Re: [Xen-devel] [PATCH v6 05/11] x86/hyperv: setup hypercall page

["Durrant, Paul" <pdurrant@xxxxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: 03 February 2020 11:39
> To: Durrant, Paul <pdurrant@xxxxxxxxxxxx>
> Cc: Wei Liu <wl@xxxxxxx>; Xen Development List <xen-
> devel@xxxxxxxxxxxxxxxxxxxx>; Michael Kelley <mikelley@xxxxxxxxxxxxx>; Wei
> Liu <liuwe@xxxxxxxxxxxxx>; Andrew Cooper <andrew.cooper3@xxxxxxxxxx>;
> Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Subject: Re: [PATCH v6 05/11] x86/hyperv: setup hypercall page
> 
> On 03.02.2020 12:37, Durrant, Paul wrote:
> >> -----Original Message-----
> >> From: Jan Beulich <jbeulich@xxxxxxxx>
> >> Sent: 03 February 2020 11:34
> >> To: Durrant, Paul <pdurrant@xxxxxxxxxxxx>
> >> Cc: Wei Liu <wl@xxxxxxx>; Xen Development List <xen-
> >> devel@xxxxxxxxxxxxxxxxxxxx>; Michael Kelley <mikelley@xxxxxxxxxxxxx>;
> Wei
> >> Liu <liuwe@xxxxxxxxxxxxx>; Andrew Cooper <andrew.cooper3@xxxxxxxxxx>;
> >> Roger Pau Monné <roger.pau@xxxxxxxxxx>
> >> Subject: Re: [PATCH v6 05/11] x86/hyperv: setup hypercall page
> >>
> >> On 03.02.2020 12:21, Durrant, Paul wrote:
> >>>> -----Original Message-----
> >>>> From: Jan Beulich <jbeulich@xxxxxxxx>
> >>>> Sent: 03 February 2020 11:06
> >>>> To: Durrant, Paul <pdurrant@xxxxxxxxxxxx>
> >>>> Cc: Wei Liu <wl@xxxxxxx>; Xen Development List <xen-
> >>>> devel@xxxxxxxxxxxxxxxxxxxx>; Michael Kelley <mikelley@xxxxxxxxxxxxx>;
> >> Wei
> >>>> Liu <liuwe@xxxxxxxxxxxxx>; Andrew Cooper <andrew.cooper3@xxxxxxxxxx>;
> >>>> Roger Pau Monné <roger.pau@xxxxxxxxxx>
> >>>> Subject: Re: [PATCH v6 05/11] x86/hyperv: setup hypercall page
> >>>>
> >>>> On 03.02.2020 11:39, Durrant, Paul wrote:
> >>>>>> -----Original Message-----
> >>>>>> From: Wei Liu <wl@xxxxxxx>
> >>>>>> Sent: 31 January 2020 17:57
> >>>>>> To: Xen Development List <xen-devel@xxxxxxxxxxxxxxxxxxxx>
> >>>>>> Cc: Durrant, Paul <pdurrant@xxxxxxxxxxxx>; Michael Kelley
> >>>>>> <mikelley@xxxxxxxxxxxxx>; Wei Liu <liuwe@xxxxxxxxxxxxx>; Wei Liu
> >>>>>> <wl@xxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>; Andrew Cooper
> >>>>>> <andrew.cooper3@xxxxxxxxxx>; Roger Pau Monné <roger.pau@xxxxxxxxxx>
> >>>>>> Subject: Re: [PATCH v6 05/11] x86/hyperv: setup hypercall page
> >>>>>>
> >>>>>> (Note to self)
> >>>>>>
> >>>>>> On Fri, Jan 31, 2020 at 05:49:24PM +0000, Wei Liu wrote:
> >>>>>> [...]
> >>>>>>> +static uint64_t generate_guest_id(void)
> >>>>>>> +{
> >>>>>>> +    union hv_guest_os_id id;
> >>>>>>> +
> >>>>>>
> >>>>>>        id.raw = 0;
> >>>>>
> >>>>> Or just use a C99 initializer to set things up. A bit neater IMO.
> >>>>
> >>>> If you mean this for ...
> >>>>
> >>>>>>> +    id.vendor = HV_XEN_VENDOR_ID;
> >>>>>>> +    id.major = xen_major_version();
> >>>>>>> +    id.minor = xen_minor_version();
> >>>>
> >>>> ... these three fields, then this won't work with rather old gcc
> >>>> we still permit to be used. Using { .raw = 0 } would work afaict.
> >>>>
> >>>
> >>> Not even { .vendor = HV_XEN_VENDOR_ID } ?
> >>
> >> No, because of it being part of an unnamed (struct) member of
> >> the union.
> >
> > Ok... shame. Presumably an empty initializer - {} -  would be ok?
> 
> I think so, yes. I understand you'd like this better than
> { .raw = 0 } ?
> 

Yes. In general, using a c99 initializer to explicitly set something to 0 seems 
a bit redundant to me.

  Paul

> Jan
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