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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 bool restart = buf->head->commit != buf->head->read;
73
74 atomic_dec(&buf->priority);
75 mutex_unlock(&buf->lock);
76
77 if (restart)
78 queue_work(system_unbound_wq, &buf->work);
79}
80EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
81
82/**
83 * tty_buffer_space_avail - return unused buffer space
84 * @port: tty port owning the flip buffer
85 *
86 * Returns: the # of bytes which can be written by the driver without reaching
87 * the buffer limit.
88 *
89 * Note: this does not guarantee that memory is available to write the returned
90 * # of bytes (use tty_prepare_flip_string() to pre-allocate if memory
91 * guarantee is required).
92 */
93unsigned int tty_buffer_space_avail(struct tty_port *port)
94{
95 int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
96
97 return max(space, 0);
98}
99EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
100
101static void tty_buffer_reset(struct tty_buffer *p, size_t size)
102{
103 p->used = 0;
104 p->size = size;
105 p->next = NULL;
106 p->commit = 0;
107 p->lookahead = 0;
108 p->read = 0;
109 p->flags = true;
110}
111
112/**
113 * tty_buffer_free_all - free buffers used by a tty
114 * @port: tty port to free from
115 *
116 * Remove all the buffers pending on a tty whether queued with data or in the
117 * free ring. Must be called when the tty is no longer in use.
118 */
119void tty_buffer_free_all(struct tty_port *port)
120{
121 struct tty_bufhead *buf = &port->buf;
122 struct tty_buffer *p, *next;
123 struct llist_node *llist;
124 unsigned int freed = 0;
125 int still_used;
126
127 while ((p = buf->head) != NULL) {
128 buf->head = p->next;
129 freed += p->size;
130 if (p->size > 0)
131 kfree(p);
132 }
133 llist = llist_del_all(&buf->free);
134 llist_for_each_entry_safe(p, next, llist, free)
135 kfree(p);
136
137 tty_buffer_reset(&buf->sentinel, 0);
138 buf->head = &buf->sentinel;
139 buf->tail = &buf->sentinel;
140
141 still_used = atomic_xchg(&buf->mem_used, 0);
142 WARN(still_used != freed, "we still have not freed %d bytes!",
143 still_used - freed);
144}
145
146/**
147 * tty_buffer_alloc - allocate a tty buffer
148 * @port: tty port
149 * @size: desired size (characters)
150 *
151 * Allocate a new tty buffer to hold the desired number of characters. We
152 * round our buffers off in 256 character chunks to get better allocation
153 * behaviour.
154 *
155 * Returns: %NULL if out of memory or the allocation would exceed the per
156 * device queue.
157 */
158static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
159{
160 struct llist_node *free;
161 struct tty_buffer *p;
162
163 /* Round the buffer size out */
164 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
165
166 if (size <= MIN_TTYB_SIZE) {
167 free = llist_del_first(&port->buf.free);
168 if (free) {
169 p = llist_entry(free, struct tty_buffer, free);
170 goto found;
171 }
172 }
173
174 /* Should possibly check if this fails for the largest buffer we
175 * have queued and recycle that ?
176 */
177 if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
178 return NULL;
179 p = kmalloc(struct_size(p, data, 2 * size), GFP_ATOMIC | __GFP_NOWARN);
180 if (p == NULL)
181 return NULL;
182
183found:
184 tty_buffer_reset(p, size);
185 atomic_add(size, &port->buf.mem_used);
186 return p;
187}
188
189/**
190 * tty_buffer_free - free a tty buffer
191 * @port: tty port owning the buffer
192 * @b: the buffer to free
193 *
194 * Free a tty buffer, or add it to the free list according to our internal
195 * strategy.
196 */
197static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
198{
199 struct tty_bufhead *buf = &port->buf;
200
201 /* Dumb strategy for now - should keep some stats */
202 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
203
204 if (b->size > MIN_TTYB_SIZE)
205 kfree(b);
206 else if (b->size > 0)
207 llist_add(&b->free, &buf->free);
208}
209
210/**
211 * tty_buffer_flush - flush full tty buffers
212 * @tty: tty to flush
213 * @ld: optional ldisc ptr (must be referenced)
214 *
215 * Flush all the buffers containing receive data. If @ld != %NULL, flush the
216 * ldisc input buffer.
217 *
218 * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
219 */
220void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
221{
222 struct tty_port *port = tty->port;
223 struct tty_bufhead *buf = &port->buf;
224 struct tty_buffer *next;
225
226 atomic_inc(&buf->priority);
227
228 mutex_lock(&buf->lock);
229 /* paired w/ release in __tty_buffer_request_room; ensures there are
230 * no pending memory accesses to the freed buffer
231 */
232 while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
233 tty_buffer_free(port, buf->head);
234 buf->head = next;
235 }
236 buf->head->read = buf->head->commit;
237 buf->head->lookahead = buf->head->read;
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 has to store flags along character data
251 *
252 * Make at least @size bytes of linear space available for the tty buffer.
253 *
254 * Will change over to a new buffer if the current buffer is encoded as
255 * %TTY_NORMAL (so has no flags buffer) and the new buffer requires a flags
256 * buffer.
257 *
258 * Returns: the size we managed to find.
259 */
260static int __tty_buffer_request_room(struct tty_port *port, size_t size,
261 bool flags)
262{
263 struct tty_bufhead *buf = &port->buf;
264 struct tty_buffer *n, *b = buf->tail;
265 size_t left = (b->flags ? 1 : 2) * b->size - b->used;
266 bool change = !b->flags && flags;
267
268 if (!change && left >= size)
269 return size;
270
271 /* This is the slow path - looking for new buffers to use */
272 n = tty_buffer_alloc(port, size);
273 if (n == NULL)
274 return change ? 0 : left;
275
276 n->flags = flags;
277 buf->tail = n;
278 /*
279 * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
280 * ensures they see all buffer data.
281 */
282 smp_store_release(&b->commit, b->used);
283 /*
284 * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
285 * ensures the latest commit value can be read before the head
286 * is advanced to the next buffer.
287 */
288 smp_store_release(&b->next, n);
289
290 return size;
291}
292
293int tty_buffer_request_room(struct tty_port *port, size_t size)
294{
295 return __tty_buffer_request_room(port, size, true);
296}
297EXPORT_SYMBOL_GPL(tty_buffer_request_room);
298
299size_t __tty_insert_flip_string_flags(struct tty_port *port, const u8 *chars,
300 const u8 *flags, bool mutable_flags,
301 size_t size)
302{
303 bool need_flags = mutable_flags || flags[0] != TTY_NORMAL;
304 size_t copied = 0;
305
306 do {
307 size_t goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
308 size_t space = __tty_buffer_request_room(port, goal, need_flags);
309 struct tty_buffer *tb = port->buf.tail;
310
311 if (unlikely(space == 0))
312 break;
313
314 memcpy(char_buf_ptr(tb, tb->used), chars, space);
315
316 if (mutable_flags) {
317 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
318 flags += space;
319 } else if (tb->flags) {
320 memset(flag_buf_ptr(tb, tb->used), flags[0], space);
321 } else {
322 /* tb->flags should be available once requested */
323 WARN_ON_ONCE(need_flags);
324 }
325
326 tb->used += space;
327 copied += space;
328 chars += space;
329
330 /* There is a small chance that we need to split the data over
331 * several buffers. If this is the case we must loop.
332 */
333 } while (unlikely(size > copied));
334
335 return copied;
336}
337EXPORT_SYMBOL(__tty_insert_flip_string_flags);
338
339/**
340 * tty_prepare_flip_string - make room for characters
341 * @port: tty port
342 * @chars: return pointer for character write area
343 * @size: desired size
344 *
345 * Prepare a block of space in the buffer for data.
346 *
347 * This is used for drivers that need their own block copy routines into the
348 * buffer. There is no guarantee the buffer is a DMA target!
349 *
350 * Returns: the length available and buffer pointer (@chars) to the space which
351 * is now allocated and accounted for as ready for normal characters.
352 */
353size_t tty_prepare_flip_string(struct tty_port *port, u8 **chars, size_t size)
354{
355 size_t space = __tty_buffer_request_room(port, size, false);
356
357 if (likely(space)) {
358 struct tty_buffer *tb = port->buf.tail;
359
360 *chars = char_buf_ptr(tb, tb->used);
361 if (tb->flags)
362 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
363 tb->used += space;
364 }
365
366 return space;
367}
368EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
369
370/**
371 * tty_ldisc_receive_buf - forward data to line discipline
372 * @ld: line discipline to process input
373 * @p: char buffer
374 * @f: %TTY_NORMAL, %TTY_BREAK, etc. flags buffer
375 * @count: number of bytes to process
376 *
377 * Callers other than flush_to_ldisc() need to exclude the kworker from
378 * concurrent use of the line discipline, see paste_selection().
379 *
380 * Returns: the number of bytes processed.
381 */
382size_t tty_ldisc_receive_buf(struct tty_ldisc *ld, const u8 *p, const u8 *f,
383 size_t count)
384{
385 if (ld->ops->receive_buf2)
386 count = ld->ops->receive_buf2(ld->tty, p, f, count);
387 else {
388 count = min_t(size_t, count, ld->tty->receive_room);
389 if (count && ld->ops->receive_buf)
390 ld->ops->receive_buf(ld->tty, p, f, count);
391 }
392 return count;
393}
394EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
395
396static void lookahead_bufs(struct tty_port *port, struct tty_buffer *head)
397{
398 head->lookahead = max(head->lookahead, head->read);
399
400 while (head) {
401 struct tty_buffer *next;
402 unsigned int count;
403
404 /*
405 * Paired w/ release in __tty_buffer_request_room();
406 * ensures commit value read is not stale if the head
407 * is advancing to the next buffer.
408 */
409 next = smp_load_acquire(&head->next);
410 /*
411 * Paired w/ release in __tty_buffer_request_room() or in
412 * tty_buffer_flush(); ensures we see the committed buffer data.
413 */
414 count = smp_load_acquire(&head->commit) - head->lookahead;
415 if (!count) {
416 head = next;
417 continue;
418 }
419
420 if (port->client_ops->lookahead_buf) {
421 u8 *p, *f = NULL;
422
423 p = char_buf_ptr(head, head->lookahead);
424 if (head->flags)
425 f = flag_buf_ptr(head, head->lookahead);
426
427 port->client_ops->lookahead_buf(port, p, f, count);
428 }
429
430 head->lookahead += count;
431 }
432}
433
434static size_t
435receive_buf(struct tty_port *port, struct tty_buffer *head, size_t count)
436{
437 u8 *p = char_buf_ptr(head, head->read);
438 const u8 *f = NULL;
439 size_t n;
440
441 if (head->flags)
442 f = flag_buf_ptr(head, head->read);
443
444 n = port->client_ops->receive_buf(port, p, f, count);
445 if (n > 0)
446 memset(p, 0, n);
447 return n;
448}
449
450/**
451 * flush_to_ldisc - flush data from buffer to ldisc
452 * @work: tty structure passed from work queue.
453 *
454 * This routine is called out of the software interrupt to flush data from the
455 * buffer chain to the line discipline.
456 *
457 * The receive_buf() method is single threaded for each tty instance.
458 *
459 * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
460 */
461static void flush_to_ldisc(struct work_struct *work)
462{
463 struct tty_port *port = container_of(work, struct tty_port, buf.work);
464 struct tty_bufhead *buf = &port->buf;
465
466 mutex_lock(&buf->lock);
467
468 while (1) {
469 struct tty_buffer *head = buf->head;
470 struct tty_buffer *next;
471 size_t count, rcvd;
472
473 /* Ldisc or user is trying to gain exclusive access */
474 if (atomic_read(&buf->priority))
475 break;
476
477 /* paired w/ release in __tty_buffer_request_room();
478 * ensures commit value read is not stale if the head
479 * is advancing to the next buffer
480 */
481 next = smp_load_acquire(&head->next);
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->read;
486 if (!count) {
487 if (next == NULL)
488 break;
489 buf->head = next;
490 tty_buffer_free(port, head);
491 continue;
492 }
493
494 rcvd = receive_buf(port, head, count);
495 head->read += rcvd;
496 if (rcvd < count)
497 lookahead_bufs(port, head);
498 if (!rcvd)
499 break;
500
501 if (need_resched())
502 cond_resched();
503 }
504
505 mutex_unlock(&buf->lock);
506
507}
508
509static inline void tty_flip_buffer_commit(struct tty_buffer *tail)
510{
511 /*
512 * Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
513 * buffer data.
514 */
515 smp_store_release(&tail->commit, tail->used);
516}
517
518/**
519 * tty_flip_buffer_push - push terminal buffers
520 * @port: tty port to push
521 *
522 * Queue a push of the terminal flip buffers to the line discipline. Can be
523 * called from IRQ/atomic context.
524 *
525 * In the event of the queue being busy for flipping the work will be held off
526 * and retried later.
527 */
528void tty_flip_buffer_push(struct tty_port *port)
529{
530 struct tty_bufhead *buf = &port->buf;
531
532 tty_flip_buffer_commit(buf->tail);
533 queue_work(system_unbound_wq, &buf->work);
534}
535EXPORT_SYMBOL(tty_flip_buffer_push);
536
537/**
538 * tty_insert_flip_string_and_push_buffer - add characters to the tty buffer and
539 * push
540 * @port: tty port
541 * @chars: characters
542 * @size: size
543 *
544 * The function combines tty_insert_flip_string() and tty_flip_buffer_push()
545 * with the exception of properly holding the @port->lock.
546 *
547 * To be used only internally (by pty currently).
548 *
549 * Returns: the number added.
550 */
551int tty_insert_flip_string_and_push_buffer(struct tty_port *port,
552 const u8 *chars, size_t size)
553{
554 struct tty_bufhead *buf = &port->buf;
555 unsigned long flags;
556
557 spin_lock_irqsave(&port->lock, flags);
558 size = tty_insert_flip_string(port, chars, size);
559 if (size)
560 tty_flip_buffer_commit(buf->tail);
561 spin_unlock_irqrestore(&port->lock, flags);
562
563 queue_work(system_unbound_wq, &buf->work);
564
565 return size;
566}
567
568/**
569 * tty_buffer_init - prepare a tty buffer structure
570 * @port: tty port to initialise
571 *
572 * Set up the initial state of the buffer management for a tty device. Must be
573 * called before the other tty buffer functions are used.
574 */
575void tty_buffer_init(struct tty_port *port)
576{
577 struct tty_bufhead *buf = &port->buf;
578
579 mutex_init(&buf->lock);
580 tty_buffer_reset(&buf->sentinel, 0);
581 buf->head = &buf->sentinel;
582 buf->tail = &buf->sentinel;
583 init_llist_head(&buf->free);
584 atomic_set(&buf->mem_used, 0);
585 atomic_set(&buf->priority, 0);
586 INIT_WORK(&buf->work, flush_to_ldisc);
587 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
588}
589
590/**
591 * tty_buffer_set_limit - change the tty buffer memory limit
592 * @port: tty port to change
593 * @limit: memory limit to set
594 *
595 * Change the tty buffer memory limit.
596 *
597 * Must be called before the other tty buffer functions are used.
598 */
599int tty_buffer_set_limit(struct tty_port *port, int limit)
600{
601 if (limit < MIN_TTYB_SIZE)
602 return -EINVAL;
603 port->buf.mem_limit = limit;
604 return 0;
605}
606EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
607
608/* slave ptys can claim nested buffer lock when handling BRK and INTR */
609void tty_buffer_set_lock_subclass(struct tty_port *port)
610{
611 lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
612}
613
614bool tty_buffer_restart_work(struct tty_port *port)
615{
616 return queue_work(system_unbound_wq, &port->buf.work);
617}
618
619bool tty_buffer_cancel_work(struct tty_port *port)
620{
621 return cancel_work_sync(&port->buf.work);
622}
623
624void tty_buffer_flush_work(struct tty_port *port)
625{
626 flush_work(&port->buf.work);
627}
1/*
2 * Tty buffer allocation management
3 */
4
5#include <linux/types.h>
6#include <linux/errno.h>
7#include <linux/tty.h>
8#include <linux/tty_driver.h>
9#include <linux/tty_flip.h>
10#include <linux/timer.h>
11#include <linux/string.h>
12#include <linux/slab.h>
13#include <linux/sched.h>
14#include <linux/wait.h>
15#include <linux/bitops.h>
16#include <linux/delay.h>
17#include <linux/module.h>
18#include <linux/ratelimit.h>
19
20
21#define MIN_TTYB_SIZE 256
22#define TTYB_ALIGN_MASK 255
23
24/*
25 * Byte threshold to limit memory consumption for flip buffers.
26 * The actual memory limit is > 2x this amount.
27 */
28#define TTYB_DEFAULT_MEM_LIMIT 65536
29
30/*
31 * We default to dicing tty buffer allocations to this many characters
32 * in order to avoid multiple page allocations. We know the size of
33 * tty_buffer itself but it must also be taken into account that the
34 * the buffer is 256 byte aligned. See tty_buffer_find for the allocation
35 * logic this must match
36 */
37
38#define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
39
40/*
41 * If all tty flip buffers have been processed by flush_to_ldisc() or
42 * dropped by tty_buffer_flush(), check if the linked pty has been closed.
43 * If so, wake the reader/poll to process
44 */
45static inline void check_other_closed(struct tty_struct *tty)
46{
47 unsigned long flags, old;
48
49 /* transition from TTY_OTHER_CLOSED => TTY_OTHER_DONE must be atomic */
50 for (flags = ACCESS_ONCE(tty->flags);
51 test_bit(TTY_OTHER_CLOSED, &flags);
52 ) {
53 old = flags;
54 __set_bit(TTY_OTHER_DONE, &flags);
55 flags = cmpxchg(&tty->flags, old, flags);
56 if (old == flags) {
57 wake_up_interruptible(&tty->read_wait);
58 break;
59 }
60 }
61}
62
63/**
64 * tty_buffer_lock_exclusive - gain exclusive access to buffer
65 * tty_buffer_unlock_exclusive - release exclusive access
66 *
67 * @port - tty_port owning the flip buffer
68 *
69 * Guarantees safe use of the line discipline's receive_buf() method by
70 * excluding the buffer work and any pending flush from using the flip
71 * buffer. Data can continue to be added concurrently to the flip buffer
72 * from the driver side.
73 *
74 * On release, the buffer work is restarted if there is data in the
75 * flip buffer
76 */
77
78void tty_buffer_lock_exclusive(struct tty_port *port)
79{
80 struct tty_bufhead *buf = &port->buf;
81
82 atomic_inc(&buf->priority);
83 mutex_lock(&buf->lock);
84}
85EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
86
87void tty_buffer_unlock_exclusive(struct tty_port *port)
88{
89 struct tty_bufhead *buf = &port->buf;
90 int restart;
91
92 restart = buf->head->commit != buf->head->read;
93
94 atomic_dec(&buf->priority);
95 mutex_unlock(&buf->lock);
96 if (restart)
97 queue_work(system_unbound_wq, &buf->work);
98}
99EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
100
101/**
102 * tty_buffer_space_avail - return unused buffer space
103 * @port - tty_port owning the flip buffer
104 *
105 * Returns the # of bytes which can be written by the driver without
106 * reaching the buffer limit.
107 *
108 * Note: this does not guarantee that memory is available to write
109 * the returned # of bytes (use tty_prepare_flip_string_xxx() to
110 * pre-allocate if memory guarantee is required).
111 */
112
113int tty_buffer_space_avail(struct tty_port *port)
114{
115 int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
116 return max(space, 0);
117}
118EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
119
120static void tty_buffer_reset(struct tty_buffer *p, size_t size)
121{
122 p->used = 0;
123 p->size = size;
124 p->next = NULL;
125 p->commit = 0;
126 p->read = 0;
127 p->flags = 0;
128}
129
130/**
131 * tty_buffer_free_all - free buffers used by a tty
132 * @tty: tty to free from
133 *
134 * Remove all the buffers pending on a tty whether queued with data
135 * or in the free ring. Must be called when the tty is no longer in use
136 */
137
138void tty_buffer_free_all(struct tty_port *port)
139{
140 struct tty_bufhead *buf = &port->buf;
141 struct tty_buffer *p, *next;
142 struct llist_node *llist;
143
144 while ((p = buf->head) != NULL) {
145 buf->head = p->next;
146 if (p->size > 0)
147 kfree(p);
148 }
149 llist = llist_del_all(&buf->free);
150 llist_for_each_entry_safe(p, next, llist, free)
151 kfree(p);
152
153 tty_buffer_reset(&buf->sentinel, 0);
154 buf->head = &buf->sentinel;
155 buf->tail = &buf->sentinel;
156
157 atomic_set(&buf->mem_used, 0);
158}
159
160/**
161 * tty_buffer_alloc - allocate a tty buffer
162 * @tty: tty device
163 * @size: desired size (characters)
164 *
165 * Allocate a new tty buffer to hold the desired number of characters.
166 * We round our buffers off in 256 character chunks to get better
167 * allocation behaviour.
168 * Return NULL if out of memory or the allocation would exceed the
169 * per device queue
170 */
171
172static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
173{
174 struct llist_node *free;
175 struct tty_buffer *p;
176
177 /* Round the buffer size out */
178 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
179
180 if (size <= MIN_TTYB_SIZE) {
181 free = llist_del_first(&port->buf.free);
182 if (free) {
183 p = llist_entry(free, struct tty_buffer, free);
184 goto found;
185 }
186 }
187
188 /* Should possibly check if this fails for the largest buffer we
189 have queued and recycle that ? */
190 if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
191 return NULL;
192 p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
193 if (p == NULL)
194 return NULL;
195
196found:
197 tty_buffer_reset(p, size);
198 atomic_add(size, &port->buf.mem_used);
199 return p;
200}
201
202/**
203 * tty_buffer_free - free a tty buffer
204 * @tty: tty owning the buffer
205 * @b: the buffer to free
206 *
207 * Free a tty buffer, or add it to the free list according to our
208 * internal strategy
209 */
210
211static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
212{
213 struct tty_bufhead *buf = &port->buf;
214
215 /* Dumb strategy for now - should keep some stats */
216 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
217
218 if (b->size > MIN_TTYB_SIZE)
219 kfree(b);
220 else if (b->size > 0)
221 llist_add(&b->free, &buf->free);
222}
223
224/**
225 * tty_buffer_flush - flush full tty buffers
226 * @tty: tty to flush
227 * @ld: optional ldisc ptr (must be referenced)
228 *
229 * flush all the buffers containing receive data. If ld != NULL,
230 * flush the ldisc input buffer.
231 *
232 * Locking: takes buffer lock to ensure single-threaded flip buffer
233 * 'consumer'
234 */
235
236void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
237{
238 struct tty_port *port = tty->port;
239 struct tty_bufhead *buf = &port->buf;
240 struct tty_buffer *next;
241
242 atomic_inc(&buf->priority);
243
244 mutex_lock(&buf->lock);
245 /* paired w/ release in __tty_buffer_request_room; ensures there are
246 * no pending memory accesses to the freed buffer
247 */
248 while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
249 tty_buffer_free(port, buf->head);
250 buf->head = next;
251 }
252 buf->head->read = buf->head->commit;
253
254 if (ld && ld->ops->flush_buffer)
255 ld->ops->flush_buffer(tty);
256
257 check_other_closed(tty);
258
259 atomic_dec(&buf->priority);
260 mutex_unlock(&buf->lock);
261}
262
263/**
264 * tty_buffer_request_room - grow tty buffer if needed
265 * @tty: tty structure
266 * @size: size desired
267 * @flags: buffer flags if new buffer allocated (default = 0)
268 *
269 * Make at least size bytes of linear space available for the tty
270 * buffer. If we fail return the size we managed to find.
271 *
272 * Will change over to a new buffer if the current buffer is encoded as
273 * TTY_NORMAL (so has no flags buffer) and the new buffer requires
274 * a flags buffer.
275 */
276static int __tty_buffer_request_room(struct tty_port *port, size_t size,
277 int flags)
278{
279 struct tty_bufhead *buf = &port->buf;
280 struct tty_buffer *b, *n;
281 int left, change;
282
283 b = buf->tail;
284 if (b->flags & TTYB_NORMAL)
285 left = 2 * b->size - b->used;
286 else
287 left = b->size - b->used;
288
289 change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
290 if (change || left < size) {
291 /* This is the slow path - looking for new buffers to use */
292 n = tty_buffer_alloc(port, size);
293 if (n != NULL) {
294 n->flags = flags;
295 buf->tail = n;
296 /* paired w/ acquire in flush_to_ldisc(); ensures
297 * flush_to_ldisc() sees buffer data.
298 */
299 smp_store_release(&b->commit, b->used);
300 /* paired w/ acquire in flush_to_ldisc(); ensures the
301 * latest commit value can be read before the head is
302 * advanced to the next buffer
303 */
304 smp_store_release(&b->next, n);
305 } else if (change)
306 size = 0;
307 else
308 size = left;
309 }
310 return size;
311}
312
313int tty_buffer_request_room(struct tty_port *port, size_t size)
314{
315 return __tty_buffer_request_room(port, size, 0);
316}
317EXPORT_SYMBOL_GPL(tty_buffer_request_room);
318
319/**
320 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
321 * @port: tty port
322 * @chars: characters
323 * @flag: flag value for each character
324 * @size: size
325 *
326 * Queue a series of bytes to the tty buffering. All the characters
327 * passed are marked with the supplied flag. Returns the number added.
328 */
329
330int tty_insert_flip_string_fixed_flag(struct tty_port *port,
331 const unsigned char *chars, char flag, size_t size)
332{
333 int copied = 0;
334 do {
335 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
336 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
337 int space = __tty_buffer_request_room(port, goal, flags);
338 struct tty_buffer *tb = port->buf.tail;
339 if (unlikely(space == 0))
340 break;
341 memcpy(char_buf_ptr(tb, tb->used), chars, space);
342 if (~tb->flags & TTYB_NORMAL)
343 memset(flag_buf_ptr(tb, tb->used), flag, space);
344 tb->used += space;
345 copied += space;
346 chars += space;
347 /* There is a small chance that we need to split the data over
348 several buffers. If this is the case we must loop */
349 } while (unlikely(size > copied));
350 return copied;
351}
352EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
353
354/**
355 * tty_insert_flip_string_flags - Add characters to the tty buffer
356 * @port: tty port
357 * @chars: characters
358 * @flags: flag bytes
359 * @size: size
360 *
361 * Queue a series of bytes to the tty buffering. For each character
362 * the flags array indicates the status of the character. Returns the
363 * number added.
364 */
365
366int tty_insert_flip_string_flags(struct tty_port *port,
367 const unsigned char *chars, const char *flags, size_t size)
368{
369 int copied = 0;
370 do {
371 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
372 int space = tty_buffer_request_room(port, goal);
373 struct tty_buffer *tb = port->buf.tail;
374 if (unlikely(space == 0))
375 break;
376 memcpy(char_buf_ptr(tb, tb->used), chars, space);
377 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
378 tb->used += space;
379 copied += space;
380 chars += space;
381 flags += space;
382 /* There is a small chance that we need to split the data over
383 several buffers. If this is the case we must loop */
384 } while (unlikely(size > copied));
385 return copied;
386}
387EXPORT_SYMBOL(tty_insert_flip_string_flags);
388
389/**
390 * tty_schedule_flip - push characters to ldisc
391 * @port: tty port to push from
392 *
393 * Takes any pending buffers and transfers their ownership to the
394 * ldisc side of the queue. It then schedules those characters for
395 * processing by the line discipline.
396 */
397
398void tty_schedule_flip(struct tty_port *port)
399{
400 struct tty_bufhead *buf = &port->buf;
401
402 /* paired w/ acquire in flush_to_ldisc(); ensures
403 * flush_to_ldisc() sees buffer data.
404 */
405 smp_store_release(&buf->tail->commit, buf->tail->used);
406 queue_work(system_unbound_wq, &buf->work);
407}
408EXPORT_SYMBOL(tty_schedule_flip);
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. Returns the length
417 * available and buffer pointer to the space which is now allocated and
418 * accounted for as ready for normal characters. This is used for drivers
419 * that need their own block copy routines into the buffer. There is no
420 * guarantee the buffer is a DMA target!
421 */
422
423int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
424 size_t size)
425{
426 int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
427 if (likely(space)) {
428 struct tty_buffer *tb = port->buf.tail;
429 *chars = char_buf_ptr(tb, tb->used);
430 if (~tb->flags & TTYB_NORMAL)
431 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
432 tb->used += space;
433 }
434 return space;
435}
436EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
437
438/**
439 * tty_ldisc_receive_buf - forward data to line discipline
440 * @ld: line discipline to process input
441 * @p: char buffer
442 * @f: TTY_* flags buffer
443 * @count: number of bytes to process
444 *
445 * Callers other than flush_to_ldisc() need to exclude the kworker
446 * from concurrent use of the line discipline, see paste_selection().
447 *
448 * Returns the number of bytes not processed
449 */
450int tty_ldisc_receive_buf(struct tty_ldisc *ld, unsigned char *p,
451 char *f, int count)
452{
453 if (ld->ops->receive_buf2)
454 count = ld->ops->receive_buf2(ld->tty, p, f, count);
455 else {
456 count = min_t(int, count, ld->tty->receive_room);
457 if (count && ld->ops->receive_buf)
458 ld->ops->receive_buf(ld->tty, p, f, count);
459 }
460 return count;
461}
462EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
463
464static int
465receive_buf(struct tty_ldisc *ld, struct tty_buffer *head, int count)
466{
467 unsigned char *p = char_buf_ptr(head, head->read);
468 char *f = NULL;
469
470 if (~head->flags & TTYB_NORMAL)
471 f = flag_buf_ptr(head, head->read);
472
473 return tty_ldisc_receive_buf(ld, p, f, count);
474}
475
476/**
477 * flush_to_ldisc
478 * @work: tty structure passed from work queue.
479 *
480 * This routine is called out of the software interrupt to flush data
481 * from the buffer chain to the line discipline.
482 *
483 * The receive_buf method is single threaded for each tty instance.
484 *
485 * Locking: takes buffer lock to ensure single-threaded flip buffer
486 * 'consumer'
487 */
488
489static void flush_to_ldisc(struct work_struct *work)
490{
491 struct tty_port *port = container_of(work, struct tty_port, buf.work);
492 struct tty_bufhead *buf = &port->buf;
493 struct tty_struct *tty;
494 struct tty_ldisc *disc;
495
496 tty = READ_ONCE(port->itty);
497 if (tty == NULL)
498 return;
499
500 disc = tty_ldisc_ref(tty);
501 if (disc == NULL)
502 return;
503
504 mutex_lock(&buf->lock);
505
506 while (1) {
507 struct tty_buffer *head = buf->head;
508 struct tty_buffer *next;
509 int count;
510
511 /* Ldisc or user is trying to gain exclusive access */
512 if (atomic_read(&buf->priority))
513 break;
514
515 /* paired w/ release in __tty_buffer_request_room();
516 * ensures commit value read is not stale if the head
517 * is advancing to the next buffer
518 */
519 next = smp_load_acquire(&head->next);
520 /* paired w/ release in __tty_buffer_request_room() or in
521 * tty_buffer_flush(); ensures we see the committed buffer data
522 */
523 count = smp_load_acquire(&head->commit) - head->read;
524 if (!count) {
525 if (next == NULL) {
526 check_other_closed(tty);
527 break;
528 }
529 buf->head = next;
530 tty_buffer_free(port, head);
531 continue;
532 }
533
534 count = receive_buf(disc, head, count);
535 if (!count)
536 break;
537 head->read += count;
538 }
539
540 mutex_unlock(&buf->lock);
541
542 tty_ldisc_deref(disc);
543}
544
545/**
546 * tty_flip_buffer_push - terminal
547 * @port: tty port to push
548 *
549 * Queue a push of the terminal flip buffers to the line discipline.
550 * Can be called from IRQ/atomic context.
551 *
552 * In the event of the queue being busy for flipping the work will be
553 * held off and retried later.
554 */
555
556void tty_flip_buffer_push(struct tty_port *port)
557{
558 tty_schedule_flip(port);
559}
560EXPORT_SYMBOL(tty_flip_buffer_push);
561
562/**
563 * tty_buffer_init - prepare a tty buffer structure
564 * @tty: tty to initialise
565 *
566 * Set up the initial state of the buffer management for a tty device.
567 * Must be called before the other tty buffer functions are used.
568 */
569
570void tty_buffer_init(struct tty_port *port)
571{
572 struct tty_bufhead *buf = &port->buf;
573
574 mutex_init(&buf->lock);
575 tty_buffer_reset(&buf->sentinel, 0);
576 buf->head = &buf->sentinel;
577 buf->tail = &buf->sentinel;
578 init_llist_head(&buf->free);
579 atomic_set(&buf->mem_used, 0);
580 atomic_set(&buf->priority, 0);
581 INIT_WORK(&buf->work, flush_to_ldisc);
582 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
583}
584
585/**
586 * tty_buffer_set_limit - change the tty buffer memory limit
587 * @port: tty port to change
588 *
589 * Change the tty buffer memory limit.
590 * Must be called before the other tty buffer functions are used.
591 */
592
593int tty_buffer_set_limit(struct tty_port *port, int limit)
594{
595 if (limit < MIN_TTYB_SIZE)
596 return -EINVAL;
597 port->buf.mem_limit = limit;
598 return 0;
599}
600EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
601
602/* slave ptys can claim nested buffer lock when handling BRK and INTR */
603void tty_buffer_set_lock_subclass(struct tty_port *port)
604{
605 lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
606}
607
608bool tty_buffer_restart_work(struct tty_port *port)
609{
610 return queue_work(system_unbound_wq, &port->buf.work);
611}
612
613bool tty_buffer_cancel_work(struct tty_port *port)
614{
615 return cancel_work_sync(&port->buf.work);
616}