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 19static 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 32int 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 */ 52unsigned 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} 80