I'm familiar with the process of installing Guest Additions and sharing host folders with the guest, but is there a way to do the reverse?
I have an XP host and Ubuntu 10.10 guest, with VBox 4.0.2.
In other words, I'd like for the host to have direct access to (at least some of the) files inside the .vdi file.
Best Answer
There is no way to do this with the Guest extensions, however, setup normal Ubuntu file sharing on your guest and you can access the files using the virtual network between the host and the guest. The OSE version of VirtualBox doesn't have shared folders, and this is the recommended sharing method for VirtualBox as described here. How-To Geek has a tutorial here on how to do it with Ubuntu specifically, and it applies to everything outside of home folders as well.
The network driver is smart enough not to send the traffic over the wire, but will still be used to communicate with the guest. I have a few virtual machines I run and use like this, both on Mac and Windows.