Deleting a snapshot when the underlying vdi files are readonly

[Robert Garfoot]

If you make a VDI file for a snapshot on disk read only to protect it against unexpected modification and then try and delete a snapshot which results in merging on the read only VDI, the snapshot dissapears from the UI but it fails to complete since the file is read only. You can't try again though since the snapshot has gone from the UI.

I.e.

A <--Read only

B <-- Read only C

Then delete snapshot B, when it tries to merge to give you A->C it'll fail, however the UI shows B missing now and you end up having to delete all snapshots and reverting back to the base disk.

If the merge operation fails then the snapshots in the UI should be left untouched.

[Robert Garfoot]

I forgot code tags on the snapshot layout. Here it is again correctly formatted.

A  <-- Readonly
|-B  <-- Readonly
  |-C