Re: [PATCH 2/8] x86/platform/uv: Return UV Hubless System Type

[Mike Travis]

On 9/3/2019 8:41 AM, Christoph Hellwig wrote:
> On Tue, Sep 03, 2019 at 07:12:28AM -0700, Mike Travis wrote:
> > > > +#define is_uv_hubless _is_uv_hubless
> > >
> > > Why the weird macro indirection?
> > >
> > > > -static inline int is_uv_hubless(void)	{ return 0; }
> > > > +static inline int _is_uv_hubless(int uv) { return 0; }
> > > > +#define is_uv_hubless _is_uv_hubless
> > >
> > > And here again.
> >
> > Sorry, I should have explained this better.  The problem arises because
> > we have a number of UV specific kernel modules that support multiple
> > distributions.  And with back porting to earlier distros we cannot
> > rely on the KERNEL_VERSION macro to define whether the source is being
> > built for an earlier kernel.  So this allows an ifdef on the function
> > name to discover if the kernel is before or after these changes.
>
> And none of these matter for upstream.  We'd rather not make the code
> more convouluted than required.  If you actually really cared about these
> modules you would simply submit them upstream.

That is always being considered for everything we include into the 
community kernel source.  The problem is a couple of the kernel modules 
(hwperf being the prime example) is much more tied to hardware and 
BIOS/FW updates so has to be updated much more often than the current 
submittal/acceptance process allows.  We do opensource these modules but 
they are built from single source directories and have to be released as 
a module into a package that can be installed on different distros. 
There is not a source version for each kernel version.

I have seen this method (declare the function with a leading underscore 
and a #define for the function reference) which is why I'm assuming it's 
a standard kernel practice?  (I'll find some examples if necessary?)