1 // SPDX-License-Identifier: GPL-2.0
3 * Tty buffer allocation management
6 #include <linux/types.h>
7 #include <linux/errno.h>
8 #include <linux/minmax.h>
10 #include <linux/tty_driver.h>
11 #include <linux/tty_flip.h>
12 #include <linux/timer.h>
13 #include <linux/string.h>
14 #include <linux/slab.h>
15 #include <linux/sched.h>
16 #include <linux/wait.h>
17 #include <linux/bitops.h>
18 #include <linux/delay.h>
19 #include <linux/module.h>
20 #include <linux/ratelimit.h>
23 #define MIN_TTYB_SIZE 256
24 #define TTYB_ALIGN_MASK 0xff
27 * Byte threshold to limit memory consumption for flip buffers.
28 * The actual memory limit is > 2x this amount.
30 #define TTYB_DEFAULT_MEM_LIMIT (640 * 1024UL)
33 * We default to dicing tty buffer allocations to this many characters
34 * in order to avoid multiple page allocations. We know the size of
35 * tty_buffer itself but it must also be taken into account that the
36 * buffer is 256 byte aligned. See tty_buffer_find for the allocation
37 * logic this must match.
40 #define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~TTYB_ALIGN_MASK)
43 * tty_buffer_lock_exclusive - gain exclusive access to buffer
44 * @port: tty port owning the flip buffer
46 * Guarantees safe use of the &tty_ldisc_ops.receive_buf() method by excluding
47 * the buffer work and any pending flush from using the flip buffer. Data can
48 * continue to be added concurrently to the flip buffer from the driver side.
50 * See also tty_buffer_unlock_exclusive().
52 void tty_buffer_lock_exclusive(struct tty_port *port)
54 struct tty_bufhead *buf = &port->buf;
56 atomic_inc(&buf->priority);
57 mutex_lock(&buf->lock);
59 EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
62 * tty_buffer_unlock_exclusive - release exclusive access
63 * @port: tty port owning the flip buffer
65 * The buffer work is restarted if there is data in the flip buffer.
67 * See also tty_buffer_lock_exclusive().
69 void tty_buffer_unlock_exclusive(struct tty_port *port)
71 struct tty_bufhead *buf = &port->buf;
74 restart = buf->head->commit != buf->head->read;
76 atomic_dec(&buf->priority);
77 mutex_unlock(&buf->lock);
79 queue_work(system_unbound_wq, &buf->work);
81 EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
84 * tty_buffer_space_avail - return unused buffer space
85 * @port: tty port owning the flip buffer
87 * Returns: the # of bytes which can be written by the driver without reaching
90 * Note: this does not guarantee that memory is available to write the returned
91 * # of bytes (use tty_prepare_flip_string() to pre-allocate if memory
92 * guarantee is required).
94 unsigned int tty_buffer_space_avail(struct tty_port *port)
96 int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
100 EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
102 static void tty_buffer_reset(struct tty_buffer *p, size_t size)
114 * tty_buffer_free_all - free buffers used by a tty
115 * @port: tty port to free from
117 * Remove all the buffers pending on a tty whether queued with data or in the
118 * free ring. Must be called when the tty is no longer in use.
120 void tty_buffer_free_all(struct tty_port *port)
122 struct tty_bufhead *buf = &port->buf;
123 struct tty_buffer *p, *next;
124 struct llist_node *llist;
125 unsigned int freed = 0;
128 while ((p = buf->head) != NULL) {
134 llist = llist_del_all(&buf->free);
135 llist_for_each_entry_safe(p, next, llist, free)
138 tty_buffer_reset(&buf->sentinel, 0);
139 buf->head = &buf->sentinel;
140 buf->tail = &buf->sentinel;
142 still_used = atomic_xchg(&buf->mem_used, 0);
143 WARN(still_used != freed, "we still have not freed %d bytes!",
148 * tty_buffer_alloc - allocate a tty buffer
150 * @size: desired size (characters)
152 * Allocate a new tty buffer to hold the desired number of characters. We
153 * round our buffers off in 256 character chunks to get better allocation
156 * Returns: %NULL if out of memory or the allocation would exceed the per
159 static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
161 struct llist_node *free;
162 struct tty_buffer *p;
164 /* Round the buffer size out */
165 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
167 if (size <= MIN_TTYB_SIZE) {
168 free = llist_del_first(&port->buf.free);
170 p = llist_entry(free, struct tty_buffer, free);
175 /* Should possibly check if this fails for the largest buffer we
176 * have queued and recycle that ?
178 if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
180 p = kmalloc(struct_size(p, data, 2 * size), GFP_ATOMIC | __GFP_NOWARN);
185 tty_buffer_reset(p, size);
186 atomic_add(size, &port->buf.mem_used);
191 * tty_buffer_free - free a tty buffer
192 * @port: tty port owning the buffer
193 * @b: the buffer to free
195 * Free a tty buffer, or add it to the free list according to our internal
198 static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
200 struct tty_bufhead *buf = &port->buf;
202 /* Dumb strategy for now - should keep some stats */
203 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
205 if (b->size > MIN_TTYB_SIZE)
207 else if (b->size > 0)
208 llist_add(&b->free, &buf->free);
212 * tty_buffer_flush - flush full tty buffers
214 * @ld: optional ldisc ptr (must be referenced)
216 * Flush all the buffers containing receive data. If @ld != %NULL, flush the
217 * ldisc input buffer.
219 * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
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;
238 buf->head->lookahead = buf->head->read;
240 if (ld && ld->ops->flush_buffer)
241 ld->ops->flush_buffer(tty);
243 atomic_dec(&buf->priority);
244 mutex_unlock(&buf->lock);
248 * __tty_buffer_request_room - grow tty buffer if needed
250 * @size: size desired
251 * @flags: buffer has to store flags along character data
253 * Make at least @size bytes of linear space available for the tty buffer.
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 a flags
259 * Returns: the size we managed to find.
261 static int __tty_buffer_request_room(struct tty_port *port, size_t size,
264 struct tty_bufhead *buf = &port->buf;
265 struct tty_buffer *b, *n;
270 left = 2 * b->size - b->used;
272 left = b->size - b->used;
274 change = !b->flags && flags;
275 if (change || left < size) {
276 /* This is the slow path - looking for new buffers to use */
277 n = tty_buffer_alloc(port, size);
282 * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
283 * ensures they see all buffer data.
285 smp_store_release(&b->commit, b->used);
287 * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
288 * ensures the latest commit value can be read before the head
289 * is advanced to the next buffer.
291 smp_store_release(&b->next, n);
300 int tty_buffer_request_room(struct tty_port *port, size_t size)
302 return __tty_buffer_request_room(port, size, true);
304 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
306 int __tty_insert_flip_string_flags(struct tty_port *port, const u8 *chars,
307 const u8 *flags, bool mutable_flags,
310 bool need_flags = mutable_flags || flags[0] != TTY_NORMAL;
314 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
315 int space = __tty_buffer_request_room(port, goal, need_flags);
316 struct tty_buffer *tb = port->buf.tail;
318 if (unlikely(space == 0))
321 memcpy(char_buf_ptr(tb, tb->used), chars, space);
324 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
326 } else if (tb->flags) {
327 memset(flag_buf_ptr(tb, tb->used), flags[0], space);
329 /* tb->flags should be available once requested */
330 WARN_ON_ONCE(need_flags);
337 /* There is a small chance that we need to split the data over
338 * several buffers. If this is the case we must loop.
340 } while (unlikely(size > copied));
344 EXPORT_SYMBOL(__tty_insert_flip_string_flags);
347 * __tty_insert_flip_char - add one character to the tty buffer
352 * Queue a single byte @ch to the tty buffering, with an optional flag. This is
353 * the slow path of tty_insert_flip_char().
355 int __tty_insert_flip_char(struct tty_port *port, u8 ch, u8 flag)
357 struct tty_buffer *tb;
358 bool flags = flag != TTY_NORMAL;
360 if (!__tty_buffer_request_room(port, 1, flags))
365 *flag_buf_ptr(tb, tb->used) = flag;
366 *char_buf_ptr(tb, tb->used++) = ch;
370 EXPORT_SYMBOL(__tty_insert_flip_char);
373 * tty_prepare_flip_string - make room for characters
375 * @chars: return pointer for character write area
376 * @size: desired size
378 * Prepare a block of space in the buffer for data.
380 * This is used for drivers that need their own block copy routines into the
381 * buffer. There is no guarantee the buffer is a DMA target!
383 * Returns: the length available and buffer pointer (@chars) to the space which
384 * is now allocated and accounted for as ready for normal characters.
386 int tty_prepare_flip_string(struct tty_port *port, u8 **chars, size_t size)
388 int space = __tty_buffer_request_room(port, size, false);
391 struct tty_buffer *tb = port->buf.tail;
393 *chars = char_buf_ptr(tb, tb->used);
395 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
400 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
403 * tty_ldisc_receive_buf - forward data to line discipline
404 * @ld: line discipline to process input
406 * @f: %TTY_NORMAL, %TTY_BREAK, etc. flags buffer
407 * @count: number of bytes to process
409 * Callers other than flush_to_ldisc() need to exclude the kworker from
410 * concurrent use of the line discipline, see paste_selection().
412 * Returns: the number of bytes processed.
414 size_t tty_ldisc_receive_buf(struct tty_ldisc *ld, const u8 *p, const u8 *f,
417 if (ld->ops->receive_buf2)
418 count = ld->ops->receive_buf2(ld->tty, p, f, count);
420 count = min_t(size_t, count, ld->tty->receive_room);
421 if (count && ld->ops->receive_buf)
422 ld->ops->receive_buf(ld->tty, p, f, count);
426 EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
428 static void lookahead_bufs(struct tty_port *port, struct tty_buffer *head)
430 head->lookahead = max(head->lookahead, head->read);
433 struct tty_buffer *next;
437 * Paired w/ release in __tty_buffer_request_room();
438 * ensures commit value read is not stale if the head
439 * is advancing to the next buffer.
441 next = smp_load_acquire(&head->next);
443 * Paired w/ release in __tty_buffer_request_room() or in
444 * tty_buffer_flush(); ensures we see the committed buffer data.
446 count = smp_load_acquire(&head->commit) - head->lookahead;
452 if (port->client_ops->lookahead_buf) {
455 p = char_buf_ptr(head, head->lookahead);
457 f = flag_buf_ptr(head, head->lookahead);
459 port->client_ops->lookahead_buf(port, p, f, count);
462 head->lookahead += count;
467 receive_buf(struct tty_port *port, struct tty_buffer *head, size_t count)
469 u8 *p = char_buf_ptr(head, head->read);
474 f = flag_buf_ptr(head, head->read);
476 n = port->client_ops->receive_buf(port, p, f, count);
483 * flush_to_ldisc - flush data from buffer to ldisc
484 * @work: tty structure passed from work queue.
486 * This routine is called out of the software interrupt to flush data from the
487 * buffer chain to the line discipline.
489 * The receive_buf() method is single threaded for each tty instance.
491 * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
493 static void flush_to_ldisc(struct work_struct *work)
495 struct tty_port *port = container_of(work, struct tty_port, buf.work);
496 struct tty_bufhead *buf = &port->buf;
498 mutex_lock(&buf->lock);
501 struct tty_buffer *head = buf->head;
502 struct tty_buffer *next;
505 /* Ldisc or user is trying to gain exclusive access */
506 if (atomic_read(&buf->priority))
509 /* paired w/ release in __tty_buffer_request_room();
510 * ensures commit value read is not stale if the head
511 * is advancing to the next buffer
513 next = smp_load_acquire(&head->next);
514 /* paired w/ release in __tty_buffer_request_room() or in
515 * tty_buffer_flush(); ensures we see the committed buffer data
517 count = smp_load_acquire(&head->commit) - head->read;
522 tty_buffer_free(port, head);
526 rcvd = receive_buf(port, head, count);
529 lookahead_bufs(port, head);
537 mutex_unlock(&buf->lock);
541 static inline void tty_flip_buffer_commit(struct tty_buffer *tail)
544 * Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
547 smp_store_release(&tail->commit, tail->used);
551 * tty_flip_buffer_push - push terminal buffers
552 * @port: tty port to push
554 * Queue a push of the terminal flip buffers to the line discipline. Can be
555 * called from IRQ/atomic context.
557 * In the event of the queue being busy for flipping the work will be held off
560 void tty_flip_buffer_push(struct tty_port *port)
562 struct tty_bufhead *buf = &port->buf;
564 tty_flip_buffer_commit(buf->tail);
565 queue_work(system_unbound_wq, &buf->work);
567 EXPORT_SYMBOL(tty_flip_buffer_push);
570 * tty_insert_flip_string_and_push_buffer - add characters to the tty buffer and
576 * The function combines tty_insert_flip_string() and tty_flip_buffer_push()
577 * with the exception of properly holding the @port->lock.
579 * To be used only internally (by pty currently).
581 * Returns: the number added.
583 int tty_insert_flip_string_and_push_buffer(struct tty_port *port,
584 const u8 *chars, size_t size)
586 struct tty_bufhead *buf = &port->buf;
589 spin_lock_irqsave(&port->lock, flags);
590 size = tty_insert_flip_string(port, chars, size);
592 tty_flip_buffer_commit(buf->tail);
593 spin_unlock_irqrestore(&port->lock, flags);
595 queue_work(system_unbound_wq, &buf->work);
601 * tty_buffer_init - prepare a tty buffer structure
602 * @port: tty port to initialise
604 * Set up the initial state of the buffer management for a tty device. Must be
605 * called before the other tty buffer functions are used.
607 void tty_buffer_init(struct tty_port *port)
609 struct tty_bufhead *buf = &port->buf;
611 mutex_init(&buf->lock);
612 tty_buffer_reset(&buf->sentinel, 0);
613 buf->head = &buf->sentinel;
614 buf->tail = &buf->sentinel;
615 init_llist_head(&buf->free);
616 atomic_set(&buf->mem_used, 0);
617 atomic_set(&buf->priority, 0);
618 INIT_WORK(&buf->work, flush_to_ldisc);
619 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
623 * tty_buffer_set_limit - change the tty buffer memory limit
624 * @port: tty port to change
625 * @limit: memory limit to set
627 * Change the tty buffer memory limit.
629 * Must be called before the other tty buffer functions are used.
631 int tty_buffer_set_limit(struct tty_port *port, int limit)
633 if (limit < MIN_TTYB_SIZE)
635 port->buf.mem_limit = limit;
638 EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
640 /* slave ptys can claim nested buffer lock when handling BRK and INTR */
641 void tty_buffer_set_lock_subclass(struct tty_port *port)
643 lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
646 bool tty_buffer_restart_work(struct tty_port *port)
648 return queue_work(system_unbound_wq, &port->buf.work);
651 bool tty_buffer_cancel_work(struct tty_port *port)
653 return cancel_work_sync(&port->buf.work);
656 void tty_buffer_flush_work(struct tty_port *port)
658 flush_work(&port->buf.work);