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

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 30 January 2014 16:39
> To: Andrew Cooper; Paul Durrant
> Cc: xen-devel@xxxxxxxxxxxxx
> Subject: Re: [Xen-devel] [RFC PATCH 5/5] ioreq-server: bring the PCI hotplug
> controller implementation into Xen
> 
> >>> 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.
> 

Sorry, I had it in my head that domids were 32-bits. You are correct... which 
is probably why I used that ordering in the first place ;-)

  Paul

> 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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