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/wait.h>
  15 #include <linux/bitops.h>
  16 #include <linux/delay.h>
  17 #include <linux/module.h>
  18 #include <linux/ratelimit.h>
  19
  20
  21 #define MIN_TTYB_SIZE   256
  22 #define TTYB_ALIGN_MASK 255
  23
  24 /*
  25  * Byte threshold to limit memory consumption for flip buffers.
  26  * The actual memory limit is > 2x this amount.
  27  */
  28 #define TTYB_DEFAULT_MEM_LIMIT  65536
  29
  30 /*
  31  * We default to dicing tty buffer allocations to this many characters
  32  * in order to avoid multiple page allocations. We know the size of
  33  * tty_buffer itself but it must also be taken into account that the
  34  * the buffer is 256 byte aligned. See tty_buffer_find for the allocation
  35  * logic this must match
  36  */
  37
  38 #define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
  39
  40 /**
  41  *      tty_buffer_lock_exclusive       -       gain exclusive access to buffer
  42  *      tty_buffer_unlock_exclusive     -       release exclusive access
  43  *
  44  *      @port - tty_port owning the flip buffer
  45  *
  46  *      Guarantees safe use of the line discipline's receive_buf() method by
  47  *      excluding the buffer work and any pending flush from using the flip
  48  *      buffer. Data can continue to be added concurrently to the flip buffer
  49  *      from the driver side.
  50  *
  51  *      On release, the buffer work is restarted if there is data in the
  52  *      flip buffer
  53  */
  54
  55 void tty_buffer_lock_exclusive(struct tty_port *port)
  56 {
  57         struct tty_bufhead *buf = &port->buf;
  58
  59         atomic_inc(&buf->priority);
  60         mutex_lock(&buf->lock);
  61 }
  62 EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
  63
  64 void tty_buffer_unlock_exclusive(struct tty_port *port)
  65 {
  66         struct tty_bufhead *buf = &port->buf;
  67         int restart;
  68
  69         restart = buf->head->commit != buf->head->read;
  70
  71         atomic_dec(&buf->priority);
  72         mutex_unlock(&buf->lock);
  73         if (restart)
  74                 queue_work(system_unbound_wq, &buf->work);
  75 }
  76 EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
  77
  78 /**
  79  *      tty_buffer_space_avail  -       return unused buffer space
  80  *      @port - tty_port owning the flip buffer
  81  *
  82  *      Returns the # of bytes which can be written by the driver without
  83  *      reaching the buffer limit.
  84  *
  85  *      Note: this does not guarantee that memory is available to write
  86  *      the returned # of bytes (use tty_prepare_flip_string_xxx() to
  87  *      pre-allocate if memory guarantee is required).
  88  */
  89
  90 int tty_buffer_space_avail(struct tty_port *port)
  91 {
  92         int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
  93         return max(space, 0);
  94 }
  95 EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
  96
  97 static void tty_buffer_reset(struct tty_buffer *p, size_t size)
  98 {
  99         p->used = 0;
 100         p->size = size;
 101         p->next = NULL;
 102         p->commit = 0;
 103         p->read = 0;
 104         p->flags = 0;
 105 }
 106
 107 /**
 108  *      tty_buffer_free_all             -       free buffers used by a tty
 109  *      @tty: tty to free from
 110  *
 111  *      Remove all the buffers pending on a tty whether queued with data
 112  *      or in the free ring. Must be called when the tty is no longer in use
 113  */
 114
 115 void tty_buffer_free_all(struct tty_port *port)
 116 {
 117         struct tty_bufhead *buf = &port->buf;
 118         struct tty_buffer *p, *next;
 119         struct llist_node *llist;
 120
 121         while ((p = buf->head) != NULL) {
 122                 buf->head = p->next;
 123                 if (p->size > 0)
 124                         kfree(p);
 125         }
 126         llist = llist_del_all(&buf->free);
 127         llist_for_each_entry_safe(p, next, llist, free)
 128                 kfree(p);
 129
 130         tty_buffer_reset(&buf->sentinel, 0);
 131         buf->head = &buf->sentinel;
 132         buf->tail = &buf->sentinel;
 133
 134         atomic_set(&buf->mem_used, 0);
 135 }
 136
 137 /**
 138  *      tty_buffer_alloc        -       allocate a tty buffer
 139  *      @tty: tty device
 140  *      @size: desired size (characters)
 141  *
 142  *      Allocate a new tty buffer to hold the desired number of characters.
 143  *      We round our buffers off in 256 character chunks to get better
 144  *      allocation behaviour.
 145  *      Return NULL if out of memory or the allocation would exceed the
 146  *      per device queue
 147  */
 148
 149 static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
 150 {
 151         struct llist_node *free;
 152         struct tty_buffer *p;
 153
 154         /* Round the buffer size out */
 155         size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
 156
 157         if (size <= MIN_TTYB_SIZE) {
 158                 free = llist_del_first(&port->buf.free);
 159                 if (free) {
 160                         p = llist_entry(free, struct tty_buffer, free);
 161                         goto found;
 162                 }
 163         }
 164
 165         /* Should possibly check if this fails for the largest buffer we
 166            have queued and recycle that ? */
 167         if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
 168                 return NULL;
 169         p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
 170         if (p == NULL)
 171                 return NULL;
 172
 173 found:
 174         tty_buffer_reset(p, size);
 175         atomic_add(size, &port->buf.mem_used);
 176         return p;
 177 }
 178
 179 /**
 180  *      tty_buffer_free         -       free a tty buffer
 181  *      @tty: tty owning the buffer
 182  *      @b: the buffer to free
 183  *
 184  *      Free a tty buffer, or add it to the free list according to our
 185  *      internal strategy
 186  */
 187
 188 static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
 189 {
 190         struct tty_bufhead *buf = &port->buf;
 191
 192         /* Dumb strategy for now - should keep some stats */
 193         WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
 194
 195         if (b->size > MIN_TTYB_SIZE)
 196                 kfree(b);
 197         else if (b->size > 0)
 198                 llist_add(&b->free, &buf->free);
 199 }
 200
 201 /**
 202  *      tty_buffer_flush                -       flush full tty buffers
 203  *      @tty: tty to flush
 204  *      @ld:  optional ldisc ptr (must be referenced)
 205  *
 206  *      flush all the buffers containing receive data. If ld != NULL,
 207  *      flush the ldisc input buffer.
 208  *
 209  *      Locking: takes buffer lock to ensure single-threaded flip buffer
 210  *               'consumer'
 211  */
 212
 213 void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
 214 {
 215         struct tty_port *port = tty->port;
 216         struct tty_bufhead *buf = &port->buf;
 217         struct tty_buffer *next;
 218
 219         atomic_inc(&buf->priority);
 220
 221         mutex_lock(&buf->lock);
 222         /* paired w/ release in __tty_buffer_request_room; ensures there are
 223          * no pending memory accesses to the freed buffer
 224          */
 225         while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
 226                 tty_buffer_free(port, buf->head);
 227                 buf->head = next;
 228         }
 229         buf->head->read = buf->head->commit;
 230
 231         if (ld && ld->ops->flush_buffer)
 232                 ld->ops->flush_buffer(tty);
 233
 234         atomic_dec(&buf->priority);
 235         mutex_unlock(&buf->lock);
 236 }
 237
 238 /**
 239  *      tty_buffer_request_room         -       grow tty buffer if needed
 240  *      @tty: tty structure
 241  *      @size: size desired
 242  *      @flags: buffer flags if new buffer allocated (default = 0)
 243  *
 244  *      Make at least size bytes of linear space available for the tty
 245  *      buffer. If we fail return the size we managed to find.
 246  *
 247  *      Will change over to a new buffer if the current buffer is encoded as
 248  *      TTY_NORMAL (so has no flags buffer) and the new buffer requires
 249  *      a flags buffer.
 250  */
 251 static int __tty_buffer_request_room(struct tty_port *port, size_t size,
 252                                      int flags)
 253 {
 254         struct tty_bufhead *buf = &port->buf;
 255         struct tty_buffer *b, *n;
 256         int left, change;
 257
 258         b = buf->tail;
 259         if (b->flags & TTYB_NORMAL)
 260                 left = 2 * b->size - b->used;
 261         else
 262                 left = b->size - b->used;
 263
 264         change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
 265         if (change || left < size) {
 266                 /* This is the slow path - looking for new buffers to use */
 267                 n = tty_buffer_alloc(port, size);
 268                 if (n != NULL) {
 269                         n->flags = flags;
 270                         buf->tail = n;
 271                         /* paired w/ acquire in flush_to_ldisc(); ensures
 272                          * flush_to_ldisc() sees buffer data.
 273                          */
 274                         smp_store_release(&b->commit, b->used);
 275                         /* paired w/ acquire in flush_to_ldisc(); ensures the
 276                          * latest commit value can be read before the head is
 277                          * advanced to the next buffer
 278                          */
 279                         smp_store_release(&b->next, n);
 280                 } else if (change)
 281                         size = 0;
 282                 else
 283                         size = left;
 284         }
 285         return size;
 286 }
 287
 288 int tty_buffer_request_room(struct tty_port *port, size_t size)
 289 {
 290         return __tty_buffer_request_room(port, size, 0);
 291 }
 292 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
 293
 294 /**
 295  *      tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
 296  *      @port: tty port
 297  *      @chars: characters
 298  *      @flag: flag value for each character
 299  *      @size: size
 300  *
 301  *      Queue a series of bytes to the tty buffering. All the characters
 302  *      passed are marked with the supplied flag. Returns the number added.
 303  */
 304
 305 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
 306                 const unsigned char *chars, char flag, size_t size)
 307 {
 308         int copied = 0;
 309         do {
 310                 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 311                 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
 312                 int space = __tty_buffer_request_room(port, goal, flags);
 313                 struct tty_buffer *tb = port->buf.tail;
 314                 if (unlikely(space == 0))
 315                         break;
 316                 memcpy(char_buf_ptr(tb, tb->used), chars, space);
 317                 if (~tb->flags & TTYB_NORMAL)
 318                         memset(flag_buf_ptr(tb, tb->used), flag, space);
 319                 tb->used += space;
 320                 copied += space;
 321                 chars += space;
 322                 /* There is a small chance that we need to split the data over
 323                    several buffers. If this is the case we must loop */
 324         } while (unlikely(size > copied));
 325         return copied;
 326 }
 327 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
 328
 329 /**
 330  *      tty_insert_flip_string_flags    -       Add characters to the tty buffer
 331  *      @port: tty port
 332  *      @chars: characters
 333  *      @flags: flag bytes
 334  *      @size: size
 335  *
 336  *      Queue a series of bytes to the tty buffering. For each character
 337  *      the flags array indicates the status of the character. Returns the
 338  *      number added.
 339  */
 340
 341 int tty_insert_flip_string_flags(struct tty_port *port,
 342                 const unsigned char *chars, const char *flags, size_t size)
 343 {
 344         int copied = 0;
 345         do {
 346                 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 347                 int space = tty_buffer_request_room(port, goal);
 348                 struct tty_buffer *tb = port->buf.tail;
 349                 if (unlikely(space == 0))
 350                         break;
 351                 memcpy(char_buf_ptr(tb, tb->used), chars, space);
 352                 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
 353                 tb->used += space;
 354                 copied += space;
 355                 chars += space;
 356                 flags += space;
 357                 /* There is a small chance that we need to split the data over
 358                    several buffers. If this is the case we must loop */
 359         } while (unlikely(size > copied));
 360         return copied;
 361 }
 362 EXPORT_SYMBOL(tty_insert_flip_string_flags);
 363
 364 /**
 365  *      tty_schedule_flip       -       push characters to ldisc
 366  *      @port: tty port to push from
 367  *
 368  *      Takes any pending buffers and transfers their ownership to the
 369  *      ldisc side of the queue. It then schedules those characters for
 370  *      processing by the line discipline.
 371  */
 372
 373 void tty_schedule_flip(struct tty_port *port)
 374 {
 375         struct tty_bufhead *buf = &port->buf;
 376
 377         /* paired w/ acquire in flush_to_ldisc(); ensures
 378          * flush_to_ldisc() sees buffer data.
 379          */
 380         smp_store_release(&buf->tail->commit, buf->tail->used);
 381         queue_work(system_unbound_wq, &buf->work);
 382 }
 383 EXPORT_SYMBOL(tty_schedule_flip);
 384
 385 /**
 386  *      tty_prepare_flip_string         -       make room for characters
 387  *      @port: tty port
 388  *      @chars: return pointer for character write area
 389  *      @size: desired size
 390  *
 391  *      Prepare a block of space in the buffer for data. Returns the length
 392  *      available and buffer pointer to the space which is now allocated and
 393  *      accounted for as ready for normal characters. This is used for drivers
 394  *      that need their own block copy routines into the buffer. There is no
 395  *      guarantee the buffer is a DMA target!
 396  */
 397
 398 int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
 399                 size_t size)
 400 {
 401         int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
 402         if (likely(space)) {
 403                 struct tty_buffer *tb = port->buf.tail;
 404                 *chars = char_buf_ptr(tb, tb->used);
 405                 if (~tb->flags & TTYB_NORMAL)
 406                         memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
 407                 tb->used += space;
 408         }
 409         return space;
 410 }
 411 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
 412
 413 /**
 414  *      tty_ldisc_receive_buf           -       forward data to line discipline
 415  *      @ld:    line discipline to process input
 416  *      @p:     char buffer
 417  *      @f:     TTY_* flags buffer
 418  *      @count: number of bytes to process
 419  *
 420  *      Callers other than flush_to_ldisc() need to exclude the kworker
 421  *      from concurrent use of the line discipline, see paste_selection().
 422  *
 423  *      Returns the number of bytes not processed
 424  */
 425 int tty_ldisc_receive_buf(struct tty_ldisc *ld, unsigned char *p,
 426                           char *f, int count)
 427 {
 428         if (ld->ops->receive_buf2)
 429                 count = ld->ops->receive_buf2(ld->tty, p, f, count);
 430         else {
 431                 count = min_t(int, count, ld->tty->receive_room);
 432                 if (count && ld->ops->receive_buf)
 433                         ld->ops->receive_buf(ld->tty, p, f, count);
 434         }
 435         return count;
 436 }
 437 EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
 438
 439 static int
 440 receive_buf(struct tty_ldisc *ld, struct tty_buffer *head, int count)
 441 {
 442         unsigned char *p = char_buf_ptr(head, head->read);
 443         char          *f = NULL;
 444
 445         if (~head->flags & TTYB_NORMAL)
 446                 f = flag_buf_ptr(head, head->read);
 447
 448         return tty_ldisc_receive_buf(ld, p, f, count);
 449 }
 450
 451 /**
 452  *      flush_to_ldisc
 453  *      @work: tty structure passed from work queue.
 454  *
 455  *      This routine is called out of the software interrupt to flush data
 456  *      from the buffer chain to the line discipline.
 457  *
 458  *      The receive_buf method is single threaded for each tty instance.
 459  *
 460  *      Locking: takes buffer lock to ensure single-threaded flip buffer
 461  *               'consumer'
 462  */
 463
 464 static void flush_to_ldisc(struct work_struct *work)
 465 {
 466         struct tty_port *port = container_of(work, struct tty_port, buf.work);
 467         struct tty_bufhead *buf = &port->buf;
 468         struct tty_struct *tty;
 469         struct tty_ldisc *disc;
 470
 471         tty = READ_ONCE(port->itty);
 472         if (tty == NULL)
 473                 return;
 474
 475         disc = tty_ldisc_ref(tty);
 476         if (disc == NULL)
 477                 return;
 478
 479         mutex_lock(&buf->lock);
 480
 481         while (1) {
 482                 struct tty_buffer *head = buf->head;
 483                 struct tty_buffer *next;
 484                 int count;
 485
 486                 /* Ldisc or user is trying to gain exclusive access */
 487                 if (atomic_read(&buf->priority))
 488                         break;
 489
 490                 /* paired w/ release in __tty_buffer_request_room();
 491                  * ensures commit value read is not stale if the head
 492                  * is advancing to the next buffer
 493                  */
 494                 next = smp_load_acquire(&head->next);
 495                 /* paired w/ release in __tty_buffer_request_room() or in
 496                  * tty_buffer_flush(); ensures we see the committed buffer data
 497                  */
 498                 count = smp_load_acquire(&head->commit) - head->read;
 499                 if (!count) {
 500                         if (next == NULL)
 501                                 break;
 502                         buf->head = next;
 503                         tty_buffer_free(port, head);
 504                         continue;
 505                 }
 506
 507                 count = receive_buf(disc, head, count);
 508                 if (!count)
 509                         break;
 510                 head->read += count;
 511         }
 512
 513         mutex_unlock(&buf->lock);
 514
 515         tty_ldisc_deref(disc);
 516 }
 517
 518 /**
 519  *      tty_flip_buffer_push    -       terminal
 520  *      @port: tty port to push
 521  *
 522  *      Queue a push of the terminal flip buffers to the line discipline.
 523  *      Can be called from IRQ/atomic context.
 524  *
 525  *      In the event of the queue being busy for flipping the work will be
 526  *      held off and retried later.
 527  */
 528
 529 void tty_flip_buffer_push(struct tty_port *port)
 530 {
 531         tty_schedule_flip(port);
 532 }
 533 EXPORT_SYMBOL(tty_flip_buffer_push);
 534
 535 /**
 536  *      tty_buffer_init         -       prepare a tty buffer structure
 537  *      @tty: tty to initialise
 538  *
 539  *      Set up the initial state of the buffer management for a tty device.
 540  *      Must be called before the other tty buffer functions are used.
 541  */
 542
 543 void tty_buffer_init(struct tty_port *port)
 544 {
 545         struct tty_bufhead *buf = &port->buf;
 546
 547         mutex_init(&buf->lock);
 548         tty_buffer_reset(&buf->sentinel, 0);
 549         buf->head = &buf->sentinel;
 550         buf->tail = &buf->sentinel;
 551         init_llist_head(&buf->free);
 552         atomic_set(&buf->mem_used, 0);
 553         atomic_set(&buf->priority, 0);
 554         INIT_WORK(&buf->work, flush_to_ldisc);
 555         buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
 556 }
 557
 558 /**
 559  *      tty_buffer_set_limit    -       change the tty buffer memory limit
 560  *      @port: tty port to change
 561  *
 562  *      Change the tty buffer memory limit.
 563  *      Must be called before the other tty buffer functions are used.
 564  */
 565
 566 int tty_buffer_set_limit(struct tty_port *port, int limit)
 567 {
 568         if (limit < MIN_TTYB_SIZE)
 569                 return -EINVAL;
 570         port->buf.mem_limit = limit;
 571         return 0;
 572 }
 573 EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
 574
 575 /* slave ptys can claim nested buffer lock when handling BRK and INTR */
 576 void tty_buffer_set_lock_subclass(struct tty_port *port)
 577 {
 578         lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
 579 }
 580
 581 bool tty_buffer_restart_work(struct tty_port *port)
 582 {
 583         return queue_work(system_unbound_wq, &port->buf.work);
 584 }
 585
 586 bool tty_buffer_cancel_work(struct tty_port *port)
 587 {
 588         return cancel_work_sync(&port->buf.work);
 589 }
 590
 591 void tty_buffer_flush_work(struct tty_port *port)
 592 {
 593         flush_work(&port->buf.work);
 594 }