On Fri, 31/07/2009 at 18:16 +0200, Artur Skawina wrote: > [linux-wireless added to cc list] > > Igor Perminov wrote: > > I have an issue related to handling power-saving stations by hostapd > > and/or mac80211 stack. A station can't reconnect after it wakes up. > > > > The problems looks similar to another one having been reported to this > > list earlier (STA can connect, but fails to reconnect within > > ap_max_inactivity): > > http://lists.shmoo.com/pipermail/hostap/2009-February/019192.html > > > > AP: Linux box with D-Link DWA-110 USB Wi-Fi stick (rt73usb kernel > > driver), kernel 2.6.30 with some patches, hostapd 0.6.9. > > Station: Toshiba G900 PDA under Windows Mobile 6.0. > > > > The environment is described in details here: > > http://rt2x00.serialmonkey.com/phpBB/viewtopic.php?f=5&t=5486&start=10 > > > > Consider the following step-by-step: > > 1. A station authenticates and associates with the AP and exchanges > > traffic. > > 2. The station indicates to the AP that it is going to sleep. > > 3. The station device goes to the stand-by mode (not only its wi-fi > > card, but the device itself). > > 4. The station device wakes up and begins authentication with an > > Authentication management frame. > > > > This is the behavior of my PDA. > > > > The problem is the mac80211 stack at the point 4 "remembers" that the > > station has gone to sleep. So, the response frames from hostapd are > > buffered by mac80211. > > The station indicates in the Authentication frame that it isn't sleeping > > anymore. But the mac80211 stack analyzes sleep/wake transitions in > > _data_ frames only, but not in management ones. See > > ieee80211_rx_h_sta_process in net/mac80211/rx.c. A comment there notes: > > "Ignore doze->wake transitions that are indicated by non-data frames, > > the standard is unclear here". > > As the result, the station never receives the authentication response > > from the AP. > > > > One solution against this problem could be implemented in hostapd: to > > force the mac80211 stack to "forget" the station just after receiving an > > authentication frame (the patch is below). After this change the station > > can reconnect successfully. > > i just did a quick test and your hostapd patch does indeed fix my problem > too (p54+hostapd with a winmobile device that couldn't reconnect after > turning the wifi module off and on). > > > Another solution (in theory) would be to improve the mac80211 > > implementation: to analyze not only data frames, but also > > management ones (or may be just some kinds of them) in > > ieee80211_rx_h_sta_process. > > would seem to make sense, but having not read the spec i have no idea > if that's the right answer; hence the linux-wireless cc... > > > I've asked this question to the linux-wireless mailing list few days > > ago, but nobody has answered still: > > http://marc.info/?l=linux-wireless&m=124879549212741&w=2 > > > > And what is your opinion, what is a better way: should this problem be > > fixed in hostapd or in mac80211? > > > > === Begin diff === > > --- a/hostapd/ieee802_11.c 2009-06-29 14:21:59.000000000 +0400 > > +++ b/hostapd/ieee802_11.c 2009-07-21 16:28:17.000000000 +0400 > > @@ -583,6 +583,13 @@ > > goto fail; > > } > > > > + res = hostapd_sta_remove(hapd, mgmt->sa); > > + if (res) { > > + wpa_printf(MSG_DEBUG, "authentication: STA=" MACSTR > > + ", hostapd_sta_remove returned %d\n", > > + MAC2STR(mgmt->sa), res); > > + } > > + > > if (vlan_id > 0) { > > if (hostapd_get_vlan_id_ifname(hapd->conf->vlan, > > sta->vlan_id) == NULL) { > > === End diff === > > Thanks for the cc, added this to my local hostapd patch set, until the > issue gets resolved one way or another. > > artur I've looked through the 802-11.2007 document and now I consider the source of the problem is misunderstanding by an AP and a STA states of each other. When the station tries to reconnect it considers itself non-authenticated. Whereas the AP considers the station both authenticated and associated. I think it would be better to fix the problem in hostapd, because it's a hostapd's responsibility - to manage the state of a station being known to the AP. So, when hostapd receives an Auth frame from a station it should consider the station being non-authenticated and force removing the station from the underlying stack. I'll submit a patch for hostapd in a nearest future. Best regards, Igor -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
