Tao Ma wrote: > Recently, my colleague Jeff tried to add fiemap support to cp(1). > http://www.mail-archive.com/[email protected]/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: Jeff Liu <[email protected]> > Cc: Chris Mason <[email protected]> > Signed-off-by: Tao Ma <[email protected]> > --- > 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, > u32 flags = 0; > u64 disko = 0; > struct extent_map *em = 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);
I have just tried a simple test against this patch, it works for me. Thanks, -Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
