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

[Chao Yu]

On 2024/11/5 19:02, Zhiguo Niu wrote:
> Chao Yu <chao@xxxxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > > > ---
> > > > > 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?

And for you case, it calculates last_blk correctly.

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,