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 65536
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 * If all tty flip buffers have been processed by flush_to_ldisc() or
42 * dropped by tty_buffer_flush(), check if the linked pty has been closed.
43 * If so, wake the reader/poll to process
45 static inline void check_other_closed(struct tty_struct
*tty
)
47 unsigned long flags
, old
;
49 /* transition from TTY_OTHER_CLOSED => TTY_OTHER_DONE must be atomic */
50 for (flags
= ACCESS_ONCE(tty
->flags
);
51 test_bit(TTY_OTHER_CLOSED
, &flags
);
54 __set_bit(TTY_OTHER_DONE
, &flags
);
55 flags
= cmpxchg(&tty
->flags
, old
, flags
);
57 wake_up_interruptible(&tty
->read_wait
);
64 * tty_buffer_lock_exclusive - gain exclusive access to buffer
65 * tty_buffer_unlock_exclusive - release exclusive access
67 * @port - tty_port owning the flip buffer
69 * Guarantees safe use of the line discipline's receive_buf() method by
70 * excluding the buffer work and any pending flush from using the flip
71 * buffer. Data can continue to be added concurrently to the flip buffer
72 * from the driver side.
74 * On release, the buffer work is restarted if there is data in the
78 void tty_buffer_lock_exclusive(struct tty_port
*port
)
80 struct tty_bufhead
*buf
= &port
->buf
;
82 atomic_inc(&buf
->priority
);
83 mutex_lock(&buf
->lock
);
85 EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive
);
87 void tty_buffer_unlock_exclusive(struct tty_port
*port
)
89 struct tty_bufhead
*buf
= &port
->buf
;
92 restart
= buf
->head
->commit
!= buf
->head
->read
;
94 atomic_dec(&buf
->priority
);
95 mutex_unlock(&buf
->lock
);
97 queue_work(system_unbound_wq
, &buf
->work
);
99 EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive
);
102 * tty_buffer_space_avail - return unused buffer space
103 * @port - tty_port owning the flip buffer
105 * Returns the # of bytes which can be written by the driver without
106 * reaching the buffer limit.
108 * Note: this does not guarantee that memory is available to write
109 * the returned # of bytes (use tty_prepare_flip_string_xxx() to
110 * pre-allocate if memory guarantee is required).
113 int tty_buffer_space_avail(struct tty_port
*port
)
115 int space
= port
->buf
.mem_limit
- atomic_read(&port
->buf
.mem_used
);
116 return max(space
, 0);
118 EXPORT_SYMBOL_GPL(tty_buffer_space_avail
);
120 static void tty_buffer_reset(struct tty_buffer
*p
, size_t size
)
131 * tty_buffer_free_all - free buffers used by a tty
132 * @tty: tty to free from
134 * Remove all the buffers pending on a tty whether queued with data
135 * or in the free ring. Must be called when the tty is no longer in use
138 void tty_buffer_free_all(struct tty_port
*port
)
140 struct tty_bufhead
*buf
= &port
->buf
;
141 struct tty_buffer
*p
, *next
;
142 struct llist_node
*llist
;
144 while ((p
= buf
->head
) != NULL
) {
149 llist
= llist_del_all(&buf
->free
);
150 llist_for_each_entry_safe(p
, next
, llist
, free
)
153 tty_buffer_reset(&buf
->sentinel
, 0);
154 buf
->head
= &buf
->sentinel
;
155 buf
->tail
= &buf
->sentinel
;
157 atomic_set(&buf
->mem_used
, 0);
161 * tty_buffer_alloc - allocate a tty buffer
163 * @size: desired size (characters)
165 * Allocate a new tty buffer to hold the desired number of characters.
166 * We round our buffers off in 256 character chunks to get better
167 * allocation behaviour.
168 * Return NULL if out of memory or the allocation would exceed the
172 static struct tty_buffer
*tty_buffer_alloc(struct tty_port
*port
, size_t size
)
174 struct llist_node
*free
;
175 struct tty_buffer
*p
;
177 /* Round the buffer size out */
178 size
= __ALIGN_MASK(size
, TTYB_ALIGN_MASK
);
180 if (size
<= MIN_TTYB_SIZE
) {
181 free
= llist_del_first(&port
->buf
.free
);
183 p
= llist_entry(free
, struct tty_buffer
, free
);
188 /* Should possibly check if this fails for the largest buffer we
189 have queued and recycle that ? */
190 if (atomic_read(&port
->buf
.mem_used
) > port
->buf
.mem_limit
)
192 p
= kmalloc(sizeof(struct tty_buffer
) + 2 * size
, GFP_ATOMIC
);
197 tty_buffer_reset(p
, size
);
198 atomic_add(size
, &port
->buf
.mem_used
);
203 * tty_buffer_free - free a tty buffer
204 * @tty: tty owning the buffer
205 * @b: the buffer to free
207 * Free a tty buffer, or add it to the free list according to our
211 static void tty_buffer_free(struct tty_port
*port
, struct tty_buffer
*b
)
213 struct tty_bufhead
*buf
= &port
->buf
;
215 /* Dumb strategy for now - should keep some stats */
216 WARN_ON(atomic_sub_return(b
->size
, &buf
->mem_used
) < 0);
218 if (b
->size
> MIN_TTYB_SIZE
)
220 else if (b
->size
> 0)
221 llist_add(&b
->free
, &buf
->free
);
225 * tty_buffer_flush - flush full tty buffers
227 * @ld: optional ldisc ptr (must be referenced)
229 * flush all the buffers containing receive data. If ld != NULL,
230 * flush the ldisc input buffer.
232 * Locking: takes buffer lock to ensure single-threaded flip buffer
236 void tty_buffer_flush(struct tty_struct
*tty
, struct tty_ldisc
*ld
)
238 struct tty_port
*port
= tty
->port
;
239 struct tty_bufhead
*buf
= &port
->buf
;
240 struct tty_buffer
*next
;
242 atomic_inc(&buf
->priority
);
244 mutex_lock(&buf
->lock
);
245 while ((next
= buf
->head
->next
) != NULL
) {
246 tty_buffer_free(port
, buf
->head
);
249 buf
->head
->read
= buf
->head
->commit
;
251 if (ld
&& ld
->ops
->flush_buffer
)
252 ld
->ops
->flush_buffer(tty
);
254 check_other_closed(tty
);
256 atomic_dec(&buf
->priority
);
257 mutex_unlock(&buf
->lock
);
261 * tty_buffer_request_room - grow tty buffer if needed
262 * @tty: tty structure
263 * @size: size desired
264 * @flags: buffer flags if new buffer allocated (default = 0)
266 * Make at least size bytes of linear space available for the tty
267 * buffer. If we fail return the size we managed to find.
269 * Will change over to a new buffer if the current buffer is encoded as
270 * TTY_NORMAL (so has no flags buffer) and the new buffer requires
273 static int __tty_buffer_request_room(struct tty_port
*port
, size_t size
,
276 struct tty_bufhead
*buf
= &port
->buf
;
277 struct tty_buffer
*b
, *n
;
281 if (b
->flags
& TTYB_NORMAL
)
282 left
= 2 * b
->size
- b
->used
;
284 left
= b
->size
- b
->used
;
286 change
= (b
->flags
& TTYB_NORMAL
) && (~flags
& TTYB_NORMAL
);
287 if (change
|| left
< size
) {
288 /* This is the slow path - looking for new buffers to use */
289 n
= tty_buffer_alloc(port
, size
);
294 /* paired w/ barrier in flush_to_ldisc(); ensures the
295 * latest commit value can be read before the head is
296 * advanced to the next buffer
308 int tty_buffer_request_room(struct tty_port
*port
, size_t size
)
310 return __tty_buffer_request_room(port
, size
, 0);
312 EXPORT_SYMBOL_GPL(tty_buffer_request_room
);
315 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
318 * @flag: flag value for each character
321 * Queue a series of bytes to the tty buffering. All the characters
322 * passed are marked with the supplied flag. Returns the number added.
325 int tty_insert_flip_string_fixed_flag(struct tty_port
*port
,
326 const unsigned char *chars
, char flag
, size_t size
)
330 int goal
= min_t(size_t, size
- copied
, TTY_BUFFER_PAGE
);
331 int flags
= (flag
== TTY_NORMAL
) ? TTYB_NORMAL
: 0;
332 int space
= __tty_buffer_request_room(port
, goal
, flags
);
333 struct tty_buffer
*tb
= port
->buf
.tail
;
334 if (unlikely(space
== 0))
336 memcpy(char_buf_ptr(tb
, tb
->used
), chars
, space
);
337 if (~tb
->flags
& TTYB_NORMAL
)
338 memset(flag_buf_ptr(tb
, tb
->used
), flag
, space
);
342 /* There is a small chance that we need to split the data over
343 several buffers. If this is the case we must loop */
344 } while (unlikely(size
> copied
));
347 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag
);
350 * tty_insert_flip_string_flags - Add characters to the tty buffer
356 * Queue a series of bytes to the tty buffering. For each character
357 * the flags array indicates the status of the character. Returns the
361 int tty_insert_flip_string_flags(struct tty_port
*port
,
362 const unsigned char *chars
, const char *flags
, size_t size
)
366 int goal
= min_t(size_t, size
- copied
, TTY_BUFFER_PAGE
);
367 int space
= tty_buffer_request_room(port
, goal
);
368 struct tty_buffer
*tb
= port
->buf
.tail
;
369 if (unlikely(space
== 0))
371 memcpy(char_buf_ptr(tb
, tb
->used
), chars
, space
);
372 memcpy(flag_buf_ptr(tb
, tb
->used
), flags
, space
);
377 /* There is a small chance that we need to split the data over
378 several buffers. If this is the case we must loop */
379 } while (unlikely(size
> copied
));
382 EXPORT_SYMBOL(tty_insert_flip_string_flags
);
385 * tty_schedule_flip - push characters to ldisc
386 * @port: tty port to push from
388 * Takes any pending buffers and transfers their ownership to the
389 * ldisc side of the queue. It then schedules those characters for
390 * processing by the line discipline.
393 void tty_schedule_flip(struct tty_port
*port
)
395 struct tty_bufhead
*buf
= &port
->buf
;
397 buf
->tail
->commit
= buf
->tail
->used
;
398 schedule_work(&buf
->work
);
400 EXPORT_SYMBOL(tty_schedule_flip
);
403 * tty_prepare_flip_string - make room for characters
405 * @chars: return pointer for character write area
406 * @size: desired size
408 * Prepare a block of space in the buffer for data. Returns the length
409 * available and buffer pointer to the space which is now allocated and
410 * accounted for as ready for normal characters. This is used for drivers
411 * that need their own block copy routines into the buffer. There is no
412 * guarantee the buffer is a DMA target!
415 int tty_prepare_flip_string(struct tty_port
*port
, unsigned char **chars
,
418 int space
= __tty_buffer_request_room(port
, size
, TTYB_NORMAL
);
420 struct tty_buffer
*tb
= port
->buf
.tail
;
421 *chars
= char_buf_ptr(tb
, tb
->used
);
422 if (~tb
->flags
& TTYB_NORMAL
)
423 memset(flag_buf_ptr(tb
, tb
->used
), TTY_NORMAL
, space
);
428 EXPORT_SYMBOL_GPL(tty_prepare_flip_string
);
432 receive_buf(struct tty_struct
*tty
, struct tty_buffer
*head
, int count
)
434 struct tty_ldisc
*disc
= tty
->ldisc
;
435 unsigned char *p
= char_buf_ptr(head
, head
->read
);
438 if (~head
->flags
& TTYB_NORMAL
)
439 f
= flag_buf_ptr(head
, head
->read
);
441 if (disc
->ops
->receive_buf2
)
442 count
= disc
->ops
->receive_buf2(tty
, p
, f
, count
);
444 count
= min_t(int, count
, tty
->receive_room
);
446 disc
->ops
->receive_buf(tty
, p
, f
, count
);
454 * @work: tty structure passed from work queue.
456 * This routine is called out of the software interrupt to flush data
457 * from the buffer chain to the line discipline.
459 * The receive_buf method is single threaded for each tty instance.
461 * Locking: takes buffer lock to ensure single-threaded flip buffer
465 static void flush_to_ldisc(struct work_struct
*work
)
467 struct tty_port
*port
= container_of(work
, struct tty_port
, buf
.work
);
468 struct tty_bufhead
*buf
= &port
->buf
;
469 struct tty_struct
*tty
;
470 struct tty_ldisc
*disc
;
476 disc
= tty_ldisc_ref(tty
);
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
))
492 /* paired w/ barrier in __tty_buffer_request_room();
493 * ensures commit value read is not stale if the head
494 * is advancing to the next buffer
497 count
= head
->commit
- head
->read
;
500 check_other_closed(tty
);
504 tty_buffer_free(port
, head
);
508 count
= receive_buf(tty
, head
, count
);
513 mutex_unlock(&buf
->lock
);
515 tty_ldisc_deref(disc
);
519 * tty_flip_buffer_push - terminal
520 * @port: tty port to push
522 * Queue a push of the terminal flip buffers to the line discipline.
523 * Can be called from IRQ/atomic context.
525 * In the event of the queue being busy for flipping the work will be
526 * held off and retried later.
529 void tty_flip_buffer_push(struct tty_port
*port
)
531 tty_schedule_flip(port
);
533 EXPORT_SYMBOL(tty_flip_buffer_push
);
536 * tty_buffer_init - prepare a tty buffer structure
537 * @tty: tty to initialise
539 * Set up the initial state of the buffer management for a tty device.
540 * Must be called before the other tty buffer functions are used.
543 void tty_buffer_init(struct tty_port
*port
)
545 struct tty_bufhead
*buf
= &port
->buf
;
547 mutex_init(&buf
->lock
);
548 tty_buffer_reset(&buf
->sentinel
, 0);
549 buf
->head
= &buf
->sentinel
;
550 buf
->tail
= &buf
->sentinel
;
551 init_llist_head(&buf
->free
);
552 atomic_set(&buf
->mem_used
, 0);
553 atomic_set(&buf
->priority
, 0);
554 INIT_WORK(&buf
->work
, flush_to_ldisc
);
555 buf
->mem_limit
= TTYB_DEFAULT_MEM_LIMIT
;
559 * tty_buffer_set_limit - change the tty buffer memory limit
560 * @port: tty port to change
562 * Change the tty buffer memory limit.
563 * Must be called before the other tty buffer functions are used.
566 int tty_buffer_set_limit(struct tty_port
*port
, int limit
)
568 if (limit
< MIN_TTYB_SIZE
)
570 port
->buf
.mem_limit
= limit
;
573 EXPORT_SYMBOL_GPL(tty_buffer_set_limit
);
575 /* slave ptys can claim nested buffer lock when handling BRK and INTR */
576 void tty_buffer_set_lock_subclass(struct tty_port
*port
)
578 lockdep_set_subclass(&port
->buf
.lock
, TTY_LOCK_SLAVE
);