linux-ext4 - Re: [PATCH] jbd2: remove useless variable chksum_seen in do_one

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Message-ID: <ac6a4fd9-f2af-bad5-ce5d-ea728e9b64b2@huawei.com>
Date:   Tue, 18 Aug 2020 19:33:31 +0800
From:   Shijie Luo <luoshijie1@...wei.com>
To:     Jan Kara <jack@...e.cz>
CC:     <linux-ext4@...r.kernel.org>, <tytso@....edu>,
        <linfeilong@...wei.com>
Subject: Re: [PATCH] jbd2: remove useless variable chksum_seen in do_one_pass


On 2020/8/18 18:48, Jan Kara wrote:
> On Mon 10-08-20 22:21:28, Shijie Luo wrote:
>> This variable only indicates that we do checksum success, while
>> chksum_err can also do. Moreover, condition "!chksum_seen" in else
>> if bracket is pointless.
>>
>> Signed-off-by: Shijie Luo <luoshijie1@...wei.com>
> Thanks for the patch! Some comments below.
>
>> @@ -709,11 +707,10 @@ static int do_one_pass(journal_t *journal,
>>   				    cbh->h_chksum_type == JBD2_CRC32_CHKSUM &&
>>   				    cbh->h_chksum_size ==
>>   						JBD2_CRC32_CHKSUM_SIZE)
>> -				       chksum_seen = 1;
>> +				       chksum_err = 0;
>>   				else if (!(cbh->h_chksum_type == 0 &&
>>   					     cbh->h_chksum_size == 0 &&
>> -					     found_chksum == 0 &&
>> -					     !chksum_seen))
>> +					     found_chksum == 0))
>>   				/*
>>   				 * If fs is mounted using an old kernel and then
>>   				 * kernel with journal_chksum is used then we
> I agree the use of chksum_err & chksum_seen looks rather arbitrary. In fact
> the code seems to be equivalent to:
>
> 				/* Neither checksum match nor unused? */
> 				if (!(crc32_sum == found_chksum &&
>                                       cbh->h_chksum_type == JBD2_CRC32_CHKSUM &&
>                                       cbh->h_chksum_size ==
>                                                  JBD2_CRC32_CHKSUM_SIZE) &&
> 				    !(cbh->h_chksum_type == 0 &&
>                                               cbh->h_chksum_size == 0 &&
>                                               found_chksum == 0)) {
> 					info->end_transaction = next_commit_ID;
> 					if (jbd2_has_feature_async_commit(journal)) {
> 						...
> 					}
> 				}
> 				crc32_sum = ~0;
>
> which would be even simpler...
>
> 								Honza

Thanks for your review，it 's definitely true to use these code as a 
substitute, but I think these are

a little bit hard to read.  By the way, I found a indentation error on 
"chksum_err = 1".

Do you think which one is better? I will take your opinion into account 
and send a v2 patch.