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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_buffer.h>
11#include <linux/tty_driver.h>
12#include <linux/tty_flip.h>
13#include <linux/timer.h>
14#include <linux/string.h>
15#include <linux/slab.h>
16#include <linux/sched.h>
17#include <linux/wait.h>
18#include <linux/bitops.h>
19#include <linux/delay.h>
20#include <linux/module.h>
21#include <linux/ratelimit.h>
22#include "tty.h"
23
24#define MIN_TTYB_SIZE 256
25#define TTYB_ALIGN_MASK 0xff
26
27/*
28 * Byte threshold to limit memory consumption for flip buffers.
29 * The actual memory limit is > 2x this amount.
30 */
31#define TTYB_DEFAULT_MEM_LIMIT (640 * 1024UL)
32
33/*
34 * We default to dicing tty buffer allocations to this many characters
35 * in order to avoid multiple page allocations. We know the size of
36 * tty_buffer itself but it must also be taken into account that the
37 * buffer is 256 byte aligned. See tty_buffer_find for the allocation
38 * logic this must match.
39 */
40
41#define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~TTYB_ALIGN_MASK)
42
43/**
44 * tty_buffer_lock_exclusive - gain exclusive access to buffer
45 * @port: tty port owning the flip buffer
46 *
47 * Guarantees safe use of the &tty_ldisc_ops.receive_buf() method by excluding
48 * the buffer work and any pending flush from using the flip buffer. Data can
49 * continue to be added concurrently to the flip buffer from the driver side.
50 *
51 * See also tty_buffer_unlock_exclusive().
52 */
53void tty_buffer_lock_exclusive(struct tty_port *port)
54{
55 struct tty_bufhead *buf = &port->buf;
56
57 atomic_inc(&buf->priority);
58 mutex_lock(&buf->lock);
59}
60EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
61
62/**
63 * tty_buffer_unlock_exclusive - release exclusive access
64 * @port: tty port owning the flip buffer
65 *
66 * The buffer work is restarted if there is data in the flip buffer.
67 *
68 * See also tty_buffer_lock_exclusive().
69 */
70void tty_buffer_unlock_exclusive(struct tty_port *port)
71{
72 struct tty_bufhead *buf = &port->buf;
73 bool restart = buf->head->commit != buf->head->read;
74
75 atomic_dec(&buf->priority);
76 mutex_unlock(&buf->lock);
77
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(struct_size(p, data, 2 * size), GFP_ATOMIC | __GFP_NOWARN);
181 if (p == NULL)
182 return NULL;
183
184found:
185 tty_buffer_reset(p, size);
186 atomic_add(size, &port->buf.mem_used);
187 return p;
188}
189
190/**
191 * tty_buffer_free - free a tty buffer
192 * @port: tty port owning the buffer
193 * @b: the buffer to free
194 *
195 * Free a tty buffer, or add it to the free list according to our internal
196 * strategy.
197 */
198static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
199{
200 struct tty_bufhead *buf = &port->buf;
201
202 /* Dumb strategy for now - should keep some stats */
203 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
204
205 if (b->size > MIN_TTYB_SIZE)
206 kfree(b);
207 else if (b->size > 0)
208 llist_add(&b->free, &buf->free);
209}
210
211/**
212 * tty_buffer_flush - flush full tty buffers
213 * @tty: tty to flush
214 * @ld: optional ldisc ptr (must be referenced)
215 *
216 * Flush all the buffers containing receive data. If @ld != %NULL, flush the
217 * ldisc input buffer.
218 *
219 * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
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 buf->head->lookahead = buf->head->read;
239
240 if (ld && ld->ops->flush_buffer)
241 ld->ops->flush_buffer(tty);
242
243 atomic_dec(&buf->priority);
244 mutex_unlock(&buf->lock);
245}
246
247/**
248 * __tty_buffer_request_room - grow tty buffer if needed
249 * @port: tty port
250 * @size: size desired
251 * @flags: buffer has to store flags along character data
252 *
253 * Make at least @size bytes of linear space available for the tty buffer.
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 a flags
257 * buffer.
258 *
259 * Returns: the size we managed to find.
260 */
261static int __tty_buffer_request_room(struct tty_port *port, size_t size,
262 bool flags)
263{
264 struct tty_bufhead *buf = &port->buf;
265 struct tty_buffer *n, *b = buf->tail;
266 size_t left = (b->flags ? 1 : 2) * b->size - b->used;
267 bool change = !b->flags && flags;
268
269 if (!change && left >= size)
270 return size;
271
272 /* This is the slow path - looking for new buffers to use */
273 n = tty_buffer_alloc(port, size);
274 if (n == NULL)
275 return change ? 0 : left;
276
277 n->flags = flags;
278 buf->tail = n;
279 /*
280 * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
281 * ensures they see all buffer data.
282 */
283 smp_store_release(&b->commit, b->used);
284 /*
285 * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
286 * ensures the latest commit value can be read before the head
287 * is advanced to the next buffer.
288 */
289 smp_store_release(&b->next, n);
290
291 return size;
292}
293
294int tty_buffer_request_room(struct tty_port *port, size_t size)
295{
296 return __tty_buffer_request_room(port, size, true);
297}
298EXPORT_SYMBOL_GPL(tty_buffer_request_room);
299
300size_t __tty_insert_flip_string_flags(struct tty_port *port, const u8 *chars,
301 const u8 *flags, bool mutable_flags,
302 size_t size)
303{
304 bool need_flags = mutable_flags || flags[0] != TTY_NORMAL;
305 size_t copied = 0;
306
307 do {
308 size_t goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
309 size_t space = __tty_buffer_request_room(port, goal, need_flags);
310 struct tty_buffer *tb = port->buf.tail;
311
312 if (unlikely(space == 0))
313 break;
314
315 memcpy(char_buf_ptr(tb, tb->used), chars, space);
316
317 if (mutable_flags) {
318 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
319 flags += space;
320 } else if (tb->flags) {
321 memset(flag_buf_ptr(tb, tb->used), flags[0], space);
322 } else {
323 /* tb->flags should be available once requested */
324 WARN_ON_ONCE(need_flags);
325 }
326
327 tb->used += space;
328 copied += space;
329 chars += space;
330
331 /* There is a small chance that we need to split the data over
332 * several buffers. If this is the case we must loop.
333 */
334 } while (unlikely(size > copied));
335
336 return copied;
337}
338EXPORT_SYMBOL(__tty_insert_flip_string_flags);
339
340/**
341 * tty_prepare_flip_string - make room for characters
342 * @port: tty port
343 * @chars: return pointer for character write area
344 * @size: desired size
345 *
346 * Prepare a block of space in the buffer for data.
347 *
348 * This is used for drivers that need their own block copy routines into the
349 * buffer. There is no guarantee the buffer is a DMA target!
350 *
351 * Returns: the length available and buffer pointer (@chars) to the space which
352 * is now allocated and accounted for as ready for normal characters.
353 */
354size_t tty_prepare_flip_string(struct tty_port *port, u8 **chars, size_t size)
355{
356 size_t space = __tty_buffer_request_room(port, size, false);
357
358 if (likely(space)) {
359 struct tty_buffer *tb = port->buf.tail;
360
361 *chars = char_buf_ptr(tb, tb->used);
362 if (tb->flags)
363 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
364 tb->used += space;
365 }
366
367 return space;
368}
369EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
370
371/**
372 * tty_ldisc_receive_buf - forward data to line discipline
373 * @ld: line discipline to process input
374 * @p: char buffer
375 * @f: %TTY_NORMAL, %TTY_BREAK, etc. flags buffer
376 * @count: number of bytes to process
377 *
378 * Callers other than flush_to_ldisc() need to exclude the kworker from
379 * concurrent use of the line discipline, see paste_selection().
380 *
381 * Returns: the number of bytes processed.
382 */
383size_t tty_ldisc_receive_buf(struct tty_ldisc *ld, const u8 *p, const u8 *f,
384 size_t count)
385{
386 if (ld->ops->receive_buf2)
387 count = ld->ops->receive_buf2(ld->tty, p, f, count);
388 else {
389 count = min_t(size_t, count, ld->tty->receive_room);
390 if (count && ld->ops->receive_buf)
391 ld->ops->receive_buf(ld->tty, p, f, count);
392 }
393 return count;
394}
395EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
396
397static void lookahead_bufs(struct tty_port *port, struct tty_buffer *head)
398{
399 head->lookahead = max(head->lookahead, head->read);
400
401 while (head) {
402 struct tty_buffer *next;
403 unsigned int count;
404
405 /*
406 * Paired w/ release in __tty_buffer_request_room();
407 * ensures commit value read is not stale if the head
408 * is advancing to the next buffer.
409 */
410 next = smp_load_acquire(&head->next);
411 /*
412 * Paired w/ release in __tty_buffer_request_room() or in
413 * tty_buffer_flush(); ensures we see the committed buffer data.
414 */
415 count = smp_load_acquire(&head->commit) - head->lookahead;
416 if (!count) {
417 head = next;
418 continue;
419 }
420
421 if (port->client_ops->lookahead_buf) {
422 u8 *p, *f = NULL;
423
424 p = char_buf_ptr(head, head->lookahead);
425 if (head->flags)
426 f = flag_buf_ptr(head, head->lookahead);
427
428 port->client_ops->lookahead_buf(port, p, f, count);
429 }
430
431 head->lookahead += count;
432 }
433}
434
435static size_t
436receive_buf(struct tty_port *port, struct tty_buffer *head, size_t count)
437{
438 u8 *p = char_buf_ptr(head, head->read);
439 const u8 *f = NULL;
440 size_t n;
441
442 if (head->flags)
443 f = flag_buf_ptr(head, head->read);
444
445 n = port->client_ops->receive_buf(port, p, f, count);
446 if (n > 0)
447 memset(p, 0, n);
448 return n;
449}
450
451/**
452 * flush_to_ldisc - flush data from buffer to ldisc
453 * @work: tty structure passed from work queue.
454 *
455 * This routine is called out of the software interrupt to flush data from the
456 * buffer chain to the line discipline.
457 *
458 * The receive_buf() method is single threaded for each tty instance.
459 *
460 * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
461 */
462static void flush_to_ldisc(struct work_struct *work)
463{
464 struct tty_port *port = container_of(work, struct tty_port, buf.work);
465 struct tty_bufhead *buf = &port->buf;
466
467 mutex_lock(&buf->lock);
468
469 while (1) {
470 struct tty_buffer *head = buf->head;
471 struct tty_buffer *next;
472 size_t count, rcvd;
473
474 /* Ldisc or user is trying to gain exclusive access */
475 if (atomic_read(&buf->priority))
476 break;
477
478 /* paired w/ release in __tty_buffer_request_room();
479 * ensures commit value read is not stale if the head
480 * is advancing to the next buffer
481 */
482 next = smp_load_acquire(&head->next);
483 /* paired w/ release in __tty_buffer_request_room() or in
484 * tty_buffer_flush(); ensures we see the committed buffer data
485 */
486 count = smp_load_acquire(&head->commit) - head->read;
487 if (!count) {
488 if (next == NULL)
489 break;
490 buf->head = next;
491 tty_buffer_free(port, head);
492 continue;
493 }
494
495 rcvd = receive_buf(port, head, count);
496 head->read += rcvd;
497 if (rcvd < count)
498 lookahead_bufs(port, head);
499 if (!rcvd)
500 break;
501
502 if (need_resched())
503 cond_resched();
504 }
505
506 mutex_unlock(&buf->lock);
507
508}
509
510static inline void tty_flip_buffer_commit(struct tty_buffer *tail)
511{
512 /*
513 * Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
514 * buffer data.
515 */
516 smp_store_release(&tail->commit, tail->used);
517}
518
519/**
520 * tty_flip_buffer_push - push terminal buffers
521 * @port: tty port to push
522 *
523 * Queue a push of the terminal flip buffers to the line discipline. Can be
524 * called from IRQ/atomic context.
525 *
526 * In the event of the queue being busy for flipping the work will be held off
527 * and retried later.
528 */
529void tty_flip_buffer_push(struct tty_port *port)
530{
531 struct tty_bufhead *buf = &port->buf;
532
533 tty_flip_buffer_commit(buf->tail);
534 queue_work(system_unbound_wq, &buf->work);
535}
536EXPORT_SYMBOL(tty_flip_buffer_push);
537
538/**
539 * tty_insert_flip_string_and_push_buffer - add characters to the tty buffer and
540 * push
541 * @port: tty port
542 * @chars: characters
543 * @size: size
544 *
545 * The function combines tty_insert_flip_string() and tty_flip_buffer_push()
546 * with the exception of properly holding the @port->lock.
547 *
548 * To be used only internally (by pty currently).
549 *
550 * Returns: the number added.
551 */
552int tty_insert_flip_string_and_push_buffer(struct tty_port *port,
553 const u8 *chars, size_t size)
554{
555 struct tty_bufhead *buf = &port->buf;
556 unsigned long flags;
557
558 spin_lock_irqsave(&port->lock, flags);
559 size = tty_insert_flip_string(port, chars, size);
560 if (size)
561 tty_flip_buffer_commit(buf->tail);
562 spin_unlock_irqrestore(&port->lock, flags);
563
564 queue_work(system_unbound_wq, &buf->work);
565
566 return size;
567}
568
569/**
570 * tty_buffer_init - prepare a tty buffer structure
571 * @port: tty port to initialise
572 *
573 * Set up the initial state of the buffer management for a tty device. Must be
574 * called before the other tty buffer functions are used.
575 */
576void tty_buffer_init(struct tty_port *port)
577{
578 struct tty_bufhead *buf = &port->buf;
579
580 mutex_init(&buf->lock);
581 tty_buffer_reset(&buf->sentinel, 0);
582 buf->head = &buf->sentinel;
583 buf->tail = &buf->sentinel;
584 init_llist_head(&buf->free);
585 atomic_set(&buf->mem_used, 0);
586 atomic_set(&buf->priority, 0);
587 INIT_WORK(&buf->work, flush_to_ldisc);
588 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
589}
590
591/**
592 * tty_buffer_set_limit - change the tty buffer memory limit
593 * @port: tty port to change
594 * @limit: memory limit to set
595 *
596 * Change the tty buffer memory limit.
597 *
598 * Must be called before the other tty buffer functions are used.
599 */
600int tty_buffer_set_limit(struct tty_port *port, int limit)
601{
602 if (limit < MIN_TTYB_SIZE)
603 return -EINVAL;
604 port->buf.mem_limit = limit;
605 return 0;
606}
607EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
608
609/* slave ptys can claim nested buffer lock when handling BRK and INTR */
610void tty_buffer_set_lock_subclass(struct tty_port *port)
611{
612 lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
613}
614
615bool tty_buffer_restart_work(struct tty_port *port)
616{
617 return queue_work(system_unbound_wq, &port->buf.work);
618}
619
620bool tty_buffer_cancel_work(struct tty_port *port)
621{
622 return cancel_work_sync(&port->buf.work);
623}
624
625void tty_buffer_flush_work(struct tty_port *port)
626{
627 flush_work(&port->buf.work);
628}
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 * tty_buffer_lock_exclusive - gain exclusive access to buffer
42 * tty_buffer_unlock_exclusive - release exclusive access
43 *
44 * @port - tty_port owning the flip buffer
45 *
46 * Guarantees safe use of the line discipline's receive_buf() method by
47 * excluding the buffer work and any pending flush from using the flip
48 * buffer. Data can continue to be added concurrently to the flip buffer
49 * from the driver side.
50 *
51 * On release, the buffer work is restarted if there is data in the
52 * flip buffer
53 */
54
55void tty_buffer_lock_exclusive(struct tty_port *port)
56{
57 struct tty_bufhead *buf = &port->buf;
58
59 atomic_inc(&buf->priority);
60 mutex_lock(&buf->lock);
61}
62EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
63
64void tty_buffer_unlock_exclusive(struct tty_port *port)
65{
66 struct tty_bufhead *buf = &port->buf;
67 int restart;
68
69 restart = buf->head->commit != buf->head->read;
70
71 atomic_dec(&buf->priority);
72 mutex_unlock(&buf->lock);
73 if (restart)
74 queue_work(system_unbound_wq, &buf->work);
75}
76EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
77
78/**
79 * tty_buffer_space_avail - return unused buffer space
80 * @port - tty_port owning the flip buffer
81 *
82 * Returns the # of bytes which can be written by the driver without
83 * reaching the buffer limit.
84 *
85 * Note: this does not guarantee that memory is available to write
86 * the returned # of bytes (use tty_prepare_flip_string_xxx() to
87 * pre-allocate if memory guarantee is required).
88 */
89
90int tty_buffer_space_avail(struct tty_port *port)
91{
92 int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
93 return max(space, 0);
94}
95EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
96
97static void tty_buffer_reset(struct tty_buffer *p, size_t size)
98{
99 p->used = 0;
100 p->size = size;
101 p->next = NULL;
102 p->commit = 0;
103 p->read = 0;
104 p->flags = 0;
105}
106
107/**
108 * tty_buffer_free_all - free buffers used by a tty
109 * @tty: tty to free from
110 *
111 * Remove all the buffers pending on a tty whether queued with data
112 * or in the free ring. Must be called when the tty is no longer in use
113 */
114
115void tty_buffer_free_all(struct tty_port *port)
116{
117 struct tty_bufhead *buf = &port->buf;
118 struct tty_buffer *p, *next;
119 struct llist_node *llist;
120
121 while ((p = buf->head) != NULL) {
122 buf->head = p->next;
123 if (p->size > 0)
124 kfree(p);
125 }
126 llist = llist_del_all(&buf->free);
127 llist_for_each_entry_safe(p, next, llist, free)
128 kfree(p);
129
130 tty_buffer_reset(&buf->sentinel, 0);
131 buf->head = &buf->sentinel;
132 buf->tail = &buf->sentinel;
133
134 atomic_set(&buf->mem_used, 0);
135}
136
137/**
138 * tty_buffer_alloc - allocate a tty buffer
139 * @tty: tty device
140 * @size: desired size (characters)
141 *
142 * Allocate a new tty buffer to hold the desired number of characters.
143 * We round our buffers off in 256 character chunks to get better
144 * allocation behaviour.
145 * Return NULL if out of memory or the allocation would exceed the
146 * per device queue
147 */
148
149static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
150{
151 struct llist_node *free;
152 struct tty_buffer *p;
153
154 /* Round the buffer size out */
155 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
156
157 if (size <= MIN_TTYB_SIZE) {
158 free = llist_del_first(&port->buf.free);
159 if (free) {
160 p = llist_entry(free, struct tty_buffer, free);
161 goto found;
162 }
163 }
164
165 /* Should possibly check if this fails for the largest buffer we
166 have queued and recycle that ? */
167 if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
168 return NULL;
169 p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
170 if (p == NULL)
171 return NULL;
172
173found:
174 tty_buffer_reset(p, size);
175 atomic_add(size, &port->buf.mem_used);
176 return p;
177}
178
179/**
180 * tty_buffer_free - free a tty buffer
181 * @tty: tty owning the buffer
182 * @b: the buffer to free
183 *
184 * Free a tty buffer, or add it to the free list according to our
185 * internal strategy
186 */
187
188static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
189{
190 struct tty_bufhead *buf = &port->buf;
191
192 /* Dumb strategy for now - should keep some stats */
193 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
194
195 if (b->size > MIN_TTYB_SIZE)
196 kfree(b);
197 else if (b->size > 0)
198 llist_add(&b->free, &buf->free);
199}
200
201/**
202 * tty_buffer_flush - flush full tty buffers
203 * @tty: tty to flush
204 * @ld: optional ldisc ptr (must be referenced)
205 *
206 * flush all the buffers containing receive data. If ld != NULL,
207 * flush the ldisc input buffer.
208 *
209 * Locking: takes buffer lock to ensure single-threaded flip buffer
210 * 'consumer'
211 */
212
213void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
214{
215 struct tty_port *port = tty->port;
216 struct tty_bufhead *buf = &port->buf;
217 struct tty_buffer *next;
218
219 atomic_inc(&buf->priority);
220
221 mutex_lock(&buf->lock);
222 /* paired w/ release in __tty_buffer_request_room; ensures there are
223 * no pending memory accesses to the freed buffer
224 */
225 while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
226 tty_buffer_free(port, buf->head);
227 buf->head = next;
228 }
229 buf->head->read = buf->head->commit;
230
231 if (ld && ld->ops->flush_buffer)
232 ld->ops->flush_buffer(tty);
233
234 atomic_dec(&buf->priority);
235 mutex_unlock(&buf->lock);
236}
237
238/**
239 * tty_buffer_request_room - grow tty buffer if needed
240 * @tty: tty structure
241 * @size: size desired
242 * @flags: buffer flags if new buffer allocated (default = 0)
243 *
244 * Make at least size bytes of linear space available for the tty
245 * buffer. If we fail return the size we managed to find.
246 *
247 * Will change over to a new buffer if the current buffer is encoded as
248 * TTY_NORMAL (so has no flags buffer) and the new buffer requires
249 * a flags buffer.
250 */
251static int __tty_buffer_request_room(struct tty_port *port, size_t size,
252 int flags)
253{
254 struct tty_bufhead *buf = &port->buf;
255 struct tty_buffer *b, *n;
256 int left, change;
257
258 b = buf->tail;
259 if (b->flags & TTYB_NORMAL)
260 left = 2 * b->size - b->used;
261 else
262 left = b->size - b->used;
263
264 change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
265 if (change || left < size) {
266 /* This is the slow path - looking for new buffers to use */
267 n = tty_buffer_alloc(port, size);
268 if (n != NULL) {
269 n->flags = flags;
270 buf->tail = n;
271 /* paired w/ acquire in flush_to_ldisc(); ensures
272 * flush_to_ldisc() sees buffer data.
273 */
274 smp_store_release(&b->commit, b->used);
275 /* paired w/ acquire in flush_to_ldisc(); ensures the
276 * latest commit value can be read before the head is
277 * advanced to the next buffer
278 */
279 smp_store_release(&b->next, n);
280 } else if (change)
281 size = 0;
282 else
283 size = left;
284 }
285 return size;
286}
287
288int tty_buffer_request_room(struct tty_port *port, size_t size)
289{
290 return __tty_buffer_request_room(port, size, 0);
291}
292EXPORT_SYMBOL_GPL(tty_buffer_request_room);
293
294/**
295 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
296 * @port: tty port
297 * @chars: characters
298 * @flag: flag value for each character
299 * @size: size
300 *
301 * Queue a series of bytes to the tty buffering. All the characters
302 * passed are marked with the supplied flag. Returns the number added.
303 */
304
305int tty_insert_flip_string_fixed_flag(struct tty_port *port,
306 const unsigned char *chars, char flag, size_t size)
307{
308 int copied = 0;
309 do {
310 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
311 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
312 int space = __tty_buffer_request_room(port, goal, flags);
313 struct tty_buffer *tb = port->buf.tail;
314 if (unlikely(space == 0))
315 break;
316 memcpy(char_buf_ptr(tb, tb->used), chars, space);
317 if (~tb->flags & TTYB_NORMAL)
318 memset(flag_buf_ptr(tb, tb->used), flag, space);
319 tb->used += space;
320 copied += space;
321 chars += space;
322 /* There is a small chance that we need to split the data over
323 several buffers. If this is the case we must loop */
324 } while (unlikely(size > copied));
325 return copied;
326}
327EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
328
329/**
330 * tty_insert_flip_string_flags - Add characters to the tty buffer
331 * @port: tty port
332 * @chars: characters
333 * @flags: flag bytes
334 * @size: size
335 *
336 * Queue a series of bytes to the tty buffering. For each character
337 * the flags array indicates the status of the character. Returns the
338 * number added.
339 */
340
341int tty_insert_flip_string_flags(struct tty_port *port,
342 const unsigned char *chars, const char *flags, size_t size)
343{
344 int copied = 0;
345 do {
346 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
347 int space = tty_buffer_request_room(port, goal);
348 struct tty_buffer *tb = port->buf.tail;
349 if (unlikely(space == 0))
350 break;
351 memcpy(char_buf_ptr(tb, tb->used), chars, space);
352 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
353 tb->used += space;
354 copied += space;
355 chars += space;
356 flags += space;
357 /* There is a small chance that we need to split the data over
358 several buffers. If this is the case we must loop */
359 } while (unlikely(size > copied));
360 return copied;
361}
362EXPORT_SYMBOL(tty_insert_flip_string_flags);
363
364/**
365 * tty_schedule_flip - push characters to ldisc
366 * @port: tty port to push from
367 *
368 * Takes any pending buffers and transfers their ownership to the
369 * ldisc side of the queue. It then schedules those characters for
370 * processing by the line discipline.
371 */
372
373void tty_schedule_flip(struct tty_port *port)
374{
375 struct tty_bufhead *buf = &port->buf;
376
377 /* paired w/ acquire in flush_to_ldisc(); ensures
378 * flush_to_ldisc() sees buffer data.
379 */
380 smp_store_release(&buf->tail->commit, buf->tail->used);
381 queue_work(system_unbound_wq, &buf->work);
382}
383EXPORT_SYMBOL(tty_schedule_flip);
384
385/**
386 * tty_prepare_flip_string - make room for characters
387 * @port: tty port
388 * @chars: return pointer for character write area
389 * @size: desired size
390 *
391 * Prepare a block of space in the buffer for data. Returns the length
392 * available and buffer pointer to the space which is now allocated and
393 * accounted for as ready for normal characters. This is used for drivers
394 * that need their own block copy routines into the buffer. There is no
395 * guarantee the buffer is a DMA target!
396 */
397
398int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
399 size_t size)
400{
401 int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
402 if (likely(space)) {
403 struct tty_buffer *tb = port->buf.tail;
404 *chars = char_buf_ptr(tb, tb->used);
405 if (~tb->flags & TTYB_NORMAL)
406 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
407 tb->used += space;
408 }
409 return space;
410}
411EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
412
413/**
414 * tty_ldisc_receive_buf - forward data to line discipline
415 * @ld: line discipline to process input
416 * @p: char buffer
417 * @f: TTY_* flags buffer
418 * @count: number of bytes to process
419 *
420 * Callers other than flush_to_ldisc() need to exclude the kworker
421 * from concurrent use of the line discipline, see paste_selection().
422 *
423 * Returns the number of bytes not processed
424 */
425int tty_ldisc_receive_buf(struct tty_ldisc *ld, unsigned char *p,
426 char *f, int count)
427{
428 if (ld->ops->receive_buf2)
429 count = ld->ops->receive_buf2(ld->tty, p, f, count);
430 else {
431 count = min_t(int, count, ld->tty->receive_room);
432 if (count && ld->ops->receive_buf)
433 ld->ops->receive_buf(ld->tty, p, f, count);
434 }
435 return count;
436}
437EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
438
439static int
440receive_buf(struct tty_ldisc *ld, struct tty_buffer *head, int count)
441{
442 unsigned char *p = char_buf_ptr(head, head->read);
443 char *f = NULL;
444
445 if (~head->flags & TTYB_NORMAL)
446 f = flag_buf_ptr(head, head->read);
447
448 return tty_ldisc_receive_buf(ld, p, f, count);
449}
450
451/**
452 * flush_to_ldisc
453 * @work: tty structure passed from work queue.
454 *
455 * This routine is called out of the software interrupt to flush data
456 * from the buffer chain to the line discipline.
457 *
458 * The receive_buf method is single threaded for each tty instance.
459 *
460 * Locking: takes buffer lock to ensure single-threaded flip buffer
461 * 'consumer'
462 */
463
464static void flush_to_ldisc(struct work_struct *work)
465{
466 struct tty_port *port = container_of(work, struct tty_port, buf.work);
467 struct tty_bufhead *buf = &port->buf;
468 struct tty_struct *tty;
469 struct tty_ldisc *disc;
470
471 tty = READ_ONCE(port->itty);
472 if (tty == NULL)
473 return;
474
475 disc = tty_ldisc_ref(tty);
476 if (disc == NULL)
477 return;
478
479 mutex_lock(&buf->lock);
480
481 while (1) {
482 struct tty_buffer *head = buf->head;
483 struct tty_buffer *next;
484 int count;
485
486 /* Ldisc or user is trying to gain exclusive access */
487 if (atomic_read(&buf->priority))
488 break;
489
490 /* paired w/ release in __tty_buffer_request_room();
491 * ensures commit value read is not stale if the head
492 * is advancing to the next buffer
493 */
494 next = smp_load_acquire(&head->next);
495 /* paired w/ release in __tty_buffer_request_room() or in
496 * tty_buffer_flush(); ensures we see the committed buffer data
497 */
498 count = smp_load_acquire(&head->commit) - head->read;
499 if (!count) {
500 if (next == NULL)
501 break;
502 buf->head = next;
503 tty_buffer_free(port, head);
504 continue;
505 }
506
507 count = receive_buf(disc, head, count);
508 if (!count)
509 break;
510 head->read += count;
511 }
512
513 mutex_unlock(&buf->lock);
514
515 tty_ldisc_deref(disc);
516}
517
518/**
519 * tty_flip_buffer_push - terminal
520 * @port: tty port to push
521 *
522 * Queue a push of the terminal flip buffers to the line discipline.
523 * Can be called from IRQ/atomic context.
524 *
525 * In the event of the queue being busy for flipping the work will be
526 * held off and retried later.
527 */
528
529void tty_flip_buffer_push(struct tty_port *port)
530{
531 tty_schedule_flip(port);
532}
533EXPORT_SYMBOL(tty_flip_buffer_push);
534
535/**
536 * tty_buffer_init - prepare a tty buffer structure
537 * @tty: tty to initialise
538 *
539 * Set up the initial state of the buffer management for a tty device.
540 * Must be called before the other tty buffer functions are used.
541 */
542
543void tty_buffer_init(struct tty_port *port)
544{
545 struct tty_bufhead *buf = &port->buf;
546
547 mutex_init(&buf->lock);
548 tty_buffer_reset(&buf->sentinel, 0);
549 buf->head = &buf->sentinel;
550 buf->tail = &buf->sentinel;
551 init_llist_head(&buf->free);
552 atomic_set(&buf->mem_used, 0);
553 atomic_set(&buf->priority, 0);
554 INIT_WORK(&buf->work, flush_to_ldisc);
555 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
556}
557
558/**
559 * tty_buffer_set_limit - change the tty buffer memory limit
560 * @port: tty port to change
561 *
562 * Change the tty buffer memory limit.
563 * Must be called before the other tty buffer functions are used.
564 */
565
566int tty_buffer_set_limit(struct tty_port *port, int limit)
567{
568 if (limit < MIN_TTYB_SIZE)
569 return -EINVAL;
570 port->buf.mem_limit = limit;
571 return 0;
572}
573EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
574
575/* slave ptys can claim nested buffer lock when handling BRK and INTR */
576void tty_buffer_set_lock_subclass(struct tty_port *port)
577{
578 lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
579}
580
581bool tty_buffer_restart_work(struct tty_port *port)
582{
583 return queue_work(system_unbound_wq, &port->buf.work);
584}
585
586bool tty_buffer_cancel_work(struct tty_port *port)
587{
588 return cancel_work_sync(&port->buf.work);
589}
590
591void tty_buffer_flush_work(struct tty_port *port)
592{
593 flush_work(&port->buf.work);
594}