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

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Message-ID: <c070fd2d-6480-4833-b03c-ec032ee37a28@kernel.org>
Date: Wed, 6 Nov 2024 10:40:17 +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 2024/11/6 10:26, Zhiguo Niu wrote:
> Chao Yu <chao@...nel.org> 于2024年11月6日周三 10:16写道：
>>
>> On 2024/11/5 19:02, Zhiguo Niu wrote:
>>> Chao Yu <chao@...nel.org> 于2024年11月5日周二 18:39写道：
>>>>
>>>> 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.
>>> Hi Chao,
>>> yes, but w/o this patch , the original code still has the same situation??
>>> for example
>>> xfs_io file -c "fiemap -v 0 16384" vs xfs_io file -c "fiemap -v 2 16384"
>>> start_blk and last_blk will be: 0, 3 and 0, 4.
>>
>> For the case "fiemap -v 2 19006", offset is 2, and length is 19006, so last_offset
>> is 19008, and last_blk should be 4 rather than 5, right?
> hi Chao,
> it is right w/o my patch.
>>
>> And for you case, it calculates last_blk correctly.
> So you suggest that "Should we round_up len after start_blk & last_blk
> calculation?"

Zhiguo,

Yes, I think alignment of len should not affect calculation of last_blk.

I mean this,

---
  fs/f2fs/data.c          | 6 +++---
  include/linux/f2fs_fs.h | 3 ++-
  2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 7d1bb9518a40..cbbb956f420d 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -1967,12 +1967,12 @@ 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);
-
  	start_blk = bytes_to_blks(inode, start);
  	last_blk = bytes_to_blks(inode, start + len - 1);

+	if (len & F2FS_BLKSIZE_MASK)
+		len = round_up(len, F2FS_BLKSIZE);
+
  next:
  	memset(&map, 0, sizeof(map));
  	map.m_lblk = start_blk;
diff --git a/include/linux/f2fs_fs.h b/include/linux/f2fs_fs.h
index b0b821edfd97..954e8e8344b7 100644
--- a/include/linux/f2fs_fs.h
+++ b/include/linux/f2fs_fs.h
@@ -24,10 +24,11 @@
  #define NEW_ADDR		((block_t)-1)	/* used as block_t addresses */
  #define COMPRESS_ADDR		((block_t)-2)	/* used as compressed data flag */

+#define F2FS_BLKSIZE_MASK		(F2FS_BLKSIZE - 1)
  #define F2FS_BYTES_TO_BLK(bytes)	((bytes) >> F2FS_BLKSIZE_BITS)
  #define F2FS_BLK_TO_BYTES(blk)		((blk) << F2FS_BLKSIZE_BITS)
  #define F2FS_BLK_END_BYTES(blk)		(F2FS_BLK_TO_BYTES(blk + 1) - 1)
-#define F2FS_BLK_ALIGN(x)			(F2FS_BYTES_TO_BLK((x) + F2FS_BLKSIZE - 1))
+#define F2FS_BLK_ALIGN(x)		(F2FS_BYTES_TO_BLK((x) + F2FS_BLKSIZE - 1))

  /* 0, 1(node nid), 2(meta nid) are reserved node id */
  #define F2FS_RESERVED_NODE_NUM		3
-- 
2.40.1



> Thanks
>>
>> Thanks,
>>
>>> but overall last_blk will change loop counts but has not affect on the results.
>>>>
>>>> Should we round_up len after start_blk & last_blk calculation?
>>> I thinks it is ok ,but just a little bit redundant with the following
>>> handling about len.
>>>
>>> if (bytes_to_blks(inode, len) == 0)
>>>      len = blks_to_bytes(inode, 1);
>>>
>>> Based on the above situation,
>>> do you have any other good suggestions? ^^
>>> thanks!
>>>
>>>>
>>>> Thanks,
>>>>
>>>>> thanks！
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>
>>