Re: [Qemu-devel] [PATCH 2/2] target-i386: make cpu_x86_create() get Error argument

[Eduardo Habkost]

On Fri, Dec 14, 2012 at 11:18:18AM +0100, Igor Mammedov wrote:
> On Wed, 12 Dec 2012 16:16:23 -0200
> Eduardo Habkost <address@hidden> wrote:
> 
> > Instead of forcing the caller to guess what went wrong while creating
> > the CPU object, return error information in a Error argument.
> > 
> > Also, as cpu_x86_create() won't print error messages itself anymore,
> > change cpu_x86_init() to print any error returned by cpu_x86_create()
> > or cpu_x86_realize().
> > 
> > Signed-off-by: Eduardo Habkost <address@hidden>
> > ---
> >  target-i386/cpu.c    |  8 ++++++--
> >  target-i386/cpu.h    |  2 +-
> >  target-i386/helper.c | 21 ++++++++++++++-------
> >  3 files changed, 21 insertions(+), 10 deletions(-)
> > 
> > diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> > index b242bf1..fba872d 100644
> > --- a/target-i386/cpu.c
> > +++ b/target-i386/cpu.c
> > @@ -1542,7 +1542,7 @@ static void filter_features_for_kvm(X86CPU *cpu)
> >  /* Create and initialize a X86CPU object, based on the full CPU model 
> > string
> >   * (that may include "+feature,-feature,feature=xxx" feature strings)
> >   */
> > -X86CPU *cpu_x86_create(const char *cpu_model)
> > +X86CPU *cpu_x86_create(const char *cpu_model, Error **errp)
> >  {
> >      X86CPU *cpu;
> >      CPUX86State *env;
> > @@ -1559,12 +1559,14 @@ X86CPU *cpu_x86_create(const char *cpu_model)
> >  
> >      model_pieces = g_strsplit(cpu_model, ",", 2);
> >      if (!model_pieces[0]) {
> > +        error_setg(errp, "invalid CPU model string: %s", cpu_model);
> >          goto error;
> >      }
> >      name = model_pieces[0];
> >      features = model_pieces[1];
> >  
> >      if (cpu_x86_find_by_name(def, name) < 0) {
> > +        error_setg(errp, "CPU model not found: %s", name);
> >          goto error;
> >      }
> >  
> > @@ -1575,13 +1577,15 @@ X86CPU *cpu_x86_create(const char *cpu_model)
> >                              &def->svm_features, 
> > &def->cpuid_7_0_ebx_features);
> >  
> >      if (cpu_x86_parse_featurestr(def, features) < 0) {
> > +        error_setg(errp, "Error parsing feature string: %s",
> > +                   features ? features : "(none)");
> It could be simplified, it shouldn't get here if features == NULL

It could be something like:

  if (features && cpu_x86_parse_featurestr(def, features) < 0) {
      ...
  }

Both options are reasonable to me.


> 
> >          goto error;
> >      }
> >  
> >      cpudef_2_x86_cpu(cpu, def, &error);
> >  
> >      if (error) {
> > -        fprintf(stderr, "%s\n", error_get_pretty(error));
> > +        error_propagate(errp, error);
> Why do it here but not above?

Because the other functions called above don't get an Error object
(yet).  :-)

> 
> >          error_free(error);
> >          goto error;
> >      }
> > diff --git a/target-i386/cpu.h b/target-i386/cpu.h
> [...]
> >  
> >  X86CPU *cpu_x86_init(const char *cpu_model)
> >  {
> > -    X86CPU *cpu;
> > +    X86CPU *cpu = NULL;
> >      Error *error = NULL;
> >  
> > -    cpu = cpu_x86_create(cpu_model);
> > -    if (!cpu) {
> > -        return NULL;
> > +    cpu = cpu_x86_create(cpu_model, &error);
> > +    if (error) {
> > +        goto error;
> >      }
> >  
> >      x86_cpu_realize(OBJECT(cpu), &error);
> if x86_cpu_realize() behave as visit* functions, i.e. return early if
> error has been already set, error check & goto could be removed here
> and above and consolidated at function exit.

I'm not sure I want to use that coding style. Expecting every function
to abort in the beginning if Error is set sounds fragile, to me. I would
even expect the maintainers to complain if I wrote the code that way (as
I never saw that style being used in any code except the visitors).

The visitors seem to be different because they are called from
automatically-generated QAPI code, that can't know if errors in a give
"visit" should abort the rest of the process, or not.


> 
> >      if (error) {
> > -        error_free(error);
> > -        object_delete(OBJECT(cpu));
> > -        return NULL;
> > +        goto error;
> >      }
> >      return cpu;
> > +
> > +error:
> > +    if (cpu) {
> > +        object_delete(OBJECT(cpu));
> > +    }
> > +    error_report("%s", error_get_pretty(error));
> > +    error_free(error);
> > +    return NULL;
> >  }
> >  
> >  #if !defined(CONFIG_USER_ONLY)
> > -- 
> > 1.7.11.7
> > 
> 
> 
> -- 
> Regards,
>   Igor

-- 
Eduardo