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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/**
42 * tty_buffer_lock_exclusive - gain exclusive access to buffer
43 * tty_buffer_unlock_exclusive - release exclusive access
44 *
45 * @port - tty_port owning the flip buffer
46 *
47 * Guarantees safe use of the line discipline's receive_buf() method by
48 * excluding the buffer work and any pending flush from using the flip
49 * buffer. Data can continue to be added concurrently to the flip buffer
50 * from the driver side.
51 *
52 * On release, the buffer work is restarted if there is data in the
53 * flip buffer
54 */
55
56void tty_buffer_lock_exclusive(struct tty_port *port)
57{
58 struct tty_bufhead *buf = &port->buf;
59
60 atomic_inc(&buf->priority);
61 mutex_lock(&buf->lock);
62}
63EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
64
65void tty_buffer_unlock_exclusive(struct tty_port *port)
66{
67 struct tty_bufhead *buf = &port->buf;
68 int restart;
69
70 restart = buf->head->commit != buf->head->read;
71
72 atomic_dec(&buf->priority);
73 mutex_unlock(&buf->lock);
74 if (restart)
75 queue_work(system_unbound_wq, &buf->work);
76}
77EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
78
79/**
80 * tty_buffer_space_avail - return unused buffer space
81 * @port - tty_port owning the flip buffer
82 *
83 * Returns the # of bytes which can be written by the driver without
84 * reaching the buffer limit.
85 *
86 * Note: this does not guarantee that memory is available to write
87 * the returned # of bytes (use tty_prepare_flip_string_xxx() to
88 * pre-allocate if memory guarantee is required).
89 */
90
91int tty_buffer_space_avail(struct tty_port *port)
92{
93 int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
94 return max(space, 0);
95}
96EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
97
98static void tty_buffer_reset(struct tty_buffer *p, size_t size)
99{
100 p->used = 0;
101 p->size = size;
102 p->next = NULL;
103 p->commit = 0;
104 p->read = 0;
105 p->flags = 0;
106}
107
108/**
109 * tty_buffer_free_all - free buffers used by a tty
110 * @tty: tty to free from
111 *
112 * Remove all the buffers pending on a tty whether queued with data
113 * or in the free ring. Must be called when the tty is no longer in use
114 */
115
116void tty_buffer_free_all(struct tty_port *port)
117{
118 struct tty_bufhead *buf = &port->buf;
119 struct tty_buffer *p, *next;
120 struct llist_node *llist;
121
122 while ((p = buf->head) != NULL) {
123 buf->head = p->next;
124 if (p->size > 0)
125 kfree(p);
126 }
127 llist = llist_del_all(&buf->free);
128 llist_for_each_entry_safe(p, next, llist, free)
129 kfree(p);
130
131 tty_buffer_reset(&buf->sentinel, 0);
132 buf->head = &buf->sentinel;
133 buf->tail = &buf->sentinel;
134
135 atomic_set(&buf->mem_used, 0);
136}
137
138/**
139 * tty_buffer_alloc - allocate a tty buffer
140 * @tty: tty device
141 * @size: desired size (characters)
142 *
143 * Allocate a new tty buffer to hold the desired number of characters.
144 * We round our buffers off in 256 character chunks to get better
145 * allocation behaviour.
146 * Return NULL if out of memory or the allocation would exceed the
147 * per device queue
148 */
149
150static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
151{
152 struct llist_node *free;
153 struct tty_buffer *p;
154
155 /* Round the buffer size out */
156 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
157
158 if (size <= MIN_TTYB_SIZE) {
159 free = llist_del_first(&port->buf.free);
160 if (free) {
161 p = llist_entry(free, struct tty_buffer, free);
162 goto found;
163 }
164 }
165
166 /* Should possibly check if this fails for the largest buffer we
167 have queued and recycle that ? */
168 if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
169 return NULL;
170 p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
171 if (p == NULL)
172 return NULL;
173
174found:
175 tty_buffer_reset(p, size);
176 atomic_add(size, &port->buf.mem_used);
177 return p;
178}
179
180/**
181 * tty_buffer_free - free a tty buffer
182 * @tty: tty owning the buffer
183 * @b: the buffer to free
184 *
185 * Free a tty buffer, or add it to the free list according to our
186 * internal strategy
187 */
188
189static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
190{
191 struct tty_bufhead *buf = &port->buf;
192
193 /* Dumb strategy for now - should keep some stats */
194 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
195
196 if (b->size > MIN_TTYB_SIZE)
197 kfree(b);
198 else if (b->size > 0)
199 llist_add(&b->free, &buf->free);
200}
201
202/**
203 * tty_buffer_flush - flush full tty buffers
204 * @tty: tty to flush
205 *
206 * flush all the buffers containing receive data.
207 *
208 * Locking: takes buffer lock to ensure single-threaded flip buffer
209 * 'consumer'
210 */
211
212void tty_buffer_flush(struct tty_struct *tty)
213{
214 struct tty_port *port = tty->port;
215 struct tty_bufhead *buf = &port->buf;
216 struct tty_buffer *next;
217
218 atomic_inc(&buf->priority);
219
220 mutex_lock(&buf->lock);
221 while ((next = buf->head->next) != NULL) {
222 tty_buffer_free(port, buf->head);
223 buf->head = next;
224 }
225 buf->head->read = buf->head->commit;
226 atomic_dec(&buf->priority);
227 mutex_unlock(&buf->lock);
228}
229
230/**
231 * tty_buffer_request_room - grow tty buffer if needed
232 * @tty: tty structure
233 * @size: size desired
234 * @flags: buffer flags if new buffer allocated (default = 0)
235 *
236 * Make at least size bytes of linear space available for the tty
237 * buffer. If we fail return the size we managed to find.
238 *
239 * Will change over to a new buffer if the current buffer is encoded as
240 * TTY_NORMAL (so has no flags buffer) and the new buffer requires
241 * a flags buffer.
242 */
243static int __tty_buffer_request_room(struct tty_port *port, size_t size,
244 int flags)
245{
246 struct tty_bufhead *buf = &port->buf;
247 struct tty_buffer *b, *n;
248 int left, change;
249
250 b = buf->tail;
251 if (b->flags & TTYB_NORMAL)
252 left = 2 * b->size - b->used;
253 else
254 left = b->size - b->used;
255
256 change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
257 if (change || left < size) {
258 /* This is the slow path - looking for new buffers to use */
259 if ((n = tty_buffer_alloc(port, size)) != NULL) {
260 n->flags = flags;
261 buf->tail = n;
262 b->commit = b->used;
263 /* paired w/ barrier in flush_to_ldisc(); ensures the
264 * latest commit value can be read before the head is
265 * advanced to the next buffer
266 */
267 smp_wmb();
268 b->next = n;
269 } else if (change)
270 size = 0;
271 else
272 size = left;
273 }
274 return size;
275}
276
277int tty_buffer_request_room(struct tty_port *port, size_t size)
278{
279 return __tty_buffer_request_room(port, size, 0);
280}
281EXPORT_SYMBOL_GPL(tty_buffer_request_room);
282
283/**
284 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
285 * @port: tty port
286 * @chars: characters
287 * @flag: flag value for each character
288 * @size: size
289 *
290 * Queue a series of bytes to the tty buffering. All the characters
291 * passed are marked with the supplied flag. Returns the number added.
292 */
293
294int tty_insert_flip_string_fixed_flag(struct tty_port *port,
295 const unsigned char *chars, char flag, size_t size)
296{
297 int copied = 0;
298 do {
299 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
300 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
301 int space = __tty_buffer_request_room(port, goal, flags);
302 struct tty_buffer *tb = port->buf.tail;
303 if (unlikely(space == 0))
304 break;
305 memcpy(char_buf_ptr(tb, tb->used), chars, space);
306 if (~tb->flags & TTYB_NORMAL)
307 memset(flag_buf_ptr(tb, tb->used), flag, space);
308 tb->used += space;
309 copied += space;
310 chars += space;
311 /* There is a small chance that we need to split the data over
312 several buffers. If this is the case we must loop */
313 } while (unlikely(size > copied));
314 return copied;
315}
316EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
317
318/**
319 * tty_insert_flip_string_flags - Add characters to the tty buffer
320 * @port: tty port
321 * @chars: characters
322 * @flags: flag bytes
323 * @size: size
324 *
325 * Queue a series of bytes to the tty buffering. For each character
326 * the flags array indicates the status of the character. Returns the
327 * number added.
328 */
329
330int tty_insert_flip_string_flags(struct tty_port *port,
331 const unsigned char *chars, const char *flags, size_t size)
332{
333 int copied = 0;
334 do {
335 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
336 int space = tty_buffer_request_room(port, goal);
337 struct tty_buffer *tb = port->buf.tail;
338 if (unlikely(space == 0))
339 break;
340 memcpy(char_buf_ptr(tb, tb->used), chars, space);
341 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
342 tb->used += space;
343 copied += space;
344 chars += space;
345 flags += space;
346 /* There is a small chance that we need to split the data over
347 several buffers. If this is the case we must loop */
348 } while (unlikely(size > copied));
349 return copied;
350}
351EXPORT_SYMBOL(tty_insert_flip_string_flags);
352
353/**
354 * tty_schedule_flip - push characters to ldisc
355 * @port: tty port to push from
356 *
357 * Takes any pending buffers and transfers their ownership to the
358 * ldisc side of the queue. It then schedules those characters for
359 * processing by the line discipline.
360 */
361
362void tty_schedule_flip(struct tty_port *port)
363{
364 struct tty_bufhead *buf = &port->buf;
365
366 buf->tail->commit = buf->tail->used;
367 schedule_work(&buf->work);
368}
369EXPORT_SYMBOL(tty_schedule_flip);
370
371/**
372 * tty_prepare_flip_string - make room for characters
373 * @port: tty port
374 * @chars: return pointer for character write area
375 * @size: desired size
376 *
377 * Prepare a block of space in the buffer for data. Returns the length
378 * available and buffer pointer to the space which is now allocated and
379 * accounted for as ready for normal characters. This is used for drivers
380 * that need their own block copy routines into the buffer. There is no
381 * guarantee the buffer is a DMA target!
382 */
383
384int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
385 size_t size)
386{
387 int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
388 if (likely(space)) {
389 struct tty_buffer *tb = port->buf.tail;
390 *chars = char_buf_ptr(tb, tb->used);
391 if (~tb->flags & TTYB_NORMAL)
392 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
393 tb->used += space;
394 }
395 return space;
396}
397EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
398
399
400static int
401receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
402{
403 struct tty_ldisc *disc = tty->ldisc;
404 unsigned char *p = char_buf_ptr(head, head->read);
405 char *f = NULL;
406
407 if (~head->flags & TTYB_NORMAL)
408 f = flag_buf_ptr(head, head->read);
409
410 if (disc->ops->receive_buf2)
411 count = disc->ops->receive_buf2(tty, p, f, count);
412 else {
413 count = min_t(int, count, tty->receive_room);
414 if (count)
415 disc->ops->receive_buf(tty, p, f, count);
416 }
417 head->read += count;
418 return count;
419}
420
421/**
422 * flush_to_ldisc
423 * @work: tty structure passed from work queue.
424 *
425 * This routine is called out of the software interrupt to flush data
426 * from the buffer chain to the line discipline.
427 *
428 * The receive_buf method is single threaded for each tty instance.
429 *
430 * Locking: takes buffer lock to ensure single-threaded flip buffer
431 * 'consumer'
432 */
433
434static void flush_to_ldisc(struct work_struct *work)
435{
436 struct tty_port *port = container_of(work, struct tty_port, buf.work);
437 struct tty_bufhead *buf = &port->buf;
438 struct tty_struct *tty;
439 struct tty_ldisc *disc;
440
441 tty = port->itty;
442 if (tty == NULL)
443 return;
444
445 disc = tty_ldisc_ref(tty);
446 if (disc == NULL)
447 return;
448
449 mutex_lock(&buf->lock);
450
451 while (1) {
452 struct tty_buffer *head = buf->head;
453 struct tty_buffer *next;
454 int count;
455
456 /* Ldisc or user is trying to gain exclusive access */
457 if (atomic_read(&buf->priority))
458 break;
459
460 next = head->next;
461 /* paired w/ barrier in __tty_buffer_request_room();
462 * ensures commit value read is not stale if the head
463 * is advancing to the next buffer
464 */
465 smp_rmb();
466 count = head->commit - head->read;
467 if (!count) {
468 if (next == NULL)
469 break;
470 buf->head = next;
471 tty_buffer_free(port, head);
472 continue;
473 }
474
475 count = receive_buf(tty, head, count);
476 if (!count)
477 break;
478 }
479
480 mutex_unlock(&buf->lock);
481
482 tty_ldisc_deref(disc);
483}
484
485/**
486 * tty_flush_to_ldisc
487 * @tty: tty to push
488 *
489 * Push the terminal flip buffers to the line discipline.
490 *
491 * Must not be called from IRQ context.
492 */
493void tty_flush_to_ldisc(struct tty_struct *tty)
494{
495 flush_work(&tty->port->buf.work);
496}
497
498/**
499 * tty_flip_buffer_push - terminal
500 * @port: tty port to push
501 *
502 * Queue a push of the terminal flip buffers to the line discipline.
503 * Can be called from IRQ/atomic context.
504 *
505 * In the event of the queue being busy for flipping the work will be
506 * held off and retried later.
507 */
508
509void tty_flip_buffer_push(struct tty_port *port)
510{
511 tty_schedule_flip(port);
512}
513EXPORT_SYMBOL(tty_flip_buffer_push);
514
515/**
516 * tty_buffer_init - prepare a tty buffer structure
517 * @tty: tty to initialise
518 *
519 * Set up the initial state of the buffer management for a tty device.
520 * Must be called before the other tty buffer functions are used.
521 */
522
523void tty_buffer_init(struct tty_port *port)
524{
525 struct tty_bufhead *buf = &port->buf;
526
527 mutex_init(&buf->lock);
528 tty_buffer_reset(&buf->sentinel, 0);
529 buf->head = &buf->sentinel;
530 buf->tail = &buf->sentinel;
531 init_llist_head(&buf->free);
532 atomic_set(&buf->mem_used, 0);
533 atomic_set(&buf->priority, 0);
534 INIT_WORK(&buf->work, flush_to_ldisc);
535 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
536}
537
538/**
539 * tty_buffer_set_limit - change the tty buffer memory limit
540 * @port: tty port to change
541 *
542 * Change the tty buffer memory limit.
543 * Must be called before the other tty buffer functions are used.
544 */
545
546int tty_buffer_set_limit(struct tty_port *port, int limit)
547{
548 if (limit < MIN_TTYB_SIZE)
549 return -EINVAL;
550 port->buf.mem_limit = limit;
551 return 0;
552}
553EXPORT_SYMBOL_GPL(tty_buffer_set_limit);