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#include <linux/cred.h>
  13
  14#include <asm/uaccess.h>
  15#include <asm/page.h>
  16
  17
  18/*
  19 * seq_files have a buffer which can may overflow. When this happens a larger
  20 * buffer is reallocated and all the data will be printed again.
  21 * The overflow state is true when m->count == m->size.
  22 */
  23static bool seq_overflow(struct seq_file *m)
  24{
  25        return m->count == m->size;
  26}
  27
  28static void seq_set_overflow(struct seq_file *m)
  29{
  30        m->count = m->size;
  31}
  32
  33/**
  34 *      seq_open -      initialize sequential file
  35 *      @file: file we initialize
  36 *      @op: method table describing the sequence
  37 *
  38 *      seq_open() sets @file, associating it with a sequence described
  39 *      by @op.  @op->start() sets the iterator up and returns the first
  40 *      element of sequence. @op->stop() shuts it down.  @op->next()
  41 *      returns the next element of sequence.  @op->show() prints element
  42 *      into the buffer.  In case of error ->start() and ->next() return
  43 *      ERR_PTR(error).  In the end of sequence they return %NULL. ->show()
  44 *      returns 0 in case of success and negative number in case of error.
  45 *      Returning SEQ_SKIP means "discard this element and move on".
  46 */
  47int seq_open(struct file *file, const struct seq_operations *op)
  48{
  49        struct seq_file *p = file->private_data;
  50
  51        if (!p) {
  52                p = kmalloc(sizeof(*p), GFP_KERNEL);
  53                if (!p)
  54                        return -ENOMEM;
  55                file->private_data = p;
  56        }
  57        memset(p, 0, sizeof(*p));
  58        mutex_init(&p->lock);
  59        p->op = op;
  60#ifdef CONFIG_USER_NS
  61        p->user_ns = file->f_cred->user_ns;
  62#endif
  63
  64        /*
  65         * Wrappers around seq_open(e.g. swaps_open) need to be
  66         * aware of this. If they set f_version themselves, they
  67         * should call seq_open first and then set f_version.
  68         */
  69        file->f_version = 0;
  70
  71        /*
  72         * seq_files support lseek() and pread().  They do not implement
  73         * write() at all, but we clear FMODE_PWRITE here for historical
  74         * reasons.
  75         *
  76         * If a client of seq_files a) implements file.write() and b) wishes to
  77         * support pwrite() then that client will need to implement its own
  78         * file.open() which calls seq_open() and then sets FMODE_PWRITE.
  79         */
  80        file->f_mode &= ~FMODE_PWRITE;
  81        return 0;
  82}
  83EXPORT_SYMBOL(seq_open);
  84
  85static int traverse(struct seq_file *m, loff_t offset)
  86{
  87        loff_t pos = 0, index;
  88        int error = 0;
  89        void *p;
  90
  91        m->version = 0;
  92        index = 0;
  93        m->count = m->from = 0;
  94        if (!offset) {
  95                m->index = index;
  96                return 0;
  97        }
  98        if (!m->buf) {
  99                m->buf = kmalloc(m->size = PAGE_SIZE, GFP_KERNEL);
 100                if (!m->buf)
 101                        return -ENOMEM;
 102        }
 103        p = m->op->start(m, &index);
 104        while (p) {
 105                error = PTR_ERR(p);
 106                if (IS_ERR(p))
 107                        break;
 108                error = m->op->show(m, p);
 109                if (error < 0)
 110                        break;
 111                if (unlikely(error)) {
 112                        error = 0;
 113                        m->count = 0;
 114                }
 115                if (seq_overflow(m))
 116                        goto Eoverflow;
 117                if (pos + m->count > offset) {
 118                        m->from = offset - pos;
 119                        m->count -= m->from;
 120                        m->index = index;
 121                        break;
 122                }
 123                pos += m->count;
 124                m->count = 0;
 125                if (pos == offset) {
 126                        index++;
 127                        m->index = index;
 128                        break;
 129                }
 130                p = m->op->next(m, p, &index);
 131        }
 132        m->op->stop(m, p);
 133        m->index = index;
 134        return error;
 135
 136Eoverflow:
 137        m->op->stop(m, p);
 138        kfree(m->buf);
 139        m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
 140        return !m->buf ? -ENOMEM : -EAGAIN;
 141}
 142
 143/**
 144 *      seq_read -      ->read() method for sequential files.
 145 *      @file: the file to read from
 146 *      @buf: the buffer to read to
 147 *      @size: the maximum number of bytes to read
 148 *      @ppos: the current position in the file
 149 *
 150 *      Ready-made ->f_op->read()
 151 */
 152ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
 153{
 154        struct seq_file *m = file->private_data;
 155        size_t copied = 0;
 156        loff_t pos;
 157        size_t n;
 158        void *p;
 159        int err = 0;
 160
 161        mutex_lock(&m->lock);
 162
 163        /*
 164         * seq_file->op->..m_start/m_stop/m_next may do special actions
 165         * or optimisations based on the file->f_version, so we want to
 166         * pass the file->f_version to those methods.
 167         *
 168         * seq_file->version is just copy of f_version, and seq_file
 169         * methods can treat it simply as file version.
 170         * It is copied in first and copied out after all operations.
 171         * It is convenient to have it as  part of structure to avoid the
 172         * need of passing another argument to all the seq_file methods.
 173         */
 174        m->version = file->f_version;
 175
 176        /* Don't assume *ppos is where we left it */
 177        if (unlikely(*ppos != m->read_pos)) {
 178                while ((err = traverse(m, *ppos)) == -EAGAIN)
 179                        ;
 180                if (err) {
 181                        /* With prejudice... */
 182                        m->read_pos = 0;
 183                        m->version = 0;
 184                        m->index = 0;
 185                        m->count = 0;
 186                        goto Done;
 187                } else {
 188                        m->read_pos = *ppos;
 189                }
 190        }
 191
 192        /* grab buffer if we didn't have one */
 193        if (!m->buf) {
 194                m->buf = kmalloc(m->size = PAGE_SIZE, GFP_KERNEL);
 195                if (!m->buf)
 196                        goto Enomem;
 197        }
 198        /* if not empty - flush it first */
 199        if (m->count) {
 200                n = min(m->count, size);
 201                err = copy_to_user(buf, m->buf + m->from, n);
 202                if (err)
 203                        goto Efault;
 204                m->count -= n;
 205                m->from += n;
 206                size -= n;
 207                buf += n;
 208                copied += n;
 209                if (!m->count)
 210                        m->index++;
 211                if (!size)
 212                        goto Done;
 213        }
 214        /* we need at least one record in buffer */
 215        pos = m->index;
 216        p = m->op->start(m, &pos);
 217        while (1) {
 218                err = PTR_ERR(p);
 219                if (!p || IS_ERR(p))
 220                        break;
 221                err = m->op->show(m, p);
 222                if (err < 0)
 223                        break;
 224                if (unlikely(err))
 225                        m->count = 0;
 226                if (unlikely(!m->count)) {
 227                        p = m->op->next(m, p, &pos);
 228                        m->index = pos;
 229                        continue;
 230                }
 231                if (m->count < m->size)
 232                        goto Fill;
 233                m->op->stop(m, p);
 234                kfree(m->buf);
 235                m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
 236                if (!m->buf)
 237                        goto Enomem;
 238                m->count = 0;
 239                m->version = 0;
 240                pos = m->index;
 241                p = m->op->start(m, &pos);
 242        }
 243        m->op->stop(m, p);
 244        m->count = 0;
 245        goto Done;
 246Fill:
 247        /* they want more? let's try to get some more */
 248        while (m->count < size) {
 249                size_t offs = m->count;
 250                loff_t next = pos;
 251                p = m->op->next(m, p, &next);
 252                if (!p || IS_ERR(p)) {
 253                        err = PTR_ERR(p);
 254                        break;
 255                }
 256                err = m->op->show(m, p);
 257                if (seq_overflow(m) || err) {
 258                        m->count = offs;
 259                        if (likely(err <= 0))
 260                                break;
 261                }
 262                pos = next;
 263        }
 264        m->op->stop(m, p);
 265        n = min(m->count, size);
 266        err = copy_to_user(buf, m->buf, n);
 267        if (err)
 268                goto Efault;
 269        copied += n;
 270        m->count -= n;
 271        if (m->count)
 272                m->from = n;
 273        else
 274                pos++;
 275        m->index = pos;
 276Done:
 277        if (!copied)
 278                copied = err;
 279        else {
 280                *ppos += copied;
 281                m->read_pos += copied;
 282        }
 283        file->f_version = m->version;
 284        mutex_unlock(&m->lock);
 285        return copied;
 286Enomem:
 287        err = -ENOMEM;
 288        goto Done;
 289Efault:
 290        err = -EFAULT;
 291        goto Done;
 292}
 293EXPORT_SYMBOL(seq_read);
 294
 295/**
 296 *      seq_lseek -     ->llseek() method for sequential files.
 297 *      @file: the file in question
 298 *      @offset: new position
 299 *      @origin: 0 for absolute, 1 for relative position
 300 *
 301 *      Ready-made ->f_op->llseek()
 302 */
 303loff_t seq_lseek(struct file *file, loff_t offset, int origin)
 304{
 305        struct seq_file *m = file->private_data;
 306        loff_t retval = -EINVAL;
 307
 308        mutex_lock(&m->lock);
 309        m->version = file->f_version;
 310        switch (origin) {
 311                case 1:
 312                        offset += file->f_pos;
 313                case 0:
 314                        if (offset < 0)
 315                                break;
 316                        retval = offset;
 317                        if (offset != m->read_pos) {
 318                                while ((retval=traverse(m, offset)) == -EAGAIN)
 319                                        ;
 320                                if (retval) {
 321                                        /* with extreme prejudice... */
 322                                        file->f_pos = 0;
 323                                        m->read_pos = 0;
 324                                        m->version = 0;
 325                                        m->index = 0;
 326                                        m->count = 0;
 327                                } else {
 328                                        m->read_pos = offset;
 329                                        retval = file->f_pos = offset;
 330                                }
 331                        }
 332        }
 333        file->f_version = m->version;
 334        mutex_unlock(&m->lock);
 335        return retval;
 336}
 337EXPORT_SYMBOL(seq_lseek);
 338
 339/**
 340 *      seq_release -   free the structures associated with sequential file.
 341 *      @file: file in question
 342 *      @inode: file->f_path.dentry->d_inode
 343 *
 344 *      Frees the structures associated with sequential file; can be used
 345 *      as ->f_op->release() if you don't have private data to destroy.
 346 */
 347int seq_release(struct inode *inode, struct file *file)
 348{
 349        struct seq_file *m = file->private_data;
 350        kfree(m->buf);
 351        kfree(m);
 352        return 0;
 353}
 354EXPORT_SYMBOL(seq_release);
 355
 356/**
 357 *      seq_escape -    print string into buffer, escaping some characters
 358 *      @m:     target buffer
 359 *      @s:     string
 360 *      @esc:   set of characters that need escaping
 361 *
 362 *      Puts string into buffer, replacing each occurrence of character from
 363 *      @esc with usual octal escape.  Returns 0 in case of success, -1 - in
 364 *      case of overflow.
 365 */
 366int seq_escape(struct seq_file *m, const char *s, const char *esc)
 367{
 368        char *end = m->buf + m->size;
 369        char *p;
 370        char c;
 371
 372        for (p = m->buf + m->count; (c = *s) != '\0' && p < end; s++) {
 373                if (!strchr(esc, c)) {
 374                        *p++ = c;
 375                        continue;
 376                }
 377                if (p + 3 < end) {
 378                        *p++ = '\\';
 379                        *p++ = '0' + ((c & 0300) >> 6);
 380                        *p++ = '0' + ((c & 070) >> 3);
 381                        *p++ = '0' + (c & 07);
 382                        continue;
 383                }
 384                seq_set_overflow(m);
 385                return -1;
 386        }
 387        m->count = p - m->buf;
 388        return 0;
 389}
 390EXPORT_SYMBOL(seq_escape);
 391
 392int seq_vprintf(struct seq_file *m, const char *f, va_list args)
 393{
 394        int len;
 395
 396        if (m->count < m->size) {
 397                len = vsnprintf(m->buf + m->count, m->size - m->count, f, args);
 398                if (m->count + len < m->size) {
 399                        m->count += len;
 400                        return 0;
 401                }
 402        }
 403        seq_set_overflow(m);
 404        return -1;
 405}
 406EXPORT_SYMBOL(seq_vprintf);
 407
 408int seq_printf(struct seq_file *m, const char *f, ...)
 409{
 410        int ret;
 411        va_list args;
 412
 413        va_start(args, f);
 414        ret = seq_vprintf(m, f, args);
 415        va_end(args);
 416
 417        return ret;
 418}
 419EXPORT_SYMBOL(seq_printf);
 420
 421/**
 422 *      mangle_path -   mangle and copy path to buffer beginning
 423 *      @s: buffer start
 424 *      @p: beginning of path in above buffer
 425 *      @esc: set of characters that need escaping
 426 *
 427 *      Copy the path from @p to @s, replacing each occurrence of character from
 428 *      @esc with usual octal escape.
 429 *      Returns pointer past last written character in @s, or NULL in case of
 430 *      failure.
 431 */
 432char *mangle_path(char *s, const char *p, const char *esc)
 433{
 434        while (s <= p) {
 435                char c = *p++;
 436                if (!c) {
 437                        return s;
 438                } else if (!strchr(esc, c)) {
 439                        *s++ = c;
 440                } else if (s + 4 > p) {
 441                        break;
 442                } else {
 443                        *s++ = '\\';
 444                        *s++ = '0' + ((c & 0300) >> 6);
 445                        *s++ = '0' + ((c & 070) >> 3);
 446                        *s++ = '0' + (c & 07);
 447                }
 448        }
 449        return NULL;
 450}
 451EXPORT_SYMBOL(mangle_path);
 452
 453/**
 454 * seq_path - seq_file interface to print a pathname
 455 * @m: the seq_file handle
 456 * @path: the struct path to print
 457 * @esc: set of characters to escape in the output
 458 *
 459 * return the absolute path of 'path', as represented by the
 460 * dentry / mnt pair in the path parameter.
 461 */
 462int seq_path(struct seq_file *m, const struct path *path, const char *esc)
 463{
 464        char *buf;
 465        size_t size = seq_get_buf(m, &buf);
 466        int res = -1;
 467
 468        if (size) {
 469                char *p = d_path(path, buf, size);
 470                if (!IS_ERR(p)) {
 471                        char *end = mangle_path(buf, p, esc);
 472                        if (end)
 473                                res = end - buf;
 474                }
 475        }
 476        seq_commit(m, res);
 477
 478        return res;
 479}
 480EXPORT_SYMBOL(seq_path);
 481
 482/*
 483 * Same as seq_path, but relative to supplied root.
 484 */
 485int seq_path_root(struct seq_file *m, const struct path *path,
 486                  const struct path *root, const char *esc)
 487{
 488        char *buf;
 489        size_t size = seq_get_buf(m, &buf);
 490        int res = -ENAMETOOLONG;
 491
 492        if (size) {
 493                char *p;
 494
 495                p = __d_path(path, root, buf, size);
 496                if (!p)
 497                        return SEQ_SKIP;
 498                res = PTR_ERR(p);
 499                if (!IS_ERR(p)) {
 500                        char *end = mangle_path(buf, p, esc);
 501                        if (end)
 502                                res = end - buf;
 503                        else
 504                                res = -ENAMETOOLONG;
 505                }
 506        }
 507        seq_commit(m, res);
 508
 509        return res < 0 && res != -ENAMETOOLONG ? res : 0;
 510}
 511
 512/*
 513 * returns the path of the 'dentry' from the root of its filesystem.
 514 */
 515int seq_dentry(struct seq_file *m, struct dentry *dentry, const char *esc)
 516{
 517        char *buf;
 518        size_t size = seq_get_buf(m, &buf);
 519        int res = -1;
 520
 521        if (size) {
 522                char *p = dentry_path(dentry, buf, size);
 523                if (!IS_ERR(p)) {
 524                        char *end = mangle_path(buf, p, esc);
 525                        if (end)
 526                                res = end - buf;
 527                }
 528        }
 529        seq_commit(m, res);
 530
 531        return res;
 532}
 533
 534int seq_bitmap(struct seq_file *m, const unsigned long *bits,
 535                                   unsigned int nr_bits)
 536{
 537        if (m->count < m->size) {
 538                int len = bitmap_scnprintf(m->buf + m->count,
 539                                m->size - m->count, bits, nr_bits);
 540                if (m->count + len < m->size) {
 541                        m->count += len;
 542                        return 0;
 543                }
 544        }
 545        seq_set_overflow(m);
 546        return -1;
 547}
 548EXPORT_SYMBOL(seq_bitmap);
 549
 550int seq_bitmap_list(struct seq_file *m, const unsigned long *bits,
 551                unsigned int nr_bits)
 552{
 553        if (m->count < m->size) {
 554                int len = bitmap_scnlistprintf(m->buf + m->count,
 555                                m->size - m->count, bits, nr_bits);
 556                if (m->count + len < m->size) {
 557                        m->count += len;
 558                        return 0;
 559                }
 560        }
 561        seq_set_overflow(m);
 562        return -1;
 563}
 564EXPORT_SYMBOL(seq_bitmap_list);
 565
 566static void *single_start(struct seq_file *p, loff_t *pos)
 567{
 568        return NULL + (*pos == 0);
 569}
 570
 571static void *single_next(struct seq_file *p, void *v, loff_t *pos)
 572{
 573        ++*pos;
 574        return NULL;
 575}
 576
 577static void single_stop(struct seq_file *p, void *v)
 578{
 579}
 580
 581int single_open(struct file *file, int (*show)(struct seq_file *, void *),
 582                void *data)
 583{
 584        struct seq_operations *op = kmalloc(sizeof(*op), GFP_KERNEL);
 585        int res = -ENOMEM;
 586
 587        if (op) {
 588                op->start = single_start;
 589                op->next = single_next;
 590                op->stop = single_stop;
 591                op->show = show;
 592                res = seq_open(file, op);
 593                if (!res)
 594                        ((struct seq_file *)file->private_data)->private = data;
 595                else
 596                        kfree(op);
 597        }
 598        return res;
 599}
 600EXPORT_SYMBOL(single_open);
 601
 602int single_release(struct inode *inode, struct file *file)
 603{
 604        const struct seq_operations *op = ((struct seq_file *)file->private_data)->op;
 605        int res = seq_release(inode, file);
 606        kfree(op);
 607        return res;
 608}
 609EXPORT_SYMBOL(single_release);
 610
 611int seq_release_private(struct inode *inode, struct file *file)
 612{
 613        struct seq_file *seq = file->private_data;
 614
 615        kfree(seq->private);
 616        seq->private = NULL;
 617        return seq_release(inode, file);
 618}
 619EXPORT_SYMBOL(seq_release_private);
 620
 621void *__seq_open_private(struct file *f, const struct seq_operations *ops,
 622                int psize)
 623{
 624        int rc;
 625        void *private;
 626        struct seq_file *seq;
 627
 628        private = kzalloc(psize, GFP_KERNEL);
 629        if (private == NULL)
 630                goto out;
 631
 632        rc = seq_open(f, ops);
 633        if (rc < 0)
 634                goto out_free;
 635
 636        seq = f->private_data;
 637        seq->private = private;
 638        return private;
 639
 640out_free:
 641        kfree(private);
 642out:
 643        return NULL;
 644}
 645EXPORT_SYMBOL(__seq_open_private);
 646
 647int seq_open_private(struct file *filp, const struct seq_operations *ops,
 648                int psize)
 649{
 650        return __seq_open_private(filp, ops, psize) ? 0 : -ENOMEM;
 651}
 652EXPORT_SYMBOL(seq_open_private);
 653
 654int seq_putc(struct seq_file *m, char c)
 655{
 656        if (m->count < m->size) {
 657                m->buf[m->count++] = c;
 658                return 0;
 659        }
 660        return -1;
 661}
 662EXPORT_SYMBOL(seq_putc);
 663
 664int seq_puts(struct seq_file *m, const char *s)
 665{
 666        int len = strlen(s);
 667        if (m->count + len < m->size) {
 668                memcpy(m->buf + m->count, s, len);
 669                m->count += len;
 670                return 0;
 671        }
 672        seq_set_overflow(m);
 673        return -1;
 674}
 675EXPORT_SYMBOL(seq_puts);
 676
 677/*
 678 * A helper routine for putting decimal numbers without rich format of printf().
 679 * only 'unsigned long long' is supported.
 680 * This routine will put one byte delimiter + number into seq_file.
 681 * This routine is very quick when you show lots of numbers.
 682 * In usual cases, it will be better to use seq_printf(). It's easier to read.
 683 */
 684int seq_put_decimal_ull(struct seq_file *m, char delimiter,
 685                        unsigned long long num)
 686{
 687        int len;
 688
 689        if (m->count + 2 >= m->size) /* we'll write 2 bytes at least */
 690                goto overflow;
 691
 692        if (delimiter)
 693                m->buf[m->count++] = delimiter;
 694
 695        if (num < 10) {
 696                m->buf[m->count++] = num + '0';
 697                return 0;
 698        }
 699
 700        len = num_to_str(m->buf + m->count, m->size - m->count, num);
 701        if (!len)
 702                goto overflow;
 703        m->count += len;
 704        return 0;
 705overflow:
 706        seq_set_overflow(m);
 707        return -1;
 708}
 709EXPORT_SYMBOL(seq_put_decimal_ull);
 710
 711int seq_put_decimal_ll(struct seq_file *m, char delimiter,
 712                        long long num)
 713{
 714        if (num < 0) {
 715                if (m->count + 3 >= m->size) {
 716                        seq_set_overflow(m);
 717                        return -1;
 718                }
 719                if (delimiter)
 720                        m->buf[m->count++] = delimiter;
 721                num = -num;
 722                delimiter = '-';
 723        }
 724        return seq_put_decimal_ull(m, delimiter, num);
 725
 726}
 727EXPORT_SYMBOL(seq_put_decimal_ll);
 728
 729/**
 730 * seq_write - write arbitrary data to buffer
 731 * @seq: seq_file identifying the buffer to which data should be written
 732 * @data: data address
 733 * @len: number of bytes
 734 *
 735 * Return 0 on success, non-zero otherwise.
 736 */
 737int seq_write(struct seq_file *seq, const void *data, size_t len)
 738{
 739        if (seq->count + len < seq->size) {
 740                memcpy(seq->buf + seq->count, data, len);
 741                seq->count += len;
 742                return 0;
 743        }
 744        seq_set_overflow(seq);
 745        return -1;
 746}
 747EXPORT_SYMBOL(seq_write);
 748
 749struct list_head *seq_list_start(struct list_head *head, loff_t pos)
 750{
 751        struct list_head *lh;
 752
 753        list_for_each(lh, head)
 754                if (pos-- == 0)
 755                        return lh;
 756
 757        return NULL;
 758}
 759EXPORT_SYMBOL(seq_list_start);
 760
 761struct list_head *seq_list_start_head(struct list_head *head, loff_t pos)
 762{
 763        if (!pos)
 764                return head;
 765
 766        return seq_list_start(head, pos - 1);
 767}
 768EXPORT_SYMBOL(seq_list_start_head);
 769
 770struct list_head *seq_list_next(void *v, struct list_head *head, loff_t *ppos)
 771{
 772        struct list_head *lh;
 773
 774        lh = ((struct list_head *)v)->next;
 775        ++*ppos;
 776        return lh == head ? NULL : lh;
 777}
 778EXPORT_SYMBOL(seq_list_next);
 779
 780/**
 781 * seq_hlist_start - start an iteration of a hlist
 782 * @head: the head of the hlist
 783 * @pos:  the start position of the sequence
 784 *
 785 * Called at seq_file->op->start().
 786 */
 787struct hlist_node *seq_hlist_start(struct hlist_head *head, loff_t pos)
 788{
 789        struct hlist_node *node;
 790
 791        hlist_for_each(node, head)
 792                if (pos-- == 0)
 793                        return node;
 794        return NULL;
 795}
 796EXPORT_SYMBOL(seq_hlist_start);
 797
 798/**
 799 * seq_hlist_start_head - start an iteration of a hlist
 800 * @head: the head of the hlist
 801 * @pos:  the start position of the sequence
 802 *
 803 * Called at seq_file->op->start(). Call this function if you want to
 804 * print a header at the top of the output.
 805 */
 806struct hlist_node *seq_hlist_start_head(struct hlist_head *head, loff_t pos)
 807{
 808        if (!pos)
 809                return SEQ_START_TOKEN;
 810
 811        return seq_hlist_start(head, pos - 1);
 812}
 813EXPORT_SYMBOL(seq_hlist_start_head);
 814
 815/**
 816 * seq_hlist_next - move to the next position of the hlist
 817 * @v:    the current iterator
 818 * @head: the head of the hlist
 819 * @ppos: the current position
 820 *
 821 * Called at seq_file->op->next().
 822 */
 823struct hlist_node *seq_hlist_next(void *v, struct hlist_head *head,
 824                                  loff_t *ppos)
 825{
 826        struct hlist_node *node = v;
 827
 828        ++*ppos;
 829        if (v == SEQ_START_TOKEN)
 830                return head->first;
 831        else
 832                return node->next;
 833}
 834EXPORT_SYMBOL(seq_hlist_next);
 835
 836/**
 837 * seq_hlist_start_rcu - start an iteration of a hlist protected by RCU
 838 * @head: the head of the hlist
 839 * @pos:  the start position of the sequence
 840 *
 841 * Called at seq_file->op->start().
 842 *
 843 * This list-traversal primitive may safely run concurrently with
 844 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 845 * as long as the traversal is guarded by rcu_read_lock().
 846 */
 847struct hlist_node *seq_hlist_start_rcu(struct hlist_head *head,
 848                                       loff_t pos)
 849{
 850        struct hlist_node *node;
 851
 852        __hlist_for_each_rcu(node, head)
 853                if (pos-- == 0)
 854                        return node;
 855        return NULL;
 856}
 857EXPORT_SYMBOL(seq_hlist_start_rcu);
 858
 859/**
 860 * seq_hlist_start_head_rcu - start an iteration of a hlist protected by RCU
 861 * @head: the head of the hlist
 862 * @pos:  the start position of the sequence
 863 *
 864 * Called at seq_file->op->start(). Call this function if you want to
 865 * print a header at the top of the output.
 866 *
 867 * This list-traversal primitive may safely run concurrently with
 868 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 869 * as long as the traversal is guarded by rcu_read_lock().
 870 */
 871struct hlist_node *seq_hlist_start_head_rcu(struct hlist_head *head,
 872                                            loff_t pos)
 873{
 874        if (!pos)
 875                return SEQ_START_TOKEN;
 876
 877        return seq_hlist_start_rcu(head, pos - 1);
 878}
 879EXPORT_SYMBOL(seq_hlist_start_head_rcu);
 880
 881/**
 882 * seq_hlist_next_rcu - move to the next position of the hlist protected by RCU
 883 * @v:    the current iterator
 884 * @head: the head of the hlist
 885 * @ppos: the current position
 886 *
 887 * Called at seq_file->op->next().
 888 *
 889 * This list-traversal primitive may safely run concurrently with
 890 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 891 * as long as the traversal is guarded by rcu_read_lock().
 892 */
 893struct hlist_node *seq_hlist_next_rcu(void *v,
 894                                      struct hlist_head *head,
 895                                      loff_t *ppos)
 896{
 897        struct hlist_node *node = v;
 898
 899        ++*ppos;
 900        if (v == SEQ_START_TOKEN)
 901                return rcu_dereference(head->first);
 902        else
 903                return rcu_dereference(node->next);
 904}
 905EXPORT_SYMBOL(seq_hlist_next_rcu);
 906
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