linux-kernel - Re: [PATCH V2] f2fs: fix to adjust appropriate length for fiemap

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Message-ID: <22873055-370b-4240-83ff-96bcfa91413a@kernel.org>
Date: Tue, 5 Nov 2024 18:39:27 +0800
From: Chao Yu <chao@...nel.org>
To: Zhiguo Niu <niuzhiguo84@...il.com>
Cc: Chao Yu <chao@...nel.org>, Zhiguo Niu <zhiguo.niu@...soc.com>,
 jaegeuk@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
 linux-kernel@...r.kernel.org, ke.wang@...soc.com, Hao_hao.Wang@...soc.com
Subject: Re: [PATCH V2] f2fs: fix to adjust appropriate length for fiemap

On 2024/11/5 15:28, Zhiguo Niu wrote:
> Chao Yu <chao@...nel.org> 于2024年11月5日周二 15:04写道：
>>
>> On 2024/11/4 9:56, Zhiguo Niu wrote:
>>> If user give a file size as "length" parameter for fiemap
>>> operations, but if this size is non-block size aligned,
>>> it will show 2 segments fiemap results even this whole file
>>> is contiguous on disk, such as the following results:
>>>
>>>    ./f2fs_io fiemap 0 19034 ylog/analyzer.py
>>> Fiemap: offset = 0 len = 19034
>>>           logical addr.    physical addr.   length           flags
>>> 0       0000000000000000 0000000020baa000 0000000000004000 00001000
>>> 1       0000000000004000 0000000020bae000 0000000000001000 00001001
>>>
>>> after this patch:
>>> ./f2fs_io fiemap 0 19034 ylog/analyzer.py
>>> Fiemap: offset = 0 len = 19034
>>>       logical addr.    physical addr.   length           flags
>>> 0    0000000000000000 00000000315f3000 0000000000005000 00001001
>>>
>>> Signed-off-by: Zhiguo Niu <zhiguo.niu@...soc.com>
>>> ---
>>> V2: correct commit msg according to Chao's questions
>>> f2fs_io has been modified for testing, the length for fiemap is
>>> real file size, not block number
>>> ---
>>>    fs/f2fs/data.c | 4 ++--
>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>> index 306b86b0..9fc229d 100644
>>> --- a/fs/f2fs/data.c
>>> +++ b/fs/f2fs/data.c
>>> @@ -1966,8 +1966,8 @@ int f2fs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>>>                        goto out;
>>>        }
>>>
>>> -     if (bytes_to_blks(inode, len) == 0)
>>> -             len = blks_to_bytes(inode, 1);
>>> +     if (len & (blks_to_bytes(inode, 1) - 1))
>>> +             len = round_up(len, blks_to_bytes(inode, 1));
>>
>> How do you think of getting rid of above alignment for len?
>>
>>>
>>>        start_blk = bytes_to_blks(inode, start);
>>>        last_blk = bytes_to_blks(inode, start + len - 1);
>>
>> And round up end position w/:
>>
>> last_blk = bytes_to_blks(inode, round_up(start + len - 1, F2FS_BLKSIZE));
> Hi Chao,
> I think this will change the current code logic
> -------------
> if (start_blk > last_blk)
>      goto out;
> -------------
> for example, a file with size 19006, but the length from the user is 16384.
> before this modification,  last_blk =  bytes_to_blks(inode, start +
> len - 1) = (inode, 16383) = 3
> after the first f2fs_map_blocks(). start_blk change to be 4,
> after the second f2fs_map_blocks(), fiemap_fill_nex_exten will be
> called to fill user parameter and then
> will goto out because start_blk > last_blk, then fiemap flow finishes.
> but after this modification, last_blk will be 4
> will do f2fs_map_blocks() until reach the max_file_blocks(inode)

Yes, you're right, however, w/ this patch, it may change last_blk, e.g.

xfs_io file -c "fiemap -v 0 19006" vs xfs_io file -c "fiemap -v 2 19006"
start_blk and last_blk will be: 0, 4 and 0, 5.

Should we round_up len after start_blk & last_blk calculation?

Thanks,

> thanks！
>>
>> Thanks,
>>