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