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_MEM_LIMIT 65536
33 * tty_buffer_space_avail - return unused buffer space
34 * @port - tty_port owning the flip buffer
36 * Returns the # of bytes which can be written by the driver without
37 * reaching the buffer limit.
39 * Note: this does not guarantee that memory is available to write
40 * the returned # of bytes (use tty_prepare_flip_string_xxx() to
41 * pre-allocate if memory guarantee is required).
44 int tty_buffer_space_avail(struct tty_port *port)
46 int space = TTYB_MEM_LIMIT - atomic_read(&port->buf.memory_used);
50 static void tty_buffer_reset(struct tty_buffer *p, size_t size)
60 * tty_buffer_free_all - free buffers used by a tty
61 * @tty: tty to free from
63 * Remove all the buffers pending on a tty whether queued with data
64 * or in the free ring. Must be called when the tty is no longer in use
67 void tty_buffer_free_all(struct tty_port *port)
69 struct tty_bufhead *buf = &port->buf;
70 struct tty_buffer *p, *next;
71 struct llist_node *llist;
73 while ((p = buf->head) != NULL) {
78 llist = llist_del_all(&buf->free);
79 llist_for_each_entry_safe(p, next, llist, free)
82 tty_buffer_reset(&buf->sentinel, 0);
83 buf->head = &buf->sentinel;
84 buf->tail = &buf->sentinel;
86 atomic_set(&buf->memory_used, 0);
90 * tty_buffer_alloc - allocate a tty buffer
92 * @size: desired size (characters)
94 * Allocate a new tty buffer to hold the desired number of characters.
95 * We round our buffers off in 256 character chunks to get better
96 * allocation behaviour.
97 * Return NULL if out of memory or the allocation would exceed the
101 static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
103 struct llist_node *free;
104 struct tty_buffer *p;
106 /* Round the buffer size out */
107 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
109 if (size <= MIN_TTYB_SIZE) {
110 free = llist_del_first(&port->buf.free);
112 p = llist_entry(free, struct tty_buffer, free);
117 /* Should possibly check if this fails for the largest buffer we
118 have queued and recycle that ? */
119 if (atomic_read(&port->buf.memory_used) > TTYB_MEM_LIMIT)
121 p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
126 tty_buffer_reset(p, size);
127 atomic_add(size, &port->buf.memory_used);
132 * tty_buffer_free - free a tty buffer
133 * @tty: tty owning the buffer
134 * @b: the buffer to free
136 * Free a tty buffer, or add it to the free list according to our
140 static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
142 struct tty_bufhead *buf = &port->buf;
144 /* Dumb strategy for now - should keep some stats */
145 WARN_ON(atomic_sub_return(b->size, &buf->memory_used) < 0);
147 if (b->size > MIN_TTYB_SIZE)
149 else if (b->size > 0)
150 llist_add(&b->free, &buf->free);
154 * __tty_buffer_flush - flush full tty buffers
157 * flush all the buffers containing receive data. Caller must
158 * hold the buffer lock and must have ensured no parallel flush to
162 static void __tty_buffer_flush(struct tty_port *port)
164 struct tty_bufhead *buf = &port->buf;
165 struct tty_buffer *next;
167 while ((next = buf->head->next) != NULL) {
168 tty_buffer_free(port, buf->head);
171 WARN_ON(buf->head != buf->tail);
172 buf->head->read = buf->head->commit;
176 * tty_buffer_flush - flush full tty buffers
179 * flush all the buffers containing receive data. If the buffer is
180 * being processed by flush_to_ldisc then we defer the processing
183 * Locking: takes flush_mutex to ensure single-threaded flip buffer
187 void tty_buffer_flush(struct tty_struct *tty)
189 struct tty_port *port = tty->port;
190 struct tty_bufhead *buf = &port->buf;
192 set_bit(TTYP_FLUSHPENDING, &port->iflags);
194 mutex_lock(&buf->flush_mutex);
195 __tty_buffer_flush(port);
196 clear_bit(TTYP_FLUSHPENDING, &port->iflags);
197 mutex_unlock(&buf->flush_mutex);
201 * tty_buffer_request_room - grow tty buffer if needed
202 * @tty: tty structure
203 * @size: size desired
205 * Make at least size bytes of linear space available for the tty
206 * buffer. If we fail return the size we managed to find.
208 int tty_buffer_request_room(struct tty_port *port, size_t size)
210 struct tty_bufhead *buf = &port->buf;
211 struct tty_buffer *b, *n;
215 left = b->size - b->used;
218 /* This is the slow path - looking for new buffers to use */
219 if ((n = tty_buffer_alloc(port, size)) != NULL) {
229 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
232 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
235 * @flag: flag value for each character
238 * Queue a series of bytes to the tty buffering. All the characters
239 * passed are marked with the supplied flag. Returns the number added.
242 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
243 const unsigned char *chars, char flag, size_t size)
247 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
248 int space = tty_buffer_request_room(port, goal);
249 struct tty_buffer *tb = port->buf.tail;
250 if (unlikely(space == 0))
252 memcpy(char_buf_ptr(tb, tb->used), chars, space);
253 memset(flag_buf_ptr(tb, tb->used), flag, space);
257 /* There is a small chance that we need to split the data over
258 several buffers. If this is the case we must loop */
259 } while (unlikely(size > copied));
262 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
265 * tty_insert_flip_string_flags - Add characters to the tty buffer
271 * Queue a series of bytes to the tty buffering. For each character
272 * the flags array indicates the status of the character. Returns the
276 int tty_insert_flip_string_flags(struct tty_port *port,
277 const unsigned char *chars, const char *flags, size_t size)
281 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
282 int space = tty_buffer_request_room(port, goal);
283 struct tty_buffer *tb = port->buf.tail;
284 if (unlikely(space == 0))
286 memcpy(char_buf_ptr(tb, tb->used), chars, space);
287 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
292 /* There is a small chance that we need to split the data over
293 several buffers. If this is the case we must loop */
294 } while (unlikely(size > copied));
297 EXPORT_SYMBOL(tty_insert_flip_string_flags);
300 * tty_schedule_flip - push characters to ldisc
301 * @port: tty port to push from
303 * Takes any pending buffers and transfers their ownership to the
304 * ldisc side of the queue. It then schedules those characters for
305 * processing by the line discipline.
306 * Note that this function can only be used when the low_latency flag
307 * is unset. Otherwise the workqueue won't be flushed.
310 void tty_schedule_flip(struct tty_port *port)
312 struct tty_bufhead *buf = &port->buf;
313 WARN_ON(port->low_latency);
315 buf->tail->commit = buf->tail->used;
316 schedule_work(&buf->work);
318 EXPORT_SYMBOL(tty_schedule_flip);
321 * tty_prepare_flip_string - make room for characters
323 * @chars: return pointer for character write area
324 * @size: desired size
326 * Prepare a block of space in the buffer for data. Returns the length
327 * available and buffer pointer to the space which is now allocated and
328 * accounted for as ready for normal characters. This is used for drivers
329 * that need their own block copy routines into the buffer. There is no
330 * guarantee the buffer is a DMA target!
333 int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
336 int space = tty_buffer_request_room(port, size);
338 struct tty_buffer *tb = port->buf.tail;
339 *chars = char_buf_ptr(tb, tb->used);
340 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
345 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
348 * tty_prepare_flip_string_flags - make room for characters
350 * @chars: return pointer for character write area
351 * @flags: return pointer for status flag write area
352 * @size: desired size
354 * Prepare a block of space in the buffer for data. Returns the length
355 * available and buffer pointer to the space which is now allocated and
356 * accounted for as ready for characters. This is used for drivers
357 * that need their own block copy routines into the buffer. There is no
358 * guarantee the buffer is a DMA target!
361 int tty_prepare_flip_string_flags(struct tty_port *port,
362 unsigned char **chars, char **flags, size_t size)
364 int space = tty_buffer_request_room(port, size);
366 struct tty_buffer *tb = port->buf.tail;
367 *chars = char_buf_ptr(tb, tb->used);
368 *flags = flag_buf_ptr(tb, tb->used);
373 EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
377 receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
379 struct tty_ldisc *disc = tty->ldisc;
380 unsigned char *p = char_buf_ptr(head, head->read);
381 char *f = flag_buf_ptr(head, head->read);
383 if (disc->ops->receive_buf2)
384 count = disc->ops->receive_buf2(tty, p, f, count);
386 count = min_t(int, count, tty->receive_room);
388 disc->ops->receive_buf(tty, p, f, count);
396 * @work: tty structure passed from work queue.
398 * This routine is called out of the software interrupt to flush data
399 * from the buffer chain to the line discipline.
401 * The receive_buf method is single threaded for each tty instance.
403 * Locking: takes flush_mutex to ensure single-threaded flip buffer
407 static void flush_to_ldisc(struct work_struct *work)
409 struct tty_port *port = container_of(work, struct tty_port, buf.work);
410 struct tty_bufhead *buf = &port->buf;
411 struct tty_struct *tty;
412 struct tty_ldisc *disc;
418 disc = tty_ldisc_ref(tty);
422 mutex_lock(&buf->flush_mutex);
425 struct tty_buffer *head = buf->head;
428 /* Ldisc or user is trying to flush the buffers. */
429 if (test_bit(TTYP_FLUSHPENDING, &port->iflags))
432 count = head->commit - head->read;
434 if (head->next == NULL)
436 buf->head = head->next;
437 tty_buffer_free(port, head);
441 count = receive_buf(tty, head, count);
446 mutex_unlock(&buf->flush_mutex);
448 tty_ldisc_deref(disc);
455 * Push the terminal flip buffers to the line discipline.
457 * Must not be called from IRQ context.
459 void tty_flush_to_ldisc(struct tty_struct *tty)
461 if (!tty->port->low_latency)
462 flush_work(&tty->port->buf.work);
466 * tty_flip_buffer_push - terminal
467 * @port: tty port to push
469 * Queue a push of the terminal flip buffers to the line discipline. This
470 * function must not be called from IRQ context if port->low_latency is
473 * In the event of the queue being busy for flipping the work will be
474 * held off and retried later.
477 void tty_flip_buffer_push(struct tty_port *port)
479 struct tty_bufhead *buf = &port->buf;
481 buf->tail->commit = buf->tail->used;
483 if (port->low_latency)
484 flush_to_ldisc(&buf->work);
486 schedule_work(&buf->work);
488 EXPORT_SYMBOL(tty_flip_buffer_push);
491 * tty_buffer_init - prepare a tty buffer structure
492 * @tty: tty to initialise
494 * Set up the initial state of the buffer management for a tty device.
495 * Must be called before the other tty buffer functions are used.
498 void tty_buffer_init(struct tty_port *port)
500 struct tty_bufhead *buf = &port->buf;
502 mutex_init(&buf->flush_mutex);
503 tty_buffer_reset(&buf->sentinel, 0);
504 buf->head = &buf->sentinel;
505 buf->tail = &buf->sentinel;
506 init_llist_head(&buf->free);
507 atomic_set(&buf->memory_used, 0);
508 INIT_WORK(&buf->work, flush_to_ldisc);