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

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Message-ID: <CAHJ8P3L9o2RJgV=TtUf_MPj36wasgPn7bn9FnGPXu=TgpE7ATQ@mail.gmail.com>
Date: Tue, 5 Nov 2024 15:28:06 +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)
thanks！
>
> Thanks,
>