Re: [Qemu-devel] [PATCH RFC v2 07/47] qapi: Generate a nicer struct for flat unions

[Eric Blake]

On 07/30/2015 09:44 AM, Markus Armbruster wrote:

>>>> which means that if we name any of the branches 'data' (that is, if
>>>> 'data' is a member of the enum discriminator), things fail to compile.
>>>> We could probably fix that by naming our dummy branch '_data'.
>>>
>>> I wonder whether member data is actually used.  I'll find out.
>>
>> The dealloc visitor uses 'data' being non-null as a flag on whether to
>> deallocate the union even if the tag was invalid for some reason; or
>> more importantly, if parsing consumed the tag but then detected an error
>> while parsing the union, leaving the union branch partially allocated.
>> To avoid a leak, we have to deallocate the branch.
>>
>> But if the tag was invalid, then why did we ever allocate the union in
>> the first place, and how do we prove we are calling the correct free-ing
>> function?  And if the tag is valid, why can't we just guarantee that the
>> union is 0-initialized and that deleting the branch will work through
>> the correct branch type instead of worrying about 'data'?
> 
> Good questions.  Someone will have to review and fix this code.  Let's
> add a FIXME so we don't forget.  Care to propose one?

Sure; see 12.6/47 (since that is close to several other patches adding
FIXME comments).

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

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