Re: [Qemu-devel] [PATCH 07/10] Introduce QError

[Luiz Capitulino <lcapitulino@redhat.com>]

On Wed, 18 Nov 2009 16:16:11 +0100
Markus Armbruster <armbru@redhat.com> wrote:

> Luiz Capitulino <lcapitulino@redhat.com> writes:

[...]

> > +static const char *append_field(QString *outstr, const QError *qerror,
> > +                                const char *start)
> > +{
> > +    QObject *obj;
> > +    QDict *qdict;
> > +    QString *key_qs;
> > +    const char *end, *key;
> > +
> > +    if (*start != '%')
> > +        parse_error(qerror, '%');
> 
> Can't happen, because it gets called only with *start == '%'.  Taking
> pointer to the character following the '%' as argument would sidestep
> the issue.  But I'm fine with leaving it as is.

 It's just an assertion.

> > +    start++;
> > +    if (*start != '(')
> > +        parse_error(qerror, '(');
> > +    start++;
> > +
> > +    end = strchr(start, ')');
> > +    if (!end)
> > +        parse_error(qerror, ')');
> > +
> > +    key_qs = qstring_from_substr(start, 0, end - start - 1);
> > +    key = qstring_get_str(key_qs);
> > +
> > +    qdict = qobject_to_qdict(qdict_get(qerror->error, "data"));
> > +    obj = qdict_get(qdict, key);
> > +    if (!obj) {
> > +        qerror_abort(qerror, "key '%s' not found in QDict", key);
> > +    }
> > +
> > +    switch (qobject_type(obj)) {
> > +        case QTYPE_QSTRING:
> > +            qstring_append(outstr, qdict_get_str(qdict, key));
> > +            break;
> > +        case QTYPE_QINT:
> > +            qstring_append_int(outstr, qdict_get_int(qdict, key));
> > +            break;
> > +        default:
> > +            qerror_abort(qerror, "invalid type '%c'", qobject_type(obj));
> > +    }
> > +
> > +    QDECREF(key_qs);
> 
> Looks like you create key_qs just because it's a convenient way to
> extract key zero-terminated.  Correct?

 Yes, as a substring of 'desc', which is passed through 'start'.

[...]

> > diff --git a/qjson.c b/qjson.c
> > index 12e6cf0..60c904d 100644
> > --- a/qjson.c
> > +++ b/qjson.c
> > @@ -224,6 +224,8 @@ static void to_json(const QObject *obj, QString *str)
> >          }
> >          break;
> >      }
> > +    case QTYPE_QERROR:
> > +        /* XXX: should QError be emitted? */
> 
> Pros & cons?

 It's probably convenient to have qjson emitting QError, I'm unsure
if we should do that for all kinds of QObjects though.

> >      case QTYPE_NONE:
> >          break;
> >      }
> > diff --git a/qobject.h b/qobject.h
> > index 2270ec1..07de211 100644
> > --- a/qobject.h
> > +++ b/qobject.h
> > @@ -43,6 +43,7 @@ typedef enum {
> >      QTYPE_QLIST,
> >      QTYPE_QFLOAT,
> >      QTYPE_QBOOL,
> > +    QTYPE_QERROR,
> >  } qtype_code;
> >  
> >  struct QObject;
> 
> Erroneous QERRs are detected only when they're passed to
> qerror_from_info() at run-time, i.e. when the error happens.  Likewise
> for erroneous qerror_table[].desc.  Perhaps a unit test to ensure
> qerror_table[] is sane would make sense.  Can't protect from passing
> unknown errors to qerror_from_info(), but that shouldn't be a problem in
> practice.

 We could also have a debug function that could run once at startup
and do the check.