Suggestion: bmap files and bmaptool

[Samuel Sieb]

On 08/14/2013 02:21 AM, Artem Bityutskiy wrote:
> I think I covered this part in the documentation. But here is a short
> description.
>
> 1. The bmap file should be created just after the image is generated.
> 2. The blocks where zeroes were explicitly written will be mapped to
> real sectors which will contain zeroes.
> 3. The blocks which were not explicitely written to, will be unmapped.
> 4. Creation of the bmap file is done using the FIEMAP ioctl
> 5. Only unmapped blocks will be omited in the bmap files.
>
> While on this, I should note that this works best on ext4 file-system. I
> did not test ext2/3, but they should work as well as ext4. Btrfs was
> also tested, but it is a little bit worse than ext4, I can explain why
> if someone is interested.

Have you looked at partimage?  It sounds like this except that it works 
on many different filesystems and doesn't need the blocks to be unmapped 
to compress it (i.e. it works on normal partitions as well as images).