Re: [Qemu-devel] [PATCH v4 0/6] Efficient VM backup for qemu

[Dietmar Maurer]

> >>> If we use nbd, how can we pass additional information to the other
> >>> side, for example information about unallocated regions?
> >>>
> >>
> >> You can either send trim commands, or just skip those regions and let
> >> the other side figure it out.
> >
> > But we are lost if we want to transfer something else? I am currently
> > not sure what we want to transfer, but I am sure we will find something in
> future.
> >
> > Or can we simply add a header to each write with additional information?
> 
> Let's discuss it once we have a clearer picture of what that additional info 
> would
> be.

OK, just discovered such case. 

For example it would be nice to pass the size of the devices somehow?