man/man9/ieee80211_node.9

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.\" Copyright (c) 2004 Bruce M. Simpson <bms@spc.org>
.\" Copyright (c) 2004 Darron Broad <darron@kewl.org>
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.Dd October 2, 2023
.Dt IEEE80211_NODE 9
.Os
.Sh NAME
.Nm ieee80211_node
.Nd software 802.11 stack node management functions
.Sh SYNOPSIS
.In net80211/ieee80211_var.h
.\"
.Ft struct ieee80211_node *
.Fo ieee80211_find_rxnode
.Fa "struct ieee80211com *"
.Fa "const struct ieee80211_frame_min *"
.Fc
.\"
.Ft struct ieee80211_node *
.Fo ieee80211_find_rxnode_withkey
.Fa "struct ieee80211com *"
.Fa "const struct ieee80211_frame_min *"
.Fa "ieee80211_keyix"
.Fc
.\"
.Ft struct ieee80211_node *
.Fn ieee80211_ref_node "struct ieee80211_node *"
.\"
.Ft void
.Fn ieee80211_free_node "struct ieee80211_node *"
.\"
.Ft void
.Fo ieee80211_iterate_nodes
.Fa "struct ieee80211_node_table *"
.Fa "ieee80211_iter_func *f"
.Fa "void *arg"
.Fc
.\"
.Ft void
.Fo ieee80211_dump_nodes
.Fa "struct ieee80211_node_table *"
.Fc
.\"
.Ft void
.Fo ieee80211_dump_node
.Fa "struct ieee80211_node *"
.Fc
.Sh DESCRIPTION
The
.Nm net80211
layer that supports 802.11 device drivers maintains a database of
peer stations called the
.Dq node table
in the
.Vt ic_sta
entry of the
.Vt ieee80211com
structure.
Station mode vaps create an entry for the access point
the station is associated to.
AP mode vaps create entries for associated stations.
Adhoc and mesh mode vaps create entries for neighbor stations.
WDS mode vaps create an entry for the peer station.
Stations for all vaps reside in the same table; each node
entry has a
.Vt ni_vap
field that identifies the vap that created it.
In some instances an entry is used by multiple vaps (e.g. for
dynamic WDS a station associated to an ap vap may also be the peer
of a WDS vap).
.Pp
Node table entries are reference counted.
That is, there is a count of all long term references that determines
when an entry may be reclaimed.
References are held by every in-flight frame sent to a station to
ensure the entry is not reclaimed while the frame is queued or otherwise
held by a driver.
Routines that lookup a table entry return a
.Dq held reference
(i.e. a pointer to a table entry with the reference count incremented).
The
.Fn ieee80211_ref_node
call explicitly increments the reference count of a node.
.Fn ieee80211_free_node
decrements the reference count of a node and if the count goes to zero
reclaims the table entry.
.Pp
The station table and its entries are exposed to drivers in several ways.
Each frame transmitted to a station includes a reference to the
associated node in the
.Vt m_pkthdr.rcvif
field.
This reference must be reclaimed by the driver when transmit processing
is done.
For each frame received the driver must lookup the table entry to
use in dispatching the frame
.Dq up the stack .
This lookup implicitly obtains a reference to the table entry and
the driver must reclaim the reference when frame processing is completed.
Otherwise drivers frequently inspect the contents of the
.Vt iv_bss
node when handling state machine changes as important information
is maintained in the data structure.
.Pp
The node table is opaque to drivers.
Entries may be looked up using one of the pre-defined API's or the
.Fn ieee80211_iterate_nodes
call may be used to iterate through all entries to do per-node
processing or implement some non-standard search mechanism.
Note that
.Fn ieee80211_iterate_nodes
is single-threaded per-device
and the effort processing involved is fairly
substantial so it should be used carefully.
.Pp
Two routines are provided to print the contents of nodes to the console
for debugging:
.Fn ieee80211_dump_node
displays the contents of a single node while
.Fn ieee80211_dump_nodes
displays the contents of the specified node table.
Nodes may also be displayed using
.Xr ddb 4
with the
.Dq show node
directive and the station node table can be displayed with
.Dq show statab .
.Sh DRIVER PRIVATE STATE
Node data structures may be extended by the driver to include
driver-private state.
This is done by overriding the
.Vt ic_node_alloc
method used to allocate a node table entry.
The driver method must allocate a structure that is an extension
of the
.Vt ieee80211_node
structure.
For example the
.Xr iwi 4
driver defines a private node structure as:
.Bd -literal -offset indent
struct iwi_node {
        struct ieee80211_node   in_node;
	int                     in_station;
};
.Ed
.Pp
and then provides a private allocation routine that does this:
.Bd -literal -offset indent
static struct ieee80211_node *
iwi_node_alloc(struct ieee80211vap *vap,
    const uint8_t mac[IEEE80211_ADDR_LEN])
{
        struct iwi_node *in;

        in = malloc(sizeof(struct iwi_node), M_80211_NODE,
		M_NOWAIT | M_ZERO);
        if (in == NULL)
                return NULL;
        in->in_station = -1;
        return &in->in_node;
}
.Ed
.Pp
Note that when reclaiming a node allocated by the driver the
.Dq parent method
must be called to ensure
.Nm net80211
state is reclaimed; for example:
.Bd -literal -offset indent
static void
iwi_node_free(struct ieee80211_node *ni)
{
        struct ieee80211com *ic = ni->ni_ic;
        struct iwi_softc *sc = ic->ic_ifp->if_softc;
        struct iwi_node *in = (struct iwi_node *)ni;

        if (in->in_station != -1)
                free_unr(sc->sc_unr, in->in_station);
        sc->sc_node_free(ni);	/* invoke net80211 free handler */
}
.Ed
.Pp
Beware that care must be taken to avoid holding references that
might cause nodes from being reclaimed.
.Nm net80211
will reclaim a node when the last reference is reclaimed in
its data structures.
However if a driver holds additional references then
.Nm net80211
will not recognize this and table entries will not be reclaimed.
Such references should not be needed if the driver overrides the
.Vt ic_node_cleanup
and/or
.Vt ic_node_free
methods.
.Sh KEY TABLE SUPPORT
Node table lookups are typically done using a hash of the stations'
mac address.
When receiving frames this is sufficient to find the node table entry
for the transmitter.
But some devices also identify the sending station in the device
state received with each frame and this data can be used to optimize
lookups on receive using a companion table called the
.Dq keytab .
This table records a separate node table reference that can be fetched
without any locking using the table index.
This logic is handled with the
.Fn ieee80211_find_rxnode_withkey
call: if a keytab entry is found using the specified index then it is
returned directly; otherwise a normal lookup is done and the keytab
entry is written using the specified index.
If the specified index is
.Dv IEEE80211_KEYIX_NONE
then a normal lookup is done without a table update.
.Sh SEE ALSO
.Xr ddb 4 ,
.Xr ieee80211 9 ,
.Xr ieee80211_proto 9