1 files changed, 78 insertions, 0 deletions
diff --git a/e2fsprogs/ext2fs/sparse.c b/e2fsprogs/ext2fs/sparse.c
new file mode 100644
index 000000000..90b028f09
--- /dev/null
+++ b/e2fsprogs/ext2fs/sparse.c
@@ -0,0 +1,78 @@
+/*
+ * sparse.c --- find the groups in an ext2 filesystem with metadata backups
+ *
+ * Copyright (C) 1993, 1994, 1995, 1996 Theodore Ts'o.
+ * Copyright (C) 2002 Andreas Dilger.
+ *
+ * %Begin-Header%
+ * This file may be redistributed under the terms of the GNU Public
+ * License.
+ * %End-Header%
+ */
+
+#include <stdio.h>
+
+#include "ext2_fs.h"
+#include "ext2fsP.h"
+
+static int test_root(int a, int b)
+{
+	if (a == 0)
+		return 1;
+	while (1) {
+		if (a == 1)
+			return 1;
+		if (a % b)
+			return 0;
+		a = a / b;
+	}
+}
+
+int ext2fs_bg_has_super(ext2_filsys fs, int group_block)
+{
+	if (!(fs->super->s_feature_ro_compat &
+	      EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER))
+		return 1;
+
+	if (test_root(group_block, 3) || (test_root(group_block, 5)) ||
+	    test_root(group_block, 7))
+		return 1;
+
+	return 0;
+}
+
+/*
+ * Iterate through the groups which hold BACKUP superblock/GDT copies in an
+ * ext3 filesystem.  The counters should be initialized to 1, 5, and 7 before
+ * calling this for the first time.  In a sparse filesystem it will be the
+ * sequence of powers of 3, 5, and 7: 1, 3, 5, 7, 9, 25, 27, 49, 81, ...
+ * For a non-sparse filesystem it will be every group: 1, 2, 3, 4, ...
+ */
+unsigned int ext2fs_list_backups(ext2_filsys fs, unsigned int *three,
+				 unsigned int *five, unsigned int *seven)
+{
+	unsigned int *min = three;
+	int mult = 3;
+	unsigned int ret;
+
+	if (!(fs->super->s_feature_ro_compat &
+	      EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER)) {
+		ret = *min;
+		*min += 1;
+		return ret;
+	}
+
+	if (*five < *min) {
+		min = five;
+		mult = 5;
+	}
+	if (*seven < *min) {
+		min = seven;
+		mult = 7;
+	}
+
+	ret = *min;
+	*min *= mult;
+
+	return ret;
+}