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#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_MEM_LIMIT  65536
  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/**
  43 *      tty_buffer_lock_exclusive       -       gain exclusive access to buffer
  44 *      tty_buffer_unlock_exclusive     -       release exclusive access
  45 *
  46 *      @port - tty_port owning the flip buffer
  47 *
  48 *      Guarantees safe use of the line discipline's receive_buf() method by
  49 *      excluding the buffer work and any pending flush from using the flip
  50 *      buffer. Data can continue to be added concurrently to the flip buffer
  51 *      from the driver side.
  52 *
  53 *      On release, the buffer work is restarted if there is data in the
  54 *      flip buffer
  55 */
  56
  57void tty_buffer_lock_exclusive(struct tty_port *port)
  58{
  59        struct tty_bufhead *buf = &port->buf;
  60
  61        atomic_inc(&buf->priority);
  62        mutex_lock(&buf->lock);
  63}
  64
  65void 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
  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
  90int tty_buffer_space_avail(struct tty_port *port)
  91{
  92        int space = TTYB_MEM_LIMIT - atomic_read(&port->buf.memory_used);
  93        return max(space, 0);
  94}
  95
  96static void tty_buffer_reset(struct tty_buffer *p, size_t size)
  97{
  98        p->used = 0;
  99        p->size = size;
 100        p->next = NULL;
 101        p->commit = 0;
 102        p->read = 0;
 103}
 104
 105/**
 106 *      tty_buffer_free_all             -       free buffers used by a tty
 107 *      @tty: tty to free from
 108 *
 109 *      Remove all the buffers pending on a tty whether queued with data
 110 *      or in the free ring. Must be called when the tty is no longer in use
 111 */
 112
 113void tty_buffer_free_all(struct tty_port *port)
 114{
 115        struct tty_bufhead *buf = &port->buf;
 116        struct tty_buffer *p, *next;
 117        struct llist_node *llist;
 118
 119        while ((p = buf->head) != NULL) {
 120                buf->head = p->next;
 121                if (p->size > 0)
 122                        kfree(p);
 123        }
 124        llist = llist_del_all(&buf->free);
 125        llist_for_each_entry_safe(p, next, llist, free)
 126                kfree(p);
 127
 128        tty_buffer_reset(&buf->sentinel, 0);
 129        buf->head = &buf->sentinel;
 130        buf->tail = &buf->sentinel;
 131
 132        atomic_set(&buf->memory_used, 0);
 133}
 134
 135/**
 136 *      tty_buffer_alloc        -       allocate a tty buffer
 137 *      @tty: tty device
 138 *      @size: desired size (characters)
 139 *
 140 *      Allocate a new tty buffer to hold the desired number of characters.
 141 *      We round our buffers off in 256 character chunks to get better
 142 *      allocation behaviour.
 143 *      Return NULL if out of memory or the allocation would exceed the
 144 *      per device queue
 145 */
 146
 147static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
 148{
 149        struct llist_node *free;
 150        struct tty_buffer *p;
 151
 152        /* Round the buffer size out */
 153        size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
 154
 155        if (size <= MIN_TTYB_SIZE) {
 156                free = llist_del_first(&port->buf.free);
 157                if (free) {
 158                        p = llist_entry(free, struct tty_buffer, free);
 159                        goto found;
 160                }
 161        }
 162
 163        /* Should possibly check if this fails for the largest buffer we
 164           have queued and recycle that ? */
 165        if (atomic_read(&port->buf.memory_used) > TTYB_MEM_LIMIT)
 166                return NULL;
 167        p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
 168        if (p == NULL)
 169                return NULL;
 170
 171found:
 172        tty_buffer_reset(p, size);
 173        atomic_add(size, &port->buf.memory_used);
 174        return p;
 175}
 176
 177/**
 178 *      tty_buffer_free         -       free a tty buffer
 179 *      @tty: tty owning the buffer
 180 *      @b: the buffer to free
 181 *
 182 *      Free a tty buffer, or add it to the free list according to our
 183 *      internal strategy
 184 */
 185
 186static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
 187{
 188        struct tty_bufhead *buf = &port->buf;
 189
 190        /* Dumb strategy for now - should keep some stats */
 191        WARN_ON(atomic_sub_return(b->size, &buf->memory_used) < 0);
 192
 193        if (b->size > MIN_TTYB_SIZE)
 194                kfree(b);
 195        else if (b->size > 0)
 196                llist_add(&b->free, &buf->free);
 197}
 198
 199/**
 200 *      tty_buffer_flush                -       flush full tty buffers
 201 *      @tty: tty to flush
 202 *
 203 *      flush all the buffers containing receive data. If the buffer is
 204 *      being processed by flush_to_ldisc then we defer the processing
 205 *      to that function
 206 *
 207 *      Locking: takes buffer lock to ensure single-threaded flip buffer
 208 *               'consumer'
 209 */
 210
 211void tty_buffer_flush(struct tty_struct *tty)
 212{
 213        struct tty_port *port = tty->port;
 214        struct tty_bufhead *buf = &port->buf;
 215        struct tty_buffer *next;
 216
 217        atomic_inc(&buf->priority);
 218
 219        mutex_lock(&buf->lock);
 220        while ((next = buf->head->next) != NULL) {
 221                tty_buffer_free(port, buf->head);
 222                buf->head = next;
 223        }
 224        buf->head->read = buf->head->commit;
 225        atomic_dec(&buf->priority);
 226        mutex_unlock(&buf->lock);
 227}
 228
 229/**
 230 *      tty_buffer_request_room         -       grow tty buffer if needed
 231 *      @tty: tty structure
 232 *      @size: size desired
 233 *
 234 *      Make at least size bytes of linear space available for the tty
 235 *      buffer. If we fail return the size we managed to find.
 236 */
 237int tty_buffer_request_room(struct tty_port *port, size_t size)
 238{
 239        struct tty_bufhead *buf = &port->buf;
 240        struct tty_buffer *b, *n;
 241        int left;
 242
 243        b = buf->tail;
 244        left = b->size - b->used;
 245
 246        if (left < size) {
 247                /* This is the slow path - looking for new buffers to use */
 248                if ((n = tty_buffer_alloc(port, size)) != NULL) {
 249                        buf->tail = n;
 250                        b->commit = b->used;
 251                        smp_mb();
 252                        b->next = n;
 253                } else
 254                        size = left;
 255        }
 256        return size;
 257}
 258EXPORT_SYMBOL_GPL(tty_buffer_request_room);
 259
 260/**
 261 *      tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
 262 *      @port: tty port
 263 *      @chars: characters
 264 *      @flag: flag value for each character
 265 *      @size: size
 266 *
 267 *      Queue a series of bytes to the tty buffering. All the characters
 268 *      passed are marked with the supplied flag. Returns the number added.
 269 */
 270
 271int tty_insert_flip_string_fixed_flag(struct tty_port *port,
 272                const unsigned char *chars, char flag, size_t size)
 273{
 274        int copied = 0;
 275        do {
 276                int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 277                int space = tty_buffer_request_room(port, goal);
 278                struct tty_buffer *tb = port->buf.tail;
 279                if (unlikely(space == 0))
 280                        break;
 281                memcpy(char_buf_ptr(tb, tb->used), chars, space);
 282                memset(flag_buf_ptr(tb, tb->used), flag, space);
 283                tb->used += space;
 284                copied += space;
 285                chars += space;
 286                /* There is a small chance that we need to split the data over
 287                   several buffers. If this is the case we must loop */
 288        } while (unlikely(size > copied));
 289        return copied;
 290}
 291EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
 292
 293/**
 294 *      tty_insert_flip_string_flags    -       Add characters to the tty buffer
 295 *      @port: tty port
 296 *      @chars: characters
 297 *      @flags: flag bytes
 298 *      @size: size
 299 *
 300 *      Queue a series of bytes to the tty buffering. For each character
 301 *      the flags array indicates the status of the character. Returns the
 302 *      number added.
 303 */
 304
 305int tty_insert_flip_string_flags(struct tty_port *port,
 306                const unsigned char *chars, const char *flags, size_t size)
 307{
 308        int copied = 0;
 309        do {
 310                int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
 311                int space = tty_buffer_request_room(port, goal);
 312                struct tty_buffer *tb = port->buf.tail;
 313                if (unlikely(space == 0))
 314                        break;
 315                memcpy(char_buf_ptr(tb, tb->used), chars, space);
 316                memcpy(flag_buf_ptr(tb, tb->used), flags, space);
 317                tb->used += space;
 318                copied += space;
 319                chars += space;
 320                flags += space;
 321                /* There is a small chance that we need to split the data over
 322                   several buffers. If this is the case we must loop */
 323        } while (unlikely(size > copied));
 324        return copied;
 325}
 326EXPORT_SYMBOL(tty_insert_flip_string_flags);
 327
 328/**
 329 *      tty_schedule_flip       -       push characters to ldisc
 330 *      @port: tty port to push from
 331 *
 332 *      Takes any pending buffers and transfers their ownership to the
 333 *      ldisc side of the queue. It then schedules those characters for
 334 *      processing by the line discipline.
 335 *      Note that this function can only be used when the low_latency flag
 336 *      is unset. Otherwise the workqueue won't be flushed.
 337 */
 338
 339void tty_schedule_flip(struct tty_port *port)
 340{
 341        struct tty_bufhead *buf = &port->buf;
 342        WARN_ON(port->low_latency);
 343
 344        buf->tail->commit = buf->tail->used;
 345        schedule_work(&buf->work);
 346}
 347EXPORT_SYMBOL(tty_schedule_flip);
 348
 349/**
 350 *      tty_prepare_flip_string         -       make room for characters
 351 *      @port: tty port
 352 *      @chars: return pointer for character write area
 353 *      @size: desired size
 354 *
 355 *      Prepare a block of space in the buffer for data. Returns the length
 356 *      available and buffer pointer to the space which is now allocated and
 357 *      accounted for as ready for normal characters. This is used for drivers
 358 *      that need their own block copy routines into the buffer. There is no
 359 *      guarantee the buffer is a DMA target!
 360 */
 361
 362int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
 363                size_t size)
 364{
 365        int space = tty_buffer_request_room(port, size);
 366        if (likely(space)) {
 367                struct tty_buffer *tb = port->buf.tail;
 368                *chars = char_buf_ptr(tb, tb->used);
 369                memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
 370                tb->used += space;
 371        }
 372        return space;
 373}
 374EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
 375
 376/**
 377 *      tty_prepare_flip_string_flags   -       make room for characters
 378 *      @port: tty port
 379 *      @chars: return pointer for character write area
 380 *      @flags: return pointer for status flag write area
 381 *      @size: desired size
 382 *
 383 *      Prepare a block of space in the buffer for data. Returns the length
 384 *      available and buffer pointer to the space which is now allocated and
 385 *      accounted for as ready for characters. This is used for drivers
 386 *      that need their own block copy routines into the buffer. There is no
 387 *      guarantee the buffer is a DMA target!
 388 */
 389
 390int tty_prepare_flip_string_flags(struct tty_port *port,
 391                        unsigned char **chars, char **flags, size_t size)
 392{
 393        int space = tty_buffer_request_room(port, size);
 394        if (likely(space)) {
 395                struct tty_buffer *tb = port->buf.tail;
 396                *chars = char_buf_ptr(tb, tb->used);
 397                *flags = flag_buf_ptr(tb, tb->used);
 398                tb->used += space;
 399        }
 400        return space;
 401}
 402EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
 403
 404
 405static int
 406receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
 407{
 408        struct tty_ldisc *disc = tty->ldisc;
 409        unsigned char *p = char_buf_ptr(head, head->read);
 410        char          *f = flag_buf_ptr(head, head->read);
 411
 412        if (disc->ops->receive_buf2)
 413                count = disc->ops->receive_buf2(tty, p, f, count);
 414        else {
 415                count = min_t(int, count, tty->receive_room);
 416                if (count)
 417                        disc->ops->receive_buf(tty, p, f, count);
 418        }
 419        head->read += count;
 420        return count;
 421}
 422
 423/**
 424 *      flush_to_ldisc
 425 *      @work: tty structure passed from work queue.
 426 *
 427 *      This routine is called out of the software interrupt to flush data
 428 *      from the buffer chain to the line discipline.
 429 *
 430 *      The receive_buf method is single threaded for each tty instance.
 431 *
 432 *      Locking: takes buffer lock to ensure single-threaded flip buffer
 433 *               'consumer'
 434 */
 435
 436static void flush_to_ldisc(struct work_struct *work)
 437{
 438        struct tty_port *port = container_of(work, struct tty_port, buf.work);
 439        struct tty_bufhead *buf = &port->buf;
 440        struct tty_struct *tty;
 441        struct tty_ldisc *disc;
 442
 443        tty = port->itty;
 444        if (tty == NULL)
 445                return;
 446
 447        disc = tty_ldisc_ref(tty);
 448        if (disc == NULL)
 449                return;
 450
 451        mutex_lock(&buf->lock);
 452
 453        while (1) {
 454                struct tty_buffer *head = buf->head;
 455                int count;
 456
 457                /* Ldisc or user is trying to gain exclusive access */
 458                if (atomic_read(&buf->priority))
 459                        break;
 460
 461                count = head->commit - head->read;
 462                if (!count) {
 463                        if (head->next == NULL)
 464                                break;
 465                        buf->head = head->next;
 466                        tty_buffer_free(port, head);
 467                        continue;
 468                }
 469
 470                count = receive_buf(tty, head, count);
 471                if (!count)
 472                        break;
 473        }
 474
 475        mutex_unlock(&buf->lock);
 476
 477        tty_ldisc_deref(disc);
 478}
 479
 480/**
 481 *      tty_flush_to_ldisc
 482 *      @tty: tty to push
 483 *
 484 *      Push the terminal flip buffers to the line discipline.
 485 *
 486 *      Must not be called from IRQ context.
 487 */
 488void tty_flush_to_ldisc(struct tty_struct *tty)
 489{
 490        if (!tty->port->low_latency)
 491                flush_work(&tty->port->buf.work);
 492}
 493
 494/**
 495 *      tty_flip_buffer_push    -       terminal
 496 *      @port: tty port to push
 497 *
 498 *      Queue a push of the terminal flip buffers to the line discipline. This
 499 *      function must not be called from IRQ context if port->low_latency is
 500 *      set.
 501 *
 502 *      In the event of the queue being busy for flipping the work will be
 503 *      held off and retried later.
 504 */
 505
 506void tty_flip_buffer_push(struct tty_port *port)
 507{
 508        struct tty_bufhead *buf = &port->buf;
 509
 510        buf->tail->commit = buf->tail->used;
 511
 512        if (port->low_latency)
 513                flush_to_ldisc(&buf->work);
 514        else
 515                schedule_work(&buf->work);
 516}
 517EXPORT_SYMBOL(tty_flip_buffer_push);
 518
 519/**
 520 *      tty_buffer_init         -       prepare a tty buffer structure
 521 *      @tty: tty to initialise
 522 *
 523 *      Set up the initial state of the buffer management for a tty device.
 524 *      Must be called before the other tty buffer functions are used.
 525 */
 526
 527void tty_buffer_init(struct tty_port *port)
 528{
 529        struct tty_bufhead *buf = &port->buf;
 530
 531        mutex_init(&buf->lock);
 532        tty_buffer_reset(&buf->sentinel, 0);
 533        buf->head = &buf->sentinel;
 534        buf->tail = &buf->sentinel;
 535        init_llist_head(&buf->free);
 536        atomic_set(&buf->memory_used, 0);
 537        atomic_set(&buf->priority, 0);
 538        INIT_WORK(&buf->work, flush_to_ldisc);
 539}
 540
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