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

[Markus Armbruster <armbru@redhat.com>]

Luiz Capitulino <lcapitulino@redhat.com> writes:

> 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.

It's not coded as an assertion.  If we ever do coverage testing, it'll
stick out.  But again, I'm fine with it.

>> > +    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'.

Funny that the convenient way to extract a substring is to go through
QString.  Fine with me.

> [...]
>
>> > 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.

For a general purpose system, I'd recommend to cover all types.  But as
long as this has just one user (QEMU), it can use the special purpose
excuse not to.

>> >      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.

Yes.