2 * Tty buffer allocation management
5 #include <linux/types.h>
6 #include <linux/errno.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 #include <linux/ratelimit.h>
22 #define MIN_TTYB_SIZE 256
23 #define TTYB_ALIGN_MASK 255
25 static void tty_buffer_reset(struct tty_buffer *p, size_t size)
35 * tty_buffer_free_all - free buffers used by a tty
36 * @tty: tty to free from
38 * Remove all the buffers pending on a tty whether queued with data
39 * or in the free ring. Must be called when the tty is no longer in use
44 void tty_buffer_free_all(struct tty_port *port)
46 struct tty_bufhead *buf = &port->buf;
47 struct tty_buffer *thead;
49 while ((thead = buf->head) != NULL) {
50 buf->head = thead->next;
53 while ((thead = buf->free) != NULL) {
54 buf->free = thead->next;
62 * tty_buffer_alloc - allocate a tty buffer
64 * @size: desired size (characters)
66 * Allocate a new tty buffer to hold the desired number of characters.
67 * Return NULL if out of memory or the allocation would exceed the
70 * Locking: Caller must hold tty->buf.lock
73 static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
77 if (port->buf.memory_used + size > 65536)
79 p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
83 tty_buffer_reset(p, size);
84 port->buf.memory_used += size;
89 * tty_buffer_free - free a tty buffer
90 * @tty: tty owning the buffer
91 * @b: the buffer to free
93 * Free a tty buffer, or add it to the free list according to our
96 * Locking: Caller must hold tty->buf.lock
99 static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
101 struct tty_bufhead *buf = &port->buf;
103 /* Dumb strategy for now - should keep some stats */
104 buf->memory_used -= b->size;
105 WARN_ON(buf->memory_used < 0);
107 if (b->size > MIN_TTYB_SIZE)
116 * __tty_buffer_flush - flush full tty buffers
119 * flush all the buffers containing receive data. Caller must
120 * hold the buffer lock and must have ensured no parallel flush to
123 * Locking: Caller must hold tty->buf.lock
126 static void __tty_buffer_flush(struct tty_port *port)
128 struct tty_bufhead *buf = &port->buf;
129 struct tty_buffer *thead;
131 if (unlikely(buf->head == NULL))
133 while ((thead = buf->head->next) != NULL) {
134 tty_buffer_free(port, buf->head);
137 WARN_ON(buf->head != buf->tail);
138 buf->head->read = buf->head->commit;
142 * tty_buffer_flush - flush full tty buffers
145 * flush all the buffers containing receive data. If the buffer is
146 * being processed by flush_to_ldisc then we defer the processing
152 void tty_buffer_flush(struct tty_struct *tty)
154 struct tty_port *port = tty->port;
155 struct tty_bufhead *buf = &port->buf;
158 spin_lock_irqsave(&buf->lock, flags);
160 /* If the data is being pushed to the tty layer then we can't
161 process it here. Instead set a flag and the flush_to_ldisc
162 path will process the flush request before it exits */
163 if (test_bit(TTYP_FLUSHING, &port->iflags)) {
164 set_bit(TTYP_FLUSHPENDING, &port->iflags);
165 spin_unlock_irqrestore(&buf->lock, flags);
166 wait_event(tty->read_wait,
167 test_bit(TTYP_FLUSHPENDING, &port->iflags) == 0);
170 __tty_buffer_flush(port);
171 spin_unlock_irqrestore(&buf->lock, flags);
175 * tty_buffer_find - find a free tty buffer
176 * @tty: tty owning the buffer
177 * @size: characters wanted
179 * Locate an existing suitable tty buffer or if we are lacking one then
180 * allocate a new one. We round our buffers off in 256 character chunks
181 * to get better allocation behaviour.
183 * Locking: Caller must hold tty->buf.lock
186 static struct tty_buffer *tty_buffer_find(struct tty_port *port, size_t size)
188 struct tty_buffer **tbh = &port->buf.free;
189 if (size <= MIN_TTYB_SIZE) {
191 struct tty_buffer *t = *tbh;
194 tty_buffer_reset(t, t->size);
195 port->buf.memory_used += t->size;
199 /* Round the buffer size out */
200 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
201 return tty_buffer_alloc(port, size);
202 /* Should possibly check if this fails for the largest buffer we
203 have queued and recycle that ? */
206 * tty_buffer_request_room - grow tty buffer if needed
207 * @tty: tty structure
208 * @size: size desired
210 * Make at least size bytes of linear space available for the tty
211 * buffer. If we fail return the size we managed to find.
213 * Locking: Takes port->buf.lock
215 int tty_buffer_request_room(struct tty_port *port, size_t size)
217 struct tty_bufhead *buf = &port->buf;
218 struct tty_buffer *b, *n;
221 spin_lock_irqsave(&buf->lock, flags);
222 /* OPTIMISATION: We could keep a per tty "zero" sized buffer to
223 remove this conditional if its worth it. This would be invisible
227 left = b->size - b->used;
232 /* This is the slow path - looking for new buffers to use */
233 if ((n = tty_buffer_find(port, size)) != NULL) {
243 spin_unlock_irqrestore(&buf->lock, flags);
246 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
249 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
252 * @flag: flag value for each character
255 * Queue a series of bytes to the tty buffering. All the characters
256 * passed are marked with the supplied flag. Returns the number added.
258 * Locking: Called functions may take port->buf.lock
261 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
262 const unsigned char *chars, char flag, size_t size)
266 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
267 int space = tty_buffer_request_room(port, goal);
268 struct tty_buffer *tb = port->buf.tail;
269 /* If there is no space then tb may be NULL */
270 if (unlikely(space == 0)) {
273 memcpy(char_buf_ptr(tb, tb->used), chars, space);
274 memset(flag_buf_ptr(tb, tb->used), flag, space);
278 /* There is a small chance that we need to split the data over
279 several buffers. If this is the case we must loop */
280 } while (unlikely(size > copied));
283 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
286 * tty_insert_flip_string_flags - Add characters to the tty buffer
292 * Queue a series of bytes to the tty buffering. For each character
293 * the flags array indicates the status of the character. Returns the
296 * Locking: Called functions may take port->buf.lock
299 int tty_insert_flip_string_flags(struct tty_port *port,
300 const unsigned char *chars, const char *flags, size_t size)
304 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
305 int space = tty_buffer_request_room(port, goal);
306 struct tty_buffer *tb = port->buf.tail;
307 /* If there is no space then tb may be NULL */
308 if (unlikely(space == 0)) {
311 memcpy(char_buf_ptr(tb, tb->used), chars, space);
312 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
317 /* There is a small chance that we need to split the data over
318 several buffers. If this is the case we must loop */
319 } while (unlikely(size > copied));
322 EXPORT_SYMBOL(tty_insert_flip_string_flags);
325 * tty_schedule_flip - push characters to ldisc
326 * @port: tty port to push from
328 * Takes any pending buffers and transfers their ownership to the
329 * ldisc side of the queue. It then schedules those characters for
330 * processing by the line discipline.
331 * Note that this function can only be used when the low_latency flag
332 * is unset. Otherwise the workqueue won't be flushed.
334 * Locking: Takes port->buf.lock
337 void tty_schedule_flip(struct tty_port *port)
339 struct tty_bufhead *buf = &port->buf;
341 WARN_ON(port->low_latency);
343 spin_lock_irqsave(&buf->lock, flags);
344 if (buf->tail != NULL)
345 buf->tail->commit = buf->tail->used;
346 spin_unlock_irqrestore(&buf->lock, flags);
347 schedule_work(&buf->work);
349 EXPORT_SYMBOL(tty_schedule_flip);
352 * tty_prepare_flip_string - make room for characters
354 * @chars: return pointer for character write area
355 * @size: desired size
357 * Prepare a block of space in the buffer for data. Returns the length
358 * available and buffer pointer to the space which is now allocated and
359 * accounted for as ready for normal characters. This is used for drivers
360 * that need their own block copy routines into the buffer. There is no
361 * guarantee the buffer is a DMA target!
363 * Locking: May call functions taking port->buf.lock
366 int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
369 int space = tty_buffer_request_room(port, size);
371 struct tty_buffer *tb = port->buf.tail;
372 *chars = char_buf_ptr(tb, tb->used);
373 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
378 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
381 * tty_prepare_flip_string_flags - make room for characters
383 * @chars: return pointer for character write area
384 * @flags: return pointer for status flag write area
385 * @size: desired size
387 * Prepare a block of space in the buffer for data. Returns the length
388 * available and buffer pointer to the space which is now allocated and
389 * accounted for as ready for characters. This is used for drivers
390 * that need their own block copy routines into the buffer. There is no
391 * guarantee the buffer is a DMA target!
393 * Locking: May call functions taking port->buf.lock
396 int tty_prepare_flip_string_flags(struct tty_port *port,
397 unsigned char **chars, char **flags, size_t size)
399 int space = tty_buffer_request_room(port, size);
401 struct tty_buffer *tb = port->buf.tail;
402 *chars = char_buf_ptr(tb, tb->used);
403 *flags = flag_buf_ptr(tb, tb->used);
408 EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
412 receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
414 struct tty_ldisc *disc = tty->ldisc;
415 unsigned char *p = char_buf_ptr(head, head->read);
416 char *f = flag_buf_ptr(head, head->read);
418 if (disc->ops->receive_buf2)
419 count = disc->ops->receive_buf2(tty, p, f, count);
421 count = min_t(int, count, tty->receive_room);
423 disc->ops->receive_buf(tty, p, f, count);
431 * @work: tty structure passed from work queue.
433 * This routine is called out of the software interrupt to flush data
434 * from the buffer chain to the line discipline.
436 * Locking: holds tty->buf.lock to guard buffer list. Drops the lock
437 * while invoking the line discipline receive_buf method. The
438 * receive_buf method is single threaded for each tty instance.
441 static void flush_to_ldisc(struct work_struct *work)
443 struct tty_port *port = container_of(work, struct tty_port, buf.work);
444 struct tty_bufhead *buf = &port->buf;
445 struct tty_struct *tty;
447 struct tty_ldisc *disc;
453 disc = tty_ldisc_ref(tty);
457 spin_lock_irqsave(&buf->lock, flags);
459 if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) {
460 struct tty_buffer *head;
461 while ((head = buf->head) != NULL) {
464 count = head->commit - head->read;
466 if (head->next == NULL)
468 buf->head = head->next;
469 tty_buffer_free(port, head);
472 spin_unlock_irqrestore(&buf->lock, flags);
474 count = receive_buf(tty, head, count);
476 spin_lock_irqsave(&buf->lock, flags);
477 /* Ldisc or user is trying to flush the buffers.
478 We may have a deferred request to flush the
479 input buffer, if so pull the chain under the lock
480 and empty the queue */
481 if (test_bit(TTYP_FLUSHPENDING, &port->iflags)) {
482 __tty_buffer_flush(port);
483 clear_bit(TTYP_FLUSHPENDING, &port->iflags);
484 wake_up(&tty->read_wait);
489 clear_bit(TTYP_FLUSHING, &port->iflags);
492 spin_unlock_irqrestore(&buf->lock, flags);
494 tty_ldisc_deref(disc);
501 * Push the terminal flip buffers to the line discipline.
503 * Must not be called from IRQ context.
505 void tty_flush_to_ldisc(struct tty_struct *tty)
507 if (!tty->port->low_latency)
508 flush_work(&tty->port->buf.work);
512 * tty_flip_buffer_push - terminal
513 * @port: tty port to push
515 * Queue a push of the terminal flip buffers to the line discipline. This
516 * function must not be called from IRQ context if port->low_latency is
519 * In the event of the queue being busy for flipping the work will be
520 * held off and retried later.
522 * Locking: tty buffer lock. Driver locks in low latency mode.
525 void tty_flip_buffer_push(struct tty_port *port)
527 struct tty_bufhead *buf = &port->buf;
530 spin_lock_irqsave(&buf->lock, flags);
531 if (buf->tail != NULL)
532 buf->tail->commit = buf->tail->used;
533 spin_unlock_irqrestore(&buf->lock, flags);
535 if (port->low_latency)
536 flush_to_ldisc(&buf->work);
538 schedule_work(&buf->work);
540 EXPORT_SYMBOL(tty_flip_buffer_push);
543 * tty_buffer_init - prepare a tty buffer structure
544 * @tty: tty to initialise
546 * Set up the initial state of the buffer management for a tty device.
547 * Must be called before the other tty buffer functions are used.
552 void tty_buffer_init(struct tty_port *port)
554 struct tty_bufhead *buf = &port->buf;
556 spin_lock_init(&buf->lock);
560 buf->memory_used = 0;
561 INIT_WORK(&buf->work, flush_to_ldisc);