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

Submitted by Darrick J. Wong on Dec. 20, 2013, 12:15 a.m.

Details

Message ID 20131220001541.GA10189@birch.djwong.org
State Accepted, archived
Headers show

Commit Message

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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Comments

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 hide | download patch | download mbox

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));
 }