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

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Message-ID: <CAHJ8P3L68mKAcSdrgk-5VZQh4cW+BBroh+50ymvuzO0f5x5kMw@mail.gmail.com>
Date: Wed, 6 Nov 2024 10:26:01 +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 10:16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?"
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,
> >>>>
> >>
>