1 // SPDX-License-Identifier: GPL-2.0
3 * Tty buffer allocation management
6 #include <linux/types.h>
7 #include <linux/errno.h>
9 #include <linux/tty_driver.h>
10 #include <linux/tty_flip.h>
11 #include <linux/timer.h>
12 #include <linux/string.h>
13 #include <linux/slab.h>
14 #include <linux/sched.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_DEFAULT_MEM_LIMIT (640 * 1024UL)
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)
42 * tty_buffer_lock_exclusive - gain exclusive access to buffer
43 * tty_buffer_unlock_exclusive - release exclusive access
45 * @port - tty_port owning the flip buffer
47 * Guarantees safe use of the line discipline's receive_buf() method by
48 * excluding the buffer work and any pending flush from using the flip
49 * buffer. Data can continue to be added concurrently to the flip buffer
50 * from the driver side.
52 * On release, the buffer work is restarted if there is data in the
56 void tty_buffer_lock_exclusive(struct tty_port *port)
58 struct tty_bufhead *buf = &port->buf;
60 atomic_inc(&buf->priority);
61 mutex_lock(&buf->lock);
63 EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
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);
77 EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
80 * tty_buffer_space_avail - return unused buffer space
81 * @port - tty_port owning the flip buffer
83 * Returns the # of bytes which can be written by the driver without
84 * reaching the buffer limit.
86 * Note: this does not guarantee that memory is available to write
87 * the returned # of bytes (use tty_prepare_flip_string_xxx() to
88 * pre-allocate if memory guarantee is required).
91 int tty_buffer_space_avail(struct tty_port *port)
93 int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
96 EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
98 static void tty_buffer_reset(struct tty_buffer *p, size_t size)
109 * tty_buffer_free_all - free buffers used by a tty
110 * @tty: tty to free from
112 * Remove all the buffers pending on a tty whether queued with data
113 * or in the free ring. Must be called when the tty is no longer in use
116 void tty_buffer_free_all(struct tty_port *port)
118 struct tty_bufhead *buf = &port->buf;
119 struct tty_buffer *p, *next;
120 struct llist_node *llist;
122 while ((p = buf->head) != NULL) {
127 llist = llist_del_all(&buf->free);
128 llist_for_each_entry_safe(p, next, llist, free)
131 tty_buffer_reset(&buf->sentinel, 0);
132 buf->head = &buf->sentinel;
133 buf->tail = &buf->sentinel;
135 atomic_set(&buf->mem_used, 0);
139 * tty_buffer_alloc - allocate a tty buffer
141 * @size: desired size (characters)
143 * Allocate a new tty buffer to hold the desired number of characters.
144 * We round our buffers off in 256 character chunks to get better
145 * allocation behaviour.
146 * Return NULL if out of memory or the allocation would exceed the
150 static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
152 struct llist_node *free;
153 struct tty_buffer *p;
155 /* Round the buffer size out */
156 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
158 if (size <= MIN_TTYB_SIZE) {
159 free = llist_del_first(&port->buf.free);
161 p = llist_entry(free, struct tty_buffer, free);
166 /* Should possibly check if this fails for the largest buffer we
167 have queued and recycle that ? */
168 if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
170 p = kmalloc(sizeof(struct tty_buffer) + 2 * size,
171 GFP_ATOMIC | __GFP_NOWARN);
176 tty_buffer_reset(p, size);
177 atomic_add(size, &port->buf.mem_used);
182 * tty_buffer_free - free a tty buffer
183 * @tty: tty owning the buffer
184 * @b: the buffer to free
186 * Free a tty buffer, or add it to the free list according to our
190 static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
192 struct tty_bufhead *buf = &port->buf;
194 /* Dumb strategy for now - should keep some stats */
195 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
197 if (b->size > MIN_TTYB_SIZE)
199 else if (b->size > 0)
200 llist_add(&b->free, &buf->free);
204 * tty_buffer_flush - flush full tty buffers
206 * @ld: optional ldisc ptr (must be referenced)
208 * flush all the buffers containing receive data. If ld != NULL,
209 * flush the ldisc input buffer.
211 * Locking: takes buffer lock to ensure single-threaded flip buffer
215 void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
217 struct tty_port *port = tty->port;
218 struct tty_bufhead *buf = &port->buf;
219 struct tty_buffer *next;
221 atomic_inc(&buf->priority);
223 mutex_lock(&buf->lock);
224 /* paired w/ release in __tty_buffer_request_room; ensures there are
225 * no pending memory accesses to the freed buffer
227 while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
228 tty_buffer_free(port, buf->head);
231 buf->head->read = buf->head->commit;
233 if (ld && ld->ops->flush_buffer)
234 ld->ops->flush_buffer(tty);
236 atomic_dec(&buf->priority);
237 mutex_unlock(&buf->lock);
241 * tty_buffer_request_room - grow tty buffer if needed
242 * @tty: tty structure
243 * @size: size desired
244 * @flags: buffer flags if new buffer allocated (default = 0)
246 * Make at least size bytes of linear space available for the tty
247 * buffer. If we fail return the size we managed to find.
249 * Will change over to a new buffer if the current buffer is encoded as
250 * TTY_NORMAL (so has no flags buffer) and the new buffer requires
253 static int __tty_buffer_request_room(struct tty_port *port, size_t size,
256 struct tty_bufhead *buf = &port->buf;
257 struct tty_buffer *b, *n;
261 if (b->flags & TTYB_NORMAL)
262 left = 2 * b->size - b->used;
264 left = b->size - b->used;
266 change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
267 if (change || left < size) {
268 /* This is the slow path - looking for new buffers to use */
269 n = tty_buffer_alloc(port, size);
273 /* paired w/ acquire in flush_to_ldisc(); ensures
274 * flush_to_ldisc() sees buffer data.
276 smp_store_release(&b->commit, b->used);
277 /* paired w/ acquire in flush_to_ldisc(); ensures the
278 * latest commit value can be read before the head is
279 * advanced to the next buffer
281 smp_store_release(&b->next, n);
290 int tty_buffer_request_room(struct tty_port *port, size_t size)
292 return __tty_buffer_request_room(port, size, 0);
294 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
297 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
300 * @flag: flag value for each character
303 * Queue a series of bytes to the tty buffering. All the characters
304 * passed are marked with the supplied flag. Returns the number added.
307 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
308 const unsigned char *chars, char flag, size_t size)
312 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
313 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
314 int space = __tty_buffer_request_room(port, goal, flags);
315 struct tty_buffer *tb = port->buf.tail;
316 if (unlikely(space == 0))
318 memcpy(char_buf_ptr(tb, tb->used), chars, space);
319 if (~tb->flags & TTYB_NORMAL)
320 memset(flag_buf_ptr(tb, tb->used), flag, space);
324 /* There is a small chance that we need to split the data over
325 several buffers. If this is the case we must loop */
326 } while (unlikely(size > copied));
329 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
332 * tty_insert_flip_string_flags - Add characters to the tty buffer
338 * Queue a series of bytes to the tty buffering. For each character
339 * the flags array indicates the status of the character. Returns the
343 int tty_insert_flip_string_flags(struct tty_port *port,
344 const unsigned char *chars, const char *flags, size_t size)
348 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
349 int space = tty_buffer_request_room(port, goal);
350 struct tty_buffer *tb = port->buf.tail;
351 if (unlikely(space == 0))
353 memcpy(char_buf_ptr(tb, tb->used), chars, space);
354 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
359 /* There is a small chance that we need to split the data over
360 several buffers. If this is the case we must loop */
361 } while (unlikely(size > copied));
364 EXPORT_SYMBOL(tty_insert_flip_string_flags);
367 * __tty_insert_flip_char - Add one character to the tty buffer
372 * Queue a single byte to the tty buffering, with an optional flag.
373 * This is the slow path of tty_insert_flip_char.
375 int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag)
377 struct tty_buffer *tb;
378 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
380 if (!__tty_buffer_request_room(port, 1, flags))
384 if (~tb->flags & TTYB_NORMAL)
385 *flag_buf_ptr(tb, tb->used) = flag;
386 *char_buf_ptr(tb, tb->used++) = ch;
390 EXPORT_SYMBOL(__tty_insert_flip_char);
393 * tty_prepare_flip_string - make room for characters
395 * @chars: return pointer for character write area
396 * @size: desired size
398 * Prepare a block of space in the buffer for data. Returns the length
399 * available and buffer pointer to the space which is now allocated and
400 * accounted for as ready for normal characters. This is used for drivers
401 * that need their own block copy routines into the buffer. There is no
402 * guarantee the buffer is a DMA target!
405 int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
408 int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
410 struct tty_buffer *tb = port->buf.tail;
411 *chars = char_buf_ptr(tb, tb->used);
412 if (~tb->flags & TTYB_NORMAL)
413 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
418 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
421 * tty_ldisc_receive_buf - forward data to line discipline
422 * @ld: line discipline to process input
424 * @f: TTY_* flags buffer
425 * @count: number of bytes to process
427 * Callers other than flush_to_ldisc() need to exclude the kworker
428 * from concurrent use of the line discipline, see paste_selection().
430 * Returns the number of bytes processed
432 int tty_ldisc_receive_buf(struct tty_ldisc *ld, const unsigned char *p,
435 if (ld->ops->receive_buf2)
436 count = ld->ops->receive_buf2(ld->tty, p, f, count);
438 count = min_t(int, count, ld->tty->receive_room);
439 if (count && ld->ops->receive_buf)
440 ld->ops->receive_buf(ld->tty, p, f, count);
444 EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
447 receive_buf(struct tty_port *port, struct tty_buffer *head, int count)
449 unsigned char *p = char_buf_ptr(head, head->read);
453 if (~head->flags & TTYB_NORMAL)
454 f = flag_buf_ptr(head, head->read);
456 n = port->client_ops->receive_buf(port, p, f, count);
464 * @work: tty structure passed from work queue.
466 * This routine is called out of the software interrupt to flush data
467 * from the buffer chain to the line discipline.
469 * The receive_buf method is single threaded for each tty instance.
471 * Locking: takes buffer lock to ensure single-threaded flip buffer
475 static void flush_to_ldisc(struct work_struct *work)
477 struct tty_port *port = container_of(work, struct tty_port, buf.work);
478 struct tty_bufhead *buf = &port->buf;
480 mutex_lock(&buf->lock);
483 struct tty_buffer *head = buf->head;
484 struct tty_buffer *next;
487 /* Ldisc or user is trying to gain exclusive access */
488 if (atomic_read(&buf->priority))
491 /* paired w/ release in __tty_buffer_request_room();
492 * ensures commit value read is not stale if the head
493 * is advancing to the next buffer
495 next = smp_load_acquire(&head->next);
496 /* paired w/ release in __tty_buffer_request_room() or in
497 * tty_buffer_flush(); ensures we see the committed buffer data
499 count = smp_load_acquire(&head->commit) - head->read;
504 tty_buffer_free(port, head);
508 count = receive_buf(port, head, count);
517 mutex_unlock(&buf->lock);
521 static inline void tty_flip_buffer_commit(struct tty_buffer *tail)
524 * Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
527 smp_store_release(&tail->commit, tail->used);
531 * tty_flip_buffer_push - terminal
532 * @port: tty port to push
534 * Queue a push of the terminal flip buffers to the line discipline.
535 * Can be called from IRQ/atomic context.
537 * In the event of the queue being busy for flipping the work will be
538 * held off and retried later.
541 void tty_flip_buffer_push(struct tty_port *port)
543 struct tty_bufhead *buf = &port->buf;
545 tty_flip_buffer_commit(buf->tail);
546 queue_work(system_unbound_wq, &buf->work);
548 EXPORT_SYMBOL(tty_flip_buffer_push);
551 * tty_insert_flip_string_and_push_buffer - add characters to the tty buffer and
557 * The function combines tty_insert_flip_string() and tty_flip_buffer_push()
558 * with the exception of properly holding the @port->lock.
560 * To be used only internally (by pty currently).
562 * Returns: the number added.
564 int tty_insert_flip_string_and_push_buffer(struct tty_port *port,
565 const unsigned char *chars, size_t size)
567 struct tty_bufhead *buf = &port->buf;
570 spin_lock_irqsave(&port->lock, flags);
571 size = tty_insert_flip_string(port, chars, size);
573 tty_flip_buffer_commit(buf->tail);
574 spin_unlock_irqrestore(&port->lock, flags);
576 queue_work(system_unbound_wq, &buf->work);
582 * tty_buffer_init - prepare a tty buffer structure
583 * @tty: tty to initialise
585 * Set up the initial state of the buffer management for a tty device.
586 * Must be called before the other tty buffer functions are used.
589 void tty_buffer_init(struct tty_port *port)
591 struct tty_bufhead *buf = &port->buf;
593 mutex_init(&buf->lock);
594 tty_buffer_reset(&buf->sentinel, 0);
595 buf->head = &buf->sentinel;
596 buf->tail = &buf->sentinel;
597 init_llist_head(&buf->free);
598 atomic_set(&buf->mem_used, 0);
599 atomic_set(&buf->priority, 0);
600 INIT_WORK(&buf->work, flush_to_ldisc);
601 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
605 * tty_buffer_set_limit - change the tty buffer memory limit
606 * @port: tty port to change
608 * Change the tty buffer memory limit.
609 * Must be called before the other tty buffer functions are used.
612 int tty_buffer_set_limit(struct tty_port *port, int limit)
614 if (limit < MIN_TTYB_SIZE)
616 port->buf.mem_limit = limit;
619 EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
621 /* slave ptys can claim nested buffer lock when handling BRK and INTR */
622 void tty_buffer_set_lock_subclass(struct tty_port *port)
624 lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
627 bool tty_buffer_restart_work(struct tty_port *port)
629 return queue_work(system_unbound_wq, &port->buf.work);
632 bool tty_buffer_cancel_work(struct tty_port *port)
634 return cancel_work_sync(&port->buf.work);
637 void tty_buffer_flush_work(struct tty_port *port)
639 flush_work(&port->buf.work);