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)
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
);
64 void tty_buffer_unlock_exclusive(struct tty_port
*port
)
66 struct tty_bufhead
*buf
= &port
->buf
;
69 restart
= buf
->head
->commit
!= buf
->head
->read
;
71 atomic_dec(&buf
->priority
);
72 mutex_unlock(&buf
->lock
);
74 queue_work(system_unbound_wq
, &buf
->work
);
78 * tty_buffer_space_avail - return unused buffer space
79 * @port - tty_port owning the flip buffer
81 * Returns the # of bytes which can be written by the driver without
82 * reaching the buffer limit.
84 * Note: this does not guarantee that memory is available to write
85 * the returned # of bytes (use tty_prepare_flip_string_xxx() to
86 * pre-allocate if memory guarantee is required).
89 int tty_buffer_space_avail(struct tty_port
*port
)
91 int space
= port
->buf
.mem_limit
- atomic_read(&port
->buf
.mem_used
);
94 EXPORT_SYMBOL_GPL(tty_buffer_space_avail
);
96 static void tty_buffer_reset(struct tty_buffer
*p
, size_t size
)
107 * tty_buffer_free_all - free buffers used by a tty
108 * @tty: tty to free from
110 * Remove all the buffers pending on a tty whether queued with data
111 * or in the free ring. Must be called when the tty is no longer in use
114 void tty_buffer_free_all(struct tty_port
*port
)
116 struct tty_bufhead
*buf
= &port
->buf
;
117 struct tty_buffer
*p
, *next
;
118 struct llist_node
*llist
;
120 while ((p
= buf
->head
) != NULL
) {
125 llist
= llist_del_all(&buf
->free
);
126 llist_for_each_entry_safe(p
, next
, llist
, free
)
129 tty_buffer_reset(&buf
->sentinel
, 0);
130 buf
->head
= &buf
->sentinel
;
131 buf
->tail
= &buf
->sentinel
;
133 atomic_set(&buf
->mem_used
, 0);
137 * tty_buffer_alloc - allocate a tty buffer
139 * @size: desired size (characters)
141 * Allocate a new tty buffer to hold the desired number of characters.
142 * We round our buffers off in 256 character chunks to get better
143 * allocation behaviour.
144 * Return NULL if out of memory or the allocation would exceed the
148 static struct tty_buffer
*tty_buffer_alloc(struct tty_port
*port
, size_t size
)
150 struct llist_node
*free
;
151 struct tty_buffer
*p
;
153 /* Round the buffer size out */
154 size
= __ALIGN_MASK(size
, TTYB_ALIGN_MASK
);
156 if (size
<= MIN_TTYB_SIZE
) {
157 free
= llist_del_first(&port
->buf
.free
);
159 p
= llist_entry(free
, struct tty_buffer
, free
);
164 /* Should possibly check if this fails for the largest buffer we
165 have queued and recycle that ? */
166 if (atomic_read(&port
->buf
.mem_used
) > port
->buf
.mem_limit
)
168 p
= kmalloc(sizeof(struct tty_buffer
) + 2 * size
, GFP_ATOMIC
);
173 tty_buffer_reset(p
, size
);
174 atomic_add(size
, &port
->buf
.mem_used
);
179 * tty_buffer_free - free a tty buffer
180 * @tty: tty owning the buffer
181 * @b: the buffer to free
183 * Free a tty buffer, or add it to the free list according to our
187 static void tty_buffer_free(struct tty_port
*port
, struct tty_buffer
*b
)
189 struct tty_bufhead
*buf
= &port
->buf
;
191 /* Dumb strategy for now - should keep some stats */
192 WARN_ON(atomic_sub_return(b
->size
, &buf
->mem_used
) < 0);
194 if (b
->size
> MIN_TTYB_SIZE
)
196 else if (b
->size
> 0)
197 llist_add(&b
->free
, &buf
->free
);
201 * tty_buffer_flush - flush full tty buffers
204 * flush all the buffers containing receive data.
206 * Locking: takes buffer lock to ensure single-threaded flip buffer
210 void tty_buffer_flush(struct tty_struct
*tty
)
212 struct tty_port
*port
= tty
->port
;
213 struct tty_bufhead
*buf
= &port
->buf
;
214 struct tty_buffer
*next
;
216 atomic_inc(&buf
->priority
);
218 mutex_lock(&buf
->lock
);
219 while ((next
= buf
->head
->next
) != NULL
) {
220 tty_buffer_free(port
, buf
->head
);
223 buf
->head
->read
= buf
->head
->commit
;
224 atomic_dec(&buf
->priority
);
225 mutex_unlock(&buf
->lock
);
229 * tty_buffer_request_room - grow tty buffer if needed
230 * @tty: tty structure
231 * @size: size desired
232 * @flags: buffer flags if new buffer allocated (default = 0)
234 * Make at least size bytes of linear space available for the tty
235 * buffer. If we fail return the size we managed to find.
237 * Will change over to a new buffer if the current buffer is encoded as
238 * TTY_NORMAL (so has no flags buffer) and the new buffer requires
241 static int __tty_buffer_request_room(struct tty_port
*port
, size_t size
,
244 struct tty_bufhead
*buf
= &port
->buf
;
245 struct tty_buffer
*b
, *n
;
249 if (b
->flags
& TTYB_NORMAL
)
250 left
= 2 * b
->size
- b
->used
;
252 left
= b
->size
- b
->used
;
254 change
= (b
->flags
& TTYB_NORMAL
) && (~flags
& TTYB_NORMAL
);
255 if (change
|| left
< size
) {
256 /* This is the slow path - looking for new buffers to use */
257 if ((n
= tty_buffer_alloc(port
, size
)) != NULL
) {
258 unsigned long iflags
;
263 spin_lock_irqsave(&buf
->flush_lock
, iflags
);
266 spin_unlock_irqrestore(&buf
->flush_lock
, iflags
);
276 int tty_buffer_request_room(struct tty_port
*port
, size_t size
)
278 return __tty_buffer_request_room(port
, size
, 0);
280 EXPORT_SYMBOL_GPL(tty_buffer_request_room
);
283 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
286 * @flag: flag value for each character
289 * Queue a series of bytes to the tty buffering. All the characters
290 * passed are marked with the supplied flag. Returns the number added.
293 int tty_insert_flip_string_fixed_flag(struct tty_port
*port
,
294 const unsigned char *chars
, char flag
, size_t size
)
298 int goal
= min_t(size_t, size
- copied
, TTY_BUFFER_PAGE
);
299 int flags
= (flag
== TTY_NORMAL
) ? TTYB_NORMAL
: 0;
300 int space
= __tty_buffer_request_room(port
, goal
, flags
);
301 struct tty_buffer
*tb
= port
->buf
.tail
;
302 if (unlikely(space
== 0))
304 memcpy(char_buf_ptr(tb
, tb
->used
), chars
, space
);
305 if (~tb
->flags
& TTYB_NORMAL
)
306 memset(flag_buf_ptr(tb
, tb
->used
), flag
, space
);
310 /* There is a small chance that we need to split the data over
311 several buffers. If this is the case we must loop */
312 } while (unlikely(size
> copied
));
315 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag
);
318 * tty_insert_flip_string_flags - Add characters to the tty buffer
324 * Queue a series of bytes to the tty buffering. For each character
325 * the flags array indicates the status of the character. Returns the
329 int tty_insert_flip_string_flags(struct tty_port
*port
,
330 const unsigned char *chars
, const char *flags
, size_t size
)
334 int goal
= min_t(size_t, size
- copied
, TTY_BUFFER_PAGE
);
335 int space
= tty_buffer_request_room(port
, goal
);
336 struct tty_buffer
*tb
= port
->buf
.tail
;
337 if (unlikely(space
== 0))
339 memcpy(char_buf_ptr(tb
, tb
->used
), chars
, space
);
340 memcpy(flag_buf_ptr(tb
, tb
->used
), flags
, space
);
345 /* There is a small chance that we need to split the data over
346 several buffers. If this is the case we must loop */
347 } while (unlikely(size
> copied
));
350 EXPORT_SYMBOL(tty_insert_flip_string_flags
);
353 * tty_schedule_flip - push characters to ldisc
354 * @port: tty port to push from
356 * Takes any pending buffers and transfers their ownership to the
357 * ldisc side of the queue. It then schedules those characters for
358 * processing by the line discipline.
361 void tty_schedule_flip(struct tty_port
*port
)
363 struct tty_bufhead
*buf
= &port
->buf
;
365 buf
->tail
->commit
= buf
->tail
->used
;
366 schedule_work(&buf
->work
);
368 EXPORT_SYMBOL(tty_schedule_flip
);
371 * tty_prepare_flip_string - make room for characters
373 * @chars: return pointer for character write area
374 * @size: desired size
376 * Prepare a block of space in the buffer for data. Returns the length
377 * available and buffer pointer to the space which is now allocated and
378 * accounted for as ready for normal characters. This is used for drivers
379 * that need their own block copy routines into the buffer. There is no
380 * guarantee the buffer is a DMA target!
383 int tty_prepare_flip_string(struct tty_port
*port
, unsigned char **chars
,
386 int space
= __tty_buffer_request_room(port
, size
, TTYB_NORMAL
);
388 struct tty_buffer
*tb
= port
->buf
.tail
;
389 *chars
= char_buf_ptr(tb
, tb
->used
);
390 if (~tb
->flags
& TTYB_NORMAL
)
391 memset(flag_buf_ptr(tb
, tb
->used
), TTY_NORMAL
, space
);
396 EXPORT_SYMBOL_GPL(tty_prepare_flip_string
);
400 receive_buf(struct tty_struct
*tty
, struct tty_buffer
*head
, int count
)
402 struct tty_ldisc
*disc
= tty
->ldisc
;
403 unsigned char *p
= char_buf_ptr(head
, head
->read
);
406 if (~head
->flags
& TTYB_NORMAL
)
407 f
= flag_buf_ptr(head
, head
->read
);
409 if (disc
->ops
->receive_buf2
)
410 count
= disc
->ops
->receive_buf2(tty
, p
, f
, count
);
412 count
= min_t(int, count
, tty
->receive_room
);
414 disc
->ops
->receive_buf(tty
, p
, f
, count
);
422 * @work: tty structure passed from work queue.
424 * This routine is called out of the software interrupt to flush data
425 * from the buffer chain to the line discipline.
427 * The receive_buf method is single threaded for each tty instance.
429 * Locking: takes buffer lock to ensure single-threaded flip buffer
433 static void flush_to_ldisc(struct work_struct
*work
)
435 struct tty_port
*port
= container_of(work
, struct tty_port
, buf
.work
);
436 struct tty_bufhead
*buf
= &port
->buf
;
437 struct tty_struct
*tty
;
438 struct tty_ldisc
*disc
;
444 disc
= tty_ldisc_ref(tty
);
448 mutex_lock(&buf
->lock
);
452 struct tty_buffer
*head
= buf
->head
;
455 /* Ldisc or user is trying to gain exclusive access */
456 if (atomic_read(&buf
->priority
))
459 spin_lock_irqsave(&buf
->flush_lock
, flags
);
460 count
= head
->commit
- head
->read
;
462 if (head
->next
== NULL
) {
463 spin_unlock_irqrestore(&buf
->flush_lock
, flags
);
466 buf
->head
= head
->next
;
467 spin_unlock_irqrestore(&buf
->flush_lock
, flags
);
468 tty_buffer_free(port
, head
);
471 spin_unlock_irqrestore(&buf
->flush_lock
, flags
);
473 count
= receive_buf(tty
, head
, count
);
478 mutex_unlock(&buf
->lock
);
480 tty_ldisc_deref(disc
);
487 * Push the terminal flip buffers to the line discipline.
489 * Must not be called from IRQ context.
491 void tty_flush_to_ldisc(struct tty_struct
*tty
)
493 flush_work(&tty
->port
->buf
.work
);
497 * tty_flip_buffer_push - terminal
498 * @port: tty port to push
500 * Queue a push of the terminal flip buffers to the line discipline.
501 * Can be called from IRQ/atomic context.
503 * In the event of the queue being busy for flipping the work will be
504 * held off and retried later.
507 void tty_flip_buffer_push(struct tty_port
*port
)
509 tty_schedule_flip(port
);
511 EXPORT_SYMBOL(tty_flip_buffer_push
);
514 * tty_buffer_init - prepare a tty buffer structure
515 * @tty: tty to initialise
517 * Set up the initial state of the buffer management for a tty device.
518 * Must be called before the other tty buffer functions are used.
521 void tty_buffer_init(struct tty_port
*port
)
523 struct tty_bufhead
*buf
= &port
->buf
;
525 mutex_init(&buf
->lock
);
526 spin_lock_init(&buf
->flush_lock
);
527 tty_buffer_reset(&buf
->sentinel
, 0);
528 buf
->head
= &buf
->sentinel
;
529 buf
->tail
= &buf
->sentinel
;
530 init_llist_head(&buf
->free
);
531 atomic_set(&buf
->mem_used
, 0);
532 atomic_set(&buf
->priority
, 0);
533 INIT_WORK(&buf
->work
, flush_to_ldisc
);
534 buf
->mem_limit
= TTYB_DEFAULT_MEM_LIMIT
;
538 * tty_buffer_set_limit - change the tty buffer memory limit
539 * @port: tty port to change
541 * Change the tty buffer memory limit.
542 * Must be called before the other tty buffer functions are used.
545 int tty_buffer_set_limit(struct tty_port
*port
, int limit
)
547 if (limit
< MIN_TTYB_SIZE
)
549 port
->buf
.mem_limit
= limit
;
552 EXPORT_SYMBOL_GPL(tty_buffer_set_limit
);