Re: [PATCH v8 1/9] machine: Use error handling when CPU type is checked

[Gavin Shan]

Hi Markus,

On 11/29/23 19:20, Markus Armbruster wrote:
> Gavin Shan <gshan@redhat.com> writes:
>
> > QEMU will be terminated if the specified CPU type isn't supported
> > in machine_run_board_init(). The list of supported CPU type names
> > is tracked by mc->valid_cpu_types.
>
> Suggest to drop the second sentence.

Indeed, it's not so helpful.

> > The error handling can be used to propagate error messages, to be
> > consistent how the errors are handled for other situations in the
> > same function.
> >
> > No functional change intended.
> >
> > Suggested-by: Igor Mammedov <imammedo@redhat.com>
> > Signed-off-by: Gavin Shan <gshan@redhat.com>
> > ---
> > v8: Drop @local_err and use @errp to be compatible with
> >      ERRP_GUARD()                                          (Phil)
> > ---
> >   hw/core/machine.c | 13 +++++++------
> >   1 file changed, 7 insertions(+), 6 deletions(-)
> >
> > diff --git a/hw/core/machine.c b/hw/core/machine.c
> > index 0c17398141..bde7f4af6d 100644
> > --- a/hw/core/machine.c
> > +++ b/hw/core/machine.c
> > @@ -1466,15 +1466,16 @@ void machine_run_board_init(MachineState *machine, 
> > const char *mem_path, Error *
> >   
> >           if (!machine_class->valid_cpu_types[i]) {
> >               /* The user specified CPU is not valid */
> > -            error_report("Invalid CPU type: %s", machine->cpu_type);
> > -            error_printf("The valid types are: %s",
> > -                         machine_class->valid_cpu_types[0]);
> > +            error_setg(errp, "Invalid CPU type: %s", machine->cpu_type);
> > +            error_append_hint(errp, "The valid types are: %s",
> > +                              machine_class->valid_cpu_types[0]);
> >               for (i = 1; machine_class->valid_cpu_types[i]; i++) {
> > -                error_printf(", %s", machine_class->valid_cpu_types[i]);
> > +                error_append_hint(errp, ", %s",
> > +                                  machine_class->valid_cpu_types[i]);
> >               }
> > -            error_printf("\n");
> >   
> > -            exit(1);
> > +            error_append_hint(&errp, "\n");
> > +            return;
> >           }
> >       }
>
> This cleans up an anti-pattern: use of error_report() within a function that
> returns errors through an Error **errp parameter.
>
> Cleanup, not bug fix, because the only caller passes &error_abort.
>
> Suggest to start the commit message with a mention of the anti-pattern.
> Here's how I'd write it:
>
>      Functions that use an Error **errp parameter to return errors should
>      not also report them to the user, because reporting is the caller's
>      job.
>
>      machine_run_board_init() violates this principle: it calls
>      error_report(), error_printf(), and exit(1) when the machine doesn't
>      support the requested CPU type.
>
>      Clean this up by using error_setg() and error_append_hint() instead.
>      No functional change, as the only caller passes &error_fatal.

Thanks for the nice write-up. I will take it if v9 is needed to address
comments from other people.

> Whether you use my suggestion or not:
> Reviewed-by: Markus Armbruster <armbru@redhat.com>

Thanks for your review.

Thanks,
Gavin