Re: [Qemu-block] [Qemu-devel] [RFC v4 19/21] blockjobs: Expose manual property

[Eric Blake]

On 02/28/2018 01:20 PM, John Snow wrote:

> > > +    if (!backup->has_manual) {
> > > +        backup->manual = false;
> > > +    }
> >
> > I think this is unnecessary these days, NULL/0/false is the default
> > value for QMP/QAPI.
>
> That's what I get for cargo cult. Eric, confirm/deny? Should I remove
> the other auto-false defaults too?
>
> Either we have them all or none of them for consistency.

Someday it would be nice to have QAPI provide decent non-0 defaults as 
desired.  But for now, Kevin is correct - the QAPI generator guarantees 
that you will have NULL/0/false values for 'has' anywhere that 'has_foo' 
is false.  We're less consistent on whether we ensure that we don't 
access 'foo' without checking 'has_foo' first, but if you want to 
simplify by relying on the default initialization to 0, you will not be 
the first person to do so.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org