IEEE80211_PROTO(9) BSD Kernel Developer's Manual IEEE80211_PROTO(9)NAME
ieee80211_proto — 802.11 state machine support
ieee80211_start_all(struct ieee80211com *);
ieee80211_stop_all(struct ieee80211com *);
ieee80211_suspend_all(struct ieee80211com *);
ieee80211_resume_all(struct ieee80211com *);
ieee80211_new_state(struct ieee80211vap *, enum ieee80211_state, int);
ieee80211_wait_for_parent(struct ieee80211com *);
The net80211 layer that supports 802.11 device drivers uses a state
machine to control operation of vaps. These state machines vary accord‐
ing to the vap operating mode. Station mode state machines follow the
802.11 MLME states in the protocol specification. Other state machines
are simpler and reflect operational work such as scanning for a BSS or
automatically selecting a channel to operate on. When multiple vaps are
operational the state machines are used to coordinate operation such as
choosing a channel. The state machine mechanism also serves to bind the
net80211 layer to a driver; this is described more below.
The following states are defined for state machines:
IEEE80211_S_INIT Default/initial state. A vap in this state should not
hold any dynamic state (e.g. entries for associated
stations in the node table). The driver must quiesce
the hardware; e.g. there should be no interrupts fir‐
IEEE80211_S_SCAN Scanning for a BSS or choosing a channel to operate
on. Note that scanning can also take place in other
states (e.g. when background scanning is active); this
state is entered when initially bringing a vap to an
operational state or after an event such as a beacon
miss (in station mode).
IEEE80211_S_AUTH Authenticating to an access point (in station mode).
This state is normally reached from IEEE80211_S_SCAN
after selecting a BSS, but may also be reached from
IEEE80211_S_ASSOC or IEEE80211_S_RUN if the authenti‐
cation handshake fails.
IEEE80211_S_ASSOC Associating to an access point (in station mode).
This state is reached from IEEE80211_S_AUTH after suc‐
cessfully authenticating or from IEEE80211_S_RUN if a
DisAssoc frame is received.
IEEE80211_S_CAC Doing Channel Availability Check (CAC). This state is
entered only when DFS is enabled and the channel
selected for operation requires CAC.
IEEE80211_S_RUN Operational. In this state a vap can transmit data
frames, accept requests for stations associating, etc.
Beware that data traffic is also gated by whether the
associated “port” is authorized. When
WPA/802.11i/802.1x is operational authorization may
happen separately; e.g. in station mode
wpa_supplicant(8) must complete the handshakes and
plumb the necessary keys before a port is authorized.
In this state a BSS is operational and associated
state is valid and may be used; e.g. ic_bss and
ic_bsschan are guaranteed to be usable.
IEEE80211_S_CSA Channel Switch Announcement (CSA) is pending. This
state is reached only from IEEE80211_S_RUN when either
a CSA is received from an access point (in station
mode) or the local station is preparing to change
channel. In this state traffic may be muted depending
on the Mute setting in the CSA.
IEEE80211_S_SLEEP Asleep to save power (in station mode). This state is
reached only from IEEE80211_S_RUN when power save
operation is enabled and the local station is deemed
sufficiently idle to enter low power mode.
Note that states are ordered (as shown above); e.g. a vap must be in the
IEEE80211_S_RUN or “greater” before it can transmit frames. Certain
net80211 data are valid only in certain states; e.g. the iv_bsschan that
specifies the channel for the operating BSS should never be used except
in IEEE80211_S_RUN or greater.
State machine changes are typically handled internal to the net80211
layer in response to ioctl(2) requests, received frames, or external
events such as a beacon miss. The ieee80211_new_state() function is used
to initiate a state machine change on a vap. The new state and an
optional argument are supplied. The request is initially processed to
handle coordination of multiple vaps. For example, only one vap at a
time can be scanning, if multiple vaps request a change to
IEEE80211_S_SCAN the first will be permitted to run and the others will
be deferred until the scan operation completes at which time the selected
channel will be adopted. Similarly net80211 handles coordination of com‐
binations of vaps such as an AP and station vap where the station may
need to roam to follow the AP it is associated to (dragging along the AP
vap to the new channel). Another important coordination is the handling
of IEEE80211_S_CAC and IEEE80211_S_CSA. No more than one vap can ever be
actively changing state at a time. In fact net80211 single-threads the
state machine logic in a dedicated taskqueue(9) thread that is also used
to synchronize work such as scanning and beacon miss handling.
After multi-vap scheduling/coordination is done the per-vap iv_newstate
method is called to carry out the state change work. Drivers use this
entry to setup private state and then dispatch the call to the net80211
layer using the previously defined method pointer (in OOP-parlance they
call the “super method” ).
net80211 handles two state changes specially. On transition to
IEEE80211_S_RUN the IFF_DRV_OACTIVE bit on the vap's transmit queue is
cleared so traffic can flow. On transition to IEEE80211_S_INIT any state
in the scan cache associated with the vap is flushed and any frames pend‐
ing on the transmit queue are flushed.
Drivers are expected to override the iv_newstate method to interpose
their own code and handle setup work required by state changes. Other‐
wise drivers must call ieee80211_start_all() in response to being marked
up through an SIOCSIFFLAGS ioctl request and they should use
ieee80211_suspend_all() and ieee80211_resume_all() to implement sus‐
There is also an ieee80211_stop_all() call to force all vaps to an
IEEE80211_S_INIT state but this should not be needed by a driver; control
is usually handled by net80211 or, in the case of card eject or vap
destroy, work will be initiated outside the driver.
SEE ALSOioctl(2), wpa_supplicant(8), ieee80211(9), ifnet(9), taskqueue(9)HISTORY
The state machine concept was part of the original ieee80211 code base
that first appeared in NetBSD 1.5,
BSD August 4, 2009 BSD