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

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Message-ID: <CAHJ8P3+VY6RYgrCPJRSjJp82qJaYGUyqR3vV3OGRO_Q774qxxw@mail.gmail.com>
Date: Fri, 1 Nov 2024 11:27:53 +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 2/2] f2fs: fix to adjust appropriate length for fiemap

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!
>
> 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);
>