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Date: Thu, 11 Sep 2014 16:35:58 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] qapi: Fix crash with enum dealloc when
	kind is invalid
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To: Michael Roth <mdroth@linux.vnet.ibm.com>, Fam Zheng <famz@redhat.com>, Eric Blake <eblake@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Hu Tao <hutao@cn.fujitsu.com>, Markus Armbruster <armbru@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, Luiz Capitulino <lcapitulino@redhat.com>

Il 11/09/2014 16:26, Michael Roth ha scritto:
> Also, the .kind field of a QAPI Union type is something we generate for use
> by the generated visitor code. In the case of an unspecified discriminator
> we generated the enum type for that field internally. In the case where it's
> specified, we use an existing enum instead...
> 
> But nothing stops us from generating a new "shadow" enum in this case as well,
> with the indexes/integer values of the corresponding strings shifted by one so
> we can reserve the 0 index for _INVALID. I think we can reasonably expect that
> nothing outside the generated code makes use of those integer values in this
> special case, and don't have to change all enum types to make that work.

But how would users fill in structs if you have to use a different enum?

What about making adding visit_start_union/visit_end_union?
visit_start_union can return false if the visit of the union has to be
skipped.

The dealloc visitor can skip it if the data field is NULL; everything
else can just use a default implementation which always returns true.

Paolo