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
67 void tty_buffer_free_all(struct tty_port *port)
69 struct tty_bufhead *buf = &port->buf;
70 struct tty_buffer *p, *next;
71 struct llist_node *llist;
73 while ((p = buf->head) != NULL) {
78 llist = llist_del_all(&buf->free);
79 llist_for_each_entry_safe(p, next, llist, free)
82 tty_buffer_reset(&buf->sentinel, 0);
83 buf->head = &buf->sentinel;
84 buf->tail = &buf->sentinel;
86 atomic_set(&buf->memory_used, 0);
90 * tty_buffer_alloc - allocate a tty buffer
92 * @size: desired size (characters)
94 * Allocate a new tty buffer to hold the desired number of characters.
95 * We round our buffers off in 256 character chunks to get better
96 * allocation behaviour.
97 * Return NULL if out of memory or the allocation would exceed the
101 static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
103 struct llist_node *free;
104 struct tty_buffer *p;
106 /* Round the buffer size out */
107 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
109 if (size <= MIN_TTYB_SIZE) {
110 free = llist_del_first(&port->buf.free);
112 p = llist_entry(free, struct tty_buffer, free);
117 /* Should possibly check if this fails for the largest buffer we
118 have queued and recycle that ? */
119 if (atomic_read(&port->buf.memory_used) > TTYB_MEM_LIMIT)
121 p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
126 tty_buffer_reset(p, size);
127 atomic_add(size, &port->buf.memory_used);
132 * tty_buffer_free - free a tty buffer
133 * @tty: tty owning the buffer
134 * @b: the buffer to free
136 * Free a tty buffer, or add it to the free list according to our
140 static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
142 struct tty_bufhead *buf = &port->buf;
144 /* Dumb strategy for now - should keep some stats */
145 WARN_ON(atomic_sub_return(b->size, &buf->memory_used) < 0);
147 if (b->size > MIN_TTYB_SIZE)
149 else if (b->size > 0)
150 llist_add(&b->free, &buf->free);
154 * __tty_buffer_flush - flush full tty buffers
157 * flush all the buffers containing receive data. Caller must
158 * hold the buffer lock and must have ensured no parallel flush to
161 * Locking: Caller must hold tty->buf.lock
164 static void __tty_buffer_flush(struct tty_port *port)
166 struct tty_bufhead *buf = &port->buf;
167 struct tty_buffer *next;
169 while ((next = buf->head->next) != NULL) {
170 tty_buffer_free(port, buf->head);
173 WARN_ON(buf->head != buf->tail);
174 buf->head->read = buf->head->commit;
178 * tty_buffer_flush - flush full tty buffers
181 * flush all the buffers containing receive data. If the buffer is
182 * being processed by flush_to_ldisc then we defer the processing
188 void tty_buffer_flush(struct tty_struct *tty)
190 struct tty_port *port = tty->port;
191 struct tty_bufhead *buf = &port->buf;
194 spin_lock_irqsave(&buf->lock, flags);
196 /* If the data is being pushed to the tty layer then we can't
197 process it here. Instead set a flag and the flush_to_ldisc
198 path will process the flush request before it exits */
199 if (test_bit(TTYP_FLUSHING, &port->iflags)) {
200 set_bit(TTYP_FLUSHPENDING, &port->iflags);
201 spin_unlock_irqrestore(&buf->lock, flags);
202 wait_event(tty->read_wait,
203 test_bit(TTYP_FLUSHPENDING, &port->iflags) == 0);
206 __tty_buffer_flush(port);
207 spin_unlock_irqrestore(&buf->lock, flags);
211 * tty_buffer_request_room - grow tty buffer if needed
212 * @tty: tty structure
213 * @size: size desired
215 * Make at least size bytes of linear space available for the tty
216 * buffer. If we fail return the size we managed to find.
218 int tty_buffer_request_room(struct tty_port *port, size_t size)
220 struct tty_bufhead *buf = &port->buf;
221 struct tty_buffer *b, *n;
225 left = b->size - b->used;
228 /* This is the slow path - looking for new buffers to use */
229 if ((n = tty_buffer_alloc(port, size)) != NULL) {
239 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
242 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
245 * @flag: flag value for each character
248 * Queue a series of bytes to the tty buffering. All the characters
249 * passed are marked with the supplied flag. Returns the number added.
252 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
253 const unsigned char *chars, char flag, size_t size)
257 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
258 int space = tty_buffer_request_room(port, goal);
259 struct tty_buffer *tb = port->buf.tail;
260 if (unlikely(space == 0))
262 memcpy(char_buf_ptr(tb, tb->used), chars, space);
263 memset(flag_buf_ptr(tb, tb->used), flag, space);
267 /* There is a small chance that we need to split the data over
268 several buffers. If this is the case we must loop */
269 } while (unlikely(size > copied));
272 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
275 * tty_insert_flip_string_flags - Add characters to the tty buffer
281 * Queue a series of bytes to the tty buffering. For each character
282 * the flags array indicates the status of the character. Returns the
286 int tty_insert_flip_string_flags(struct tty_port *port,
287 const unsigned char *chars, const char *flags, size_t size)
291 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
292 int space = tty_buffer_request_room(port, goal);
293 struct tty_buffer *tb = port->buf.tail;
294 if (unlikely(space == 0))
296 memcpy(char_buf_ptr(tb, tb->used), chars, space);
297 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
302 /* There is a small chance that we need to split the data over
303 several buffers. If this is the case we must loop */
304 } while (unlikely(size > copied));
307 EXPORT_SYMBOL(tty_insert_flip_string_flags);
310 * tty_schedule_flip - push characters to ldisc
311 * @port: tty port to push from
313 * Takes any pending buffers and transfers their ownership to the
314 * ldisc side of the queue. It then schedules those characters for
315 * processing by the line discipline.
316 * Note that this function can only be used when the low_latency flag
317 * is unset. Otherwise the workqueue won't be flushed.
320 void tty_schedule_flip(struct tty_port *port)
322 struct tty_bufhead *buf = &port->buf;
323 WARN_ON(port->low_latency);
325 buf->tail->commit = buf->tail->used;
326 schedule_work(&buf->work);
328 EXPORT_SYMBOL(tty_schedule_flip);
331 * tty_prepare_flip_string - make room for characters
333 * @chars: return pointer for character write area
334 * @size: desired size
336 * Prepare a block of space in the buffer for data. Returns the length
337 * available and buffer pointer to the space which is now allocated and
338 * accounted for as ready for normal characters. This is used for drivers
339 * that need their own block copy routines into the buffer. There is no
340 * guarantee the buffer is a DMA target!
343 int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
346 int space = tty_buffer_request_room(port, size);
348 struct tty_buffer *tb = port->buf.tail;
349 *chars = char_buf_ptr(tb, tb->used);
350 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
355 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
358 * tty_prepare_flip_string_flags - make room for characters
360 * @chars: return pointer for character write area
361 * @flags: return pointer for status flag write area
362 * @size: desired size
364 * Prepare a block of space in the buffer for data. Returns the length
365 * available and buffer pointer to the space which is now allocated and
366 * accounted for as ready for characters. This is used for drivers
367 * that need their own block copy routines into the buffer. There is no
368 * guarantee the buffer is a DMA target!
371 int tty_prepare_flip_string_flags(struct tty_port *port,
372 unsigned char **chars, char **flags, size_t size)
374 int space = tty_buffer_request_room(port, size);
376 struct tty_buffer *tb = port->buf.tail;
377 *chars = char_buf_ptr(tb, tb->used);
378 *flags = flag_buf_ptr(tb, tb->used);
383 EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
387 receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
389 struct tty_ldisc *disc = tty->ldisc;
390 unsigned char *p = char_buf_ptr(head, head->read);
391 char *f = flag_buf_ptr(head, head->read);
393 if (disc->ops->receive_buf2)
394 count = disc->ops->receive_buf2(tty, p, f, count);
396 count = min_t(int, count, tty->receive_room);
398 disc->ops->receive_buf(tty, p, f, count);
406 * @work: tty structure passed from work queue.
408 * This routine is called out of the software interrupt to flush data
409 * from the buffer chain to the line discipline.
411 * Locking: holds tty->buf.lock to guard buffer list. Drops the lock
412 * while invoking the line discipline receive_buf method. The
413 * receive_buf method is single threaded for each tty instance.
416 static void flush_to_ldisc(struct work_struct *work)
418 struct tty_port *port = container_of(work, struct tty_port, buf.work);
419 struct tty_bufhead *buf = &port->buf;
420 struct tty_struct *tty;
422 struct tty_ldisc *disc;
428 disc = tty_ldisc_ref(tty);
432 spin_lock_irqsave(&buf->lock, flags);
434 if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) {
436 struct tty_buffer *head = buf->head;
439 count = head->commit - head->read;
441 if (head->next == NULL)
443 buf->head = head->next;
444 tty_buffer_free(port, head);
447 spin_unlock_irqrestore(&buf->lock, flags);
449 count = receive_buf(tty, head, count);
451 spin_lock_irqsave(&buf->lock, flags);
452 /* Ldisc or user is trying to flush the buffers.
453 We may have a deferred request to flush the
454 input buffer, if so pull the chain under the lock
455 and empty the queue */
456 if (test_bit(TTYP_FLUSHPENDING, &port->iflags)) {
457 __tty_buffer_flush(port);
458 clear_bit(TTYP_FLUSHPENDING, &port->iflags);
459 wake_up(&tty->read_wait);
464 clear_bit(TTYP_FLUSHING, &port->iflags);
467 spin_unlock_irqrestore(&buf->lock, flags);
469 tty_ldisc_deref(disc);
476 * Push the terminal flip buffers to the line discipline.
478 * Must not be called from IRQ context.
480 void tty_flush_to_ldisc(struct tty_struct *tty)
482 if (!tty->port->low_latency)
483 flush_work(&tty->port->buf.work);
487 * tty_flip_buffer_push - terminal
488 * @port: tty port to push
490 * Queue a push of the terminal flip buffers to the line discipline. This
491 * function must not be called from IRQ context if port->low_latency is
494 * In the event of the queue being busy for flipping the work will be
495 * held off and retried later.
498 void tty_flip_buffer_push(struct tty_port *port)
500 struct tty_bufhead *buf = &port->buf;
502 buf->tail->commit = buf->tail->used;
504 if (port->low_latency)
505 flush_to_ldisc(&buf->work);
507 schedule_work(&buf->work);
509 EXPORT_SYMBOL(tty_flip_buffer_push);
512 * tty_buffer_init - prepare a tty buffer structure
513 * @tty: tty to initialise
515 * Set up the initial state of the buffer management for a tty device.
516 * Must be called before the other tty buffer functions are used.
521 void tty_buffer_init(struct tty_port *port)
523 struct tty_bufhead *buf = &port->buf;
525 spin_lock_init(&buf->lock);
526 tty_buffer_reset(&buf->sentinel, 0);
527 buf->head = &buf->sentinel;
528 buf->tail = &buf->sentinel;
529 init_llist_head(&buf->free);
530 atomic_set(&buf->memory_used, 0);
531 INIT_WORK(&buf->work, flush_to_ldisc);