Parent vhd info lost during snapshot merge

[940607]

The header of a differencing VHD usually contains path to parent VHD. It is not used by VBox, but is important, if you want to attach a differencing disk to host.
For example:

Code: Select all

original state:
snap   vhd    parent
-----  ------ -------
a      a.vhd    -
b      b.vhd  a.vhd
c      c.vhd  b.vhd

after delete snapshot b:
snap   vhd    parent
-----  ------ -------
a      a.vhd    -
c      c.vhd  b.vhd

If now you try to attach c.vhd with diskpart, it will print:
DiskPart has encountered an error: The chain of virtual hard disks is inaccessible. There was an error opening a virtual hard disk further up the chain.

[mpack]

IMHO maintaining and verifying the correctness of a file path which VirtualBox has no use for goes beyond what's necessary in supporting a foreign file format.