Re: [PATCH v5] xen: introduce CONFIG_HAS_SHARED_INFO for archs without a shared page

[Jan Beulich <jbeulich@xxxxxxxx>]

On 10.07.2026 15:31, Oleksii Kurochko wrote:
> On 7/8/26 12:52 PM, Jan Beulich wrote:
>>> +#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 */
>> ... we wondering whether any of this is needed when FIFO is available. In
>> v4 all that was noticed was that SHARED_INFO=n together with EVTCHN_FIFO=n
>> is a problem. And having fewer cf_check functions in the build is always a
>> win (I think).
> 
> I thought an opposite that it is good to have cf_check when pointer to 
> function is used. So why we have to make an exception in this case?

I didn't ask to drop the cf_check (and you can't really as long as these
functions may be used by x86). I asked to limit the number of them we have
(in a particular configuration) as much as possible. I.e. I was merely
trying to explain why it is relevant to have the #if around this as tight
as possible.

Jan