ext4: find the group descriptors on a 1k-block bigalloc,meta_bg filesystem

On a filesystem with a 1k block size, the group descriptors live in
block 2, not block 1.  If the filesystem has bigalloc,meta_bg set,
however, the calculation of the group descriptor table location does
not take this into account and returns the wrong block number.  Fix
the calculation to return the correct value for this case.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 1f8cb1812723a1a1d4127780dba100a1b3310eaf..e38dd7d37a691dcc26b9bf3ae415c21af07a8940 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2405,6 +2405,16 @@ static ext4_fsblk_t descriptor_loc(struct super_block *sb,
        if (ext4_bg_has_super(sb, bg))
                has_super = 1;
 
+       /*
+        * If we have a meta_bg fs with 1k blocks, group 0's GDT is at
+        * block 2, not 1.  If s_first_data_block == 0 (bigalloc is enabled
+        * on modern mke2fs or blksize > 1k on older mke2fs) then we must
+        * compensate.
+        */
+       if (sb->s_blocksize == 1024 && nr == 0 &&
+           le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block) == 0)
+               has_super++;
+
        return (has_super + ext4_group_first_block_no(sb, bg));
 }