linux-kernel - Re: [PATCH 1/2] f2fs: use flexible array for f2fs_checkpoint::sit_nat_version

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Message-ID: <a69e7840-3759-0280-fde6-2ce327e22e8d@huawei.com>
Date:   Thu, 4 Jan 2018 14:28:34 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <chao@...nel.org>
Subject: Re: [PATCH 1/2] f2fs: use flexible array for
 f2fs_checkpoint::sit_nat_version_bitmap

On 2018/1/4 14:16, Jaegeuk Kim wrote:
> On 01/04, Chao Yu wrote:
>> On 2018/1/4 4:12, Jaegeuk Kim wrote:
>>> On 01/03, Chao Yu wrote:
>>>> If we need an array with variable size in the end of structure, we
>>>> can utilize flexible array feature which is supported in C99, so
>>>> let's change sit_nat_version_bitmap[] to flexible array in struct
>>>> f2fs_checkpoint for readability.
>>>>
>>>> Signed-off-by: Chao Yu <yuchao0@...wei.com>
>>>> ---
>>>>  fs/f2fs/f2fs.h          | 4 ++--
>>>>  include/linux/f2fs_fs.h | 2 +-
>>>>  2 files changed, 3 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>> index 83d1f697388b..ad19d29688ae 100644
>>>> --- a/fs/f2fs/f2fs.h
>>>> +++ b/fs/f2fs/f2fs.h
>>>> @@ -1719,13 +1719,13 @@ static inline void *__bitmap_ptr(struct f2fs_sb_info *sbi, int flag)
>>>>  
>>>>  	if (__cp_payload(sbi) > 0) {
>>>>  		if (flag == NAT_BITMAP)
>>>> -			return &ckpt->sit_nat_version_bitmap;
>>>> +			return ckpt->sit_nat_version_bitmap;
>>>>  		else
>>>>  			return (unsigned char *)ckpt + F2FS_BLKSIZE;
>>>>  	} else {
>>>>  		offset = (flag == NAT_BITMAP) ?
>>>>  			le32_to_cpu(ckpt->sit_ver_bitmap_bytesize) : 0;
>>>> -		return &ckpt->sit_nat_version_bitmap + offset;
>>>> +		return ckpt->sit_nat_version_bitmap + offset;
>>>>  	}
>>>>  }
>>>>  
>>>> diff --git a/include/linux/f2fs_fs.h b/include/linux/f2fs_fs.h
>>>> index 43e98d30d2df..564f65fc192f 100644
>>>> --- a/include/linux/f2fs_fs.h
>>>> +++ b/include/linux/f2fs_fs.h
>>>> @@ -157,7 +157,7 @@ struct f2fs_checkpoint {
>>>>  	unsigned char alloc_type[MAX_ACTIVE_LOGS];
>>>>  
>>>>  	/* SIT and NAT version bitmap */
>>>> -	unsigned char sit_nat_version_bitmap[1];
>>>> +	unsigned char sit_nat_version_bitmap[];
>>>
>>> I cannot find any benefit to do this. Moreover, it just makes the header
>>
>> I intend to change both kernel and tools, sorry, I didn't send out the
>> patch on tools. Anyway, I think it could be used to avoid checkpoint
>> structure size calculation by "sizeof(struct checkpoint) - 1", with the
>> patch, readability can be improved. Right?
> 
> I don't think so. It's even defined only in f2fs-tools, and well covered by a
> macro. There's no reason to spend time to sync it between f2fs and f2fs-tools.

OK, this is only about readability, it's really not a big deal to drop this
patch.

Thanks,

> 
>>
>> Thanks,
>>
>>> structure be different from the one in f2fs-tools.
>>>
>>>>  } __packed;
>>>>  
>>>>  /*
>>>> -- 
>>>> 2.15.0.55.gc2ece9dc4de6
>>>
>>> .
>>>
> 
> .
>