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
, GFP_ATOMIC
);
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_schedule_flip - push characters to ldisc
393 * @port: tty port to push from
395 * Takes any pending buffers and transfers their ownership to the
396 * ldisc side of the queue. It then schedules those characters for
397 * processing by the line discipline.
400 void tty_schedule_flip(struct tty_port
*port
)
402 struct tty_bufhead
*buf
= &port
->buf
;
404 /* paired w/ acquire in flush_to_ldisc(); ensures
405 * flush_to_ldisc() sees buffer data.
407 smp_store_release(&buf
->tail
->commit
, buf
->tail
->used
);
408 queue_work(system_unbound_wq
, &buf
->work
);
410 EXPORT_SYMBOL(tty_schedule_flip
);
413 * tty_prepare_flip_string - make room for characters
415 * @chars: return pointer for character write area
416 * @size: desired size
418 * Prepare a block of space in the buffer for data. Returns the length
419 * available and buffer pointer to the space which is now allocated and
420 * accounted for as ready for normal characters. This is used for drivers
421 * that need their own block copy routines into the buffer. There is no
422 * guarantee the buffer is a DMA target!
425 int tty_prepare_flip_string(struct tty_port
*port
, unsigned char **chars
,
428 int space
= __tty_buffer_request_room(port
, size
, TTYB_NORMAL
);
430 struct tty_buffer
*tb
= port
->buf
.tail
;
431 *chars
= char_buf_ptr(tb
, tb
->used
);
432 if (~tb
->flags
& TTYB_NORMAL
)
433 memset(flag_buf_ptr(tb
, tb
->used
), TTY_NORMAL
, space
);
438 EXPORT_SYMBOL_GPL(tty_prepare_flip_string
);
441 * tty_ldisc_receive_buf - forward data to line discipline
442 * @ld: line discipline to process input
444 * @f: TTY_* flags buffer
445 * @count: number of bytes to process
447 * Callers other than flush_to_ldisc() need to exclude the kworker
448 * from concurrent use of the line discipline, see paste_selection().
450 * Returns the number of bytes processed
452 int tty_ldisc_receive_buf(struct tty_ldisc
*ld
, const unsigned char *p
,
455 if (ld
->ops
->receive_buf2
)
456 count
= ld
->ops
->receive_buf2(ld
->tty
, p
, f
, count
);
458 count
= min_t(int, count
, ld
->tty
->receive_room
);
459 if (count
&& ld
->ops
->receive_buf
)
460 ld
->ops
->receive_buf(ld
->tty
, p
, f
, count
);
464 EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf
);
467 receive_buf(struct tty_port
*port
, struct tty_buffer
*head
, int count
)
469 unsigned char *p
= char_buf_ptr(head
, head
->read
);
473 if (~head
->flags
& TTYB_NORMAL
)
474 f
= flag_buf_ptr(head
, head
->read
);
476 n
= port
->client_ops
->receive_buf(port
, p
, f
, count
);
484 * @work: tty structure passed from work queue.
486 * This routine is called out of the software interrupt to flush data
487 * from the 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
495 static void flush_to_ldisc(struct work_struct
*work
)
497 struct tty_port
*port
= container_of(work
, struct tty_port
, buf
.work
);
498 struct tty_bufhead
*buf
= &port
->buf
;
500 mutex_lock(&buf
->lock
);
503 struct tty_buffer
*head
= buf
->head
;
504 struct tty_buffer
*next
;
507 /* Ldisc or user is trying to gain exclusive access */
508 if (atomic_read(&buf
->priority
))
511 /* paired w/ release in __tty_buffer_request_room();
512 * ensures commit value read is not stale if the head
513 * is advancing to the next buffer
515 next
= smp_load_acquire(&head
->next
);
516 /* paired w/ release in __tty_buffer_request_room() or in
517 * tty_buffer_flush(); ensures we see the committed buffer data
519 count
= smp_load_acquire(&head
->commit
) - head
->read
;
524 tty_buffer_free(port
, head
);
528 count
= receive_buf(port
, head
, count
);
534 mutex_unlock(&buf
->lock
);
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 tty_schedule_flip(port
);
553 EXPORT_SYMBOL(tty_flip_buffer_push
);
556 * tty_buffer_init - prepare a tty buffer structure
557 * @tty: tty to initialise
559 * Set up the initial state of the buffer management for a tty device.
560 * Must be called before the other tty buffer functions are used.
563 void tty_buffer_init(struct tty_port
*port
)
565 struct tty_bufhead
*buf
= &port
->buf
;
567 mutex_init(&buf
->lock
);
568 tty_buffer_reset(&buf
->sentinel
, 0);
569 buf
->head
= &buf
->sentinel
;
570 buf
->tail
= &buf
->sentinel
;
571 init_llist_head(&buf
->free
);
572 atomic_set(&buf
->mem_used
, 0);
573 atomic_set(&buf
->priority
, 0);
574 INIT_WORK(&buf
->work
, flush_to_ldisc
);
575 buf
->mem_limit
= TTYB_DEFAULT_MEM_LIMIT
;
579 * tty_buffer_set_limit - change the tty buffer memory limit
580 * @port: tty port to change
582 * Change the tty buffer memory limit.
583 * Must be called before the other tty buffer functions are used.
586 int tty_buffer_set_limit(struct tty_port
*port
, int limit
)
588 if (limit
< MIN_TTYB_SIZE
)
590 port
->buf
.mem_limit
= limit
;
593 EXPORT_SYMBOL_GPL(tty_buffer_set_limit
);
595 /* slave ptys can claim nested buffer lock when handling BRK and INTR */
596 void tty_buffer_set_lock_subclass(struct tty_port
*port
)
598 lockdep_set_subclass(&port
->buf
.lock
, TTY_LOCK_SLAVE
);
601 bool tty_buffer_restart_work(struct tty_port
*port
)
603 return queue_work(system_unbound_wq
, &port
->buf
.work
);
606 bool tty_buffer_cancel_work(struct tty_port
*port
)
608 return cancel_work_sync(&port
->buf
.work
);
611 void tty_buffer_flush_work(struct tty_port
*port
)
613 flush_work(&port
->buf
.work
);