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 * 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 unsigned int tty_buffer_space_avail(struct tty_port *port)
93 int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
97 EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
99 static void tty_buffer_reset(struct tty_buffer *p, size_t size)
110 * tty_buffer_free_all - free buffers used by a tty
111 * @port: tty port to free from
113 * Remove all the buffers pending on a tty whether queued with data
114 * or in the free ring. Must be called when the tty is no longer in use
117 void tty_buffer_free_all(struct tty_port *port)
119 struct tty_bufhead *buf = &port->buf;
120 struct tty_buffer *p, *next;
121 struct llist_node *llist;
122 unsigned int freed = 0;
125 while ((p = buf->head) != NULL) {
131 llist = llist_del_all(&buf->free);
132 llist_for_each_entry_safe(p, next, llist, free)
135 tty_buffer_reset(&buf->sentinel, 0);
136 buf->head = &buf->sentinel;
137 buf->tail = &buf->sentinel;
139 still_used = atomic_xchg(&buf->mem_used, 0);
140 WARN(still_used != freed, "we still have not freed %d bytes!",
145 * tty_buffer_alloc - allocate a tty buffer
147 * @size: desired size (characters)
149 * Allocate a new tty buffer to hold the desired number of characters.
150 * We round our buffers off in 256 character chunks to get better
151 * allocation behaviour.
152 * Return NULL if out of memory or the allocation would exceed the
156 static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
158 struct llist_node *free;
159 struct tty_buffer *p;
161 /* Round the buffer size out */
162 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
164 if (size <= MIN_TTYB_SIZE) {
165 free = llist_del_first(&port->buf.free);
167 p = llist_entry(free, struct tty_buffer, free);
172 /* Should possibly check if this fails for the largest buffer we
173 * have queued and recycle that ?
175 if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
177 p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
182 tty_buffer_reset(p, size);
183 atomic_add(size, &port->buf.mem_used);
188 * tty_buffer_free - free a tty buffer
189 * @port: tty port owning the buffer
190 * @b: the buffer to free
192 * Free a tty buffer, or add it to the free list according to our
196 static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
198 struct tty_bufhead *buf = &port->buf;
200 /* Dumb strategy for now - should keep some stats */
201 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
203 if (b->size > MIN_TTYB_SIZE)
205 else if (b->size > 0)
206 llist_add(&b->free, &buf->free);
210 * tty_buffer_flush - flush full tty buffers
212 * @ld: optional ldisc ptr (must be referenced)
214 * flush all the buffers containing receive data. If ld != NULL,
215 * flush the ldisc input buffer.
217 * Locking: takes buffer lock to ensure single-threaded flip buffer
221 void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
223 struct tty_port *port = tty->port;
224 struct tty_bufhead *buf = &port->buf;
225 struct tty_buffer *next;
227 atomic_inc(&buf->priority);
229 mutex_lock(&buf->lock);
230 /* paired w/ release in __tty_buffer_request_room; ensures there are
231 * no pending memory accesses to the freed buffer
233 while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
234 tty_buffer_free(port, buf->head);
237 buf->head->read = buf->head->commit;
239 if (ld && ld->ops->flush_buffer)
240 ld->ops->flush_buffer(tty);
242 atomic_dec(&buf->priority);
243 mutex_unlock(&buf->lock);
247 * __tty_buffer_request_room - grow tty buffer if needed
249 * @size: size desired
250 * @flags: buffer flags if new buffer allocated (default = 0)
252 * Make at least size bytes of linear space available for the tty
253 * buffer. If we fail return the size we managed to find.
255 * Will change over to a new buffer if the current buffer is encoded as
256 * TTY_NORMAL (so has no flags buffer) and the new buffer requires
259 static int __tty_buffer_request_room(struct tty_port *port, size_t size,
262 struct tty_bufhead *buf = &port->buf;
263 struct tty_buffer *b, *n;
267 if (b->flags & TTYB_NORMAL)
268 left = 2 * b->size - b->used;
270 left = b->size - b->used;
272 change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
273 if (change || left < size) {
274 /* This is the slow path - looking for new buffers to use */
275 n = tty_buffer_alloc(port, size);
279 /* paired w/ acquire in flush_to_ldisc(); ensures
280 * flush_to_ldisc() sees buffer data.
282 smp_store_release(&b->commit, b->used);
283 /* paired w/ acquire in flush_to_ldisc(); ensures the
284 * latest commit value can be read before the head is
285 * advanced to the next buffer
287 smp_store_release(&b->next, n);
296 int tty_buffer_request_room(struct tty_port *port, size_t size)
298 return __tty_buffer_request_room(port, size, 0);
300 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
303 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
306 * @flag: flag value for each character
309 * Queue a series of bytes to the tty buffering. All the characters
310 * passed are marked with the supplied flag. Returns the number added.
313 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
314 const unsigned char *chars, char flag, size_t size)
319 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
320 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
321 int space = __tty_buffer_request_room(port, goal, flags);
322 struct tty_buffer *tb = port->buf.tail;
324 if (unlikely(space == 0))
326 memcpy(char_buf_ptr(tb, tb->used), chars, space);
327 if (~tb->flags & TTYB_NORMAL)
328 memset(flag_buf_ptr(tb, tb->used), flag, space);
332 /* There is a small chance that we need to split the data over
333 * several buffers. If this is the case we must loop.
335 } while (unlikely(size > copied));
338 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
341 * tty_insert_flip_string_flags - Add characters to the tty buffer
347 * Queue a series of bytes to the tty buffering. For each character
348 * the flags array indicates the status of the character. Returns the
352 int tty_insert_flip_string_flags(struct tty_port *port,
353 const unsigned char *chars, const char *flags, size_t size)
358 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
359 int space = tty_buffer_request_room(port, goal);
360 struct tty_buffer *tb = port->buf.tail;
362 if (unlikely(space == 0))
364 memcpy(char_buf_ptr(tb, tb->used), chars, space);
365 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
370 /* There is a small chance that we need to split the data over
371 * several buffers. If this is the case we must loop.
373 } while (unlikely(size > copied));
376 EXPORT_SYMBOL(tty_insert_flip_string_flags);
379 * __tty_insert_flip_char - Add one character to the tty buffer
384 * Queue a single byte to the tty buffering, with an optional flag.
385 * This is the slow path of tty_insert_flip_char.
387 int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag)
389 struct tty_buffer *tb;
390 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
392 if (!__tty_buffer_request_room(port, 1, flags))
396 if (~tb->flags & TTYB_NORMAL)
397 *flag_buf_ptr(tb, tb->used) = flag;
398 *char_buf_ptr(tb, tb->used++) = ch;
402 EXPORT_SYMBOL(__tty_insert_flip_char);
405 * tty_schedule_flip - push characters to ldisc
406 * @port: tty port to push from
408 * Takes any pending buffers and transfers their ownership to the
409 * ldisc side of the queue. It then schedules those characters for
410 * processing by the line discipline.
413 void tty_schedule_flip(struct tty_port *port)
415 struct tty_bufhead *buf = &port->buf;
417 /* paired w/ acquire in flush_to_ldisc(); ensures
418 * flush_to_ldisc() sees buffer data.
420 smp_store_release(&buf->tail->commit, buf->tail->used);
421 queue_work(system_unbound_wq, &buf->work);
423 EXPORT_SYMBOL(tty_schedule_flip);
426 * tty_prepare_flip_string - make room for characters
428 * @chars: return pointer for character write area
429 * @size: desired size
431 * Prepare a block of space in the buffer for data. Returns the length
432 * available and buffer pointer to the space which is now allocated and
433 * accounted for as ready for normal characters. This is used for drivers
434 * that need their own block copy routines into the buffer. There is no
435 * guarantee the buffer is a DMA target!
438 int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
441 int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
444 struct tty_buffer *tb = port->buf.tail;
446 *chars = char_buf_ptr(tb, tb->used);
447 if (~tb->flags & TTYB_NORMAL)
448 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
453 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
456 * tty_ldisc_receive_buf - forward data to line discipline
457 * @ld: line discipline to process input
459 * @f: TTY_* flags buffer
460 * @count: number of bytes to process
462 * Callers other than flush_to_ldisc() need to exclude the kworker
463 * from concurrent use of the line discipline, see paste_selection().
465 * Returns the number of bytes processed
467 int tty_ldisc_receive_buf(struct tty_ldisc *ld, const unsigned char *p,
468 const char *f, int count)
470 if (ld->ops->receive_buf2)
471 count = ld->ops->receive_buf2(ld->tty, p, f, count);
473 count = min_t(int, count, ld->tty->receive_room);
474 if (count && ld->ops->receive_buf)
475 ld->ops->receive_buf(ld->tty, p, f, count);
479 EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
482 receive_buf(struct tty_port *port, struct tty_buffer *head, int count)
484 unsigned char *p = char_buf_ptr(head, head->read);
485 const char *f = NULL;
488 if (~head->flags & TTYB_NORMAL)
489 f = flag_buf_ptr(head, head->read);
491 n = port->client_ops->receive_buf(port, p, f, count);
499 * @work: tty structure passed from work queue.
501 * This routine is called out of the software interrupt to flush data
502 * from the buffer chain to the line discipline.
504 * The receive_buf method is single threaded for each tty instance.
506 * Locking: takes buffer lock to ensure single-threaded flip buffer
510 static void flush_to_ldisc(struct work_struct *work)
512 struct tty_port *port = container_of(work, struct tty_port, buf.work);
513 struct tty_bufhead *buf = &port->buf;
515 mutex_lock(&buf->lock);
518 struct tty_buffer *head = buf->head;
519 struct tty_buffer *next;
522 /* Ldisc or user is trying to gain exclusive access */
523 if (atomic_read(&buf->priority))
526 /* paired w/ release in __tty_buffer_request_room();
527 * ensures commit value read is not stale if the head
528 * is advancing to the next buffer
530 next = smp_load_acquire(&head->next);
531 /* paired w/ release in __tty_buffer_request_room() or in
532 * tty_buffer_flush(); ensures we see the committed buffer data
534 count = smp_load_acquire(&head->commit) - head->read;
539 tty_buffer_free(port, head);
543 count = receive_buf(port, head, count);
549 mutex_unlock(&buf->lock);
554 * tty_flip_buffer_push - terminal
555 * @port: tty port to push
557 * Queue a push of the terminal flip buffers to the line discipline.
558 * Can be called from IRQ/atomic context.
560 * In the event of the queue being busy for flipping the work will be
561 * held off and retried later.
564 void tty_flip_buffer_push(struct tty_port *port)
566 tty_schedule_flip(port);
568 EXPORT_SYMBOL(tty_flip_buffer_push);
571 * tty_buffer_init - prepare a tty buffer structure
572 * @port: tty port to initialise
574 * Set up the initial state of the buffer management for a tty device.
575 * Must be called before the other tty buffer functions are used.
578 void tty_buffer_init(struct tty_port *port)
580 struct tty_bufhead *buf = &port->buf;
582 mutex_init(&buf->lock);
583 tty_buffer_reset(&buf->sentinel, 0);
584 buf->head = &buf->sentinel;
585 buf->tail = &buf->sentinel;
586 init_llist_head(&buf->free);
587 atomic_set(&buf->mem_used, 0);
588 atomic_set(&buf->priority, 0);
589 INIT_WORK(&buf->work, flush_to_ldisc);
590 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
594 * tty_buffer_set_limit - change the tty buffer memory limit
595 * @port: tty port to change
596 * @limit: memory limit to set
598 * Change the tty buffer memory limit.
599 * Must be called before the other tty buffer functions are used.
602 int tty_buffer_set_limit(struct tty_port *port, int limit)
604 if (limit < MIN_TTYB_SIZE)
606 port->buf.mem_limit = limit;
609 EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
611 /* slave ptys can claim nested buffer lock when handling BRK and INTR */
612 void tty_buffer_set_lock_subclass(struct tty_port *port)
614 lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
617 bool tty_buffer_restart_work(struct tty_port *port)
619 return queue_work(system_unbound_wq, &port->buf.work);
622 bool tty_buffer_cancel_work(struct tty_port *port)
624 return cancel_work_sync(&port->buf.work);
627 void tty_buffer_flush_work(struct tty_port *port)
629 flush_work(&port->buf.work);