Re: [Qemu-devel] [PATCH v2 2/4] spapr: fix error reporting in xics_system_init()

[Greg Kurz <groug@kaod.org>]

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On Sat, 20 May 2017 16:45:09 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Fri, May 19, 2017 at 12:32:12PM +0200, Greg Kurz wrote:
> > If the user explicitely asked for kernel-irqchip support and "xics-kvm"
> > initialization fails, we shouldn't fallback to emulated "xics" as we
> > do now. It is also awkward to print an error message when we have an
> > errp pointer argument.
> > 
> > Let's use the errp argument to report the error and let the caller decide.
> > This simplifies the code as we don't need a local Error * here.
> > 
> > Signed-off-by: Greg Kurz <groug@kaod.org>  
> 
> Concept looks good, but..
> 
> > ---
> > v2: - total rewrite
> > ---
> >  hw/ppc/spapr.c |   13 ++++++-------
> >  1 file changed, 6 insertions(+), 7 deletions(-)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index 91f7434861a8..75e298b4c6be 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -128,18 +128,14 @@ static void xics_system_init(MachineState *machine, int nr_irqs, Error **errp)
> >      sPAPRMachineState *spapr = SPAPR_MACHINE(machine);
> >  
> >      if (kvm_enabled()) {
> > -        Error *err = NULL;
> > -
> >          if (machine_kernel_irqchip_allowed(machine) &&
> >              !xics_kvm_init(spapr, errp)) {
> >              spapr->icp_type = TYPE_KVM_ICP;
> > -            spapr->ics = spapr_ics_create(spapr, TYPE_ICS_KVM, nr_irqs, &err);
> > +            spapr->ics = spapr_ics_create(spapr, TYPE_ICS_KVM, nr_irqs, errp);  
> 
> I believe there are reasons you're not supposed to just pass an errp
> through to a subordinate function.  Instead you're supposed to have a
> local Error * and use error_propagate().
> 

You only need to have a local Error * if it is used to check the return status
of the function (ie, you cannot check *errp because errp could be NULL) as
described in error.h. This isn't the case here but...

> >          }
> >          if (machine_kernel_irqchip_required(machine) && !spapr->ics) {
> > -            error_reportf_err(err,
> > -                              "kernel_irqchip requested but unavailable: ");
> > -        } else {
> > -            error_free(err);
> > +            error_prepend(errp, "kernel_irqchip requested but unavailable: ");
> > +            return;
> >          }
> >      }
> >  
> > @@ -147,6 +143,9 @@ static void xics_system_init(MachineState *machine, int nr_irqs, Error **errp)
> >          xics_spapr_init(spapr);
> >          spapr->icp_type = TYPE_ICP;
> >          spapr->ics = spapr_ics_create(spapr, TYPE_ICS_SIMPLE, nr_irqs, errp);
> > +        if (!spapr->ics) {  
> 
> It would also be more standard to check the returned error, rather
> than the other result.
> 

... if you prefer to use a local Error *, I'll gladly do that. :)

> > +            return;
> > +        }
> >      }
> >  }
> >  
> >   
> 


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