Root/drivers/tty/tty_buffer.c

1/*
2 * Tty buffer allocation management
3 */
4
5#include <linux/types.h>
6#include <linux/errno.h>
7#include <linux/tty.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>
20
21/**
22 * tty_buffer_free_all - free buffers used by a tty
23 * @tty: tty to free from
24 *
25 * Remove all the buffers pending on a tty whether queued with data
26 * or in the free ring. Must be called when the tty is no longer in use
27 *
28 * Locking: none
29 */
30
31void tty_buffer_free_all(struct tty_port *port)
32{
33    struct tty_bufhead *buf = &port->buf;
34    struct tty_buffer *thead;
35
36    while ((thead = buf->head) != NULL) {
37        buf->head = thead->next;
38        kfree(thead);
39    }
40    while ((thead = buf->free) != NULL) {
41        buf->free = thead->next;
42        kfree(thead);
43    }
44    buf->tail = NULL;
45    buf->memory_used = 0;
46}
47
48/**
49 * tty_buffer_alloc - allocate a tty buffer
50 * @tty: tty device
51 * @size: desired size (characters)
52 *
53 * Allocate a new tty buffer to hold the desired number of characters.
54 * Return NULL if out of memory or the allocation would exceed the
55 * per device queue
56 *
57 * Locking: Caller must hold tty->buf.lock
58 */
59
60static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
61{
62    struct tty_buffer *p;
63
64    if (port->buf.memory_used + size > 65536)
65        return NULL;
66    p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
67    if (p == NULL)
68        return NULL;
69    p->used = 0;
70    p->size = size;
71    p->next = NULL;
72    p->commit = 0;
73    p->read = 0;
74    p->char_buf_ptr = (char *)(p->data);
75    p->flag_buf_ptr = (unsigned char *)p->char_buf_ptr + size;
76    port->buf.memory_used += size;
77    return p;
78}
79
80/**
81 * tty_buffer_free - free a tty buffer
82 * @tty: tty owning the buffer
83 * @b: the buffer to free
84 *
85 * Free a tty buffer, or add it to the free list according to our
86 * internal strategy
87 *
88 * Locking: Caller must hold tty->buf.lock
89 */
90
91static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
92{
93    struct tty_bufhead *buf = &port->buf;
94
95    /* Dumb strategy for now - should keep some stats */
96    buf->memory_used -= b->size;
97    WARN_ON(buf->memory_used < 0);
98
99    if (b->size >= 512)
100        kfree(b);
101    else {
102        b->next = buf->free;
103        buf->free = b;
104    }
105}
106
107/**
108 * __tty_buffer_flush - flush full tty buffers
109 * @tty: tty to flush
110 *
111 * flush all the buffers containing receive data. Caller must
112 * hold the buffer lock and must have ensured no parallel flush to
113 * ldisc is running.
114 *
115 * Locking: Caller must hold tty->buf.lock
116 */
117
118static void __tty_buffer_flush(struct tty_port *port)
119{
120    struct tty_bufhead *buf = &port->buf;
121    struct tty_buffer *thead;
122
123    if (unlikely(buf->head == NULL))
124        return;
125    while ((thead = buf->head->next) != NULL) {
126        tty_buffer_free(port, buf->head);
127        buf->head = thead;
128    }
129    WARN_ON(buf->head != buf->tail);
130    buf->head->read = buf->head->commit;
131}
132
133/**
134 * tty_buffer_flush - flush full tty buffers
135 * @tty: tty to flush
136 *
137 * flush all the buffers containing receive data. If the buffer is
138 * being processed by flush_to_ldisc then we defer the processing
139 * to that function
140 *
141 * Locking: none
142 */
143
144void tty_buffer_flush(struct tty_struct *tty)
145{
146    struct tty_port *port = tty->port;
147    struct tty_bufhead *buf = &port->buf;
148    unsigned long flags;
149
150    spin_lock_irqsave(&buf->lock, flags);
151
152    /* If the data is being pushed to the tty layer then we can't
153       process it here. Instead set a flag and the flush_to_ldisc
154       path will process the flush request before it exits */
155    if (test_bit(TTYP_FLUSHING, &port->iflags)) {
156        set_bit(TTYP_FLUSHPENDING, &port->iflags);
157        spin_unlock_irqrestore(&buf->lock, flags);
158        wait_event(tty->read_wait,
159                test_bit(TTYP_FLUSHPENDING, &port->iflags) == 0);
160        return;
161    } else
162        __tty_buffer_flush(port);
163    spin_unlock_irqrestore(&buf->lock, flags);
164}
165
166/**
167 * tty_buffer_find - find a free tty buffer
168 * @tty: tty owning the buffer
169 * @size: characters wanted
170 *
171 * Locate an existing suitable tty buffer or if we are lacking one then
172 * allocate a new one. We round our buffers off in 256 character chunks
173 * to get better allocation behaviour.
174 *
175 * Locking: Caller must hold tty->buf.lock
176 */
177
178static struct tty_buffer *tty_buffer_find(struct tty_port *port, size_t size)
179{
180    struct tty_buffer **tbh = &port->buf.free;
181    while ((*tbh) != NULL) {
182        struct tty_buffer *t = *tbh;
183        if (t->size >= size) {
184            *tbh = t->next;
185            t->next = NULL;
186            t->used = 0;
187            t->commit = 0;
188            t->read = 0;
189            port->buf.memory_used += t->size;
190            return t;
191        }
192        tbh = &((*tbh)->next);
193    }
194    /* Round the buffer size out */
195    size = (size + 0xFF) & ~0xFF;
196    return tty_buffer_alloc(port, size);
197    /* Should possibly check if this fails for the largest buffer we
198       have queued and recycle that ? */
199}
200/**
201 * tty_buffer_request_room - grow tty buffer if needed
202 * @tty: tty structure
203 * @size: size desired
204 *
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.
207 *
208 * Locking: Takes port->buf.lock
209 */
210int tty_buffer_request_room(struct tty_port *port, size_t size)
211{
212    struct tty_bufhead *buf = &port->buf;
213    struct tty_buffer *b, *n;
214    int left;
215    unsigned long flags;
216    spin_lock_irqsave(&buf->lock, flags);
217    /* OPTIMISATION: We could keep a per tty "zero" sized buffer to
218       remove this conditional if its worth it. This would be invisible
219       to the callers */
220    b = buf->tail;
221    if (b != NULL)
222        left = b->size - b->used;
223    else
224        left = 0;
225
226    if (left < size) {
227        /* This is the slow path - looking for new buffers to use */
228        if ((n = tty_buffer_find(port, size)) != NULL) {
229            if (b != NULL) {
230                b->next = n;
231                b->commit = b->used;
232            } else
233                buf->head = n;
234            buf->tail = n;
235        } else
236            size = left;
237    }
238    spin_unlock_irqrestore(&buf->lock, flags);
239    return size;
240}
241EXPORT_SYMBOL_GPL(tty_buffer_request_room);
242
243/**
244 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
245 * @port: tty port
246 * @chars: characters
247 * @flag: flag value for each character
248 * @size: size
249 *
250 * Queue a series of bytes to the tty buffering. All the characters
251 * passed are marked with the supplied flag. Returns the number added.
252 *
253 * Locking: Called functions may take port->buf.lock
254 */
255
256int tty_insert_flip_string_fixed_flag(struct tty_port *port,
257        const unsigned char *chars, char flag, size_t size)
258{
259    int copied = 0;
260    do {
261        int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
262        int space = tty_buffer_request_room(port, goal);
263        struct tty_buffer *tb = port->buf.tail;
264        /* If there is no space then tb may be NULL */
265        if (unlikely(space == 0)) {
266            break;
267        }
268        memcpy(tb->char_buf_ptr + tb->used, chars, space);
269        memset(tb->flag_buf_ptr + tb->used, flag, space);
270        tb->used += space;
271        copied += space;
272        chars += space;
273        /* There is a small chance that we need to split the data over
274           several buffers. If this is the case we must loop */
275    } while (unlikely(size > copied));
276    return copied;
277}
278EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
279
280/**
281 * tty_insert_flip_string_flags - Add characters to the tty buffer
282 * @port: tty port
283 * @chars: characters
284 * @flags: flag bytes
285 * @size: size
286 *
287 * Queue a series of bytes to the tty buffering. For each character
288 * the flags array indicates the status of the character. Returns the
289 * number added.
290 *
291 * Locking: Called functions may take port->buf.lock
292 */
293
294int tty_insert_flip_string_flags(struct tty_port *port,
295        const unsigned char *chars, const char *flags, size_t size)
296{
297    int copied = 0;
298    do {
299        int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
300        int space = tty_buffer_request_room(port, goal);
301        struct tty_buffer *tb = port->buf.tail;
302        /* If there is no space then tb may be NULL */
303        if (unlikely(space == 0)) {
304            break;
305        }
306        memcpy(tb->char_buf_ptr + tb->used, chars, space);
307        memcpy(tb->flag_buf_ptr + tb->used, flags, space);
308        tb->used += space;
309        copied += space;
310        chars += space;
311        flags += space;
312        /* There is a small chance that we need to split the data over
313           several buffers. If this is the case we must loop */
314    } while (unlikely(size > copied));
315    return copied;
316}
317EXPORT_SYMBOL(tty_insert_flip_string_flags);
318
319/**
320 * tty_schedule_flip - push characters to ldisc
321 * @port: tty port to push from
322 *
323 * Takes any pending buffers and transfers their ownership to the
324 * ldisc side of the queue. It then schedules those characters for
325 * processing by the line discipline.
326 * Note that this function can only be used when the low_latency flag
327 * is unset. Otherwise the workqueue won't be flushed.
328 *
329 * Locking: Takes port->buf.lock
330 */
331
332void tty_schedule_flip(struct tty_port *port)
333{
334    struct tty_bufhead *buf = &port->buf;
335    unsigned long flags;
336    WARN_ON(port->low_latency);
337
338    spin_lock_irqsave(&buf->lock, flags);
339    if (buf->tail != NULL)
340        buf->tail->commit = buf->tail->used;
341    spin_unlock_irqrestore(&buf->lock, flags);
342    schedule_work(&buf->work);
343}
344EXPORT_SYMBOL(tty_schedule_flip);
345
346/**
347 * tty_prepare_flip_string - make room for characters
348 * @port: tty port
349 * @chars: return pointer for character write area
350 * @size: desired size
351 *
352 * Prepare a block of space in the buffer for data. Returns the length
353 * available and buffer pointer to the space which is now allocated and
354 * accounted for as ready for normal characters. This is used for drivers
355 * that need their own block copy routines into the buffer. There is no
356 * guarantee the buffer is a DMA target!
357 *
358 * Locking: May call functions taking port->buf.lock
359 */
360
361int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
362        size_t size)
363{
364    int space = tty_buffer_request_room(port, size);
365    if (likely(space)) {
366        struct tty_buffer *tb = port->buf.tail;
367        *chars = tb->char_buf_ptr + tb->used;
368        memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
369        tb->used += space;
370    }
371    return space;
372}
373EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
374
375/**
376 * tty_prepare_flip_string_flags - make room for characters
377 * @port: tty port
378 * @chars: return pointer for character write area
379 * @flags: return pointer for status flag write area
380 * @size: desired size
381 *
382 * Prepare a block of space in the buffer for data. Returns the length
383 * available and buffer pointer to the space which is now allocated and
384 * accounted for as ready for characters. This is used for drivers
385 * that need their own block copy routines into the buffer. There is no
386 * guarantee the buffer is a DMA target!
387 *
388 * Locking: May call functions taking port->buf.lock
389 */
390
391int tty_prepare_flip_string_flags(struct tty_port *port,
392            unsigned char **chars, char **flags, size_t size)
393{
394    int space = tty_buffer_request_room(port, size);
395    if (likely(space)) {
396        struct tty_buffer *tb = port->buf.tail;
397        *chars = tb->char_buf_ptr + tb->used;
398        *flags = tb->flag_buf_ptr + tb->used;
399        tb->used += space;
400    }
401    return space;
402}
403EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
404
405
406
407/**
408 * flush_to_ldisc
409 * @work: tty structure passed from work queue.
410 *
411 * This routine is called out of the software interrupt to flush data
412 * from the buffer chain to the line discipline.
413 *
414 * Locking: holds tty->buf.lock to guard buffer list. Drops the lock
415 * while invoking the line discipline receive_buf method. The
416 * receive_buf method is single threaded for each tty instance.
417 */
418
419static void flush_to_ldisc(struct work_struct *work)
420{
421    struct tty_port *port = container_of(work, struct tty_port, buf.work);
422    struct tty_bufhead *buf = &port->buf;
423    struct tty_struct *tty;
424    unsigned long flags;
425    struct tty_ldisc *disc;
426
427    tty = port->itty;
428    if (tty == NULL)
429        return;
430
431    disc = tty_ldisc_ref(tty);
432    if (disc == NULL) /* !TTY_LDISC */
433        return;
434
435    spin_lock_irqsave(&buf->lock, flags);
436
437    if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) {
438        struct tty_buffer *head;
439        while ((head = buf->head) != NULL) {
440            int count;
441            char *char_buf;
442            unsigned char *flag_buf;
443
444            count = head->commit - head->read;
445            if (!count) {
446                if (head->next == NULL)
447                    break;
448                buf->head = head->next;
449                tty_buffer_free(port, head);
450                continue;
451            }
452            /* Ldisc or user is trying to flush the buffers
453               we are feeding to the ldisc, stop feeding the
454               line discipline as we want to empty the queue */
455            if (test_bit(TTYP_FLUSHPENDING, &port->iflags))
456                break;
457            if (!tty->receive_room)
458                break;
459            if (count > tty->receive_room)
460                count = tty->receive_room;
461            char_buf = head->char_buf_ptr + head->read;
462            flag_buf = head->flag_buf_ptr + head->read;
463            head->read += count;
464            spin_unlock_irqrestore(&buf->lock, flags);
465            disc->ops->receive_buf(tty, char_buf,
466                            flag_buf, count);
467            spin_lock_irqsave(&buf->lock, flags);
468        }
469        clear_bit(TTYP_FLUSHING, &port->iflags);
470    }
471
472    /* We may have a deferred request to flush the input buffer,
473       if so pull the chain under the lock and empty the queue */
474    if (test_bit(TTYP_FLUSHPENDING, &port->iflags)) {
475        __tty_buffer_flush(port);
476        clear_bit(TTYP_FLUSHPENDING, &port->iflags);
477        wake_up(&tty->read_wait);
478    }
479    spin_unlock_irqrestore(&buf->lock, flags);
480
481    tty_ldisc_deref(disc);
482}
483
484/**
485 * tty_flush_to_ldisc
486 * @tty: tty to push
487 *
488 * Push the terminal flip buffers to the line discipline.
489 *
490 * Must not be called from IRQ context.
491 */
492void tty_flush_to_ldisc(struct tty_struct *tty)
493{
494    if (!tty->port->low_latency)
495        flush_work(&tty->port->buf.work);
496}
497
498/**
499 * tty_flip_buffer_push - terminal
500 * @port: tty port to push
501 *
502 * Queue a push of the terminal flip buffers to the line discipline. This
503 * function must not be called from IRQ context if port->low_latency is
504 * set.
505 *
506 * In the event of the queue being busy for flipping the work will be
507 * held off and retried later.
508 *
509 * Locking: tty buffer lock. Driver locks in low latency mode.
510 */
511
512void tty_flip_buffer_push(struct tty_port *port)
513{
514    struct tty_bufhead *buf = &port->buf;
515    unsigned long flags;
516
517    spin_lock_irqsave(&buf->lock, flags);
518    if (buf->tail != NULL)
519        buf->tail->commit = buf->tail->used;
520    spin_unlock_irqrestore(&buf->lock, flags);
521
522    if (port->low_latency)
523        flush_to_ldisc(&buf->work);
524    else
525        schedule_work(&buf->work);
526}
527EXPORT_SYMBOL(tty_flip_buffer_push);
528
529/**
530 * tty_buffer_init - prepare a tty buffer structure
531 * @tty: tty to initialise
532 *
533 * Set up the initial state of the buffer management for a tty device.
534 * Must be called before the other tty buffer functions are used.
535 *
536 * Locking: none
537 */
538
539void tty_buffer_init(struct tty_port *port)
540{
541    struct tty_bufhead *buf = &port->buf;
542
543    spin_lock_init(&buf->lock);
544    buf->head = NULL;
545    buf->tail = NULL;
546    buf->free = NULL;
547    buf->memory_used = 0;
548    INIT_WORK(&buf->work, flush_to_ldisc);
549}
550
551

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