fs/seq_file.c

   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  */
  23 static bool seq_overflow(struct seq_file *m)
  24 {
  25         return m->count == m->size;
  26 }
  27
  28 static 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  */
  47 int 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 }
  83 EXPORT_SYMBOL(seq_open);
  84
  85 static 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
 136 Eoverflow:
 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  */
 152 ssize_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;
 246 Fill:
 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;
 276 Done:
 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;
 286 Enomem:
 287         err = -ENOMEM;
 288         goto Done;
 289 Efault:
 290         err = -EFAULT;
 291         goto Done;
 292 }
 293 EXPORT_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  */
 303 loff_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                 }
 332         }
 333         file->f_version = m->version;
 334         mutex_unlock(&m->lock);
 335         return retval;
 336 }
 337 EXPORT_SYMBOL(seq_lseek);
 338
 339 /**
 340  *      seq_release -   free the structures associated with sequential file.
 341  *      @file: file in question
 342  *      @inode: its 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  */
 347 int 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 }
 354 EXPORT_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  */
 366 int 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 }
 390 EXPORT_SYMBOL(seq_escape);
 391
 392 int 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 }
 406 EXPORT_SYMBOL(seq_vprintf);
 407
 408 int 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 }
 419 EXPORT_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  */
 432 char *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 }
 451 EXPORT_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  */
 462 int 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 }
 480 EXPORT_SYMBOL(seq_path);
 481
 482 /*
 483  * Same as seq_path, but relative to supplied root.
 484  */
 485 int 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  */
 515 int 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
 534 int 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 }
 548 EXPORT_SYMBOL(seq_bitmap);
 549
 550 int 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 }
 564 EXPORT_SYMBOL(seq_bitmap_list);
 565
 566 static void *single_start(struct seq_file *p, loff_t *pos)
 567 {
 568         return NULL + (*pos == 0);
 569 }
 570
 571 static void *single_next(struct seq_file *p, void *v, loff_t *pos)
 572 {
 573         ++*pos;
 574         return NULL;
 575 }
 576
 577 static void single_stop(struct seq_file *p, void *v)
 578 {
 579 }
 580
 581 int 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 }
 600 EXPORT_SYMBOL(single_open);
 601
 602 int single_open_size(struct file *file, int (*show)(struct seq_file *, void *),
 603                 void *data, size_t size)
 604 {
 605         char *buf = kmalloc(size, GFP_KERNEL);
 606         int ret;
 607         if (!buf)
 608                 return -ENOMEM;
 609         ret = single_open(file, show, data);
 610         if (ret) {
 611                 kfree(buf);
 612                 return ret;
 613         }
 614         ((struct seq_file *)file->private_data)->buf = buf;
 615         ((struct seq_file *)file->private_data)->size = size;
 616         return 0;
 617 }
 618 EXPORT_SYMBOL(single_open_size);
 619
 620 int single_release(struct inode *inode, struct file *file)
 621 {
 622         const struct seq_operations *op = ((struct seq_file *)file->private_data)->op;
 623         int res = seq_release(inode, file);
 624         kfree(op);
 625         return res;
 626 }
 627 EXPORT_SYMBOL(single_release);
 628
 629 int seq_release_private(struct inode *inode, struct file *file)
 630 {
 631         struct seq_file *seq = file->private_data;
 632
 633         kfree(seq->private);
 634         seq->private = NULL;
 635         return seq_release(inode, file);
 636 }
 637 EXPORT_SYMBOL(seq_release_private);
 638
 639 void *__seq_open_private(struct file *f, const struct seq_operations *ops,
 640                 int psize)
 641 {
 642         int rc;
 643         void *private;
 644         struct seq_file *seq;
 645
 646         private = kzalloc(psize, GFP_KERNEL);
 647         if (private == NULL)
 648                 goto out;
 649
 650         rc = seq_open(f, ops);
 651         if (rc < 0)
 652                 goto out_free;
 653
 654         seq = f->private_data;
 655         seq->private = private;
 656         return private;
 657
 658 out_free:
 659         kfree(private);
 660 out:
 661         return NULL;
 662 }
 663 EXPORT_SYMBOL(__seq_open_private);
 664
 665 int seq_open_private(struct file *filp, const struct seq_operations *ops,
 666                 int psize)
 667 {
 668         return __seq_open_private(filp, ops, psize) ? 0 : -ENOMEM;
 669 }
 670 EXPORT_SYMBOL(seq_open_private);
 671
 672 int seq_putc(struct seq_file *m, char c)
 673 {
 674         if (m->count < m->size) {
 675                 m->buf[m->count++] = c;
 676                 return 0;
 677         }
 678         return -1;
 679 }
 680 EXPORT_SYMBOL(seq_putc);
 681
 682 int seq_puts(struct seq_file *m, const char *s)
 683 {
 684         int len = strlen(s);
 685         if (m->count + len < m->size) {
 686                 memcpy(m->buf + m->count, s, len);
 687                 m->count += len;
 688                 return 0;
 689         }
 690         seq_set_overflow(m);
 691         return -1;
 692 }
 693 EXPORT_SYMBOL(seq_puts);
 694
 695 /*
 696  * A helper routine for putting decimal numbers without rich format of printf().
 697  * only 'unsigned long long' is supported.
 698  * This routine will put one byte delimiter + number into seq_file.
 699  * This routine is very quick when you show lots of numbers.
 700  * In usual cases, it will be better to use seq_printf(). It's easier to read.
 701  */
 702 int seq_put_decimal_ull(struct seq_file *m, char delimiter,
 703                         unsigned long long num)
 704 {
 705         int len;
 706
 707         if (m->count + 2 >= m->size) /* we'll write 2 bytes at least */
 708                 goto overflow;
 709
 710         if (delimiter)
 711                 m->buf[m->count++] = delimiter;
 712
 713         if (num < 10) {
 714                 m->buf[m->count++] = num + '0';
 715                 return 0;
 716         }
 717
 718         len = num_to_str(m->buf + m->count, m->size - m->count, num);
 719         if (!len)
 720                 goto overflow;
 721         m->count += len;
 722         return 0;
 723 overflow:
 724         seq_set_overflow(m);
 725         return -1;
 726 }
 727 EXPORT_SYMBOL(seq_put_decimal_ull);
 728
 729 int seq_put_decimal_ll(struct seq_file *m, char delimiter,
 730                         long long num)
 731 {
 732         if (num < 0) {
 733                 if (m->count + 3 >= m->size) {
 734                         seq_set_overflow(m);
 735                         return -1;
 736                 }
 737                 if (delimiter)
 738                         m->buf[m->count++] = delimiter;
 739                 num = -num;
 740                 delimiter = '-';
 741         }
 742         return seq_put_decimal_ull(m, delimiter, num);
 743
 744 }
 745 EXPORT_SYMBOL(seq_put_decimal_ll);
 746
 747 /**
 748  * seq_write - write arbitrary data to buffer
 749  * @seq: seq_file identifying the buffer to which data should be written
 750  * @data: data address
 751  * @len: number of bytes
 752  *
 753  * Return 0 on success, non-zero otherwise.
 754  */
 755 int seq_write(struct seq_file *seq, const void *data, size_t len)
 756 {
 757         if (seq->count + len < seq->size) {
 758                 memcpy(seq->buf + seq->count, data, len);
 759                 seq->count += len;
 760                 return 0;
 761         }
 762         seq_set_overflow(seq);
 763         return -1;
 764 }
 765 EXPORT_SYMBOL(seq_write);
 766
 767 struct list_head *seq_list_start(struct list_head *head, loff_t pos)
 768 {
 769         struct list_head *lh;
 770
 771         list_for_each(lh, head)
 772                 if (pos-- == 0)
 773                         return lh;
 774
 775         return NULL;
 776 }
 777 EXPORT_SYMBOL(seq_list_start);
 778
 779 struct list_head *seq_list_start_head(struct list_head *head, loff_t pos)
 780 {
 781         if (!pos)
 782                 return head;
 783
 784         return seq_list_start(head, pos - 1);
 785 }
 786 EXPORT_SYMBOL(seq_list_start_head);
 787
 788 struct list_head *seq_list_next(void *v, struct list_head *head, loff_t *ppos)
 789 {
 790         struct list_head *lh;
 791
 792         lh = ((struct list_head *)v)->next;
 793         ++*ppos;
 794         return lh == head ? NULL : lh;
 795 }
 796 EXPORT_SYMBOL(seq_list_next);
 797
 798 /**
 799  * seq_hlist_start - 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().
 804  */
 805 struct hlist_node *seq_hlist_start(struct hlist_head *head, loff_t pos)
 806 {
 807         struct hlist_node *node;
 808
 809         hlist_for_each(node, head)
 810                 if (pos-- == 0)
 811                         return node;
 812         return NULL;
 813 }
 814 EXPORT_SYMBOL(seq_hlist_start);
 815
 816 /**
 817  * seq_hlist_start_head - start an iteration of a hlist
 818  * @head: the head of the hlist
 819  * @pos:  the start position of the sequence
 820  *
 821  * Called at seq_file->op->start(). Call this function if you want to
 822  * print a header at the top of the output.
 823  */
 824 struct hlist_node *seq_hlist_start_head(struct hlist_head *head, loff_t pos)
 825 {
 826         if (!pos)
 827                 return SEQ_START_TOKEN;
 828
 829         return seq_hlist_start(head, pos - 1);
 830 }
 831 EXPORT_SYMBOL(seq_hlist_start_head);
 832
 833 /**
 834  * seq_hlist_next - move to the next position of the hlist
 835  * @v:    the current iterator
 836  * @head: the head of the hlist
 837  * @ppos: the current position
 838  *
 839  * Called at seq_file->op->next().
 840  */
 841 struct hlist_node *seq_hlist_next(void *v, struct hlist_head *head,
 842                                   loff_t *ppos)
 843 {
 844         struct hlist_node *node = v;
 845
 846         ++*ppos;
 847         if (v == SEQ_START_TOKEN)
 848                 return head->first;
 849         else
 850                 return node->next;
 851 }
 852 EXPORT_SYMBOL(seq_hlist_next);
 853
 854 /**
 855  * seq_hlist_start_rcu - start an iteration of a hlist protected by RCU
 856  * @head: the head of the hlist
 857  * @pos:  the start position of the sequence
 858  *
 859  * Called at seq_file->op->start().
 860  *
 861  * This list-traversal primitive may safely run concurrently with
 862  * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 863  * as long as the traversal is guarded by rcu_read_lock().
 864  */
 865 struct hlist_node *seq_hlist_start_rcu(struct hlist_head *head,
 866                                        loff_t pos)
 867 {
 868         struct hlist_node *node;
 869
 870         __hlist_for_each_rcu(node, head)
 871                 if (pos-- == 0)
 872                         return node;
 873         return NULL;
 874 }
 875 EXPORT_SYMBOL(seq_hlist_start_rcu);
 876
 877 /**
 878  * seq_hlist_start_head_rcu - start an iteration of a hlist protected by RCU
 879  * @head: the head of the hlist
 880  * @pos:  the start position of the sequence
 881  *
 882  * Called at seq_file->op->start(). Call this function if you want to
 883  * print a header at the top of the output.
 884  *
 885  * This list-traversal primitive may safely run concurrently with
 886  * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 887  * as long as the traversal is guarded by rcu_read_lock().
 888  */
 889 struct hlist_node *seq_hlist_start_head_rcu(struct hlist_head *head,
 890                                             loff_t pos)
 891 {
 892         if (!pos)
 893                 return SEQ_START_TOKEN;
 894
 895         return seq_hlist_start_rcu(head, pos - 1);
 896 }
 897 EXPORT_SYMBOL(seq_hlist_start_head_rcu);
 898
 899 /**
 900  * seq_hlist_next_rcu - move to the next position of the hlist protected by RCU
 901  * @v:    the current iterator
 902  * @head: the head of the hlist
 903  * @ppos: the current position
 904  *
 905  * Called at seq_file->op->next().
 906  *
 907  * This list-traversal primitive may safely run concurrently with
 908  * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 909  * as long as the traversal is guarded by rcu_read_lock().
 910  */
 911 struct hlist_node *seq_hlist_next_rcu(void *v,
 912                                       struct hlist_head *head,
 913                                       loff_t *ppos)
 914 {
 915         struct hlist_node *node = v;
 916
 917         ++*ppos;
 918         if (v == SEQ_START_TOKEN)
 919                 return rcu_dereference(head->first);
 920         else
 921                 return rcu_dereference(node->next);
 922 }
 923 EXPORT_SYMBOL(seq_hlist_next_rcu);