Re: [PATCH v6 01/10] xen: vnuma topology and subop hypercalls

From: Dario Faggioli <dario.faggioli@citrix.com>
To: Wei Liu <wei.liu2@citrix.com>
Cc: Keir Fraser <keir@xen.org>,
	Ian Campbell <Ian.Campbell@citrix.com>,
	Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	George Dunlap <george.dunlap@eu.citrix.com>,
	Matt Wilson <msw@linux.com>, Li Yechen <lccycc123@gmail.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
	Jan Beulich <JBeulich@suse.com>,
	Elena Ufimtseva <ufimtseva@gmail.com>
Subject: Re: [PATCH v6 01/10] xen: vnuma topology and subop hypercalls
Date: Tue, 22 Jul 2014 17:18:07 +0200	[thread overview]
Message-ID: <1406042287.17850.78.camel@Solace> (raw)
In-Reply-To: <20140720155918.GB26184@zion.uk.xensource.com>


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On dom, 2014-07-20 at 16:59 +0100, Wei Liu wrote:
> On Sun, Jul 20, 2014 at 09:16:11AM -0400, Elena Ufimtseva wrote:

> > >> +struct vnuma_topology_info {
> > >> +    /* IN */
> > >> +    domid_t domid;
> > >> +    /* IN/OUT */
> > >> +    unsigned int nr_vnodes;
> > >> +    unsigned int nr_vcpus;
> > >> +    /* OUT */
> > >> +    union {
> > >> +        XEN_GUEST_HANDLE(uint) h;
> > >> +        uint64_t pad;
> > >> +    } vdistance;
> > >> +    union {
> > >> +        XEN_GUEST_HANDLE(uint) h;
> > >> +        uint64_t pad;
> > >> +    } vcpu_to_vnode;
> > >> +    union {
> > >> +        XEN_GUEST_HANDLE(vmemrange_t) h;
> > >> +        uint64_t pad;
> > >> +    } vmemrange;
> > >
> > > Why do you need to use union? The other interface you introduce in this
> > > patch doesn't use union.
> > 
> > This is one is for making sure on 32 and 64 bits the structures are of
> > the same size.
> > 
> 
> I can see other similiar occurences of XEN_GUEST_HANDLE don't need
> padding. Did I miss something?
> 
I remember this coming up during review of an earlier version of Elena's
series, and I think I also remember the union with padding solution
being suggested, but I don't remember which round it was, and who
suggested it... Elena, up for some digging in your inbox (or xen-devel
archives)? :-P

Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)


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