1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
|
/*
* Tty buffer allocation management
*/
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/tty.h>
#include <linux/tty_driver.h>
#include <linux/tty_flip.h>
#include <linux/timer.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/wait.h>
#include <linux/bitops.h>
#include <linux/delay.h>
#include <linux/module.h>
#include <linux/ratelimit.h>
#define MIN_TTYB_SIZE 256
#define TTYB_ALIGN_MASK 255
/*
* Byte threshold to limit memory consumption for flip buffers.
* The actual memory limit is > 2x this amount.
*/
#define TTYB_MEM_LIMIT 65536
/**
* tty_buffer_lock_exclusive - gain exclusive access to buffer
* tty_buffer_unlock_exclusive - release exclusive access
*
* @port - tty_port owning the flip buffer
*
* Guarantees safe use of the line discipline's receive_buf() method by
* excluding the buffer work and any pending flush from using the flip
* buffer. Data can continue to be added concurrently to the flip buffer
* from the driver side.
*
* On release, the buffer work is restarted if there is data in the
* flip buffer
*/
void tty_buffer_lock_exclusive(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
atomic_inc(&buf->priority);
mutex_lock(&buf->lock);
}
void tty_buffer_unlock_exclusive(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
int restart;
restart = buf->head->commit != buf->head->read;
atomic_dec(&buf->priority);
mutex_unlock(&buf->lock);
if (restart)
queue_work(system_unbound_wq, &buf->work);
}
/**
* tty_buffer_space_avail - return unused buffer space
* @port - tty_port owning the flip buffer
*
* Returns the # of bytes which can be written by the driver without
* reaching the buffer limit.
*
* Note: this does not guarantee that memory is available to write
* the returned # of bytes (use tty_prepare_flip_string_xxx() to
* pre-allocate if memory guarantee is required).
*/
int tty_buffer_space_avail(struct tty_port *port)
{
int space = TTYB_MEM_LIMIT - atomic_read(&port->buf.memory_used);
return max(space, 0);
}
static void tty_buffer_reset(struct tty_buffer *p, size_t size)
{
p->used = 0;
p->size = size;
p->next = NULL;
p->commit = 0;
p->read = 0;
}
/**
* tty_buffer_free_all - free buffers used by a tty
* @tty: tty to free from
*
* Remove all the buffers pending on a tty whether queued with data
* or in the free ring. Must be called when the tty is no longer in use
*/
void tty_buffer_free_all(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
struct tty_buffer *p, *next;
struct llist_node *llist;
while ((p = buf->head) != NULL) {
buf->head = p->next;
if (p->size > 0)
kfree(p);
}
llist = llist_del_all(&buf->free);
llist_for_each_entry_safe(p, next, llist, free)
kfree(p);
tty_buffer_reset(&buf->sentinel, 0);
buf->head = &buf->sentinel;
buf->tail = &buf->sentinel;
atomic_set(&buf->memory_used, 0);
}
/**
* tty_buffer_alloc - allocate a tty buffer
* @tty: tty device
* @size: desired size (characters)
*
* Allocate a new tty buffer to hold the desired number of characters.
* We round our buffers off in 256 character chunks to get better
* allocation behaviour.
* Return NULL if out of memory or the allocation would exceed the
* per device queue
*/
static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
{
struct llist_node *free;
struct tty_buffer *p;
/* Round the buffer size out */
size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
if (size <= MIN_TTYB_SIZE) {
free = llist_del_first(&port->buf.free);
if (free) {
p = llist_entry(free, struct tty_buffer, free);
goto found;
}
}
/* Should possibly check if this fails for the largest buffer we
have queued and recycle that ? */
if (atomic_read(&port->buf.memory_used) > TTYB_MEM_LIMIT)
return NULL;
p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
if (p == NULL)
return NULL;
found:
tty_buffer_reset(p, size);
atomic_add(size, &port->buf.memory_used);
return p;
}
/**
* tty_buffer_free - free a tty buffer
* @tty: tty owning the buffer
* @b: the buffer to free
*
* Free a tty buffer, or add it to the free list according to our
* internal strategy
*/
static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
{
struct tty_bufhead *buf = &port->buf;
/* Dumb strategy for now - should keep some stats */
WARN_ON(atomic_sub_return(b->size, &buf->memory_used) < 0);
if (b->size > MIN_TTYB_SIZE)
kfree(b);
else if (b->size > 0)
llist_add(&b->free, &buf->free);
}
/**
* tty_buffer_flush - flush full tty buffers
* @tty: tty to flush
*
* flush all the buffers containing receive data. If the buffer is
* being processed by flush_to_ldisc then we defer the processing
* to that function
*
* Locking: takes buffer lock to ensure single-threaded flip buffer
* 'consumer'
*/
void tty_buffer_flush(struct tty_struct *tty)
{
struct tty_port *port = tty->port;
struct tty_bufhead *buf = &port->buf;
struct tty_buffer *next;
atomic_inc(&buf->priority);
mutex_lock(&buf->lock);
while ((next = buf->head->next) != NULL) {
tty_buffer_free(port, buf->head);
buf->head = next;
}
buf->head->read = buf->head->commit;
atomic_dec(&buf->priority);
mutex_unlock(&buf->lock);
}
/**
* tty_buffer_request_room - grow tty buffer if needed
* @tty: tty structure
* @size: size desired
*
* Make at least size bytes of linear space available for the tty
* buffer. If we fail return the size we managed to find.
*/
int tty_buffer_request_room(struct tty_port *port, size_t size)
{
struct tty_bufhead *buf = &port->buf;
struct tty_buffer *b, *n;
int left;
b = buf->tail;
left = b->size - b->used;
if (left < size) {
/* This is the slow path - looking for new buffers to use */
if ((n = tty_buffer_alloc(port, size)) != NULL) {
buf->tail = n;
b->commit = b->used;
smp_mb();
b->next = n;
} else
size = left;
}
return size;
}
EXPORT_SYMBOL_GPL(tty_buffer_request_room);
/**
* tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
* @port: tty port
* @chars: characters
* @flag: flag value for each character
* @size: size
*
* Queue a series of bytes to the tty buffering. All the characters
* passed are marked with the supplied flag. Returns the number added.
*/
int tty_insert_flip_string_fixed_flag(struct tty_port *port,
const unsigned char *chars, char flag, size_t size)
{
int copied = 0;
do {
int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
int space = tty_buffer_request_room(port, goal);
struct tty_buffer *tb = port->buf.tail;
if (unlikely(space == 0))
break;
memcpy(char_buf_ptr(tb, tb->used), chars, space);
memset(flag_buf_ptr(tb, tb->used), flag, space);
tb->used += space;
copied += space;
chars += space;
/* There is a small chance that we need to split the data over
several buffers. If this is the case we must loop */
} while (unlikely(size > copied));
return copied;
}
EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
/**
* tty_insert_flip_string_flags - Add characters to the tty buffer
* @port: tty port
* @chars: characters
* @flags: flag bytes
* @size: size
*
* Queue a series of bytes to the tty buffering. For each character
* the flags array indicates the status of the character. Returns the
* number added.
*/
int tty_insert_flip_string_flags(struct tty_port *port,
const unsigned char *chars, const char *flags, size_t size)
{
int copied = 0;
do {
int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
int space = tty_buffer_request_room(port, goal);
struct tty_buffer *tb = port->buf.tail;
if (unlikely(space == 0))
break;
memcpy(char_buf_ptr(tb, tb->used), chars, space);
memcpy(flag_buf_ptr(tb, tb->used), flags, space);
tb->used += space;
copied += space;
chars += space;
flags += space;
/* There is a small chance that we need to split the data over
several buffers. If this is the case we must loop */
} while (unlikely(size > copied));
return copied;
}
EXPORT_SYMBOL(tty_insert_flip_string_flags);
/**
* tty_schedule_flip - push characters to ldisc
* @port: tty port to push from
*
* Takes any pending buffers and transfers their ownership to the
* ldisc side of the queue. It then schedules those characters for
* processing by the line discipline.
* Note that this function can only be used when the low_latency flag
* is unset. Otherwise the workqueue won't be flushed.
*/
void tty_schedule_flip(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
WARN_ON(port->low_latency);
buf->tail->commit = buf->tail->used;
schedule_work(&buf->work);
}
EXPORT_SYMBOL(tty_schedule_flip);
/**
* tty_prepare_flip_string - make room for characters
* @port: tty port
* @chars: return pointer for character write area
* @size: desired size
*
* Prepare a block of space in the buffer for data. Returns the length
* available and buffer pointer to the space which is now allocated and
* accounted for as ready for normal characters. This is used for drivers
* that need their own block copy routines into the buffer. There is no
* guarantee the buffer is a DMA target!
*/
int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
size_t size)
{
int space = tty_buffer_request_room(port, size);
if (likely(space)) {
struct tty_buffer *tb = port->buf.tail;
*chars = char_buf_ptr(tb, tb->used);
memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
tb->used += space;
}
return space;
}
EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
/**
* tty_prepare_flip_string_flags - make room for characters
* @port: tty port
* @chars: return pointer for character write area
* @flags: return pointer for status flag write area
* @size: desired size
*
* Prepare a block of space in the buffer for data. Returns the length
* available and buffer pointer to the space which is now allocated and
* accounted for as ready for characters. This is used for drivers
* that need their own block copy routines into the buffer. There is no
* guarantee the buffer is a DMA target!
*/
int tty_prepare_flip_string_flags(struct tty_port *port,
unsigned char **chars, char **flags, size_t size)
{
int space = tty_buffer_request_room(port, size);
if (likely(space)) {
struct tty_buffer *tb = port->buf.tail;
*chars = char_buf_ptr(tb, tb->used);
*flags = flag_buf_ptr(tb, tb->used);
tb->used += space;
}
return space;
}
EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
static int
receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
{
struct tty_ldisc *disc = tty->ldisc;
unsigned char *p = char_buf_ptr(head, head->read);
char *f = flag_buf_ptr(head, head->read);
if (disc->ops->receive_buf2)
count = disc->ops->receive_buf2(tty, p, f, count);
else {
count = min_t(int, count, tty->receive_room);
if (count)
disc->ops->receive_buf(tty, p, f, count);
}
head->read += count;
return count;
}
/**
* flush_to_ldisc
* @work: tty structure passed from work queue.
*
* This routine is called out of the software interrupt to flush data
* from the buffer chain to the line discipline.
*
* The receive_buf method is single threaded for each tty instance.
*
* Locking: takes buffer lock to ensure single-threaded flip buffer
* 'consumer'
*/
static void flush_to_ldisc(struct work_struct *work)
{
struct tty_port *port = container_of(work, struct tty_port, buf.work);
struct tty_bufhead *buf = &port->buf;
struct tty_struct *tty;
struct tty_ldisc *disc;
tty = port->itty;
if (tty == NULL)
return;
disc = tty_ldisc_ref(tty);
if (disc == NULL)
return;
mutex_lock(&buf->lock);
while (1) {
struct tty_buffer *head = buf->head;
int count;
/* Ldisc or user is trying to gain exclusive access */
if (atomic_read(&buf->priority))
break;
count = head->commit - head->read;
if (!count) {
if (head->next == NULL)
break;
buf->head = head->next;
tty_buffer_free(port, head);
continue;
}
count = receive_buf(tty, head, count);
if (!count)
break;
}
mutex_unlock(&buf->lock);
tty_ldisc_deref(disc);
}
/**
* tty_flush_to_ldisc
* @tty: tty to push
*
* Push the terminal flip buffers to the line discipline.
*
* Must not be called from IRQ context.
*/
void tty_flush_to_ldisc(struct tty_struct *tty)
{
if (!tty->port->low_latency)
flush_work(&tty->port->buf.work);
}
/**
* tty_flip_buffer_push - terminal
* @port: tty port to push
*
* Queue a push of the terminal flip buffers to the line discipline. This
* function must not be called from IRQ context if port->low_latency is
* set.
*
* In the event of the queue being busy for flipping the work will be
* held off and retried later.
*/
void tty_flip_buffer_push(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
buf->tail->commit = buf->tail->used;
if (port->low_latency)
flush_to_ldisc(&buf->work);
else
schedule_work(&buf->work);
}
EXPORT_SYMBOL(tty_flip_buffer_push);
/**
* tty_buffer_init - prepare a tty buffer structure
* @tty: tty to initialise
*
* Set up the initial state of the buffer management for a tty device.
* Must be called before the other tty buffer functions are used.
*/
void tty_buffer_init(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
mutex_init(&buf->lock);
tty_buffer_reset(&buf->sentinel, 0);
buf->head = &buf->sentinel;
buf->tail = &buf->sentinel;
init_llist_head(&buf->free);
atomic_set(&buf->memory_used, 0);
atomic_set(&buf->priority, 0);
INIT_WORK(&buf->work, flush_to_ldisc);
}
|