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
tty_buffer_free_all(struct tty_struct * tty)30 void 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
tty_buffer_alloc(struct tty_struct * tty,size_t size)57 static 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
tty_buffer_free(struct tty_struct * tty,struct tty_buffer * b)88 static 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
__tty_buffer_flush(struct tty_struct * tty)113 static 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
tty_buffer_flush(struct tty_struct * tty)135 void 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
tty_buffer_find(struct tty_struct * tty,size_t size)166 static 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 */
tty_buffer_request_room(struct tty_struct * tty,size_t size)199 int 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 }
231 EXPORT_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
tty_insert_flip_string_fixed_flag(struct tty_struct * tty,const unsigned char * chars,char flag,size_t size)246 int 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 }
267 EXPORT_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
tty_insert_flip_string_flags(struct tty_struct * tty,const unsigned char * chars,const char * flags,size_t size)283 int 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 }
305 EXPORT_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
tty_schedule_flip(struct tty_struct * tty)318 void 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 }
327 EXPORT_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
tty_prepare_flip_string(struct tty_struct * tty,unsigned char ** chars,size_t size)344 int 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 }
356 EXPORT_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
tty_prepare_flip_string_flags(struct tty_struct * tty,unsigned char ** chars,char ** flags,size_t size)374 int 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 }
386 EXPORT_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
flush_to_ldisc(struct work_struct * work)402 static 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 */
tty_flush_to_ldisc(struct tty_struct * tty)470 void 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
tty_flip_buffer_push(struct tty_struct * tty)488 void 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 }
501 EXPORT_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
tty_buffer_init(struct tty_struct * tty)513 void 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
523