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

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Message-ID: <97501a36-d001-b3fa-5b57-8672bc7d71da@163.com>
Date: Fri, 11 Oct 2024 11:54:08 +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,
 chizhiling <chizhiling@...inos.cn>
Subject: Re: [PATCH] xfs_logprint: Fix super block buffer interpretation issue


On 2024/10/11 11:24, Darrick J. Wong wrote:
> On Fri, Oct 11, 2024 at 11:08:10AM +0800, Chi Zhiling wrote:
>> From: chizhiling <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
>>
>> Signed-off-by: chizhiling <chizhiling@...inos.cn>
>> ---
>>   logprint/log_misc.c | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/logprint/log_misc.c b/logprint/log_misc.c
>> index 8e86ac34..21da5b8b 100644
>> --- a/logprint/log_misc.c
>> +++ b/logprint/log_misc.c
>> @@ -288,13 +288,13 @@ xlog_print_trans_buffer(char **ptr, int len, int *i, int num_ops)
>>   			/*
>>   			 * memmove because *ptr may not be 8-byte aligned
>>   			 */
>> -			memmove(&a, *ptr, sizeof(__be64));
>> -			memmove(&b, *ptr+8, sizeof(__be64));
> How did this ever work??  This even looks wrong in "Release_1.0.0".
>
Yes, I was surprised when I find this issue
>> +			memmove(&a, *ptr + offsetof(struct xfs_dsb, sb_icount), sizeof(__be64));
>> +			memmove(&b, *ptr + offsetof(struct xfs_dsb, sb_ifree), sizeof(__be64));
> Why not do:
>
> 			struct xfs_dsb *dsb = *ptr;
>
> 			memcpy(&a, &dsb->sb_icount, sizeof(a));
>
> or better yet, skip the indirection and do
>
> 			printf(_("icount: %llu  ifree: %llu  "),
> 					(unsigned long long)be64_to_cpu(dsb->sb_icount),
> 					(unsigned long long)be64_to_cpu(dsb->sb_ifree));
>
> Hm?

Yes, of course we can do it this way, I just want the fix patch to look 
smaller :)

I think both ok.


chi

>
> --D
>
>>   			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));
>> +			memmove(&a, *ptr + offsetof(struct xfs_dsb, sb_fdblocks), sizeof(__be64));
>> +			memmove(&b, *ptr + offsetof(struct xfs_dsb, sb_frextents), sizeof(__be64));
>>   			printf(_("fdblks: %llu  frext: %llu\n"),
>>   			       (unsigned long long) be64_to_cpu(a),
>>   			       (unsigned long long) be64_to_cpu(b));
>> -- 
>> 2.43.0
>>