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_buffer *thead;
  33         while ((thead = tty->buf.head) != NULL) {
  34                 tty->buf.head = thead->next;
  35                 kfree(thead);
  36         }
  37         while ((thead = tty->buf.free) != NULL) {
  38                 tty->buf.free = thead->next;
  39                 kfree(thead);
  40         }
  41         tty->buf.tail = NULL;
  42         tty->buf.memory_used = 0;
  43 }
  44
  45 /**
  46  *      tty_buffer_alloc        -       allocate a tty buffer
  47  *      @tty: tty device
  48  *      @size: desired size (characters)
  49  *
  50  *      Allocate a new tty buffer to hold the desired number of characters.
  51  *      Return NULL if out of memory or the allocation would exceed the
  52  *      per device queue
  53  *
  54  *      Locking: Caller must hold tty->buf.lock
  55  */
  56
  57 static struct tty_buffer *tty_buffer_alloc(struct tty_struct *tty, size_t size)
  58 {
  59         struct tty_buffer *p;
  60
  61         if (tty->buf.memory_used + size > 65536)
  62                 return NULL;
  63         p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
  64         if (p == NULL)
  65                 return NULL;
  66         p->used = 0;
  67         p->size = size;
  68         p->next = NULL;
  69         p->commit = 0;
  70         p->read = 0;
  71         p->char_buf_ptr = (char *)(p->data);
  72         p->flag_buf_ptr = (unsigned char *)p->char_buf_ptr + size;
  73         tty->buf.memory_used += size;
  74         return p;
  75 }
  76
  77 /**
  78  *      tty_buffer_free         -       free a tty buffer
  79  *      @tty: tty owning the buffer
  80  *      @b: the buffer to free
  81  *
  82  *      Free a tty buffer, or add it to the free list according to our
  83  *      internal strategy
  84  *
  85  *      Locking: Caller must hold tty->buf.lock
  86  */
  87
  88 static void tty_buffer_free(struct tty_struct *tty, struct tty_buffer *b)
  89 {
  90         /* Dumb strategy for now - should keep some stats */
  91         tty->buf.memory_used -= b->size;
  92         WARN_ON(tty->buf.memory_used < 0);
  93
  94         if (b->size >= 512)
  95                 kfree(b);
  96         else {
  97                 b->next = tty->buf.free;
  98                 tty->buf.free = b;
  99         }
 100 }
 101
 102 /**
 103  *      __tty_buffer_flush              -       flush full tty buffers
 104  *      @tty: tty to flush
 105  *
 106  *      flush all the buffers containing receive data. Caller must
 107  *      hold the buffer lock and must have ensured no parallel flush to
 108  *      ldisc is running.
 109  *
 110  *      Locking: Caller must hold tty->buf.lock
 111  */
 112
 113 static void __tty_buffer_flush(struct tty_struct *tty)
 114 {
 115         struct tty_buffer *thead;
 116
 117         while ((thead = tty->buf.head) != NULL) {
 118                 tty->buf.head = thead->next;
 119                 tty_buffer_free(tty, thead);
 120         }
 121         tty->buf.tail = NULL;
 122 }
 123
 124 /**
 125  *      tty_buffer_flush                -       flush full tty buffers
 126  *      @tty: tty to flush
 127  *
 128  *      flush all the buffers containing receive data. If the buffer is
 129  *      being processed by flush_to_ldisc then we defer the processing
 130  *      to that function
 131  *
 132  *      Locking: none
 133  */
 134
 135 void tty_buffer_flush(struct tty_struct *tty)
 136 {
 137         struct tty_port *port = tty->port;
 138         unsigned long flags;
 139         spin_lock_irqsave(&tty->buf.lock, flags);
 140
 141         /* If the data is being pushed to the tty layer then we can't
 142            process it here. Instead set a flag and the flush_to_ldisc
 143            path will process the flush request before it exits */
 144         if (test_bit(TTYP_FLUSHING, &port->iflags)) {
 145                 set_bit(TTYP_FLUSHPENDING, &port->iflags);
 146                 spin_unlock_irqrestore(&tty->buf.lock, flags);
 147                 wait_event(tty->read_wait,
 148                                 test_bit(TTYP_FLUSHPENDING, &port->iflags) == 0);
 149                 return;
 150         } else
 151                 __tty_buffer_flush(tty);
 152         spin_unlock_irqrestore(&tty->buf.lock, flags);
 153 }
 154
 155 /**
 156  *      tty_buffer_find         -       find a free tty buffer
 157  *      @tty: tty owning the buffer
 158  *      @size: characters wanted
 159  *
 160  *      Locate an existing suitable tty buffer or if we are lacking one then
 161  *      allocate a new one. We round our buffers off in 256 character chunks
 162  *      to get better allocation behaviour.
 163  *
 164  *      Locking: Caller must hold tty->buf.lock
 165  */
 166
 167 static struct tty_buffer *tty_buffer_find(struct tty_struct *tty, size_t size)
 168 {
 169         struct tty_buffer **tbh = &tty->buf.free;
 170         while ((*tbh) != NULL) {
 171                 struct tty_buffer *t = *tbh;
 172                 if (t->size >= size) {
 173                         *tbh = t->next;
 174                         t->next = NULL;
 175                         t->used = 0;
 176                         t->commit = 0;
 177                         t->read = 0;
 178                         tty->buf.memory_used += t->size;
 179                         return t;
 180                 }
 181                 tbh = &((*tbh)->next);
 182         }
 183         /* Round the buffer size out */
 184         size = (size + 0xFF) & ~0xFF;
 185         return tty_buffer_alloc(tty, size);
 186         /* Should possibly check if this fails for the largest buffer we
 187            have queued and recycle that ? */
 188 }
 189 /**
 190  *      __tty_buffer_request_room               -       grow tty buffer if needed
 191  *      @tty: tty structure
 192  *      @size: size desired
 193  *
 194  *      Make at least size bytes of linear space available for the tty
 195  *      buffer. If we fail return the size we managed to find.
 196  *      Locking: Caller must hold tty->buf.lock
 197  */
 198 static int __tty_buffer_request_room(struct tty_struct *tty, size_t size)
 199 {
 200         struct tty_buffer *b, *n;
 201         int left;
 202         /* OPTIMISATION: We could keep a per tty "zero" sized buffer to
 203            remove this conditional if its worth it. This would be invisible
 204            to the callers */
 205         if ((b = tty->buf.tail) != NULL)
 206                 left = b->size - b->used;
 207         else
 208                 left = 0;
 209
 210         if (left < size) {
 211                 /* This is the slow path - looking for new buffers to use */
 212                 if ((n = tty_buffer_find(tty, size)) != NULL) {
 213                         if (b != NULL) {
 214                                 b->next = n;
 215                                 b->commit = b->used;
 216                         } else
 217                                 tty->buf.head = n;
 218                         tty->buf.tail = n;
 219                 } else
 220                         size = left;
 221         }
 222
 223         return size;
 224 }
 225
 226
 227 /**
 228  *      tty_buffer_request_room         -       grow tty buffer if needed
 229  *      @tty: tty structure
 230  *      @size: size desired
 231  *
 232  *      Make at least size bytes of linear space available for the tty
 233  *      buffer. If we fail return the size we managed to find.
 234  *
 235  *      Locking: Takes tty->buf.lock
 236  */
 237 int tty_buffer_request_room(struct tty_struct *tty, size_t size)
 238 {
 239         unsigned long flags;
 240         int length;
 241
 242         spin_lock_irqsave(&tty->buf.lock, flags);
 243         length = __tty_buffer_request_room(tty, size);
 244         spin_unlock_irqrestore(&tty->buf.lock, flags);
 245         return length;
 246 }
 247 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
 248
 249 /**
 250  *      tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
 251  *      @tty: tty structure
 252  *      @chars: characters
 253  *      @flag: flag value for each character
 254  *      @size: size
 255  *
 256  *      Queue a series of bytes to the tty buffering. All the characters
 257  *      passed are marked with the supplied flag. Returns the number added.
 258  *
 259  *      Locking: Called functions may take tty->buf.lock
 260  */
 261
 262 int tty_insert_flip_string_fixed_flag(struct tty_struct *tty,
 263                 const unsigned char *chars, char flag, size_t size)
 264 {
 265         int copied = 0;
 266         do {
 267                 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 268                 int space;
 269                 unsigned long flags;
 270                 struct tty_buffer *tb;
 271
 272                 spin_lock_irqsave(&tty->buf.lock, flags);
 273                 space = __tty_buffer_request_room(tty, goal);
 274                 tb = tty->buf.tail;
 275                 /* If there is no space then tb may be NULL */
 276                 if (unlikely(space == 0)) {
 277                         spin_unlock_irqrestore(&tty->buf.lock, flags);
 278                         break;
 279                 }
 280                 memcpy(tb->char_buf_ptr + tb->used, chars, space);
 281                 memset(tb->flag_buf_ptr + tb->used, flag, space);
 282                 tb->used += space;
 283                 spin_unlock_irqrestore(&tty->buf.lock, flags);
 284                 copied += space;
 285                 chars += space;
 286                 /* There is a small chance that we need to split the data over
 287                    several buffers. If this is the case we must loop */
 288         } while (unlikely(size > copied));
 289         return copied;
 290 }
 291 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
 292
 293 /**
 294  *      tty_insert_flip_string_flags    -       Add characters to the tty buffer
 295  *      @tty: tty structure
 296  *      @chars: characters
 297  *      @flags: flag bytes
 298  *      @size: size
 299  *
 300  *      Queue a series of bytes to the tty buffering. For each character
 301  *      the flags array indicates the status of the character. Returns the
 302  *      number added.
 303  *
 304  *      Locking: Called functions may take tty->buf.lock
 305  */
 306
 307 int tty_insert_flip_string_flags(struct tty_struct *tty,
 308                 const unsigned char *chars, const char *flags, size_t size)
 309 {
 310         int copied = 0;
 311         do {
 312                 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 313                 int space;
 314                 unsigned long __flags;
 315                 struct tty_buffer *tb;
 316
 317                 spin_lock_irqsave(&tty->buf.lock, __flags);
 318                 space = __tty_buffer_request_room(tty, goal);
 319                 tb = tty->buf.tail;
 320                 /* If there is no space then tb may be NULL */
 321                 if (unlikely(space == 0)) {
 322                         spin_unlock_irqrestore(&tty->buf.lock, __flags);
 323                         break;
 324                 }
 325                 memcpy(tb->char_buf_ptr + tb->used, chars, space);
 326                 memcpy(tb->flag_buf_ptr + tb->used, flags, space);
 327                 tb->used += space;
 328                 spin_unlock_irqrestore(&tty->buf.lock, __flags);
 329                 copied += space;
 330                 chars += space;
 331                 flags += space;
 332                 /* There is a small chance that we need to split the data over
 333                    several buffers. If this is the case we must loop */
 334         } while (unlikely(size > copied));
 335         return copied;
 336 }
 337 EXPORT_SYMBOL(tty_insert_flip_string_flags);
 338
 339 /**
 340  *      tty_schedule_flip       -       push characters to ldisc
 341  *      @tty: tty to push from
 342  *
 343  *      Takes any pending buffers and transfers their ownership to the
 344  *      ldisc side of the queue. It then schedules those characters for
 345  *      processing by the line discipline.
 346  *      Note that this function can only be used when the low_latency flag
 347  *      is unset. Otherwise the workqueue won't be flushed.
 348  *
 349  *      Locking: Takes tty->buf.lock
 350  */
 351
 352 void tty_schedule_flip(struct tty_struct *tty)
 353 {
 354         unsigned long flags;
 355         spin_lock_irqsave(&tty->buf.lock, flags);
 356         if (tty->buf.tail != NULL)
 357                 tty->buf.tail->commit = tty->buf.tail->used;
 358         spin_unlock_irqrestore(&tty->buf.lock, flags);
 359         schedule_work(&tty->buf.work);
 360 }
 361 EXPORT_SYMBOL(tty_schedule_flip);
 362
 363 /**
 364  *      tty_prepare_flip_string         -       make room for characters
 365  *      @tty: tty
 366  *      @chars: return pointer for character write area
 367  *      @size: desired size
 368  *
 369  *      Prepare a block of space in the buffer for data. Returns the length
 370  *      available and buffer pointer to the space which is now allocated and
 371  *      accounted for as ready for normal characters. This is used for drivers
 372  *      that need their own block copy routines into the buffer. There is no
 373  *      guarantee the buffer is a DMA target!
 374  *
 375  *      Locking: May call functions taking tty->buf.lock
 376  */
 377
 378 int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars,
 379                                                                 size_t size)
 380 {
 381         int space;
 382         unsigned long flags;
 383         struct tty_buffer *tb;
 384
 385         spin_lock_irqsave(&tty->buf.lock, flags);
 386         space = __tty_buffer_request_room(tty, size);
 387
 388         tb = tty->buf.tail;
 389         if (likely(space)) {
 390                 *chars = tb->char_buf_ptr + tb->used;
 391                 memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
 392                 tb->used += space;
 393         }
 394         spin_unlock_irqrestore(&tty->buf.lock, flags);
 395         return space;
 396 }
 397 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
 398
 399 /**
 400  *      tty_prepare_flip_string_flags   -       make room for characters
 401  *      @tty: tty
 402  *      @chars: return pointer for character write area
 403  *      @flags: return pointer for status flag write area
 404  *      @size: desired size
 405  *
 406  *      Prepare a block of space in the buffer for data. Returns the length
 407  *      available and buffer pointer to the space which is now allocated and
 408  *      accounted for as ready for characters. This is used for drivers
 409  *      that need their own block copy routines into the buffer. There is no
 410  *      guarantee the buffer is a DMA target!
 411  *
 412  *      Locking: May call functions taking tty->buf.lock
 413  */
 414
 415 int tty_prepare_flip_string_flags(struct tty_struct *tty,
 416                         unsigned char **chars, char **flags, size_t size)
 417 {
 418         int space;
 419         unsigned long __flags;
 420         struct tty_buffer *tb;
 421
 422         spin_lock_irqsave(&tty->buf.lock, __flags);
 423         space = __tty_buffer_request_room(tty, size);
 424
 425         tb = tty->buf.tail;
 426         if (likely(space)) {
 427                 *chars = tb->char_buf_ptr + tb->used;
 428                 *flags = tb->flag_buf_ptr + tb->used;
 429                 tb->used += space;
 430         }
 431         spin_unlock_irqrestore(&tty->buf.lock, __flags);
 432         return space;
 433 }
 434 EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
 435
 436
 437
 438 /**
 439  *      flush_to_ldisc
 440  *      @work: tty structure passed from work queue.
 441  *
 442  *      This routine is called out of the software interrupt to flush data
 443  *      from the buffer chain to the line discipline.
 444  *
 445  *      Locking: holds tty->buf.lock to guard buffer list. Drops the lock
 446  *      while invoking the line discipline receive_buf method. The
 447  *      receive_buf method is single threaded for each tty instance.
 448  */
 449
 450 static void flush_to_ldisc(struct work_struct *work)
 451 {
 452         struct tty_struct *tty =
 453                 container_of(work, struct tty_struct, buf.work);
 454         struct tty_port *port = tty->port;
 455         unsigned long   flags;
 456         struct tty_ldisc *disc;
 457
 458         disc = tty_ldisc_ref(tty);
 459         if (disc == NULL)       /*  !TTY_LDISC */
 460                 return;
 461
 462         spin_lock_irqsave(&tty->buf.lock, flags);
 463
 464         if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) {
 465                 struct tty_buffer *head;
 466                 while ((head = tty->buf.head) != NULL) {
 467                         int count;
 468                         char *char_buf;
 469                         unsigned char *flag_buf;
 470
 471                         count = head->commit - head->read;
 472                         if (!count) {
 473                                 if (head->next == NULL)
 474                                         break;
 475                                 tty->buf.head = head->next;
 476                                 tty_buffer_free(tty, head);
 477                                 continue;
 478                         }
 479                         /* Ldisc or user is trying to flush the buffers
 480                            we are feeding to the ldisc, stop feeding the
 481                            line discipline as we want to empty the queue */
 482                         if (test_bit(TTYP_FLUSHPENDING, &port->iflags))
 483                                 break;
 484                         if (!tty->receive_room)
 485                                 break;
 486                         if (count > tty->receive_room)
 487                                 count = tty->receive_room;
 488                         char_buf = head->char_buf_ptr + head->read;
 489                         flag_buf = head->flag_buf_ptr + head->read;
 490                         head->read += count;
 491                         spin_unlock_irqrestore(&tty->buf.lock, flags);
 492                         disc->ops->receive_buf(tty, char_buf,
 493                                                         flag_buf, count);
 494                         spin_lock_irqsave(&tty->buf.lock, flags);
 495                 }
 496                 clear_bit(TTYP_FLUSHING, &port->iflags);
 497         }
 498
 499         /* We may have a deferred request to flush the input buffer,
 500            if so pull the chain under the lock and empty the queue */
 501         if (test_bit(TTYP_FLUSHPENDING, &port->iflags)) {
 502                 __tty_buffer_flush(tty);
 503                 clear_bit(TTYP_FLUSHPENDING, &port->iflags);
 504                 wake_up(&tty->read_wait);
 505         }
 506         spin_unlock_irqrestore(&tty->buf.lock, flags);
 507
 508         tty_ldisc_deref(disc);
 509 }
 510
 511 /**
 512  *      tty_flush_to_ldisc
 513  *      @tty: tty to push
 514  *
 515  *      Push the terminal flip buffers to the line discipline.
 516  *
 517  *      Must not be called from IRQ context.
 518  */
 519 void tty_flush_to_ldisc(struct tty_struct *tty)
 520 {
 521         if (!tty->low_latency)
 522                 flush_work(&tty->buf.work);
 523 }
 524
 525 /**
 526  *      tty_flip_buffer_push    -       terminal
 527  *      @tty: tty to push
 528  *
 529  *      Queue a push of the terminal flip buffers to the line discipline. This
 530  *      function must not be called from IRQ context if tty->low_latency is set.
 531  *
 532  *      In the event of the queue being busy for flipping the work will be
 533  *      held off and retried later.
 534  *
 535  *      Locking: tty buffer lock. Driver locks in low latency mode.
 536  */
 537
 538 void tty_flip_buffer_push(struct tty_struct *tty)
 539 {
 540         unsigned long flags;
 541         spin_lock_irqsave(&tty->buf.lock, flags);
 542         if (tty->buf.tail != NULL)
 543                 tty->buf.tail->commit = tty->buf.tail->used;
 544         spin_unlock_irqrestore(&tty->buf.lock, flags);
 545
 546         if (tty->low_latency)
 547                 flush_to_ldisc(&tty->buf.work);
 548         else
 549                 schedule_work(&tty->buf.work);
 550 }
 551 EXPORT_SYMBOL(tty_flip_buffer_push);
 552
 553 /**
 554  *      tty_buffer_init         -       prepare a tty buffer structure
 555  *      @tty: tty to initialise
 556  *
 557  *      Set up the initial state of the buffer management for a tty device.
 558  *      Must be called before the other tty buffer functions are used.
 559  *
 560  *      Locking: none
 561  */
 562
 563 void tty_buffer_init(struct tty_struct *tty)
 564 {
 565         spin_lock_init(&tty->buf.lock);
 566         tty->buf.head = NULL;
 567         tty->buf.tail = NULL;
 568         tty->buf.free = NULL;
 569         tty->buf.memory_used = 0;
 570         INIT_WORK(&tty->buf.work, flush_to_ldisc);
 571 }
 572