Re: [Qemu-devel] BlockDriverState stack and BlockListeners

[Paolo Bonzini]

On 02/21/2012 02:10 PM, Kevin Wolf wrote:
>> > I think it depends, but both possibilities should be doable in this model.
> 
> Meh. :-)

Agreed. :)

> Maybe we need to introduce something outside of the whole stack, an
> entity that is referred to by the device (as in IDE, virtio-blk, ...)
> and that refers to a stack of top-level listeners (which would be moved
> to the new top-level BlockSource on live snapshot) and to the first
> BlockSource (which can have more listeners, and those would stick with
> the same BlockSource even if moves down the chain).

That would be a nested BlockSource.  I'm not sure why this is needed
though.  You can move BlockDrivers to another BlockSource down the chain
(stacking them on top of those that are there already), and leave the
upper BlockSource with the Protocol/View only.

> Oh, and just to open another can of worms: We should probably design in
> the notion of media (which can be ejected etc.) and drives (which always
> stay there). We don't have a clean separation today.

It is there: the drive is the BlockSource, the medium is the Protocol.
An empty drive is just another protocol.

Paolo