195 lines
6.2 KiB
Groff
195 lines
6.2 KiB
Groff
.\"
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.\" Copyright (c) 2004 Bruce M. Simpson <bms@spc.org>
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.\" Copyright (c) 2004 Darron Broad <darron@kewl.org>
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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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.\" $Id: ieee80211_output.9,v 1.5 2004/03/04 12:31:18 bruce Exp $
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.\"
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.Dd August 4, 2009
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.Dt IEEE80211_OUTPUT 9
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.Os
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.Sh NAME
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.Nm ieee80211_output
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.Nd software 802.11 stack output functions
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.Sh SYNOPSIS
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.In net80211/ieee80211_var.h
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.\"
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.Ft int
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.Fn M_WME_GETAC "struct mbuf *"
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.\"
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.Ft int
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.Fn M_SEQNO_GET "struct mbuf *"
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.\"
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.Ft struct ieee80211_key *
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.Fn ieee80211_crypto_encap "struct ieee80211_node *" "struct mbuf *"
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.\"
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.Ft void
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.Fo ieee80211_process_callback
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.Fa "struct ieee80211_node *"
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.Fa "struct mbuf *"
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.Fa "int"
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.Fc
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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 handles most of the
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work required to transmit frames.
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Drivers usually receive fully-encapsulated 802.11 frames that
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have been classified and assigned a transmit priority;
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all that is left is to do
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crypto encapsulation,
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prepare any hardware-specific state,
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and
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push the packet out to the device.
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Outbound frames are either generated by the
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.Nm net80211
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layer (e.g. management frames) or are passed down
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from upper layers through the
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.Xr ifnet 9
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transmit queue.
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Data frames passed down for transmit flow through
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.Nm net80211
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which handles aggregation, 802.11 encapsulation, and then
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dispatches the frames to the driver through it's transmit queue.
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.Pp
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There are two control paths by which frames reach a driver for transmit.
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Data packets are queued to the device's
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.Vt if_snd
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queue and the driver's
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.Vt if_start
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method is called.
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Other frames are passed down using the
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.Vt ic_raw_xmit
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method without queueing (unless done by the driver).
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The raw transmit path may include data frames from user applications
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that inject them through
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.Xr bpf 4
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and NullData frames generated by
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.Nm net80211
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to probe for idle stations (when operating as an access point).
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.Pp
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.Nm net80211
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handles all state-related bookkeeping and management for the handling
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of data frames.
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Data frames are only transmit for a vap in the
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.Dv IEEE80211_S_RUN
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state; there is no need, for example, to check for frames sent down
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when CAC or CSA is active.
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Similarly,
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.Nm net80211
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handles activities such as background scanning and power save mode,
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frames will not be sent to a driver unless it is operating on the
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BSS channel with
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.Dq full power .
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.Pp
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All frames passed to a driver for transmit hold a reference to a
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node table entry in the
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.Vt m_pkthdr.rcvif
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field.
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The node is associated with the frame destination.
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Typically it is the receiver's entry but in some situations it may be
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a placeholder entry or the
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.Dq next hop station
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(such as in a mesh network).
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In all cases the reference must be reclaimed with
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.Fn ieee80211_free_node
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when the transmit work is completed.
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The rule to remember is:
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.Nm net80211
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passes responsibility for the
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.Vt mbuf
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and
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.Dq node reference
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to the driver with each frame it hands off for transmit.
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.Sh PACKET CLASSIFICATION
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All frames passed by
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.Nm net80211
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for transmit are assigned a priority based on any vlan tag
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assigned to the receiving station and/or any Diffserv setting
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in an IP or IPv6 header.
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If both vlan and Diffserv priority are present the higher of the
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two is used.
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If WME/WMM is being used then any ACM policy (in station mode) is
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also enforced.
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The resulting AC is attached to the mbuf and may be read back using the
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.Fn M_WME_GETAC
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macro.
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.Pp
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PAE/EAPOL frames are tagged with an
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.Dv M_EAPOL
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mbuf flag; drivers should transmit them with care, usually by
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using the transmit rate for management frames.
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Multicast/broadcast frames are marked with the
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.Dv M_MCAST
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mbuf flag.
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Frames coming out of a station's power save queue and that have
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more frames immediately following are marked with the
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.Dv M_MORE_DATA
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mbuf flag.
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Such frames will be queued consecutively in the driver's
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.Vt if_snd
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queue and drivers should preserve the ordering when passing
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them to the device.
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.Sh FRAGMENTED FRAMES
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The
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.Nm net80211
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layer will fragment data frames according to the setting of
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.Vt iv_fragthreshold
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if a driver marks the
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.Dv IEEE80211_C_TXFRAG
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capability.
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Fragmented frames are placed
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in the devices transmit queue with the fragments chained together with
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.Vt m_nextpkt .
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Each frame is marked with the
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.Dv M_FRAG
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mbuf flag, and the first and last are marked with
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.Dv M_FIRSTFRAG
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and
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.Dv M_LASTFRAG ,
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respectively.
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Drivers are expected to process all fragments or none.
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.Sh TRANSMIT CALLBACKS
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Frames sent by
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.Nm net80211
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may be tagged with the
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.Dv M_TXCB
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mbuf flag to indicate a callback should be done
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when their transmission completes.
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The callback is done using
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.Fn ieee80211_process_callback
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with the last parameter set to a non-zero value if an error occurred
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and zero otherwise.
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Note
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.Nm net80211
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understands that drivers may be incapable of determining status;
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a device may not report if an ACK frame is received and/or a device may queue
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transmit requests in its hardware and only report status on whether
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the frame was successfully queued.
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.Sh SEE ALSO
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.Xr bpf 4
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.Xr ieee80211 9 ,
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.Xr ifnet 9
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