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
  20 /**
  21  *      tty_buffer_free_all             -       free buffers used by a tty
  22  *      @tty: tty to free from
  23  *
  24  *      Remove all the buffers pending on a tty whether queued with data
  25  *      or in the free ring. Must be called when the tty is no longer in use
  26  *
  27  *      Locking: none
  28  */
  29
  30 void tty_buffer_free_all(struct tty_struct *tty)
  31 {
  32         struct tty_bufhead *buf = &tty->buf;
  33         struct tty_buffer *thead;
  34
  35         while ((thead = buf->head) != NULL) {
  36                 buf->head = thead->next;
  37                 kfree(thead);
  38         }
  39         while ((thead = buf->free) != NULL) {
  40                 buf->free = thead->next;
  41                 kfree(thead);
  42         }
  43         buf->tail = NULL;
  44         buf->memory_used = 0;
  45 }
  46
  47 /**
  48  *      tty_buffer_alloc        -       allocate a tty buffer
  49  *      @tty: tty device
  50  *      @size: desired size (characters)
  51  *
  52  *      Allocate a new tty buffer to hold the desired number of characters.
  53  *      Return NULL if out of memory or the allocation would exceed the
  54  *      per device queue
  55  *
  56  *      Locking: Caller must hold tty->buf.lock
  57  */
  58
  59 static struct tty_buffer *tty_buffer_alloc(struct tty_struct *tty, size_t size)
  60 {
  61         struct tty_buffer *p;
  62
  63         if (tty->buf.memory_used + size > 65536)
  64                 return NULL;
  65         p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
  66         if (p == NULL)
  67                 return NULL;
  68         p->used = 0;
  69         p->size = size;
  70         p->next = NULL;
  71         p->commit = 0;
  72         p->read = 0;
  73         p->char_buf_ptr = (char *)(p->data);
  74         p->flag_buf_ptr = (unsigned char *)p->char_buf_ptr + size;
  75         tty->buf.memory_used += size;
  76         return p;
  77 }
  78
  79 /**
  80  *      tty_buffer_free         -       free a tty buffer
  81  *      @tty: tty owning the buffer
  82  *      @b: the buffer to free
  83  *
  84  *      Free a tty buffer, or add it to the free list according to our
  85  *      internal strategy
  86  *
  87  *      Locking: Caller must hold tty->buf.lock
  88  */
  89
  90 static void tty_buffer_free(struct tty_struct *tty, struct tty_buffer *b)
  91 {
  92         struct tty_bufhead *buf = &tty->buf;
  93
  94         /* Dumb strategy for now - should keep some stats */
  95         buf->memory_used -= b->size;
  96         WARN_ON(buf->memory_used < 0);
  97
  98         if (b->size >= 512)
  99                 kfree(b);
 100         else {
 101                 b->next = buf->free;
 102                 buf->free = b;
 103         }
 104 }
 105
 106 /**
 107  *      __tty_buffer_flush              -       flush full tty buffers
 108  *      @tty: tty to flush
 109  *
 110  *      flush all the buffers containing receive data. Caller must
 111  *      hold the buffer lock and must have ensured no parallel flush to
 112  *      ldisc is running.
 113  *
 114  *      Locking: Caller must hold tty->buf.lock
 115  */
 116
 117 static void __tty_buffer_flush(struct tty_struct *tty)
 118 {
 119         struct tty_bufhead *buf = &tty->buf;
 120         struct tty_buffer *thead;
 121
 122         while ((thead = buf->head) != NULL) {
 123                 buf->head = thead->next;
 124                 tty_buffer_free(tty, thead);
 125         }
 126         buf->tail = NULL;
 127 }
 128
 129 /**
 130  *      tty_buffer_flush                -       flush full tty buffers
 131  *      @tty: tty to flush
 132  *
 133  *      flush all the buffers containing receive data. If the buffer is
 134  *      being processed by flush_to_ldisc then we defer the processing
 135  *      to that function
 136  *
 137  *      Locking: none
 138  */
 139
 140 void tty_buffer_flush(struct tty_struct *tty)
 141 {
 142         struct tty_port *port = tty->port;
 143         struct tty_bufhead *buf = &tty->buf;
 144         unsigned long flags;
 145
 146         spin_lock_irqsave(&buf->lock, flags);
 147
 148         /* If the data is being pushed to the tty layer then we can't
 149            process it here. Instead set a flag and the flush_to_ldisc
 150            path will process the flush request before it exits */
 151         if (test_bit(TTYP_FLUSHING, &port->iflags)) {
 152                 set_bit(TTYP_FLUSHPENDING, &port->iflags);
 153                 spin_unlock_irqrestore(&buf->lock, flags);
 154                 wait_event(tty->read_wait,
 155                                 test_bit(TTYP_FLUSHPENDING, &port->iflags) == 0);
 156                 return;
 157         } else
 158                 __tty_buffer_flush(tty);
 159         spin_unlock_irqrestore(&buf->lock, flags);
 160 }
 161
 162 /**
 163  *      tty_buffer_find         -       find a free tty buffer
 164  *      @tty: tty owning the buffer
 165  *      @size: characters wanted
 166  *
 167  *      Locate an existing suitable tty buffer or if we are lacking one then
 168  *      allocate a new one. We round our buffers off in 256 character chunks
 169  *      to get better allocation behaviour.
 170  *
 171  *      Locking: Caller must hold tty->buf.lock
 172  */
 173
 174 static struct tty_buffer *tty_buffer_find(struct tty_struct *tty, size_t size)
 175 {
 176         struct tty_buffer **tbh = &tty->buf.free;
 177         while ((*tbh) != NULL) {
 178                 struct tty_buffer *t = *tbh;
 179                 if (t->size >= size) {
 180                         *tbh = t->next;
 181                         t->next = NULL;
 182                         t->used = 0;
 183                         t->commit = 0;
 184                         t->read = 0;
 185                         tty->buf.memory_used += t->size;
 186                         return t;
 187                 }
 188                 tbh = &((*tbh)->next);
 189         }
 190         /* Round the buffer size out */
 191         size = (size + 0xFF) & ~0xFF;
 192         return tty_buffer_alloc(tty, size);
 193         /* Should possibly check if this fails for the largest buffer we
 194            have queued and recycle that ? */
 195 }
 196 /**
 197  *      __tty_buffer_request_room               -       grow tty buffer if needed
 198  *      @tty: tty structure
 199  *      @size: size desired
 200  *
 201  *      Make at least size bytes of linear space available for the tty
 202  *      buffer. If we fail return the size we managed to find.
 203  *      Locking: Caller must hold tty->buf.lock
 204  */
 205 static int __tty_buffer_request_room(struct tty_struct *tty, size_t size)
 206 {
 207         struct tty_bufhead *buf = &tty->buf;
 208         struct tty_buffer *b, *n;
 209         int left;
 210         /* OPTIMISATION: We could keep a per tty "zero" sized buffer to
 211            remove this conditional if its worth it. This would be invisible
 212            to the callers */
 213         b = buf->tail;
 214         if (b != NULL)
 215                 left = b->size - b->used;
 216         else
 217                 left = 0;
 218
 219         if (left < size) {
 220                 /* This is the slow path - looking for new buffers to use */
 221                 if ((n = tty_buffer_find(tty, size)) != NULL) {
 222                         if (b != NULL) {
 223                                 b->next = n;
 224                                 b->commit = b->used;
 225                         } else
 226                                 buf->head = n;
 227                         buf->tail = n;
 228                 } else
 229                         size = left;
 230         }
 231
 232         return size;
 233 }
 234
 235
 236 /**
 237  *      tty_buffer_request_room         -       grow tty buffer if needed
 238  *      @tty: tty structure
 239  *      @size: size desired
 240  *
 241  *      Make at least size bytes of linear space available for the tty
 242  *      buffer. If we fail return the size we managed to find.
 243  *
 244  *      Locking: Takes tty->buf.lock
 245  */
 246 int tty_buffer_request_room(struct tty_struct *tty, size_t size)
 247 {
 248         unsigned long flags;
 249         int length;
 250
 251         spin_lock_irqsave(&tty->buf.lock, flags);
 252         length = __tty_buffer_request_room(tty, size);
 253         spin_unlock_irqrestore(&tty->buf.lock, flags);
 254         return length;
 255 }
 256 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
 257
 258 /**
 259  *      tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
 260  *      @tty: tty structure
 261  *      @chars: characters
 262  *      @flag: flag value for each character
 263  *      @size: size
 264  *
 265  *      Queue a series of bytes to the tty buffering. All the characters
 266  *      passed are marked with the supplied flag. Returns the number added.
 267  *
 268  *      Locking: Called functions may take tty->buf.lock
 269  */
 270
 271 int tty_insert_flip_string_fixed_flag(struct tty_struct *tty,
 272                 const unsigned char *chars, char flag, size_t size)
 273 {
 274         struct tty_bufhead *buf = &tty->buf;
 275         int copied = 0;
 276         do {
 277                 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 278                 int space;
 279                 unsigned long flags;
 280                 struct tty_buffer *tb;
 281
 282                 spin_lock_irqsave(&buf->lock, flags);
 283                 space = __tty_buffer_request_room(tty, goal);
 284                 tb = buf->tail;
 285                 /* If there is no space then tb may be NULL */
 286                 if (unlikely(space == 0)) {
 287                         spin_unlock_irqrestore(&buf->lock, flags);
 288                         break;
 289                 }
 290                 memcpy(tb->char_buf_ptr + tb->used, chars, space);
 291                 memset(tb->flag_buf_ptr + tb->used, flag, space);
 292                 tb->used += space;
 293                 spin_unlock_irqrestore(&buf->lock, flags);
 294                 copied += space;
 295                 chars += space;
 296                 /* There is a small chance that we need to split the data over
 297                    several buffers. If this is the case we must loop */
 298         } while (unlikely(size > copied));
 299         return copied;
 300 }
 301 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
 302
 303 /**
 304  *      tty_insert_flip_string_flags    -       Add characters to the tty buffer
 305  *      @tty: tty structure
 306  *      @chars: characters
 307  *      @flags: flag bytes
 308  *      @size: size
 309  *
 310  *      Queue a series of bytes to the tty buffering. For each character
 311  *      the flags array indicates the status of the character. Returns the
 312  *      number added.
 313  *
 314  *      Locking: Called functions may take tty->buf.lock
 315  */
 316
 317 int tty_insert_flip_string_flags(struct tty_struct *tty,
 318                 const unsigned char *chars, const char *flags, size_t size)
 319 {
 320         struct tty_bufhead *buf = &tty->buf;
 321         int copied = 0;
 322         do {
 323                 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 324                 int space;
 325                 unsigned long __flags;
 326                 struct tty_buffer *tb;
 327
 328                 spin_lock_irqsave(&buf->lock, __flags);
 329                 space = __tty_buffer_request_room(tty, goal);
 330                 tb = buf->tail;
 331                 /* If there is no space then tb may be NULL */
 332                 if (unlikely(space == 0)) {
 333                         spin_unlock_irqrestore(&buf->lock, __flags);
 334                         break;
 335                 }
 336                 memcpy(tb->char_buf_ptr + tb->used, chars, space);
 337                 memcpy(tb->flag_buf_ptr + tb->used, flags, space);
 338                 tb->used += space;
 339                 spin_unlock_irqrestore(&buf->lock, __flags);
 340                 copied += space;
 341                 chars += space;
 342                 flags += space;
 343                 /* There is a small chance that we need to split the data over
 344                    several buffers. If this is the case we must loop */
 345         } while (unlikely(size > copied));
 346         return copied;
 347 }
 348 EXPORT_SYMBOL(tty_insert_flip_string_flags);
 349
 350 /**
 351  *      tty_schedule_flip       -       push characters to ldisc
 352  *      @tty: tty to push from
 353  *
 354  *      Takes any pending buffers and transfers their ownership to the
 355  *      ldisc side of the queue. It then schedules those characters for
 356  *      processing by the line discipline.
 357  *      Note that this function can only be used when the low_latency flag
 358  *      is unset. Otherwise the workqueue won't be flushed.
 359  *
 360  *      Locking: Takes tty->buf.lock
 361  */
 362
 363 void tty_schedule_flip(struct tty_struct *tty)
 364 {
 365         struct tty_bufhead *buf = &tty->buf;
 366         unsigned long flags;
 367
 368         spin_lock_irqsave(&buf->lock, flags);
 369         if (buf->tail != NULL)
 370                 buf->tail->commit = buf->tail->used;
 371         spin_unlock_irqrestore(&buf->lock, flags);
 372         schedule_work(&buf->work);
 373 }
 374 EXPORT_SYMBOL(tty_schedule_flip);
 375
 376 /**
 377  *      tty_prepare_flip_string         -       make room for characters
 378  *      @tty: tty
 379  *      @chars: return pointer for character 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 normal 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 tty->buf.lock
 389  */
 390
 391 int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars,
 392                                                                 size_t size)
 393 {
 394         struct tty_bufhead *buf = &tty->buf;
 395         int space;
 396         unsigned long flags;
 397         struct tty_buffer *tb;
 398
 399         spin_lock_irqsave(&buf->lock, flags);
 400         space = __tty_buffer_request_room(tty, size);
 401
 402         tb = buf->tail;
 403         if (likely(space)) {
 404                 *chars = tb->char_buf_ptr + tb->used;
 405                 memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
 406                 tb->used += space;
 407         }
 408         spin_unlock_irqrestore(&buf->lock, flags);
 409         return space;
 410 }
 411 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
 412
 413 /**
 414  *      tty_prepare_flip_string_flags   -       make room for characters
 415  *      @tty: tty
 416  *      @chars: return pointer for character write area
 417  *      @flags: return pointer for status flag write area
 418  *      @size: desired size
 419  *
 420  *      Prepare a block of space in the buffer for data. Returns the length
 421  *      available and buffer pointer to the space which is now allocated and
 422  *      accounted for as ready for characters. This is used for drivers
 423  *      that need their own block copy routines into the buffer. There is no
 424  *      guarantee the buffer is a DMA target!
 425  *
 426  *      Locking: May call functions taking tty->buf.lock
 427  */
 428
 429 int tty_prepare_flip_string_flags(struct tty_struct *tty,
 430                         unsigned char **chars, char **flags, size_t size)
 431 {
 432         struct tty_bufhead *buf = &tty->buf;
 433         int space;
 434         unsigned long __flags;
 435         struct tty_buffer *tb;
 436
 437         spin_lock_irqsave(&buf->lock, __flags);
 438         space = __tty_buffer_request_room(tty, size);
 439
 440         tb = buf->tail;
 441         if (likely(space)) {
 442                 *chars = tb->char_buf_ptr + tb->used;
 443                 *flags = tb->flag_buf_ptr + tb->used;
 444                 tb->used += space;
 445         }
 446         spin_unlock_irqrestore(&buf->lock, __flags);
 447         return space;
 448 }
 449 EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
 450
 451
 452
 453 /**
 454  *      flush_to_ldisc
 455  *      @work: tty structure passed from work queue.
 456  *
 457  *      This routine is called out of the software interrupt to flush data
 458  *      from the buffer chain to the line discipline.
 459  *
 460  *      Locking: holds tty->buf.lock to guard buffer list. Drops the lock
 461  *      while invoking the line discipline receive_buf method. The
 462  *      receive_buf method is single threaded for each tty instance.
 463  */
 464
 465 static void flush_to_ldisc(struct work_struct *work)
 466 {
 467         struct tty_struct *tty =
 468                 container_of(work, struct tty_struct, buf.work);
 469         struct tty_port *port = tty->port;
 470         struct tty_bufhead *buf = &tty->buf;
 471         unsigned long   flags;
 472         struct tty_ldisc *disc;
 473
 474         disc = tty_ldisc_ref(tty);
 475         if (disc == NULL)       /*  !TTY_LDISC */
 476                 return;
 477
 478         spin_lock_irqsave(&buf->lock, flags);
 479
 480         if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) {
 481                 struct tty_buffer *head;
 482                 while ((head = buf->head) != NULL) {
 483                         int count;
 484                         char *char_buf;
 485                         unsigned char *flag_buf;
 486
 487                         count = head->commit - head->read;
 488                         if (!count) {
 489                                 if (head->next == NULL)
 490                                         break;
 491                                 buf->head = head->next;
 492                                 tty_buffer_free(tty, head);
 493                                 continue;
 494                         }
 495                         /* Ldisc or user is trying to flush the buffers
 496                            we are feeding to the ldisc, stop feeding the
 497                            line discipline as we want to empty the queue */
 498                         if (test_bit(TTYP_FLUSHPENDING, &port->iflags))
 499                                 break;
 500                         if (!tty->receive_room)
 501                                 break;
 502                         if (count > tty->receive_room)
 503                                 count = tty->receive_room;
 504                         char_buf = head->char_buf_ptr + head->read;
 505                         flag_buf = head->flag_buf_ptr + head->read;
 506                         head->read += count;
 507                         spin_unlock_irqrestore(&buf->lock, flags);
 508                         disc->ops->receive_buf(tty, char_buf,
 509                                                         flag_buf, count);
 510                         spin_lock_irqsave(&buf->lock, flags);
 511                 }
 512                 clear_bit(TTYP_FLUSHING, &port->iflags);
 513         }
 514
 515         /* We may have a deferred request to flush the input buffer,
 516            if so pull the chain under the lock and empty the queue */
 517         if (test_bit(TTYP_FLUSHPENDING, &port->iflags)) {
 518                 __tty_buffer_flush(tty);
 519                 clear_bit(TTYP_FLUSHPENDING, &port->iflags);
 520                 wake_up(&tty->read_wait);
 521         }
 522         spin_unlock_irqrestore(&buf->lock, flags);
 523
 524         tty_ldisc_deref(disc);
 525 }
 526
 527 /**
 528  *      tty_flush_to_ldisc
 529  *      @tty: tty to push
 530  *
 531  *      Push the terminal flip buffers to the line discipline.
 532  *
 533  *      Must not be called from IRQ context.
 534  */
 535 void tty_flush_to_ldisc(struct tty_struct *tty)
 536 {
 537         if (!tty->low_latency)
 538                 flush_work(&tty->buf.work);
 539 }
 540
 541 /**
 542  *      tty_flip_buffer_push    -       terminal
 543  *      @tty: tty to push
 544  *
 545  *      Queue a push of the terminal flip buffers to the line discipline. This
 546  *      function must not be called from IRQ context if tty->low_latency is set.
 547  *
 548  *      In the event of the queue being busy for flipping the work will be
 549  *      held off and retried later.
 550  *
 551  *      Locking: tty buffer lock. Driver locks in low latency mode.
 552  */
 553
 554 void tty_flip_buffer_push(struct tty_struct *tty)
 555 {
 556         struct tty_bufhead *buf = &tty->buf;
 557         unsigned long flags;
 558
 559         spin_lock_irqsave(&buf->lock, flags);
 560         if (buf->tail != NULL)
 561                 buf->tail->commit = buf->tail->used;
 562         spin_unlock_irqrestore(&buf->lock, flags);
 563
 564         if (tty->low_latency)
 565                 flush_to_ldisc(&buf->work);
 566         else
 567                 schedule_work(&buf->work);
 568 }
 569 EXPORT_SYMBOL(tty_flip_buffer_push);
 570
 571 /**
 572  *      tty_buffer_init         -       prepare a tty buffer structure
 573  *      @tty: tty to initialise
 574  *
 575  *      Set up the initial state of the buffer management for a tty device.
 576  *      Must be called before the other tty buffer functions are used.
 577  *
 578  *      Locking: none
 579  */
 580
 581 void tty_buffer_init(struct tty_struct *tty)
 582 {
 583         struct tty_bufhead *buf = &tty->buf;
 584
 585         spin_lock_init(&buf->lock);
 586         buf->head = NULL;
 587         buf->tail = NULL;
 588         buf->free = NULL;
 589         buf->memory_used = 0;
 590         INIT_WORK(&buf->work, flush_to_ldisc);
 591 }
 592