Re: [Qemu-devel] [PATCH v2 5/5] block: keep AioContext pointer in BlockBackend

[Fam Zheng <famz@redhat.com>]

On Thu, 09/29 09:47, Paolo Bonzini wrote:
> 
> 
> On 29/09/2016 05:05, Fam Zheng wrote:
> > > So whether we can move a certain BB from some context to another depends
> > > on what the frontend supports, I don't think there is a generic answer
> > > we can implement here in the generic BB code. NBD for instance allows
> > > any movement; but devices probably only allow movements they have
> > > initiated themselves (e.g. dataplane will allow exactly what you
> > > describe here with that assertion, and any other device will probably
> > > not allow anything but the main loop).
> > 
> > Indeed, you make me think this should be an op blocker (that applies on whole
> > graph).
> 
> The concept of a BDS or BB's AioContext is going to disappear sooner or
> later, take this into account to decide how much effort to put into
> fixing this.

Taking one step back, the whole thing is so broken considering the node
reference. Currently, even this is possible:

    -drive file=null-co://,if=virtio,id=d0 \
    -drive file.file=d0,driver=raw,file.driver=raw,if=virtio

AioContext is actually a factor to make it worse. Maybe we should instead think
about some generic protection mechanism? Is this in the scope of new op
blocker?

Fam