242 lines
8.0 KiB
Groff
242 lines
8.0 KiB
Groff
.\"
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.\" Copyright (c) 2009 Sam Leffler, Errno Consulting
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd August 4, 2009
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.Dt IEEE80211_PROTO 9
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.Os
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.Sh NAME
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.Nm ieee80211_proto
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.Nd 802.11 state machine support
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.Sh SYNOPSIS
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.In net80211/ieee80211_var.h
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.Pp
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.Ft void
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.Fn ieee80211_start_all "struct ieee80211com *"
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.Ft void
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.Fn ieee80211_stop_all "struct ieee80211com *"
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.Ft void
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.Fn ieee80211_suspend_all "struct ieee80211com *"
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.Ft void
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.Fn ieee80211_resume_all "struct ieee80211com *"
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.Pp
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.Dv enum ieee80211_state ;
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.Ft int
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.Fn ieee80211_new_state "struct ieee80211vap *" "enum ieee80211_state" "int"
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.Pp
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.Ft void
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.Fn ieee80211_wait_for_parent "struct ieee80211com *"
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.Sh DESCRIPTION
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The
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.Nm net80211
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layer that supports 802.11 device drivers uses a state machine
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to control operation of vaps.
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These state machines vary according to the vap operating mode.
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Station mode state machines follow the 802.11 MLME states
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in the protocol specification.
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Other state machines are simpler and reflect operational work
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such as scanning for a BSS or automatically selecting a channel to
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operate on.
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When multiple vaps are operational the state machines are used to
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coordinate operation such as choosing a channel.
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The state machine mechanism also serves to bind the
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.Nm net80211
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layer to a driver; this is described more below.
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.Pp
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The following states are defined for state machines:
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.Bl -tag -width IEEE80211_S_ASSOC
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.It Dv IEEE80211_S_INIT
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Default/initial state.
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A vap in this state should not hold any dynamic state (e.g. entries
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for associated stations in the node table).
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The driver must quiesce the hardware; e.g. there should be no
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interrupts firing.
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.It Dv IEEE80211_S_SCAN
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Scanning for a BSS or choosing a channel to operate on.
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Note that scanning can also take place in other states (e.g. when
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background scanning is active); this state is entered when
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initially bringing a vap to an operational state or after an
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event such as a beacon miss (in station mode).
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.It Dv IEEE80211_S_AUTH
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Authenticating to an access point (in station mode).
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This state is normally reached from
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.Dv IEEE80211_S_SCAN
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after selecting a BSS, but may also be reached from
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.Dv IEEE80211_S_ASSOC
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or
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.Dv IEEE80211_S_RUN
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if the authentication handshake fails.
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.It Dv IEEE80211_S_ASSOC
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Associating to an access point (in station mode).
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This state is reached from
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.Dv IEEE80211_S_AUTH
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after successfully authenticating or from
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.Dv IEEE80211_S_RUN
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if a DisAssoc frame is received.
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.It Dv IEEE80211_S_CAC
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Doing Channel Availability Check (CAC).
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This state is entered only when DFS is enabled and the channel selected
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for operation requires CAC.
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.It Dv IEEE80211_S_RUN
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Operational.
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In this state a vap can transmit data frames, accept requests for
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stations associating, etc.
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Beware that data traffic is also gated by whether the associated
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.Dq port
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is authorized.
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When WPA/802.11i/802.1x is operational authorization may happen separately;
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e.g. in station mode
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.Xr wpa_supplicant 8
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must complete the handshakes and plumb the necessary keys before a port
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is authorized.
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In this state a BSS is operational and associated state is valid and may
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be used; e.g.
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.Vt ic_bss
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and
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.Vt ic_bsschan
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are guaranteed to be usable.
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.It Dv IEEE80211_S_CSA
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Channel Switch Announcement (CSA) is pending.
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This state is reached only from
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.Dv IEEE80211_S_RUN
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when either a CSA is received from an access point (in station mode)
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or the local station is preparing to change channel.
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In this state traffic may be muted depending on the Mute setting in the CSA.
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.It Dv IEEE80211_S_SLEEP
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Asleep to save power (in station mode).
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This state is reached only from
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.Dv IEEE80211_S_RUN
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when power save operation is enabled and the local station is deemed
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sufficiently idle to enter low power mode.
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.El
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.Pp
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Note that states are ordered (as shown above);
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e.g. a vap must be in the
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.Dv IEEE80211_S_RUN
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or
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.Dq greater
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before it can transmit frames.
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Certain
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.Nm net80211
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data are valid only in certain states; e.g. the
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.Vt iv_bsschan
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that specifies the channel for the operating BSS should never be used
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except in
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.Dv IEEE80211_S_RUN
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or greater.
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.Sh STATE CHANGES
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State machine changes are typically handled internal to the
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.Nm net80211
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layer in response to
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.Xr ioctl 2
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requests, received frames, or external events such as a beacon miss.
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The
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.Fn ieee80211_new_state
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function is used to initiate a state machine change on a vap.
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The new state and an optional argument are supplied.
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The request is initially processed to handle coordination of multiple vaps.
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For example, only one vap at a time can be scanning, if multiple vaps
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request a change to
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.Dv IEEE80211_S_SCAN
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the first will be permitted to run and the others will be
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.Em deferred
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until the scan operation completes at which time the selected channel
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will be adopted.
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Similarly
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.Nm net80211
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handles coordination of combinations of vaps such as an AP and station vap
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where the station may need to roam to follow the AP it is associated to
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(dragging along the AP vap to the new channel).
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Another important coordination is the handling of
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.Dv IEEE80211_S_CAC
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and
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.Dv IEEE80211_S_CSA .
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No more than one vap can ever be actively changing state at a time.
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In fact
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.Nm net80211
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single-threads the state machine logic in a dedicated
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.Xr taskqueue 9
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thread that is also used to synchronize work such as scanning and
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beacon miss handling.
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.Pp
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After multi-vap scheduling/coordination is done the per-vap
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.Vt iv_newstate
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method is called to carry out the state change work.
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Drivers use this entry to setup private state and then dispatch
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the call to the
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.Nm net80211
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layer using the previously defined method pointer (in OOP-parlance they
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call the
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.Dq super method
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).
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.Pp
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.Nm net80211
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handles two state changes specially.
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On transition to
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.Dv IEEE80211_S_RUN
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the
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.Dv IFF_DRV_OACTIVE
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bit on the vap's transmit queue is cleared so traffic can flow.
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On transition to
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.Dv IEEE80211_S_INIT
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any state in the scan cache associated with the vap is flushed
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and any frames pending on the transmit queue are flushed.
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.Sh DRIVER INTEGRATION
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Drivers are expected to override the
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.Vt iv_newstate
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method to interpose their own code and handle setup work required
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by state changes.
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Otherwise drivers must call
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.Fn ieee80211_start_all
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in response to being marked up through an
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.Dv SIOCSIFFLAGS
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ioctl request and they should use
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.Fn ieee80211_suspend_all
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and
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.Fn ieee80211_resume_all
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to implement suspend/resume support.
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.Pp
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There is also an
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.Fn ieee80211_stop_all
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call to force all vaps to an
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.Dv IEEE80211_S_INIT
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state but this should not be needed by a driver; control is usually
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handled by
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.Nm net80211
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or, in the case of card eject or vap destroy,
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work will be initiated outside the driver.
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.Sh SEE ALSO
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.Xr ioctl 2 ,
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.Xr wpa_supplicant 8 ,
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.Xr ieee80211 9 ,
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.Xr ifnet 9 ,
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.Xr taskqueue 9
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.Sh HISTORY
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The state machine concept was part of the original
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.Nm ieee80211
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code base that first appeared in
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.Nx 1.5 .
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