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Re: [Qemu-devel] [PATCH v9 02/37] qapi: Avoid use of misnamed DO_UPCAST(

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v9 02/37] qapi: Avoid use of misnamed DO_UPCAST()
Date: Wed, 20 Jan 2016 08:59:14 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0

On 01/20/2016 03:04 AM, Markus Armbruster wrote:
> Eric Blake <address@hidden> writes:
>> The macro DO_UPCAST() is incorrectly named: it converts from a
>> parent class to a derived class (which is a downcast).  Better,
>> and more consistent with some of the other qapi visitors, is
>> to use the container_of() macro through a to_FOO() helper.
>> Our current definition of container_of() is weaker than
>> DO_UPCAST(), in that it does not require the derived class to
>> have Visitor as its first member, but this does not hurt our
>> usage patterns in qapi visitors.
>> Signed-off-by: Eric Blake <address@hidden>
>> Reviewed-by: Marc-André Lureau <address@hidden>

>> +static OptsVisitor *to_ov(Visitor *v)
>> +{
>> +    return container_of(v, OptsVisitor, visitor);
>> +}
>> +
>> +
> The name to_ov() is rather laconic even for my taste.  Tolerable, since
> it's static.

And matches existing practice pre-patch:

qapi/qapi-dealloc-visitor.c:static QapiDeallocVisitor *to_qov(Visitor *v)
qapi/qmp-input-visitor.c:static QmpInputVisitor *to_qiv(Visitor *v)
qapi/qmp-output-visitor.c:static QmpOutputVisitor *to_qov(Visitor *v)

> Patch gets rid of all DO_UPCAST() in qapi/.  PATCH 33 brings one back;
> it should use to_ov() instead.

D'oh. You can tell what order I wrote the patches in :)

If I need to respin, I'll fix it; otherwise, I assume you can handle it.

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

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