Re: [Qemu-devel] [PATCH 1/3] pvpanic: use FWCfgState explicitly

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, May 30, 2013 at 05:05:51PM +0200, Laszlo Ersek wrote:
> On 05/30/13 15:27, Michael S. Tsirkin wrote:
> > Use the type-safe FWCfgState structure instead
> > of the unsafe void *.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >  hw/misc/pvpanic.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/hw/misc/pvpanic.c b/hw/misc/pvpanic.c
> > index 31e1b1d..1483f27 100644
> > --- a/hw/misc/pvpanic.c
> > +++ b/hw/misc/pvpanic.c
> > @@ -90,7 +90,7 @@ static int pvpanic_isa_initfn(ISADevice *dev)
> >  {
> >      PVPanicState *s = ISA_PVPANIC_DEVICE(dev);
> >      static bool port_configured;
> > -    void *fw_cfg;
> > +    FWCfgState *fw_cfg;
> >  
> >      memory_region_init_io(&s->io, &pvpanic_ops, s, "pvpanic", 1);
> >      isa_register_ioport(dev, &s->io, s->ioport);
> > 
> 
> Doesn't this break your build? Lower down in the function there's
> 
>         fw_cfg = object_resolve_path("/machine/fw_cfg", NULL);
> 
> and object_resolve_path() returns a pointer-to-Object, not
> pointer-to-FWCfgState.

I see, I think I should reorder the patches.

> But for starters I'm quite confused about how the unpatched function
> works. What it does amounts to:
> 
>   fw_cfg_add_file(object_resolve_path(...), ...);
> 
> But, again object_resolve_path() returns pointer-to-Object. I'm checking
> "struct Object" in "include/qom/object.h", and it suggests that derived
> structs should embed Object as first member. However FWCfgState is *not*
> such a derived member. What's going on here?
> 
> http://thread.gmane.org/gmane.comp.emulators.qemu/201544/focus=201564
> http://thread.gmane.org/gmane.comp.emulators.qemu/204452/focus=204450
> 
> Laszlo