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

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Message-ID: <CAHJ8P3Jm1+BdGsHNB03tDug8JgEtxkM9A3BE9wectE_khGgDhQ@mail.gmail.com>
Date: Wed, 6 Nov 2024 10:54:53 +0800
From: Zhiguo Niu <niuzhiguo84@...il.com>
To: Chao Yu <chao@...nel.org>
Cc: 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

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,
It looks well and clear, Let me verify this.
another unimportant questions, do we need to use macor
F2FS_BLKSIZE_xxx for round_up?
because in fiemap, it all use bytes_to_blks(inode, xxx) /
blks_to_bytes(inode, xxx)
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,
> >>>>>>
> >>>>
> >>
>