release/src/router/busybox/e2fsprogs/ext2fs/sparse.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * sparse.c --- find the groups in an ext2 filesystem with metadata backups
   4  *
   5  * Copyright (C) 1993, 1994, 1995, 1996 Theodore Ts'o.
   6  * Copyright (C) 2002 Andreas Dilger.
   7  *
   8  * %Begin-Header%
   9  * This file may be redistributed under the terms of the GNU Public
  10  * License.
  11  * %End-Header%
  12  */
  13
  14 #include <stdio.h>
  15
  16 #include "ext2_fs.h"
  17 #include "ext2fsP.h"
  18
  19 static int test_root(int a, int b)
  20 {
  21         if (a == 0)
  22                 return 1;
  23         while (1) {
  24                 if (a == 1)
  25                         return 1;
  26                 if (a % b)
  27                         return 0;
  28                 a = a / b;
  29         }
  30 }
  31
  32 int ext2fs_bg_has_super(ext2_filsys fs, int group_block)
  33 {
  34         if (!(fs->super->s_feature_ro_compat &
  35               EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER))
  36                 return 1;
  37
  38         if (test_root(group_block, 3) || (test_root(group_block, 5)) ||
  39             test_root(group_block, 7))
  40                 return 1;
  41
  42         return 0;
  43 }
  44
  45 /*
  46  * Iterate through the groups which hold BACKUP superblock/GDT copies in an
  47  * ext3 filesystem.  The counters should be initialized to 1, 5, and 7 before
  48  * calling this for the first time.  In a sparse filesystem it will be the
  49  * sequence of powers of 3, 5, and 7: 1, 3, 5, 7, 9, 25, 27, 49, 81, ...
  50  * For a non-sparse filesystem it will be every group: 1, 2, 3, 4, ...
  51  */
  52 unsigned int ext2fs_list_backups(ext2_filsys fs, unsigned int *three,
  53                                  unsigned int *five, unsigned int *seven)
  54 {
  55         unsigned int *min = three;
  56         int mult = 3;
  57         unsigned int ret;
  58
  59         if (!(fs->super->s_feature_ro_compat &
  60               EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER)) {
  61                 ret = *min;
  62                 *min += 1;
  63                 return ret;
  64         }
  65
  66         if (*five < *min) {
  67                 min = five;
  68                 mult = 5;
  69         }
  70         if (*seven < *min) {
  71                 min = seven;
  72                 mult = 7;
  73         }
  74
  75         ret = *min;
  76         *min *= mult;
  77
  78         return ret;
  79 }