linux-kernel - Re: [PATCH v4] xfs_logprint: Fix super block buffer interpretation issue

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Message-ID: <43a586fb-5cee-4668-b15e-f75b294a243a@163.com>
Date: Thu, 16 Jan 2025 09:38:26 +0800
From: Chi Zhiling <chizhiling@....com>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: cem@...nel.org, linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
 Chi Zhiling <chizhiling@...inos.cn>, Dave Chinner <david@...morbit.com>,
 Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v4] xfs_logprint: Fix super block buffer interpretation
 issue

On 2025/1/16 08:33, Darrick J. Wong wrote:
> On Sun, Oct 13, 2024 at 12:29:52PM +0800, Chi Zhiling wrote:
>> From: Chi Zhiling <chizhiling@...inos.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@...nel.org>
>> Suggested-by: Dave Chinner <david@...morbit.com>
>> Signed-off-by: Chi Zhiling <chizhiling@...inos.cn>
>> Reviewed-by: Christoph Hellwig <hch@....de>
>> Reviewed-by: Darrick J. Wong <djwong@...nel.org>
>> ---
>>   logprint/log_misc.c | 17 +++++------------
> 
> Hmm, I don't think this ever got merged...
> 
> but shouldn't log_print_all.c also get fixed?  I think it has the same
> pointer arithmetic problem that could be replaced by get_unaligned_be64
> calls just like you did below.

Indeed, the same issue also exists in log_print_all.c. I will fix it in
the next push.

Thanks,
Chi Zhiling

> 
> --D
> 
>>   1 file changed, 5 insertions(+), 12 deletions(-)
>>
>> diff --git a/logprint/log_misc.c b/logprint/log_misc.c
>> index 8e86ac34..803e4d2f 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;
>>   
>>   			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) get_unaligned_be64(dsb->sb_icount),
>> +			       (unsigned long long) get_unaligned_be64(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) get_unaligned_be64(dsb->sb_fdblocks),
>> +			       (unsigned long long) get_unaligned_be64(dsb->sb_frextents));
>>   		}
>>   		super_block = 0;
>>   	} else if (be32_to_cpu(*(__be32 *)(*ptr)) == XFS_AGI_MAGIC) {
>> -- 
>>
>> 2.43.0
>>
>>