+ Johannes (to confirm/correct my understanding regarding "supported
commands")
On 4/18/2018 4:35 AM, Dan Williams wrote:
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?
My understanding is that in general the "supported commands" list is not
well-maintained. Not every nl80211 command is represented in the list so
user-space can not know whether it is missing or not supported.
For this particular START_SCHED_SCAN command it can be used still and
indeed probably for a long time. I just wanted to point out that it is
not recommended for new user-space functionality.
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.
I was actually considering to do that. The netlink messages are easily
checked for presence of an attribute so deciding on whether to use the
fallback is trivial.
Regards,
Arend
