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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/init.h>
15#include <linux/wait.h>
16#include <linux/bitops.h>
17#include <linux/delay.h>
18#include <linux/module.h>
19
20/**
21 * tty_buffer_free_all - free buffers used by a tty
22 * @tty: tty to free from
23 *
24 * Remove all the buffers pending on a tty whether queued with data
25 * or in the free ring. Must be called when the tty is no longer in use
26 *
27 * Locking: none
28 */
29
30void tty_buffer_free_all(struct tty_struct *tty)
31{
32 struct tty_buffer *thead;
33 while ((thead = tty->buf.head) != NULL) {
34 tty->buf.head = thead->next;
35 kfree(thead);
36 }
37 while ((thead = tty->buf.free) != NULL) {
38 tty->buf.free = thead->next;
39 kfree(thead);
40 }
41 tty->buf.tail = NULL;
42 tty->buf.memory_used = 0;
43}
44
45/**
46 * tty_buffer_alloc - allocate a tty buffer
47 * @tty: tty device
48 * @size: desired size (characters)
49 *
50 * Allocate a new tty buffer to hold the desired number of characters.
51 * Return NULL if out of memory or the allocation would exceed the
52 * per device queue
53 *
54 * Locking: Caller must hold tty->buf.lock
55 */
56
57static struct tty_buffer *tty_buffer_alloc(struct tty_struct *tty, size_t size)
58{
59 struct tty_buffer *p;
60
61 if (tty->buf.memory_used + size > 65536)
62 return NULL;
63 p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
64 if (p == NULL)
65 return NULL;
66 p->used = 0;
67 p->size = size;
68 p->next = NULL;
69 p->commit = 0;
70 p->read = 0;
71 p->char_buf_ptr = (char *)(p->data);
72 p->flag_buf_ptr = (unsigned char *)p->char_buf_ptr + size;
73 tty->buf.memory_used += size;
74 return p;
75}
76
77/**
78 * tty_buffer_free - free a tty buffer
79 * @tty: tty owning the buffer
80 * @b: the buffer to free
81 *
82 * Free a tty buffer, or add it to the free list according to our
83 * internal strategy
84 *
85 * Locking: Caller must hold tty->buf.lock
86 */
87
88static void tty_buffer_free(struct tty_struct *tty, struct tty_buffer *b)
89{
90 /* Dumb strategy for now - should keep some stats */
91 tty->buf.memory_used -= b->size;
92 WARN_ON(tty->buf.memory_used < 0);
93
94 if (b->size >= 512)
95 kfree(b);
96 else {
97 b->next = tty->buf.free;
98 tty->buf.free = b;
99 }
100}
101
102/**
103 * __tty_buffer_flush - flush full tty buffers
104 * @tty: tty to flush
105 *
106 * flush all the buffers containing receive data. Caller must
107 * hold the buffer lock and must have ensured no parallel flush to
108 * ldisc is running.
109 *
110 * Locking: Caller must hold tty->buf.lock
111 */
112
113static void __tty_buffer_flush(struct tty_struct *tty)
114{
115 struct tty_buffer *thead;
116
117 while ((thead = tty->buf.head) != NULL) {
118 tty->buf.head = thead->next;
119 tty_buffer_free(tty, thead);
120 }
121 tty->buf.tail = NULL;
122}
123
124/**
125 * tty_buffer_flush - flush full tty buffers
126 * @tty: tty to flush
127 *
128 * flush all the buffers containing receive data. If the buffer is
129 * being processed by flush_to_ldisc then we defer the processing
130 * to that function
131 *
132 * Locking: none
133 */
134
135void tty_buffer_flush(struct tty_struct *tty)
136{
137 unsigned long flags;
138 spin_lock_irqsave(&tty->buf.lock, flags);
139
140 /* If the data is being pushed to the tty layer then we can't
141 process it here. Instead set a flag and the flush_to_ldisc
142 path will process the flush request before it exits */
143 if (test_bit(TTY_FLUSHING, &tty->flags)) {
144 set_bit(TTY_FLUSHPENDING, &tty->flags);
145 spin_unlock_irqrestore(&tty->buf.lock, flags);
146 wait_event(tty->read_wait,
147 test_bit(TTY_FLUSHPENDING, &tty->flags) == 0);
148 return;
149 } else
150 __tty_buffer_flush(tty);
151 spin_unlock_irqrestore(&tty->buf.lock, flags);
152}
153
154/**
155 * tty_buffer_find - find a free tty buffer
156 * @tty: tty owning the buffer
157 * @size: characters wanted
158 *
159 * Locate an existing suitable tty buffer or if we are lacking one then
160 * allocate a new one. We round our buffers off in 256 character chunks
161 * to get better allocation behaviour.
162 *
163 * Locking: Caller must hold tty->buf.lock
164 */
165
166static struct tty_buffer *tty_buffer_find(struct tty_struct *tty, size_t size)
167{
168 struct tty_buffer **tbh = &tty->buf.free;
169 while ((*tbh) != NULL) {
170 struct tty_buffer *t = *tbh;
171 if (t->size >= size) {
172 *tbh = t->next;
173 t->next = NULL;
174 t->used = 0;
175 t->commit = 0;
176 t->read = 0;
177 tty->buf.memory_used += t->size;
178 return t;
179 }
180 tbh = &((*tbh)->next);
181 }
182 /* Round the buffer size out */
183 size = (size + 0xFF) & ~0xFF;
184 return tty_buffer_alloc(tty, size);
185 /* Should possibly check if this fails for the largest buffer we
186 have queued and recycle that ? */
187}
188
189/**
190 * tty_buffer_request_room - grow tty buffer if needed
191 * @tty: tty structure
192 * @size: size desired
193 *
194 * Make at least size bytes of linear space available for the tty
195 * buffer. If we fail return the size we managed to find.
196 *
197 * Locking: Takes tty->buf.lock
198 */
199int tty_buffer_request_room(struct tty_struct *tty, size_t size)
200{
201 struct tty_buffer *b, *n;
202 int left;
203 unsigned long flags;
204
205 spin_lock_irqsave(&tty->buf.lock, flags);
206
207 /* OPTIMISATION: We could keep a per tty "zero" sized buffer to
208 remove this conditional if its worth it. This would be invisible
209 to the callers */
210 if ((b = tty->buf.tail) != NULL)
211 left = b->size - b->used;
212 else
213 left = 0;
214
215 if (left < size) {
216 /* This is the slow path - looking for new buffers to use */
217 if ((n = tty_buffer_find(tty, size)) != NULL) {
218 if (b != NULL) {
219 b->next = n;
220 b->commit = b->used;
221 } else
222 tty->buf.head = n;
223 tty->buf.tail = n;
224 } else
225 size = left;
226 }
227
228 spin_unlock_irqrestore(&tty->buf.lock, flags);
229 return size;
230}
231EXPORT_SYMBOL_GPL(tty_buffer_request_room);
232
233/**
234 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
235 * @tty: tty structure
236 * @chars: characters
237 * @flag: flag value for each character
238 * @size: size
239 *
240 * Queue a series of bytes to the tty buffering. All the characters
241 * passed are marked with the supplied flag. Returns the number added.
242 *
243 * Locking: Called functions may take tty->buf.lock
244 */
245
246int tty_insert_flip_string_fixed_flag(struct tty_struct *tty,
247 const unsigned char *chars, char flag, size_t size)
248{
249 int copied = 0;
250 do {
251 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
252 int space = tty_buffer_request_room(tty, goal);
253 struct tty_buffer *tb = tty->buf.tail;
254 /* If there is no space then tb may be NULL */
255 if (unlikely(space == 0))
256 break;
257 memcpy(tb->char_buf_ptr + tb->used, chars, space);
258 memset(tb->flag_buf_ptr + tb->used, flag, space);
259 tb->used += space;
260 copied += space;
261 chars += space;
262 /* There is a small chance that we need to split the data over
263 several buffers. If this is the case we must loop */
264 } while (unlikely(size > copied));
265 return copied;
266}
267EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
268
269/**
270 * tty_insert_flip_string_flags - Add characters to the tty buffer
271 * @tty: tty structure
272 * @chars: characters
273 * @flags: flag bytes
274 * @size: size
275 *
276 * Queue a series of bytes to the tty buffering. For each character
277 * the flags array indicates the status of the character. Returns the
278 * number added.
279 *
280 * Locking: Called functions may take tty->buf.lock
281 */
282
283int tty_insert_flip_string_flags(struct tty_struct *tty,
284 const unsigned char *chars, const char *flags, size_t size)
285{
286 int copied = 0;
287 do {
288 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
289 int space = tty_buffer_request_room(tty, goal);
290 struct tty_buffer *tb = tty->buf.tail;
291 /* If there is no space then tb may be NULL */
292 if (unlikely(space == 0))
293 break;
294 memcpy(tb->char_buf_ptr + tb->used, chars, space);
295 memcpy(tb->flag_buf_ptr + tb->used, flags, space);
296 tb->used += space;
297 copied += space;
298 chars += space;
299 flags += space;
300 /* There is a small chance that we need to split the data over
301 several buffers. If this is the case we must loop */
302 } while (unlikely(size > copied));
303 return copied;
304}
305EXPORT_SYMBOL(tty_insert_flip_string_flags);
306
307/**
308 * tty_schedule_flip - push characters to ldisc
309 * @tty: tty to push from
310 *
311 * Takes any pending buffers and transfers their ownership to the
312 * ldisc side of the queue. It then schedules those characters for
313 * processing by the line discipline.
314 *
315 * Locking: Takes tty->buf.lock
316 */
317
318void tty_schedule_flip(struct tty_struct *tty)
319{
320 unsigned long flags;
321 spin_lock_irqsave(&tty->buf.lock, flags);
322 if (tty->buf.tail != NULL)
323 tty->buf.tail->commit = tty->buf.tail->used;
324 spin_unlock_irqrestore(&tty->buf.lock, flags);
325 schedule_work(&tty->buf.work);
326}
327EXPORT_SYMBOL(tty_schedule_flip);
328
329/**
330 * tty_prepare_flip_string - make room for characters
331 * @tty: tty
332 * @chars: return pointer for character write area
333 * @size: desired size
334 *
335 * Prepare a block of space in the buffer for data. Returns the length
336 * available and buffer pointer to the space which is now allocated and
337 * accounted for as ready for normal characters. This is used for drivers
338 * that need their own block copy routines into the buffer. There is no
339 * guarantee the buffer is a DMA target!
340 *
341 * Locking: May call functions taking tty->buf.lock
342 */
343
344int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars,
345 size_t size)
346{
347 int space = tty_buffer_request_room(tty, size);
348 if (likely(space)) {
349 struct tty_buffer *tb = tty->buf.tail;
350 *chars = tb->char_buf_ptr + tb->used;
351 memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
352 tb->used += space;
353 }
354 return space;
355}
356EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
357
358/**
359 * tty_prepare_flip_string_flags - make room for characters
360 * @tty: tty
361 * @chars: return pointer for character write area
362 * @flags: return pointer for status flag write area
363 * @size: desired size
364 *
365 * Prepare a block of space in the buffer for data. Returns the length
366 * available and buffer pointer to the space which is now allocated and
367 * accounted for as ready for characters. This is used for drivers
368 * that need their own block copy routines into the buffer. There is no
369 * guarantee the buffer is a DMA target!
370 *
371 * Locking: May call functions taking tty->buf.lock
372 */
373
374int tty_prepare_flip_string_flags(struct tty_struct *tty,
375 unsigned char **chars, char **flags, size_t size)
376{
377 int space = tty_buffer_request_room(tty, size);
378 if (likely(space)) {
379 struct tty_buffer *tb = tty->buf.tail;
380 *chars = tb->char_buf_ptr + tb->used;
381 *flags = tb->flag_buf_ptr + tb->used;
382 tb->used += space;
383 }
384 return space;
385}
386EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
387
388
389
390/**
391 * flush_to_ldisc
392 * @work: tty structure passed from work queue.
393 *
394 * This routine is called out of the software interrupt to flush data
395 * from the buffer chain to the line discipline.
396 *
397 * Locking: holds tty->buf.lock to guard buffer list. Drops the lock
398 * while invoking the line discipline receive_buf method. The
399 * receive_buf method is single threaded for each tty instance.
400 */
401
402static void flush_to_ldisc(struct work_struct *work)
403{
404 struct tty_struct *tty =
405 container_of(work, struct tty_struct, buf.work);
406 unsigned long flags;
407 struct tty_ldisc *disc;
408
409 disc = tty_ldisc_ref(tty);
410 if (disc == NULL) /* !TTY_LDISC */
411 return;
412
413 spin_lock_irqsave(&tty->buf.lock, flags);
414
415 if (!test_and_set_bit(TTY_FLUSHING, &tty->flags)) {
416 struct tty_buffer *head;
417 while ((head = tty->buf.head) != NULL) {
418 int count;
419 char *char_buf;
420 unsigned char *flag_buf;
421
422 count = head->commit - head->read;
423 if (!count) {
424 if (head->next == NULL)
425 break;
426 tty->buf.head = head->next;
427 tty_buffer_free(tty, head);
428 continue;
429 }
430 /* Ldisc or user is trying to flush the buffers
431 we are feeding to the ldisc, stop feeding the
432 line discipline as we want to empty the queue */
433 if (test_bit(TTY_FLUSHPENDING, &tty->flags))
434 break;
435 if (!tty->receive_room)
436 break;
437 if (count > tty->receive_room)
438 count = tty->receive_room;
439 char_buf = head->char_buf_ptr + head->read;
440 flag_buf = head->flag_buf_ptr + head->read;
441 head->read += count;
442 spin_unlock_irqrestore(&tty->buf.lock, flags);
443 disc->ops->receive_buf(tty, char_buf,
444 flag_buf, count);
445 spin_lock_irqsave(&tty->buf.lock, flags);
446 }
447 clear_bit(TTY_FLUSHING, &tty->flags);
448 }
449
450 /* We may have a deferred request to flush the input buffer,
451 if so pull the chain under the lock and empty the queue */
452 if (test_bit(TTY_FLUSHPENDING, &tty->flags)) {
453 __tty_buffer_flush(tty);
454 clear_bit(TTY_FLUSHPENDING, &tty->flags);
455 wake_up(&tty->read_wait);
456 }
457 spin_unlock_irqrestore(&tty->buf.lock, flags);
458
459 tty_ldisc_deref(disc);
460}
461
462/**
463 * tty_flush_to_ldisc
464 * @tty: tty to push
465 *
466 * Push the terminal flip buffers to the line discipline.
467 *
468 * Must not be called from IRQ context.
469 */
470void tty_flush_to_ldisc(struct tty_struct *tty)
471{
472 flush_work(&tty->buf.work);
473}
474
475/**
476 * tty_flip_buffer_push - terminal
477 * @tty: tty to push
478 *
479 * Queue a push of the terminal flip buffers to the line discipline. This
480 * function must not be called from IRQ context if tty->low_latency is set.
481 *
482 * In the event of the queue being busy for flipping the work will be
483 * held off and retried later.
484 *
485 * Locking: tty buffer lock. Driver locks in low latency mode.
486 */
487
488void tty_flip_buffer_push(struct tty_struct *tty)
489{
490 unsigned long flags;
491 spin_lock_irqsave(&tty->buf.lock, flags);
492 if (tty->buf.tail != NULL)
493 tty->buf.tail->commit = tty->buf.tail->used;
494 spin_unlock_irqrestore(&tty->buf.lock, flags);
495
496 if (tty->low_latency)
497 flush_to_ldisc(&tty->buf.work);
498 else
499 schedule_work(&tty->buf.work);
500}
501EXPORT_SYMBOL(tty_flip_buffer_push);
502
503/**
504 * tty_buffer_init - prepare a tty buffer structure
505 * @tty: tty to initialise
506 *
507 * Set up the initial state of the buffer management for a tty device.
508 * Must be called before the other tty buffer functions are used.
509 *
510 * Locking: none
511 */
512
513void tty_buffer_init(struct tty_struct *tty)
514{
515 spin_lock_init(&tty->buf.lock);
516 tty->buf.head = NULL;
517 tty->buf.tail = NULL;
518 tty->buf.free = NULL;
519 tty->buf.memory_used = 0;
520 INIT_WORK(&tty->buf.work, flush_to_ldisc);
521}
522
1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Tty buffer allocation management
4 */
5
6#include <linux/types.h>
7#include <linux/errno.h>
8#include <linux/minmax.h>
9#include <linux/tty.h>
10#include <linux/tty_driver.h>
11#include <linux/tty_flip.h>
12#include <linux/timer.h>
13#include <linux/string.h>
14#include <linux/slab.h>
15#include <linux/sched.h>
16#include <linux/wait.h>
17#include <linux/bitops.h>
18#include <linux/delay.h>
19#include <linux/module.h>
20#include <linux/ratelimit.h>
21#include "tty.h"
22
23#define MIN_TTYB_SIZE 256
24#define TTYB_ALIGN_MASK 0xff
25
26/*
27 * Byte threshold to limit memory consumption for flip buffers.
28 * The actual memory limit is > 2x this amount.
29 */
30#define TTYB_DEFAULT_MEM_LIMIT (640 * 1024UL)
31
32/*
33 * We default to dicing tty buffer allocations to this many characters
34 * in order to avoid multiple page allocations. We know the size of
35 * tty_buffer itself but it must also be taken into account that the
36 * buffer is 256 byte aligned. See tty_buffer_find for the allocation
37 * logic this must match.
38 */
39
40#define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~TTYB_ALIGN_MASK)
41
42/**
43 * tty_buffer_lock_exclusive - gain exclusive access to buffer
44 * @port: tty port owning the flip buffer
45 *
46 * Guarantees safe use of the &tty_ldisc_ops.receive_buf() method by excluding
47 * the buffer work and any pending flush from using the flip buffer. Data can
48 * continue to be added concurrently to the flip buffer from the driver side.
49 *
50 * See also tty_buffer_unlock_exclusive().
51 */
52void tty_buffer_lock_exclusive(struct tty_port *port)
53{
54 struct tty_bufhead *buf = &port->buf;
55
56 atomic_inc(&buf->priority);
57 mutex_lock(&buf->lock);
58}
59EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
60
61/**
62 * tty_buffer_unlock_exclusive - release exclusive access
63 * @port: tty port owning the flip buffer
64 *
65 * The buffer work is restarted if there is data in the flip buffer.
66 *
67 * See also tty_buffer_lock_exclusive().
68 */
69void tty_buffer_unlock_exclusive(struct tty_port *port)
70{
71 struct tty_bufhead *buf = &port->buf;
72 int restart;
73
74 restart = buf->head->commit != buf->head->read;
75
76 atomic_dec(&buf->priority);
77 mutex_unlock(&buf->lock);
78 if (restart)
79 queue_work(system_unbound_wq, &buf->work);
80}
81EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
82
83/**
84 * tty_buffer_space_avail - return unused buffer space
85 * @port: tty port owning the flip buffer
86 *
87 * Returns: the # of bytes which can be written by the driver without reaching
88 * the buffer limit.
89 *
90 * Note: this does not guarantee that memory is available to write the returned
91 * # of bytes (use tty_prepare_flip_string() to pre-allocate if memory
92 * guarantee is required).
93 */
94unsigned int tty_buffer_space_avail(struct tty_port *port)
95{
96 int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
97
98 return max(space, 0);
99}
100EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
101
102static void tty_buffer_reset(struct tty_buffer *p, size_t size)
103{
104 p->used = 0;
105 p->size = size;
106 p->next = NULL;
107 p->commit = 0;
108 p->lookahead = 0;
109 p->read = 0;
110 p->flags = true;
111}
112
113/**
114 * tty_buffer_free_all - free buffers used by a tty
115 * @port: tty port to free from
116 *
117 * Remove all the buffers pending on a tty whether queued with data or in the
118 * free ring. Must be called when the tty is no longer in use.
119 */
120void tty_buffer_free_all(struct tty_port *port)
121{
122 struct tty_bufhead *buf = &port->buf;
123 struct tty_buffer *p, *next;
124 struct llist_node *llist;
125 unsigned int freed = 0;
126 int still_used;
127
128 while ((p = buf->head) != NULL) {
129 buf->head = p->next;
130 freed += p->size;
131 if (p->size > 0)
132 kfree(p);
133 }
134 llist = llist_del_all(&buf->free);
135 llist_for_each_entry_safe(p, next, llist, free)
136 kfree(p);
137
138 tty_buffer_reset(&buf->sentinel, 0);
139 buf->head = &buf->sentinel;
140 buf->tail = &buf->sentinel;
141
142 still_used = atomic_xchg(&buf->mem_used, 0);
143 WARN(still_used != freed, "we still have not freed %d bytes!",
144 still_used - freed);
145}
146
147/**
148 * tty_buffer_alloc - allocate a tty buffer
149 * @port: tty port
150 * @size: desired size (characters)
151 *
152 * Allocate a new tty buffer to hold the desired number of characters. We
153 * round our buffers off in 256 character chunks to get better allocation
154 * behaviour.
155 *
156 * Returns: %NULL if out of memory or the allocation would exceed the per
157 * device queue.
158 */
159static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
160{
161 struct llist_node *free;
162 struct tty_buffer *p;
163
164 /* Round the buffer size out */
165 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
166
167 if (size <= MIN_TTYB_SIZE) {
168 free = llist_del_first(&port->buf.free);
169 if (free) {
170 p = llist_entry(free, struct tty_buffer, free);
171 goto found;
172 }
173 }
174
175 /* Should possibly check if this fails for the largest buffer we
176 * have queued and recycle that ?
177 */
178 if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
179 return NULL;
180 p = kmalloc(sizeof(struct tty_buffer) + 2 * size,
181 GFP_ATOMIC | __GFP_NOWARN);
182 if (p == NULL)
183 return NULL;
184
185found:
186 tty_buffer_reset(p, size);
187 atomic_add(size, &port->buf.mem_used);
188 return p;
189}
190
191/**
192 * tty_buffer_free - free a tty buffer
193 * @port: tty port owning the buffer
194 * @b: the buffer to free
195 *
196 * Free a tty buffer, or add it to the free list according to our internal
197 * strategy.
198 */
199static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
200{
201 struct tty_bufhead *buf = &port->buf;
202
203 /* Dumb strategy for now - should keep some stats */
204 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
205
206 if (b->size > MIN_TTYB_SIZE)
207 kfree(b);
208 else if (b->size > 0)
209 llist_add(&b->free, &buf->free);
210}
211
212/**
213 * tty_buffer_flush - flush full tty buffers
214 * @tty: tty to flush
215 * @ld: optional ldisc ptr (must be referenced)
216 *
217 * Flush all the buffers containing receive data. If @ld != %NULL, flush the
218 * ldisc input buffer.
219 *
220 * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
221 */
222void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
223{
224 struct tty_port *port = tty->port;
225 struct tty_bufhead *buf = &port->buf;
226 struct tty_buffer *next;
227
228 atomic_inc(&buf->priority);
229
230 mutex_lock(&buf->lock);
231 /* paired w/ release in __tty_buffer_request_room; ensures there are
232 * no pending memory accesses to the freed buffer
233 */
234 while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
235 tty_buffer_free(port, buf->head);
236 buf->head = next;
237 }
238 buf->head->read = buf->head->commit;
239 buf->head->lookahead = buf->head->read;
240
241 if (ld && ld->ops->flush_buffer)
242 ld->ops->flush_buffer(tty);
243
244 atomic_dec(&buf->priority);
245 mutex_unlock(&buf->lock);
246}
247
248/**
249 * __tty_buffer_request_room - grow tty buffer if needed
250 * @port: tty port
251 * @size: size desired
252 * @flags: buffer has to store flags along character data
253 *
254 * Make at least @size bytes of linear space available for the tty buffer.
255 *
256 * Will change over to a new buffer if the current buffer is encoded as
257 * %TTY_NORMAL (so has no flags buffer) and the new buffer requires a flags
258 * buffer.
259 *
260 * Returns: the size we managed to find.
261 */
262static int __tty_buffer_request_room(struct tty_port *port, size_t size,
263 bool flags)
264{
265 struct tty_bufhead *buf = &port->buf;
266 struct tty_buffer *b, *n;
267 int left, change;
268
269 b = buf->tail;
270 if (!b->flags)
271 left = 2 * b->size - b->used;
272 else
273 left = b->size - b->used;
274
275 change = !b->flags && flags;
276 if (change || left < size) {
277 /* This is the slow path - looking for new buffers to use */
278 n = tty_buffer_alloc(port, size);
279 if (n != NULL) {
280 n->flags = flags;
281 buf->tail = n;
282 /*
283 * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
284 * ensures they see all buffer data.
285 */
286 smp_store_release(&b->commit, b->used);
287 /*
288 * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
289 * ensures the latest commit value can be read before the head
290 * is advanced to the next buffer.
291 */
292 smp_store_release(&b->next, n);
293 } else if (change)
294 size = 0;
295 else
296 size = left;
297 }
298 return size;
299}
300
301int tty_buffer_request_room(struct tty_port *port, size_t size)
302{
303 return __tty_buffer_request_room(port, size, true);
304}
305EXPORT_SYMBOL_GPL(tty_buffer_request_room);
306
307/**
308 * tty_insert_flip_string_fixed_flag - add characters to the tty buffer
309 * @port: tty port
310 * @chars: characters
311 * @flag: flag value for each character
312 * @size: size
313 *
314 * Queue a series of bytes to the tty buffering. All the characters passed are
315 * marked with the supplied flag.
316 *
317 * Returns: the number added.
318 */
319int tty_insert_flip_string_fixed_flag(struct tty_port *port,
320 const unsigned char *chars, char flag, size_t size)
321{
322 int copied = 0;
323 bool flags = flag != TTY_NORMAL;
324
325 do {
326 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
327 int space = __tty_buffer_request_room(port, goal, flags);
328 struct tty_buffer *tb = port->buf.tail;
329
330 if (unlikely(space == 0))
331 break;
332 memcpy(char_buf_ptr(tb, tb->used), chars, space);
333 if (tb->flags)
334 memset(flag_buf_ptr(tb, tb->used), flag, space);
335 tb->used += space;
336 copied += space;
337 chars += space;
338 /* There is a small chance that we need to split the data over
339 * several buffers. If this is the case we must loop.
340 */
341 } while (unlikely(size > copied));
342 return copied;
343}
344EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
345
346/**
347 * tty_insert_flip_string_flags - add characters to the tty buffer
348 * @port: tty port
349 * @chars: characters
350 * @flags: flag bytes
351 * @size: size
352 *
353 * Queue a series of bytes to the tty buffering. For each character the flags
354 * array indicates the status of the character.
355 *
356 * Returns: the number added.
357 */
358int tty_insert_flip_string_flags(struct tty_port *port,
359 const unsigned char *chars, const char *flags, size_t size)
360{
361 int copied = 0;
362
363 do {
364 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
365 int space = tty_buffer_request_room(port, goal);
366 struct tty_buffer *tb = port->buf.tail;
367
368 if (unlikely(space == 0))
369 break;
370 memcpy(char_buf_ptr(tb, tb->used), chars, space);
371 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
372 tb->used += space;
373 copied += space;
374 chars += space;
375 flags += space;
376 /* There is a small chance that we need to split the data over
377 * several buffers. If this is the case we must loop.
378 */
379 } while (unlikely(size > copied));
380 return copied;
381}
382EXPORT_SYMBOL(tty_insert_flip_string_flags);
383
384/**
385 * __tty_insert_flip_char - add one character to the tty buffer
386 * @port: tty port
387 * @ch: character
388 * @flag: flag byte
389 *
390 * Queue a single byte @ch to the tty buffering, with an optional flag. This is
391 * the slow path of tty_insert_flip_char().
392 */
393int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag)
394{
395 struct tty_buffer *tb;
396 bool flags = flag != TTY_NORMAL;
397
398 if (!__tty_buffer_request_room(port, 1, flags))
399 return 0;
400
401 tb = port->buf.tail;
402 if (tb->flags)
403 *flag_buf_ptr(tb, tb->used) = flag;
404 *char_buf_ptr(tb, tb->used++) = ch;
405
406 return 1;
407}
408EXPORT_SYMBOL(__tty_insert_flip_char);
409
410/**
411 * tty_prepare_flip_string - make room for characters
412 * @port: tty port
413 * @chars: return pointer for character write area
414 * @size: desired size
415 *
416 * Prepare a block of space in the buffer for data.
417 *
418 * This is used for drivers that need their own block copy routines into the
419 * buffer. There is no guarantee the buffer is a DMA target!
420 *
421 * Returns: the length available and buffer pointer (@chars) to the space which
422 * is now allocated and accounted for as ready for normal characters.
423 */
424int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
425 size_t size)
426{
427 int space = __tty_buffer_request_room(port, size, false);
428
429 if (likely(space)) {
430 struct tty_buffer *tb = port->buf.tail;
431
432 *chars = char_buf_ptr(tb, tb->used);
433 if (tb->flags)
434 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
435 tb->used += space;
436 }
437 return space;
438}
439EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
440
441/**
442 * tty_ldisc_receive_buf - forward data to line discipline
443 * @ld: line discipline to process input
444 * @p: char buffer
445 * @f: %TTY_NORMAL, %TTY_BREAK, etc. flags buffer
446 * @count: number of bytes to process
447 *
448 * Callers other than flush_to_ldisc() need to exclude the kworker from
449 * concurrent use of the line discipline, see paste_selection().
450 *
451 * Returns: the number of bytes processed.
452 */
453int tty_ldisc_receive_buf(struct tty_ldisc *ld, const unsigned char *p,
454 const char *f, int count)
455{
456 if (ld->ops->receive_buf2)
457 count = ld->ops->receive_buf2(ld->tty, p, f, count);
458 else {
459 count = min_t(int, count, ld->tty->receive_room);
460 if (count && ld->ops->receive_buf)
461 ld->ops->receive_buf(ld->tty, p, f, count);
462 }
463 return count;
464}
465EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
466
467static void lookahead_bufs(struct tty_port *port, struct tty_buffer *head)
468{
469 head->lookahead = max(head->lookahead, head->read);
470
471 while (head) {
472 struct tty_buffer *next;
473 unsigned int count;
474
475 /*
476 * Paired w/ release in __tty_buffer_request_room();
477 * ensures commit value read is not stale if the head
478 * is advancing to the next buffer.
479 */
480 next = smp_load_acquire(&head->next);
481 /*
482 * Paired w/ release in __tty_buffer_request_room() or in
483 * tty_buffer_flush(); ensures we see the committed buffer data.
484 */
485 count = smp_load_acquire(&head->commit) - head->lookahead;
486 if (!count) {
487 head = next;
488 continue;
489 }
490
491 if (port->client_ops->lookahead_buf) {
492 unsigned char *p, *f = NULL;
493
494 p = char_buf_ptr(head, head->lookahead);
495 if (head->flags)
496 f = flag_buf_ptr(head, head->lookahead);
497
498 port->client_ops->lookahead_buf(port, p, f, count);
499 }
500
501 head->lookahead += count;
502 }
503}
504
505static int
506receive_buf(struct tty_port *port, struct tty_buffer *head, int count)
507{
508 unsigned char *p = char_buf_ptr(head, head->read);
509 const char *f = NULL;
510 int n;
511
512 if (head->flags)
513 f = flag_buf_ptr(head, head->read);
514
515 n = port->client_ops->receive_buf(port, p, f, count);
516 if (n > 0)
517 memset(p, 0, n);
518 return n;
519}
520
521/**
522 * flush_to_ldisc - flush data from buffer to ldisc
523 * @work: tty structure passed from work queue.
524 *
525 * This routine is called out of the software interrupt to flush data from the
526 * buffer chain to the line discipline.
527 *
528 * The receive_buf() method is single threaded for each tty instance.
529 *
530 * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
531 */
532static void flush_to_ldisc(struct work_struct *work)
533{
534 struct tty_port *port = container_of(work, struct tty_port, buf.work);
535 struct tty_bufhead *buf = &port->buf;
536
537 mutex_lock(&buf->lock);
538
539 while (1) {
540 struct tty_buffer *head = buf->head;
541 struct tty_buffer *next;
542 int count, rcvd;
543
544 /* Ldisc or user is trying to gain exclusive access */
545 if (atomic_read(&buf->priority))
546 break;
547
548 /* paired w/ release in __tty_buffer_request_room();
549 * ensures commit value read is not stale if the head
550 * is advancing to the next buffer
551 */
552 next = smp_load_acquire(&head->next);
553 /* paired w/ release in __tty_buffer_request_room() or in
554 * tty_buffer_flush(); ensures we see the committed buffer data
555 */
556 count = smp_load_acquire(&head->commit) - head->read;
557 if (!count) {
558 if (next == NULL)
559 break;
560 buf->head = next;
561 tty_buffer_free(port, head);
562 continue;
563 }
564
565 rcvd = receive_buf(port, head, count);
566 head->read += rcvd;
567 if (rcvd < count)
568 lookahead_bufs(port, head);
569 if (!rcvd)
570 break;
571
572 if (need_resched())
573 cond_resched();
574 }
575
576 mutex_unlock(&buf->lock);
577
578}
579
580static inline void tty_flip_buffer_commit(struct tty_buffer *tail)
581{
582 /*
583 * Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
584 * buffer data.
585 */
586 smp_store_release(&tail->commit, tail->used);
587}
588
589/**
590 * tty_flip_buffer_push - push terminal buffers
591 * @port: tty port to push
592 *
593 * Queue a push of the terminal flip buffers to the line discipline. Can be
594 * called from IRQ/atomic context.
595 *
596 * In the event of the queue being busy for flipping the work will be held off
597 * and retried later.
598 */
599void tty_flip_buffer_push(struct tty_port *port)
600{
601 struct tty_bufhead *buf = &port->buf;
602
603 tty_flip_buffer_commit(buf->tail);
604 queue_work(system_unbound_wq, &buf->work);
605}
606EXPORT_SYMBOL(tty_flip_buffer_push);
607
608/**
609 * tty_insert_flip_string_and_push_buffer - add characters to the tty buffer and
610 * push
611 * @port: tty port
612 * @chars: characters
613 * @size: size
614 *
615 * The function combines tty_insert_flip_string() and tty_flip_buffer_push()
616 * with the exception of properly holding the @port->lock.
617 *
618 * To be used only internally (by pty currently).
619 *
620 * Returns: the number added.
621 */
622int tty_insert_flip_string_and_push_buffer(struct tty_port *port,
623 const unsigned char *chars, size_t size)
624{
625 struct tty_bufhead *buf = &port->buf;
626 unsigned long flags;
627
628 spin_lock_irqsave(&port->lock, flags);
629 size = tty_insert_flip_string(port, chars, size);
630 if (size)
631 tty_flip_buffer_commit(buf->tail);
632 spin_unlock_irqrestore(&port->lock, flags);
633
634 queue_work(system_unbound_wq, &buf->work);
635
636 return size;
637}
638
639/**
640 * tty_buffer_init - prepare a tty buffer structure
641 * @port: tty port to initialise
642 *
643 * Set up the initial state of the buffer management for a tty device. Must be
644 * called before the other tty buffer functions are used.
645 */
646void tty_buffer_init(struct tty_port *port)
647{
648 struct tty_bufhead *buf = &port->buf;
649
650 mutex_init(&buf->lock);
651 tty_buffer_reset(&buf->sentinel, 0);
652 buf->head = &buf->sentinel;
653 buf->tail = &buf->sentinel;
654 init_llist_head(&buf->free);
655 atomic_set(&buf->mem_used, 0);
656 atomic_set(&buf->priority, 0);
657 INIT_WORK(&buf->work, flush_to_ldisc);
658 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
659}
660
661/**
662 * tty_buffer_set_limit - change the tty buffer memory limit
663 * @port: tty port to change
664 * @limit: memory limit to set
665 *
666 * Change the tty buffer memory limit.
667 *
668 * Must be called before the other tty buffer functions are used.
669 */
670int tty_buffer_set_limit(struct tty_port *port, int limit)
671{
672 if (limit < MIN_TTYB_SIZE)
673 return -EINVAL;
674 port->buf.mem_limit = limit;
675 return 0;
676}
677EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
678
679/* slave ptys can claim nested buffer lock when handling BRK and INTR */
680void tty_buffer_set_lock_subclass(struct tty_port *port)
681{
682 lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
683}
684
685bool tty_buffer_restart_work(struct tty_port *port)
686{
687 return queue_work(system_unbound_wq, &port->buf.work);
688}
689
690bool tty_buffer_cancel_work(struct tty_port *port)
691{
692 return cancel_work_sync(&port->buf.work);
693}
694
695void tty_buffer_flush_work(struct tty_port *port)
696{
697 flush_work(&port->buf.work);
698}