Re: [Qemu-devel] [PATCH] QJSON: Use OBJECT_CHECK

[Michael Roth <mdroth@linux.vnet.ibm.com>]

Quoting Michael Roth (2015-05-01 11:19:05)
> Quoting Eduardo Habkost (2015-04-29 07:55:48)
> > On Wed, Apr 29, 2015 at 08:38:02AM -0400, Luiz Capitulino wrote:
> > > On Mon, 27 Apr 2015 14:23:20 -0300
> > > Eduardo Habkost <ehabkost@redhat.com> wrote:
> > > 
> > > > On Sat, Apr 25, 2015 at 07:05:55PM +0200, Andreas Färber wrote:
> > > > > Am 25.04.2015 um 17:28 schrieb Eduardo Habkost:
> > > > > > The QJSON code used casts to (QJSON*) directly, instead of OBJECT_CHECK.
> > > > > > There were even some functions using object_dynamic_cast() calls
> > > > > > followed by assert(), which is exactly what OBJECT_CHECK does (by
> > > > > > calling object_dynamic_cast_assert()).
> > > > > 
> > > > > Suggest s/OBJECT_CHECK/OBJECT_CHECK()/g everywhere for clarity.
> > > 
> > > Everywhere? You mean, in other places? In this case someone has to
> > > post a different patch.
> > 
> > Just in the commit message.
> > 
> > > 
> > > > I assume it can be fixed during commit by whoever is going to queue it.
> > > > 
> > > > > 
> > > > > > 
> > > > > > Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> > > > > > ---
> > > > > >  qjson.c | 10 +++++-----
> > > > > >  1 file changed, 5 insertions(+), 5 deletions(-)
> > > > > 
> > > > > Reviewed-by: Andreas Färber <afaerber@suse.de>
> > > > > 
> > > > > Wasn't aware QJSON is using QOM - assuming this will go through some
> > > > > QAPI/QMP tree.
> > > > 
> > > > The only user of qjson.c right now is migration code. Should it go through
> > > > the migration tree?
> > > 
> > > It could be, but I can take it if nobody does.
> > 
> > Thanks!
> > 
> > > 
> > > > Also, why do we have two JSON writers in QEMU? And why do they have
> > > > exactly the same name?
> > > 
> > > Not sure I got it, which writers?
> > 
> > qjson.c and qobject/qjson.c:to_json().
> 
> I'm guessing it's to avoid the need to build up a QObject throughout
> the migration code, as opposed to just serializing metadata/vmstate
> fields directly to string.
> 
> Does make me wonder though why we don't just use visit_type_{int,etc}()
> interfaces to build up the QObject through a QMPOutputVisitor, then feed
> the resulting QObject through the existing qobject/qjson.c code.

I guess that would affect downtime. Don't imagine it would by much
though. A JSONOutputVisitor that simply wraps JSONMessageParser
and avoids the QObject intermediate might be another option.

> 
> > 
> > -- 
> > Eduardo
> >