252 lines
8.0 KiB
Groff
252 lines
8.0 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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.\"
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.Dd April 28, 2010
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.Dt IEEE80211_NODE 9
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.Os
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.Sh NAME
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.Nm ieee80211_node
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.Nd software 802.11 stack node management 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 struct ieee80211_node *
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.Fo ieee80211_find_rxnode
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.Fa "struct ieee80211com *"
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.Fa "const struct ieee80211_frame_min *"
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.Fc
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.\"
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.Ft struct ieee80211_node *
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.Fo ieee80211_find_rxnode_withkey
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.Fa "struct ieee80211com *"
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.Fa "const struct ieee80211_frame_min *"
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.Fa "ieee80211_keyix"
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.Fc
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.\"
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.Ft struct ieee80211_node *
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.Fn ieee80211_ref_node "struct ieee80211_node *"
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.\"
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.Ft void
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.Fn ieee80211_unref_node "struct ieee80211_node *"
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.\"
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.Ft void
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.Fn ieee80211_free_node "struct ieee80211_node *"
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.\"
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.Ft void
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.Fo ieee80211_iterate_nodes
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.Fa "struct ieee80211_node_table *"
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.Fa "ieee80211_iter_func *f"
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.Fa "void *arg"
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.Fc
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.\"
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.Ft void
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.Fo ieee80211_dump_nodes
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.Fa "struct ieee80211_node_table *"
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.Fc
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.\"
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.Ft void
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.Fo ieee80211_dump_node
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.Fa "struct ieee80211_node *"
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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 maintains a database of
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peer stations called the
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.Dq node table
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in the
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.Vt ic_sta
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entry of the
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.Vt ieee80211com
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structure.
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Station mode vaps create an entry for the access point
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the station is associated to.
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AP mode vaps create entries for associated stations.
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Adhoc and mesh mode vaps create entries for neighbor stations.
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WDS mode vaps create an entry for the peer station.
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Stations for all vaps reside in the same table; each node
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entry has a
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.Vt ni_vap
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field that identifies the vap that created it.
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In some instances an entry is used by multiple vaps (e.g. for
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dynamic WDS a station associated to an ap vap may also be the peer
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of a WDS vap).
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.Pp
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Node table entries are reference counted.
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That is, there is a count of all long term references that determines
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when an entry may be reclaimed.
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References are held by every in-flight frame sent to a station to
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ensure the entry is not reclaimed while the frame is queued or otherwise
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held by a driver.
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Routines that lookup a table entry return a
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.Dq held reference
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(i.e. a pointer to a table entry with the reference count incremented).
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The
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.Fn ieee80211_ref_node
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and
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.Fn ieee80211_unref_node
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calls explicitly increment/decrement the reference count of a node,
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but are rarely used.
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Instead most callers use
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.Fn ieee80211_free_node
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to release a reference and, if the count goes to zero, reclaim the
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table entry.
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.Pp
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The station table and its entries are exposed to drivers in several ways.
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Each frame transmitted to a station includes a reference to the
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associated node in the
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.Vt m_pkthdr.rcvif
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field.
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This reference must be reclaimed by the driver when transmit processing
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is done.
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For each frame received the driver must lookup the table entry to
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use in dispatching the frame
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.Dq up the stack .
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This lookup implicitly obtains a reference to the table entry and
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the driver must reclaim the reference when frame processing is completed.
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Otherwise drivers frequently inspect the contents of the
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.Vt iv_bss
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node when handling state machine changes as important information
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is maintained in the data structure.
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.Pp
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The node table is opaque to drivers.
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Entries may be looked up using one of the pre-defined API's or the
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.Fn ieee80211_iterate_nodes
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call may be used to iterate through all entries to do per-node
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processing or implement some non-standard search mechanism.
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Note that
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.Fn ieee80211_iterate_nodes
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is single-threaded per-device
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and the effort processing involved is fairly
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substantial so it should be used carefully.
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.Pp
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Two routines are provided to print the contents of nodes to the console
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for debugging:
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.Fn ieee80211_dump_node
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displays the contents of a single node while
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.Fn ieee80211_dump_nodes
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displays the contents of the specified node table.
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Nodes may also be displayed using
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.Xr ddb 4
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with the
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.Dq show node
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directive and the station node table can be displayed with
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.Dq show statab .
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.Sh DRIVER PRIVATE STATE
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Node data structures may be extended by the driver to include
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driver-private state.
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This is done by overriding the
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.Vt ic_node_alloc
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method used to allocate a node table entry.
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The driver method must allocate a structure that is an extension
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of the
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.Vt ieee80211_node
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structure.
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For example the
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.Xr iwi 4
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driver defines a private node structure as:
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.Bd -literal -offset indent
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struct iwi_node {
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struct ieee80211_node in_node;
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int in_station;
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};
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.Ed
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.Pp
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and then provides a private allocation routine that does this:
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.Bd -literal -offset indent
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static struct ieee80211_node *
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iwi_node_alloc(struct ieee80211vap *vap,
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const uint8_t mac[IEEE80211_ADDR_LEN])
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{
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struct iwi_node *in;
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in = malloc(sizeof (struct iwi_node), M_80211_NODE,
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M_NOWAIT | M_ZERO);
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if (in == NULL)
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return NULL;
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in->in_station = -1;
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return &in->in_node;
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}
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.Ed
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.Pp
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Note that when reclaiming a node allocated by the driver the
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.Dq parent method
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must be called to ensure
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.Nm net80211
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state is reclaimed; for example:
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.Bd -literal -offset indent
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static void
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iwi_node_free(struct ieee80211_node *ni)
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{
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struct ieee80211com *ic = ni->ni_ic;
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struct iwi_softc *sc = ic->ic_ifp->if_softc;
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struct iwi_node *in = (struct iwi_node *)ni;
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if (in->in_station != -1)
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free_unr(sc->sc_unr, in->in_station);
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sc->sc_node_free(ni); /* invoke net80211 free handler */
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}
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.Ed
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.Pp
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Beware that care must be taken to avoid holding references that
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might cause nodes from being reclaimed.
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.Nm net80211
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will reclaim a node when the last reference is reclaimed in
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its data structures.
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However if a driver holds additional references then
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.Nm net80211
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will not recognize this and table entries will not be reclaimed.
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Such references should not be needed if the driver overrides the
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.Vt ic_node_cleanup
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and/or
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.Vt ic_node_free
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methods.
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.Sh KEY TABLE SUPPORT
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Node table lookups are typically done using a hash of the stations'
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mac address.
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When receiving frames this is sufficient to find the node table entry
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for the transmitter.
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But some devices also identify the sending station in the device
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state received with each frame and this data can be used to optimize
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lookups on receive using a companion table called the
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.Dq keytab .
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This table records a separate node table reference that can be fetched
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without any locking using the table index.
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This logic is handled with the
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.Fn ieee80211_find_rxnode_withkey
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call: if a keytab entry is found using the specified index then it is
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returned directly; otherwise a normal lookup is done and the keytab
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entry is written using the specified index.
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If the specified index is
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.Dv IEEE80211_KEYIX_NONE
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then a normal lookup is done without a table update.
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.Sh SEE ALSO
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.Xr ddb 9 ,
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.Xr ieee80211 9 ,
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.Xr ieee80211_proto 9
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