[PATCH] Revert "ext4: remove unnecessary check in ext4_bg_num_gdb_nometa"

[PATCH] Revert "ext4: remove unnecessary check in ext4_bg_num_gdb_nometa"

[Kemeng Shi]

This reverts commit ad3f09be6cfe332be8ff46c78e6ec0f8839107aa.

The reverted commit was intended to simpfy the code to get group
descriptor block number in non-meta block group by assuming
s_gdb_count is block number used for all non-meta block group descriptors.
However s_gdb_count is block number used for all meta *and* non-meta
group descriptors. So s_gdb_group will be > actual group descriptor block
number used for all non-meta block group which should be "total non-meta
block group" / "group descriptors per block", e.g. s_first_meta_bg.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
---
 fs/ext4/balloc.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index c1edde817be8..09c75a3127c7 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -886,7 +886,10 @@ static unsigned long ext4_bg_num_gdb_nometa(struct super_block *sb,
 	if (!ext4_bg_has_super(sb, group))
 		return 0;
 
-	return EXT4_SB(sb)->s_gdb_count;
+	if (ext4_has_feature_meta_bg(sb))
+		return le32_to_cpu(EXT4_SB(sb)->s_es->s_first_meta_bg);
+	else
+		return EXT4_SB(sb)->s_gdb_count;
 }
 
 /**
-- 
2.30.0

Re: [PATCH] Revert "ext4: remove unnecessary check in ext4_bg_num_gdb_nometa"

[Theodore Ts'o]

On Wed, 14 Jun 2023 06:50:25 +0800, Kemeng Shi wrote:
> This reverts commit ad3f09be6cfe332be8ff46c78e6ec0f8839107aa.
> 
> The reverted commit was intended to simpfy the code to get group
> descriptor block number in non-meta block group by assuming
> s_gdb_count is block number used for all non-meta block group descriptors.
> However s_gdb_count is block number used for all meta *and* non-meta
> group descriptors. So s_gdb_group will be > actual group descriptor block
> number used for all non-meta block group which should be "total non-meta
> block group" / "group descriptors per block", e.g. s_first_meta_bg.
> 
> [...]

Applied, thanks!

[1/1] Revert "ext4: remove unnecessary check in ext4_bg_num_gdb_nometa"
      commit: 19482792113fa1dc419f9bc7b04b9dbdaa5256fd

Best regards,
-- 
Theodore Ts'o <tytso@mit.edu>