Re: [Qemu-devel] [RFC PATCH 1/1] ceph/rbd block driver for qemu-kvm

[Anthony Liguori]

On 05/25/2010 08:31 AM, Avi Kivity wrote:
> > A protocol based mechanism has the advantage of being more robust in 
> > the face of poorly written block backends so if it's possible to make 
> > it perform as well as a plugin, it's a preferable approach.
>
> May be hard due to difficulty of exposing guest memory.

If someone did a series to add plugins, I would expect a very strong 
argument as to why a shared memory mechanism was not possible or at 
least plausible.

I'm not sure I understand why shared memory is such a bad thing wrt 
KVM.  Can you elaborate?  Is it simply a matter of fork()?

> > Plugins that just expose chunks of QEMU internal state directly (like 
> > BlockDriver) are a really bad idea IMHO.
>
> Also, we don't want to expose all of the qemu API.  We should default 
> the visibility attribute to "hidden" and expose only select functions, 
> perhaps under their own interface.  And no inlines.

Yeah, if we did plugins, this would be a key requirement.

Regards,

Anthony Liguori