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ieee80211_start_scan(struct ieee80211vap *, int flags, u_int duration, u_int mindwell, u_int maxdwell, u_int nssid, const struct ieee80211_scan_ssid ssids);
ieee80211_check_scan(struct ieee80211vap *, int flags, u_int duration, u_int mindwell, u_int maxdwell, u_int nssid, const struct ieee80211_scan_ssid ssids);
ieee80211_check_scan_current(struct ieee80211vap *);
ieee80211_bg_scan(struct ieee80211vap *, int);
ieee80211_cancel_scan(struct ieee80211vap *);
ieee80211_cancel_scan_any(struct ieee80211vap *);
ieee80211_scan_next(struct ieee80211vap *);
ieee80211_scan_done(struct ieee80211vap *);
ieee80211_probe_curchan(struct ieee80211vap *, int);
ieee80211_add_scan(struct ieee80211vap *, const struct ieee80211_scanparams *, const struct ieee80211_frame *, int subtype, int rssi, int noise);
ieee80211_scan_timeout(struct ieee80211com *);
ieee80211_scan_assoc_fail(struct ieee80211vap *, const uint8_t mac[IEEE80211_ADDR_LEN], int reason);
ieee80211_scan_flush(struct ieee80211vap *);
ieee80211_scan_iterate(struct ieee80211vap *, ieee80211_scan_iter_func, void *);
ieee80211_scan_dump_channels(const struct ieee80211_scan_state *);
ieee80211_scanner_register(enum ieee80211_opmode, const struct ieee80211_scanner *);
ieee80211_scanner_unregister(enum ieee80211_opmode, const struct ieee80211_scanner *);
ieee80211_scanner_unregister_all(const struct ieee80211_scanner *);
const struct ieee80211_scanner *
A scan operation involves constructing a set of channels to inspect (the scan set), visiting each channel and collecting information (e.g. what BSS are present), and then analyzing the results to make decisions such as which BSS to join. This process needs to be as fast as possible so net80211 does things like intelligently construct scan sets and dwell on a channel only as long as necessary. Scan results are cached and the scan cache is used to avoid scanning when possible and to enable roaming between access points when operating in infrastructure mode.
Scanning is handled by pluggable modules that implement policy per-operating mode. The core scanning support provides an infrastructure to support these modules and exports a common API to the rest of the net80211 layer. Policy modules decide what channels to visit, what state to record to make decisions, and selects the final station/channel to return as the result of a scan.
Scanning is done synchronously when initially bringing a vap to an operational state and optionally in the background to maintain the scan cache for doing roaming and rogue AP monitoring. Scanning is not tied to the net80211 state machine that governs vaps except for linkage to the IEEE80211_S_SCAN state. Only one vap at a time may be scanning; this scheduling policy is handled in ieee80211_new_state() and is transparent to scanning code.
Scanning is controlled by a set of parameters that (potentially) constrains the channel set and any desired SSID's and BSSID's. net80211 comes with a standard scanner module that works with all available operating modes and supports "background scanning" and "roaming" operation.
Background scanning is done using ieee80211_bg_scan() in a co-routine fashion. The first call to this routine will start a background scan that runs for a limited period of time before returning to the BSS channel. Subsequent calls advance through the scan set until all channels are visited. Typically these later calls are timed to allow receipt of frames buffered by an access point for the station.
A scan operation can be canceled using ieee80211_cancel_scan() if it was initiated by the specified vap, or ieee80211_cancel_scan_any() to force termination regardless which vap started it. These requests are mostly used by net80211 in the transmit path to cancel background scans when frames are to be sent. Drivers should not need to use these calls (or most of the calls described on this page).
The ieee80211_scan_next() and ieee80211_scan_done() routines do explicit iteration through the scan set and should not normally be used by drivers. ieee80211_probe_curchan() handles the work of transmitting ProbeRequest frames when visiting a channel during an active scan. When the channel attributes are marked with IEEE80211_CHAN_PASSIVE this function will arrange that before any frame is transmitted 802.11 traffic is first received (in order to comply with regulatory constraints).
Min/max dwell time parameters are used to constrain time spent visiting a channel. The maximum dwell time constrains the time spent listening for traffic. The minimum dwell time is used to reduce this time--when it is reached and one or more frames have been received then an immediate channel change will be done. Drivers can override this behaviour through the iv_scan_mindwell method.
The cache contents can be explicitly flushed with ieee80211_scan_flush() or by setting the IEEE80211_SCAN_FLUSH flag when starting a scan operation.
Scan cache entries are created with the ieee80211_add_scan() routine; usually on receipt of Beacon or ProbeResponse frames. Existing entries are typically updated based on the latest information though some information such as RSSI and noise floor readings may be combined to present an average.
The cache contents is aged through ieee80211_scan_timeout() calls. Typically these happen together with other station table activity; every IEEE80211_INACT_WAIT seconds (default 15).
Individual cache entries are marked usable with ieee80211_scan_assoc_success() and faulty with ieee80211_scan_assoc_fail() with the latter taking an argument to identify if there was no response to Authentication/Association requests or if a negative response was received (which might hasten cache eviction or blacklist the entry).
The cache contents can be viewed using the ieee80211_scan_iterate() call. Cache entries are exported in a public format that is exported to user applications through the IEEE80211_SCAN_RESULTS request.
|IEEE80211_SCAN (9)||March 29, 2010|
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