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

[Laszlo Ersek <lersek@redhat.com>]

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.

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