Re: [Qemu-devel] [PATCH v3 09/21] qapi: add QMP dispatch functions

[Luiz Capitulino <lcapitulino@redhat.com>]

On Wed, 15 Jun 2011 14:45:30 -0500
Anthony Liguori <aliguori@us.ibm.com> wrote:

> On 06/15/2011 02:33 PM, Luiz Capitulino wrote:
> > On Mon, 13 Jun 2011 21:31:14 -0500
> > Michael Roth<mdroth@linux.vnet.ibm.com>  wrote:
> >
> >
> >> +{
> >> +    const char *command;
> >> +    QDict *args, *dict;
> >> +    QmpCommand *cmd;
> >> +    QObject *ret = NULL;
> >> +
> >> +    if (qobject_type(request) != QTYPE_QDICT) {
> >> +        error_set(errp, QERR_JSON_PARSE_ERROR, "request is not a dictionary");
> >> +        goto out;
> >> +    }
> >> +
> >> +    dict = qobject_to_qdict(request);
> >> +    if (!qdict_haskey(dict, "execute")) {
> >> +        error_set(errp, QERR_JSON_PARSE_ERROR, "no execute key");
> >> +        goto out;
> >> +    }
> >> +
> >> +    command = qdict_get_str(dict, "execute");
> >> +    cmd = qmp_find_command(command);
> >> +    if (cmd == NULL) {
> >> +        error_set(errp, QERR_COMMAND_NOT_FOUND, command);
> >> +        goto out;
> >> +    }
> >> +
> >> +    if (!qdict_haskey(dict, "arguments")) {
> >> +        args = qdict_new();
> >> +    } else {
> >> +        args = qdict_get_qdict(dict, "arguments");
> >> +        QINCREF(args);
> >> +    }
> >
> > This function doesn't seem to handle extra keys in the command dict, like:
> >
> >   { "execute": "query-block", "foo": "bar" }
> >
> > You probably want to use qmp_check_input_obj() here.
> 
> That's a feature, no?
> 
> "Be liberal in what you accept, conservative in what you send."

I'm not sure the principle applies in this case, as this is an invalid
argument. This is the kind of thing that could give a hard time to clients,
like using a new argument on an old command and wonder why it doesn't work.

Libvirt did something like this in the past when we weren't doing the check,
they were passing an additional key for some command and expecting it would
have the desired functionality.

> >> +
> >> +    switch (cmd->type) {
> >> +    case QCT_NORMAL:
> >> +        cmd->fn(args,&ret, errp);
> >> +        if (!error_is_set(errp)&&  ret == NULL) {
> >> +            ret = QOBJECT(qdict_new());
> >> +        }
> >> +        break;
> >> +    }
> >> +
> >> +    QDECREF(args);
> >> +
> >> +out:
> >> +
> >> +    return ret;
> >> +}
> >> +
> >> +QObject *qmp_dispatch(QObject *request)
> >> +{
> >> +    Error *err = NULL;
> >> +    QObject *ret;
> >> +    QDict *rsp;
> >> +
> >> +    ret = qmp_dispatch_err(request,&err);
> >> +
> >> +    rsp = qdict_new();
> >> +    if (err) {
> >> +        qdict_put_obj(rsp, "error", error_get_qobject(err));
> >> +        error_free(err);
> >> +    } else if (ret) {
> >> +        qdict_put_obj(rsp, "return", ret);
> >> +    } else {
> >> +        QDECREF(rsp);
> >> +        return NULL;
> >
> > When does the 'else' condition happens?
> 
> Signals which aren't in this patch series.

It can be dropped then.

> 
> Regards,
> 
> Anthony Liguori
> 
> >
> >> +    }
> >> +
> >> +    return QOBJECT(rsp);
> >> +}
> >
>