On Tue, 2018-04-17 at 15:26 -0700, Brian Norris wrote:
> On Tue, Apr 17, 2018 at 2:49 PM, Arend van Spriel
> <arend.vanspriel@xxxxxxxxxxxx> wrote:
> > On 4/17/2018 6:07 PM, Brian Norris wrote:
> > > On Tue, Apr 17, 2018 at 10:22:13AM +0200, Arend van Spriel wrote:
> > > > I believe checking command support is not really recommended.
> > > > Instead, you
> > > > better check NL80211_ATTR_SCHED_SCAN_MAX_REQS being non-zero
> > > > (since kernel
> > > > 4.12 that is).
> > >
> > >
> > > Why not? Command support checking is what wpa_supplicant is
> > > doing.
> >
> >
> > That's not really a good argument. A couple (or more) years ago
> > wpa_supplicant was not doing nl80211 but wext and some other using
> > driver private ioctls, but that did not make it the best approach.
>
> I see what you're saying (though your comparison doesn't seem that
> fair either; private ioctls are nothing like a well-defined nl80211
> support list), and I'm totally good on looking at the new flag
> eventually. But you still haven't answered my question ("why not?").
> Is there a problem with the "supported commands" list?
>
> > The START_SCHED_SCAN command is indeed still provided to user-
> > space:
>
> And as I see it, it probably needs to be for essentially forever. Or
> at least a significant amount of time after wpa_supplicant stops
> relying on it. (Hint: it's still using it today, with no reference to
> NL80211_ATTR_SCHED_SCAN_MAX_REQS.) There's a reason the kernel has
> ABI
> guarantees. I suspect you only get a chance to rewrite the world
> (WEXT
> -> nl80211) a few times in the life of kernel ABIs.
It sometimes feels like wpa_supplicant gets treated as a static entity
that can never be changed. In fact, send a patch to Jouni implementing
the best practice, with a fallback to preserve compat for old kernels,
and I'm sure he'd entertain it. Just because the supplicant does
something a certain way, doesn't mean it's the *best* way, but it too
evolves.
Dan
