Re: [Qemu-devel] Error propagation in generated visitors and command marshallers

[Eric Blake <eblake@redhat.com>]

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On 04/09/2014 09:48 AM, Markus Armbruster wrote:
> I stumbled over this while trying to purge error_is_set() from the code.
> 

> But: is it a good idea to have both patterns in the code?  Should we
> perhaps use the common pattern for visiting, too?  Like this:
> 
>     visit_type_str(v, &foo, "foo", &err);
>     if (err) {
>         goto out;
>     }
>     visit_type_str(v, &bar, "bar", &err);
>     if (err) {
>         goto out;
>     }
> 
> Then we can assume *errp is clear on function entry, like this:
> 
>     void visit_type_str(Visitor *v, char **obj, const char *name, Error **errp)
>     {
>         v->type_str(v, obj, name, errp);
>     }
> 
> Should execute roughly the same number of conditional branches.
> 
> Tedious repetition of "if (err) goto out" in the caller, but that's what
> we do elsewhere, and unlike elsewhere, these one's are generated.
> 
> Opinions?

Putting the tedium into the generated code is WHY we have generated
code; so that the rest of the code that is hand-written can be concise.
 I like this latter idea of letting the visitors assume that errp is
clean on entry with the caller responsible for checking err after each step.

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


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