linux-ext4 - Re: [PATCH 3/4] e2fsprogs/tune2fs: rewrite metadata checksums when resizing inode size

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Date:	Tue, 11 Nov 2014 00:33:29 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	Xiaoguang Wang <wangxg.fnst@...fujitsu.com>
Cc:	linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH 3/4] e2fsprogs/tune2fs: rewrite metadata checksums when
 resizing inode size

On Tue, Nov 11, 2014 at 02:59:28PM +0800, Xiaoguang Wang wrote:
> When we use tune2fs -I new_ino_size to change inode size, if everything is OK,
> the corresponding ext4_group_desc.bg_free_blocks_count will be decreased, so
> obviously, we need to re-compute the group descriptor checksums, fix this. If
> not doing this, mount operation will fail.
> 
> Meanwhile, the patch will trigger an existing memory write overflow, which will
> casue segfault, please see the next patch.
> 
> Signed-off-by: Xiaoguang Wang <wangxg.fnst@...fujitsu.com>
> ---
>  misc/tune2fs.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/misc/tune2fs.c b/misc/tune2fs.c
> index 065b483..91dc7c1 100644
> --- a/misc/tune2fs.c
> +++ b/misc/tune2fs.c
> @@ -2908,8 +2908,7 @@ retry_open:
>  				EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
>  			rewrite_checksums = 1;
>  	}
> -	if (rewrite_checksums)
> -		rewrite_metadata_checksums(fs);
> +
>  	if (I_flag) {
>  		if (mount_flags & EXT2_MF_MOUNTED) {
>  			fputs(_("The inode size may only be "
> @@ -2935,6 +2934,7 @@ retry_open:
>  		if (resize_inode(fs, new_inode_size) == 0) {
>  			printf(_("Setting inode size %lu\n"),
>  							new_inode_size);
> +			rewrite_checksums = 1;

rewrite_metadata_checksums() was designed to rewrite checksums on every
metadata object in the filesystem (extents, ACLs, directory blocks), which I
think does more work than necessary for your use case (if I'm reading this
correctly) of simply rewriting the block group descriptor checksums.  Would it
suffice to call ext2fs_group_desc_csum_set() when setting bg_free_blocks_count?
I think this could be done in ext2fs_calculate_summary_stats().

--D

>  		} else {
>  			printf("%s", _("Failed to change inode size\n"));
>  			rc = 1;
> @@ -2942,6 +2942,9 @@ retry_open:
>  		}
>  	}
>  
> +	if (rewrite_checksums)
> +		rewrite_metadata_checksums(fs);
> +
>  	if (l_flag)
>  		list_super(sb);
>  	if (stride_set) {
> -- 
> 1.8.2.1
> 
> --
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