root/drivers/tty/tty_buffer.c

DEFINITIONS

1. tty_buffer_unlock_exclusive
2. tty_buffer_space_avail
3. tty_buffer_reset
4. tty_buffer_free_all
5. tty_buffer_alloc
6. tty_buffer_free
7. tty_buffer_flush
8. __tty_buffer_request_room
9. tty_buffer_request_room
10. tty_insert_flip_string_fixed_flag
11. tty_insert_flip_string_flags
12. __tty_insert_flip_char
13. tty_schedule_flip
14. tty_prepare_flip_string
15. tty_ldisc_receive_buf
16. receive_buf
17. flush_to_ldisc
18. tty_flip_buffer_push
19. tty_buffer_init
20. tty_buffer_set_limit
21. tty_buffer_set_lock_subclass
22. tty_buffer_restart_work
23. tty_buffer_cancel_work
24. tty_buffer_flush_work

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Tty buffer allocation management
   4  */
   5 
   6 #include <linux/types.h>
   7 #include <linux/errno.h>
   8 #include <linux/tty.h>
   9 #include <linux/tty_driver.h>
  10 #include <linux/tty_flip.h>
  11 #include <linux/timer.h>
  12 #include <linux/string.h>
  13 #include <linux/slab.h>
  14 #include <linux/sched.h>
  15 #include <linux/wait.h>
  16 #include <linux/bitops.h>
  17 #include <linux/delay.h>
  18 #include <linux/module.h>
  19 #include <linux/ratelimit.h>
  20 
  21 
  22 #define MIN_TTYB_SIZE   256
  23 #define TTYB_ALIGN_MASK 255
  24 
  25 /*
  26  * Byte threshold to limit memory consumption for flip buffers.
  27  * The actual memory limit is > 2x this amount.
  28  */
  29 #define TTYB_DEFAULT_MEM_LIMIT  (640 * 1024UL)
  30 
  31 /*
  32  * We default to dicing tty buffer allocations to this many characters
  33  * in order to avoid multiple page allocations. We know the size of
  34  * tty_buffer itself but it must also be taken into account that the
  35  * the buffer is 256 byte aligned. See tty_buffer_find for the allocation
  36  * logic this must match
  37  */
  38 
  39 #define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
  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         unsigned int freed = 0;
 122         int still_used;
 123 
 124         while ((p = buf->head) != NULL) {
 125                 buf->head = p->next;
 126                 freed += p->size;
 127                 if (p->size > 0)
 128                         kfree(p);
 129         }
 130         llist = llist_del_all(&buf->free);
 131         llist_for_each_entry_safe(p, next, llist, free)
 132                 kfree(p);
 133 
 134         tty_buffer_reset(&buf->sentinel, 0);
 135         buf->head = &buf->sentinel;
 136         buf->tail = &buf->sentinel;
 137 
 138         still_used = atomic_xchg(&buf->mem_used, 0);
 139         WARN(still_used != freed, "we still have not freed %d bytes!",
 140                         still_used - freed);
 141 }
 142 
 143 /**
 144  *      tty_buffer_alloc        -       allocate a tty buffer
 145  *      @tty: tty device
 146  *      @size: desired size (characters)
 147  *
 148  *      Allocate a new tty buffer to hold the desired number of characters.
 149  *      We round our buffers off in 256 character chunks to get better
 150  *      allocation behaviour.
 151  *      Return NULL if out of memory or the allocation would exceed the
 152  *      per device queue
 153  */
 154 
 155 static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
 156 {
 157         struct llist_node *free;
 158         struct tty_buffer *p;
 159 
 160         /* Round the buffer size out */
 161         size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
 162 
 163         if (size <= MIN_TTYB_SIZE) {
 164                 free = llist_del_first(&port->buf.free);
 165                 if (free) {
 166                         p = llist_entry(free, struct tty_buffer, free);
 167                         goto found;
 168                 }
 169         }
 170 
 171         /* Should possibly check if this fails for the largest buffer we
 172            have queued and recycle that ? */
 173         if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
 174                 return NULL;
 175         p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
 176         if (p == NULL)
 177                 return NULL;
 178 
 179 found:
 180         tty_buffer_reset(p, size);
 181         atomic_add(size, &port->buf.mem_used);
 182         return p;
 183 }
 184 
 185 /**
 186  *      tty_buffer_free         -       free a tty buffer
 187  *      @tty: tty owning the buffer
 188  *      @b: the buffer to free
 189  *
 190  *      Free a tty buffer, or add it to the free list according to our
 191  *      internal strategy
 192  */
 193 
 194 static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
 195 {
 196         struct tty_bufhead *buf = &port->buf;
 197 
 198         /* Dumb strategy for now - should keep some stats */
 199         WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
 200 
 201         if (b->size > MIN_TTYB_SIZE)
 202                 kfree(b);
 203         else if (b->size > 0)
 204                 llist_add(&b->free, &buf->free);
 205 }
 206 
 207 /**
 208  *      tty_buffer_flush                -       flush full tty buffers
 209  *      @tty: tty to flush
 210  *      @ld:  optional ldisc ptr (must be referenced)
 211  *
 212  *      flush all the buffers containing receive data. If ld != NULL,
 213  *      flush the ldisc input buffer.
 214  *
 215  *      Locking: takes buffer lock to ensure single-threaded flip buffer
 216  *               'consumer'
 217  */
 218 
 219 void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
 220 {
 221         struct tty_port *port = tty->port;
 222         struct tty_bufhead *buf = &port->buf;
 223         struct tty_buffer *next;
 224 
 225         atomic_inc(&buf->priority);
 226 
 227         mutex_lock(&buf->lock);
 228         /* paired w/ release in __tty_buffer_request_room; ensures there are
 229          * no pending memory accesses to the freed buffer
 230          */
 231         while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
 232                 tty_buffer_free(port, buf->head);
 233                 buf->head = next;
 234         }
 235         buf->head->read = buf->head->commit;
 236 
 237         if (ld && ld->ops->flush_buffer)
 238                 ld->ops->flush_buffer(tty);
 239 
 240         atomic_dec(&buf->priority);
 241         mutex_unlock(&buf->lock);
 242 }
 243 
 244 /**
 245  *      tty_buffer_request_room         -       grow tty buffer if needed
 246  *      @tty: tty structure
 247  *      @size: size desired
 248  *      @flags: buffer flags if new buffer allocated (default = 0)
 249  *
 250  *      Make at least size bytes of linear space available for the tty
 251  *      buffer. If we fail return the size we managed to find.
 252  *
 253  *      Will change over to a new buffer if the current buffer is encoded as
 254  *      TTY_NORMAL (so has no flags buffer) and the new buffer requires
 255  *      a flags buffer.
 256  */
 257 static int __tty_buffer_request_room(struct tty_port *port, size_t size,
 258                                      int flags)
 259 {
 260         struct tty_bufhead *buf = &port->buf;
 261         struct tty_buffer *b, *n;
 262         int left, change;
 263 
 264         b = buf->tail;
 265         if (b->flags & TTYB_NORMAL)
 266                 left = 2 * b->size - b->used;
 267         else
 268                 left = b->size - b->used;
 269 
 270         change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
 271         if (change || left < size) {
 272                 /* This is the slow path - looking for new buffers to use */
 273                 n = tty_buffer_alloc(port, size);
 274                 if (n != NULL) {
 275                         n->flags = flags;
 276                         buf->tail = n;
 277                         /* paired w/ acquire in flush_to_ldisc(); ensures
 278                          * flush_to_ldisc() sees buffer data.
 279                          */
 280                         smp_store_release(&b->commit, b->used);
 281                         /* paired w/ acquire in flush_to_ldisc(); ensures the
 282                          * latest commit value can be read before the head is
 283                          * advanced to the next buffer
 284                          */
 285                         smp_store_release(&b->next, n);
 286                 } else if (change)
 287                         size = 0;
 288                 else
 289                         size = left;
 290         }
 291         return size;
 292 }
 293 
 294 int tty_buffer_request_room(struct tty_port *port, size_t size)
 295 {
 296         return __tty_buffer_request_room(port, size, 0);
 297 }
 298 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
 299 
 300 /**
 301  *      tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
 302  *      @port: tty port
 303  *      @chars: characters
 304  *      @flag: flag value for each character
 305  *      @size: size
 306  *
 307  *      Queue a series of bytes to the tty buffering. All the characters
 308  *      passed are marked with the supplied flag. Returns the number added.
 309  */
 310 
 311 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
 312                 const unsigned char *chars, char flag, size_t size)
 313 {
 314         int copied = 0;
 315         do {
 316                 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 317                 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
 318                 int space = __tty_buffer_request_room(port, goal, flags);
 319                 struct tty_buffer *tb = port->buf.tail;
 320                 if (unlikely(space == 0))
 321                         break;
 322                 memcpy(char_buf_ptr(tb, tb->used), chars, space);
 323                 if (~tb->flags & TTYB_NORMAL)
 324                         memset(flag_buf_ptr(tb, tb->used), flag, space);
 325                 tb->used += space;
 326                 copied += space;
 327                 chars += space;
 328                 /* There is a small chance that we need to split the data over
 329                    several buffers. If this is the case we must loop */
 330         } while (unlikely(size > copied));
 331         return copied;
 332 }
 333 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
 334 
 335 /**
 336  *      tty_insert_flip_string_flags    -       Add characters to the tty buffer
 337  *      @port: tty port
 338  *      @chars: characters
 339  *      @flags: flag bytes
 340  *      @size: size
 341  *
 342  *      Queue a series of bytes to the tty buffering. For each character
 343  *      the flags array indicates the status of the character. Returns the
 344  *      number added.
 345  */
 346 
 347 int tty_insert_flip_string_flags(struct tty_port *port,
 348                 const unsigned char *chars, const char *flags, size_t size)
 349 {
 350         int copied = 0;
 351         do {
 352                 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 353                 int space = tty_buffer_request_room(port, goal);
 354                 struct tty_buffer *tb = port->buf.tail;
 355                 if (unlikely(space == 0))
 356                         break;
 357                 memcpy(char_buf_ptr(tb, tb->used), chars, space);
 358                 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
 359                 tb->used += space;
 360                 copied += space;
 361                 chars += space;
 362                 flags += space;
 363                 /* There is a small chance that we need to split the data over
 364                    several buffers. If this is the case we must loop */
 365         } while (unlikely(size > copied));
 366         return copied;
 367 }
 368 EXPORT_SYMBOL(tty_insert_flip_string_flags);
 369 
 370 /**
 371  *      __tty_insert_flip_char   -      Add one character to the tty buffer
 372  *      @port: tty port
 373  *      @ch: character
 374  *      @flag: flag byte
 375  *
 376  *      Queue a single byte to the tty buffering, with an optional flag.
 377  *      This is the slow path of tty_insert_flip_char.
 378  */
 379 int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag)
 380 {
 381         struct tty_buffer *tb;
 382         int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
 383 
 384         if (!__tty_buffer_request_room(port, 1, flags))
 385                 return 0;
 386 
 387         tb = port->buf.tail;
 388         if (~tb->flags & TTYB_NORMAL)
 389                 *flag_buf_ptr(tb, tb->used) = flag;
 390         *char_buf_ptr(tb, tb->used++) = ch;
 391 
 392         return 1;
 393 }
 394 EXPORT_SYMBOL(__tty_insert_flip_char);
 395 
 396 /**
 397  *      tty_schedule_flip       -       push characters to ldisc
 398  *      @port: tty port to push from
 399  *
 400  *      Takes any pending buffers and transfers their ownership to the
 401  *      ldisc side of the queue. It then schedules those characters for
 402  *      processing by the line discipline.
 403  */
 404 
 405 void tty_schedule_flip(struct tty_port *port)
 406 {
 407         struct tty_bufhead *buf = &port->buf;
 408 
 409         /* paired w/ acquire in flush_to_ldisc(); ensures
 410          * flush_to_ldisc() sees buffer data.
 411          */
 412         smp_store_release(&buf->tail->commit, buf->tail->used);
 413         queue_work(system_unbound_wq, &buf->work);
 414 }
 415 EXPORT_SYMBOL(tty_schedule_flip);
 416 
 417 /**
 418  *      tty_prepare_flip_string         -       make room for characters
 419  *      @port: tty port
 420  *      @chars: return pointer for character write area
 421  *      @size: desired size
 422  *
 423  *      Prepare a block of space in the buffer for data. Returns the length
 424  *      available and buffer pointer to the space which is now allocated and
 425  *      accounted for as ready for normal characters. This is used for drivers
 426  *      that need their own block copy routines into the buffer. There is no
 427  *      guarantee the buffer is a DMA target!
 428  */
 429 
 430 int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
 431                 size_t size)
 432 {
 433         int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
 434         if (likely(space)) {
 435                 struct tty_buffer *tb = port->buf.tail;
 436                 *chars = char_buf_ptr(tb, tb->used);
 437                 if (~tb->flags & TTYB_NORMAL)
 438                         memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
 439                 tb->used += space;
 440         }
 441         return space;
 442 }
 443 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
 444 
 445 /**
 446  *      tty_ldisc_receive_buf           -       forward data to line discipline
 447  *      @ld:    line discipline to process input
 448  *      @p:     char buffer
 449  *      @f:     TTY_* flags buffer
 450  *      @count: number of bytes to process
 451  *
 452  *      Callers other than flush_to_ldisc() need to exclude the kworker
 453  *      from concurrent use of the line discipline, see paste_selection().
 454  *
 455  *      Returns the number of bytes processed
 456  */
 457 int tty_ldisc_receive_buf(struct tty_ldisc *ld, const unsigned char *p,
 458                           char *f, int count)
 459 {
 460         if (ld->ops->receive_buf2)
 461                 count = ld->ops->receive_buf2(ld->tty, p, f, count);
 462         else {
 463                 count = min_t(int, count, ld->tty->receive_room);
 464                 if (count && ld->ops->receive_buf)
 465                         ld->ops->receive_buf(ld->tty, p, f, count);
 466         }
 467         return count;
 468 }
 469 EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
 470 
 471 static int
 472 receive_buf(struct tty_port *port, struct tty_buffer *head, int count)
 473 {
 474         unsigned char *p = char_buf_ptr(head, head->read);
 475         char          *f = NULL;
 476         int n;
 477 
 478         if (~head->flags & TTYB_NORMAL)
 479                 f = flag_buf_ptr(head, head->read);
 480 
 481         n = port->client_ops->receive_buf(port, p, f, count);
 482         if (n > 0)
 483                 memset(p, 0, n);
 484         return n;
 485 }
 486 
 487 /**
 488  *      flush_to_ldisc
 489  *      @work: tty structure passed from work queue.
 490  *
 491  *      This routine is called out of the software interrupt to flush data
 492  *      from the buffer chain to the line discipline.
 493  *
 494  *      The receive_buf method is single threaded for each tty instance.
 495  *
 496  *      Locking: takes buffer lock to ensure single-threaded flip buffer
 497  *               'consumer'
 498  */
 499 
 500 static void flush_to_ldisc(struct work_struct *work)
 501 {
 502         struct tty_port *port = container_of(work, struct tty_port, buf.work);
 503         struct tty_bufhead *buf = &port->buf;
 504 
 505         mutex_lock(&buf->lock);
 506 
 507         while (1) {
 508                 struct tty_buffer *head = buf->head;
 509                 struct tty_buffer *next;
 510                 int count;
 511 
 512                 /* Ldisc or user is trying to gain exclusive access */
 513                 if (atomic_read(&buf->priority))
 514                         break;
 515 
 516                 /* paired w/ release in __tty_buffer_request_room();
 517                  * ensures commit value read is not stale if the head
 518                  * is advancing to the next buffer
 519                  */
 520                 next = smp_load_acquire(&head->next);
 521                 /* paired w/ release in __tty_buffer_request_room() or in
 522                  * tty_buffer_flush(); ensures we see the committed buffer data
 523                  */
 524                 count = smp_load_acquire(&head->commit) - head->read;
 525                 if (!count) {
 526                         if (next == NULL)
 527                                 break;
 528                         buf->head = next;
 529                         tty_buffer_free(port, head);
 530                         continue;
 531                 }
 532 
 533                 count = receive_buf(port, head, count);
 534                 if (!count)
 535                         break;
 536                 head->read += count;
 537         }
 538 
 539         mutex_unlock(&buf->lock);
 540 
 541 }
 542 
 543 /**
 544  *      tty_flip_buffer_push    -       terminal
 545  *      @port: tty port to push
 546  *
 547  *      Queue a push of the terminal flip buffers to the line discipline.
 548  *      Can be called from IRQ/atomic context.
 549  *
 550  *      In the event of the queue being busy for flipping the work will be
 551  *      held off and retried later.
 552  */
 553 
 554 void tty_flip_buffer_push(struct tty_port *port)
 555 {
 556         tty_schedule_flip(port);
 557 }
 558 EXPORT_SYMBOL(tty_flip_buffer_push);
 559 
 560 /**
 561  *      tty_buffer_init         -       prepare a tty buffer structure
 562  *      @tty: tty to initialise
 563  *
 564  *      Set up the initial state of the buffer management for a tty device.
 565  *      Must be called before the other tty buffer functions are used.
 566  */
 567 
 568 void tty_buffer_init(struct tty_port *port)
 569 {
 570         struct tty_bufhead *buf = &port->buf;
 571 
 572         mutex_init(&buf->lock);
 573         tty_buffer_reset(&buf->sentinel, 0);
 574         buf->head = &buf->sentinel;
 575         buf->tail = &buf->sentinel;
 576         init_llist_head(&buf->free);
 577         atomic_set(&buf->mem_used, 0);
 578         atomic_set(&buf->priority, 0);
 579         INIT_WORK(&buf->work, flush_to_ldisc);
 580         buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
 581 }
 582 
 583 /**
 584  *      tty_buffer_set_limit    -       change the tty buffer memory limit
 585  *      @port: tty port to change
 586  *
 587  *      Change the tty buffer memory limit.
 588  *      Must be called before the other tty buffer functions are used.
 589  */
 590 
 591 int tty_buffer_set_limit(struct tty_port *port, int limit)
 592 {
 593         if (limit < MIN_TTYB_SIZE)
 594                 return -EINVAL;
 595         port->buf.mem_limit = limit;
 596         return 0;
 597 }
 598 EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
 599 
 600 /* slave ptys can claim nested buffer lock when handling BRK and INTR */
 601 void tty_buffer_set_lock_subclass(struct tty_port *port)
 602 {
 603         lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
 604 }
 605 
 606 bool tty_buffer_restart_work(struct tty_port *port)
 607 {
 608         return queue_work(system_unbound_wq, &port->buf.work);
 609 }
 610 
 611 bool tty_buffer_cancel_work(struct tty_port *port)
 612 {
 613         return cancel_work_sync(&port->buf.work);
 614 }
 615 
 616 void tty_buffer_flush_work(struct tty_port *port)
 617 {
 618         flush_work(&port->buf.work);
 619 }