linux/drivers/tty/tty_buffer.c
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   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#include <linux/ratelimit.h>
  20
  21/**
  22 *      tty_buffer_free_all             -       free buffers used by a tty
  23 *      @tty: tty to free from
  24 *
  25 *      Remove all the buffers pending on a tty whether queued with data
  26 *      or in the free ring. Must be called when the tty is no longer in use
  27 *
  28 *      Locking: none
  29 */
  30
  31void tty_buffer_free_all(struct tty_port *port)
  32{
  33        struct tty_bufhead *buf = &port->buf;
  34        struct tty_buffer *thead;
  35
  36        while ((thead = buf->head) != NULL) {
  37                buf->head = thead->next;
  38                kfree(thead);
  39        }
  40        while ((thead = buf->free) != NULL) {
  41                buf->free = thead->next;
  42                kfree(thead);
  43        }
  44        buf->tail = NULL;
  45        buf->memory_used = 0;
  46}
  47
  48/**
  49 *      tty_buffer_alloc        -       allocate a tty buffer
  50 *      @tty: tty device
  51 *      @size: desired size (characters)
  52 *
  53 *      Allocate a new tty buffer to hold the desired number of characters.
  54 *      Return NULL if out of memory or the allocation would exceed the
  55 *      per device queue
  56 *
  57 *      Locking: Caller must hold tty->buf.lock
  58 */
  59
  60static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
  61{
  62        struct tty_buffer *p;
  63
  64        if (port->buf.memory_used + size > 65536)
  65                return NULL;
  66        p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
  67        if (p == NULL)
  68                return NULL;
  69        p->used = 0;
  70        p->size = size;
  71        p->next = NULL;
  72        p->commit = 0;
  73        p->read = 0;
  74        p->char_buf_ptr = (char *)(p->data);
  75        p->flag_buf_ptr = (unsigned char *)p->char_buf_ptr + size;
  76        port->buf.memory_used += size;
  77        return p;
  78}
  79
  80/**
  81 *      tty_buffer_free         -       free a tty buffer
  82 *      @tty: tty owning the buffer
  83 *      @b: the buffer to free
  84 *
  85 *      Free a tty buffer, or add it to the free list according to our
  86 *      internal strategy
  87 *
  88 *      Locking: Caller must hold tty->buf.lock
  89 */
  90
  91static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
  92{
  93        struct tty_bufhead *buf = &port->buf;
  94
  95        /* Dumb strategy for now - should keep some stats */
  96        buf->memory_used -= b->size;
  97        WARN_ON(buf->memory_used < 0);
  98
  99        if (b->size >= 512)
 100                kfree(b);
 101        else {
 102                b->next = buf->free;
 103                buf->free = b;
 104        }
 105}
 106
 107/**
 108 *      __tty_buffer_flush              -       flush full tty buffers
 109 *      @tty: tty to flush
 110 *
 111 *      flush all the buffers containing receive data. Caller must
 112 *      hold the buffer lock and must have ensured no parallel flush to
 113 *      ldisc is running.
 114 *
 115 *      Locking: Caller must hold tty->buf.lock
 116 */
 117
 118static void __tty_buffer_flush(struct tty_port *port)
 119{
 120        struct tty_bufhead *buf = &port->buf;
 121        struct tty_buffer *thead;
 122
 123        if (unlikely(buf->head == NULL))
 124                return;
 125        while ((thead = buf->head->next) != NULL) {
 126                tty_buffer_free(port, buf->head);
 127                buf->head = thead;
 128        }
 129        WARN_ON(buf->head != buf->tail);
 130        buf->head->read = buf->head->commit;
 131}
 132
 133/**
 134 *      tty_buffer_flush                -       flush full tty buffers
 135 *      @tty: tty to flush
 136 *
 137 *      flush all the buffers containing receive data. If the buffer is
 138 *      being processed by flush_to_ldisc then we defer the processing
 139 *      to that function
 140 *
 141 *      Locking: none
 142 */
 143
 144void tty_buffer_flush(struct tty_struct *tty)
 145{
 146        struct tty_port *port = tty->port;
 147        struct tty_bufhead *buf = &port->buf;
 148        unsigned long flags;
 149
 150        spin_lock_irqsave(&buf->lock, flags);
 151
 152        /* If the data is being pushed to the tty layer then we can't
 153           process it here. Instead set a flag and the flush_to_ldisc
 154           path will process the flush request before it exits */
 155        if (test_bit(TTYP_FLUSHING, &port->iflags)) {
 156                set_bit(TTYP_FLUSHPENDING, &port->iflags);
 157                spin_unlock_irqrestore(&buf->lock, flags);
 158                wait_event(tty->read_wait,
 159                                test_bit(TTYP_FLUSHPENDING, &port->iflags) == 0);
 160                return;
 161        } else
 162                __tty_buffer_flush(port);
 163        spin_unlock_irqrestore(&buf->lock, flags);
 164}
 165
 166/**
 167 *      tty_buffer_find         -       find a free tty buffer
 168 *      @tty: tty owning the buffer
 169 *      @size: characters wanted
 170 *
 171 *      Locate an existing suitable tty buffer or if we are lacking one then
 172 *      allocate a new one. We round our buffers off in 256 character chunks
 173 *      to get better allocation behaviour.
 174 *
 175 *      Locking: Caller must hold tty->buf.lock
 176 */
 177
 178static struct tty_buffer *tty_buffer_find(struct tty_port *port, size_t size)
 179{
 180        struct tty_buffer **tbh = &port->buf.free;
 181        while ((*tbh) != NULL) {
 182                struct tty_buffer *t = *tbh;
 183                if (t->size >= size) {
 184                        *tbh = t->next;
 185                        t->next = NULL;
 186                        t->used = 0;
 187                        t->commit = 0;
 188                        t->read = 0;
 189                        port->buf.memory_used += t->size;
 190                        return t;
 191                }
 192                tbh = &((*tbh)->next);
 193        }
 194        /* Round the buffer size out */
 195        size = (size + 0xFF) & ~0xFF;
 196        return tty_buffer_alloc(port, size);
 197        /* Should possibly check if this fails for the largest buffer we
 198           have queued and recycle that ? */
 199}
 200/**
 201 *      tty_buffer_request_room         -       grow tty buffer if needed
 202 *      @tty: tty structure
 203 *      @size: size desired
 204 *
 205 *      Make at least size bytes of linear space available for the tty
 206 *      buffer. If we fail return the size we managed to find.
 207 *
 208 *      Locking: Takes port->buf.lock
 209 */
 210int tty_buffer_request_room(struct tty_port *port, size_t size)
 211{
 212        struct tty_bufhead *buf = &port->buf;
 213        struct tty_buffer *b, *n;
 214        int left;
 215        unsigned long flags;
 216        spin_lock_irqsave(&buf->lock, flags);
 217        /* OPTIMISATION: We could keep a per tty "zero" sized buffer to
 218           remove this conditional if its worth it. This would be invisible
 219           to the callers */
 220        b = buf->tail;
 221        if (b != NULL)
 222                left = b->size - b->used;
 223        else
 224                left = 0;
 225
 226        if (left < size) {
 227                /* This is the slow path - looking for new buffers to use */
 228                if ((n = tty_buffer_find(port, size)) != NULL) {
 229                        if (b != NULL) {
 230                                b->next = n;
 231                                b->commit = b->used;
 232                        } else
 233                                buf->head = n;
 234                        buf->tail = n;
 235                } else
 236                        size = left;
 237        }
 238        spin_unlock_irqrestore(&buf->lock, flags);
 239        return size;
 240}
 241EXPORT_SYMBOL_GPL(tty_buffer_request_room);
 242
 243/**
 244 *      tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
 245 *      @port: tty port
 246 *      @chars: characters
 247 *      @flag: flag value for each character
 248 *      @size: size
 249 *
 250 *      Queue a series of bytes to the tty buffering. All the characters
 251 *      passed are marked with the supplied flag. Returns the number added.
 252 *
 253 *      Locking: Called functions may take port->buf.lock
 254 */
 255
 256int tty_insert_flip_string_fixed_flag(struct tty_port *port,
 257                const unsigned char *chars, char flag, size_t size)
 258{
 259        int copied = 0;
 260        do {
 261                int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 262                int space = tty_buffer_request_room(port, goal);
 263                struct tty_buffer *tb = port->buf.tail;
 264                /* If there is no space then tb may be NULL */
 265                if (unlikely(space == 0)) {
 266                        break;
 267                }
 268                memcpy(tb->char_buf_ptr + tb->used, chars, space);
 269                memset(tb->flag_buf_ptr + tb->used, flag, space);
 270                tb->used += space;
 271                copied += space;
 272                chars += space;
 273                /* There is a small chance that we need to split the data over
 274                   several buffers. If this is the case we must loop */
 275        } while (unlikely(size > copied));
 276        return copied;
 277}
 278EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
 279
 280/**
 281 *      tty_insert_flip_string_flags    -       Add characters to the tty buffer
 282 *      @port: tty port
 283 *      @chars: characters
 284 *      @flags: flag bytes
 285 *      @size: size
 286 *
 287 *      Queue a series of bytes to the tty buffering. For each character
 288 *      the flags array indicates the status of the character. Returns the
 289 *      number added.
 290 *
 291 *      Locking: Called functions may take port->buf.lock
 292 */
 293
 294int tty_insert_flip_string_flags(struct tty_port *port,
 295                const unsigned char *chars, const char *flags, size_t size)
 296{
 297        int copied = 0;
 298        do {
 299                int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 300                int space = tty_buffer_request_room(port, goal);
 301                struct tty_buffer *tb = port->buf.tail;
 302                /* If there is no space then tb may be NULL */
 303                if (unlikely(space == 0)) {
 304                        break;
 305                }
 306                memcpy(tb->char_buf_ptr + tb->used, chars, space);
 307                memcpy(tb->flag_buf_ptr + tb->used, flags, space);
 308                tb->used += space;
 309                copied += space;
 310                chars += space;
 311                flags += space;
 312                /* There is a small chance that we need to split the data over
 313                   several buffers. If this is the case we must loop */
 314        } while (unlikely(size > copied));
 315        return copied;
 316}
 317EXPORT_SYMBOL(tty_insert_flip_string_flags);
 318
 319/**
 320 *      tty_schedule_flip       -       push characters to ldisc
 321 *      @port: tty port to push from
 322 *
 323 *      Takes any pending buffers and transfers their ownership to the
 324 *      ldisc side of the queue. It then schedules those characters for
 325 *      processing by the line discipline.
 326 *      Note that this function can only be used when the low_latency flag
 327 *      is unset. Otherwise the workqueue won't be flushed.
 328 *
 329 *      Locking: Takes port->buf.lock
 330 */
 331
 332void tty_schedule_flip(struct tty_port *port)
 333{
 334        struct tty_bufhead *buf = &port->buf;
 335        unsigned long flags;
 336        WARN_ON(port->low_latency);
 337
 338        spin_lock_irqsave(&buf->lock, flags);
 339        if (buf->tail != NULL)
 340                buf->tail->commit = buf->tail->used;
 341        spin_unlock_irqrestore(&buf->lock, flags);
 342        schedule_work(&buf->work);
 343}
 344EXPORT_SYMBOL(tty_schedule_flip);
 345
 346/**
 347 *      tty_prepare_flip_string         -       make room for characters
 348 *      @port: tty port
 349 *      @chars: return pointer for character write area
 350 *      @size: desired size
 351 *
 352 *      Prepare a block of space in the buffer for data. Returns the length
 353 *      available and buffer pointer to the space which is now allocated and
 354 *      accounted for as ready for normal characters. This is used for drivers
 355 *      that need their own block copy routines into the buffer. There is no
 356 *      guarantee the buffer is a DMA target!
 357 *
 358 *      Locking: May call functions taking port->buf.lock
 359 */
 360
 361int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
 362                size_t size)
 363{
 364        int space = tty_buffer_request_room(port, size);
 365        if (likely(space)) {
 366                struct tty_buffer *tb = port->buf.tail;
 367                *chars = tb->char_buf_ptr + tb->used;
 368                memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
 369                tb->used += space;
 370        }
 371        return space;
 372}
 373EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
 374
 375/**
 376 *      tty_prepare_flip_string_flags   -       make room for characters
 377 *      @port: tty port
 378 *      @chars: return pointer for character write area
 379 *      @flags: return pointer for status flag write area
 380 *      @size: desired size
 381 *
 382 *      Prepare a block of space in the buffer for data. Returns the length
 383 *      available and buffer pointer to the space which is now allocated and
 384 *      accounted for as ready for characters. This is used for drivers
 385 *      that need their own block copy routines into the buffer. There is no
 386 *      guarantee the buffer is a DMA target!
 387 *
 388 *      Locking: May call functions taking port->buf.lock
 389 */
 390
 391int tty_prepare_flip_string_flags(struct tty_port *port,
 392                        unsigned char **chars, char **flags, size_t size)
 393{
 394        int space = tty_buffer_request_room(port, size);
 395        if (likely(space)) {
 396                struct tty_buffer *tb = port->buf.tail;
 397                *chars = tb->char_buf_ptr + tb->used;
 398                *flags = tb->flag_buf_ptr + tb->used;
 399                tb->used += space;
 400        }
 401        return space;
 402}
 403EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
 404
 405
 406
 407/**
 408 *      flush_to_ldisc
 409 *      @work: tty structure passed from work queue.
 410 *
 411 *      This routine is called out of the software interrupt to flush data
 412 *      from the buffer chain to the line discipline.
 413 *
 414 *      Locking: holds tty->buf.lock to guard buffer list. Drops the lock
 415 *      while invoking the line discipline receive_buf method. The
 416 *      receive_buf method is single threaded for each tty instance.
 417 */
 418
 419static void flush_to_ldisc(struct work_struct *work)
 420{
 421        struct tty_port *port = container_of(work, struct tty_port, buf.work);
 422        struct tty_bufhead *buf = &port->buf;
 423        struct tty_struct *tty;
 424        unsigned long   flags;
 425        struct tty_ldisc *disc;
 426
 427        tty = port->itty;
 428        if (tty == NULL)
 429                return;
 430
 431        disc = tty_ldisc_ref(tty);
 432        if (disc == NULL)       /*  !TTY_LDISC */
 433                return;
 434
 435        spin_lock_irqsave(&buf->lock, flags);
 436
 437        if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) {
 438                struct tty_buffer *head;
 439                while ((head = buf->head) != NULL) {
 440                        int count;
 441                        char *char_buf;
 442                        unsigned char *flag_buf;
 443
 444                        count = head->commit - head->read;
 445                        if (!count) {
 446                                if (head->next == NULL)
 447                                        break;
 448                                buf->head = head->next;
 449                                tty_buffer_free(port, head);
 450                                continue;
 451                        }
 452                        /* Ldisc or user is trying to flush the buffers
 453                           we are feeding to the ldisc, stop feeding the
 454                           line discipline as we want to empty the queue */
 455                        if (test_bit(TTYP_FLUSHPENDING, &port->iflags))
 456                                break;
 457                        if (!tty->receive_room)
 458                                break;
 459                        if (count > tty->receive_room)
 460                                count = tty->receive_room;
 461                        char_buf = head->char_buf_ptr + head->read;
 462                        flag_buf = head->flag_buf_ptr + head->read;
 463                        head->read += count;
 464                        spin_unlock_irqrestore(&buf->lock, flags);
 465                        disc->ops->receive_buf(tty, char_buf,
 466                                                        flag_buf, count);
 467                        spin_lock_irqsave(&buf->lock, flags);
 468                }
 469                clear_bit(TTYP_FLUSHING, &port->iflags);
 470        }
 471
 472        /* We may have a deferred request to flush the input buffer,
 473           if so pull the chain under the lock and empty the queue */
 474        if (test_bit(TTYP_FLUSHPENDING, &port->iflags)) {
 475                __tty_buffer_flush(port);
 476                clear_bit(TTYP_FLUSHPENDING, &port->iflags);
 477                wake_up(&tty->read_wait);
 478        }
 479        spin_unlock_irqrestore(&buf->lock, flags);
 480
 481        tty_ldisc_deref(disc);
 482}
 483
 484/**
 485 *      tty_flush_to_ldisc
 486 *      @tty: tty to push
 487 *
 488 *      Push the terminal flip buffers to the line discipline.
 489 *
 490 *      Must not be called from IRQ context.
 491 */
 492void tty_flush_to_ldisc(struct tty_struct *tty)
 493{
 494        if (!tty->port->low_latency)
 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. This
 503 *      function must not be called from IRQ context if port->low_latency is
 504 *      set.
 505 *
 506 *      In the event of the queue being busy for flipping the work will be
 507 *      held off and retried later.
 508 *
 509 *      Locking: tty buffer lock. Driver locks in low latency mode.
 510 */
 511
 512void tty_flip_buffer_push(struct tty_port *port)
 513{
 514        struct tty_bufhead *buf = &port->buf;
 515        unsigned long flags;
 516
 517        spin_lock_irqsave(&buf->lock, flags);
 518        if (buf->tail != NULL)
 519                buf->tail->commit = buf->tail->used;
 520        spin_unlock_irqrestore(&buf->lock, flags);
 521
 522        if (port->low_latency)
 523                flush_to_ldisc(&buf->work);
 524        else
 525                schedule_work(&buf->work);
 526}
 527EXPORT_SYMBOL(tty_flip_buffer_push);
 528
 529/**
 530 *      tty_buffer_init         -       prepare a tty buffer structure
 531 *      @tty: tty to initialise
 532 *
 533 *      Set up the initial state of the buffer management for a tty device.
 534 *      Must be called before the other tty buffer functions are used.
 535 *
 536 *      Locking: none
 537 */
 538
 539void tty_buffer_init(struct tty_port *port)
 540{
 541        struct tty_bufhead *buf = &port->buf;
 542
 543        spin_lock_init(&buf->lock);
 544        buf->head = NULL;
 545        buf->tail = NULL;
 546        buf->free = NULL;
 547        buf->memory_used = 0;
 548        INIT_WORK(&buf->work, flush_to_ldisc);
 549}
 550
 551
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