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

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Submitter Darrick J. Wong
Date Dec. 20, 2013, 12:15 a.m.
Message ID <20131220001541.GA10189@birch.djwong.org>
Download mbox | patch
Permalink /patch/303775/
State Accepted
Headers show

Comments

Darrick J. Wong - Dec. 20, 2013, 12:15 a.m.
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>
---
 fs/ext4/super.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

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Darrick J. Wong - March 11, 2014, 7:02 a.m.
On Thu, Dec 19, 2013 at 04:15:42PM -0800, Darrick J. Wong wrote:
> 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.

Hey Ted,

Any comments on this one?

--D
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/ext4/super.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 7f52a54..d968c64 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -2420,6 +2420,16 @@ 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));
>  }
>  
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Theodore Ts'o - May 12, 2014, 2:07 p.m.
On Thu, Dec 19, 2013 at 04:15:42PM -0800, Darrick J. Wong wrote:
> 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>

Thanks, applied.

					- Ted
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Patch

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 7f52a54..d968c64 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2420,6 +2420,16 @@  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));
 }