[RFC] Convert VMWARE vmdk (snapshot) to raw disk

[Jinpu Wang]

Hi,

We want to convert some VMWARE VM to KVM, and to reduce the VM down
time, we want to do it in two steps copy approach:

1. a snapshot is taken
- source VM continues to run on VMware => diff creates

2. snapshot is available for download as vmdk
- we need a software to copy snapshot to target VM raw disk

3. source VM is shut down
- diff is available

4. diff needs to be applied to target raw disk
is qemu-img able to do it, or is there another tool?  I saw commit
98eb9733f4cf2eeab6d12db7e758665d2fd5367b
Author: Sam Eiderman <shmuel.eiderman@oracle.com>
Date:   Thu Jun 20 12:10:57 2019 +0300

    vmdk: Add read-only support for seSparse snapshots

So it seems qemu vmdk already support the seSparse snapshot format,
but it is unclear for us how to connect all these features together.

In short we want to
1 vmdk => raw (big size)
2 vmdk delta => same raw disk (later time, with less content)

Can you give us some suggestions?

Thx!
Jinpu Wang