被动扫描问题求解
本帖最后由 九阳神功爱喝茶 于 2015-11-25 19:06 编辑小弟最近在看主动扫描和被动扫描的ath9k源代码，遇到一个问题想和大家一起讨论下。
被动扫描是Client接收AP的beacon帧，然后对这个信道进行扫描，扫描之后获取该AP的BSS信息，保存下来，即完成了扫描过程;然后进入ieee80211_rx_mgmt_beacon函数，我分析了下其中的与创建连接有关的代码，如下：
static void ieee80211_rx_mgmt_beacon(struct ieee80211_sub_if_data *sdata,
struct ieee80211_mgmt *mgmt, size_t len,
struct ieee80211_rx_status *rx_status)
{
struct ieee80211_if_managed *ifmgd = &sdata->u.mgd;
struct ieee80211_bss_conf *bss_conf = &sdata->vif.bss_conf;
size_t baselen;
struct ieee802_11_elems elems;
struct ieee80211_local *local = sdata->local;
struct ieee80211_chanctx_conf *chanctx_conf;
struct ieee80211_channel *chan;
struct sta_info *sta;
u32 changed = 0;
bool erp_valid;
u8 erp_value = 0;
u32 ncrc;
u8 *bssid;
u8 deauth_buf;
sdata_assert_lock(sdata);
/* Process beacon from the current BSS */
baselen = (u8 *) mgmt->u.beacon.variable - (u8 *) mgmt;
if (baselen > len)
return;
rcu_read_lock();
chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf);
if (!chanctx_conf) {
rcu_read_unlock();
return;
}
if (rx_status->freq != chanctx_conf->def.chan->center_freq) {
rcu_read_unlock();
return;
}
chan = chanctx_conf->def.chan;
rcu_read_unlock();
//也就是说第一次等到该AP的beacon帧
if (ifmgd->assoc_data && ifmgd->assoc_data->need_beacon &&
ether_addr_equal(mgmt->bssid, ifmgd->assoc_data->bss->bssid)) {
ieee802_11_parse_elems(mgmt->u.beacon.variable,
len - baselen, false, &elems);
ieee80211_rx_bss_info(sdata, mgmt, len, rx_status, &elems);
if (elems.tim && !elems.parse_error) {
const struct ieee80211_tim_ie *tim_ie = elems.tim;
ifmgd->dtim_period = tim_ie->dtim_period;
}
ifmgd->have_beacon = true;
ifmgd->assoc_data->need_beacon = false;
if (local->hw.flags & IEEE80211_HW_TIMING_BEACON_ONLY) {
sdata->vif.bss_conf.sync_tsf =
le64_to_cpu(mgmt->u.beacon.timestamp);
sdata->vif.bss_conf.sync_device_ts =
rx_status->device_timestamp;
if (elems.tim)
sdata->vif.bss_conf.sync_dtim_count =
elems.tim->dtim_count;
else
sdata->vif.bss_conf.sync_dtim_count = 0;
}
/* continue assoc process */
ifmgd->assoc_data->timeout = jiffies;
ifmgd->assoc_data->timeout_started = true;
run_again(sdata, ifmgd->assoc_data->timeout);
return;
}
//如果当前未连接或者说收到的BSSID与当前连接的BSSID不匹配，直接return。。。
if (!ifmgd->associated ||
!ether_addr_equal(mgmt->bssid, ifmgd->associated->bssid))
return;
bssid = ifmgd->associated->bssid;
/* Track average RSSI from the Beacon frames of the current AP */
ifmgd->last_beacon_signal = rx_status->signal;
if (ifmgd->flags & IEEE80211_STA_RESET_SIGNAL_AVE) {
ifmgd->flags &= ~IEEE80211_STA_RESET_SIGNAL_AVE;
ifmgd->ave_beacon_signal = rx_status->signal * 16;
ifmgd->last_cqm_event_signal = 0;
ifmgd->count_beacon_signal = 1;
ifmgd->last_ave_beacon_signal = 0;
} else {
ifmgd->ave_beacon_signal =
(IEEE80211_SIGNAL_AVE_WEIGHT * rx_status->signal * 16 +
(16 - IEEE80211_SIGNAL_AVE_WEIGHT) *
ifmgd->ave_beacon_signal) / 16;
ifmgd->count_beacon_signal++;
}
if (ifmgd->rssi_min_thold != ifmgd->rssi_max_thold &&
ifmgd->count_beacon_signal >= IEEE80211_SIGNAL_AVE_MIN_COUNT) {
int sig = ifmgd->ave_beacon_signal;
int last_sig = ifmgd->last_ave_beacon_signal;
/*
* if signal crosses either of the boundaries, invoke callback
* with appropriate parameters
*/
if (sig > ifmgd->rssi_max_thold &&
(last_sig <= ifmgd->rssi_min_thold || last_sig == 0)) {
ifmgd->last_ave_beacon_signal = sig;
drv_rssi_callback(local, sdata, RSSI_EVENT_HIGH);
} else if (sig < ifmgd->rssi_min_thold &&
(last_sig >= ifmgd->rssi_max_thold ||
last_sig == 0)) {
ifmgd->last_ave_beacon_signal = sig;
drv_rssi_callback(local, sdata, RSSI_EVENT_LOW);
}
}
if (bss_conf->cqm_rssi_thold &&
ifmgd->count_beacon_signal >= IEEE80211_SIGNAL_AVE_MIN_COUNT &&
!(sdata->vif.driver_flags & IEEE80211_VIF_SUPPORTS_CQM_RSSI)) {
int sig = ifmgd->ave_beacon_signal / 16;
int last_event = ifmgd->last_cqm_event_signal;
int thold = bss_conf->cqm_rssi_thold;
int hyst = bss_conf->cqm_rssi_hyst;
if (sig < thold &&
(last_event == 0 || sig < last_event - hyst)) {
ifmgd->last_cqm_event_signal = sig;
ieee80211_cqm_rssi_notify(
&sdata->vif,
NL80211_CQM_RSSI_THRESHOLD_EVENT_LOW,
GFP_KERNEL);
} else if (sig > thold &&
(last_event == 0 || sig > last_event + hyst)) {
ifmgd->last_cqm_event_signal = sig;
ieee80211_cqm_rssi_notify(
&sdata->vif,
NL80211_CQM_RSSI_THRESHOLD_EVENT_HIGH,
GFP_KERNEL);
}
}
if (ifmgd->flags & IEEE80211_STA_CONNECTION_POLL) {
mlme_dbg_ratelimited(sdata,
"cancelling AP probe due to a received beacon\n");
ieee80211_reset_ap_probe(sdata);
}
/*
* Push the beacon loss detection into the future since
* we are processing a beacon from the AP just now.
*/
ieee80211_sta_reset_beacon_monitor(sdata);
ncrc = crc32_be(0, (void *)&mgmt->u.beacon.beacon_int, 4);
ncrc = ieee802_11_parse_elems_crc(mgmt->u.beacon.variable,
len - baselen, false, &elems,
care_about_ies, ncrc);
if (local->hw.flags & IEEE80211_HW_PS_NULLFUNC_STACK) {
bool directed_tim = ieee80211_check_tim(elems.tim,
elems.tim_len,
ifmgd->aid);
if (directed_tim) {
if (local->hw.conf.dynamic_ps_timeout > 0) {
if (local->hw.conf.flags & IEEE80211_CONF_PS) {
local->hw.conf.flags &= ~IEEE80211_CONF_PS;
ieee80211_hw_config(local,
IEEE80211_CONF_CHANGE_PS);
}
ieee80211_send_nullfunc(local, sdata, 0);
} else if (!local->pspolling && sdata->u.mgd.powersave) {
local->pspolling = true;
/*
* Here is assumed that the driver will be
* able to send ps-poll frame and receive a
* response even though power save mode is
* enabled, but some drivers might require
* to disable power save here. This needs
* to be investigated.
*/
ieee80211_send_pspoll(local, sdata);
}
}
}
if (sdata->vif.p2p) {
struct ieee80211_p2p_noa_attr noa = {};
int ret;
ret = cfg80211_get_p2p_attr(mgmt->u.beacon.variable,
len - baselen,
IEEE80211_P2P_ATTR_ABSENCE_NOTICE,
(u8 *) &noa, sizeof(noa));
if (ret >= 2) {
if (sdata->u.mgd.p2p_noa_index != noa.index) {
/* valid noa_attr and index changed */
sdata->u.mgd.p2p_noa_index = noa.index;
memcpy(&bss_conf->p2p_noa_attr, &noa, sizeof(noa));
changed |= BSS_CHANGED_P2P_PS;
/*
* make sure we update all information, the CRC
* mechanism doesn't look at P2P attributes.
*/
ifmgd->beacon_crc_valid = false;
}
} else if (sdata->u.mgd.p2p_noa_index != -1) {
/* noa_attr not found and we had valid noa_attr before */
sdata->u.mgd.p2p_noa_index = -1;
memset(&bss_conf->p2p_noa_attr, 0, sizeof(bss_conf->p2p_noa_attr));
changed |= BSS_CHANGED_P2P_PS;
ifmgd->beacon_crc_valid = false;
}
}
if (ncrc == ifmgd->beacon_crc && ifmgd->beacon_crc_valid)
return;
ifmgd->beacon_crc = ncrc;
ifmgd->beacon_crc_valid = true;
ieee80211_rx_bss_info(sdata, mgmt, len, rx_status, &elems);
ieee80211_sta_process_chanswitch(sdata, rx_status->mactime,
&elems, true);
if (!(ifmgd->flags & IEEE80211_STA_DISABLE_WMM) &&
ieee80211_sta_wmm_params(local, sdata, elems.wmm_param,
elems.wmm_param_len))
changed |= BSS_CHANGED_QOS;
/*
* If we haven't had a beacon before, tell the driver about the
* DTIM period (and beacon timing if desired) now.
*/
if (!ifmgd->have_beacon) {
/* a few bogus AP send dtim_period = 0 or no TIM IE */
if (elems.tim)
bss_conf->dtim_period = elems.tim->dtim_period ?: 1;
else
bss_conf->dtim_period = 1;
if (local->hw.flags & IEEE80211_HW_TIMING_BEACON_ONLY) {
sdata->vif.bss_conf.sync_tsf =
le64_to_cpu(mgmt->u.beacon.timestamp);
sdata->vif.bss_conf.sync_device_ts =
rx_status->device_timestamp;
if (elems.tim)
sdata->vif.bss_conf.sync_dtim_count =
elems.tim->dtim_count;
else
sdata->vif.bss_conf.sync_dtim_count = 0;
}
changed |= BSS_CHANGED_BEACON_INFO;
ifmgd->have_beacon = true;
mutex_lock(&local->iflist_mtx);
ieee80211_recalc_ps(local, -1);
mutex_unlock(&local->iflist_mtx);
ieee80211_recalc_ps_vif(sdata);
}
if (elems.erp_info) {
erp_valid = true;
erp_value = elems.erp_info;
} else {
erp_valid = false;
}
changed |= ieee80211_handle_bss_capability(sdata,
le16_to_cpu(mgmt->u.beacon.capab_info),
erp_valid, erp_value);
mutex_lock(&local->sta_mtx);
sta = sta_info_get(sdata, bssid);
if (ieee80211_config_bw(sdata, sta, elems.ht_operation,
elems.vht_operation, bssid, &changed)) {
mutex_unlock(&local->sta_mtx);
ieee80211_set_disassoc(sdata, IEEE80211_STYPE_DEAUTH,
WLAN_REASON_DEAUTH_LEAVING,
true, deauth_buf);
cfg80211_tx_mlme_mgmt(sdata->dev, deauth_buf,
sizeof(deauth_buf));
return;
}
if (sta && elems.opmode_notif)
ieee80211_vht_handle_opmode(sdata, sta, *elems.opmode_notif,
rx_status->band, true);
mutex_unlock(&local->sta_mtx);
if (elems.country_elem && elems.pwr_constr_elem &&
mgmt->u.probe_resp.capab_info &
cpu_to_le16(WLAN_CAPABILITY_SPECTRUM_MGMT))
changed |= ieee80211_handle_pwr_constr(sdata, chan,
elems.country_elem,
elems.country_elem_len,
elems.pwr_constr_elem);
ieee80211_bss_info_change_notify(sdata, changed);
}
还请各位大神指导下，小弟分析对吗？
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