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 (640 * 1024UL)
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 * tty_buffer_lock_exclusive - gain exclusive access to buffer
42 * tty_buffer_unlock_exclusive - release exclusive access
44 * @port - tty_port owning the flip buffer
46 * Guarantees safe use of the line discipline's receive_buf() method by
47 * excluding the buffer work and any pending flush from using the flip
48 * buffer. Data can continue to be added concurrently to the flip buffer
49 * from the driver side.
51 * On release, the buffer work is restarted if there is data in the
55 void tty_buffer_lock_exclusive(struct tty_port *port)
57 struct tty_bufhead *buf = &port->buf;
59 atomic_inc(&buf->priority);
60 mutex_lock(&buf->lock);
62 EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
64 void tty_buffer_unlock_exclusive(struct tty_port *port)
66 struct tty_bufhead *buf = &port->buf;
69 restart = buf->head->commit != buf->head->read;
71 atomic_dec(&buf->priority);
72 mutex_unlock(&buf->lock);
74 queue_work(system_unbound_wq, &buf->work);
76 EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
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 = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
95 EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
97 static void tty_buffer_reset(struct tty_buffer *p, size_t size)
108 * tty_buffer_free_all - free buffers used by a tty
109 * @tty: tty to free from
111 * Remove all the buffers pending on a tty whether queued with data
112 * or in the free ring. Must be called when the tty is no longer in use
115 void tty_buffer_free_all(struct tty_port *port)
117 struct tty_bufhead *buf = &port->buf;
118 struct tty_buffer *p, *next;
119 struct llist_node *llist;
121 while ((p = buf->head) != NULL) {
126 llist = llist_del_all(&buf->free);
127 llist_for_each_entry_safe(p, next, llist, free)
130 tty_buffer_reset(&buf->sentinel, 0);
131 buf->head = &buf->sentinel;
132 buf->tail = &buf->sentinel;
134 atomic_set(&buf->mem_used, 0);
138 * tty_buffer_alloc - allocate a tty buffer
140 * @size: desired size (characters)
142 * Allocate a new tty buffer to hold the desired number of characters.
143 * We round our buffers off in 256 character chunks to get better
144 * allocation behaviour.
145 * Return NULL if out of memory or the allocation would exceed the
149 static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
151 struct llist_node *free;
152 struct tty_buffer *p;
154 /* Round the buffer size out */
155 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
157 if (size <= MIN_TTYB_SIZE) {
158 free = llist_del_first(&port->buf.free);
160 p = llist_entry(free, struct tty_buffer, free);
165 /* Should possibly check if this fails for the largest buffer we
166 have queued and recycle that ? */
167 if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
169 p = kmalloc(sizeof(struct tty_buffer) + 2 * size,
170 GFP_ATOMIC | __GFP_NOWARN);
175 tty_buffer_reset(p, size);
176 atomic_add(size, &port->buf.mem_used);
181 * tty_buffer_free - free a tty buffer
182 * @tty: tty owning the buffer
183 * @b: the buffer to free
185 * Free a tty buffer, or add it to the free list according to our
189 static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
191 struct tty_bufhead *buf = &port->buf;
193 /* Dumb strategy for now - should keep some stats */
194 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
196 if (b->size > MIN_TTYB_SIZE)
198 else if (b->size > 0)
199 llist_add(&b->free, &buf->free);
203 * tty_buffer_flush - flush full tty buffers
205 * @ld: optional ldisc ptr (must be referenced)
207 * flush all the buffers containing receive data. If ld != NULL,
208 * flush the ldisc input buffer.
210 * Locking: takes buffer lock to ensure single-threaded flip buffer
214 void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
216 struct tty_port *port = tty->port;
217 struct tty_bufhead *buf = &port->buf;
218 struct tty_buffer *next;
220 atomic_inc(&buf->priority);
222 mutex_lock(&buf->lock);
223 /* paired w/ release in __tty_buffer_request_room; ensures there are
224 * no pending memory accesses to the freed buffer
226 while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
227 tty_buffer_free(port, buf->head);
230 buf->head->read = buf->head->commit;
232 if (ld && ld->ops->flush_buffer)
233 ld->ops->flush_buffer(tty);
235 atomic_dec(&buf->priority);
236 mutex_unlock(&buf->lock);
240 * tty_buffer_request_room - grow tty buffer if needed
241 * @tty: tty structure
242 * @size: size desired
243 * @flags: buffer flags if new buffer allocated (default = 0)
245 * Make at least size bytes of linear space available for the tty
246 * buffer. If we fail return the size we managed to find.
248 * Will change over to a new buffer if the current buffer is encoded as
249 * TTY_NORMAL (so has no flags buffer) and the new buffer requires
252 static int __tty_buffer_request_room(struct tty_port *port, size_t size,
255 struct tty_bufhead *buf = &port->buf;
256 struct tty_buffer *b, *n;
260 if (b->flags & TTYB_NORMAL)
261 left = 2 * b->size - b->used;
263 left = b->size - b->used;
265 change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
266 if (change || left < size) {
267 /* This is the slow path - looking for new buffers to use */
268 n = tty_buffer_alloc(port, size);
272 /* paired w/ acquire in flush_to_ldisc(); ensures
273 * flush_to_ldisc() sees buffer data.
275 smp_store_release(&b->commit, b->used);
276 /* paired w/ acquire in flush_to_ldisc(); ensures the
277 * latest commit value can be read before the head is
278 * advanced to the next buffer
280 smp_store_release(&b->next, n);
289 int tty_buffer_request_room(struct tty_port *port, size_t size)
291 return __tty_buffer_request_room(port, size, 0);
293 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
296 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
299 * @flag: flag value for each character
302 * Queue a series of bytes to the tty buffering. All the characters
303 * passed are marked with the supplied flag. Returns the number added.
306 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
307 const unsigned char *chars, char flag, size_t size)
311 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
312 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
313 int space = __tty_buffer_request_room(port, goal, flags);
314 struct tty_buffer *tb = port->buf.tail;
315 if (unlikely(space == 0))
317 memcpy(char_buf_ptr(tb, tb->used), chars, space);
318 if (~tb->flags & TTYB_NORMAL)
319 memset(flag_buf_ptr(tb, tb->used), flag, space);
323 /* There is a small chance that we need to split the data over
324 several buffers. If this is the case we must loop */
325 } while (unlikely(size > copied));
328 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
331 * tty_insert_flip_string_flags - Add characters to the tty buffer
337 * Queue a series of bytes to the tty buffering. For each character
338 * the flags array indicates the status of the character. Returns the
342 int tty_insert_flip_string_flags(struct tty_port *port,
343 const unsigned char *chars, const char *flags, size_t size)
347 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
348 int space = tty_buffer_request_room(port, goal);
349 struct tty_buffer *tb = port->buf.tail;
350 if (unlikely(space == 0))
352 memcpy(char_buf_ptr(tb, tb->used), chars, space);
353 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
358 /* There is a small chance that we need to split the data over
359 several buffers. If this is the case we must loop */
360 } while (unlikely(size > copied));
363 EXPORT_SYMBOL(tty_insert_flip_string_flags);
366 * __tty_insert_flip_char - Add one character to the tty buffer
371 * Queue a single byte to the tty buffering, with an optional flag.
372 * This is the slow path of tty_insert_flip_char.
374 int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag)
376 struct tty_buffer *tb;
377 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
379 if (!__tty_buffer_request_room(port, 1, flags))
383 if (~tb->flags & TTYB_NORMAL)
384 *flag_buf_ptr(tb, tb->used) = flag;
385 *char_buf_ptr(tb, tb->used++) = ch;
389 EXPORT_SYMBOL(__tty_insert_flip_char);
392 * tty_prepare_flip_string - make room for characters
394 * @chars: return pointer for character write area
395 * @size: desired size
397 * Prepare a block of space in the buffer for data. Returns the length
398 * available and buffer pointer to the space which is now allocated and
399 * accounted for as ready for normal characters. This is used for drivers
400 * that need their own block copy routines into the buffer. There is no
401 * guarantee the buffer is a DMA target!
404 int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
407 int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
409 struct tty_buffer *tb = port->buf.tail;
410 *chars = char_buf_ptr(tb, tb->used);
411 if (~tb->flags & TTYB_NORMAL)
412 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
417 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
420 * tty_ldisc_receive_buf - forward data to line discipline
421 * @ld: line discipline to process input
423 * @f: TTY_* flags buffer
424 * @count: number of bytes to process
426 * Callers other than flush_to_ldisc() need to exclude the kworker
427 * from concurrent use of the line discipline, see paste_selection().
429 * Returns the number of bytes processed
431 int tty_ldisc_receive_buf(struct tty_ldisc *ld, unsigned char *p,
434 if (ld->ops->receive_buf2)
435 count = ld->ops->receive_buf2(ld->tty, p, f, count);
437 count = min_t(int, count, ld->tty->receive_room);
438 if (count && ld->ops->receive_buf)
439 ld->ops->receive_buf(ld->tty, p, f, count);
445 EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
448 receive_buf(struct tty_ldisc *ld, struct tty_buffer *head, int count)
450 unsigned char *p = char_buf_ptr(head, head->read);
453 if (~head->flags & TTYB_NORMAL)
454 f = flag_buf_ptr(head, head->read);
456 return tty_ldisc_receive_buf(ld, p, f, count);
461 * @work: tty structure passed from work queue.
463 * This routine is called out of the software interrupt to flush data
464 * from the buffer chain to the line discipline.
466 * The receive_buf method is single threaded for each tty instance.
468 * Locking: takes buffer lock to ensure single-threaded flip buffer
472 static void flush_to_ldisc(struct work_struct *work)
474 struct tty_port *port = container_of(work, struct tty_port, buf.work);
475 struct tty_bufhead *buf = &port->buf;
476 struct tty_struct *tty;
477 struct tty_ldisc *disc;
479 tty = READ_ONCE(port->itty);
483 disc = tty_ldisc_ref(tty);
487 mutex_lock(&buf->lock);
490 struct tty_buffer *head = buf->head;
491 struct tty_buffer *next;
494 /* Ldisc or user is trying to gain exclusive access */
495 if (atomic_read(&buf->priority))
498 /* paired w/ release in __tty_buffer_request_room();
499 * ensures commit value read is not stale if the head
500 * is advancing to the next buffer
502 next = smp_load_acquire(&head->next);
503 /* paired w/ release in __tty_buffer_request_room() or in
504 * tty_buffer_flush(); ensures we see the committed buffer data
506 count = smp_load_acquire(&head->commit) - head->read;
511 tty_buffer_free(port, head);
515 count = receive_buf(disc, head, count);
524 mutex_unlock(&buf->lock);
526 tty_ldisc_deref(disc);
529 static inline void tty_flip_buffer_commit(struct tty_buffer *tail)
532 * Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
535 smp_store_release(&tail->commit, tail->used);
539 * tty_flip_buffer_push - terminal
540 * @port: tty port to push
542 * Queue a push of the terminal flip buffers to the line discipline.
543 * Can be called from IRQ/atomic context.
545 * In the event of the queue being busy for flipping the work will be
546 * held off and retried later.
549 void tty_flip_buffer_push(struct tty_port *port)
551 struct tty_bufhead *buf = &port->buf;
553 tty_flip_buffer_commit(buf->tail);
554 queue_work(system_unbound_wq, &buf->work);
556 EXPORT_SYMBOL(tty_flip_buffer_push);
559 * tty_insert_flip_string_and_push_buffer - add characters to the tty buffer and
565 * The function combines tty_insert_flip_string() and tty_flip_buffer_push()
566 * with the exception of properly holding the @port->lock.
568 * To be used only internally (by pty currently).
570 * Returns: the number added.
572 int tty_insert_flip_string_and_push_buffer(struct tty_port *port,
573 const unsigned char *chars, size_t size)
575 struct tty_bufhead *buf = &port->buf;
578 spin_lock_irqsave(&port->lock, flags);
579 size = tty_insert_flip_string(port, chars, size);
581 tty_flip_buffer_commit(buf->tail);
582 spin_unlock_irqrestore(&port->lock, flags);
584 queue_work(system_unbound_wq, &buf->work);
590 * tty_buffer_init - prepare a tty buffer structure
591 * @tty: tty to initialise
593 * Set up the initial state of the buffer management for a tty device.
594 * Must be called before the other tty buffer functions are used.
597 void tty_buffer_init(struct tty_port *port)
599 struct tty_bufhead *buf = &port->buf;
601 mutex_init(&buf->lock);
602 tty_buffer_reset(&buf->sentinel, 0);
603 buf->head = &buf->sentinel;
604 buf->tail = &buf->sentinel;
605 init_llist_head(&buf->free);
606 atomic_set(&buf->mem_used, 0);
607 atomic_set(&buf->priority, 0);
608 INIT_WORK(&buf->work, flush_to_ldisc);
609 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
613 * tty_buffer_set_limit - change the tty buffer memory limit
614 * @port: tty port to change
616 * Change the tty buffer memory limit.
617 * Must be called before the other tty buffer functions are used.
620 int tty_buffer_set_limit(struct tty_port *port, int limit)
622 if (limit < MIN_TTYB_SIZE)
624 port->buf.mem_limit = limit;
627 EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
629 /* slave ptys can claim nested buffer lock when handling BRK and INTR */
630 void tty_buffer_set_lock_subclass(struct tty_port *port)
632 lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
635 bool tty_buffer_restart_work(struct tty_port *port)
637 return queue_work(system_unbound_wq, &port->buf.work);
640 bool tty_buffer_cancel_work(struct tty_port *port)
642 return cancel_work_sync(&port->buf.work);
645 void tty_buffer_flush_work(struct tty_port *port)
647 flush_work(&port->buf.work);