linux-kernel - Re: [PATCH 2/2] f2fs: fix to adjust appropriate length for fiemap

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Message-ID: <CAHJ8P3LFDBwgm1SUr3A3fNOLbP37vybPLuUJ=aYBtKgEh66BfQ@mail.gmail.com>
Date: Fri, 1 Nov 2024 13:48:22 +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 2/2] f2fs: fix to adjust appropriate length for fiemap

Zhiguo Niu <niuzhiguo84@...il.com> 于2024年11月1日周五 11:27写道：
>
> Chao Yu <chao@...nel.org> 于2024年11月1日周五 10:36写道：
> >
> > On 2024/10/31 13:59, Zhiguo Niu wrote:
> > > If user give a file size as "length" parameter for fiemap
> > > operations, but 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, please
> > > note that this f2fs_io has been modified for testing.
> > >
> > >   ./f2fs_io fiemap 0 19304 ylog/analyzer.py
> > > Fiemap: offset = 0 len = 19304
> > >          logical addr.    physical addr.   length           flags
> > > 0       0000000000000000 0000000020baa000 0000000000004000 00001000
> > > 1       0000000000004000 0000000020bae000 0000000000001000 00001001
> > >
> > > after this patch:
> > >   ./f2fs_io fiemap 0 19304 ylog/analyzer.py
> > > Fiemap: offset = 0 len = 19304
> > >       logical addr.    physical addr.   length           flags
> > > 0     0000000000000000 00000000315f3000 0000000000005000 00001000
> >
> > Why is FIEMAP_EXTENT_LAST missing in #0 extent? As we can see it
> > in #1 extent before your change.
> Hi Chao,
> for normal fiemap, we just  can tag  FIEMAP_EXTENT_LAST in the following:
>
> /* HOLE */
> if (!compr_cluster && !(map.m_flags & F2FS_MAP_FLAGS)) {
> start_blk = next_pgofs;
>
> if (blks_to_bytes(inode, start_blk) < blks_to_bytes(inode,
> max_inode_blocks(inode)))
> goto prep_next;
>
> flags |= FIEMAP_EXTENT_LAST;
> }
> but after this patch, if file length = 19304, blk len =5(page size=4096),
> and f2fs_map_blocks will run once if the file is  contiguous on disk,
> and will tag
> F2FS_MAP_FLAGS to map.m_flags, so the following case will not run.
> then
>
> if (size) {
> flags |= FIEMAP_EXTENT_MERGED;
> if (IS_ENCRYPTED(inode))
> flags |= FIEMAP_EXTENT_DATA_ENCRYPTED;
>
> ret = fiemap_fill_next_extent(fieinfo, logical,
> phys, size, flags);
> trace_f2fs_fiemap(inode, logical, phys, size, flags, ret);
> if (ret)
> goto out;
> size = 0;
> }
> fiemap_fill_next_extent will return 1, then go out , this fiemap flow finishes.
>
> >
> > 1       0000000000004000 0000000020bae000 0000000000001000 00001001
> but back to this case, because
>
> next:
> memset(&map, 0, sizeof(map));
> map.m_lblk = start_blk;
> map.m_len = bytes_to_blks(inode, len);
> map.m_next_pgofs = &next_pgofs;
> map.m_seg_type = NO_CHECK_TYPE;
>
> map.m_len will not  reduce the part that has beed maped even map.m_lbk
> has changed,
> for example, if file length = 19304, before patch, map.m_len=4,
> after once f2fs_map_block,  map.m_lbk=4, map.m_len still =4, so
> there will be "HOLE" case in the follow-up f2fs_map_block
> so it will loop until start_blk reaches the maxbytes.
> /* HOLE */
> if (!compr_cluster && !(map.m_flags & F2FS_MAP_FLAGS)) {
> start_blk = next_pgofs;
>
> if (blks_to_bytes(inode, start_blk) < blks_to_bytes(inode,
> max_inode_blocks(inode)))
> goto prep_next;
>
> flags |= FIEMAP_EXTENT_LAST;
> }
>
> there is another case before this patch, file size = 5 blocks, if we
> pass the len not
> greater than or equal to 5， it will not tag FIEMAP_EXTENT_LAST
>
>  # ./f2fs_io_new fiemap 0 4 file.apk
> Fiemap: offset = 0 len = 4
>         logical addr.    physical addr.   length           flags
> 0       0000000000000000 000000070e08f000 0000000000004000 00001008
>
> but if len equal or greater than 5,   it will tag FIEMAP_EXTENT_LAST
>  # ./f2fs_io_new fiemap 0 5 file.apk
> Fiemap: offset = 0 len = 5
>         logical addr.    physical addr.   length           flags
> 0       0000000000000000 000000070e08f000 0000000000004000 00001008
> 1       0000000000004000 000000070e090000 0000000000001000 00001001
> thanks!
Hi Chao, pls ignore this reply , I will confirm your questions.
thanks a lot~
> >
> > Thanks,
> >
> > >
> > > Signed-off-by: Zhiguo Niu <zhiguo.niu@...soc.com>
> > > ---
> > > 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 90fa8ab..8c9bb42 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));
> > >
> > >       start_blk = bytes_to_blks(inode, start);
> > >       last_blk = bytes_to_blks(inode, start + len - 1);
> >