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. If the buffer is
158 * being processed by flush_to_ldisc then we defer the processing
161 * Locking: takes flush_mutex to ensure single-threaded flip buffer
165 void tty_buffer_flush(struct tty_struct *tty)
167 struct tty_port *port = tty->port;
168 struct tty_bufhead *buf = &port->buf;
169 struct tty_buffer *next;
171 buf->flushpending = 1;
173 mutex_lock(&buf->flush_mutex);
174 while ((next = buf->head->next) != NULL) {
175 tty_buffer_free(port, buf->head);
178 buf->head->read = buf->head->commit;
179 buf->flushpending = 0;
180 mutex_unlock(&buf->flush_mutex);
184 * tty_buffer_request_room - grow tty buffer if needed
185 * @tty: tty structure
186 * @size: size desired
188 * Make at least size bytes of linear space available for the tty
189 * buffer. If we fail return the size we managed to find.
191 int tty_buffer_request_room(struct tty_port *port, size_t size)
193 struct tty_bufhead *buf = &port->buf;
194 struct tty_buffer *b, *n;
198 left = b->size - b->used;
201 /* This is the slow path - looking for new buffers to use */
202 if ((n = tty_buffer_alloc(port, size)) != NULL) {
212 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
215 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
218 * @flag: flag value for each character
221 * Queue a series of bytes to the tty buffering. All the characters
222 * passed are marked with the supplied flag. Returns the number added.
225 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
226 const unsigned char *chars, char flag, size_t size)
230 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
231 int space = tty_buffer_request_room(port, goal);
232 struct tty_buffer *tb = port->buf.tail;
233 if (unlikely(space == 0))
235 memcpy(char_buf_ptr(tb, tb->used), chars, space);
236 memset(flag_buf_ptr(tb, tb->used), flag, space);
240 /* There is a small chance that we need to split the data over
241 several buffers. If this is the case we must loop */
242 } while (unlikely(size > copied));
245 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
248 * tty_insert_flip_string_flags - Add characters to the tty buffer
254 * Queue a series of bytes to the tty buffering. For each character
255 * the flags array indicates the status of the character. Returns the
259 int tty_insert_flip_string_flags(struct tty_port *port,
260 const unsigned char *chars, const char *flags, size_t size)
264 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
265 int space = tty_buffer_request_room(port, goal);
266 struct tty_buffer *tb = port->buf.tail;
267 if (unlikely(space == 0))
269 memcpy(char_buf_ptr(tb, tb->used), chars, space);
270 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
275 /* There is a small chance that we need to split the data over
276 several buffers. If this is the case we must loop */
277 } while (unlikely(size > copied));
280 EXPORT_SYMBOL(tty_insert_flip_string_flags);
283 * tty_schedule_flip - push characters to ldisc
284 * @port: tty port to push from
286 * Takes any pending buffers and transfers their ownership to the
287 * ldisc side of the queue. It then schedules those characters for
288 * processing by the line discipline.
289 * Note that this function can only be used when the low_latency flag
290 * is unset. Otherwise the workqueue won't be flushed.
293 void tty_schedule_flip(struct tty_port *port)
295 struct tty_bufhead *buf = &port->buf;
296 WARN_ON(port->low_latency);
298 buf->tail->commit = buf->tail->used;
299 schedule_work(&buf->work);
301 EXPORT_SYMBOL(tty_schedule_flip);
304 * tty_prepare_flip_string - make room for characters
306 * @chars: return pointer for character write area
307 * @size: desired size
309 * Prepare a block of space in the buffer for data. Returns the length
310 * available and buffer pointer to the space which is now allocated and
311 * accounted for as ready for normal characters. This is used for drivers
312 * that need their own block copy routines into the buffer. There is no
313 * guarantee the buffer is a DMA target!
316 int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
319 int space = tty_buffer_request_room(port, size);
321 struct tty_buffer *tb = port->buf.tail;
322 *chars = char_buf_ptr(tb, tb->used);
323 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
328 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
331 * tty_prepare_flip_string_flags - make room for characters
333 * @chars: return pointer for character write area
334 * @flags: return pointer for status flag write area
335 * @size: desired size
337 * Prepare a block of space in the buffer for data. Returns the length
338 * available and buffer pointer to the space which is now allocated and
339 * accounted for as ready for characters. This is used for drivers
340 * that need their own block copy routines into the buffer. There is no
341 * guarantee the buffer is a DMA target!
344 int tty_prepare_flip_string_flags(struct tty_port *port,
345 unsigned char **chars, char **flags, size_t size)
347 int space = tty_buffer_request_room(port, size);
349 struct tty_buffer *tb = port->buf.tail;
350 *chars = char_buf_ptr(tb, tb->used);
351 *flags = flag_buf_ptr(tb, tb->used);
356 EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
360 receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
362 struct tty_ldisc *disc = tty->ldisc;
363 unsigned char *p = char_buf_ptr(head, head->read);
364 char *f = flag_buf_ptr(head, head->read);
366 if (disc->ops->receive_buf2)
367 count = disc->ops->receive_buf2(tty, p, f, count);
369 count = min_t(int, count, tty->receive_room);
371 disc->ops->receive_buf(tty, p, f, count);
379 * @work: tty structure passed from work queue.
381 * This routine is called out of the software interrupt to flush data
382 * from the buffer chain to the line discipline.
384 * The receive_buf method is single threaded for each tty instance.
386 * Locking: takes flush_mutex to ensure single-threaded flip buffer
390 static void flush_to_ldisc(struct work_struct *work)
392 struct tty_port *port = container_of(work, struct tty_port, buf.work);
393 struct tty_bufhead *buf = &port->buf;
394 struct tty_struct *tty;
395 struct tty_ldisc *disc;
401 disc = tty_ldisc_ref(tty);
405 mutex_lock(&buf->flush_mutex);
408 struct tty_buffer *head = buf->head;
411 /* Ldisc or user is trying to flush the buffers. */
412 if (buf->flushpending)
415 count = head->commit - head->read;
417 if (head->next == NULL)
419 buf->head = head->next;
420 tty_buffer_free(port, head);
424 count = receive_buf(tty, head, count);
429 mutex_unlock(&buf->flush_mutex);
431 tty_ldisc_deref(disc);
438 * Push the terminal flip buffers to the line discipline.
440 * Must not be called from IRQ context.
442 void tty_flush_to_ldisc(struct tty_struct *tty)
444 if (!tty->port->low_latency)
445 flush_work(&tty->port->buf.work);
449 * tty_flip_buffer_push - terminal
450 * @port: tty port to push
452 * Queue a push of the terminal flip buffers to the line discipline. This
453 * function must not be called from IRQ context if port->low_latency is
456 * In the event of the queue being busy for flipping the work will be
457 * held off and retried later.
460 void tty_flip_buffer_push(struct tty_port *port)
462 struct tty_bufhead *buf = &port->buf;
464 buf->tail->commit = buf->tail->used;
466 if (port->low_latency)
467 flush_to_ldisc(&buf->work);
469 schedule_work(&buf->work);
471 EXPORT_SYMBOL(tty_flip_buffer_push);
474 * tty_buffer_init - prepare a tty buffer structure
475 * @tty: tty to initialise
477 * Set up the initial state of the buffer management for a tty device.
478 * Must be called before the other tty buffer functions are used.
481 void tty_buffer_init(struct tty_port *port)
483 struct tty_bufhead *buf = &port->buf;
485 mutex_init(&buf->flush_mutex);
486 tty_buffer_reset(&buf->sentinel, 0);
487 buf->head = &buf->sentinel;
488 buf->tail = &buf->sentinel;
489 init_llist_head(&buf->free);
490 atomic_set(&buf->memory_used, 0);
491 buf->flushpending = 0;
492 INIT_WORK(&buf->work, flush_to_ldisc);