oracular (9) ieee80211_dump_node.9freebsd.gz

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)