Re: [PATCH v2 6/9] qapi: Generalize command policy checking

[Eric Blake]

On Thu, Oct 28, 2021 at 12:25:17PM +0200, Markus Armbruster wrote:
> The code to check command policy can see special feature flag
> 'deprecated' as command flag QCO_DEPRECATED.  I want to make feature
> flag 'unstable' visible there as well, so I can add policy for it.
> 
> To let me make it visible, add member @special_features (a bitset of
> QapiSpecialFeature) to QmpCommand, and adjust the generator to pass it
> through qmp_register_command().  Then replace "QCO_DEPRECATED in
> @flags" by QAPI_DEPRECATED in @special_features", and drop
> QCO_DEPRECATED.
> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> Acked-by: John Snow <jsnow@redhat.com>
> ---

> +++ b/qapi/qmp-dispatch.c
> @@ -176,7 +176,7 @@ QDict *qmp_dispatch(const QmpCommandList *cmds, QObject 
> *request,
>                    "The command %s has not been found", command);
>          goto out;
>      }
> -    if (cmd->options & QCO_DEPRECATED) {
> +    if (cmd->special_features & 1u << QAPI_DEPRECATED) {

I admit having to check the C operator precedence table when reading
this (<< is higher than &); if writing it myself, I would probably
have used explicit () to avoid reviewer confusion, but what you have
is correct.  (After grepping for ' & 1.*<<' and ' & (1.*<<', it looks
like authors using explicit precedence happens more often, but that
there are other instances in the code base relying on implicit
precedence.)

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org