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

[Paolo Bonzini]

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
> <address@hidden>? 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 think doing it for error_set was just for symmetry and to avoid
introducing excessive complexity.

Paolo