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

[Stefan Hajnoczi]

On Fri, Dec 15, 2017 at 03:55:06PM +0800, Peter Xu wrote:
> 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.

I prefer dropping it.  Smaller patch series get reviewed quicker, cause
fewer merge conflicts, are lower risk, etc.

Stefan

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