The test case verifies behavior of ext4 unwritten extents:
- Create a unwritten (preallocated) extent on ext4
- Fill the on-disk extent with random garbage
This is to make sure if btrfs tries to read the on-disk data, it would
definitely get some garbage.
As I found sometimes mkfs.ext4 can fill the unused bg with zeros.
- Fill the preallocated file range with some data
This is to make sure btrfs-convert can handle mixed written and
unwritten ranges.
- Save the checksum of the file.
- Convert the fs
- Verify the checksum
For older btrfs-convert, there would be only one regular file extent,
and reading the file would read out some garbage and cause checksum to
mismatch.
For the fixed btrfs-convert, we punch holes for unwritten extents,
thus only the written part would be read out and match the checksum.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
3c35adb2f7