linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: fix to tag FIEMAP_EXTENT_DELALLOC in fiemap() for delay allocated extent

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Message-ID: <ZDWUGr2c3TT2tTgu@google.com>
Date:   Tue, 11 Apr 2023 10:08:42 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: fix to tag FIEMAP_EXTENT_DELALLOC in
 fiemap() for delay allocated extent

On 04/11, Chao Yu wrote:
> On 2023/4/11 16:14, Chao Yu wrote:
> > On 2023/4/11 1:57, Jaegeuk Kim wrote:
> > > On 04/08, Chao Yu wrote:
> > > > On 2023/4/8 4:59, Jaegeuk Kim wrote:
> > > > > This breaks generic/009?
> > > > 
> > > > I guess it is as expected?
> > > > 
> > > > Please check description of fiemap ioctl manual from [1]:
> > > > 
> > > > FIEMAP_EXTENT_UNKNOWN
> > > > The location of this extent is currently unknown. This may
> > > > indicate the data is stored on an inaccessible volume or that
> > > > no storage has been allocated for the file yet.
> > > > 
> > > > FIEMAP_EXTENT_DELALLOC
> > > > This will also set FIEMAP_EXTENT_UNKNOWN.
> > > > 
> > > > Delayed allocation - while there is data for this extent, its
> > > > physical location has not been allocated yet.
> > > > 
> > > > FIEMAP_EXTENT_UNWRITTEN
> > > > Unwritten extent - the extent is allocated but its data has not
> > > > been initialized. This indicates the extent’s data will be all
> > > > zero if read through the filesystem but the contents are undefined
> > > > if read directly from the device.
> > > > 
> > > > [1] https://www.kernel.org/doc/html/latest/filesystems/fiemap.html
> > > > 
> > > > According to its description, f2fs only support
> > > > FIEMAP_EXTENT_{UNKNOWN, DELALLOC}, but not support
> > > > FIEMAP_EXTENT_UNWRITTEN.
> > > 
> > > No, I don't think so.
> > 
> > Jaegeuk,
> > 
> > Could you please check the detailed description of FIEMAP_EXTENT_UNWRITTEN?
> > The flag indicates two conditions:
> > 1. on-disk blkaddrs were allocated for extent, and the extent is tagged as
> > unwritten status.
> > 2. data readed on those blocks will be all zero.
> 
> Sorry, I mean:
> 
> 1. on-disk blkaddrs were allocated for extent;
> 2. extent is tagged as unwritten status, data readed on those blocks will be
> all zero.

I was thinking fallocate/pin cases to give zero data. But, we may need to check
the space discarded securely or disk support?

> 
> Thanks,
> 
> > 
> > So, let's check f2fs' status:
> > - fallocate only reserve valid block count and set NEW_ADDR in dnode, so
> > it does not match condition 1)
> > - pin & fallocate preallocates blkaddrs and set blkaddrs in dnode, but
> > content on those blkaddrs may contain zero or random data, so it does not
> > match  condition 2)
> > 
> > Christoph describes this issue in below patch as well, you can check it.
> > da8c7fecc9c7 ("f2fs: rename F2FS_MAP_UNWRITTEN to F2FS_MAP_DELALLOC")
> > 
> > Am I missing something?
> > 
> > Thanks,
> > 
> > > 
> > > > 
> > > > So 009, 092, 094 .. which expects unwritten status from extent will
> > > > fail.
> > > > 
> > > > How about disabling those testcase?
> > > > 
> > > > Thanks,
> > > > 
> > > > > 
> > > > > On 04/05, Chao Yu wrote:
> > > > > > xfstest generic/614 fails to run due below reason:
> > > > > > 
> > > > > > generic/614 1s ... [not run] test requires delayed allocation buffered writes
> > > > > > 
> > > > > > The root cause is f2fs tags wrong fiemap flag for delay allocated
> > > > > > extent.
> > > > > > 
> > > > > > Quoted from fiemap.h:
> > > > > > FIEMAP_EXTENT_UNKNOWN        0x00000002 /* Data location unknown. */
> > > > > > FIEMAP_EXTENT_DELALLOC        0x00000004 /* Location still pending.
> > > > > >                             * Sets EXTENT_UNKNOWN. */
> > > > > > FIEMAP_EXTENT_UNWRITTEN        0x00000800 /* Space allocated, but
> > > > > >                             * no data (i.e. zero). */
> > > > > > 
> > > > > > FIEMAP_EXTENT_UNWRITTEN means block address is preallocated, but w/o
> > > > > > been written any data, which status f2fs is not supported now, for all
> > > > > > NEW_ADDR block addresses, it means delay allocated blocks, so let's
> > > > > > tag FIEMAP_EXTENT_DELALLOC instead.
> > > > > > 
> > > > > > Testcase:
> > > > > > xfs_io -f -c 'pwrite 0 64k' /mnt/f2fs/file;
> > > > > > filefrag -v /mnt/f2fs/file
> > > > > > 
> > > > > > Output:
> > > > > > - Before
> > > > > > Filesystem type is: f2f52010
> > > > > > Fize of /mnt/f2fs/file is 65536 (16 blocks of 4096 bytes)
> > > > > >    ext:     logical_offset:        physical_offset: length:   expected: flags:
> > > > > >      0:        0..      15:          0..        15:     16:             last,unwritten,merged,eof
> > > > > > /mnt/f2fs/file: 1 extent found
> > > > > > 
> > > > > > After:
> > > > > > Filesystem type is: f2f52010
> > > > > > File size of /mnt/f2fs/file is 65536 (16 blocks of 4096 bytes)
> > > > > >    ext:     logical_offset:        physical_offset: length:   expected: flags:
> > > > > >      0:        0..      15:          0..         0:      0:             last,unknown_loc,delalloc,eof
> > > > > > /mnt/f2fs/file: 1 extent found
> > > > > > 
> > > > > > Fixes: 7f63eb77af7b ("f2fs: report unwritten area in f2fs_fiemap")
> > > > > > Signed-off-by: Chao Yu <chao@...nel.org>
> > > > > > ---
> > > > > >    fs/f2fs/data.c | 7 +++++--
> > > > > >    1 file changed, 5 insertions(+), 2 deletions(-)
> > > > > > 
> > > > > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > > > > > index 359de650772e..3afc9764743e 100644
> > > > > > --- a/fs/f2fs/data.c
> > > > > > +++ b/fs/f2fs/data.c
> > > > > > @@ -1995,7 +1995,10 @@ int f2fs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
> > > > > >        }
> > > > > >        if (size) {
> > > > > > -        flags |= FIEMAP_EXTENT_MERGED;
> > > > > > +        if (flags & FIEMAP_EXTENT_DELALLOC)
> > > > > > +            phys = 0;
> > > > > > +        else
> > > > > > +            flags |= FIEMAP_EXTENT_MERGED;
> > > > > >            if (IS_ENCRYPTED(inode))
> > > > > >                flags |= FIEMAP_EXTENT_DATA_ENCRYPTED;
> > > > > > @@ -2035,7 +2038,7 @@ int f2fs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
> > > > > >                    size += blks_to_bytes(inode, 1);
> > > > > >                }
> > > > > >            } else if (map.m_flags & F2FS_MAP_DELALLOC) {
> > > > > > -            flags = FIEMAP_EXTENT_UNWRITTEN;
> > > > > > +            flags = FIEMAP_EXTENT_DELALLOC;
> > > > > >            }
> > > > > >            start_blk += bytes_to_blks(inode, size);
> > > > > > -- 
> > > > > > 2.36.1
> > 
> > 
> > _______________________________________________
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