Re: [Qemu-devel] [PATCH v2 10/15] qapi: Clean up fragile use of error_is_set()

[Michael Roth]

Quoting Markus Armbruster (2014-04-28 15:27:49)
> Using error_is_set(ERRP) to find out whether a function failed is
> either wrong, fragile, or unnecessarily opaque.  It's wrong when ERRP
> may be null, because errors go undetected when it is.  It's fragile
> when proving ERRP non-null involves a non-local argument.  Else, it's
> unnecessarily opaque (see commit 84d18f0).
> 
> The error_is_set(errp) in do_qmp_dispatch() is merely fragile, because
> the caller never passes a null errp argument.
> 
> Make the code more robust and more obviously correct: receive the
> error in a local variable, then propagate it through the parameter.
> 
> Signed-off-by: Markus Armbruster <address@hidden>
> Reviewed-by: Eric Blake <address@hidden>

Reviewed-by: Michael Roth <address@hidden>

> ---
>  qapi/qmp-dispatch.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/qapi/qmp-dispatch.c b/qapi/qmp-dispatch.c
> index 187af56..168b083 100644
> --- a/qapi/qmp-dispatch.c
> +++ b/qapi/qmp-dispatch.c
> @@ -62,6 +62,7 @@ static QDict *qmp_dispatch_check_obj(const QObject 
> *request, Error **errp)
> 
>  static QObject *do_qmp_dispatch(QObject *request, Error **errp)
>  {
> +    Error *local_err = NULL;
>      const char *command;
>      QDict *args, *dict;
>      QmpCommand *cmd;
> @@ -93,13 +94,13 @@ static QObject *do_qmp_dispatch(QObject *request, Error 
> **errp)
> 
>      switch (cmd->type) {
>      case QCT_NORMAL:
> -        cmd->fn(args, &ret, errp);
> -        if (!error_is_set(errp)) {
> -            if (cmd->options & QCO_NO_SUCCESS_RESP) {
> -                g_assert(!ret);
> -            } else if (!ret) {
> -                ret = QOBJECT(qdict_new());
> -            }
> +        cmd->fn(args, &ret, &local_err);
> +        if (local_err) {
> +            error_propagate(errp, local_err);
> +        } else if (cmd->options & QCO_NO_SUCCESS_RESP) {
> +            g_assert(!ret);
> +        } else if (!ret) {
> +            ret = QOBJECT(qdict_new());
>          }
>          break;
>      }
> -- 
> 1.8.1.4