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); -- 1.6.3.3.334.g916e1.dirty -- 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
