linux-ext4 - Re: [PATCH] ext4: Find the group descriptors on a 1k-block bigalloc,meta

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Date:	Tue, 11 Mar 2014 00:02:30 -0700
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: Find the group descriptors on a 1k-block
 bigalloc,meta_bg filesystem

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@...cle.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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