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

[Wei Liu <wl@xxxxxxx>]

On Mon, Feb 03, 2020 at 11:41:57AM +0000, Durrant, Paul wrote:
> > -----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.

Alright. I have changed it to

  union hv_guest_os_id id = {};

in my local branch.

Wei.

> 
>   Paul
> 
> > Jan

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