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/wait.h>
15 #include <linux/bitops.h>
16 #include <linux/delay.h>
17 #include <linux/module.h>
18 #include <linux/ratelimit.h>
21 #define MIN_TTYB_SIZE 256
22 #define TTYB_ALIGN_MASK 255
25 * Byte threshold to limit memory consumption for flip buffers.
26 * The actual memory limit is > 2x this amount.
28 #define TTYB_DEFAULT_MEM_LIMIT 65536
31 * We default to dicing tty buffer allocations to this many characters
32 * in order to avoid multiple page allocations. We know the size of
33 * tty_buffer itself but it must also be taken into account that the
34 * the buffer is 256 byte aligned. See tty_buffer_find for the allocation
35 * logic this must match
38 #define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
41 * If all tty flip buffers have been processed by flush_to_ldisc() or
42 * dropped by tty_buffer_flush(), check if the linked pty has been closed.
43 * If so, wake the reader/poll to process
45 static inline void check_other_closed(struct tty_struct *tty)
47 unsigned long flags, old;
49 /* transition from TTY_OTHER_CLOSED => TTY_OTHER_DONE must be atomic */
50 for (flags = ACCESS_ONCE(tty->flags);
51 test_bit(TTY_OTHER_CLOSED, &flags);
54 __set_bit(TTY_OTHER_DONE, &flags);
55 flags = cmpxchg(&tty->flags, old, flags);
57 wake_up_interruptible(&tty->read_wait);
64 * tty_buffer_lock_exclusive - gain exclusive access to buffer
65 * tty_buffer_unlock_exclusive - release exclusive access
67 * @port - tty_port owning the flip buffer
69 * Guarantees safe use of the line discipline's receive_buf() method by
70 * excluding the buffer work and any pending flush from using the flip
71 * buffer. Data can continue to be added concurrently to the flip buffer
72 * from the driver side.
74 * On release, the buffer work is restarted if there is data in the
78 void tty_buffer_lock_exclusive(struct tty_port *port)
80 struct tty_bufhead *buf = &port->buf;
82 atomic_inc(&buf->priority);
83 mutex_lock(&buf->lock);
85 EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
87 void tty_buffer_unlock_exclusive(struct tty_port *port)
89 struct tty_bufhead *buf = &port->buf;
92 restart = buf->head->commit != buf->head->read;
94 atomic_dec(&buf->priority);
95 mutex_unlock(&buf->lock);
97 queue_work(system_unbound_wq, &buf->work);
99 EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
102 * tty_buffer_space_avail - return unused buffer space
103 * @port - tty_port owning the flip buffer
105 * Returns the # of bytes which can be written by the driver without
106 * reaching the buffer limit.
108 * Note: this does not guarantee that memory is available to write
109 * the returned # of bytes (use tty_prepare_flip_string_xxx() to
110 * pre-allocate if memory guarantee is required).
113 int tty_buffer_space_avail(struct tty_port *port)
115 int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
116 return max(space, 0);
118 EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
120 static void tty_buffer_reset(struct tty_buffer *p, size_t size)
131 * tty_buffer_free_all - free buffers used by a tty
132 * @tty: tty to free from
134 * Remove all the buffers pending on a tty whether queued with data
135 * or in the free ring. Must be called when the tty is no longer in use
138 void tty_buffer_free_all(struct tty_port *port)
140 struct tty_bufhead *buf = &port->buf;
141 struct tty_buffer *p, *next;
142 struct llist_node *llist;
144 while ((p = buf->head) != NULL) {
149 llist = llist_del_all(&buf->free);
150 llist_for_each_entry_safe(p, next, llist, free)
153 tty_buffer_reset(&buf->sentinel, 0);
154 buf->head = &buf->sentinel;
155 buf->tail = &buf->sentinel;
157 atomic_set(&buf->mem_used, 0);
161 * tty_buffer_alloc - allocate a tty buffer
163 * @size: desired size (characters)
165 * Allocate a new tty buffer to hold the desired number of characters.
166 * We round our buffers off in 256 character chunks to get better
167 * allocation behaviour.
168 * Return NULL if out of memory or the allocation would exceed the
172 static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
174 struct llist_node *free;
175 struct tty_buffer *p;
177 /* Round the buffer size out */
178 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
180 if (size <= MIN_TTYB_SIZE) {
181 free = llist_del_first(&port->buf.free);
183 p = llist_entry(free, struct tty_buffer, free);
188 /* Should possibly check if this fails for the largest buffer we
189 have queued and recycle that ? */
190 if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
192 p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
197 tty_buffer_reset(p, size);
198 atomic_add(size, &port->buf.mem_used);
203 * tty_buffer_free - free a tty buffer
204 * @tty: tty owning the buffer
205 * @b: the buffer to free
207 * Free a tty buffer, or add it to the free list according to our
211 static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
213 struct tty_bufhead *buf = &port->buf;
215 /* Dumb strategy for now - should keep some stats */
216 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
218 if (b->size > MIN_TTYB_SIZE)
220 else if (b->size > 0)
221 llist_add(&b->free, &buf->free);
225 * tty_buffer_flush - flush full tty buffers
227 * @ld: optional ldisc ptr (must be referenced)
229 * flush all the buffers containing receive data. If ld != NULL,
230 * flush the ldisc input buffer.
232 * Locking: takes buffer lock to ensure single-threaded flip buffer
236 void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
238 struct tty_port *port = tty->port;
239 struct tty_bufhead *buf = &port->buf;
240 struct tty_buffer *next;
242 atomic_inc(&buf->priority);
244 mutex_lock(&buf->lock);
245 while ((next = buf->head->next) != NULL) {
246 tty_buffer_free(port, buf->head);
249 buf->head->read = buf->head->commit;
251 if (ld && ld->ops->flush_buffer)
252 ld->ops->flush_buffer(tty);
254 check_other_closed(tty);
256 atomic_dec(&buf->priority);
257 mutex_unlock(&buf->lock);
261 * tty_buffer_request_room - grow tty buffer if needed
262 * @tty: tty structure
263 * @size: size desired
264 * @flags: buffer flags if new buffer allocated (default = 0)
266 * Make at least size bytes of linear space available for the tty
267 * buffer. If we fail return the size we managed to find.
269 * Will change over to a new buffer if the current buffer is encoded as
270 * TTY_NORMAL (so has no flags buffer) and the new buffer requires
273 static int __tty_buffer_request_room(struct tty_port *port, size_t size,
276 struct tty_bufhead *buf = &port->buf;
277 struct tty_buffer *b, *n;
281 if (b->flags & TTYB_NORMAL)
282 left = 2 * b->size - b->used;
284 left = b->size - b->used;
286 change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
287 if (change || left < size) {
288 /* This is the slow path - looking for new buffers to use */
289 n = tty_buffer_alloc(port, size);
294 /* paired w/ acquire in flush_to_ldisc(); ensures the
295 * latest commit value can be read before the head is
296 * advanced to the next buffer
298 smp_store_release(&b->next, n);
307 int tty_buffer_request_room(struct tty_port *port, size_t size)
309 return __tty_buffer_request_room(port, size, 0);
311 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
314 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
317 * @flag: flag value for each character
320 * Queue a series of bytes to the tty buffering. All the characters
321 * passed are marked with the supplied flag. Returns the number added.
324 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
325 const unsigned char *chars, char flag, size_t size)
329 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
330 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
331 int space = __tty_buffer_request_room(port, goal, flags);
332 struct tty_buffer *tb = port->buf.tail;
333 if (unlikely(space == 0))
335 memcpy(char_buf_ptr(tb, tb->used), chars, space);
336 if (~tb->flags & TTYB_NORMAL)
337 memset(flag_buf_ptr(tb, tb->used), flag, space);
341 /* There is a small chance that we need to split the data over
342 several buffers. If this is the case we must loop */
343 } while (unlikely(size > copied));
346 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
349 * tty_insert_flip_string_flags - Add characters to the tty buffer
355 * Queue a series of bytes to the tty buffering. For each character
356 * the flags array indicates the status of the character. Returns the
360 int tty_insert_flip_string_flags(struct tty_port *port,
361 const unsigned char *chars, const char *flags, size_t size)
365 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
366 int space = tty_buffer_request_room(port, goal);
367 struct tty_buffer *tb = port->buf.tail;
368 if (unlikely(space == 0))
370 memcpy(char_buf_ptr(tb, tb->used), chars, space);
371 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
376 /* There is a small chance that we need to split the data over
377 several buffers. If this is the case we must loop */
378 } while (unlikely(size > copied));
381 EXPORT_SYMBOL(tty_insert_flip_string_flags);
384 * tty_schedule_flip - push characters to ldisc
385 * @port: tty port to push from
387 * Takes any pending buffers and transfers their ownership to the
388 * ldisc side of the queue. It then schedules those characters for
389 * processing by the line discipline.
392 void tty_schedule_flip(struct tty_port *port)
394 struct tty_bufhead *buf = &port->buf;
396 buf->tail->commit = buf->tail->used;
397 schedule_work(&buf->work);
399 EXPORT_SYMBOL(tty_schedule_flip);
402 * tty_prepare_flip_string - make room for characters
404 * @chars: return pointer for character write area
405 * @size: desired size
407 * Prepare a block of space in the buffer for data. Returns the length
408 * available and buffer pointer to the space which is now allocated and
409 * accounted for as ready for normal characters. This is used for drivers
410 * that need their own block copy routines into the buffer. There is no
411 * guarantee the buffer is a DMA target!
414 int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
417 int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
419 struct tty_buffer *tb = port->buf.tail;
420 *chars = char_buf_ptr(tb, tb->used);
421 if (~tb->flags & TTYB_NORMAL)
422 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
427 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
431 receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
433 struct tty_ldisc *disc = tty->ldisc;
434 unsigned char *p = char_buf_ptr(head, head->read);
437 if (~head->flags & TTYB_NORMAL)
438 f = flag_buf_ptr(head, head->read);
440 if (disc->ops->receive_buf2)
441 count = disc->ops->receive_buf2(tty, p, f, count);
443 count = min_t(int, count, tty->receive_room);
445 disc->ops->receive_buf(tty, p, f, count);
452 * @work: tty structure passed from work queue.
454 * This routine is called out of the software interrupt to flush data
455 * from the buffer chain to the line discipline.
457 * The receive_buf method is single threaded for each tty instance.
459 * Locking: takes buffer lock to ensure single-threaded flip buffer
463 static void flush_to_ldisc(struct work_struct *work)
465 struct tty_port *port = container_of(work, struct tty_port, buf.work);
466 struct tty_bufhead *buf = &port->buf;
467 struct tty_struct *tty;
468 struct tty_ldisc *disc;
474 disc = tty_ldisc_ref(tty);
478 mutex_lock(&buf->lock);
481 struct tty_buffer *head = buf->head;
482 struct tty_buffer *next;
485 /* Ldisc or user is trying to gain exclusive access */
486 if (atomic_read(&buf->priority))
489 /* paired w/ release in __tty_buffer_request_room();
490 * ensures commit value read is not stale if the head
491 * is advancing to the next buffer
493 next = smp_load_acquire(&head->next);
494 count = head->commit - head->read;
497 check_other_closed(tty);
501 tty_buffer_free(port, head);
505 count = receive_buf(tty, head, count);
511 mutex_unlock(&buf->lock);
513 tty_ldisc_deref(disc);
517 * tty_flip_buffer_push - terminal
518 * @port: tty port to push
520 * Queue a push of the terminal flip buffers to the line discipline.
521 * Can be called from IRQ/atomic context.
523 * In the event of the queue being busy for flipping the work will be
524 * held off and retried later.
527 void tty_flip_buffer_push(struct tty_port *port)
529 tty_schedule_flip(port);
531 EXPORT_SYMBOL(tty_flip_buffer_push);
534 * tty_buffer_init - prepare a tty buffer structure
535 * @tty: tty to initialise
537 * Set up the initial state of the buffer management for a tty device.
538 * Must be called before the other tty buffer functions are used.
541 void tty_buffer_init(struct tty_port *port)
543 struct tty_bufhead *buf = &port->buf;
545 mutex_init(&buf->lock);
546 tty_buffer_reset(&buf->sentinel, 0);
547 buf->head = &buf->sentinel;
548 buf->tail = &buf->sentinel;
549 init_llist_head(&buf->free);
550 atomic_set(&buf->mem_used, 0);
551 atomic_set(&buf->priority, 0);
552 INIT_WORK(&buf->work, flush_to_ldisc);
553 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
557 * tty_buffer_set_limit - change the tty buffer memory limit
558 * @port: tty port to change
560 * Change the tty buffer memory limit.
561 * Must be called before the other tty buffer functions are used.
564 int tty_buffer_set_limit(struct tty_port *port, int limit)
566 if (limit < MIN_TTYB_SIZE)
568 port->buf.mem_limit = limit;
571 EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
573 /* slave ptys can claim nested buffer lock when handling BRK and INTR */
574 void tty_buffer_set_lock_subclass(struct tty_port *port)
576 lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);