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/init.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 65536
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)
43 * tty_buffer_lock_exclusive - gain exclusive access to buffer
44 * tty_buffer_unlock_exclusive - release exclusive access
46 * @port - tty_port owning the flip buffer
48 * Guarantees safe use of the line discipline's receive_buf() method by
49 * excluding the buffer work and any pending flush from using the flip
50 * buffer. Data can continue to be added concurrently to the flip buffer
51 * from the driver side.
53 * On release, the buffer work is restarted if there is data in the
57 void tty_buffer_lock_exclusive(struct tty_port *port)
59 struct tty_bufhead *buf = &port->buf;
61 atomic_inc(&buf->priority);
62 mutex_lock(&buf->lock);
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);
79 * tty_buffer_space_avail - return unused buffer space
80 * @port - tty_port owning the flip buffer
82 * Returns the # of bytes which can be written by the driver without
83 * reaching the buffer limit.
85 * Note: this does not guarantee that memory is available to write
86 * the returned # of bytes (use tty_prepare_flip_string_xxx() to
87 * pre-allocate if memory guarantee is required).
90 int tty_buffer_space_avail(struct tty_port *port)
92 int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
95 EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
97 static void tty_buffer_reset(struct tty_buffer *p, size_t size)
108 * tty_buffer_free_all - free buffers used by a tty
109 * @tty: tty to free from
111 * Remove all the buffers pending on a tty whether queued with data
112 * or in the free ring. Must be called when the tty is no longer in use
115 void tty_buffer_free_all(struct tty_port *port)
117 struct tty_bufhead *buf = &port->buf;
118 struct tty_buffer *p, *next;
119 struct llist_node *llist;
121 while ((p = buf->head) != NULL) {
126 llist = llist_del_all(&buf->free);
127 llist_for_each_entry_safe(p, next, llist, free)
130 tty_buffer_reset(&buf->sentinel, 0);
131 buf->head = &buf->sentinel;
132 buf->tail = &buf->sentinel;
134 atomic_set(&buf->mem_used, 0);
138 * tty_buffer_alloc - allocate a tty buffer
140 * @size: desired size (characters)
142 * Allocate a new tty buffer to hold the desired number of characters.
143 * We round our buffers off in 256 character chunks to get better
144 * allocation behaviour.
145 * Return NULL if out of memory or the allocation would exceed the
149 static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
151 struct llist_node *free;
152 struct tty_buffer *p;
154 /* Round the buffer size out */
155 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
157 if (size <= MIN_TTYB_SIZE) {
158 free = llist_del_first(&port->buf.free);
160 p = llist_entry(free, struct tty_buffer, free);
165 /* Should possibly check if this fails for the largest buffer we
166 have queued and recycle that ? */
167 if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
169 p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
174 tty_buffer_reset(p, size);
175 atomic_add(size, &port->buf.mem_used);
180 * tty_buffer_free - free a tty buffer
181 * @tty: tty owning the buffer
182 * @b: the buffer to free
184 * Free a tty buffer, or add it to the free list according to our
188 static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
190 struct tty_bufhead *buf = &port->buf;
192 /* Dumb strategy for now - should keep some stats */
193 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
195 if (b->size > MIN_TTYB_SIZE)
197 else if (b->size > 0)
198 llist_add(&b->free, &buf->free);
202 * tty_buffer_flush - flush full tty buffers
205 * flush all the buffers containing receive data.
207 * Locking: takes buffer lock to ensure single-threaded flip buffer
211 void tty_buffer_flush(struct tty_struct *tty)
213 struct tty_port *port = tty->port;
214 struct tty_bufhead *buf = &port->buf;
215 struct tty_buffer *next;
217 atomic_inc(&buf->priority);
219 mutex_lock(&buf->lock);
220 while ((next = buf->head->next) != NULL) {
221 tty_buffer_free(port, buf->head);
224 buf->head->read = buf->head->commit;
225 atomic_dec(&buf->priority);
226 mutex_unlock(&buf->lock);
230 * tty_buffer_request_room - grow tty buffer if needed
231 * @tty: tty structure
232 * @size: size desired
233 * @flags: buffer flags if new buffer allocated (default = 0)
235 * Make at least size bytes of linear space available for the tty
236 * buffer. If we fail return the size we managed to find.
238 * Will change over to a new buffer if the current buffer is encoded as
239 * TTY_NORMAL (so has no flags buffer) and the new buffer requires
242 static int __tty_buffer_request_room(struct tty_port *port, size_t size,
245 struct tty_bufhead *buf = &port->buf;
246 struct tty_buffer *b, *n;
250 if (b->flags & TTYB_NORMAL)
251 left = 2 * b->size - b->used;
253 left = b->size - b->used;
255 change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
256 if (change || left < size) {
257 /* This is the slow path - looking for new buffers to use */
258 if ((n = tty_buffer_alloc(port, size)) != NULL) {
272 int tty_buffer_request_room(struct tty_port *port, size_t size)
274 return __tty_buffer_request_room(port, size, 0);
276 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
279 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
282 * @flag: flag value for each character
285 * Queue a series of bytes to the tty buffering. All the characters
286 * passed are marked with the supplied flag. Returns the number added.
289 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
290 const unsigned char *chars, char flag, size_t size)
294 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
295 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
296 int space = __tty_buffer_request_room(port, goal, flags);
297 struct tty_buffer *tb = port->buf.tail;
298 if (unlikely(space == 0))
300 memcpy(char_buf_ptr(tb, tb->used), chars, space);
301 if (~tb->flags & TTYB_NORMAL)
302 memset(flag_buf_ptr(tb, tb->used), flag, space);
306 /* There is a small chance that we need to split the data over
307 several buffers. If this is the case we must loop */
308 } while (unlikely(size > copied));
311 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
314 * tty_insert_flip_string_flags - Add characters to the tty buffer
320 * Queue a series of bytes to the tty buffering. For each character
321 * the flags array indicates the status of the character. Returns the
325 int tty_insert_flip_string_flags(struct tty_port *port,
326 const unsigned char *chars, const char *flags, size_t size)
330 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
331 int space = tty_buffer_request_room(port, goal);
332 struct tty_buffer *tb = port->buf.tail;
333 if (unlikely(space == 0))
335 memcpy(char_buf_ptr(tb, tb->used), chars, space);
336 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
341 /* There is a small chance that we need to split the data over
342 several buffers. If this is the case we must loop */
343 } while (unlikely(size > copied));
346 EXPORT_SYMBOL(tty_insert_flip_string_flags);
349 * tty_schedule_flip - push characters to ldisc
350 * @port: tty port to push from
352 * Takes any pending buffers and transfers their ownership to the
353 * ldisc side of the queue. It then schedules those characters for
354 * processing by the line discipline.
355 * Note that this function can only be used when the low_latency flag
356 * is unset. Otherwise the workqueue won't be flushed.
359 void tty_schedule_flip(struct tty_port *port)
361 struct tty_bufhead *buf = &port->buf;
362 WARN_ON(port->low_latency);
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;
453 /* Ldisc or user is trying to gain exclusive access */
454 if (atomic_read(&buf->priority))
457 count = head->commit - head->read;
459 if (head->next == NULL)
461 buf->head = head->next;
462 tty_buffer_free(port, head);
466 count = receive_buf(tty, head, count);
471 mutex_unlock(&buf->lock);
473 tty_ldisc_deref(disc);
480 * Push the terminal flip buffers to the line discipline.
482 * Must not be called from IRQ context.
484 void tty_flush_to_ldisc(struct tty_struct *tty)
486 if (!tty->port->low_latency)
487 flush_work(&tty->port->buf.work);
491 * tty_flip_buffer_push - terminal
492 * @port: tty port to push
494 * Queue a push of the terminal flip buffers to the line discipline. This
495 * function must not be called from IRQ context if port->low_latency is
498 * In the event of the queue being busy for flipping the work will be
499 * held off and retried later.
502 void tty_flip_buffer_push(struct tty_port *port)
504 struct tty_bufhead *buf = &port->buf;
506 buf->tail->commit = buf->tail->used;
508 if (port->low_latency)
509 flush_to_ldisc(&buf->work);
511 schedule_work(&buf->work);
513 EXPORT_SYMBOL(tty_flip_buffer_push);
516 * tty_buffer_init - prepare a tty buffer structure
517 * @tty: tty to initialise
519 * Set up the initial state of the buffer management for a tty device.
520 * Must be called before the other tty buffer functions are used.
523 void tty_buffer_init(struct tty_port *port)
525 struct tty_bufhead *buf = &port->buf;
527 mutex_init(&buf->lock);
528 tty_buffer_reset(&buf->sentinel, 0);
529 buf->head = &buf->sentinel;
530 buf->tail = &buf->sentinel;
531 init_llist_head(&buf->free);
532 atomic_set(&buf->mem_used, 0);
533 atomic_set(&buf->priority, 0);
534 INIT_WORK(&buf->work, flush_to_ldisc);
535 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
539 * tty_buffer_set_limit - change the tty buffer memory limit
540 * @port: tty port to change
542 * Change the tty buffer memory limit.
543 * Must be called before the other tty buffer functions are used.
546 int tty_buffer_set_limit(struct tty_port *port, int limit)
548 if (limit < MIN_TTYB_SIZE)
550 port->buf.mem_limit = limit;
553 EXPORT_SYMBOL_GPL(tty_buffer_set_limit);