On 09/24/2015 10:14 AM, Eric Blake wrote:
>>>
>>> visit_start_implicit_struct(m, (void **)obj, sizeof(FOO), &err);
>>> if (!err) {
>>> visit_type_FOO_fields(m, obj, &err);
>>> visit_end_implicit_struct(m, err ? NULL : &err);
>>> }
>>> error_propagate(errp, err);
>>
>> Hmmmmm... not sure we do this anywhere else, yet. The ternary isn't
>> exactly pretty, but the intent to ignore additional error is clear
>> enough, I think.
>>
>> If we elect to adopt this new error handling pattern, we should perhaps
>> document it in error.h.
>>
>> Third option: drop visit_end_implicit_struct()'s errp parameter. If we
>> find a compelling use for it, we'll put it back and solve the problem.
>>
>
> Ooh, interesting idea. It changes the contract - but since the contract
> isn't (yet) documented, and happens to work with existing uses without a
> contract, it could indeed be nicer. It would have knock-on effects to
> 24/46 where I first try documenting the contract.
Oh well. We do have a compelling use: qmp-input-visitor.c can set errp
during visit_end_struct() when in strict mode (basically, the mode which
warns if the input QDict has leftover key:value pairs that were not
consumed by visit_type_FOO() between the start/end call). I don't know
if visit_end_list() or visit_end_implicit_struct() care; but then we
have the argument that it is worth keeping them consistent with
visit_end_struct() which can indeed raise an error.
One other potential alternative: What if we split visit_end_struct()
into two visitor functions, one that checks for success, and the other
that is called unconditionally to clean up resources. That is, go from:
visit_start_struct(m, (void **)obj, "foo", name, sizeof(FOO), &err);
if (!err) {
if (*obj) {
visit_type_FOO_fields(m, obj, errp);
}
visit_end_struct(m, &err);
}
error_propagate(errp, err);
to a form where the check for leftover key/value pairs is only done on
success with a new visit_check_struct():
visit_start_struct(m, (void **)obj, "foo", name, sizeof(FOO), &err);
if (!err) {
if (*obj) {
visit_type_FOO_fields(m, obj, &err);
}
if (!err) {
visit_check_struct(m, &err);
}
visit_end_struct(m);
}
error_propagate(errp, err);
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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