On Wed 06 Apr 2016 11:59:47 AM CEST, Kevin Wolf wrote: > Let me draw some ASCII art. I'm drawing I/O throttling like a filter > to make the difference clear; in reality it's part of the BDS now or > of the BB in 2.7, so don't let this confuse you. > > Let's assume these command line options: > > -drive file=backimg.img,if=none,id=backing,iops=1024 > -drive file=overlay.qcow2,id=overlay,backing=backing > > If we didn't catch this configuration and error out, this is what we > would end up with in 2.6: > > [BB] overlay > | > | > [BDS] qcow2 [BB] backing > | | > +--------------------+ > . | > . I/O throttling > . | > [BDS] raw > . > . > .
I see, thanks for the explanation! But what's the use of having a BlockBackend on a node that is used as a backing image? Is it because "we allow this so let's prevent the user from doing weird things", or is there anything useful we can do with it? Berto
