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         unsigned long flags;
 138         spin_lock_irqsave(&tty->buf.lock, flags);
 139
 140         /* If the data is being pushed to the tty layer then we can't
 141            process it here. Instead set a flag and the flush_to_ldisc
 142            path will process the flush request before it exits */
 143         if (test_bit(TTY_FLUSHING, &tty->flags)) {
 144                 set_bit(TTY_FLUSHPENDING, &tty->flags);
 145                 spin_unlock_irqrestore(&tty->buf.lock, flags);
 146                 wait_event(tty->read_wait,
 147                                 test_bit(TTY_FLUSHPENDING, &tty->flags) == 0);
 148                 return;
 149         } else
 150                 __tty_buffer_flush(tty);
 151         spin_unlock_irqrestore(&tty->buf.lock, flags);
 152 }
 153
 154 /**
 155  *      tty_buffer_find         -       find a free tty buffer
 156  *      @tty: tty owning the buffer
 157  *      @size: characters wanted
 158  *
 159  *      Locate an existing suitable tty buffer or if we are lacking one then
 160  *      allocate a new one. We round our buffers off in 256 character chunks
 161  *      to get better allocation behaviour.
 162  *
 163  *      Locking: Caller must hold tty->buf.lock
 164  */
 165
 166 static struct tty_buffer *tty_buffer_find(struct tty_struct *tty, size_t size)
 167 {
 168         struct tty_buffer **tbh = &tty->buf.free;
 169         while ((*tbh) != NULL) {
 170                 struct tty_buffer *t = *tbh;
 171                 if (t->size >= size) {
 172                         *tbh = t->next;
 173                         t->next = NULL;
 174                         t->used = 0;
 175                         t->commit = 0;
 176                         t->read = 0;
 177                         tty->buf.memory_used += t->size;
 178                         return t;
 179                 }
 180                 tbh = &((*tbh)->next);
 181         }
 182         /* Round the buffer size out */
 183         size = (size + 0xFF) & ~0xFF;
 184         return tty_buffer_alloc(tty, size);
 185         /* Should possibly check if this fails for the largest buffer we
 186            have queued and recycle that ? */
 187 }
 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  *
 197  *      Locking: Takes tty->buf.lock
 198  */
 199 int tty_buffer_request_room(struct tty_struct *tty, size_t size)
 200 {
 201         struct tty_buffer *b, *n;
 202         int left;
 203         unsigned long flags;
 204
 205         spin_lock_irqsave(&tty->buf.lock, flags);
 206
 207         /* OPTIMISATION: We could keep a per tty "zero" sized buffer to
 208            remove this conditional if its worth it. This would be invisible
 209            to the callers */
 210         if ((b = tty->buf.tail) != NULL)
 211                 left = b->size - b->used;
 212         else
 213                 left = 0;
 214
 215         if (left < size) {
 216                 /* This is the slow path - looking for new buffers to use */
 217                 if ((n = tty_buffer_find(tty, size)) != NULL) {
 218                         if (b != NULL) {
 219                                 b->next = n;
 220                                 b->commit = b->used;
 221                         } else
 222                                 tty->buf.head = n;
 223                         tty->buf.tail = n;
 224                 } else
 225                         size = left;
 226         }
 227
 228         spin_unlock_irqrestore(&tty->buf.lock, flags);
 229         return size;
 230 }
 231 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
 232
 233 /**
 234  *      tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
 235  *      @tty: tty structure
 236  *      @chars: characters
 237  *      @flag: flag value for each character
 238  *      @size: size
 239  *
 240  *      Queue a series of bytes to the tty buffering. All the characters
 241  *      passed are marked with the supplied flag. Returns the number added.
 242  *
 243  *      Locking: Called functions may take tty->buf.lock
 244  */
 245
 246 int tty_insert_flip_string_fixed_flag(struct tty_struct *tty,
 247                 const unsigned char *chars, char flag, size_t size)
 248 {
 249         int copied = 0;
 250         do {
 251                 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 252                 int space = tty_buffer_request_room(tty, goal);
 253                 struct tty_buffer *tb = tty->buf.tail;
 254                 /* If there is no space then tb may be NULL */
 255                 if (unlikely(space == 0))
 256                         break;
 257                 memcpy(tb->char_buf_ptr + tb->used, chars, space);
 258                 memset(tb->flag_buf_ptr + tb->used, flag, space);
 259                 tb->used += space;
 260                 copied += space;
 261                 chars += space;
 262                 /* There is a small chance that we need to split the data over
 263                    several buffers. If this is the case we must loop */
 264         } while (unlikely(size > copied));
 265         return copied;
 266 }
 267 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
 268
 269 /**
 270  *      tty_insert_flip_string_flags    -       Add characters to the tty buffer
 271  *      @tty: tty structure
 272  *      @chars: characters
 273  *      @flags: flag bytes
 274  *      @size: size
 275  *
 276  *      Queue a series of bytes to the tty buffering. For each character
 277  *      the flags array indicates the status of the character. Returns the
 278  *      number added.
 279  *
 280  *      Locking: Called functions may take tty->buf.lock
 281  */
 282
 283 int tty_insert_flip_string_flags(struct tty_struct *tty,
 284                 const unsigned char *chars, const char *flags, size_t size)
 285 {
 286         int copied = 0;
 287         do {
 288                 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 289                 int space = tty_buffer_request_room(tty, goal);
 290                 struct tty_buffer *tb = tty->buf.tail;
 291                 /* If there is no space then tb may be NULL */
 292                 if (unlikely(space == 0))
 293                         break;
 294                 memcpy(tb->char_buf_ptr + tb->used, chars, space);
 295                 memcpy(tb->flag_buf_ptr + tb->used, flags, space);
 296                 tb->used += space;
 297                 copied += space;
 298                 chars += space;
 299                 flags += space;
 300                 /* There is a small chance that we need to split the data over
 301                    several buffers. If this is the case we must loop */
 302         } while (unlikely(size > copied));
 303         return copied;
 304 }
 305 EXPORT_SYMBOL(tty_insert_flip_string_flags);
 306
 307 /**
 308  *      tty_schedule_flip       -       push characters to ldisc
 309  *      @tty: tty to push from
 310  *
 311  *      Takes any pending buffers and transfers their ownership to the
 312  *      ldisc side of the queue. It then schedules those characters for
 313  *      processing by the line discipline.
 314  *
 315  *      Locking: Takes tty->buf.lock
 316  */
 317
 318 void tty_schedule_flip(struct tty_struct *tty)
 319 {
 320         unsigned long flags;
 321         spin_lock_irqsave(&tty->buf.lock, flags);
 322         if (tty->buf.tail != NULL)
 323                 tty->buf.tail->commit = tty->buf.tail->used;
 324         spin_unlock_irqrestore(&tty->buf.lock, flags);
 325         schedule_work(&tty->buf.work);
 326 }
 327 EXPORT_SYMBOL(tty_schedule_flip);
 328
 329 /**
 330  *      tty_prepare_flip_string         -       make room for characters
 331  *      @tty: tty
 332  *      @chars: return pointer for character write area
 333  *      @size: desired size
 334  *
 335  *      Prepare a block of space in the buffer for data. Returns the length
 336  *      available and buffer pointer to the space which is now allocated and
 337  *      accounted for as ready for normal characters. This is used for drivers
 338  *      that need their own block copy routines into the buffer. There is no
 339  *      guarantee the buffer is a DMA target!
 340  *
 341  *      Locking: May call functions taking tty->buf.lock
 342  */
 343
 344 int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars,
 345                                                                 size_t size)
 346 {
 347         int space = tty_buffer_request_room(tty, size);
 348         if (likely(space)) {
 349                 struct tty_buffer *tb = tty->buf.tail;
 350                 *chars = tb->char_buf_ptr + tb->used;
 351                 memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
 352                 tb->used += space;
 353         }
 354         return space;
 355 }
 356 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
 357
 358 /**
 359  *      tty_prepare_flip_string_flags   -       make room for characters
 360  *      @tty: tty
 361  *      @chars: return pointer for character write area
 362  *      @flags: return pointer for status flag write area
 363  *      @size: desired size
 364  *
 365  *      Prepare a block of space in the buffer for data. Returns the length
 366  *      available and buffer pointer to the space which is now allocated and
 367  *      accounted for as ready for characters. This is used for drivers
 368  *      that need their own block copy routines into the buffer. There is no
 369  *      guarantee the buffer is a DMA target!
 370  *
 371  *      Locking: May call functions taking tty->buf.lock
 372  */
 373
 374 int tty_prepare_flip_string_flags(struct tty_struct *tty,
 375                         unsigned char **chars, char **flags, size_t size)
 376 {
 377         int space = tty_buffer_request_room(tty, size);
 378         if (likely(space)) {
 379                 struct tty_buffer *tb = tty->buf.tail;
 380                 *chars = tb->char_buf_ptr + tb->used;
 381                 *flags = tb->flag_buf_ptr + tb->used;
 382                 tb->used += space;
 383         }
 384         return space;
 385 }
 386 EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
 387
 388
 389
 390 /**
 391  *      flush_to_ldisc
 392  *      @work: tty structure passed from work queue.
 393  *
 394  *      This routine is called out of the software interrupt to flush data
 395  *      from the buffer chain to the line discipline.
 396  *
 397  *      Locking: holds tty->buf.lock to guard buffer list. Drops the lock
 398  *      while invoking the line discipline receive_buf method. The
 399  *      receive_buf method is single threaded for each tty instance.
 400  */
 401
 402 static void flush_to_ldisc(struct work_struct *work)
 403 {
 404         struct tty_struct *tty =
 405                 container_of(work, struct tty_struct, buf.work);
 406         unsigned long   flags;
 407         struct tty_ldisc *disc;
 408
 409         disc = tty_ldisc_ref(tty);
 410         if (disc == NULL)       /*  !TTY_LDISC */
 411                 return;
 412
 413         spin_lock_irqsave(&tty->buf.lock, flags);
 414
 415         if (!test_and_set_bit(TTY_FLUSHING, &tty->flags)) {
 416                 struct tty_buffer *head, *tail = tty->buf.tail;
 417                 int seen_tail = 0;
 418                 while ((head = tty->buf.head) != NULL) {
 419                         int count;
 420                         char *char_buf;
 421                         unsigned char *flag_buf;
 422
 423                         count = head->commit - head->read;
 424                         if (!count) {
 425                                 if (head->next == NULL)
 426                                         break;
 427                                 /*
 428                                   There's a possibility tty might get new buffer
 429                                   added during the unlock window below. We could
 430                                   end up spinning in here forever hogging the CPU
 431                                   completely. To avoid this let's have a rest each
 432                                   time we processed the tail buffer.
 433                                 */
 434                                 if (tail == head)
 435                                         seen_tail = 1;
 436                                 tty->buf.head = head->next;
 437                                 tty_buffer_free(tty, head);
 438                                 continue;
 439                         }
 440                         /* Ldisc or user is trying to flush the buffers
 441                            we are feeding to the ldisc, stop feeding the
 442                            line discipline as we want to empty the queue */
 443                         if (test_bit(TTY_FLUSHPENDING, &tty->flags))
 444                                 break;
 445                         if (!tty->receive_room || seen_tail) {
 446                                 schedule_work(&tty->buf.work);
 447                                 break;
 448                         }
 449                         if (count > tty->receive_room)
 450                                 count = tty->receive_room;
 451                         char_buf = head->char_buf_ptr + head->read;
 452                         flag_buf = head->flag_buf_ptr + head->read;
 453                         head->read += count;
 454                         spin_unlock_irqrestore(&tty->buf.lock, flags);
 455                         disc->ops->receive_buf(tty, char_buf,
 456                                                         flag_buf, count);
 457                         spin_lock_irqsave(&tty->buf.lock, flags);
 458                 }
 459                 clear_bit(TTY_FLUSHING, &tty->flags);
 460         }
 461
 462         /* We may have a deferred request to flush the input buffer,
 463            if so pull the chain under the lock and empty the queue */
 464         if (test_bit(TTY_FLUSHPENDING, &tty->flags)) {
 465                 __tty_buffer_flush(tty);
 466                 clear_bit(TTY_FLUSHPENDING, &tty->flags);
 467                 wake_up(&tty->read_wait);
 468         }
 469         spin_unlock_irqrestore(&tty->buf.lock, flags);
 470
 471         tty_ldisc_deref(disc);
 472 }
 473
 474 /**
 475  *      tty_flush_to_ldisc
 476  *      @tty: tty to push
 477  *
 478  *      Push the terminal flip buffers to the line discipline.
 479  *
 480  *      Must not be called from IRQ context.
 481  */
 482 void tty_flush_to_ldisc(struct tty_struct *tty)
 483 {
 484         flush_work(&tty->buf.work);
 485 }
 486
 487 /**
 488  *      tty_flip_buffer_push    -       terminal
 489  *      @tty: tty to push
 490  *
 491  *      Queue a push of the terminal flip buffers to the line discipline. This
 492  *      function must not be called from IRQ context if tty->low_latency is set.
 493  *
 494  *      In the event of the queue being busy for flipping the work will be
 495  *      held off and retried later.
 496  *
 497  *      Locking: tty buffer lock. Driver locks in low latency mode.
 498  */
 499
 500 void tty_flip_buffer_push(struct tty_struct *tty)
 501 {
 502         unsigned long flags;
 503         spin_lock_irqsave(&tty->buf.lock, flags);
 504         if (tty->buf.tail != NULL)
 505                 tty->buf.tail->commit = tty->buf.tail->used;
 506         spin_unlock_irqrestore(&tty->buf.lock, flags);
 507
 508         if (tty->low_latency)
 509                 flush_to_ldisc(&tty->buf.work);
 510         else
 511                 schedule_work(&tty->buf.work);
 512 }
 513 EXPORT_SYMBOL(tty_flip_buffer_push);
 514
 515 /**
 516  *      tty_buffer_init         -       prepare a tty buffer structure
 517  *      @tty: tty to initialise
 518  *
 519  *      Set up the initial state of the buffer management for a tty device.
 520  *      Must be called before the other tty buffer functions are used.
 521  *
 522  *      Locking: none
 523  */
 524
 525 void tty_buffer_init(struct tty_struct *tty)
 526 {
 527         spin_lock_init(&tty->buf.lock);
 528         tty->buf.head = NULL;
 529         tty->buf.tail = NULL;
 530         tty->buf.free = NULL;
 531         tty->buf.memory_used = 0;
 532         INIT_WORK(&tty->buf.work, flush_to_ldisc);
 533 }
 534