cpio: File digest mismatch

[Jan Palus]

I've created a basic package for libguestfs fixed appliance 
(http://download.libguestfs.org/binaries/appliance/) however there seems to be 
an issue with how filesystem image is packaged by rpm. It's an ext2 fs file with 
size of 4G and only about ~256M used space:

$ file root
root: Linux rev 1.0 ext2 filesystem data, UUID=99344094-4997-41f9-9e01-73452b284ab3 (large files)

$ ls -lh root
-rw-r--r-- 1 jan users 4.0G 08-14 20:16 root

$ du -h root
275M	root

Now rpm installation fails with:

error: unpacking of archive failed on file /usr/lib64/guestfs/root;5991e7a3: cpio: File digest mismatch

Looking at cpio output:

$ rpm2cpio libguestfs-appliance-fixed-1.36.1-1.x86_64.rpm|cpio -idmv
./usr/lib64/guestfs/initrd
./usr/lib64/guestfs/kernel
./usr/lib64/guestfs/root
cpio: warning: skipped 4026531840 bytes of junk
...

it seems like "free space" is just considered "junk". Not really sure if that's 
the issue but is there a way to tell rpm not to treat it as junk?