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

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [RFC v4 19/21] blockjobs: Expose manual property
Date: Wed, 28 Feb 2018 13:27:00 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0

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

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