[PATCH] ext3: Properly report backup block present in a group

In filesystems with the meta block group flag on, ext3_bg_num_gdb() fails
to report the correct number of blocks used to store the group descriptor
backups in a given group.  It happens because meta_bg follows a different
logic from the original ext3 backup placement in groups multiples of 3, 5
and 7.
Signed-off-by: Glauber de Oliveira Costa <glommer@br.ibm.com>
Cc: Andreas Dilger <adilger@clusterfs.com>
Cc: "Stephen C. Tweedie" <sct@redhat.com>
Cc: Alex Tomas <alex@clusterfs.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/ext3/balloc.c

@@ -1493,12 +1493,33 @@ static int ext3_group_sparse(int group)
  */
 int ext3_bg_has_super(struct super_block *sb, int group)
 {
-	if (EXT3_HAS_RO_COMPAT_FEATURE(sb,EXT3_FEATURE_RO_COMPAT_SPARSE_SUPER)&&
-	    !ext3_group_sparse(group))
+	if (EXT3_HAS_RO_COMPAT_FEATURE(sb,
+				EXT3_FEATURE_RO_COMPAT_SPARSE_SUPER) &&
+			!ext3_group_sparse(group))
 		return 0;
 	return 1;
 }
 
+static unsigned long ext3_bg_num_gdb_meta(struct super_block *sb, int group)
+{
+	unsigned long metagroup = group / EXT3_DESC_PER_BLOCK(sb);
+	unsigned long first = metagroup * EXT3_DESC_PER_BLOCK(sb);
+	unsigned long last = first + EXT3_DESC_PER_BLOCK(sb) - 1;
+
+	if (group == first || group == first + 1 || group == last)
+		return 1;
+	return 0;
+}
+
+static unsigned long ext3_bg_num_gdb_nometa(struct super_block *sb, int group)
+{
+	if (EXT3_HAS_RO_COMPAT_FEATURE(sb,
+				EXT3_FEATURE_RO_COMPAT_SPARSE_SUPER) &&
+			!ext3_group_sparse(group))
+		return 0;
+	return EXT3_SB(sb)->s_gdb_count;
+}
+
 /**
  *	ext3_bg_num_gdb - number of blocks used by the group table in group
  *	@sb: superblock for filesystem
@@ -1510,9 +1531,14 @@ int ext3_bg_has_super(struct super_block *sb, int group)
  */
 unsigned long ext3_bg_num_gdb(struct super_block *sb, int group)
 {
-	if (EXT3_HAS_RO_COMPAT_FEATURE(sb,EXT3_FEATURE_RO_COMPAT_SPARSE_SUPER)&&
-	    !ext3_group_sparse(group))
-		return 0;
-	return EXT3_SB(sb)->s_gdb_count;
-}
+	unsigned long first_meta_bg =
+			le32_to_cpu(EXT3_SB(sb)->s_es->s_first_meta_bg);
+	unsigned long metagroup = group / EXT3_DESC_PER_BLOCK(sb);
+
+	if (!EXT3_HAS_INCOMPAT_FEATURE(sb,EXT3_FEATURE_INCOMPAT_META_BG) ||
+			metagroup < first_meta_bg)
+		return ext3_bg_num_gdb_nometa(sb,group);
 
+	return ext3_bg_num_gdb_meta(sb,group);
+
+}