Re: [Qemu-devel] [PATCH v11 06/15] qapi: Visit variants in visit_type_FOO_fields()

[Eric Blake <eblake@redhat.com>]

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On 02/18/2016 06:58 AM, Markus Armbruster wrote:
> Eric Blake <eblake@redhat.com> writes:
> 
>> We initially created the static visit_type_FOO_fields() helper
>> function for reuse of code - we have cases where the initial
>> setup for a visit has different allocation (depending on whether
>> the fields represent a stand-alone type or are embedded as part
>> of a larger type), but where the actual field visits are
>> identical once a pointer is available.
>>
>> Up until the previous patch, visit_type_FOO_fields() was only
>> used for structs (no variants), so it was covering every field
>> for each type where it was emitted.
>>
>> Meanwhile, the code for visiting unions looks like:

Maybe reword this to:

Meanwhile, the previous patch updated the code for visiting unions to
look like:


>> The resulting diff to the generated code is a bit hard to read,
> 
> Mostly because a few visit_type_T_fields() get generated in a different
> place.  If I move them back manually for a diff, the patch's effect
> becomes clear enough: the switch to visit the variants and the
> visit_start_union() guarding it moves from visit_type_T() to
> visit_type_T_fields().  That's what the commit message promises.

I debated about splitting out a separate patch so that the motion of
visit_type_T_fields() is separate from the variant visiting, but it
wasn't worth the effort.  I'm glad you managed to see through the churn
in the generated code.


>> -def gen_visit_struct_fields(name, base, members):
>> +def gen_visit_struct_fields(name, base, members, variants=None):
> 
> Two callers:
> 
> * gen_visit_union(): the new code here comes from there, except it's now
>   completely guarded by if variants.  Effect: generated code motion.
> 
> * gen_visit_struct(): passes no variants, guard false, thus no change.
> 
> I think the patch becomes slightly clearer if you make the variants
> parameter mandatory.  It'll probably become mandatory anyway when we
> unify gen_visit_struct() and gen_visit_union().

You beat me to it - yes, I realized that after sending the series.  We
can either squash in the fix here to make variants mandatory (and
gen_visit_struct() pass an explicit None, which disappears in the next
patch), or squash in a fix to 7/15 to delete the '=None'.  Either way,
I'm fine if you tackle that, if no other major findings turn up.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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