Starting out in associated (not down!) state:
ifconfig iwn0 down; ifconfig iwn0 scan
shows 2 GHz and 5 GHz APs, whereas just
ifconfig iwn0 scan
does not show all APs. The diff below makes both cases show all APs.
ok?
Index: ieee80211.c
===================================================================
RCS file: /cvs/src/sys/net80211/ieee80211.c,v
retrieving revision 1.62
diff -u -p -r1.62 ieee80211.c
--- ieee80211.c 20 Jun 2017 13:51:46 -0000 1.62
+++ ieee80211.c 3 Sep 2017 18:44:31 -0000
@@ -877,7 +877,9 @@ ieee80211_next_mode(struct ifnet *ifp)
if (ic->ic_curmode == IEEE80211_MODE_11N)
continue;
- if (ic->ic_curmode >= IEEE80211_MODE_MAX) {
+ /* Always scan in AUTO mode if the driver scans all bands. */
+ if (ic->ic_curmode >= IEEE80211_MODE_MAX ||
+ (ic->ic_caps & IEEE80211_C_SCANALLBAND)) {
ic->ic_curmode = IEEE80211_MODE_AUTO;
break;
}
Long explanation:
The iwn, iwm, and wpi drivers run a firmware-based scan which receives
beacons from all channels the device supports, across 2 and 5 GHz bands.
Such drivers set a capability flag called 'SCANALLBAND'.
The net80211 stack filters received beacons based on the current active
channel set. The active channel set depends on the current mode (11a/b/g/n).
For example, set the interface to 11g mode and scan:
ifconfig iwn0 mode 11g; ifconfig iwn0 scan
Only 2GHz APs will be shown because net80211 filters out 5GHz ones.
Conversely, with:
ifconfig iwn0 mode 11a; ifconfig iwn0 scan
only 5GHz APs will be shown.
Reset the mode to default (autoselect): ifconfig iwn0 -mode
The autoselect mode puts all channels in the active channel set during
its first scan iteration. However, the automatic mode then also tries
all fixed modes in sequence and recalculates the active channel set
during each iteration (see net80211/ieee80211.c:ieee80211_setmode()).
This behaviour makes sense for devices which can only scan distinct
channel sets, e.g. 11b and 11a, like ath(4).
But with firmware-based scans which return beacons from all supported
channels every time, it gets in the way.
While iwn is associated to a 2GHz AP, 'ifconfig iwn0 scan' will start out
in 11g mode. The active channel set is restricted accordingly and only
2GHz APs will be seen during the first scan iteration. Even if there
is a better 5GHz AP around it will only be selected if association to
the 2GHz AP fails for some reason and another mode is tried.
If the interface is reset (ifconfig iwn0 down) then a scan always starts
out in the initial 'auto' iteration with all channels in the initial active
channel set. So to switch from a 2GHz AP to a better 5GHz AP, the interface
must be stopped and restarted. Just running a scan is not enough.
The diff fixes this inconsistency by always keeping iwn, iwm, and wpi in
auto mode during scans. This allows reception of beacons on all channels,
unless 'ifconfig mode' was used to force a particular mode (not visible in
context of the diff: this function returns early if a specific mode has
been configured).
