NAME

     ieee80211_node — software 802.11 stack node management functions

SYNOPSIS

     #include <net80211/ieee80211_var.h>

     struct ieee80211_node *
     ieee80211_find_rxnode(struct ieee80211com *, const struct ieee80211_frame_min *);

     struct ieee80211_node *
     ieee80211_find_rxnode_withkey(struct ieee80211com *, const struct ieee80211_frame_min *,
         ieee80211_keyix);

     struct ieee80211_node *
     ieee80211_ref_node(struct ieee80211_node *);

     void
     ieee80211_unref_node(struct ieee80211_node *);

     void
     ieee80211_free_node(struct ieee80211_node *);

     void
     ieee80211_iterate_nodes(struct ieee80211_node_table *, ieee80211_iter_func *f, void *arg);

     void
     ieee80211_dump_nodes(struct ieee80211_node_table *);

     void
     ieee80211_dump_node(struct ieee80211_node *);

DESCRIPTION

     The net80211 layer that supports 802.11 device drivers maintains a database of peer stations
     called the “node table” in the ic_sta entry of the 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 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).

     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 “held
     reference” (i.e. a pointer to a table entry with the reference count incremented).  The
     ieee80211_ref_node() and ieee80211_unref_node() calls explicitly increment/decrement the
     reference count of a node, but are rarely used.  Instead most callers use
     ieee80211_free_node() to release a reference and, if the count goes to zero, reclaim the
     table entry.

     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 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 “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 iv_bss node when handling state machine changes as
     important information is maintained in the data structure.

     The node table is opaque to drivers.  Entries may be looked up using one of the pre-defined
     API's or the 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
     ieee80211_iterate_nodes() is single-threaded per-device and the effort processing involved
     is fairly substantial so it should be used carefully.

     Two routines are provided to print the contents of nodes to the console for debugging:
     ieee80211_dump_node() displays the contents of a single node while ieee80211_dump_nodes()
     displays the contents of the specified node table.  Nodes may also be displayed using ddb(4)
     with the “show node” directive and the station node table can be displayed with “show
     statab”.

DRIVER PRIVATE STATE

     Node data structures may be extended by the driver to include driver-private state.  This is
     done by overriding the ic_node_alloc method used to allocate a node table entry.  The driver
     method must allocate a structure that is an extension of the ieee80211_node structure.  For
     example the iwi(4) driver defines a private node structure as:

           struct iwi_node {
                   struct ieee80211_node   in_node;
                   int                     in_station;
           };

     and then provides a private allocation routine that does this:

           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;
           }

     Note that when reclaiming a node allocated by the driver the “parent method” must be called
     to ensure net80211 state is reclaimed; for example:

           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 */
           }

     Beware that care must be taken to avoid holding references that might cause nodes from being
     reclaimed.  net80211 will reclaim a node when the last reference is reclaimed in its data
     structures.  However if a driver holds additional references then net80211 will not
     recognize this and table entries will not be reclaimed.  Such references should not be
     needed if the driver overrides the ic_node_cleanup and/or ic_node_free methods.

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
     “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
     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 IEEE80211_KEYIX_NONE then a
     normal lookup is done without a table update.

SEE ALSO

     ddb(4), ieee80211(9), ieee80211_proto(9)