* Markus Armbruster (arm...@redhat.com) wrote:
> "Dr. David Alan Gilbert" <dgilb...@redhat.com> writes:
>
> > * Markus Armbruster (arm...@redhat.com) wrote:
> >> "Dr. David Alan Gilbert (git)" <dgilb...@redhat.com> writes:
> >>
> >> > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
> >> >
> >> > Avoid a segfault when visiting, e.g., the QOM rtc-time property,
> >> > by implementing the struct callbacks and raising an Error.
> >> >
> >> > Signed-off-by: Andreas Färber <afaer...@suse.de>
> >> >
> >> > Updated for changed interface:
> >> > Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> >> > ---
> >> > qapi/string-output-visitor.c | 13 +++++++++++++
> >> > 1 file changed, 13 insertions(+)
> >> >
> >> > diff --git a/qapi/string-output-visitor.c b/qapi/string-output-visitor.c
> >> > index 94ac821..4e7e97f 100644
> >> > --- a/qapi/string-output-visitor.c
> >> > +++ b/qapi/string-output-visitor.c
> >> > @@ -12,6 +12,7 @@
> >> >
> >> > #include "qemu/osdep.h"
> >> > #include "qemu-common.h"
> >> > +#include "qapi/error.h"
> >> > #include "qapi/string-output-visitor.h"
> >> > #include "qapi/visitor-impl.h"
> >> > #include "qemu/host-utils.h"
> >> > @@ -266,6 +267,16 @@ static void print_type_number(Visitor *v, const
> >> > char *name, double *obj,
> >> > string_output_set(sov, g_strdup_printf("%f", *obj));
> >> > }
> >> >
> >> > +static void start_struct(Visitor *v, const char *name, void **obj,
> >> > size_t size,
> >> > + Error **errp)
> >> > +{
> >> > + error_setg(errp, "struct type not implemented");
> >> > +}
> >> > +
> >> > +static void end_struct(Visitor *v, void **obj)
> >> > +{
> >> > +}
> >> > +
> >>
> >> This is just one of the several things this visitor doesn't implement.
> >> See the comment in string-output-visitor.h.
> >>
> >> String input visitor and options visitor have similar holes; see the
> >> comments in string-input-visitor.h and opts-visitor.h.
> >>
> >> Should we change all of them together to report errors instead of crash?
> >> With common "error out because this isn't implemented" methods?
> >
> > In that case wouldn't it be best to change
> > visit_start_struct/visit_end_struct
> > to do the check (Like visit_check_struct does).
>
> In my opinion.
>
> if (v->foo) {
> v->foo(...);
> } else {
> ... default action ...
> }
>
> is an anti-pattern. Wrap the default action in a default method, and
> put that in the function pointer.
I've got some sympathy to that, but with the way our visitors are
built that's a pain.
Lets say you add a new eat_struct method, and a eat_struct_default
implementation,
now you have to go around and fix all the visitor implementations to initialise
their eat_struct member to eat_struct_default. Of course you'll forget some
and then we'll end up segging when you fall down the NULL pointer.
Now, if our visitors had nice shared constructor functions that wouldn't
be a problem, and you wouldn't need most of the visit_ wrapper functions;
but they don't, so the if (v->foo) { ... } else { error; } is the
current cleanest we can do.
Dave
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
