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

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

On 2024/11/6 16:41, Zhiguo Niu wrote:
> Chao Yu <chao@kernel.org> 于2024年11月6日周三 15:40写道：
>>
>> On 2024/11/6 14:08, Zhiguo Niu wrote:
>>> Chao Yu <chao@kernel.org> 于2024年11月6日周三 10:40写道：
>>>>
>>>> On 2024/11/6 10:26, Zhiguo Niu wrote:
>>>>> Chao Yu <chao@kernel.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@kernel.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@kernel.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@unisoc.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);
>>>> +
>>> Hi Chao,
>>> this verion verify pass with my test case.
>>>
>>> but there is still another issue in orginal code:
>>> ylog/analyzer.py  size = 19034
>>> if I input the following cmd(start/length are both real size, not block number)
>>> /f2fs_io fiemap 2 16384 ylog/analyzer.py
>>> and the results shows:
>>> Fiemap: offset = 2 len = 16384
>>>       logical addr.    physical addr.   length           flags
>>> 0    0000000000000000 0000000e2ebca000 0000000000004000 00001000
>>> 1    0000000000004000 0000000e2ebce000 0000000000001000 00001001
>>> so start_blk/last_blk should be calculate it in the following way?
>>
>> IIUC, the root cause is f2fs_map_blocks() will truncate size of
>> returned extent to F2FS_BYTES_TO_BLK(len), so whenever parameter
>> @len doesn't cover last extent, it triggers this bug.
>>
>> next:
>>          memset(&map, 0, sizeof(map));
>>          map.m_lblk = start_blk;
>>          map.m_len = F2FS_BYTES_TO_BLK(len);  --- limit max size of extent it founds
> yes, I think so too.
>>          map.m_next_pgofs = &next_pgofs;
>>          map.m_seg_type = NO_CHECK_TYPE;
>> ...
>>          ret = f2fs_map_blocks(inode, &map, F2FS_GET_BLOCK_FIEMAP);
>>
>> xfs_io file -c "fiemap -v 2 16384"
>> file:
>>    EXT: FILE-OFFSET      BLOCK-RANGE      TOTAL FLAGS
>>      0: [0..31]:         139272..139303      32 0x1000
>>      1: [32..39]:        139304..139311       8 0x1001
>> xfs_io file -c "fiemap -v 0 16384"
>> file:
>>    EXT: FILE-OFFSET      BLOCK-RANGE      TOTAL FLAGS
>>      0: [0..31]:         139272..139303      32 0x1000
>> xfs_io file -c "fiemap -v 0 16385"
>> file:
>>    EXT: FILE-OFFSET      BLOCK-RANGE      TOTAL FLAGS
>>      0: [0..39]:         139272..139311      40 0x1001
> 
> But  If the correct last_blk is calculated correctly, fiemap can be
> ended as soon as possible?  so the results shown is also right?

Zhiguo,

IMO, it's not, due to 1) if the extent is last one, FIEMAP_EXTENT_LAST
must be tagged to notice user that it doesn't need further fiemap on
latter LBA, 2) one continuous extent should not be split to two.

Let me figure out a fix for that.

Thanks,

> such as this special case "xfs_io file -c "fiemap -v 2 16384" we discussed.
> but it is fine for me to keep the current codes.
> thanks!
>>
>> Thoughts?
>>
>> Thanks,
>>
>>> before:
>>> start_blk = bytes_to_blks(inode, start);
>>> last_blk = bytes_to_blks(inode, start + len - 1);
>>> after:
>>>
>>> start_blk = bytes_to_blks(inode, start);
>>> last_blk = start_blk + bytes_to_blks(inode, len - 1);
>>> thanks!
>>>>     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,
>>>>>>>>>>
>>>>>>>>
>>>>>>
>>>>
>>



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