Re: [PATCH v4] xen: introduce CONFIG_HAS_SHARED_INFO for archs without a shared page

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 6/30/26 5:02 PM, Oleksii Kurochko wrote:
> > > @@ -55,6 +59,7 @@ struct evtchn_expand_array;
> > >   int evtchn_fifo_init_control(struct evtchn_init_control 
> > > *init_control);
> > >   int evtchn_fifo_expand_array(const struct evtchn_expand_array 
> > > *expand_array);
> > >   void evtchn_fifo_destroy(struct domain *d);
> > > +void evtchn_fifo_init_ops(struct domain *d);
> > >   #else
> > >   static inline int evtchn_fifo_init_control(struct 
> > > evtchn_init_control *init_control)
> > >   {
> > > @@ -68,6 +73,7 @@ static inline void evtchn_fifo_destroy(struct 
> > > domain *d)
> > >   {
> > >       return;
> > >   }
> > > +static inline void evtchn_fifo_init_ops(struct domain *d) {}
> > >   #endif /* CONFIG_EVTCHN_FIFO */
> > Unlike these two. Which raise a different question though: What will 
> > be the
> > behavior when EVTCHN_FIFO=n and HAS_SHARED_INFO=n? Taking
> > evtchn_alloc_unbound() as example, afaict evtchn_port_init() will stumble
> > over a NULL pointer. Looks like for that (and only that) case we still 
> > need
> > your earlier dummy fallback.
> I will introduce dummy fallback (I will shrunk some stubs in final 
> version):
> +#ifndef CONFIG_HAS_SHARED_INFO
> +static void cf_check evtchn_none_set_pending(
> +    struct vcpu *v, struct evtchn *evtchn) {}
> +static void cf_check evtchn_none_clear_pending(
> +    struct domain *d, struct evtchn *evtchn) {}
> +static void cf_check evtchn_none_unmask(
> +    struct domain *d, struct evtchn *evtchn) {}
> +static bool cf_check evtchn_none_is_pending(
> +    const struct domain *d, const struct evtchn *evtchn) { return false; }
> +static bool cf_check evtchn_none_is_masked(
> +    const struct domain *d, const struct evtchn *evtchn) { return true; }
> +static void cf_check evtchn_none_print_state(
> +    struct domain *d, const struct evtchn *evtchn) {}
> +
> +static const struct evtchn_port_ops evtchn_port_ops_none = {
> +    .set_pending   = evtchn_none_set_pending,
> +    .clear_pending = evtchn_none_clear_pending,
> +    .unmask        = evtchn_none_unmask,
> +    .is_pending    = evtchn_none_is_pending,
> +    .is_masked     = evtchn_none_is_masked,
> +    .print_state   = evtchn_none_print_state,
> +};
> +
> +static void evtchn_none_init(struct domain *d)
> +{
> +    d->evtchn_port_ops = &evtchn_port_ops_none;
> +}
> +#endif
I will shrink it to::

#ifndef CONFIG_HAS_SHARED_INFO
/*
 * Placeholder ops for domains with neither a shared_info page nor (yet)
 * a FIFO control block.  None of these are ever reachable in practice;
 * they only exist to keep d->evtchn_port_ops non-NULL.
 */
static void cf_check evtchn_none_set_pending(
    struct vcpu *v, struct evtchn *evtchn) {}

static void cf_check evtchn_none_noop(
    struct domain *d, struct evtchn *evtchn) {}

static bool cf_check evtchn_none_false(
    const struct domain *d, const struct evtchn *evtchn) { return false; }

static void cf_check evtchn_none_print_state(
    struct domain *d, const struct evtchn *evtchn) {}

static const struct evtchn_port_ops evtchn_port_ops_none = {
    .set_pending   = evtchn_none_set_pending,
    .clear_pending = evtchn_none_noop,
    .unmask        = evtchn_none_noop,
    .is_pending    = evtchn_none_false,
    .is_masked     = evtchn_none_false,
    .print_state   = evtchn_none_print_state,
};

void evtchn_none_init(struct domain *d)
{
    d->evtchn_port_ops = &evtchn_port_ops_none;
}
#endif /* CONFIG_HAS_SHARED_INFO */

~ Oleksii