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