Re: [Xen-devel] [PATCH v8 6/6] tools: enable Cache QoS Monitoring feature for libxl/libxc

["Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx>]

> -----Original Message-----
> From: Xu, Dongxiao
> Sent: Monday, February 10, 2014 7:19 PM
> To: Ian Campbell
> Cc: xen-devel@xxxxxxxxxxxxx; keir@xxxxxxx; JBeulich@xxxxxxxx;
> Ian.Jackson@xxxxxxxxxxxxx; stefano.stabellini@xxxxxxxxxxxxx;
> andrew.cooper3@xxxxxxxxxx; konrad.wilk@xxxxxxxxxx; dgdegra@xxxxxxxxxxxxx
> Subject: RE: [PATCH v8 6/6] tools: enable Cache QoS Monitoring feature for
> libxl/libxc
> 
> > > diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
> > > index 649ce50..43c0f48 100644
> > > --- a/tools/libxl/libxl_types.idl
> > > +++ b/tools/libxl/libxl_types.idl
> > > @@ -596,3 +596,10 @@ libxl_event = Struct("event",[
> > >                                   ])),
> > >             ("domain_create_console_available", Struct(None, [])),
> > >             ]))])
> > > +
> > > +libxl_cqminfo = Struct("cqminfo", [
> >
> > You need to also patch libxl.h to add a suitable LIBXL_HAVE_FOO define,
> > see the existing examples in that header.
> 
> OK.

Hi Ian,

Just had another look at the comments:

* In the event that a change is required which cannot be made
 * backwards compatible in this manner a #define of the form
 * LIBXL_HAVE_<interface> will always be added in order to make it
 * possible to write applciations which build against any version of
 * libxl. Such changes are expected to be exceptional and used as a
 * last resort. The barrier for backporting such a change to a stable
 * branch will be very high.

LIBXL_HAVE_<interface> is to address the back compatibility issue, and mostly 
it is used in cases like "adding a new field to the existing data structure".

In this patch, the libxl_cqminfo is a new added data structure, and it seems 
that there is no such compatibility issue. Do we really need to add the 
LIBXL_HAVE_<interface> macro?

Thanks,
Dongxiao

> 
> Thanks,
> Dongxiao
> 
> >
> > Ian.

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