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
32 * We default to dicing tty buffer allocations to this many characters
33 * in order to avoid multiple page allocations. We know the size of
34 * tty_buffer itself but it must also be taken into account that the
35 * the buffer is 256 byte aligned. See tty_buffer_find for the allocation
36 * logic this must match
39 #define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
43 * tty_buffer_lock_exclusive - gain exclusive access to buffer
44 * tty_buffer_unlock_exclusive - release exclusive access
46 * @port - tty_port owning the flip buffer
48 * Guarantees safe use of the line discipline's receive_buf() method by
49 * excluding the buffer work and any pending flush from using the flip
50 * buffer. Data can continue to be added concurrently to the flip buffer
51 * from the driver side.
53 * On release, the buffer work is restarted if there is data in the
57 void tty_buffer_lock_exclusive(struct tty_port *port)
59 struct tty_bufhead *buf = &port->buf;
61 atomic_inc(&buf->priority);
62 mutex_lock(&buf->lock);
65 void tty_buffer_unlock_exclusive(struct tty_port *port)
67 struct tty_bufhead *buf = &port->buf;
70 restart = buf->head->commit != buf->head->read;
72 atomic_dec(&buf->priority);
73 mutex_unlock(&buf->lock);
75 queue_work(system_unbound_wq, &buf->work);
79 * tty_buffer_space_avail - return unused buffer space
80 * @port - tty_port owning the flip buffer
82 * Returns the # of bytes which can be written by the driver without
83 * reaching the buffer limit.
85 * Note: this does not guarantee that memory is available to write
86 * the returned # of bytes (use tty_prepare_flip_string_xxx() to
87 * pre-allocate if memory guarantee is required).
90 int tty_buffer_space_avail(struct tty_port *port)
92 int space = TTYB_MEM_LIMIT - atomic_read(&port->buf.memory_used);
96 static void tty_buffer_reset(struct tty_buffer *p, size_t size)
106 * tty_buffer_free_all - free buffers used by a tty
107 * @tty: tty to free from
109 * Remove all the buffers pending on a tty whether queued with data
110 * or in the free ring. Must be called when the tty is no longer in use
113 void tty_buffer_free_all(struct tty_port *port)
115 struct tty_bufhead *buf = &port->buf;
116 struct tty_buffer *p, *next;
117 struct llist_node *llist;
119 while ((p = buf->head) != NULL) {
124 llist = llist_del_all(&buf->free);
125 llist_for_each_entry_safe(p, next, llist, free)
128 tty_buffer_reset(&buf->sentinel, 0);
129 buf->head = &buf->sentinel;
130 buf->tail = &buf->sentinel;
132 atomic_set(&buf->memory_used, 0);
136 * tty_buffer_alloc - allocate a tty buffer
138 * @size: desired size (characters)
140 * Allocate a new tty buffer to hold the desired number of characters.
141 * We round our buffers off in 256 character chunks to get better
142 * allocation behaviour.
143 * Return NULL if out of memory or the allocation would exceed the
147 static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
149 struct llist_node *free;
150 struct tty_buffer *p;
152 /* Round the buffer size out */
153 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
155 if (size <= MIN_TTYB_SIZE) {
156 free = llist_del_first(&port->buf.free);
158 p = llist_entry(free, struct tty_buffer, free);
163 /* Should possibly check if this fails for the largest buffer we
164 have queued and recycle that ? */
165 if (atomic_read(&port->buf.memory_used) > TTYB_MEM_LIMIT)
167 p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
172 tty_buffer_reset(p, size);
173 atomic_add(size, &port->buf.memory_used);
178 * tty_buffer_free - free a tty buffer
179 * @tty: tty owning the buffer
180 * @b: the buffer to free
182 * Free a tty buffer, or add it to the free list according to our
186 static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
188 struct tty_bufhead *buf = &port->buf;
190 /* Dumb strategy for now - should keep some stats */
191 WARN_ON(atomic_sub_return(b->size, &buf->memory_used) < 0);
193 if (b->size > MIN_TTYB_SIZE)
195 else if (b->size > 0)
196 llist_add(&b->free, &buf->free);
200 * tty_buffer_flush - flush full tty buffers
203 * flush all the buffers containing receive data. If the buffer is
204 * being processed by flush_to_ldisc then we defer the processing
207 * Locking: takes buffer lock to ensure single-threaded flip buffer
211 void tty_buffer_flush(struct tty_struct *tty)
213 struct tty_port *port = tty->port;
214 struct tty_bufhead *buf = &port->buf;
215 struct tty_buffer *next;
217 atomic_inc(&buf->priority);
219 mutex_lock(&buf->lock);
220 while ((next = buf->head->next) != NULL) {
221 tty_buffer_free(port, buf->head);
224 buf->head->read = buf->head->commit;
225 atomic_dec(&buf->priority);
226 mutex_unlock(&buf->lock);
230 * tty_buffer_request_room - grow tty buffer if needed
231 * @tty: tty structure
232 * @size: size desired
234 * Make at least size bytes of linear space available for the tty
235 * buffer. If we fail return the size we managed to find.
237 int tty_buffer_request_room(struct tty_port *port, size_t size)
239 struct tty_bufhead *buf = &port->buf;
240 struct tty_buffer *b, *n;
244 left = b->size - b->used;
247 /* This is the slow path - looking for new buffers to use */
248 if ((n = tty_buffer_alloc(port, size)) != NULL) {
258 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
261 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
264 * @flag: flag value for each character
267 * Queue a series of bytes to the tty buffering. All the characters
268 * passed are marked with the supplied flag. Returns the number added.
271 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
272 const unsigned char *chars, char flag, size_t size)
276 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
277 int space = tty_buffer_request_room(port, goal);
278 struct tty_buffer *tb = port->buf.tail;
279 if (unlikely(space == 0))
281 memcpy(char_buf_ptr(tb, tb->used), chars, space);
282 memset(flag_buf_ptr(tb, tb->used), flag, space);
286 /* There is a small chance that we need to split the data over
287 several buffers. If this is the case we must loop */
288 } while (unlikely(size > copied));
291 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
294 * tty_insert_flip_string_flags - Add characters to the tty buffer
300 * Queue a series of bytes to the tty buffering. For each character
301 * the flags array indicates the status of the character. Returns the
305 int tty_insert_flip_string_flags(struct tty_port *port,
306 const unsigned char *chars, const char *flags, size_t size)
310 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
311 int space = tty_buffer_request_room(port, goal);
312 struct tty_buffer *tb = port->buf.tail;
313 if (unlikely(space == 0))
315 memcpy(char_buf_ptr(tb, tb->used), chars, space);
316 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
321 /* There is a small chance that we need to split the data over
322 several buffers. If this is the case we must loop */
323 } while (unlikely(size > copied));
326 EXPORT_SYMBOL(tty_insert_flip_string_flags);
329 * tty_schedule_flip - push characters to ldisc
330 * @port: tty port to push from
332 * Takes any pending buffers and transfers their ownership to the
333 * ldisc side of the queue. It then schedules those characters for
334 * processing by the line discipline.
335 * Note that this function can only be used when the low_latency flag
336 * is unset. Otherwise the workqueue won't be flushed.
339 void tty_schedule_flip(struct tty_port *port)
341 struct tty_bufhead *buf = &port->buf;
342 WARN_ON(port->low_latency);
344 buf->tail->commit = buf->tail->used;
345 schedule_work(&buf->work);
347 EXPORT_SYMBOL(tty_schedule_flip);
350 * tty_prepare_flip_string - make room for characters
352 * @chars: return pointer for character write area
353 * @size: desired size
355 * Prepare a block of space in the buffer for data. Returns the length
356 * available and buffer pointer to the space which is now allocated and
357 * accounted for as ready for normal characters. This is used for drivers
358 * that need their own block copy routines into the buffer. There is no
359 * guarantee the buffer is a DMA target!
362 int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
365 int space = tty_buffer_request_room(port, size);
367 struct tty_buffer *tb = port->buf.tail;
368 *chars = char_buf_ptr(tb, tb->used);
369 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
374 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
377 * tty_prepare_flip_string_flags - make room for characters
379 * @chars: return pointer for character write area
380 * @flags: return pointer for status flag write area
381 * @size: desired size
383 * Prepare a block of space in the buffer for data. Returns the length
384 * available and buffer pointer to the space which is now allocated and
385 * accounted for as ready for characters. This is used for drivers
386 * that need their own block copy routines into the buffer. There is no
387 * guarantee the buffer is a DMA target!
390 int tty_prepare_flip_string_flags(struct tty_port *port,
391 unsigned char **chars, char **flags, size_t size)
393 int space = tty_buffer_request_room(port, size);
395 struct tty_buffer *tb = port->buf.tail;
396 *chars = char_buf_ptr(tb, tb->used);
397 *flags = flag_buf_ptr(tb, tb->used);
402 EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
406 receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
408 struct tty_ldisc *disc = tty->ldisc;
409 unsigned char *p = char_buf_ptr(head, head->read);
410 char *f = flag_buf_ptr(head, head->read);
412 if (disc->ops->receive_buf2)
413 count = disc->ops->receive_buf2(tty, p, f, count);
415 count = min_t(int, count, tty->receive_room);
417 disc->ops->receive_buf(tty, p, f, count);
425 * @work: tty structure passed from work queue.
427 * This routine is called out of the software interrupt to flush data
428 * from the buffer chain to the line discipline.
430 * The receive_buf method is single threaded for each tty instance.
432 * Locking: takes buffer lock to ensure single-threaded flip buffer
436 static void flush_to_ldisc(struct work_struct *work)
438 struct tty_port *port = container_of(work, struct tty_port, buf.work);
439 struct tty_bufhead *buf = &port->buf;
440 struct tty_struct *tty;
441 struct tty_ldisc *disc;
447 disc = tty_ldisc_ref(tty);
451 mutex_lock(&buf->lock);
454 struct tty_buffer *head = buf->head;
457 /* Ldisc or user is trying to gain exclusive access */
458 if (atomic_read(&buf->priority))
461 count = head->commit - head->read;
463 if (head->next == NULL)
465 buf->head = head->next;
466 tty_buffer_free(port, head);
470 count = receive_buf(tty, head, count);
475 mutex_unlock(&buf->lock);
477 tty_ldisc_deref(disc);
484 * Push the terminal flip buffers to the line discipline.
486 * Must not be called from IRQ context.
488 void tty_flush_to_ldisc(struct tty_struct *tty)
490 if (!tty->port->low_latency)
491 flush_work(&tty->port->buf.work);
495 * tty_flip_buffer_push - terminal
496 * @port: tty port to push
498 * Queue a push of the terminal flip buffers to the line discipline. This
499 * function must not be called from IRQ context if port->low_latency is
502 * In the event of the queue being busy for flipping the work will be
503 * held off and retried later.
506 void tty_flip_buffer_push(struct tty_port *port)
508 struct tty_bufhead *buf = &port->buf;
510 buf->tail->commit = buf->tail->used;
512 if (port->low_latency)
513 flush_to_ldisc(&buf->work);
515 schedule_work(&buf->work);
517 EXPORT_SYMBOL(tty_flip_buffer_push);
520 * tty_buffer_init - prepare a tty buffer structure
521 * @tty: tty to initialise
523 * Set up the initial state of the buffer management for a tty device.
524 * Must be called before the other tty buffer functions are used.
527 void tty_buffer_init(struct tty_port *port)
529 struct tty_bufhead *buf = &port->buf;
531 mutex_init(&buf->lock);
532 tty_buffer_reset(&buf->sentinel, 0);
533 buf->head = &buf->sentinel;
534 buf->tail = &buf->sentinel;
535 init_llist_head(&buf->free);
536 atomic_set(&buf->memory_used, 0);
537 atomic_set(&buf->priority, 0);
538 INIT_WORK(&buf->work, flush_to_ldisc);