xref: /freebsd/share/man/man9/ieee80211.9 (revision bcf5c7a8b1dcdcd5f27c1aa694f66208dc07a0dd)
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2.\" Copyright (c) 2004 Bruce M. Simpson <bms@spc.org>
3.\" Copyright (c) 2004 Darron Broad <darron@kewl.org>
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28.\" $FreeBSD$
29.\"
30.Dd January 26, 2021
31.Dt IEEE80211 9
32.Os
33.Sh NAME
34.Nm IEEE80211
35.Nd 802.11 network layer
36.Sh SYNOPSIS
37.In net80211/ieee80211_var.h
38.Ft void
39.Fn ieee80211_ifattach "struct ieee80211com *ic"
40.Ft void
41.Fn ieee80211_ifdetach "struct ieee80211com *ic"
42.Ft int
43.Fn ieee80211_mhz2ieee "u_int freq" "u_int flags"
44.Ft int
45.Fn ieee80211_chan2ieee "struct ieee80211com *ic" "const struct ieee80211_channel *c"
46.Ft u_int
47.Fn ieee80211_ieee2mhz "u_int chan" "u_int flags"
48.Ft int
49.Fn ieee80211_media_change "struct ifnet *ifp"
50.Ft void
51.Fn ieee80211_media_status "struct ifnet *ifp" "struct ifmediareq *imr"
52.Ft int
53.Fn ieee80211_setmode "struct ieee80211com *ic" "enum ieee80211_phymode mode"
54.Ft enum ieee80211_phymode
55.Fo ieee80211_chan2mode
56.Fa "const struct ieee80211_channel *chan"
57.Fc
58.Ft int
59.Fo ieee80211_rate2media
60.Fa "struct ieee80211com *ic" "int rate" "enum ieee80211_phymode mode"
61.Fc
62.Ft int
63.Fn ieee80211_media2rate "int mword"
64.Sh DESCRIPTION
65IEEE 802.11 device drivers are written to use the infrastructure provided
66by the
67.Nm
68software layer.
69This software provides a support framework for drivers that includes
70ifnet cloning, state management, and a user management API by which
71applications interact with 802.11 devices.
72Most drivers depend on the
73.Nm
74layer for protocol services but devices that off-load functionality
75may bypass the layer to connect directly to the device.
76.Pp
77A
78.Nm
79device driver implements a virtual radio API that is exported to
80users through network interfaces (aka vaps) that are cloned from the
81underlying device.
82These interfaces have an operating mode
83(station, adhoc, hostap, wds, monitor, etc.\&)
84that is fixed for the lifetime of the interface.
85Devices that can support multiple concurrent interfaces allow
86multiple vaps to be cloned.
87This enables construction of interesting applications such as
88an AP vap and one or more WDS vaps
89or multiple AP vaps, each with a different security model.
90The
91.Nm
92layer virtualizes most 802.11 state
93and coordinates vap state changes including scheduling multiple vaps.
94State that is not virtualized includes the current channel and
95WME/WMM parameters.
96Protocol processing is typically handled entirely in the
97.Nm
98layer with drivers responsible purely for moving data between the host
99and device.
100Similarly,
101.Nm
102handles most
103.Xr ioctl 2
104requests without entering the driver;
105instead drivers are notified of state changes that
106require their involvement.
107.Pp
108The virtual radio interface defined by the
109.Nm
110layer means that drivers must be structured to follow specific rules.
111Drivers that support only a single interface at any time must still
112follow these rules.
113.Pp
114Most of these functions require that attachment to the stack is performed
115before calling.
116.Pp
117.\"
118The
119.Fn ieee80211_ifattach
120function attaches the wireless network interface
121.Fa ic
122to the 802.11 network stack layer.
123This function must be called before using any of the
124.Nm
125functions which need to store driver state across invocations.
126.Pp
127.\"
128The
129.Fn ieee80211_ifdetach
130function frees any
131.Nm
132structures associated with the driver, and performs Ethernet and BPF
133detachment on behalf of the caller.
134.Pp
135.\"
136The
137.Fn ieee80211_mhz2ieee
138utility function converts the frequency
139.Fa freq
140(specified in MHz) to an IEEE 802.11 channel number.
141The
142.Fa flags
143argument is a hint which specifies whether the frequency is in
144the 2GHz ISM band
145.Pq Vt IEEE80211_CHAN_2GHZ
146or the 5GHz band
147.Pq Vt IEEE80211_CHAN_5GHZ ;
148appropriate clipping of the result is then performed.
149.Pp
150.\"
151The
152.Fn ieee80211_chan2ieee
153function converts the channel specified in
154.Fa *c
155to an IEEE channel number for the driver
156.Fa ic .
157If the conversion would be invalid, an error message is printed to the
158system console.
159This function REQUIRES that the driver is hooked up to the
160.Nm
161subsystem.
162.Pp
163.\"
164The
165.Fn ieee80211_ieee2mhz
166utility function converts the IEEE channel number
167.Ft chan
168to a frequency (in MHz).
169The
170.Fa flags
171argument is a hint which specifies whether the frequency is in
172the 2GHz ISM band
173.Pq Vt IEEE80211_CHAN_2GHZ
174or the 5GHz band
175.Pq Vt IEEE80211_CHAN_5GHZ ;
176appropriate clipping of the result is then performed.
177.Pp
178.\"
179The
180.Fn ieee80211_media_status
181and
182.Fn ieee80211_media_change
183functions are device-independent handlers for
184.Vt ifmedia
185commands and are not intended to be called directly.
186.Pp
187.\"
188The
189.Fn ieee80211_setmode
190function is called from within the 802.11 stack to change the mode
191of the driver's PHY; it is not intended to be called directly.
192.Pp
193.\"
194The
195.Fn ieee80211_chan2mode
196function returns the PHY mode required for use with the channel
197.Fa chan .
198This is typically used when selecting a rate set, to be advertised in
199beacons, for example.
200.Pp
201.\"
202The
203.Fn ieee80211_rate2media
204function converts the bit rate
205.Fa rate
206(measured in units of 0.5Mbps) to an
207.Vt ifmedia
208sub-type, for the device
209.Fa ic
210running in PHY mode
211.Fa mode .
212The
213.Fn ieee80211_media2rate
214performs the reverse of this conversion, returning the bit rate (in 0.5Mbps
215units) corresponding to an
216.Vt ifmedia
217sub-type.
218.
219.Sh DATA STRUCTURES
220The virtual radio architecture splits state between a single per-device
221.Vt ieee80211com
222structure and one or more
223.Vt ieee80211vap
224structures.
225Drivers are expected to setup various shared state in these structures
226at device attach and during vap creation but otherwise should treat them
227as read-only.
228The
229.Vt ieee80211com
230structure is allocated by the
231.Nm
232layer as adjunct data to a device's
233.Vt ifnet ;
234it is accessed through the
235.Vt if_l2com
236structure member.
237The
238.Vt ieee80211vap
239structure is allocated by the driver in the
240.Dq vap create
241method
242and should be extended with any driver-private state.
243This technique of giving the driver control to allocate data structures
244is used for other
245.Nm
246data structures and should be exploited to maintain driver-private state
247together with public
248.Nm
249state.
250.Pp
251The other main data structures are the station, or node, table
252that tracks peers in the local BSS, and the channel table that defines
253the current set of available radio channels.
254Both tables are bound to the
255.Vt ieee80211com
256structure and shared by all vaps.
257Long-lasting references to a node are counted to guard against
258premature reclamation.
259In particular every packet sent/received holds a node reference
260(either explicitly for transmit or implicitly on receive).
261.Pp
262The
263.Vt ieee80211com
264and
265.Vt ieee80211vap
266structures also hold a collection of method pointers that drivers
267fill-in and/or override to take control of certain operations.
268These methods are the primary way drivers are bound to the
269.Nm
270layer and are described below.
271.Sh DRIVER ATTACH/DETACH
272Drivers attach to the
273.Nm
274layer with the
275.Fn ieee80211_ifattach
276function.
277The driver is expected to allocate and setup any device-private
278data structures before passing control.
279The
280.Vt ieee80211com
281structure must be pre-initialized with state required to setup the
282.Nm
283layer:
284.Bl -tag -width ic_channels
285.It Dv ic_ifp
286Backpointer to the physical device's ifnet.
287.It Dv ic_caps
288Device/driver capabilities; see below for a complete description.
289.It Dv ic_channels
290Table of channels the device is capable of operating on.
291This is initially provided by the driver but may be changed
292through calls that change the regulatory state.
293.It Dv ic_nchan
294Number of entries in
295.Dv ic_channels .
296.El
297.Pp
298On return from
299.Fn ieee80211_ifattach
300the driver is expected to override default callback functions in the
301.Vt ieee80211com
302structure to register it's private routines.
303Methods marked with a
304.Dq *
305must be provided by the driver.
306.Bl -tag -width ic_channels
307.It Dv ic_vap_create*
308Create a vap instance of the specified type (operating mode).
309Any fixed BSSID and/or MAC address is provided.
310Drivers that support multi-bssid operation may honor the requested BSSID
311or assign their own.
312.It Dv ic_vap_delete*
313Destroy a vap instance created with
314.Dv ic_vap_create .
315.It Dv ic_getradiocaps
316Return the list of calibrated channels for the radio.
317The default method returns the current list of channels
318(space permitting).
319.It Dv ic_setregdomain
320Process a request to change regulatory state.
321The routine may reject a request or constrain changes (e.g. reduce
322transmit power caps).
323The default method accepts all proposed changes.
324.It Dv ic_send_mgmt
325Send an 802.11 management frame.
326The default method fabricates the frame using
327.Nm
328state and passes it to the driver through the
329.Dv ic_raw_xmit
330method.
331.It Dv ic_raw_xmit
332Transmit a raw 802.11 frame.
333The default method drops the frame and generates a message on the console.
334.It Dv ic_updateslot
335Update hardware state after an 802.11 IFS slot time change.
336There is no default method; the pointer may be NULL in which case
337it will not be used.
338.It Dv ic_update_mcast
339Update hardware for a change in the multicast packet filter.
340The default method prints a console message.
341.It Dv ic_update_promisc
342Update hardware for a change in the promiscuous mode setting.
343The default method prints a console message.
344.It Dv ic_newassoc
345Update driver/device state for association to a new AP (in station mode)
346or when a new station associates (e.g. in AP mode).
347There is no default method; the pointer may be NULL in which case
348it will not be used.
349.It Dv ic_node_alloc
350Allocate and initialize a
351.Vt ieee80211_node
352structure.
353This method cannot sleep.
354The default method allocates zero'd memory using
355.Xr malloc 9 .
356Drivers should override this method to allocate extended storage
357for their own needs.
358Memory allocated by the driver must be tagged with
359.Dv M_80211_NODE
360to balance the memory allocation statistics.
361.It Dv ic_node_free
362Reclaim storage of a node allocated by
363.Dv ic_node_alloc  .
364Drivers are expected to
365.Em interpose
366their own method to cleanup private state but must call through
367this method to allow
368.Nm
369to reclaim it's private state.
370.It Dv ic_node_cleanup
371Cleanup state in a
372.Vt ieee80211_node
373created by
374.Dv ic_node_alloc .
375This operation is distinguished from
376.Dv ic_node_free
377in that it may be called long before the node is actually reclaimed
378to cleanup adjunct state.
379This can happen, for example, when a node must not be reclaimed
380due to references held by packets in the transmit queue.
381Drivers typically interpose
382.Dv ic_node_cleanup
383instead of
384.Dv ic_node_free .
385.It Dv ic_node_age
386Age, and potentially reclaim, resources associated with a node.
387The default method ages frames on the power-save queue (in AP mode)
388and pending frames in the receive reorder queues (for stations using A-MPDU).
389.It Dv ic_node_drain
390Reclaim all optional resources associated with a node.
391This call is used to free up resources when they are in short supply.
392.It Dv ic_node_getrssi
393Return the Receive Signal Strength Indication (RSSI) in .5 dBm units for
394the specified node.
395This interface returns a subset of the information
396returned by
397.Dv ic_node_getsignal .
398The default method calculates a filtered average over the last ten
399samples passed in to
400.Xr ieee80211_input 9
401or
402.Xr ieee80211_input_all 9 .
403.It Dv ic_node_getsignal
404Return the RSSI and noise floor (in .5 dBm units) for a station.
405The default method calculates RSSI as described above;
406the noise floor returned is the last value supplied to
407.Xr ieee80211_input 9
408or
409.Xr ieee80211_input_all 9 .
410.It Dv ic_node_getmimoinfo
411Return MIMO radio state for a station in support of the
412.Dv IEEE80211_IOC_STA_INFO
413ioctl request.
414The default method returns nothing.
415.It Dv ic_scan_start*
416Prepare driver/hardware state for scanning.
417This callback is done in a sleepable context.
418.It Dv ic_scan_end*
419Restore driver/hardware state after scanning completes.
420This callback is done in a sleepable context.
421.It Dv ic_set_channel*
422Set the current radio channel using
423.Vt ic_curchan .
424This callback is done in a sleepable context.
425.It Dv ic_scan_curchan
426Start scanning on a channel.
427This method is called immediately after each channel change
428and must initiate the work to scan a channel and schedule a timer
429to advance to the next channel in the scan list.
430This callback is done in a sleepable context.
431The default method handles active scan work (e.g. sending ProbeRequest
432frames), and schedules a call to
433.Xr ieee80211_scan_next 9
434according to the maximum dwell time for the channel.
435Drivers that off-load scan work to firmware typically use this method
436to trigger per-channel scan activity.
437.It Dv ic_scan_mindwell
438Handle reaching the minimum dwell time on a channel when scanning.
439This event is triggered when one or more stations have been found on
440a channel and the minimum dwell time has been reached.
441This callback is done in a sleepable context.
442The default method signals the scan machinery to advance
443to the next channel as soon as possible.
444Drivers can use this method to preempt further work (e.g. if scanning
445is handled by firmware) or ignore the request to force maximum dwell time
446on a channel.
447.It Dv ic_recv_action
448Process a received Action frame.
449The default method points to
450.Xr ieee80211_recv_action 9
451which provides a mechanism for setting up handlers for each Action frame class.
452.It Dv ic_send_action
453Transmit an Action frame.
454The default method points to
455.Xr ieee80211_send_action 9
456which provides a mechanism for setting up handlers for each Action frame class.
457.It Dv ic_ampdu_enable
458Check if transmit A-MPDU should be enabled for the specified station and AC.
459The default method checks a per-AC traffic rate against a per-vap
460threshold to decide if A-MPDU should be enabled.
461This method also rate-limits ADDBA requests so that requests are not
462made too frequently when a receiver has limited resources.
463.It Dv ic_addba_request
464Request A-MPDU transmit aggregation.
465The default method sets up local state and issues an
466ADDBA Request Action frame.
467Drivers may interpose this method if they need to setup private state
468for handling transmit A-MPDU.
469.It Dv ic_addb_response
470Process a received ADDBA Response Action frame and setup resources as
471needed for doing transmit A-MPDU.
472.It Dv ic_addb_stop
473Shutdown an A-MPDU transmit stream for the specified station and AC.
474The default method reclaims local state after sending a DelBA Action frame.
475.It Dv ic_bar_response
476Process a response to a transmitted BAR control frame.
477.It Dv ic_ampdu_rx_start
478Prepare to receive A-MPDU data from the specified station for the TID.
479.It Dv ic_ampdu_rx_stop
480Terminate receipt of A-MPDU data from the specified station for the TID.
481.El
482.Pp
483Once the
484.Nm
485layer is attached to a driver there are two more steps typically done
486to complete the work:
487.Bl -enum
488.It
489Setup
490.Dq radiotap support
491for capturing raw 802.11 packets that pass through the device.
492This is done with a call to
493.Xr ieee80211_radiotap_attach 9 .
494.It
495Do any final device setup like enabling interrupts.
496.El
497.Pp
498State is torn down and reclaimed with a call to
499.Fn ieee80211_ifdetach .
500Note this call may result in multiple callbacks into the driver
501so it should be done before any critical driver state is reclaimed.
502On return from
503.Fn ieee80211_ifdetach
504all associated vaps and ifnet structures are reclaimed or inaccessible
505to user applications so it is safe to teardown driver state without
506worry about being re-entered.
507The driver is responsible for calling
508.Xr if_free 9
509on the ifnet it allocated for the physical device.
510.Sh DRIVER CAPABILITIES
511Driver/device capabilities are specified using several sets of flags
512in the
513.Vt ieee80211com
514structure.
515General capabilities are specified by
516.Vt ic_caps .
517Hardware cryptographic capabilities are specified by
518.Vt ic_cryptocaps .
519802.11n capabilities, if any, are specified by
520.Vt ic_htcaps .
521The
522.Nm
523layer propagates a subset of these capabilities to each vap through
524the equivalent fields:
525.Vt iv_caps ,
526.Vt iv_cryptocaps ,
527and
528.Vt iv_htcaps .
529The following general capabilities are defined:
530.Bl -tag -width IEEE80211_C_8023ENCAP
531.It Dv IEEE80211_C_STA
532Device is capable of operating in station (aka Infrastructure) mode.
533.It Dv IEEE80211_C_8023ENCAP
534Device requires 802.3-encapsulated frames be passed for transmit.
535By default
536.Nm
537will encapsulate all outbound frames as 802.11 frames (without a PLCP header).
538.It Dv IEEE80211_C_FF
539Device supports Atheros Fast-Frames.
540.It Dv IEEE80211_C_TURBOP
541Device supports Atheros Dynamic Turbo mode.
542.It Dv IEEE80211_C_IBSS
543Device is capable of operating in adhoc/IBSS mode.
544.It Dv IEEE80211_C_PMGT
545Device supports dynamic power-management (aka power save) in station mode.
546.It Dv IEEE80211_C_HOSTAP
547Device is capable of operating as an Access Point in Infrastructure mode.
548.It Dv IEEE80211_C_AHDEMO
549Device is capable of operating in Adhoc Demo mode.
550In this mode the device is used purely to send/receive raw 802.11 frames.
551.It Dv IEEE80211_C_SWRETRY
552Device supports software retry of transmitted frames.
553.It Dv IEEE80211_C_TXPMGT
554Device support dynamic transmit power changes on transmitted frames;
555also known as Transmit Power Control (TPC).
556.It Dv IEEE80211_C_SHSLOT
557Device supports short slot time operation (for 802.11g).
558.It Dv IEEE80211_C_SHPREAMBLE
559Device supports short preamble operation (for 802.11g).
560.It Dv IEEE80211_C_MONITOR
561Device is capable of operating in monitor mode.
562.It Dv IEEE80211_C_DFS
563Device supports radar detection and/or DFS.
564DFS protocol support can be handled by
565.Nm
566but the device must be capable of detecting radar events.
567.It Dv IEEE80211_C_MBSS
568Device is capable of operating in MeshBSS (MBSS) mode
569(as defined by 802.11s Draft 3.0).
570.It Dv IEEE80211_C_WPA1
571Device supports WPA1 operation.
572.It Dv IEEE80211_C_WPA2
573Device supports WPA2/802.11i operation.
574.It Dv IEEE80211_C_BURST
575Device supports frame bursting.
576.It Dv IEEE80211_C_WME
577Device supports WME/WMM operation
578(at the moment this is mostly support for sending and receiving
579QoS frames with EDCF).
580.It Dv IEEE80211_C_WDS
581Device supports transmit/receive of 4-address frames.
582.It Dv IEEE80211_C_BGSCAN
583Device supports background scanning.
584.It Dv IEEE80211_C_TXFRAG
585Device supports transmit of fragmented 802.11 frames.
586.It Dv IEEE80211_C_TDMA
587Device is capable of operating in TDMA mode.
588.El
589.Pp
590The follow general crypto capabilities are defined.
591In general
592.Nm
593will fall-back to software support when a device is not capable
594of hardware acceleration of a cipher.
595This can be done on a per-key basis.
596.Nm
597can also handle software
598.Dv Michael
599calculation combined with hardware
600.Dv AES
601acceleration.
602.Bl -tag -width IEEE80211_C_8023ENCAP
603.It Dv IEEE80211_CRYPTO_WEP
604Device supports hardware WEP cipher.
605.It Dv IEEE80211_CRYPTO_TKIP
606Device supports hardware TKIP cipher.
607.It Dv IEEE80211_CRYPTO_AES_OCB
608Device supports hardware AES-OCB cipher.
609.It Dv IEEE80211_CRYPTO_AES_CCM
610Device supports hardware AES-CCM cipher.
611.It Dv IEEE80211_CRYPTO_TKIPMIC
612Device supports hardware Michael for use with TKIP.
613.It Dv IEEE80211_CRYPTO_CKIP
614Devices supports hardware CKIP cipher.
615.El
616.Pp
617The follow general 802.11n capabilities are defined.
618The first capabilities are defined exactly as they appear in the
619802.11n specification.
620Capabilities beginning with IEEE80211_HTC_AMPDU are used solely by the
621.Nm
622layer.
623.Bl -tag -width IEEE80211_C_8023ENCAP
624.It Dv IEEE80211_HTCAP_CHWIDTH40
625Device supports 20/40 channel width operation.
626.It Dv IEEE80211_HTCAP_SMPS_DYNAMIC
627Device supports dynamic SM power save operation.
628.It Dv IEEE80211_HTCAP_SMPS_ENA
629Device supports static SM power save operation.
630.It Dv IEEE80211_HTCAP_GREENFIELD
631Device supports Greenfield preamble.
632.It Dv IEEE80211_HTCAP_SHORTGI20
633Device supports Short Guard Interval on 20MHz channels.
634.It Dv IEEE80211_HTCAP_SHORTGI40
635Device supports Short Guard Interval on 40MHz channels.
636.It Dv IEEE80211_HTCAP_TXSTBC
637Device supports Space Time Block Convolution (STBC) for transmit.
638.It Dv IEEE80211_HTCAP_RXSTBC_1STREAM
639Device supports 1 spatial stream for STBC receive.
640.It Dv IEEE80211_HTCAP_RXSTBC_2STREAM
641Device supports 1-2 spatial streams for STBC receive.
642.It Dv IEEE80211_HTCAP_RXSTBC_3STREAM
643Device supports 1-3 spatial streams for STBC receive.
644.It Dv IEEE80211_HTCAP_MAXAMSDU_7935
645Device supports A-MSDU frames up to 7935 octets.
646.It Dv IEEE80211_HTCAP_MAXAMSDU_3839
647Device supports A-MSDU frames up to 3839 octets.
648.It Dv IEEE80211_HTCAP_DSSSCCK40
649Device supports use of DSSS/CCK on 40MHz channels.
650.It Dv IEEE80211_HTCAP_PSMP
651Device supports PSMP.
652.It Dv IEEE80211_HTCAP_40INTOLERANT
653Device is intolerant of 40MHz wide channel use.
654.It Dv IEEE80211_HTCAP_LSIGTXOPPROT
655Device supports L-SIG TXOP protection.
656.It Dv IEEE80211_HTC_AMPDU
657Device supports A-MPDU aggregation.
658Note that any 802.11n compliant device must support A-MPDU receive
659so this implicitly means support for
660.Em transmit
661of A-MPDU frames.
662.It Dv IEEE80211_HTC_AMSDU
663Device supports A-MSDU aggregation.
664Note that any 802.11n compliant device must support A-MSDU receive
665so this implicitly means support for
666.Em transmit
667of A-MSDU frames.
668.It Dv IEEE80211_HTC_HT
669Device supports High Throughput (HT) operation.
670This capability must be set to enable 802.11n functionality
671in
672.Nm .
673.It Dv IEEE80211_HTC_SMPS
674Device supports MIMO Power Save operation.
675.It Dv IEEE80211_HTC_RIFS
676Device supports Reduced Inter Frame Spacing (RIFS).
677.El
678.Sh SEE ALSO
679.Xr ioctl 2 ,
680.Xr ieee80211_amrr 9 ,
681.Xr ieee80211_beacon 9 ,
682.Xr ieee80211_bmiss 9 ,
683.Xr ieee80211_crypto 9 ,
684.Xr ieee80211_ddb 9 ,
685.Xr ieee80211_input 9 ,
686.Xr ieee80211_node 9 ,
687.Xr ieee80211_output 9 ,
688.Xr ieee80211_proto 9 ,
689.Xr ieee80211_radiotap 9 ,
690.Xr ieee80211_regdomain 9 ,
691.Xr ieee80211_scan 9 ,
692.Xr ieee80211_vap 9 ,
693.Xr ifnet 9 ,
694.Xr malloc 9
695.Sh HISTORY
696The
697.Nm
698series of functions first appeared in
699.Nx 1.5 ,
700and were later ported to
701.Fx 4.6 .
702This man page was updated with the information from
703.Nx
704.Nm
705man page.
706.Sh AUTHORS
707.An -nosplit
708The original
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711man page was written by
712.An Bruce M. Simpson Aq Mt bms@FreeBSD.org
713and
714.An Darron Broad Aq Mt darron@kewl.org .
715