Re: [Qemu-devel] [RFC v5 05/26] qjson: add "opaque" field to JSONMessageParser

[Peter Xu]

On Wed, Dec 13, 2017 at 03:37:02PM +0000, Stefan Hajnoczi wrote:
> On Tue, Dec 05, 2017 at 01:51:39PM +0800, Peter Xu wrote:
> > diff --git a/qga/main.c b/qga/main.c
> > index 62a62755bd..3b5ebbc1ee 100644
> > --- a/qga/main.c
> > +++ b/qga/main.c
> > @@ -593,7 +593,8 @@ static void process_command(GAState *s, QDict *req)
> >  }
> >  
> >  /* handle requests/control events coming in over the channel */
> > -static void process_event(JSONMessageParser *parser, GQueue *tokens)
> > +static void process_event(JSONMessageParser *parser, GQueue *tokens,
> > +                          void *opaque)
> >  {
> >      GAState *s = container_of(parser, GAState, parser);
> >      QDict *qdict;
> > @@ -1320,7 +1321,7 @@ static int run_agent(GAState *s, GAConfig *config, 
> > int socket_activation)
> >      s->command_state = ga_command_state_new();
> >      ga_command_state_init(s, s->command_state);
> >      ga_command_state_init_all(s->command_state);
> > -    json_message_parser_init(&s->parser, process_event);
> > +    json_message_parser_init(&s->parser, process_event, NULL);
> 
> This patch leaves the code with 2 ways of getting at state from the
> parser pointer:
> 1. Use container_of() like existing users.
> 2. Use the new (unused) opaque argument.
> 
> Given that #1 exists, is this patch really necessary?

I didn't really notice that.  Thanks for pointing out.

However even if so I would still prefer the opaque way to do it if
asked.  Existing #1 of course works but IMHO is less flexible and has
dependency between structure layouts.

How about I append another patch to convert existing users (or, I can
post as separate patches after this series)?  It's not really a lot,
and the conversion would be obvious:

*** qga/main.c:
run_agent[1324]                json_message_parser_init(&s->parser, 
process_event, NULL);
*** qobject/qjson.c:
qobject_from_jsonv[45]         json_message_parser_init(&state.parser, 
parse_json, NULL);
*** tests/libqtest.c:
qmp_fd_receive[438]            json_message_parser_init(&qmp.parser, 
qmp_response, NULL);

Though, if you still insist, I can drop it too.

> 
> Please explain in the commit description, don't make me look ahead in
> the patch series.

I will add some comments if this patch is still alive in next
version.  Thanks,

-- 
Peter Xu