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    SubjectRe: [PATCH RESEND] btrfs: Don't return extent in fiemap if we meet with a hole.
    On Mon, Jun 21, 2010 at 02:37:02PM +0800, Tao Ma wrote:
    > Hi Chris,
    > could you please consider merging this patch? It should be
    > trivial enough. It helps Jeff adding fiemap support to cp.

    Yes, I'll add this in, thanks!

    -chris

    >
    > Regards,
    > Tao
    >
    > From 909effe7240be30dbc9403dd8cbb326587c3cc02 Mon Sep 17 00:00:00 2001
    > From: Tao Ma <tao.ma@oracle.com>
    > Date: Thu, 22 Apr 2010 12:38:57 +0800
    > Subject: [PATCH RESEND] btrfs: Don't return extent in fiemap if we meet with a hole.
    >
    > Recently, my colleague Jeff tried to add fiemap support to cp(1).
    > http://www.mail-archive.com/bug-coreutils@gnu.org/msg19987.html
    >
    > He just meet with a strange issue with following command:
    > dd if=/dev/null of=/btrfs/sparse bs=1 seek=4096
    > When we use fiemap to the file, btrfs returns an extent with len '4096'
    > and flag 'unwritten' while actually there is no data allocated.
    >
    > I just dived into this and to my surprise, it is done by btrfs
    > intentionally. I checked other file systems which support fiemap.
    > Actually with the file created by the script, ocfs2, ext3/4 and
    > xfs all return zero extent. And according to the documentation file
    > Documentation/filesystems/fiemap.txt, FIEMAP_EXTENT_UNWRITTEN should
    > be used when the extent is allocated but it's data has not been
    > initialized. So I think btrfs should work like other filesystems.
    >
    > Cc: Chris Mason <chris.mason@oracle.com>
    > Signed-off-by: Tao Ma <tao.ma@oracle.com>
    > Tested-by: Jeff Liu <jeff.liu@oracle.com>
    > ---
    > fs/btrfs/extent_io.c | 15 +++++++++------
    > 1 files changed, 9 insertions(+), 6 deletions(-)
    >
    > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
    > index b177ed3..7eb4d77 100644
    > --- a/fs/btrfs/extent_io.c
    > +++ b/fs/btrfs/extent_io.c
    > @@ -2951,7 +2951,7 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
    > u64 disko = 0;
    > struct extent_map *em = NULL;
    > struct extent_state *cached_state = NULL;
    > - int end = 0;
    > + int end = 0, hole = 0;
    > u64 em_start = 0, em_len = 0;
    > unsigned long emflags;
    > ret = 0;
    > @@ -2978,12 +2978,13 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
    >
    > disko = 0;
    > flags = 0;
    > + hole = 0;
    >
    > if (em->block_start == EXTENT_MAP_LAST_BYTE) {
    > end = 1;
    > flags |= FIEMAP_EXTENT_LAST;
    > } else if (em->block_start == EXTENT_MAP_HOLE) {
    > - flags |= FIEMAP_EXTENT_UNWRITTEN;
    > + hole = 1;
    > } else if (em->block_start == EXTENT_MAP_INLINE) {
    > flags |= (FIEMAP_EXTENT_DATA_INLINE |
    > FIEMAP_EXTENT_NOT_ALIGNED);
    > @@ -3015,10 +3016,12 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
    > end = 1;
    > }
    >
    > - ret = fiemap_fill_next_extent(fieinfo, em_start, disko,
    > - em_len, flags);
    > - if (ret)
    > - goto out_free;
    > + if (!hole) {
    > + ret = fiemap_fill_next_extent(fieinfo, em_start, disko,
    > + em_len, flags);
    > + if (ret)
    > + goto out_free;
    > + }
    > }
    > out_free:
    > free_extent_map(em);
    > --
    > 1.6.3.3.334.g916e1.dirty
    >


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