Re: [PATCH v2 6/7] flask: drop dead compat translation code

["Roger Pau Monné" <roger.pau@citrix.com>]

On Wed, Jul 15, 2020 at 10:52:28AM +0200, Jan Beulich wrote:
> On 15.07.2020 10:41, Roger Pau Monné wrote:
> > On Wed, Jul 15, 2020 at 08:42:44AM +0200, Jan Beulich wrote:
> >> On 14.07.2020 16:58, Roger Pau Monné wrote:
> >>> On Wed, Jul 01, 2020 at 12:28:07PM +0200, Jan Beulich wrote:
> >>>> Translation macros aren't needed at all (or else a devicetree_label
> >>>> entry would have been missing), and userlist has been removed quite some
> >>>> time ago.
> >>>>
> >>>> No functional change.
> >>>>
> >>>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> >>>>
> >>>> --- a/xen/include/xlat.lst
> >>>> +++ b/xen/include/xlat.lst
> >>>> @@ -148,14 +148,11 @@
> >>>>  ?	xenoprof_init			xenoprof.h
> >>>>  ?	xenoprof_passive		xenoprof.h
> >>>>  ?	flask_access			xsm/flask_op.h
> >>>> -!	flask_boolean			xsm/flask_op.h
> >>>>  ?	flask_cache_stats		xsm/flask_op.h
> >>>>  ?	flask_hash_stats		xsm/flask_op.h
> >>>> -!	flask_load			xsm/flask_op.h
> >>>>  ?	flask_ocontext			xsm/flask_op.h
> >>>>  ?	flask_peersid			xsm/flask_op.h
> >>>>  ?	flask_relabel			xsm/flask_op.h
> >>>>  ?	flask_setavc_threshold		xsm/flask_op.h
> >>>>  ?	flask_setenforce		xsm/flask_op.h
> >>>> -!	flask_sid_context		xsm/flask_op.h
> >>>>  ?	flask_transition		xsm/flask_op.h
> >>>
> >>> Shouldn't those become checks then?
> >>
> >> No, checking will never succeed for structures containing
> >> XEN_GUEST_HANDLE(). But there's no point in generating xlat macros
> >> when they're never used. There are two fundamentally different
> >> strategies for handling the compat hypercalls: One is to wrap a
> >> translation layer around the native hypercall. That's where the
> >> xlat macros come into play. The other, used here, is to compile
> >> the entire hypercall function a second time, arranging for the
> >> compat structures to get used in place of the native ones. There
> >> are no xlat macros involved here, all that's needed are correctly
> >> translated structures. (For completeness, x86's MCA hypercall
> >> uses yet another, quite adhoc strategy for handling, but also not
> >> involving any xlat macro use. Hence the consideration there to
> >> possibly drop the respective lines from the file here.)
> > 
> > Thanks, I think this explanation is helpful and I wonder whether it
> > would be possible to have something along this lines in a file or as a
> > comment somewhere, maybe at the top of xlat.lst?
> 
> To be honest - I'm not sure: Such a comment may indeed be helpful
> to have, but I don't think I can see any single good place for it
> to live. For people editing xlat.lst (a file the existence of which
> many aren't even aware of), this would be a good place. But how
> would others have any chance of running into this comment?

I would add it to xlat.lst rather than not adding it at all.

If we can find a better place to add it I'm all in, but as said I
would rather add it somewhere right now than just defer adding it
until the perfect placement is found.

> > Also could you add a line to the commit message noting that flask code
> > doesn't use any of the translation macros because it follows a
> > different approach to compat handling?
> 
> I've made the sentence start "Translation macros aren't used (and
> hence needed) at all ..." - is that enough of an adjustment?

Yes, that's fine.

Thanks.