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 *      @whence: 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 whence)
 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 (whence) {
 311        case SEEK_CUR:
 312                offset += file->f_pos;
 313        case SEEK_SET:
 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                } else {
 332                        file->f_pos = offset;
 333                }
 334        }
 335        file->f_version = m->version;
 336        mutex_unlock(&m->lock);
 337        return retval;
 338}
 339EXPORT_SYMBOL(seq_lseek);
 340
 341/**
 342 *      seq_release -   free the structures associated with sequential file.
 343 *      @file: file in question
 344 *      @inode: its inode
 345 *
 346 *      Frees the structures associated with sequential file; can be used
 347 *      as ->f_op->release() if you don't have private data to destroy.
 348 */
 349int seq_release(struct inode *inode, struct file *file)
 350{
 351        struct seq_file *m = file->private_data;
 352        kfree(m->buf);
 353        kfree(m);
 354        return 0;
 355}
 356EXPORT_SYMBOL(seq_release);
 357
 358/**
 359 *      seq_escape -    print string into buffer, escaping some characters
 360 *      @m:     target buffer
 361 *      @s:     string
 362 *      @esc:   set of characters that need escaping
 363 *
 364 *      Puts string into buffer, replacing each occurrence of character from
 365 *      @esc with usual octal escape.  Returns 0 in case of success, -1 - in
 366 *      case of overflow.
 367 */
 368int seq_escape(struct seq_file *m, const char *s, const char *esc)
 369{
 370        char *end = m->buf + m->size;
 371        char *p;
 372        char c;
 373
 374        for (p = m->buf + m->count; (c = *s) != '\0' && p < end; s++) {
 375                if (!strchr(esc, c)) {
 376                        *p++ = c;
 377                        continue;
 378                }
 379                if (p + 3 < end) {
 380                        *p++ = '\\';
 381                        *p++ = '0' + ((c & 0300) >> 6);
 382                        *p++ = '0' + ((c & 070) >> 3);
 383                        *p++ = '0' + (c & 07);
 384                        continue;
 385                }
 386                seq_set_overflow(m);
 387                return -1;
 388        }
 389        m->count = p - m->buf;
 390        return 0;
 391}
 392EXPORT_SYMBOL(seq_escape);
 393
 394int seq_vprintf(struct seq_file *m, const char *f, va_list args)
 395{
 396        int len;
 397
 398        if (m->count < m->size) {
 399                len = vsnprintf(m->buf + m->count, m->size - m->count, f, args);
 400                if (m->count + len < m->size) {
 401                        m->count += len;
 402                        return 0;
 403                }
 404        }
 405        seq_set_overflow(m);
 406        return -1;
 407}
 408EXPORT_SYMBOL(seq_vprintf);
 409
 410int seq_printf(struct seq_file *m, const char *f, ...)
 411{
 412        int ret;
 413        va_list args;
 414
 415        va_start(args, f);
 416        ret = seq_vprintf(m, f, args);
 417        va_end(args);
 418
 419        return ret;
 420}
 421EXPORT_SYMBOL(seq_printf);
 422
 423/**
 424 *      mangle_path -   mangle and copy path to buffer beginning
 425 *      @s: buffer start
 426 *      @p: beginning of path in above buffer
 427 *      @esc: set of characters that need escaping
 428 *
 429 *      Copy the path from @p to @s, replacing each occurrence of character from
 430 *      @esc with usual octal escape.
 431 *      Returns pointer past last written character in @s, or NULL in case of
 432 *      failure.
 433 */
 434char *mangle_path(char *s, const char *p, const char *esc)
 435{
 436        while (s <= p) {
 437                char c = *p++;
 438                if (!c) {
 439                        return s;
 440                } else if (!strchr(esc, c)) {
 441                        *s++ = c;
 442                } else if (s + 4 > p) {
 443                        break;
 444                } else {
 445                        *s++ = '\\';
 446                        *s++ = '0' + ((c & 0300) >> 6);
 447                        *s++ = '0' + ((c & 070) >> 3);
 448                        *s++ = '0' + (c & 07);
 449                }
 450        }
 451        return NULL;
 452}
 453EXPORT_SYMBOL(mangle_path);
 454
 455/**
 456 * seq_path - seq_file interface to print a pathname
 457 * @m: the seq_file handle
 458 * @path: the struct path to print
 459 * @esc: set of characters to escape in the output
 460 *
 461 * return the absolute path of 'path', as represented by the
 462 * dentry / mnt pair in the path parameter.
 463 */
 464int seq_path(struct seq_file *m, const struct path *path, const char *esc)
 465{
 466        char *buf;
 467        size_t size = seq_get_buf(m, &buf);
 468        int res = -1;
 469
 470        if (size) {
 471                char *p = d_path(path, buf, size);
 472                if (!IS_ERR(p)) {
 473                        char *end = mangle_path(buf, p, esc);
 474                        if (end)
 475                                res = end - buf;
 476                }
 477        }
 478        seq_commit(m, res);
 479
 480        return res;
 481}
 482EXPORT_SYMBOL(seq_path);
 483
 484/*
 485 * Same as seq_path, but relative to supplied root.
 486 */
 487int seq_path_root(struct seq_file *m, const struct path *path,
 488                  const struct path *root, const char *esc)
 489{
 490        char *buf;
 491        size_t size = seq_get_buf(m, &buf);
 492        int res = -ENAMETOOLONG;
 493
 494        if (size) {
 495                char *p;
 496
 497                p = __d_path(path, root, buf, size);
 498                if (!p)
 499                        return SEQ_SKIP;
 500                res = PTR_ERR(p);
 501                if (!IS_ERR(p)) {
 502                        char *end = mangle_path(buf, p, esc);
 503                        if (end)
 504                                res = end - buf;
 505                        else
 506                                res = -ENAMETOOLONG;
 507                }
 508        }
 509        seq_commit(m, res);
 510
 511        return res < 0 && res != -ENAMETOOLONG ? res : 0;
 512}
 513
 514/*
 515 * returns the path of the 'dentry' from the root of its filesystem.
 516 */
 517int seq_dentry(struct seq_file *m, struct dentry *dentry, const char *esc)
 518{
 519        char *buf;
 520        size_t size = seq_get_buf(m, &buf);
 521        int res = -1;
 522
 523        if (size) {
 524                char *p = dentry_path(dentry, buf, size);
 525                if (!IS_ERR(p)) {
 526                        char *end = mangle_path(buf, p, esc);
 527                        if (end)
 528                                res = end - buf;
 529                }
 530        }
 531        seq_commit(m, res);
 532
 533        return res;
 534}
 535
 536int seq_bitmap(struct seq_file *m, const unsigned long *bits,
 537                                   unsigned int nr_bits)
 538{
 539        if (m->count < m->size) {
 540                int len = bitmap_scnprintf(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);
 551
 552int seq_bitmap_list(struct seq_file *m, const unsigned long *bits,
 553                unsigned int nr_bits)
 554{
 555        if (m->count < m->size) {
 556                int len = bitmap_scnlistprintf(m->buf + m->count,
 557                                m->size - m->count, bits, nr_bits);
 558                if (m->count + len < m->size) {
 559                        m->count += len;
 560                        return 0;
 561                }
 562        }
 563        seq_set_overflow(m);
 564        return -1;
 565}
 566EXPORT_SYMBOL(seq_bitmap_list);
 567
 568static void *single_start(struct seq_file *p, loff_t *pos)
 569{
 570        return NULL + (*pos == 0);
 571}
 572
 573static void *single_next(struct seq_file *p, void *v, loff_t *pos)
 574{
 575        ++*pos;
 576        return NULL;
 577}
 578
 579static void single_stop(struct seq_file *p, void *v)
 580{
 581}
 582
 583int single_open(struct file *file, int (*show)(struct seq_file *, void *),
 584                void *data)
 585{
 586        struct seq_operations *op = kmalloc(sizeof(*op), GFP_KERNEL);
 587        int res = -ENOMEM;
 588
 589        if (op) {
 590                op->start = single_start;
 591                op->next = single_next;
 592                op->stop = single_stop;
 593                op->show = show;
 594                res = seq_open(file, op);
 595                if (!res)
 596                        ((struct seq_file *)file->private_data)->private = data;
 597                else
 598                        kfree(op);
 599        }
 600        return res;
 601}
 602EXPORT_SYMBOL(single_open);
 603
 604int single_open_size(struct file *file, int (*show)(struct seq_file *, void *),
 605                void *data, size_t size)
 606{
 607        char *buf = kmalloc(size, GFP_KERNEL);
 608        int ret;
 609        if (!buf)
 610                return -ENOMEM;
 611        ret = single_open(file, show, data);
 612        if (ret) {
 613                kfree(buf);
 614                return ret;
 615        }
 616        ((struct seq_file *)file->private_data)->buf = buf;
 617        ((struct seq_file *)file->private_data)->size = size;
 618        return 0;
 619}
 620EXPORT_SYMBOL(single_open_size);
 621
 622int single_release(struct inode *inode, struct file *file)
 623{
 624        const struct seq_operations *op = ((struct seq_file *)file->private_data)->op;
 625        int res = seq_release(inode, file);
 626        kfree(op);
 627        return res;
 628}
 629EXPORT_SYMBOL(single_release);
 630
 631int seq_release_private(struct inode *inode, struct file *file)
 632{
 633        struct seq_file *seq = file->private_data;
 634
 635        kfree(seq->private);
 636        seq->private = NULL;
 637        return seq_release(inode, file);
 638}
 639EXPORT_SYMBOL(seq_release_private);
 640
 641void *__seq_open_private(struct file *f, const struct seq_operations *ops,
 642                int psize)
 643{
 644        int rc;
 645        void *private;
 646        struct seq_file *seq;
 647
 648        private = kzalloc(psize, GFP_KERNEL);
 649        if (private == NULL)
 650                goto out;
 651
 652        rc = seq_open(f, ops);
 653        if (rc < 0)
 654                goto out_free;
 655
 656        seq = f->private_data;
 657        seq->private = private;
 658        return private;
 659
 660out_free:
 661        kfree(private);
 662out:
 663        return NULL;
 664}
 665EXPORT_SYMBOL(__seq_open_private);
 666
 667int seq_open_private(struct file *filp, const struct seq_operations *ops,
 668                int psize)
 669{
 670        return __seq_open_private(filp, ops, psize) ? 0 : -ENOMEM;
 671}
 672EXPORT_SYMBOL(seq_open_private);
 673
 674int seq_putc(struct seq_file *m, char c)
 675{
 676        if (m->count < m->size) {
 677                m->buf[m->count++] = c;
 678                return 0;
 679        }
 680        return -1;
 681}
 682EXPORT_SYMBOL(seq_putc);
 683
 684int seq_puts(struct seq_file *m, const char *s)
 685{
 686        int len = strlen(s);
 687        if (m->count + len < m->size) {
 688                memcpy(m->buf + m->count, s, len);
 689                m->count += len;
 690                return 0;
 691        }
 692        seq_set_overflow(m);
 693        return -1;
 694}
 695EXPORT_SYMBOL(seq_puts);
 696
 697/*
 698 * A helper routine for putting decimal numbers without rich format of printf().
 699 * only 'unsigned long long' is supported.
 700 * This routine will put one byte delimiter + number into seq_file.
 701 * This routine is very quick when you show lots of numbers.
 702 * In usual cases, it will be better to use seq_printf(). It's easier to read.
 703 */
 704int seq_put_decimal_ull(struct seq_file *m, char delimiter,
 705                        unsigned long long num)
 706{
 707        int len;
 708
 709        if (m->count + 2 >= m->size) /* we'll write 2 bytes at least */
 710                goto overflow;
 711
 712        if (delimiter)
 713                m->buf[m->count++] = delimiter;
 714
 715        if (num < 10) {
 716                m->buf[m->count++] = num + '0';
 717                return 0;
 718        }
 719
 720        len = num_to_str(m->buf + m->count, m->size - m->count, num);
 721        if (!len)
 722                goto overflow;
 723        m->count += len;
 724        return 0;
 725overflow:
 726        seq_set_overflow(m);
 727        return -1;
 728}
 729EXPORT_SYMBOL(seq_put_decimal_ull);
 730
 731int seq_put_decimal_ll(struct seq_file *m, char delimiter,
 732                        long long num)
 733{
 734        if (num < 0) {
 735                if (m->count + 3 >= m->size) {
 736                        seq_set_overflow(m);
 737                        return -1;
 738                }
 739                if (delimiter)
 740                        m->buf[m->count++] = delimiter;
 741                num = -num;
 742                delimiter = '-';
 743        }
 744        return seq_put_decimal_ull(m, delimiter, num);
 745
 746}
 747EXPORT_SYMBOL(seq_put_decimal_ll);
 748
 749/**
 750 * seq_write - write arbitrary data to buffer
 751 * @seq: seq_file identifying the buffer to which data should be written
 752 * @data: data address
 753 * @len: number of bytes
 754 *
 755 * Return 0 on success, non-zero otherwise.
 756 */
 757int seq_write(struct seq_file *seq, const void *data, size_t len)
 758{
 759        if (seq->count + len < seq->size) {
 760                memcpy(seq->buf + seq->count, data, len);
 761                seq->count += len;
 762                return 0;
 763        }
 764        seq_set_overflow(seq);
 765        return -1;
 766}
 767EXPORT_SYMBOL(seq_write);
 768
 769struct list_head *seq_list_start(struct list_head *head, loff_t pos)
 770{
 771        struct list_head *lh;
 772
 773        list_for_each(lh, head)
 774                if (pos-- == 0)
 775                        return lh;
 776
 777        return NULL;
 778}
 779EXPORT_SYMBOL(seq_list_start);
 780
 781struct list_head *seq_list_start_head(struct list_head *head, loff_t pos)
 782{
 783        if (!pos)
 784                return head;
 785
 786        return seq_list_start(head, pos - 1);
 787}
 788EXPORT_SYMBOL(seq_list_start_head);
 789
 790struct list_head *seq_list_next(void *v, struct list_head *head, loff_t *ppos)
 791{
 792        struct list_head *lh;
 793
 794        lh = ((struct list_head *)v)->next;
 795        ++*ppos;
 796        return lh == head ? NULL : lh;
 797}
 798EXPORT_SYMBOL(seq_list_next);
 799
 800/**
 801 * seq_hlist_start - start an iteration of a hlist
 802 * @head: the head of the hlist
 803 * @pos:  the start position of the sequence
 804 *
 805 * Called at seq_file->op->start().
 806 */
 807struct hlist_node *seq_hlist_start(struct hlist_head *head, loff_t pos)
 808{
 809        struct hlist_node *node;
 810
 811        hlist_for_each(node, head)
 812                if (pos-- == 0)
 813                        return node;
 814        return NULL;
 815}
 816EXPORT_SYMBOL(seq_hlist_start);
 817
 818/**
 819 * seq_hlist_start_head - start an iteration of a hlist
 820 * @head: the head of the hlist
 821 * @pos:  the start position of the sequence
 822 *
 823 * Called at seq_file->op->start(). Call this function if you want to
 824 * print a header at the top of the output.
 825 */
 826struct hlist_node *seq_hlist_start_head(struct hlist_head *head, loff_t pos)
 827{
 828        if (!pos)
 829                return SEQ_START_TOKEN;
 830
 831        return seq_hlist_start(head, pos - 1);
 832}
 833EXPORT_SYMBOL(seq_hlist_start_head);
 834
 835/**
 836 * seq_hlist_next - move to the next position of the hlist
 837 * @v:    the current iterator
 838 * @head: the head of the hlist
 839 * @ppos: the current position
 840 *
 841 * Called at seq_file->op->next().
 842 */
 843struct hlist_node *seq_hlist_next(void *v, struct hlist_head *head,
 844                                  loff_t *ppos)
 845{
 846        struct hlist_node *node = v;
 847
 848        ++*ppos;
 849        if (v == SEQ_START_TOKEN)
 850                return head->first;
 851        else
 852                return node->next;
 853}
 854EXPORT_SYMBOL(seq_hlist_next);
 855
 856/**
 857 * seq_hlist_start_rcu - start an iteration of a hlist protected by RCU
 858 * @head: the head of the hlist
 859 * @pos:  the start position of the sequence
 860 *
 861 * Called at seq_file->op->start().
 862 *
 863 * This list-traversal primitive may safely run concurrently with
 864 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 865 * as long as the traversal is guarded by rcu_read_lock().
 866 */
 867struct hlist_node *seq_hlist_start_rcu(struct hlist_head *head,
 868                                       loff_t pos)
 869{
 870        struct hlist_node *node;
 871
 872        __hlist_for_each_rcu(node, head)
 873                if (pos-- == 0)
 874                        return node;
 875        return NULL;
 876}
 877EXPORT_SYMBOL(seq_hlist_start_rcu);
 878
 879/**
 880 * seq_hlist_start_head_rcu - start an iteration of a hlist protected by RCU
 881 * @head: the head of the hlist
 882 * @pos:  the start position of the sequence
 883 *
 884 * Called at seq_file->op->start(). Call this function if you want to
 885 * print a header at the top of the output.
 886 *
 887 * This list-traversal primitive may safely run concurrently with
 888 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 889 * as long as the traversal is guarded by rcu_read_lock().
 890 */
 891struct hlist_node *seq_hlist_start_head_rcu(struct hlist_head *head,
 892                                            loff_t pos)
 893{
 894        if (!pos)
 895                return SEQ_START_TOKEN;
 896
 897        return seq_hlist_start_rcu(head, pos - 1);
 898}
 899EXPORT_SYMBOL(seq_hlist_start_head_rcu);
 900
 901/**
 902 * seq_hlist_next_rcu - move to the next position of the hlist protected by RCU
 903 * @v:    the current iterator
 904 * @head: the head of the hlist
 905 * @ppos: the current position
 906 *
 907 * Called at seq_file->op->next().
 908 *
 909 * This list-traversal primitive may safely run concurrently with
 910 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 911 * as long as the traversal is guarded by rcu_read_lock().
 912 */
 913struct hlist_node *seq_hlist_next_rcu(void *v,
 914                                      struct hlist_head *head,
 915                                      loff_t *ppos)
 916{
 917        struct hlist_node *node = v;
 918
 919        ++*ppos;
 920        if (v == SEQ_START_TOKEN)
 921                return rcu_dereference(head->first);
 922        else
 923                return rcu_dereference(node->next);
 924}
 925EXPORT_SYMBOL(seq_hlist_next_rcu);
 926
 927/**
 928 * seq_hlist_start_precpu - start an iteration of a percpu hlist array
 929 * @head: pointer to percpu array of struct hlist_heads
 930 * @cpu:  pointer to cpu "cursor"
 931 * @pos:  start position of sequence
 932 *
 933 * Called at seq_file->op->start().
 934 */
 935struct hlist_node *
 936seq_hlist_start_percpu(struct hlist_head __percpu *head, int *cpu, loff_t pos)
 937{
 938        struct hlist_node *node;
 939
 940        for_each_possible_cpu(*cpu) {
 941                hlist_for_each(node, per_cpu_ptr(head, *cpu)) {
 942                        if (pos-- == 0)
 943                                return node;
 944                }
 945        }
 946        return NULL;
 947}
 948EXPORT_SYMBOL(seq_hlist_start_percpu);
 949
 950/**
 951 * seq_hlist_next_percpu - move to the next position of the percpu hlist array
 952 * @v:    pointer to current hlist_node
 953 * @head: pointer to percpu array of struct hlist_heads
 954 * @cpu:  pointer to cpu "cursor"
 955 * @pos:  start position of sequence
 956 *
 957 * Called at seq_file->op->next().
 958 */
 959struct hlist_node *
 960seq_hlist_next_percpu(void *v, struct hlist_head __percpu *head,
 961                        int *cpu, loff_t *pos)
 962{
 963        struct hlist_node *node = v;
 964
 965        ++*pos;
 966
 967        if (node->next)
 968                return node->next;
 969
 970        for (*cpu = cpumask_next(*cpu, cpu_possible_mask); *cpu < nr_cpu_ids;
 971             *cpu = cpumask_next(*cpu, cpu_possible_mask)) {
 972                struct hlist_head *bucket = per_cpu_ptr(head, *cpu);
 973
 974                if (!hlist_empty(bucket))
 975                        return bucket->first;
 976        }
 977        return NULL;
 978}
 979EXPORT_SYMBOL(seq_hlist_next_percpu);
 980
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