Re: [Xen-devel] [RFC PATCH 5/5] ioreq-server: bring the PCI hotplug controller implementation into Xen

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.01.14 at 17:06, Paul Durrant <Paul.Durrant@xxxxxxxxxx> wrote:
>> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
>> > +struct xen_hvm_pci_hotplug {
>> > +    domid_t domid;          /* IN - domain to be serviced */
>> > +    uint8_t enable;         /* IN - enable or disable? */
>> > +    uint32_t slot;          /* IN - slot to enable/disable */
>> 
>> Reordering these two will make the structure smaller.
>> 
> 
> It will indeed.

Now I'm confused: domid_t being 16 bits, afaict re-ordering would
make it larger (from 8 to 12 bytes) rather than smaller.

What I'd certainly recommend is filling the 1 byte that's currently
unused (either by widening "enabled" or with a padding field) such
that eventual future extensions (flags?) could be added (i.e. the
field would need to be checked to be zero).

Jan


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