Is there a protocol for interacting with a Linux Host where another Linux guest is the virtio guest?

["Pincus, Josh" <Josh.Pincus@windriver.com>]

HI,

Thanks in advance for all the newbie help, especially to Stefan who graciously responded yesterday.

The current spec doesn't say a word about what's presented to the Linux Host (see attached graphic).  It speaks directly to what's presented to the Linux Guest, the user of the virtual device.  By Linux Host, I mean the VM responsible for virtualizing the actual hardware and providing a "virtio device" that receives raw content via the queues from the guest, translates the content into commands that can be understood by the hardware device driver in question, and eventually sends back responses to the guest.  What standard or interface is used by compliant HYPs to configure the Linux Host to fire up a virtual device, negotiate with the guest based on features the HOST supports, respond to register reads/writes performed by the guest, and initiate interrupts back to the guest as needed?  

Is there any kind of standard or documentation that governs how compliant Hypervisors are supposed to present such an interface to the Linux Host?  Are folks using vhost in the Linux Host to provide an interface to the Host's virtio device and then relying on the HYP to interact with that service when the Guest makes register requests?  

Thank you for your help,
JP

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