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

[Glauber de Oliveira Costa]

This is a resend of a patch I sent on Jan 20th. Andrew, could you 
please consider applying it ?
 
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@xxxxxxxxxx>

---

 fs/ext3/balloc.c |   33 +++++++++++++++++++++++++++++----
 1 files changed, 29 insertions(+), 4 deletions(-)

1164cfd9b1b413f6c4b86bac11006ba2b933ccb1
diff --git a/fs/ext3/balloc.c b/fs/ext3/balloc.c
index 6250fcd..8bf87b0 100644
--- a/fs/ext3/balloc.c
+++ b/fs/ext3/balloc.c
@@ -1499,6 +1499,25 @@ int ext3_bg_has_super(struct super_block
        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 +1529,15 @@ int ext3_bg_has_super(struct super_block
  */
 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);
+
 }
 
-- 
1.0.4
-
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