linux/fs/seq_file.c
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   1/*
   2 * linux/fs/seq_file.c
   3 *
   4 * helper functions for making synthetic files from sequences of records.
   5 * initial implementation -- AV, Oct 2001.
   6 */
   7
   8#include <linux/fs.h>
   9#include <linux/export.h>
  10#include <linux/seq_file.h>
  11#include <linux/slab.h>
  12
  13#include <asm/uaccess.h>
  14#include <asm/page.h>
  15
  16
  17/*
  18 * seq_files have a buffer which can may overflow. When this happens a larger
  19 * buffer is reallocated and all the data will be printed again.
  20 * The overflow state is true when m->count == m->size.
  21 */
  22static bool seq_overflow(struct seq_file *m)
  23{
  24        return m->count == m->size;
  25}
  26
  27static void seq_set_overflow(struct seq_file *m)
  28{
  29        m->count = m->size;
  30}
  31
  32/**
  33 *      seq_open -      initialize sequential file
  34 *      @file: file we initialize
  35 *      @op: method table describing the sequence
  36 *
  37 *      seq_open() sets @file, associating it with a sequence described
  38 *      by @op.  @op->start() sets the iterator up and returns the first
  39 *      element of sequence. @op->stop() shuts it down.  @op->next()
  40 *      returns the next element of sequence.  @op->show() prints element
  41 *      into the buffer.  In case of error ->start() and ->next() return
  42 *      ERR_PTR(error).  In the end of sequence they return %NULL. ->show()
  43 *      returns 0 in case of success and negative number in case of error.
  44 *      Returning SEQ_SKIP means "discard this element and move on".
  45 */
  46int seq_open(struct file *file, const struct seq_operations *op)
  47{
  48        struct seq_file *p = file->private_data;
  49
  50        if (!p) {
  51                p = kmalloc(sizeof(*p), GFP_KERNEL);
  52                if (!p)
  53                        return -ENOMEM;
  54                file->private_data = p;
  55        }
  56        memset(p, 0, sizeof(*p));
  57        mutex_init(&p->lock);
  58        p->op = op;
  59
  60        /*
  61         * Wrappers around seq_open(e.g. swaps_open) need to be
  62         * aware of this. If they set f_version themselves, they
  63         * should call seq_open first and then set f_version.
  64         */
  65        file->f_version = 0;
  66
  67        /*
  68         * seq_files support lseek() and pread().  They do not implement
  69         * write() at all, but we clear FMODE_PWRITE here for historical
  70         * reasons.
  71         *
  72         * If a client of seq_files a) implements file.write() and b) wishes to
  73         * support pwrite() then that client will need to implement its own
  74         * file.open() which calls seq_open() and then sets FMODE_PWRITE.
  75         */
  76        file->f_mode &= ~FMODE_PWRITE;
  77        return 0;
  78}
  79EXPORT_SYMBOL(seq_open);
  80
  81static int traverse(struct seq_file *m, loff_t offset)
  82{
  83        loff_t pos = 0, index;
  84        int error = 0;
  85        void *p;
  86
  87        m->version = 0;
  88        index = 0;
  89        m->count = m->from = 0;
  90        if (!offset) {
  91                m->index = index;
  92                return 0;
  93        }
  94        if (!m->buf) {
  95                m->buf = kmalloc(m->size = PAGE_SIZE, GFP_KERNEL);
  96                if (!m->buf)
  97                        return -ENOMEM;
  98        }
  99        p = m->op->start(m, &index);
 100        while (p) {
 101                error = PTR_ERR(p);
 102                if (IS_ERR(p))
 103                        break;
 104                error = m->op->show(m, p);
 105                if (error < 0)
 106                        break;
 107                if (unlikely(error)) {
 108                        error = 0;
 109                        m->count = 0;
 110                }
 111                if (seq_overflow(m))
 112                        goto Eoverflow;
 113                if (pos + m->count > offset) {
 114                        m->from = offset - pos;
 115                        m->count -= m->from;
 116                        m->index = index;
 117                        break;
 118                }
 119                pos += m->count;
 120                m->count = 0;
 121                if (pos == offset) {
 122                        index++;
 123                        m->index = index;
 124                        break;
 125                }
 126                p = m->op->next(m, p, &index);
 127        }
 128        m->op->stop(m, p);
 129        m->index = index;
 130        return error;
 131
 132Eoverflow:
 133        m->op->stop(m, p);
 134        kfree(m->buf);
 135        m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
 136        return !m->buf ? -ENOMEM : -EAGAIN;
 137}
 138
 139/**
 140 *      seq_read -      ->read() method for sequential files.
 141 *      @file: the file to read from
 142 *      @buf: the buffer to read to
 143 *      @size: the maximum number of bytes to read
 144 *      @ppos: the current position in the file
 145 *
 146 *      Ready-made ->f_op->read()
 147 */
 148ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
 149{
 150        struct seq_file *m = file->private_data;
 151        size_t copied = 0;
 152        loff_t pos;
 153        size_t n;
 154        void *p;
 155        int err = 0;
 156
 157        mutex_lock(&m->lock);
 158
 159        /*
 160         * seq_file->op->..m_start/m_stop/m_next may do special actions
 161         * or optimisations based on the file->f_version, so we want to
 162         * pass the file->f_version to those methods.
 163         *
 164         * seq_file->version is just copy of f_version, and seq_file
 165         * methods can treat it simply as file version.
 166         * It is copied in first and copied out after all operations.
 167         * It is convenient to have it as  part of structure to avoid the
 168         * need of passing another argument to all the seq_file methods.
 169         */
 170        m->version = file->f_version;
 171
 172        /* Don't assume *ppos is where we left it */
 173        if (unlikely(*ppos != m->read_pos)) {
 174                while ((err = traverse(m, *ppos)) == -EAGAIN)
 175                        ;
 176                if (err) {
 177                        /* With prejudice... */
 178                        m->read_pos = 0;
 179                        m->version = 0;
 180                        m->index = 0;
 181                        m->count = 0;
 182                        goto Done;
 183                } else {
 184                        m->read_pos = *ppos;
 185                }
 186        }
 187
 188        /* grab buffer if we didn't have one */
 189        if (!m->buf) {
 190                m->buf = kmalloc(m->size = PAGE_SIZE, GFP_KERNEL);
 191                if (!m->buf)
 192                        goto Enomem;
 193        }
 194        /* if not empty - flush it first */
 195        if (m->count) {
 196                n = min(m->count, size);
 197                err = copy_to_user(buf, m->buf + m->from, n);
 198                if (err)
 199                        goto Efault;
 200                m->count -= n;
 201                m->from += n;
 202                size -= n;
 203                buf += n;
 204                copied += n;
 205                if (!m->count)
 206                        m->index++;
 207                if (!size)
 208                        goto Done;
 209        }
 210        /* we need at least one record in buffer */
 211        pos = m->index;
 212        p = m->op->start(m, &pos);
 213        while (1) {
 214                err = PTR_ERR(p);
 215                if (!p || IS_ERR(p))
 216                        break;
 217                err = m->op->show(m, p);
 218                if (err < 0)
 219                        break;
 220                if (unlikely(err))
 221                        m->count = 0;
 222                if (unlikely(!m->count)) {
 223                        p = m->op->next(m, p, &pos);
 224                        m->index = pos;
 225                        continue;
 226                }
 227                if (m->count < m->size)
 228                        goto Fill;
 229                m->op->stop(m, p);
 230                kfree(m->buf);
 231                m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
 232                if (!m->buf)
 233                        goto Enomem;
 234                m->count = 0;
 235                m->version = 0;
 236                pos = m->index;
 237                p = m->op->start(m, &pos);
 238        }
 239        m->op->stop(m, p);
 240        m->count = 0;
 241        goto Done;
 242Fill:
 243        /* they want more? let's try to get some more */
 244        while (m->count < size) {
 245                size_t offs = m->count;
 246                loff_t next = pos;
 247                p = m->op->next(m, p, &next);
 248                if (!p || IS_ERR(p)) {
 249                        err = PTR_ERR(p);
 250                        break;
 251                }
 252                err = m->op->show(m, p);
 253                if (seq_overflow(m) || err) {
 254                        m->count = offs;
 255                        if (likely(err <= 0))
 256                                break;
 257                }
 258                pos = next;
 259        }
 260        m->op->stop(m, p);
 261        n = min(m->count, size);
 262        err = copy_to_user(buf, m->buf, n);
 263        if (err)
 264                goto Efault;
 265        copied += n;
 266        m->count -= n;
 267        if (m->count)
 268                m->from = n;
 269        else
 270                pos++;
 271        m->index = pos;
 272Done:
 273        if (!copied)
 274                copied = err;
 275        else {
 276                *ppos += copied;
 277                m->read_pos += copied;
 278        }
 279        file->f_version = m->version;
 280        mutex_unlock(&m->lock);
 281        return copied;
 282Enomem:
 283        err = -ENOMEM;
 284        goto Done;
 285Efault:
 286        err = -EFAULT;
 287        goto Done;
 288}
 289EXPORT_SYMBOL(seq_read);
 290
 291/**
 292 *      seq_lseek -     ->llseek() method for sequential files.
 293 *      @file: the file in question
 294 *      @offset: new position
 295 *      @origin: 0 for absolute, 1 for relative position
 296 *
 297 *      Ready-made ->f_op->llseek()
 298 */
 299loff_t seq_lseek(struct file *file, loff_t offset, int origin)
 300{
 301        struct seq_file *m = file->private_data;
 302        loff_t retval = -EINVAL;
 303
 304        mutex_lock(&m->lock);
 305        m->version = file->f_version;
 306        switch (origin) {
 307                case 1:
 308                        offset += file->f_pos;
 309                case 0:
 310                        if (offset < 0)
 311                                break;
 312                        retval = offset;
 313                        if (offset != m->read_pos) {
 314                                while ((retval=traverse(m, offset)) == -EAGAIN)
 315                                        ;
 316                                if (retval) {
 317                                        /* with extreme prejudice... */
 318                                        file->f_pos = 0;
 319                                        m->read_pos = 0;
 320                                        m->version = 0;
 321                                        m->index = 0;
 322                                        m->count = 0;
 323                                } else {
 324                                        m->read_pos = offset;
 325                                        retval = file->f_pos = offset;
 326                                }
 327                        }
 328        }
 329        file->f_version = m->version;
 330        mutex_unlock(&m->lock);
 331        return retval;
 332}
 333EXPORT_SYMBOL(seq_lseek);
 334
 335/**
 336 *      seq_release -   free the structures associated with sequential file.
 337 *      @file: file in question
 338 *      @inode: file->f_path.dentry->d_inode
 339 *
 340 *      Frees the structures associated with sequential file; can be used
 341 *      as ->f_op->release() if you don't have private data to destroy.
 342 */
 343int seq_release(struct inode *inode, struct file *file)
 344{
 345        struct seq_file *m = file->private_data;
 346        kfree(m->buf);
 347        kfree(m);
 348        return 0;
 349}
 350EXPORT_SYMBOL(seq_release);
 351
 352/**
 353 *      seq_escape -    print string into buffer, escaping some characters
 354 *      @m:     target buffer
 355 *      @s:     string
 356 *      @esc:   set of characters that need escaping
 357 *
 358 *      Puts string into buffer, replacing each occurrence of character from
 359 *      @esc with usual octal escape.  Returns 0 in case of success, -1 - in
 360 *      case of overflow.
 361 */
 362int seq_escape(struct seq_file *m, const char *s, const char *esc)
 363{
 364        char *end = m->buf + m->size;
 365        char *p;
 366        char c;
 367
 368        for (p = m->buf + m->count; (c = *s) != '\0' && p < end; s++) {
 369                if (!strchr(esc, c)) {
 370                        *p++ = c;
 371                        continue;
 372                }
 373                if (p + 3 < end) {
 374                        *p++ = '\\';
 375                        *p++ = '0' + ((c & 0300) >> 6);
 376                        *p++ = '0' + ((c & 070) >> 3);
 377                        *p++ = '0' + (c & 07);
 378                        continue;
 379                }
 380                seq_set_overflow(m);
 381                return -1;
 382        }
 383        m->count = p - m->buf;
 384        return 0;
 385}
 386EXPORT_SYMBOL(seq_escape);
 387
 388int seq_printf(struct seq_file *m, const char *f, ...)
 389{
 390        va_list args;
 391        int len;
 392
 393        if (m->count < m->size) {
 394                va_start(args, f);
 395                len = vsnprintf(m->buf + m->count, m->size - m->count, f, args);
 396                va_end(args);
 397                if (m->count + len < m->size) {
 398                        m->count += len;
 399                        return 0;
 400                }
 401        }
 402        seq_set_overflow(m);
 403        return -1;
 404}
 405EXPORT_SYMBOL(seq_printf);
 406
 407/**
 408 *      mangle_path -   mangle and copy path to buffer beginning
 409 *      @s: buffer start
 410 *      @p: beginning of path in above buffer
 411 *      @esc: set of characters that need escaping
 412 *
 413 *      Copy the path from @p to @s, replacing each occurrence of character from
 414 *      @esc with usual octal escape.
 415 *      Returns pointer past last written character in @s, or NULL in case of
 416 *      failure.
 417 */
 418char *mangle_path(char *s, const char *p, const char *esc)
 419{
 420        while (s <= p) {
 421                char c = *p++;
 422                if (!c) {
 423                        return s;
 424                } else if (!strchr(esc, c)) {
 425                        *s++ = c;
 426                } else if (s + 4 > p) {
 427                        break;
 428                } else {
 429                        *s++ = '\\';
 430                        *s++ = '0' + ((c & 0300) >> 6);
 431                        *s++ = '0' + ((c & 070) >> 3);
 432                        *s++ = '0' + (c & 07);
 433                }
 434        }
 435        return NULL;
 436}
 437EXPORT_SYMBOL(mangle_path);
 438
 439/**
 440 * seq_path - seq_file interface to print a pathname
 441 * @m: the seq_file handle
 442 * @path: the struct path to print
 443 * @esc: set of characters to escape in the output
 444 *
 445 * return the absolute path of 'path', as represented by the
 446 * dentry / mnt pair in the path parameter.
 447 */
 448int seq_path(struct seq_file *m, const struct path *path, const char *esc)
 449{
 450        char *buf;
 451        size_t size = seq_get_buf(m, &buf);
 452        int res = -1;
 453
 454        if (size) {
 455                char *p = d_path(path, buf, size);
 456                if (!IS_ERR(p)) {
 457                        char *end = mangle_path(buf, p, esc);
 458                        if (end)
 459                                res = end - buf;
 460                }
 461        }
 462        seq_commit(m, res);
 463
 464        return res;
 465}
 466EXPORT_SYMBOL(seq_path);
 467
 468/*
 469 * Same as seq_path, but relative to supplied root.
 470 */
 471int seq_path_root(struct seq_file *m, const struct path *path,
 472                  const struct path *root, const char *esc)
 473{
 474        char *buf;
 475        size_t size = seq_get_buf(m, &buf);
 476        int res = -ENAMETOOLONG;
 477
 478        if (size) {
 479                char *p;
 480
 481                p = __d_path(path, root, buf, size);
 482                if (!p)
 483                        return SEQ_SKIP;
 484                res = PTR_ERR(p);
 485                if (!IS_ERR(p)) {
 486                        char *end = mangle_path(buf, p, esc);
 487                        if (end)
 488                                res = end - buf;
 489                        else
 490                                res = -ENAMETOOLONG;
 491                }
 492        }
 493        seq_commit(m, res);
 494
 495        return res < 0 && res != -ENAMETOOLONG ? res : 0;
 496}
 497
 498/*
 499 * returns the path of the 'dentry' from the root of its filesystem.
 500 */
 501int seq_dentry(struct seq_file *m, struct dentry *dentry, const char *esc)
 502{
 503        char *buf;
 504        size_t size = seq_get_buf(m, &buf);
 505        int res = -1;
 506
 507        if (size) {
 508                char *p = dentry_path(dentry, buf, size);
 509                if (!IS_ERR(p)) {
 510                        char *end = mangle_path(buf, p, esc);
 511                        if (end)
 512                                res = end - buf;
 513                }
 514        }
 515        seq_commit(m, res);
 516
 517        return res;
 518}
 519
 520int seq_bitmap(struct seq_file *m, const unsigned long *bits,
 521                                   unsigned int nr_bits)
 522{
 523        if (m->count < m->size) {
 524                int len = bitmap_scnprintf(m->buf + m->count,
 525                                m->size - m->count, bits, nr_bits);
 526                if (m->count + len < m->size) {
 527                        m->count += len;
 528                        return 0;
 529                }
 530        }
 531        seq_set_overflow(m);
 532        return -1;
 533}
 534EXPORT_SYMBOL(seq_bitmap);
 535
 536int seq_bitmap_list(struct seq_file *m, const unsigned long *bits,
 537                unsigned int nr_bits)
 538{
 539        if (m->count < m->size) {
 540                int len = bitmap_scnlistprintf(m->buf + m->count,
 541                                m->size - m->count, bits, nr_bits);
 542                if (m->count + len < m->size) {
 543                        m->count += len;
 544                        return 0;
 545                }
 546        }
 547        seq_set_overflow(m);
 548        return -1;
 549}
 550EXPORT_SYMBOL(seq_bitmap_list);
 551
 552static void *single_start(struct seq_file *p, loff_t *pos)
 553{
 554        return NULL + (*pos == 0);
 555}
 556
 557static void *single_next(struct seq_file *p, void *v, loff_t *pos)
 558{
 559        ++*pos;
 560        return NULL;
 561}
 562
 563static void single_stop(struct seq_file *p, void *v)
 564{
 565}
 566
 567int single_open(struct file *file, int (*show)(struct seq_file *, void *),
 568                void *data)
 569{
 570        struct seq_operations *op = kmalloc(sizeof(*op), GFP_KERNEL);
 571        int res = -ENOMEM;
 572
 573        if (op) {
 574                op->start = single_start;
 575                op->next = single_next;
 576                op->stop = single_stop;
 577                op->show = show;
 578                res = seq_open(file, op);
 579                if (!res)
 580                        ((struct seq_file *)file->private_data)->private = data;
 581                else
 582                        kfree(op);
 583        }
 584        return res;
 585}
 586EXPORT_SYMBOL(single_open);
 587
 588int single_release(struct inode *inode, struct file *file)
 589{
 590        const struct seq_operations *op = ((struct seq_file *)file->private_data)->op;
 591        int res = seq_release(inode, file);
 592        kfree(op);
 593        return res;
 594}
 595EXPORT_SYMBOL(single_release);
 596
 597int seq_release_private(struct inode *inode, struct file *file)
 598{
 599        struct seq_file *seq = file->private_data;
 600
 601        kfree(seq->private);
 602        seq->private = NULL;
 603        return seq_release(inode, file);
 604}
 605EXPORT_SYMBOL(seq_release_private);
 606
 607void *__seq_open_private(struct file *f, const struct seq_operations *ops,
 608                int psize)
 609{
 610        int rc;
 611        void *private;
 612        struct seq_file *seq;
 613
 614        private = kzalloc(psize, GFP_KERNEL);
 615        if (private == NULL)
 616                goto out;
 617
 618        rc = seq_open(f, ops);
 619        if (rc < 0)
 620                goto out_free;
 621
 622        seq = f->private_data;
 623        seq->private = private;
 624        return private;
 625
 626out_free:
 627        kfree(private);
 628out:
 629        return NULL;
 630}
 631EXPORT_SYMBOL(__seq_open_private);
 632
 633int seq_open_private(struct file *filp, const struct seq_operations *ops,
 634                int psize)
 635{
 636        return __seq_open_private(filp, ops, psize) ? 0 : -ENOMEM;
 637}
 638EXPORT_SYMBOL(seq_open_private);
 639
 640int seq_putc(struct seq_file *m, char c)
 641{
 642        if (m->count < m->size) {
 643                m->buf[m->count++] = c;
 644                return 0;
 645        }
 646        return -1;
 647}
 648EXPORT_SYMBOL(seq_putc);
 649
 650int seq_puts(struct seq_file *m, const char *s)
 651{
 652        int len = strlen(s);
 653        if (m->count + len < m->size) {
 654                memcpy(m->buf + m->count, s, len);
 655                m->count += len;
 656                return 0;
 657        }
 658        seq_set_overflow(m);
 659        return -1;
 660}
 661EXPORT_SYMBOL(seq_puts);
 662
 663/*
 664 * A helper routine for putting decimal numbers without rich format of printf().
 665 * only 'unsigned long long' is supported.
 666 * This routine will put one byte delimiter + number into seq_file.
 667 * This routine is very quick when you show lots of numbers.
 668 * In usual cases, it will be better to use seq_printf(). It's easier to read.
 669 */
 670int seq_put_decimal_ull(struct seq_file *m, char delimiter,
 671                        unsigned long long num)
 672{
 673        int len;
 674
 675        if (m->count + 2 >= m->size) /* we'll write 2 bytes at least */
 676                goto overflow;
 677
 678        if (delimiter)
 679                m->buf[m->count++] = delimiter;
 680
 681        if (num < 10) {
 682                m->buf[m->count++] = num + '0';
 683                return 0;
 684        }
 685
 686        len = num_to_str(m->buf + m->count, m->size - m->count, num);
 687        if (!len)
 688                goto overflow;
 689        m->count += len;
 690        return 0;
 691overflow:
 692        seq_set_overflow(m);
 693        return -1;
 694}
 695EXPORT_SYMBOL(seq_put_decimal_ull);
 696
 697int seq_put_decimal_ll(struct seq_file *m, char delimiter,
 698                        long long num)
 699{
 700        if (num < 0) {
 701                if (m->count + 3 >= m->size) {
 702                        seq_set_overflow(m);
 703                        return -1;
 704                }
 705                if (delimiter)
 706                        m->buf[m->count++] = delimiter;
 707                num = -num;
 708                delimiter = '-';
 709        }
 710        return seq_put_decimal_ull(m, delimiter, num);
 711
 712}
 713EXPORT_SYMBOL(seq_put_decimal_ll);
 714
 715/**
 716 * seq_write - write arbitrary data to buffer
 717 * @seq: seq_file identifying the buffer to which data should be written
 718 * @data: data address
 719 * @len: number of bytes
 720 *
 721 * Return 0 on success, non-zero otherwise.
 722 */
 723int seq_write(struct seq_file *seq, const void *data, size_t len)
 724{
 725        if (seq->count + len < seq->size) {
 726                memcpy(seq->buf + seq->count, data, len);
 727                seq->count += len;
 728                return 0;
 729        }
 730        seq_set_overflow(seq);
 731        return -1;
 732}
 733EXPORT_SYMBOL(seq_write);
 734
 735struct list_head *seq_list_start(struct list_head *head, loff_t pos)
 736{
 737        struct list_head *lh;
 738
 739        list_for_each(lh, head)
 740                if (pos-- == 0)
 741                        return lh;
 742
 743        return NULL;
 744}
 745EXPORT_SYMBOL(seq_list_start);
 746
 747struct list_head *seq_list_start_head(struct list_head *head, loff_t pos)
 748{
 749        if (!pos)
 750                return head;
 751
 752        return seq_list_start(head, pos - 1);
 753}
 754EXPORT_SYMBOL(seq_list_start_head);
 755
 756struct list_head *seq_list_next(void *v, struct list_head *head, loff_t *ppos)
 757{
 758        struct list_head *lh;
 759
 760        lh = ((struct list_head *)v)->next;
 761        ++*ppos;
 762        return lh == head ? NULL : lh;
 763}
 764EXPORT_SYMBOL(seq_list_next);
 765
 766/**
 767 * seq_hlist_start - start an iteration of a hlist
 768 * @head: the head of the hlist
 769 * @pos:  the start position of the sequence
 770 *
 771 * Called at seq_file->op->start().
 772 */
 773struct hlist_node *seq_hlist_start(struct hlist_head *head, loff_t pos)
 774{
 775        struct hlist_node *node;
 776
 777        hlist_for_each(node, head)
 778                if (pos-- == 0)
 779                        return node;
 780        return NULL;
 781}
 782EXPORT_SYMBOL(seq_hlist_start);
 783
 784/**
 785 * seq_hlist_start_head - start an iteration of a hlist
 786 * @head: the head of the hlist
 787 * @pos:  the start position of the sequence
 788 *
 789 * Called at seq_file->op->start(). Call this function if you want to
 790 * print a header at the top of the output.
 791 */
 792struct hlist_node *seq_hlist_start_head(struct hlist_head *head, loff_t pos)
 793{
 794        if (!pos)
 795                return SEQ_START_TOKEN;
 796
 797        return seq_hlist_start(head, pos - 1);
 798}
 799EXPORT_SYMBOL(seq_hlist_start_head);
 800
 801/**
 802 * seq_hlist_next - move to the next position of the hlist
 803 * @v:    the current iterator
 804 * @head: the head of the hlist
 805 * @ppos: the current position
 806 *
 807 * Called at seq_file->op->next().
 808 */
 809struct hlist_node *seq_hlist_next(void *v, struct hlist_head *head,
 810                                  loff_t *ppos)
 811{
 812        struct hlist_node *node = v;
 813
 814        ++*ppos;
 815        if (v == SEQ_START_TOKEN)
 816                return head->first;
 817        else
 818                return node->next;
 819}
 820EXPORT_SYMBOL(seq_hlist_next);
 821
 822/**
 823 * seq_hlist_start_rcu - start an iteration of a hlist protected by RCU
 824 * @head: the head of the hlist
 825 * @pos:  the start position of the sequence
 826 *
 827 * Called at seq_file->op->start().
 828 *
 829 * This list-traversal primitive may safely run concurrently with
 830 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 831 * as long as the traversal is guarded by rcu_read_lock().
 832 */
 833struct hlist_node *seq_hlist_start_rcu(struct hlist_head *head,
 834                                       loff_t pos)
 835{
 836        struct hlist_node *node;
 837
 838        __hlist_for_each_rcu(node, head)
 839                if (pos-- == 0)
 840                        return node;
 841        return NULL;
 842}
 843EXPORT_SYMBOL(seq_hlist_start_rcu);
 844
 845/**
 846 * seq_hlist_start_head_rcu - start an iteration of a hlist protected by RCU
 847 * @head: the head of the hlist
 848 * @pos:  the start position of the sequence
 849 *
 850 * Called at seq_file->op->start(). Call this function if you want to
 851 * print a header at the top of the output.
 852 *
 853 * This list-traversal primitive may safely run concurrently with
 854 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 855 * as long as the traversal is guarded by rcu_read_lock().
 856 */
 857struct hlist_node *seq_hlist_start_head_rcu(struct hlist_head *head,
 858                                            loff_t pos)
 859{
 860        if (!pos)
 861                return SEQ_START_TOKEN;
 862
 863        return seq_hlist_start_rcu(head, pos - 1);
 864}
 865EXPORT_SYMBOL(seq_hlist_start_head_rcu);
 866
 867/**
 868 * seq_hlist_next_rcu - move to the next position of the hlist protected by RCU
 869 * @v:    the current iterator
 870 * @head: the head of the hlist
 871 * @ppos: the current position
 872 *
 873 * Called at seq_file->op->next().
 874 *
 875 * This list-traversal primitive may safely run concurrently with
 876 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 877 * as long as the traversal is guarded by rcu_read_lock().
 878 */
 879struct hlist_node *seq_hlist_next_rcu(void *v,
 880                                      struct hlist_head *head,
 881                                      loff_t *ppos)
 882{
 883        struct hlist_node *node = v;
 884
 885        ++*ppos;
 886        if (v == SEQ_START_TOKEN)
 887                return rcu_dereference(head->first);
 888        else
 889                return rcu_dereference(node->next);
 890}
 891EXPORT_SYMBOL(seq_hlist_next_rcu);
 892
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