[vbox-dev] VirtualBox virtual device development

[Sander van Leeuwen]

  There are three different contexts in which device code can be run:
- ring 3; host VM process context
- ring 0; host kernel context (vt-x/amd-v only)
- raw mode context; guest hypervisor context (software virtualization only)

The last two are optimizations to prevent an expensive switch to the VM 
host process to
handle e.g. very simple port I/O.

If you want to start writing a virtual device, I suggest you focus on 
the ring 3 context only for now.
The other two contexts have restrictions to which operations you're 
allowed to perform.

Sander

On 14-9-2010 17:22, Jaka Bac wrote:
> Hello
>
> I was looking at the code for the virtualbox's virtual devices and
> there is something that I don't exacly understand.
> I saw noticed that the one device implementation file actually
> includes different handlers for device i/o (memory or port i/o), and
> these are apparently compiled in more passes with different #define-s.
> Could someone please explain what the IN_RING3 define specifies, and
> what is the relationship with the handlers in the different contexts.
>
> Thank you in advance and Best Regards,
> Jaka Bac
>
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