freebsd-nq/share/man/man9/ieee80211_proto.9

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.Dd August 4, 2009
.Dt IEEE80211_PROTO 9
.Os
.Sh NAME
.Nm ieee80211_proto
.Nd 802.11 state machine support
.Sh SYNOPSIS
.In net80211/ieee80211_var.h
.Pp
.Ft void
.Fn ieee80211_start_all "struct ieee80211com *"
.Ft void
.Fn ieee80211_stop_all "struct ieee80211com *"
.Ft void
.Fn ieee80211_suspend_all "struct ieee80211com *"
.Ft void
.Fn ieee80211_resume_all "struct ieee80211com *"
.Pp
.Dv enum ieee80211_state ;
.Ft int
.Fn ieee80211_new_state "struct ieee80211vap *" "enum ieee80211_state" "int"
.Pp
.Ft void
.Fn ieee80211_wait_for_parent "struct ieee80211com *"
.Sh DESCRIPTION
The
.Nm net80211
layer that supports 802.11 device drivers uses a state machine
to control operation of vaps.
These state machines vary according 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
.Nm net80211
layer to a driver; this is described more below.
.Pp
The following states are defined for state machines:
.Bl -tag -width IEEE80211_S_ASSOC
.It Dv 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 firing.
.It Dv 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).
.It Dv IEEE80211_S_AUTH
Authenticating to an access point (in station mode).
This state is normally reached from
.Dv IEEE80211_S_SCAN
after selecting a BSS, but may also be reached from
.Dv IEEE80211_S_ASSOC
or
.Dv IEEE80211_S_RUN
if the authentication handshake fails.
.It Dv IEEE80211_S_ASSOC
Associating to an access point (in station mode).
This state is reached from
.Dv IEEE80211_S_AUTH
after successfully authenticating or from
.Dv IEEE80211_S_RUN
if a DisAssoc frame is received.
.It Dv 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.
.It Dv 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
.Dq port
is authorized.
When WPA/802.11i/802.1x is operational authorization may happen separately;
e.g. in station mode
.Xr 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.
.Vt ic_bss
and
.Vt ic_bsschan
are guaranteed to be usable.
.It Dv IEEE80211_S_CSA
Channel Switch Announcement (CSA) is pending.
This state is reached only from
.Dv 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.
.It Dv IEEE80211_S_SLEEP
Asleep to save power (in station mode).
This state is reached only from
.Dv IEEE80211_S_RUN
when power save operation is enabled and the local station is deemed
sufficiently idle to enter low power mode.
.El
.Pp
Note that states are ordered (as shown above);
e.g. a vap must be in the
.Dv IEEE80211_S_RUN
or
.Dq greater
before it can transmit frames.
Certain
.Nm net80211
data are valid only in certain states; e.g. the
.Vt iv_bsschan
that specifies the channel for the operating BSS should never be used
except in
.Dv IEEE80211_S_RUN
or greater.
.Sh STATE CHANGES
State machine changes are typically handled internal to the
.Nm net80211
layer in response to
.Xr ioctl 2
requests, received frames, or external events such as a beacon miss.
The
.Fn 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
.Dv IEEE80211_S_SCAN
the first will be permitted to run and the others will be
.Em deferred
until the scan operation completes at which time the selected channel
will be adopted.
Similarly
.Nm net80211
handles coordination of combinations 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
.Dv IEEE80211_S_CAC
and
.Dv IEEE80211_S_CSA .
No more than one vap can ever be actively changing state at a time.
In fact
.Nm net80211
single-threads the state machine logic in a dedicated
.Xr taskqueue 9
thread that is also used to synchronize work such as scanning and
beacon miss handling.
.Pp
After multi-vap scheduling/coordination is done the per-vap
.Vt 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
.Nm net80211
layer using the previously defined method pointer (in OOP-parlance they
call the
.Dq super method
).
.Pp
.Nm net80211
handles two state changes specially.
On transition to
.Dv IEEE80211_S_RUN
the
.Dv IFF_DRV_OACTIVE
bit on the vap's transmit queue is cleared so traffic can flow.
On transition to
.Dv IEEE80211_S_INIT
any state in the scan cache associated with the vap is flushed
and any frames pending on the transmit queue are flushed.
.Sh DRIVER INTEGRATION
Drivers are expected to override the
.Vt iv_newstate
method to interpose their own code and handle setup work required
by state changes.
Otherwise drivers must call
.Fn ieee80211_start_all
in response to being marked up through an
.Dv SIOCSIFFLAGS
ioctl request and they should use
.Fn ieee80211_suspend_all
and
.Fn ieee80211_resume_all
to implement suspend/resume support.
.Pp
There is also an
.Fn ieee80211_stop_all
call to force all vaps to an
.Dv IEEE80211_S_INIT
state but this should not be needed by a driver; control is usually
handled by
.Nm net80211
or, in the case of card eject or vap destroy,
work will be initiated outside the driver.
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr wpa_supplicant 8 ,
.Xr ieee80211 9 ,
.Xr ifnet 9 ,
.Xr taskqueue 9
.Sh HISTORY
The state machine concept was part of the original
.Nm ieee80211
code base that first appeared in
.Nx 1.5 .