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
26 * Byte threshold to limit memory consumption for flip buffers.
27 * The actual memory limit is > 2x this amount.
29 #define TTYB_MEM_LIMIT 65536
33 * tty_buffer_space_avail - return unused buffer space
34 * @port - tty_port owning the flip buffer
36 * Returns the # of bytes which can be written by the driver without
37 * reaching the buffer limit.
39 * Note: this does not guarantee that memory is available to write
40 * the returned # of bytes (use tty_prepare_flip_string_xxx() to
41 * pre-allocate if memory guarantee is required).
44 int tty_buffer_space_avail(struct tty_port *port)
46 int space = TTYB_MEM_LIMIT - atomic_read(&port->buf.memory_used);
50 static void tty_buffer_reset(struct tty_buffer *p, size_t size)
60 * tty_buffer_free_all - free buffers used by a tty
61 * @tty: tty to free from
63 * Remove all the buffers pending on a tty whether queued with data
64 * or in the free ring. Must be called when the tty is no longer in use
69 void tty_buffer_free_all(struct tty_port *port)
71 struct tty_bufhead *buf = &port->buf;
72 struct tty_buffer *p, *next;
73 struct llist_node *llist;
75 while ((p = buf->head) != NULL) {
80 llist = llist_del_all(&buf->free);
81 llist_for_each_entry_safe(p, next, llist, free)
84 tty_buffer_reset(&buf->sentinel, 0);
85 buf->head = &buf->sentinel;
86 buf->tail = &buf->sentinel;
88 atomic_set(&buf->memory_used, 0);
92 * tty_buffer_alloc - allocate a tty buffer
94 * @size: desired size (characters)
96 * Allocate a new tty buffer to hold the desired number of characters.
97 * We round our buffers off in 256 character chunks to get better
98 * allocation behaviour.
99 * Return NULL if out of memory or the allocation would exceed the
103 static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
105 struct llist_node *free;
106 struct tty_buffer *p;
108 /* Round the buffer size out */
109 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
111 if (size <= MIN_TTYB_SIZE) {
112 free = llist_del_first(&port->buf.free);
114 p = llist_entry(free, struct tty_buffer, free);
119 /* Should possibly check if this fails for the largest buffer we
120 have queued and recycle that ? */
121 if (atomic_read(&port->buf.memory_used) > TTYB_MEM_LIMIT)
123 p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
128 tty_buffer_reset(p, size);
129 atomic_add(size, &port->buf.memory_used);
134 * tty_buffer_free - free a tty buffer
135 * @tty: tty owning the buffer
136 * @b: the buffer to free
138 * Free a tty buffer, or add it to the free list according to our
142 static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
144 struct tty_bufhead *buf = &port->buf;
146 /* Dumb strategy for now - should keep some stats */
147 WARN_ON(atomic_sub_return(b->size, &buf->memory_used) < 0);
149 if (b->size > MIN_TTYB_SIZE)
151 else if (b->size > 0)
152 llist_add(&b->free, &buf->free);
156 * __tty_buffer_flush - flush full tty buffers
159 * flush all the buffers containing receive data. Caller must
160 * hold the buffer lock and must have ensured no parallel flush to
163 * Locking: Caller must hold tty->buf.lock
166 static void __tty_buffer_flush(struct tty_port *port)
168 struct tty_bufhead *buf = &port->buf;
169 struct tty_buffer *next;
171 while ((next = buf->head->next) != NULL) {
172 tty_buffer_free(port, buf->head);
175 WARN_ON(buf->head != buf->tail);
176 buf->head->read = buf->head->commit;
180 * tty_buffer_flush - flush full tty buffers
183 * flush all the buffers containing receive data. If the buffer is
184 * being processed by flush_to_ldisc then we defer the processing
190 void tty_buffer_flush(struct tty_struct *tty)
192 struct tty_port *port = tty->port;
193 struct tty_bufhead *buf = &port->buf;
196 spin_lock_irqsave(&buf->lock, flags);
198 /* If the data is being pushed to the tty layer then we can't
199 process it here. Instead set a flag and the flush_to_ldisc
200 path will process the flush request before it exits */
201 if (test_bit(TTYP_FLUSHING, &port->iflags)) {
202 set_bit(TTYP_FLUSHPENDING, &port->iflags);
203 spin_unlock_irqrestore(&buf->lock, flags);
204 wait_event(tty->read_wait,
205 test_bit(TTYP_FLUSHPENDING, &port->iflags) == 0);
208 __tty_buffer_flush(port);
209 spin_unlock_irqrestore(&buf->lock, flags);
213 * tty_buffer_request_room - grow tty buffer if needed
214 * @tty: tty structure
215 * @size: size desired
217 * Make at least size bytes of linear space available for the tty
218 * buffer. If we fail return the size we managed to find.
220 * Locking: Takes port->buf.lock
222 int tty_buffer_request_room(struct tty_port *port, size_t size)
224 struct tty_bufhead *buf = &port->buf;
225 struct tty_buffer *b, *n;
228 spin_lock_irqsave(&buf->lock, flags);
230 left = b->size - b->used;
233 /* This is the slow path - looking for new buffers to use */
234 if ((n = tty_buffer_alloc(port, size)) != NULL) {
241 spin_unlock_irqrestore(&buf->lock, flags);
244 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
247 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
250 * @flag: flag value for each character
253 * Queue a series of bytes to the tty buffering. All the characters
254 * passed are marked with the supplied flag. Returns the number added.
256 * Locking: Called functions may take port->buf.lock
259 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
260 const unsigned char *chars, char flag, size_t size)
264 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
265 int space = tty_buffer_request_room(port, goal);
266 struct tty_buffer *tb = port->buf.tail;
267 if (unlikely(space == 0))
269 memcpy(char_buf_ptr(tb, tb->used), chars, space);
270 memset(flag_buf_ptr(tb, tb->used), flag, space);
274 /* There is a small chance that we need to split the data over
275 several buffers. If this is the case we must loop */
276 } while (unlikely(size > copied));
279 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
282 * tty_insert_flip_string_flags - Add characters to the tty buffer
288 * Queue a series of bytes to the tty buffering. For each character
289 * the flags array indicates the status of the character. Returns the
292 * Locking: Called functions may take port->buf.lock
295 int tty_insert_flip_string_flags(struct tty_port *port,
296 const unsigned char *chars, const char *flags, size_t size)
300 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
301 int space = tty_buffer_request_room(port, goal);
302 struct tty_buffer *tb = port->buf.tail;
303 if (unlikely(space == 0))
305 memcpy(char_buf_ptr(tb, tb->used), chars, space);
306 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
311 /* There is a small chance that we need to split the data over
312 several buffers. If this is the case we must loop */
313 } while (unlikely(size > copied));
316 EXPORT_SYMBOL(tty_insert_flip_string_flags);
319 * tty_schedule_flip - push characters to ldisc
320 * @port: tty port to push from
322 * Takes any pending buffers and transfers their ownership to the
323 * ldisc side of the queue. It then schedules those characters for
324 * processing by the line discipline.
325 * Note that this function can only be used when the low_latency flag
326 * is unset. Otherwise the workqueue won't be flushed.
328 * Locking: Takes port->buf.lock
331 void tty_schedule_flip(struct tty_port *port)
333 struct tty_bufhead *buf = &port->buf;
335 WARN_ON(port->low_latency);
337 spin_lock_irqsave(&buf->lock, flags);
338 buf->tail->commit = buf->tail->used;
339 spin_unlock_irqrestore(&buf->lock, flags);
340 schedule_work(&buf->work);
342 EXPORT_SYMBOL(tty_schedule_flip);
345 * tty_prepare_flip_string - make room for characters
347 * @chars: return pointer for character write area
348 * @size: desired size
350 * Prepare a block of space in the buffer for data. Returns the length
351 * available and buffer pointer to the space which is now allocated and
352 * accounted for as ready for normal characters. This is used for drivers
353 * that need their own block copy routines into the buffer. There is no
354 * guarantee the buffer is a DMA target!
356 * Locking: May call functions taking port->buf.lock
359 int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
362 int space = tty_buffer_request_room(port, size);
364 struct tty_buffer *tb = port->buf.tail;
365 *chars = char_buf_ptr(tb, tb->used);
366 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
371 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
374 * tty_prepare_flip_string_flags - make room for characters
376 * @chars: return pointer for character write area
377 * @flags: return pointer for status flag write area
378 * @size: desired size
380 * Prepare a block of space in the buffer for data. Returns the length
381 * available and buffer pointer to the space which is now allocated and
382 * accounted for as ready for characters. This is used for drivers
383 * that need their own block copy routines into the buffer. There is no
384 * guarantee the buffer is a DMA target!
386 * Locking: May call functions taking port->buf.lock
389 int tty_prepare_flip_string_flags(struct tty_port *port,
390 unsigned char **chars, char **flags, size_t size)
392 int space = tty_buffer_request_room(port, size);
394 struct tty_buffer *tb = port->buf.tail;
395 *chars = char_buf_ptr(tb, tb->used);
396 *flags = flag_buf_ptr(tb, tb->used);
401 EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
405 receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
407 struct tty_ldisc *disc = tty->ldisc;
408 unsigned char *p = char_buf_ptr(head, head->read);
409 char *f = flag_buf_ptr(head, head->read);
411 if (disc->ops->receive_buf2)
412 count = disc->ops->receive_buf2(tty, p, f, count);
414 count = min_t(int, count, tty->receive_room);
416 disc->ops->receive_buf(tty, p, f, count);
424 * @work: tty structure passed from work queue.
426 * This routine is called out of the software interrupt to flush data
427 * from the buffer chain to the line discipline.
429 * Locking: holds tty->buf.lock to guard buffer list. Drops the lock
430 * while invoking the line discipline receive_buf method. The
431 * receive_buf method is single threaded for each tty instance.
434 static void flush_to_ldisc(struct work_struct *work)
436 struct tty_port *port = container_of(work, struct tty_port, buf.work);
437 struct tty_bufhead *buf = &port->buf;
438 struct tty_struct *tty;
440 struct tty_ldisc *disc;
446 disc = tty_ldisc_ref(tty);
450 spin_lock_irqsave(&buf->lock, flags);
452 if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) {
454 struct tty_buffer *head = buf->head;
457 count = head->commit - head->read;
459 if (head->next == NULL)
461 buf->head = head->next;
462 tty_buffer_free(port, head);
465 spin_unlock_irqrestore(&buf->lock, flags);
467 count = receive_buf(tty, head, count);
469 spin_lock_irqsave(&buf->lock, flags);
470 /* Ldisc or user is trying to flush the buffers.
471 We may have a deferred request to flush the
472 input buffer, if so pull the chain under the lock
473 and empty the queue */
474 if (test_bit(TTYP_FLUSHPENDING, &port->iflags)) {
475 __tty_buffer_flush(port);
476 clear_bit(TTYP_FLUSHPENDING, &port->iflags);
477 wake_up(&tty->read_wait);
482 clear_bit(TTYP_FLUSHING, &port->iflags);
485 spin_unlock_irqrestore(&buf->lock, flags);
487 tty_ldisc_deref(disc);
494 * Push the terminal flip buffers to the line discipline.
496 * Must not be called from IRQ context.
498 void tty_flush_to_ldisc(struct tty_struct *tty)
500 if (!tty->port->low_latency)
501 flush_work(&tty->port->buf.work);
505 * tty_flip_buffer_push - terminal
506 * @port: tty port to push
508 * Queue a push of the terminal flip buffers to the line discipline. This
509 * function must not be called from IRQ context if port->low_latency is
512 * In the event of the queue being busy for flipping the work will be
513 * held off and retried later.
515 * Locking: tty buffer lock. Driver locks in low latency mode.
518 void tty_flip_buffer_push(struct tty_port *port)
520 struct tty_bufhead *buf = &port->buf;
523 spin_lock_irqsave(&buf->lock, flags);
524 buf->tail->commit = buf->tail->used;
525 spin_unlock_irqrestore(&buf->lock, flags);
527 if (port->low_latency)
528 flush_to_ldisc(&buf->work);
530 schedule_work(&buf->work);
532 EXPORT_SYMBOL(tty_flip_buffer_push);
535 * tty_buffer_init - prepare a tty buffer structure
536 * @tty: tty to initialise
538 * Set up the initial state of the buffer management for a tty device.
539 * Must be called before the other tty buffer functions are used.
544 void tty_buffer_init(struct tty_port *port)
546 struct tty_bufhead *buf = &port->buf;
548 spin_lock_init(&buf->lock);
549 tty_buffer_reset(&buf->sentinel, 0);
550 buf->head = &buf->sentinel;
551 buf->tail = &buf->sentinel;
552 init_llist_head(&buf->free);
553 atomic_set(&buf->memory_used, 0);
554 INIT_WORK(&buf->work, flush_to_ldisc);