Re: [Qemu-devel] [PATCH v2 01/17] qapi: fix error propagation

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri, 13 Jul 2012 21:11:15 +0200
Paolo Bonzini <pbonzini@redhat.com> wrote:

> Il 13/07/2012 19:30, Laszlo Ersek ha scritto:
> >>> >> -    if (errp == NULL) {
> >>> >> +    if (errp == NULL || *errp != NULL) {
> >> > 
> >> > I think we should use assert() here.
> >> > 
> >> > If the error is already set, that most probably indicates a bug in the caller, as
> >> > it's the caller's responsibility to decide which error to return.
> > I believe we had a good argument against this, but I can't precisely
> > recall (or find) it now. Paolo, do you remember? Can you please both
> > search your respective mailboxen for Message-ID
> > <4FB21B71.7030804@redhat.com>? That's where we started to discuss this.
> > 
> > I believe I saw some paths in the code that tripped on this leak, and
> > generally keeping the first error seemed like a good idea.
> > opts_end_struct() originally checked for any pre-existent error
> > explicitly, but then the check was moved to the common code.
> 
> The reason to do this for error_propagate was to allow this idiom:
> 
>           /* Always call end_struct if start_struct succeeded.  */
>           error_propagate(errp, err);
>           err = NULL;
>           visit_end_struct(v, &err);
>           error_propagate(errp, err);

I agree with this change for error_propagate() because it encapsulates our
rules for error propagation.

> I think doing it for error_set was just for symmetry and to avoid
> introducing excessive complexity.

We already check if the error is set in several places, and I don't think
it will add much complexity. I still think that an assert() is better.