drivers/char/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  -       Add characters to the tty buffer
 235  *      @tty: tty structure
 236  *      @chars: characters
 237  *      @size: size
 238  *
 239  *      Queue a series of bytes to the tty buffering. All the characters
 240  *      passed are marked as without error. Returns the number added.
 241  *
 242  *      Locking: Called functions may take tty->buf.lock
 243  */
 244
 245 int tty_insert_flip_string(struct tty_struct *tty, const unsigned char *chars,
 246                                 size_t size)
 247 {
 248         int copied = 0;
 249         do {
 250                 int space = tty_buffer_request_room(tty, size - copied);
 251                 struct tty_buffer *tb = tty->buf.tail;
 252                 /* If there is no space then tb may be NULL */
 253                 if (unlikely(space == 0))
 254                         break;
 255                 memcpy(tb->char_buf_ptr + tb->used, chars, space);
 256                 memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
 257                 tb->used += space;
 258                 copied += space;
 259                 chars += space;
 260                 /* There is a small chance that we need to split the data over
 261                    several buffers. If this is the case we must loop */
 262         } while (unlikely(size > copied));
 263         return copied;
 264 }
 265 EXPORT_SYMBOL(tty_insert_flip_string);
 266
 267 /**
 268  *      tty_insert_flip_string_flags    -       Add characters to the tty buffer
 269  *      @tty: tty structure
 270  *      @chars: characters
 271  *      @flags: flag bytes
 272  *      @size: size
 273  *
 274  *      Queue a series of bytes to the tty buffering. For each character
 275  *      the flags array indicates the status of the character. Returns the
 276  *      number added.
 277  *
 278  *      Locking: Called functions may take tty->buf.lock
 279  */
 280
 281 int tty_insert_flip_string_flags(struct tty_struct *tty,
 282                 const unsigned char *chars, const char *flags, size_t size)
 283 {
 284         int copied = 0;
 285         do {
 286                 int space = tty_buffer_request_room(tty, size - copied);
 287                 struct tty_buffer *tb = tty->buf.tail;
 288                 /* If there is no space then tb may be NULL */
 289                 if (unlikely(space == 0))
 290                         break;
 291                 memcpy(tb->char_buf_ptr + tb->used, chars, space);
 292                 memcpy(tb->flag_buf_ptr + tb->used, flags, space);
 293                 tb->used += space;
 294                 copied += space;
 295                 chars += space;
 296                 flags += space;
 297                 /* There is a small chance that we need to split the data over
 298                    several buffers. If this is the case we must loop */
 299         } while (unlikely(size > copied));
 300         return copied;
 301 }
 302 EXPORT_SYMBOL(tty_insert_flip_string_flags);
 303
 304 /**
 305  *      tty_schedule_flip       -       push characters to ldisc
 306  *      @tty: tty to push from
 307  *
 308  *      Takes any pending buffers and transfers their ownership to the
 309  *      ldisc side of the queue. It then schedules those characters for
 310  *      processing by the line discipline.
 311  *
 312  *      Locking: Takes tty->buf.lock
 313  */
 314
 315 void tty_schedule_flip(struct tty_struct *tty)
 316 {
 317         unsigned long flags;
 318         spin_lock_irqsave(&tty->buf.lock, flags);
 319         if (tty->buf.tail != NULL)
 320                 tty->buf.tail->commit = tty->buf.tail->used;
 321         spin_unlock_irqrestore(&tty->buf.lock, flags);
 322         schedule_delayed_work(&tty->buf.work, 1);
 323 }
 324 EXPORT_SYMBOL(tty_schedule_flip);
 325
 326 /**
 327  *      tty_prepare_flip_string         -       make room for characters
 328  *      @tty: tty
 329  *      @chars: return pointer for character write area
 330  *      @size: desired size
 331  *
 332  *      Prepare a block of space in the buffer for data. Returns the length
 333  *      available and buffer pointer to the space which is now allocated and
 334  *      accounted for as ready for normal characters. This is used for drivers
 335  *      that need their own block copy routines into the buffer. There is no
 336  *      guarantee the buffer is a DMA target!
 337  *
 338  *      Locking: May call functions taking tty->buf.lock
 339  */
 340
 341 int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars,
 342                                                                 size_t size)
 343 {
 344         int space = tty_buffer_request_room(tty, size);
 345         if (likely(space)) {
 346                 struct tty_buffer *tb = tty->buf.tail;
 347                 *chars = tb->char_buf_ptr + tb->used;
 348                 memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
 349                 tb->used += space;
 350         }
 351         return space;
 352 }
 353 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
 354
 355 /**
 356  *      tty_prepare_flip_string_flags   -       make room for characters
 357  *      @tty: tty
 358  *      @chars: return pointer for character write area
 359  *      @flags: return pointer for status flag write area
 360  *      @size: desired size
 361  *
 362  *      Prepare a block of space in the buffer for data. Returns the length
 363  *      available and buffer pointer to the space which is now allocated and
 364  *      accounted for as ready for characters. This is used for drivers
 365  *      that need their own block copy routines into the buffer. There is no
 366  *      guarantee the buffer is a DMA target!
 367  *
 368  *      Locking: May call functions taking tty->buf.lock
 369  */
 370
 371 int tty_prepare_flip_string_flags(struct tty_struct *tty,
 372                         unsigned char **chars, char **flags, size_t size)
 373 {
 374         int space = tty_buffer_request_room(tty, size);
 375         if (likely(space)) {
 376                 struct tty_buffer *tb = tty->buf.tail;
 377                 *chars = tb->char_buf_ptr + tb->used;
 378                 *flags = tb->flag_buf_ptr + tb->used;
 379                 tb->used += space;
 380         }
 381         return space;
 382 }
 383 EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
 384
 385
 386
 387 /**
 388  *      flush_to_ldisc
 389  *      @work: tty structure passed from work queue.
 390  *
 391  *      This routine is called out of the software interrupt to flush data
 392  *      from the buffer chain to the line discipline.
 393  *
 394  *      Locking: holds tty->buf.lock to guard buffer list. Drops the lock
 395  *      while invoking the line discipline receive_buf method. The
 396  *      receive_buf method is single threaded for each tty instance.
 397  */
 398
 399 static void flush_to_ldisc(struct work_struct *work)
 400 {
 401         struct tty_struct *tty =
 402                 container_of(work, struct tty_struct, buf.work.work);
 403         unsigned long   flags;
 404         struct tty_ldisc *disc;
 405         struct tty_buffer *tbuf, *head;
 406         char *char_buf;
 407         unsigned char *flag_buf;
 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         /* So we know a flush is running */
 415         set_bit(TTY_FLUSHING, &tty->flags);
 416         head = tty->buf.head;
 417         if (head != NULL) {
 418                 tty->buf.head = NULL;
 419                 for (;;) {
 420                         int count = head->commit - head->read;
 421                         if (!count) {
 422                                 if (head->next == NULL)
 423                                         break;
 424                                 tbuf = head;
 425                                 head = head->next;
 426                                 tty_buffer_free(tty, tbuf);
 427                                 continue;
 428                         }
 429                         /* Ldisc or user is trying to flush the buffers
 430                            we are feeding to the ldisc, stop feeding the
 431                            line discipline as we want to empty the queue */
 432                         if (test_bit(TTY_FLUSHPENDING, &tty->flags))
 433                                 break;
 434                         if (!tty->receive_room) {
 435                                 schedule_delayed_work(&tty->buf.work, 1);
 436                                 break;
 437                         }
 438                         if (count > tty->receive_room)
 439                                 count = tty->receive_room;
 440                         char_buf = head->char_buf_ptr + head->read;
 441                         flag_buf = head->flag_buf_ptr + head->read;
 442                         head->read += count;
 443                         spin_unlock_irqrestore(&tty->buf.lock, flags);
 444                         disc->ops->receive_buf(tty, char_buf,
 445                                                         flag_buf, count);
 446                         spin_lock_irqsave(&tty->buf.lock, flags);
 447                 }
 448                 /* Restore the queue head */
 449                 tty->buf.head = head;
 450         }
 451         /* We may have a deferred request to flush the input buffer,
 452            if so pull the chain under the lock and empty the queue */
 453         if (test_bit(TTY_FLUSHPENDING, &tty->flags)) {
 454                 __tty_buffer_flush(tty);
 455                 clear_bit(TTY_FLUSHPENDING, &tty->flags);
 456                 wake_up(&tty->read_wait);
 457         }
 458         clear_bit(TTY_FLUSHING, &tty->flags);
 459         spin_unlock_irqrestore(&tty->buf.lock, flags);
 460
 461         tty_ldisc_deref(disc);
 462 }
 463
 464 /**
 465  *      tty_flip_buffer_push    -       terminal
 466  *      @tty: tty to push
 467  *
 468  *      Queue a push of the terminal flip buffers to the line discipline. This
 469  *      function must not be called from IRQ context if tty->low_latency is set.
 470  *
 471  *      In the event of the queue being busy for flipping the work will be
 472  *      held off and retried later.
 473  *
 474  *      Locking: tty buffer lock. Driver locks in low latency mode.
 475  */
 476
 477 void tty_flip_buffer_push(struct tty_struct *tty)
 478 {
 479         unsigned long flags;
 480         spin_lock_irqsave(&tty->buf.lock, flags);
 481         if (tty->buf.tail != NULL)
 482                 tty->buf.tail->commit = tty->buf.tail->used;
 483         spin_unlock_irqrestore(&tty->buf.lock, flags);
 484
 485         if (tty->low_latency)
 486                 flush_to_ldisc(&tty->buf.work.work);
 487         else
 488                 schedule_delayed_work(&tty->buf.work, 1);
 489 }
 490 EXPORT_SYMBOL(tty_flip_buffer_push);
 491
 492 /**
 493  *      tty_buffer_init         -       prepare a tty buffer structure
 494  *      @tty: tty to initialise
 495  *
 496  *      Set up the initial state of the buffer management for a tty device.
 497  *      Must be called before the other tty buffer functions are used.
 498  *
 499  *      Locking: none
 500  */
 501
 502 void tty_buffer_init(struct tty_struct *tty)
 503 {
 504         spin_lock_init(&tty->buf.lock);
 505         tty->buf.head = NULL;
 506         tty->buf.tail = NULL;
 507         tty->buf.free = NULL;
 508         tty->buf.memory_used = 0;
 509         INIT_DELAYED_WORK(&tty->buf.work, flush_to_ldisc);
 510 }
 511