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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <2da23a16-51c7-fdcc-dfc5-7eed08f60d6f@redhat.com>
Date: Wed, 21 Mar 2018 17:23:57 +0100
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Subject: Re: [Qemu-devel] [PATCH 2/3] qobject: assume base of a qobject is
 at offset 0
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To: =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= <marcandre.lureau@redhat.com>
Cc: qemu-devel <qemu-devel@nongnu.org>, "P. Berrange, Daniel" <berrange@redhat.com>, "Blake, Eric" <eblake@redhat.com>, "Armbruster, Markus" <armbru@redhat.com>

On 21/03/2018 17:11, Marc-Andr=C3=A9 Lureau wrote:
> Hi
>=20
> On Wed, Mar 21, 2018 at 5:00 PM, Paolo Bonzini <pbonzini@redhat.com> wr=
ote:
>> On 21/03/2018 16:55, Marc-Andr=C3=A9 Lureau wrote:
>>> That would work with an anonymous union though:
>>>
>>> struct QObject {
>>>     union {
>>>         QType type;
>>>         QType base;
>>>     };
>>>     size_t refcnt;
>>> };
>>>
>>> If it's acceptable, I think I'll take this approach.
>>
>> You don't need QEMU_GENERIC at all then, don't you?
>=20
> Ah ah, that's what I thought too, but the type of QObject * &x->base
> isn't QObject * :)
>=20
> I don't think we can fool it there (without loosing some type safety)

Hmm, perhaps by making it "struct {} base"?

Or even:

struct QObjectCommon {
    QType type;
    size_t refcnt;
}

struct QObject {
    QObjectCommon base;
}

struct QString {
    QObjectCommon base;
    ...
}

Paolo