On 09/24/2015 08:58 AM, Markus Armbruster wrote:
> Eric Blake <ebl...@redhat.com> writes:
>
>> Due to the existing semantics of the error_set() family,
>> generated sequences in the qapi visitors such as:
>>
>> visit_start_implicit_struct(m, (void **)obj, sizeof(FOO), &err);
>> if (!err) {
>> visit_type_FOO_fields(m, obj, errp);
>> visit_end_implicit_struct(m, &err);
>> }
>> error_propagate(errp, err);
>
> Indentation seems off. Intentional?
>
>>
>> are risky: if visit_type_FOO_fields() sets errp, and then
>> visit_end_implicit_struct() also encounters an error, the
>> attempt to overwrite the first error will cause an abort().I didn't even read error_propagate()'s contract correctly. It specifically specifies that if errp is already set, then err is ignored. So the above sequence is actually just fine, because only the following paths exist: visit_start_implicit_struct() fails into &err, error_propagate() passes err into caller's errp visit_start_implicit_struct() succeeds, visit_type_FOO_fields() fails into caller's errp, visit_end_implicit_struct() succeeds, error_propagate() does nothing visit_start_implicit_struct() succeeds, visit_type_FOO_fields() fails into caller's errp, visit_end_implicit_struct() fails int &err, error_propagate() does nothing (errp trumps err) visit_start_implicit_struct() succeeds, visit_type_FOO_fields() succeeds, visit_end_implicit_struct() fails int &err, error_propagate() passes err into caller's errp visit_start_implicit_struct() succeeds, visit_type_FOO_fields() succeeds, visit_end_implicit_struct() succeeds, error_propagate() does nothing As such, I'm revisiting if anything is needed at all, other than making the various visit_start/visit_end patterns consistent with one another using existing idioms, and it may turn out we don't need the ternary after all. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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