WPA_Sup scan_results speed using DBus

[Dan Williams]

On Tue, 2017-08-08 at 09:24 -0600, Matthew Stanger wrote:
> Hello,
> 
> I'm having trouble getting a reasonable speed for scan results using
> DBus and I'm wondering if I'm fundamentally missing the design
> intent.
> As I understand it, I should be using the
> 'fi.w1.wpa_supplicant1.Interface' with 'BSSs' property to get a list
> of BSS and then use 'GetAll' on each of the BSS's to build the scan
> results. This takes about 5-7 sec's when having 50-60 SSID's visible,
> with each DBus call taking 50-100mS per DBus call to 'BSSs' (230Mhz
> ARM). Now if I just link against wpa_sup like wpa_cli does then I can
> use the 'scan_results' method and get the list in milliseconds.

Typically you'd listen to the D-Bus property change signals rather than
a GetAll(), so that you can get each AP as it gets added to the list. 
But if you've got a 230MHz machine, I can see how things would be a bit
slower.

One improvement would be to implement the ObjectManager interface for
the supplicant, which allows you to retrieve *all* the objects at once
rather than getting each AP individually.

> 1) Is the DBus approach correct for getting scan_results? Is there a
> better way?

There's also the supplicant's socket-based interface which wpa_cli
uses.  I don't think you can categorize any method as "better" overall,
just that for some applications the socket interface is better, and for
some the D-Bus interface is better.

> 2) If it is, are there any other way to get the scan_results without
> linking/socket against wpa_sup?

Take a look at wpa_cli perhaps.  You'd need to write some socket
read/write code, but if your program's license is compatible, you might
be able to lift some of the wpa_cli code and repurpose.

Dan