Re: [PATCH v2] xfs_logprint: Fix super block buffer interpretation issue

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Oct 11, 2024 at 03:52:53PM +0800, Chi Zhiling wrote:
> From: Chi Zhiling <chizhiling@kylinos.cn>
> 
> When using xfs_logprint to interpret the buffer of the super block, the
> icount will always be 6360863066640355328 (0x5846534200001000). This is
> because the offset of icount is incorrect, causing xfs_logprint to
> misinterpret the MAGIC number as icount.
> This patch fixes the offset value of the SB counters in xfs_logprint.
> 
> Before this patch:
> icount: 6360863066640355328  ifree: 5242880  fdblks: 0  frext: 0
> 
> After this patch:
> icount: 10240  ifree: 4906  fdblks: 37  frext: 0
> 
> Suggested-by: Darrick J. Wong <djwong@kernel.org>
> Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
> ---
>  logprint/log_misc.c | 17 +++++------------
>  1 file changed, 5 insertions(+), 12 deletions(-)
> 
> diff --git a/logprint/log_misc.c b/logprint/log_misc.c
> index 8e86ac34..0da92744 100644
> --- a/logprint/log_misc.c
> +++ b/logprint/log_misc.c
> @@ -282,22 +282,15 @@ xlog_print_trans_buffer(char **ptr, int len, int *i, int num_ops)
>  		if (be32_to_cpu(head->oh_len) < 4*8) {
>  			printf(_("Out of space\n"));
>  		} else {
> -			__be64		 a, b;
> +			struct xfs_dsb *dsb = (struct xfs_dsb *) *ptr;

Nit: tab between type and variable    ^ name

With that fixed,
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

>  
>  			printf("\n");
> -			/*
> -			 * memmove because *ptr may not be 8-byte aligned
> -			 */
> -			memmove(&a, *ptr, sizeof(__be64));
> -			memmove(&b, *ptr+8, sizeof(__be64));
>  			printf(_("icount: %llu  ifree: %llu  "),
> -			       (unsigned long long) be64_to_cpu(a),
> -			       (unsigned long long) be64_to_cpu(b));
> -			memmove(&a, *ptr+16, sizeof(__be64));
> -			memmove(&b, *ptr+24, sizeof(__be64));
> +			       (unsigned long long) be64_to_cpu(dsb->sb_icount),
> +			       (unsigned long long) be64_to_cpu(dsb->sb_ifree));
>  			printf(_("fdblks: %llu  frext: %llu\n"),
> -			       (unsigned long long) be64_to_cpu(a),
> -			       (unsigned long long) be64_to_cpu(b));
> +			       (unsigned long long) be64_to_cpu(dsb->sb_fdblocks),
> +			       (unsigned long long) be64_to_cpu(dsb->sb_frextents));
>  		}
>  		super_block = 0;
>  	} else if (be32_to_cpu(*(__be32 *)(*ptr)) == XFS_AGI_MAGIC) {
> -- 
> 2.43.0
> 
>