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Re: [Qemu-block] [Qemu-devel] [PATCH v4 04/28] qapi: Add parameter to vi

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v4 04/28] qapi: Add parameter to visit_end_*
Date: Tue, 7 Jun 2016 17:20:56 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0

On 06/01/2016 09:36 AM, Markus Armbruster wrote:
> Eric Blake <address@hidden> writes:
>> Rather than making the dealloc visitor track of stack of pointers
>> remembered during visit_start_* in order to free them during
>> visit_end_*, it's a lot easier to just make all callers pass the
>> same pointer to visit_end_*.  The generated code has access to the
>> same pointer, while all other users are doing virtual walks and
>> can pass NULL.  The dealloc visitor is then greatly simplified.
>> All three visit_end_*() functions intentionally take a void**,
>> even though the visit_start_*() functions differ between void**,
>> GenericList**, and GenericAlternate**.  This is done for several
>> reasons: when doing a virtual walk, passing NULL doesn't care
>> what the type is, but when doing a generated walk, we already
>> have to cast the caller's specific FOO* to call visit_start,
>> while using void** lets us use visit_end without a cast. Also,
>> an upcoming patch will add a clone visitor that wants to use
>> the same implementation for all three visit_end callbacks,
>> which is made easier if all three share the same signature.
>> Signed-off-by: Eric Blake <address@hidden>
> [...]
>> diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c
>> index aea90a1..84f32fc 100644
>> --- a/qapi/qmp-input-visitor.c
>> +++ b/qapi/qmp-input-visitor.c
>> @@ -145,7 +145,7 @@ static void qmp_input_check_struct(Visitor *v, Error 
>> **errp)
>>      }
>>  }
>> -static void qmp_input_pop(Visitor *v)
>> +static void qmp_input_pop(Visitor *v, void **obj)
>>  {
>>      QmpInputVisitor *qiv = to_qiv(v);
>>      StackObject *tos = &qiv->stack[qiv->nb_stack - 1];
> You could assert @obj matches tos->obj.  Same for the other visitors
> that still need a stack.  Adding a stack to the ones that don't just for
> the assertion seems excessive, though.

At this point, only the QMP visitors track a stack (the OptsVisitor does
not, and we just got rid of the dealloc visitor stack); but since the
string visitors only support a top-level visit with no struct or nested
list, those can also support an assert. That makes 4 of the 6 visitors
at this stage in the series; and only 4/8 when the clone and json
visitors are added.  I'll go ahead and add it in, though.

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

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