Re: [PATCH v3 12/13] xen/iommu: smmu: Add Xen specific code to be able to use the driver

[Ian Campbell <ian.campbell@citrix.com>]

On Mon, 2015-02-09 at 23:40 +0800, Julien Grall wrote:
> Hi Stefano,
> 
> On 06/02/2015 21:20, Stefano Stabellini wrote:
> > On Fri, 30 Jan 2015, Julien Grall wrote:
> >> -static int force_stage;
> >> -module_param_named(force_stage, force_stage, int, S_IRUGO | S_IWUSR);
> >> -MODULE_PARM_DESC(force_stage,
> >> -	"Force SMMU mappings to be installed at a particular stage of translation. A value of '1' or '2' forces the corresponding stage. All other values are ignored (i.e. no stage is forced). Note that selecting a specific stage will disable support for nested translation.");
> >
> > for the sake of minimizing the diff, I would add
> >
> > #define module_param_named(a, b, c, d)
> > #define MODULE_PARM_DESC(a, b)
> >
> > to the Xen definitions above
> 
> We still have to drop force_stage because it will get unused and won't 
> compile.
> So it's not too bad to remove the 2 other lines.

You currently redefine it as a const int -- is it really unused?

> All the Xen code is beginning with /* Xen: */. Though, I could add a /* 
> Xen: End */ to make the separation clearer.

BTW, I was thinking to suggest replacing all the #if 0 with #ifndef
CONFIG_XEN or something, which might make some of the comments shorter
or even mean they aren't really needed.

Either way I would write it as:
   #if 0 /* Xen: Comment comment */
(similarly any if (0) ...)

> > For the sake of minimizing the changes to Linux functions, could you
> > write a wrapper around this function instead? That might allow you to
> > remove the changes related to the return value.
> 
> We should avoid to try to minimize the code against the clarity of the 
> code...
> 
> The change you suggest would require to modify the caller of this 
> function, which is less clearer than this one.

Given an original function foo can you do

static void foo(void)
{
  original code, unmodified
}
static void foo_wrapper(void)
{
   wrapper
   foo_orig
   wrapper
}
#define foo foo_wrapper

or something along those lines?