Re: [Xen-devel] [PATCH 2/5] x86/vioapic: allow the vIO APIC to have a variable number of pins

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.02.17 at 12:52, <roger.pau@xxxxxxxxxx> wrote:
> @@ -424,40 +424,141 @@ void vioapic_update_EOI(struct domain *d, u8 vector)
>      spin_unlock(&d->arch.hvm_domain.irq_lock);
>  }
>  
> -static int ioapic_save(struct domain *d, hvm_domain_context_t *h)
> +#define VIOAPIC_SAVE_CONST offsetof(struct hvm_hw_vioapic, redirtbl)

What is this redirtbl field, which oddly enough is a pointer (not allowed
in the public interface) good for? I can't seem to find any use of it
other than as marker (for use with offsetof()). With all the
complications here and below plus the fixed number of entries
remaining to be fixed for actual migration purposes I wonder if you
wouldn't be better off by keeping the structure mostly as is, simply
converting the redirtbl[] field to a union (guarded by a __XEN__
conditional) containing both a fixed size array and a variable size
one (or to be precise, a zero size one, as a variable size one is not
allowed there).

Another alternative would be to introduce a Xen internal sibling
struct with a variable size array, and with all fields properly build-
time-asserted to be identical between both.

I'll skip the rest of the patch assuming much of it could be dropped
this way.

Jan


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