[Libguestfs] [PATCH] Non-working support for GObject Introspection.

[Daniel P. Berrange]

On Tue, Mar 16, 2010 at 03:49:21PM +0000, Daniel P. Berrange wrote:
> On Tue, Mar 16, 2010 at 03:45:17PM +0000, Richard W.M. Jones wrote:
> > On Tue, Mar 16, 2010 at 02:53:29PM +0000, Daniel P. Berrange wrote:
> > > GObject is the primary root object, but things don't neccessarily need
> > > to inherit from GObject. Since you're trying to directly expose libguestfs'
> > > own object(s) you'll probably need to register them as base types  using
> > > the GType APIs. This section of the API docs gives a semi-useful intro to
> > > GTypes
> > > 
> > >   http://library.gnome.org/devel/gobject/stable/chapter-gtype.html
> > > 
> > > Ultimately this comes down to a call to g_type_register_static()
> > > 
> > >   http://library.gnome.org/devel/gobject/stable/gobject-Type-Information.html#g-type-register-static
> > > 
> > > but it is not very well documented because 99% of apps just inherit
> > > from GObject instead of introducing new base types like libguestfs
> > > would need todo.
> > 
> > Unfortunately this doesn't work.  The handle (guestfs_h *) is wrapped
> > inside a GType:
> > 
> > typedef struct _GuestfsH {
> >   GObject parent;
> >   guestfs_h *h;
> > } GuestfsH;
> > 
> > I can now register this easily enough, but GObject won't automatically
> > unpack that handle when it passes it to the other functions.  ie.  The
> > other functions would receive a GuestfsH, instead of a guestfs_h *,
> > and they won't know what to do with the former.
> 
> Oh I see - this struct is actually attempting to create a GObject subclass
> containing a guestfs_h *. This definitely don't work, because of the 
> mis-matched ptrs you mention. I thought you were registering 'guestfs_h *'
> itself as the type without the 'struct _GuestfsH' wrapper. This avoids
> GObject entirely introducing a new base type.  

Actually this won't work either because of this 2nd requirement from GType

 1. All class structures must contain as first member a GTypeClass structure. 
 2. All instance structures must contain as first member a GTypeInstance structure.


So AFAICT, the only option would be to generate a guestfs-glib library which
had a full set of wrappers around every C API, that accept 'struct _GuestfsH' 
instead of 'guestfs_h' and de-refernce the ->h field before calling the real
libguestfs APIs.

Daniel
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