On 07/19/2013 05:04 AM, Pawit Pornkitprasan wrote: > On Fri, Jul 19, 2013 at 7:57 PM, Eric Blake <ebl...@redhat.com> wrote: >> >> However, wouldn't it be nice if we improved the qapi generator to >> guarantee a sane default value for optional parameters, even when >> has_value is false? >> > > I'm not a qemu expert or anything, but wouldn't that destroy the point > of has_value in the first place?
There are two uses for has_value. One: on output, the user knows whether the variable has been set to anything sane. Two: on input, the receiver knows if the caller passed an optional value. For output, has_value is always needed. But for input, we could probably simplify a LOT of code if 'value' already had a sane default of 0, without having to first check 'has_value', instead of the current state where 'value' must be treated as uninitialized if 'has_value' is false. Improving the qapi generator to guarantee 0 value of optional parameters that were not specified in JSON should not block your patch (it would be a series by itself), it's just a question of whether it is worth making the change and the resulting simplifications we can make to code that can assume sane default values. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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