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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}
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}