Re: [Xen-devel] [PATCH 1/5] xen: improve changes to xen_add_to_physmap

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.08.12 at 17:43, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
wrote:
> On Mon, 6 Aug 2012, Jan Beulich wrote:
>> >>> On 06.08.12 at 16:12, Stefano Stabellini 
>> >>> <stefano.stabellini@xxxxxxxxxxxxx>
>> wrote:
>> > This is an incremental patch on top of
>> > c0bc926083b5987a3e9944eec2c12ad0580100e2: in order to retain binary
>> > compatibility, it is better to introduce foreign_domid as part of a
>> > union containing both size and foreign_domid.
>> > 
>> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
>> > ---
>> >  xen/include/public/memory.h |   11 +++++++----
>> >  1 files changed, 7 insertions(+), 4 deletions(-)
>> > 
>> > diff --git a/xen/include/public/memory.h b/xen/include/public/memory.h
>> > index b2adfbe..b0af2fd 100644
>> > --- a/xen/include/public/memory.h
>> > +++ b/xen/include/public/memory.h
>> > @@ -208,8 +208,12 @@ struct xen_add_to_physmap {
>> >      /* Which domain to change the mapping for. */
>> >      domid_t domid;
>> >  
>> > -    /* Number of pages to go through for gmfn_range */
>> > -    uint16_t    size;
>> > +    union {
>> > +        /* Number of pages to go through for gmfn_range */
>> > +        uint16_t    size;
>> > +        /* IFF gmfn_foreign */
>> > +        domid_t foreign_domid;
>> > +    };
>> 
>> But you're clear that this isn't standard C, and hence can't go
>> in this way?
>> 
> 
> Why? It is c11 if I am not mistaken.

Yes. But the common baseline is C89.

Jan


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