @port: tty port
612 * @chars: characters
613 * @size: size
614 *
615 * The function combines tty_insert_flip_string() and tty_flip_buffer_push()
616 * with the exception of properly holding the @port->lock.
617 *
618 * To be used only internally (by pty currently).
619 *
620 * Returns: the number added.
621 */
622int tty_insert_flip_string_and_push_buffer(struct tty_port *port,
623 const unsigned char *chars, size_t size)
624{
625 struct tty_bufhead *buf = &port->buf;
626 unsigned long flags;
627
628 spin_lock_irqsave(&port->lock, flags);
629 size = tty_insert_flip_string(port, chars, size);
630 if (size)
631 tty_flip_buffer_commit(buf->tail);
632 spin_unlock_irqrestore(&port->lock, flags);
633
634 queue_work(system_unbound_wq, &buf->work);
635
636 return size;
637}
638
639/**
640 * tty_buffer_init - prepare a tty buffer structure
641 * @port: tty port to initialise
642 *
643 * Set up the initial state of the buffer management for a tty device. Must be
644 * called before the other tty buffer functions are used.
645 */
646void tty_buffer_init(struct tty_port *port)
647{
648 struct tty_bufhead *buf = &port->buf;
649
650 mutex_init(&buf->lock);
651 tty_buffer_reset(&buf->sentinel, 0);
652 buf->head = &buf->sentinel;
653 buf->tail = &buf->sentinel;
654 init_llist_head(&buf->free);
655 atomic_set(&buf->mem_used, 0);
656 atomic_set(&buf->priority, 0);
657 INIT_WORK(&buf->work, flush_to_ldisc);
658 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
659}
660
661/**
662 * tty_buffer_set_limit - change the tty buffer memory limit
663 * @port: tty port to change
664 * @limit: memory limit to set
665 *
666 * Change the tty buffer memory limit.
667 *
668 * Must be called before the other tty buffer functions are used.
669 */
670int tty_buffer_set_limit(struct tty_port *port, int limit)
671{
672 if (limit < MIN_TTYB_SIZE)
673 return -EINVAL;
674 port->buf.mem_limit = limit;
675 return 0;
676}
677EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
678
679/* slave ptys can claim nested buffer lock when handling BRK and INTR */
680void tty_buffer_set_lock_subclass(struct tty_port *port)
681{
682 lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
683}
684
685bool tty_buffer_restart_work(struct tty_port *port)
686{
687 return queue_work(system_unbound_wq, &port->buf.work);
688}
689
690bool tty_buffer_cancel_work(struct tty_port *port)
691{
692 return cancel_work_sync(&port->buf.work);
693}
694
695void tty_buffer_flush_work(struct tty_port *port)
696{
697 flush_work(&port->buf.work);
698}
1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Tty buffer allocation management
4 */
5
6#include <linux/types.h>
7#include <linux/errno.h>
8#include <linux/tty.h>
9#include <linux/tty_driver.h>
10#include <linux/tty_flip.h>
11#include <linux/timer.h>
12#include <linux/string.h>
13#include <linux/slab.h>
14#include <linux/sched.h>
15#include <linux/wait.h>
16#include <linux/bitops.h>
17#include <linux/delay.h>
18#include <linux/module.h>
19#include <linux/ratelimit.h>
20#include "tty.h"
21
22#define MIN_TTYB_SIZE 256
23#define TTYB_ALIGN_MASK 255
24
25/*
26 * Byte threshold to limit memory consumption for flip buffers.
27 * The actual memory limit is > 2x this amount.
28 */
29#define TTYB_DEFAULT_MEM_LIMIT (640 * 1024UL)
30
31/*
32 * We default to dicing tty buffer allocations to this many characters
33 * in order to avoid multiple page allocations. We know the size of
34 * tty_buffer itself but it must also be taken into account that the
35 * buffer is 256 byte aligned. See tty_buffer_find for the allocation
36 * logic this must match.
37 */
38
39#define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
40
41/**
42 * tty_buffer_lock_exclusive - gain exclusive access to buffer
43 * tty_buffer_unlock_exclusive - release exclusive access
44 *
45 * @port: tty port owning the flip buffer
46 *
47 * Guarantees safe use of the line discipline's receive_buf() method by
48 * excluding the buffer work and any pending flush from using the flip
49 * buffer. Data can continue to be added concurrently to the flip buffer
50 * from the driver side.
51 *
52 * On release, the buffer work is restarted if there is data in the
53 * flip buffer
54 */
55
56void tty_buffer_lock_exclusive(struct tty_port *port)
57{
58 struct tty_bufhead *buf = &port->buf;
59
60 atomic_inc(&buf->priority);
61 mutex_lock(&buf->lock);
62}
63EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
64
65void tty_buffer_unlock_exclusive(struct tty_port *port)
66{
67 struct tty_bufhead *buf = &port->buf;
68 int restart;
69
70 restart = buf->head->commit != buf->head->read;
71
72 atomic_dec(&buf->priority);
73 mutex_unlock(&buf->lock);
74 if (restart)
75 queue_work(system_unbound_wq, &buf->work);
76}
77EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
78
79/**
80 * tty_buffer_space_avail - return unused buffer space
81 * @port: tty port owning the flip buffer
82 *
83 * Returns the # of bytes which can be written by the driver without
84 * reaching the buffer limit.
85 *
86 * Note: this does not guarantee that memory is available to write
87 * the returned # of bytes (use tty_prepare_flip_string_xxx() to
88 * pre-allocate if memory guarantee is required).
89 */
90
91unsigned int tty_buffer_space_avail(struct tty_port *port)
92{
93 int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
94
95 return max(space, 0);
96}
97EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
98
99static void tty_buffer_reset(struct tty_buffer *p, size_t size)
100{
101 p->used = 0;
102 p->size = size;
103 p->next = NULL;
104 p->commit = 0;
105 p->read = 0;
106 p->flags = 0;
107}
108
109/**
110 * tty_buffer_free_all - free buffers used by a tty
111 * @port: tty port to free from
112 *
113 * Remove all the buffers pending on a tty whether queued with data
114 * or in the free ring. Must be called when the tty is no longer in use
115 */
116
117void tty_buffer_free_all(struct tty_port *port)
118{
119 struct tty_bufhead *buf = &port->buf;
120 struct tty_buffer *p, *next;
121 struct llist_node *llist;
122 unsigned int freed = 0;
123 int still_used;
124
125 while ((p = buf->head) != NULL) {
126 buf->head = p->next;
127 freed += p->size;
128 if (p->size > 0)
129 kfree(p);
130 }
131 llist = llist_del_all(&buf->free);
132 llist_for_each_entry_safe(p, next, llist, free)
133 kfree(p);
134
135 tty_buffer_reset(&buf->sentinel, 0);
136 buf->head = &buf->sentinel;
137 buf->tail = &buf->sentinel;
138
139 still_used = atomic_xchg(&buf->mem_used, 0);
140 WARN(still_used != freed, "we still have not freed %d bytes!",
141 still_used - freed);
142}
143
144/**
145 * tty_buffer_alloc - allocate a tty buffer
146 * @port: tty port
147 * @size: desired size (characters)
148 *
149 * Allocate a new tty buffer to hold the desired number of characters.
150 * We round our buffers off in 256 character chunks to get better
151 * allocation behaviour.
152 * Return NULL if out of memory or the allocation would exceed the
153 * per device queue
154 */
155
156static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
157{
158 struct llist_node *free;
159 struct tty_buffer *p;
160
161 /* Round the buffer size out */
162 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
163
164 if (size <= MIN_TTYB_SIZE) {
165 free = llist_del_first(&port->buf.free);
166 if (free) {
167 p = llist_entry(free, struct tty_buffer, free);
168 goto found;
169 }
170 }
171
172 /* Should possibly check if this fails for the largest buffer we
173 * have queued and recycle that ?
174 */
175 if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
176 return NULL;
177 p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
178 if (p == NULL)
179 return NULL;
180
181found:
182 tty_buffer_reset(p, size);
183 atomic_add(size, &port->buf.mem_used);
184 return p;
185}
186
187/**
188 * tty_buffer_free - free a tty buffer
189 * @port: tty port owning the buffer
190 * @b: the buffer to free
191 *
192 * Free a tty buffer, or add it to the free list according to our
193 * internal strategy
194 */
195
196static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
197{
198 struct tty_bufhead *buf = &port->buf;
199
200 /* Dumb strategy for now - should keep some stats */
201 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
202
203 if (b->size > MIN_TTYB_SIZE)
204 kfree(b);
205 else if (b->size > 0)
206 llist_add(&b->free, &buf->free);
207}
208
209/**
210 * tty_buffer_flush - flush full tty buffers
211 * @tty: tty to flush
212 * @ld: optional ldisc ptr (must be referenced)
213 *
214 * flush all the buffers containing receive data. If ld != NULL,
215 * flush the ldisc input buffer.
216 *
217 * Locking: takes buffer lock to ensure single-threaded flip buffer
218 * 'consumer'
219 */
220
221void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
222{
223 struct tty_port *port = tty->port;
224 struct tty_bufhead *buf = &port->buf;
225 struct tty_buffer *next;
226
227 atomic_inc(&buf->priority);
228
229 mutex_lock(&buf->lock);
230 /* paired w/ release in __tty_buffer_request_room; ensures there are
231 * no pending memory accesses to the freed buffer
232 */
233 while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
234 tty_buffer_free(port, buf->head);
235 buf->head = next;
236 }
237 buf->head->read = buf->head->commit;
238
239 if (ld && ld->ops->flush_buffer)
240 ld->ops->flush_buffer(tty);
241
242 atomic_dec(&buf->priority);
243 mutex_unlock(&buf->lock);
244}
245
246/**
247 * __tty_buffer_request_room - grow tty buffer if needed
248 * @port: tty port
249 * @size: size desired
250 * @flags: buffer flags if new buffer allocated (default = 0)
251 *
252 * Make at least size bytes of linear space available for the tty
253 * buffer. If we fail return the size we managed to find.
254 *
255 * Will change over to a new buffer if the current buffer is encoded as
256 * TTY_NORMAL (so has no flags buffer) and the new buffer requires
257 * a flags buffer.
258 */
259static int __tty_buffer_request_room(struct tty_port *port, size_t size,
260 int flags)
261{
262 struct tty_bufhead *buf = &port->buf;
263 struct tty_buffer *b, *n;
264 int left, change;
265
266 b = buf->tail;
267 if (b->flags & TTYB_NORMAL)
268 left = 2 * b->size - b->used;
269 else
270 left = b->size - b->used;
271
272 change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
273 if (change || left < size) {
274 /* This is the slow path - looking for new buffers to use */
275 n = tty_buffer_alloc(port, size);
276 if (n != NULL) {
277 n->flags = flags;
278 buf->tail = n;
279 /* paired w/ acquire in flush_to_ldisc(); ensures
280 * flush_to_ldisc() sees buffer data.
281 */
282 smp_store_release(&b->commit, b->used);
283 /* paired w/ acquire in flush_to_ldisc(); ensures the
284 * latest commit value can be read before the head is
285 * advanced to the next buffer
286 */
287 smp_store_release(&b->next, n);
288 } else if (change)
289 size = 0;
290 else
291 size = left;
292 }
293 return size;
294}
295
296int tty_buffer_request_room(struct tty_port *port, size_t size)
297{
298 return __tty_buffer_request_room(port, size, 0);
299}
300EXPORT_SYMBOL_GPL(tty_buffer_request_room);
301
302/**
303 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
304 * @port: tty port
305 * @chars: characters
306 * @flag: flag value for each character
307 * @size: size
308 *
309 * Queue a series of bytes to the tty buffering. All the characters
310 * passed are marked with the supplied flag. Returns the number added.
311 */
312
313int tty_insert_flip_string_fixed_flag(struct tty_port *port,
314 const unsigned char *chars, char flag, size_t size)
315{
316 int copied = 0;
317
318 do {
319 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
320 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
321 int space = __tty_buffer_request_room(port, goal, flags);
322 struct tty_buffer *tb = port->buf.tail;
323
324 if (unlikely(space == 0))
325 break;
326 memcpy(char_buf_ptr(tb, tb->used), chars, space);
327 if (~tb->flags & TTYB_NORMAL)
328 memset(flag_buf_ptr(tb, tb->used), flag, space);
329 tb->used += space;
330 copied += space;
331 chars += space;
332 /* There is a small chance that we need to split the data over
333 * several buffers. If this is the case we must loop.
334 */
335 } while (unlikely(size > copied));
336 return copied;
337}
338EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
339
340/**
341 * tty_insert_flip_string_flags - Add characters to the tty buffer
342 * @port: tty port
343 * @chars: characters
344 * @flags: flag bytes
345 * @size: size
346 *
347 * Queue a series of bytes to the tty buffering. For each character
348 * the flags array indicates the status of the character. Returns the
349 * number added.
350 */
351
352int tty_insert_flip_string_flags(struct tty_port *port,
353 const unsigned char *chars, const char *flags, size_t size)
354{
355 int copied = 0;
356
357 do {
358 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
359 int space = tty_buffer_request_room(port, goal);
360 struct tty_buffer *tb = port->buf.tail;
361
362 if (unlikely(space == 0))
363 break;
364 memcpy(char_buf_ptr(tb, tb->used), chars, space);
365 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
366 tb->used += space;
367 copied += space;
368 chars += space;
369 flags += space;
370 /* There is a small chance that we need to split the data over
371 * several buffers. If this is the case we must loop.
372 */
373 } while (unlikely(size > copied));
374 return copied;
375}
376EXPORT_SYMBOL(tty_insert_flip_string_flags);
377
378/**
379 * __tty_insert_flip_char - Add one character to the tty buffer
380 * @port: tty port
381 * @ch: character
382 * @flag: flag byte
383 *
384 * Queue a single byte to the tty buffering, with an optional flag.
385 * This is the slow path of tty_insert_flip_char.
386 */
387int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag)
388{
389 struct tty_buffer *tb;
390 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
391
392 if (!__tty_buffer_request_room(port, 1, flags))
393 return 0;
394
395 tb = port->buf.tail;
396 if (~tb->flags & TTYB_NORMAL)
397 *flag_buf_ptr(tb, tb->used) = flag;
398 *char_buf_ptr(tb, tb->used++) = ch;
399
400 return 1;
401}
402EXPORT_SYMBOL(__tty_insert_flip_char);
403
404/**
405 * tty_schedule_flip - push characters to ldisc
406 * @port: tty port to push from
407 *
408 * Takes any pending buffers and transfers their ownership to the
409 * ldisc side of the queue. It then schedules those characters for
410 * processing by the line discipline.
411 */
412
413void tty_schedule_flip(struct tty_port *port)
414{
415 struct tty_bufhead *buf = &port->buf;
416
417 /* paired w/ acquire in flush_to_ldisc(); ensures
418 * flush_to_ldisc() sees buffer data.
419 */
420 smp_store_release(&buf->tail->commit, buf->tail->used);
421 queue_work(system_unbound_wq, &buf->work);
422}
423EXPORT_SYMBOL(tty_schedule_flip);
424
425/**
426 * tty_prepare_flip_string - make room for characters
427 * @port: tty port
428 * @chars: return pointer for character write area
429 * @size: desired size
430 *
431 * Prepare a block of space in the buffer for data. Returns the length
432 * available and buffer pointer to the space which is now allocated and
433 * accounted for as ready for normal characters. This is used for drivers
434 * that need their own block copy routines into the buffer. There is no
435 * guarantee the buffer is a DMA target!
436 */
437
438int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
439 size_t size)
440{
441 int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
442
443 if (likely(space)) {
444 struct tty_buffer *tb = port->buf.tail;
445
446 *chars = char_buf_ptr(tb, tb->used);
447 if (~tb->flags & TTYB_NORMAL)
448 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
449 tb->used += space;
450 }
451 return space;
452}
453EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
454
455/**
456 * tty_ldisc_receive_buf - forward data to line discipline
457 * @ld: line discipline to process input
458 * @p: char buffer
459 * @f: TTY_* flags buffer
460 * @count: number of bytes to process
461 *
462 * Callers other than flush_to_ldisc() need to exclude the kworker
463 * from concurrent use of the line discipline, see paste_selection().
464 *
465 * Returns the number of bytes processed
466 */
467int tty_ldisc_receive_buf(struct tty_ldisc *ld, const unsigned char *p,
468 const char *f, int count)
469{
470 if (ld->ops->receive_buf2)
471 count = ld->ops->receive_buf2(ld->tty, p, f, count);
472 else {
473 count = min_t(int, count, ld->tty->receive_room);
474 if (count && ld->ops->receive_buf)
475 ld->ops->receive_buf(ld->tty, p, f, count);
476 }
477 return count;
478}
479EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
480
481static int
482receive_buf(struct tty_port *port, struct tty_buffer *head, int count)
483{
484 unsigned char *p = char_buf_ptr(head, head->read);
485 const char *f = NULL;
486 int n;
487
488 if (~head->flags & TTYB_NORMAL)
489 f = flag_buf_ptr(head, head->read);
490
491 n = port->client_ops->receive_buf(port, p, f, count);
492 if (n > 0)
493 memset(p, 0, n);
494 return n;
495}
496
497/**
498 * flush_to_ldisc
499 * @work: tty structure passed from work queue.
500 *
501 * This routine is called out of the software interrupt to flush data
502 * from the buffer chain to the line discipline.
503 *
504 * The receive_buf method is single threaded for each tty instance.
505 *
506 * Locking: takes buffer lock to ensure single-threaded flip buffer
507 * 'consumer'
508 */
509
510static void flush_to_ldisc(struct work_struct *work)
511{
512 struct tty_port *port = container_of(work, struct tty_port, buf.work);
513 struct tty_bufhead *buf = &port->buf;
514
515 mutex_lock(&buf->lock);
516
517 while (1) {
518 struct tty_buffer *head = buf->head;
519 struct tty_buffer *next;
520 int count;
521
522 /* Ldisc or user is trying to gain exclusive access */
523 if (atomic_read(&buf->priority))
524 break;
525
526 /* paired w/ release in __tty_buffer_request_room();
527 * ensures commit value read is not stale if the head
528 * is advancing to the next buffer
529 */
530 next = smp_load_acquire(&head->next);
531 /* paired w/ release in __tty_buffer_request_room() or in
532 * tty_buffer_flush(); ensures we see the committed buffer data
533 */
534 count = smp_load_acquire(&head->commit) - head->read;
535 if (!count) {
536 if (next == NULL)
537 break;
538 buf->head = next;
539 tty_buffer_free(port, head);
540 continue;
541 }
542
543 count = receive_buf(port, head, count);
544 if (!count)
545 break;
546 head->read += count;
547 }
548
549 mutex_unlock(&buf->lock);
550
551}
552
553/**
554 * tty_flip_buffer_push - terminal
555 * @port: tty port to push
556 *
557 * Queue a push of the terminal flip buffers to the line discipline.
558 * Can be called from IRQ/atomic context.
559 *
560 * In the event of the queue being busy for flipping the work will be
561 * held off and retried later.
562 */
563
564void tty_flip_buffer_push(struct tty_port *port)
565{
566 tty_schedule_flip(port);
567}
568EXPORT_SYMBOL(tty_flip_buffer_push);
569
570/**
571 * tty_buffer_init - prepare a tty buffer structure
572 * @port: tty port to initialise
573 *
574 * Set up the initial state of the buffer management for a tty device.
575 * Must be called before the other tty buffer functions are used.
576 */
577
578void tty_buffer_init(struct tty_port *port)
579{
580 struct tty_bufhead *buf = &port->buf;
581
582 mutex_init(&buf->lock);
583 tty_buffer_reset(&buf->sentinel, 0);
584 buf->head = &buf->sentinel;
585 buf->tail = &buf->sentinel;
586 init_llist_head(&buf->free);
587 atomic_set(&buf->mem_used, 0);
588 atomic_set(&buf->priority, 0);
589 INIT_WORK(&buf->work, flush_to_ldisc);
590 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
591}
592
593/**
594 * tty_buffer_set_limit - change the tty buffer memory limit
595 * @port: tty port to change
596 * @limit: memory limit to set
597 *
598 * Change the tty buffer memory limit.
599 * Must be called before the other tty buffer functions are used.
600 */
601
602int tty_buffer_set_limit(struct tty_port *port, int limit)
603{
604 if (limit < MIN_TTYB_SIZE)
605 return -EINVAL;
606 port->buf.mem_limit = limit;
607 return 0;
608}
609EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
610
611/* slave ptys can claim nested buffer lock when handling BRK and INTR */
612void tty_buffer_set_lock_subclass(struct tty_port *port)
613{
614 lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
615}
616
617bool tty_buffer_restart_work(struct tty_port *port)
618{
619 return queue_work(system_unbound_wq, &port->buf.work);
620}
621
622bool tty_buffer_cancel_work(struct tty_port *port)
623{
624 return cancel_work_sync(&port->buf.work);
625}
626
627void tty_buffer_flush_work(struct tty_port *port)
628{
629 flush_work(&port->buf.work);
630}