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Message-ID: <0a8f96da-302d-4d6c-9ab6-0b66a05cbcfd@kernel.org>
Date: Wed, 6 Nov 2024 15:40:50 +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 14:08, Zhiguo Niu wrote:
> Chao Yu <chao@...nel.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@...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);
>> +
> 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
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
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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