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         if (tty->buf.head == NULL)
 118                 return;
 119         while ((thead = tty->buf.head->next) != NULL) {
 120                 tty_buffer_free(tty, tty->buf.head);
 121                 tty->buf.head = thead;
 122         }
 123         WARN_ON(tty->buf.head != tty->buf.tail);
 124         tty->buf.head->read = tty->buf.head->commit;
 125 }
 126
 127 /**
 128  *      tty_buffer_flush                -       flush full tty buffers
 129  *      @tty: tty to flush
 130  *
 131  *      flush all the buffers containing receive data. If the buffer is
 132  *      being processed by flush_to_ldisc then we defer the processing
 133  *      to that function
 134  *
 135  *      Locking: none
 136  */
 137
 138 void tty_buffer_flush(struct tty_struct *tty)
 139 {
 140         unsigned long flags;
 141         spin_lock_irqsave(&tty->buf.lock, flags);
 142
 143         /* If the data is being pushed to the tty layer then we can't
 144            process it here. Instead set a flag and the flush_to_ldisc
 145            path will process the flush request before it exits */
 146         if (test_bit(TTY_FLUSHING, &tty->flags)) {
 147                 set_bit(TTY_FLUSHPENDING, &tty->flags);
 148                 spin_unlock_irqrestore(&tty->buf.lock, flags);
 149                 wait_event(tty->read_wait,
 150                                 test_bit(TTY_FLUSHPENDING, &tty->flags) == 0);
 151                 return;
 152         } else
 153                 __tty_buffer_flush(tty);
 154         spin_unlock_irqrestore(&tty->buf.lock, flags);
 155 }
 156
 157 /**
 158  *      tty_buffer_find         -       find a free tty buffer
 159  *      @tty: tty owning the buffer
 160  *      @size: characters wanted
 161  *
 162  *      Locate an existing suitable tty buffer or if we are lacking one then
 163  *      allocate a new one. We round our buffers off in 256 character chunks
 164  *      to get better allocation behaviour.
 165  *
 166  *      Locking: Caller must hold tty->buf.lock
 167  */
 168
 169 static struct tty_buffer *tty_buffer_find(struct tty_struct *tty, size_t size)
 170 {
 171         struct tty_buffer **tbh = &tty->buf.free;
 172         while ((*tbh) != NULL) {
 173                 struct tty_buffer *t = *tbh;
 174                 if (t->size >= size) {
 175                         *tbh = t->next;
 176                         t->next = NULL;
 177                         t->used = 0;
 178                         t->commit = 0;
 179                         t->read = 0;
 180                         tty->buf.memory_used += t->size;
 181                         return t;
 182                 }
 183                 tbh = &((*tbh)->next);
 184         }
 185         /* Round the buffer size out */
 186         size = (size + 0xFF) & ~0xFF;
 187         return tty_buffer_alloc(tty, size);
 188         /* Should possibly check if this fails for the largest buffer we
 189            have queued and recycle that ? */
 190 }
 191
 192 /**
 193  *      tty_buffer_request_room         -       grow tty buffer if needed
 194  *      @tty: tty structure
 195  *      @size: size desired
 196  *
 197  *      Make at least size bytes of linear space available for the tty
 198  *      buffer. If we fail return the size we managed to find.
 199  *
 200  *      Locking: Takes tty->buf.lock
 201  */
 202 int tty_buffer_request_room(struct tty_struct *tty, size_t size)
 203 {
 204         struct tty_buffer *b, *n;
 205         int left;
 206         unsigned long flags;
 207
 208         spin_lock_irqsave(&tty->buf.lock, flags);
 209
 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         if ((b = tty->buf.tail) != NULL)
 214                 left = b->size - b->used;
 215         else
 216                 left = 0;
 217
 218         if (left < size) {
 219                 /* This is the slow path - looking for new buffers to use */
 220                 if ((n = tty_buffer_find(tty, size)) != NULL) {
 221                         if (b != NULL) {
 222                                 b->next = n;
 223                                 b->commit = b->used;
 224                         } else
 225                                 tty->buf.head = n;
 226                         tty->buf.tail = n;
 227                 } else
 228                         size = left;
 229         }
 230
 231         spin_unlock_irqrestore(&tty->buf.lock, flags);
 232         return size;
 233 }
 234 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
 235
 236 /**
 237  *      tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
 238  *      @tty: tty structure
 239  *      @chars: characters
 240  *      @flag: flag value for each character
 241  *      @size: size
 242  *
 243  *      Queue a series of bytes to the tty buffering. All the characters
 244  *      passed are marked with the supplied flag. Returns the number added.
 245  *
 246  *      Locking: Called functions may take tty->buf.lock
 247  */
 248
 249 int tty_insert_flip_string_fixed_flag(struct tty_struct *tty,
 250                 const unsigned char *chars, char flag, size_t size)
 251 {
 252         int copied = 0;
 253         do {
 254                 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 255                 int space = tty_buffer_request_room(tty, goal);
 256                 struct tty_buffer *tb = tty->buf.tail;
 257                 /* If there is no space then tb may be NULL */
 258                 if (unlikely(space == 0))
 259                         break;
 260                 memcpy(tb->char_buf_ptr + tb->used, chars, space);
 261                 memset(tb->flag_buf_ptr + tb->used, flag, space);
 262                 tb->used += space;
 263                 copied += space;
 264                 chars += space;
 265                 /* There is a small chance that we need to split the data over
 266                    several buffers. If this is the case we must loop */
 267         } while (unlikely(size > copied));
 268         return copied;
 269 }
 270 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
 271
 272 /**
 273  *      tty_insert_flip_string_flags    -       Add characters to the tty buffer
 274  *      @tty: tty structure
 275  *      @chars: characters
 276  *      @flags: flag bytes
 277  *      @size: size
 278  *
 279  *      Queue a series of bytes to the tty buffering. For each character
 280  *      the flags array indicates the status of the character. Returns the
 281  *      number added.
 282  *
 283  *      Locking: Called functions may take tty->buf.lock
 284  */
 285
 286 int tty_insert_flip_string_flags(struct tty_struct *tty,
 287                 const unsigned char *chars, const char *flags, size_t size)
 288 {
 289         int copied = 0;
 290         do {
 291                 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 292                 int space = tty_buffer_request_room(tty, goal);
 293                 struct tty_buffer *tb = tty->buf.tail;
 294                 /* If there is no space then tb may be NULL */
 295                 if (unlikely(space == 0))
 296                         break;
 297                 memcpy(tb->char_buf_ptr + tb->used, chars, space);
 298                 memcpy(tb->flag_buf_ptr + tb->used, flags, space);
 299                 tb->used += space;
 300                 copied += space;
 301                 chars += space;
 302                 flags += space;
 303                 /* There is a small chance that we need to split the data over
 304                    several buffers. If this is the case we must loop */
 305         } while (unlikely(size > copied));
 306         return copied;
 307 }
 308 EXPORT_SYMBOL(tty_insert_flip_string_flags);
 309
 310 /**
 311  *      tty_schedule_flip       -       push characters to ldisc
 312  *      @tty: tty to push from
 313  *
 314  *      Takes any pending buffers and transfers their ownership to the
 315  *      ldisc side of the queue. It then schedules those characters for
 316  *      processing by the line discipline.
 317  *
 318  *      Locking: Takes tty->buf.lock
 319  */
 320
 321 void tty_schedule_flip(struct tty_struct *tty)
 322 {
 323         unsigned long flags;
 324         spin_lock_irqsave(&tty->buf.lock, flags);
 325         if (tty->buf.tail != NULL)
 326                 tty->buf.tail->commit = tty->buf.tail->used;
 327         spin_unlock_irqrestore(&tty->buf.lock, flags);
 328         schedule_work(&tty->buf.work);
 329 }
 330 EXPORT_SYMBOL(tty_schedule_flip);
 331
 332 /**
 333  *      tty_prepare_flip_string         -       make room for characters
 334  *      @tty: tty
 335  *      @chars: return pointer for character write area
 336  *      @size: desired size
 337  *
 338  *      Prepare a block of space in the buffer for data. Returns the length
 339  *      available and buffer pointer to the space which is now allocated and
 340  *      accounted for as ready for normal characters. This is used for drivers
 341  *      that need their own block copy routines into the buffer. There is no
 342  *      guarantee the buffer is a DMA target!
 343  *
 344  *      Locking: May call functions taking tty->buf.lock
 345  */
 346
 347 int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars,
 348                                                                 size_t size)
 349 {
 350         int space = tty_buffer_request_room(tty, size);
 351         if (likely(space)) {
 352                 struct tty_buffer *tb = tty->buf.tail;
 353                 *chars = tb->char_buf_ptr + tb->used;
 354                 memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
 355                 tb->used += space;
 356         }
 357         return space;
 358 }
 359 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
 360
 361 /**
 362  *      tty_prepare_flip_string_flags   -       make room for characters
 363  *      @tty: tty
 364  *      @chars: return pointer for character write area
 365  *      @flags: return pointer for status flag write area
 366  *      @size: desired size
 367  *
 368  *      Prepare a block of space in the buffer for data. Returns the length
 369  *      available and buffer pointer to the space which is now allocated and
 370  *      accounted for as ready for characters. This is used for drivers
 371  *      that need their own block copy routines into the buffer. There is no
 372  *      guarantee the buffer is a DMA target!
 373  *
 374  *      Locking: May call functions taking tty->buf.lock
 375  */
 376
 377 int tty_prepare_flip_string_flags(struct tty_struct *tty,
 378                         unsigned char **chars, char **flags, size_t size)
 379 {
 380         int space = tty_buffer_request_room(tty, size);
 381         if (likely(space)) {
 382                 struct tty_buffer *tb = tty->buf.tail;
 383                 *chars = tb->char_buf_ptr + tb->used;
 384                 *flags = tb->flag_buf_ptr + tb->used;
 385                 tb->used += space;
 386         }
 387         return space;
 388 }
 389 EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
 390
 391
 392
 393 /**
 394  *      flush_to_ldisc
 395  *      @work: tty structure passed from work queue.
 396  *
 397  *      This routine is called out of the software interrupt to flush data
 398  *      from the buffer chain to the line discipline.
 399  *
 400  *      Locking: holds tty->buf.lock to guard buffer list. Drops the lock
 401  *      while invoking the line discipline receive_buf method. The
 402  *      receive_buf method is single threaded for each tty instance.
 403  */
 404
 405 static void flush_to_ldisc(struct work_struct *work)
 406 {
 407         struct tty_struct *tty =
 408                 container_of(work, struct tty_struct, buf.work);
 409         unsigned long   flags;
 410         struct tty_ldisc *disc;
 411
 412         disc = tty_ldisc_ref(tty);
 413         if (disc == NULL)       /*  !TTY_LDISC */
 414                 return;
 415
 416         spin_lock_irqsave(&tty->buf.lock, flags);
 417
 418         if (!test_and_set_bit(TTY_FLUSHING, &tty->flags)) {
 419                 struct tty_buffer *head;
 420                 while ((head = tty->buf.head) != NULL) {
 421                         int count;
 422                         char *char_buf;
 423                         unsigned char *flag_buf;
 424
 425                         count = head->commit - head->read;
 426                         if (!count) {
 427                                 if (head->next == NULL)
 428                                         break;
 429                                 tty->buf.head = head->next;
 430                                 tty_buffer_free(tty, head);
 431                                 continue;
 432                         }
 433                         /* Ldisc or user is trying to flush the buffers
 434                            we are feeding to the ldisc, stop feeding the
 435                            line discipline as we want to empty the queue */
 436                         if (test_bit(TTY_FLUSHPENDING, &tty->flags))
 437                                 break;
 438                         if (!tty->receive_room)
 439                                 break;
 440                         if (count > tty->receive_room)
 441                                 count = tty->receive_room;
 442                         char_buf = head->char_buf_ptr + head->read;
 443                         flag_buf = head->flag_buf_ptr + head->read;
 444                         head->read += count;
 445                         if (disc->ops->receive_buf) {
 446                                 spin_unlock_irqrestore(&tty->buf.lock, flags);
 447                                 disc->ops->receive_buf(tty, char_buf,
 448                                                         flag_buf, count);
 449                                 spin_lock_irqsave(&tty->buf.lock, flags);
 450                         }
 451                 }
 452                 clear_bit(TTY_FLUSHING, &tty->flags);
 453         }
 454
 455         /* We may have a deferred request to flush the input buffer,
 456            if so pull the chain under the lock and empty the queue */
 457         if (test_bit(TTY_FLUSHPENDING, &tty->flags)) {
 458                 __tty_buffer_flush(tty);
 459                 clear_bit(TTY_FLUSHPENDING, &tty->flags);
 460                 wake_up(&tty->read_wait);
 461         }
 462         spin_unlock_irqrestore(&tty->buf.lock, flags);
 463
 464         tty_ldisc_deref(disc);
 465 }
 466
 467 /**
 468  *      tty_flush_to_ldisc
 469  *      @tty: tty to push
 470  *
 471  *      Push the terminal flip buffers to the line discipline.
 472  *
 473  *      Must not be called from IRQ context.
 474  */
 475 void tty_flush_to_ldisc(struct tty_struct *tty)
 476 {
 477         flush_work(&tty->buf.work);
 478 }
 479
 480 /**
 481  *      tty_flip_buffer_push    -       terminal
 482  *      @tty: tty to push
 483  *
 484  *      Queue a push of the terminal flip buffers to the line discipline. This
 485  *      function must not be called from IRQ context if tty->low_latency is set.
 486  *
 487  *      In the event of the queue being busy for flipping the work will be
 488  *      held off and retried later.
 489  *
 490  *      Locking: tty buffer lock. Driver locks in low latency mode.
 491  */
 492
 493 void tty_flip_buffer_push(struct tty_struct *tty)
 494 {
 495         unsigned long flags;
 496         spin_lock_irqsave(&tty->buf.lock, flags);
 497         if (tty->buf.tail != NULL)
 498                 tty->buf.tail->commit = tty->buf.tail->used;
 499         spin_unlock_irqrestore(&tty->buf.lock, flags);
 500
 501         if (tty->low_latency)
 502                 flush_to_ldisc(&tty->buf.work);
 503         else
 504                 schedule_work(&tty->buf.work);
 505 }
 506 EXPORT_SYMBOL(tty_flip_buffer_push);
 507
 508 /**
 509  *      tty_buffer_init         -       prepare a tty buffer structure
 510  *      @tty: tty to initialise
 511  *
 512  *      Set up the initial state of the buffer management for a tty device.
 513  *      Must be called before the other tty buffer functions are used.
 514  *
 515  *      Locking: none
 516  */
 517
 518 void tty_buffer_init(struct tty_struct *tty)
 519 {
 520         spin_lock_init(&tty->buf.lock);
 521         tty->buf.head = NULL;
 522         tty->buf.tail = NULL;
 523         tty->buf.free = NULL;
 524         tty->buf.memory_used = 0;
 525         INIT_WORK(&tty->buf.work, flush_to_ldisc);
 526 }
 527