Re: [PATCH] cfg80211: use IDA to allocate wiphy indeces

[Ben Greear]

On 06/29/2018 11:48 AM, Brian Norris wrote:
> Hi Johannes,
>
> On Fri, Jun 29, 2018 at 09:42:20AM +0200, Johannes Berg wrote:
> > On Wed, 2018-06-20 at 18:29 -0700, Brian Norris wrote:
> > > It's annoying to see the phy index increase arbitrarily, just because a
> > > device got removed and re-probed (e.g., during a device reset, or due to
> > > probe testing). We can use the in-kernel index allocator for this,
> > > instead of just an increasing counter.
> >
> > I can understand that it's somewhat annoying to people, but it was
> > actually done on purpose to avoid userspace talking to the wrong device.
>
> Hmm, interesting. I'm not dead-set on this patch, so if there are good
> reasons to reject it, I won't fret.
>
> > Imagine you have some userspace process running that has remembered the
> > wiphy index to use it to talk to nl80211, and now underneath the device
> > goes away and reappears. This process should understand that situation,
> > and handle it accordingly, rather than being blind to the reset.
>
> How is this different from the wlan (netdev) device naming? We allow
> 'wlan0' to leave and return under the same name. Isn't the right answer
> that user space should be listening for udev and/or netlink events?
>
> Brian

For what it is worth, we use udev to rename the phyX to wiphyZ devices based on
their MAC address, and that seems to work OK.

I can't think of any reason why user-space would need the phy index number
to increase as modules are loaded/unloaded though.

Thanks,
Ben

--
Ben Greear <greearb@xxxxxxxxxxxxxxx>
Candela Technologies Inc  http://www.candelatech.com