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Re: [Qemu-ppc] [Qemu-devel] [PATCH v2 1/2] spapr: introduce SPAPR_MACHIN
From: |
David Gibson |
Subject: |
Re: [Qemu-ppc] [Qemu-devel] [PATCH v2 1/2] spapr: introduce SPAPR_MACHINE_NOASSERT() |
Date: |
Mon, 9 Oct 2017 10:26:38 +1100 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
On Sun, Oct 08, 2017 at 09:05:37PM +0100, Peter Maydell wrote:
> On 8 October 2017 at 18:17, Greg Kurz <address@hidden> wrote:
> > A spapr-cpu-core device can only be plugged into a pseries machine. This
> > is checked in spapr_cpu_core_realize() with object_dynamic_cast() instead
> > of the usual SPAPR_MACHINE() macro because we don't want QEMU to abort.
> >
> > This patch moves the gory details to a SPAPR_MACHINE_NOASSERT() macro
> > that acts like the SPAPR_MACHINE() one, except it returns NULL instead
> > of aborting if its argument doesn't point to a pseries machine type.
> >
> > This is done for two reasons:
> > - it makes the code nicer
> > - it may be used by other pseries-specific devices like PHBs for example
> >
> > Signed-off-by: Greg Kurz <address@hidden>
> > ---
> > hw/ppc/spapr_cpu_core.c | 7 +++----
> > include/hw/ppc/spapr.h | 3 +++
> > 2 files changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> > index 37beb56e8b18..5fde07614218 100644
> > --- a/hw/ppc/spapr_cpu_core.c
> > +++ b/hw/ppc/spapr_cpu_core.c
> > @@ -199,7 +199,7 @@ error:
> >
> > static void spapr_cpu_core_realize(DeviceState *dev, Error **errp)
> > {
> > - sPAPRMachineState *spapr;
> > + sPAPRMachineState *spapr = SPAPR_MACHINE_NOASSERT(qdev_get_machine());
> > sPAPRCPUCore *sc = SPAPR_CPU_CORE(OBJECT(dev));
> > sPAPRCPUCoreClass *scc = SPAPR_CPU_CORE_GET_CLASS(OBJECT(dev));
> > CPUCore *cc = CPU_CORE(OBJECT(dev));
> > @@ -209,9 +209,8 @@ static void spapr_cpu_core_realize(DeviceState *dev,
> > Error **errp)
> > void *obj;
> > int i, j;
> >
> > - spapr = (sPAPRMachineState *) qdev_get_machine();
> > - if (!object_dynamic_cast((Object *) spapr, TYPE_SPAPR_MACHINE)) {
> > - error_setg(errp, "spapr-cpu-core needs a pseries machine");
> > + if (!spapr) {
> > + error_setg(errp, TYPE_SPAPR_CPU_CORE " needs a pseries machine");
> > return;
> > }
> >
> > diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> > index c1b365f56431..4933da8083df 100644
> > --- a/include/hw/ppc/spapr.h
> > +++ b/include/hw/ppc/spapr.h
> > @@ -43,6 +43,9 @@ typedef struct sPAPRMachineClass sPAPRMachineClass;
> > #define SPAPR_MACHINE_CLASS(klass) \
> > OBJECT_CLASS_CHECK(sPAPRMachineClass, klass, TYPE_SPAPR_MACHINE)
> >
> > +#define SPAPR_MACHINE_NOASSERT(obj) \
> > + ((sPAPRMachineState *) object_dynamic_cast(obj, TYPE_SPAPR_MACHINE))
> > +
>
> I don't think this is a great idea. Doing things with pointers
> that might not be of the right type should be obvious, not hidden
> under macros. An opencoded call to object_dynamic_cast is how the
> rest of the codebase does this; it's a bit of a weird way
> to write "isinstance()" but there you go. If we want to
> improve the way we write this sort of thing we should do
> so as a general improvement to the QOM APIs and conventions,
> not just a single thing in SPAPR code.
Yeah, I tend to agree. Sorry, the original advice I gave on not using
object_dynamic_cast() directly was bogus - I didn't think it through
clearly.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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