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) {
261 /* paired w/ barrier in flush_to_ldisc(); ensures the
262 * latest commit value can be read before the head is
263 * advanced to the next buffer
275 int tty_buffer_request_room(struct tty_port *port, size_t size)
277 return __tty_buffer_request_room(port, size, 0);
279 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
282 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
285 * @flag: flag value for each character
288 * Queue a series of bytes to the tty buffering. All the characters
289 * passed are marked with the supplied flag. Returns the number added.
292 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
293 const unsigned char *chars, char flag, size_t size)
297 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
298 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
299 int space = __tty_buffer_request_room(port, goal, flags);
300 struct tty_buffer *tb = port->buf.tail;
301 if (unlikely(space == 0))
303 memcpy(char_buf_ptr(tb, tb->used), chars, space);
304 if (~tb->flags & TTYB_NORMAL)
305 memset(flag_buf_ptr(tb, tb->used), flag, space);
309 /* There is a small chance that we need to split the data over
310 several buffers. If this is the case we must loop */
311 } while (unlikely(size > copied));
314 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
317 * tty_insert_flip_string_flags - Add characters to the tty buffer
323 * Queue a series of bytes to the tty buffering. For each character
324 * the flags array indicates the status of the character. Returns the
328 int tty_insert_flip_string_flags(struct tty_port *port,
329 const unsigned char *chars, const char *flags, size_t size)
333 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
334 int space = tty_buffer_request_room(port, goal);
335 struct tty_buffer *tb = port->buf.tail;
336 if (unlikely(space == 0))
338 memcpy(char_buf_ptr(tb, tb->used), chars, space);
339 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
344 /* There is a small chance that we need to split the data over
345 several buffers. If this is the case we must loop */
346 } while (unlikely(size > copied));
349 EXPORT_SYMBOL(tty_insert_flip_string_flags);
352 * tty_schedule_flip - push characters to ldisc
353 * @port: tty port to push from
355 * Takes any pending buffers and transfers their ownership to the
356 * ldisc side of the queue. It then schedules those characters for
357 * processing by the line discipline.
360 void tty_schedule_flip(struct tty_port *port)
362 struct tty_bufhead *buf = &port->buf;
364 buf->tail->commit = buf->tail->used;
365 schedule_work(&buf->work);
367 EXPORT_SYMBOL(tty_schedule_flip);
370 * tty_prepare_flip_string - make room for characters
372 * @chars: return pointer for character write area
373 * @size: desired size
375 * Prepare a block of space in the buffer for data. Returns the length
376 * available and buffer pointer to the space which is now allocated and
377 * accounted for as ready for normal characters. This is used for drivers
378 * that need their own block copy routines into the buffer. There is no
379 * guarantee the buffer is a DMA target!
382 int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
385 int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
387 struct tty_buffer *tb = port->buf.tail;
388 *chars = char_buf_ptr(tb, tb->used);
389 if (~tb->flags & TTYB_NORMAL)
390 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
395 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
399 receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
401 struct tty_ldisc *disc = tty->ldisc;
402 unsigned char *p = char_buf_ptr(head, head->read);
405 if (~head->flags & TTYB_NORMAL)
406 f = flag_buf_ptr(head, head->read);
408 if (disc->ops->receive_buf2)
409 count = disc->ops->receive_buf2(tty, p, f, count);
411 count = min_t(int, count, tty->receive_room);
413 disc->ops->receive_buf(tty, p, f, count);
421 * @work: tty structure passed from work queue.
423 * This routine is called out of the software interrupt to flush data
424 * from the buffer chain to the line discipline.
426 * The receive_buf method is single threaded for each tty instance.
428 * Locking: takes buffer lock to ensure single-threaded flip buffer
432 static void flush_to_ldisc(struct work_struct *work)
434 struct tty_port *port = container_of(work, struct tty_port, buf.work);
435 struct tty_bufhead *buf = &port->buf;
436 struct tty_struct *tty;
437 struct tty_ldisc *disc;
443 disc = tty_ldisc_ref(tty);
447 mutex_lock(&buf->lock);
450 struct tty_buffer *head = buf->head;
451 struct tty_buffer *next;
454 /* Ldisc or user is trying to gain exclusive access */
455 if (atomic_read(&buf->priority))
459 /* paired w/ barrier in __tty_buffer_request_room();
460 * ensures commit value read is not stale if the head
461 * is advancing to the next buffer
464 count = head->commit - head->read;
469 tty_buffer_free(port, head);
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 tty_buffer_reset(&buf->sentinel, 0);
527 buf->head = &buf->sentinel;
528 buf->tail = &buf->sentinel;
529 init_llist_head(&buf->free);
530 atomic_set(&buf->mem_used, 0);
531 atomic_set(&buf->priority, 0);
532 INIT_WORK(&buf->work, flush_to_ldisc);
533 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
537 * tty_buffer_set_limit - change the tty buffer memory limit
538 * @port: tty port to change
540 * Change the tty buffer memory limit.
541 * Must be called before the other tty buffer functions are used.
544 int tty_buffer_set_limit(struct tty_port *port, int limit)
546 if (limit < MIN_TTYB_SIZE)
548 port->buf.mem_limit = limit;
551 EXPORT_SYMBOL_GPL(tty_buffer_set_limit);