scheduled scan api

Hi Johannes,

I received a couple of reports from people who got problem with brcmfmac when a scheduled scan is requested, without any ssid specified. Currently, brcmfmac basically rejects the request. So what are valid usage scenarios for scheduled scans with respect to the n_ssid, n_channels, and n_matchsets. In the kernel doc below it says a zero-length ssid means 'no match'. I suppose it means any ssid which signal is above RRSI threshold will match.

Regards,
Arend ---8<---------------------------------------------------------- /**
* struct cfg80211_match_set - sets of attributes to match
*
* @ssid: SSID to be matched; may be zero-length for no match (RSSI only)
* @rssi_thold: don't report scan results below this threshold (in s32 dBm) */

Hi Arend,

I'm replying to this since I've been "somewhat" involved in the implementation. ;)

I think it will make more sense if you check the nl80211 doc:

---8<----
* @NL80211_ATTR_SCHED_SCAN_MATCH: Nested attribute with one or more
* sets of attributes to match during scheduled scans. Only BSSs
* that match any of the sets will be reported. These are
* pass-thru filter rules.
* For a match to succeed, the BSS must match all attributes of a
* set. Since not every hardware supports matching all types of
* attributes, there is no guarantee that the reported BSSs are
* fully complying with the match sets and userspace needs to be
* able to ignore them by itself.
* Thus, the implementation is somewhat hardware-dependent, but
* this is only an optimization and the userspace application
* needs to handle all the non-filtered results anyway.
* If the match attributes don't make sense when combined with
* the values passed in @NL80211_ATTR_SCAN_SSIDS (eg. if an SSID
* is included in the probe request, but the match attributes
* will never let it go through), -EINVAL may be returned.
* If ommited, no filtering is done.
---8<----

Especially the second paragraph. This means that for the SSIDs, a broadcast SSID means that everything goes through, there is no filtering of SSIDs. You can use that for RSSI-only matches with a single RSSI match attribute (so you don't need to specify an RSSI attribute for every SSID you need to match).

This is a bit unclear, but it's due to some confusion that was introduced when the RSSI match attribute was added.

--
Luca.