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NAME

     net80211_vap - 802.11 network layer virtual radio support

SYNOPSIS

     #include <net80211/ieee80211_var.h>

     int
     ieee80211_vap_setup(struct ieee80211com *, struct ieee80211vap *,
             const char name[IFNAMSIZ], int unit, int opmode, int flags,
             const uint8_t bssid[IEEE80211_ADDR_LEN],
             const uint8_t macaddr[IEEE80211_ADDR_LEN]);

     int
     ieee80211_vap_attach(struct ieee80211vap *, ifm_change_cb_t media_change,
             ifm_stat_cb_t media_stat);

     void
     ieee80211_vap_detach(struct ieee80211vap *);

DESCRIPTION

     The net80211 software layer provides a support framework for drivers that
     includes a virtual radio API that is exported to users through network
     interfaces (aka vaps) that are cloned from the underlying device.  These
     interfaces have an operating mode (station, adhoc, hostap, wds, monitor,
     etc.)  that is fixed for the lifetime of the interface.  Devices that can
     support multiple concurrent interfaces allow multiple vaps to be cloned.

     The virtual radio interface defined by the net80211 layer means that
     drivers must be structured to follow specific rules.  Drivers that
     support only a single interface at any time must still follow these
     rules.

     The virtual radio architecture splits state between a single per-device
     ieee80211com structure and one or more ieee80211vap structures.  Vaps are
     created with the SIOCIFCREATE2 request.  This results in a call into the
     driver’s ic_vap_create method where the driver can decide if the request
     should be accepted.

     The vap creation process is done in three steps.  First the driver
     allocates the data structure with malloc(9).  This data structure must
     have an ieee80211vap structure at the front but is usually extended with
     driver-private state.  Next the vap is setup with a call to
     ieee80211_vap_setup().  This request initializes net80211 state but does
     not activate the interface.  The driver can then override methods setup
     by net80211 and setup driver resources before finally calling
     ieee80211_vap_attach() to complete the process.  Both these calls must be
     done without holding any driver locks as work may require the process
     block/sleep.

     A vap is deleted when an SIOCIFDESTROY ioctl request is made or when the
     device detaches (causing all associated vaps to automatically be
     deleted).  Delete requests cause the ic_vap_delete method to be called.
     Drivers must quiesce the device before calling ieee80211_vap_detach() to
     deactivate the vap and isolate it from activities such as requests from
     user applications.  The driver can then reclaim resources held by the vap
     and re-enable device operation.  The exact procedure for quiesceing a
     device is unspecified but typically it involves blocking interrupts and
     stopping transmit and receive processing.

MULTI-VAP OPERATION

     Drivers are responsible for deciding if multiple vaps can be created and
     how to manage them.  Whether or not multiple concurrent vaps can be
     supported depends on a device’s capabilities.  For example, multiple
     hostap vaps can usually be supported but many devices do not support
     assigning each vap a unique BSSID.  If a device supports hostap operation
     it can usually support concurrent station mode vaps but possibly with
     limitations such as losing support for hardware beacon miss support.
     Devices that are capable of hostap operation and can send and receive
     4-address frames should be able to support WDS vaps together with an ap
     vap.  But in contrast some devices cannot support WDS vaps without at
     least one ap vap (this however can be finessed by forcing the ap vap to
     not transmit beacon frames).  All devices should support the creation of
     any number of monitor mode vaps concurrent with other vaps but it is the
     responsibility of the driver to allow this.

     An important consequence of supporting multiple concurrent vaps is that a
     driver’s iv_newstate method must be written to handle being called for
     each vap.  Where necessary, drivers must track private state for all vaps
     and not just the one whose state is being changed (e.g. for handling
     beacon timers the driver may need to know if all vaps that beacon are
     stopped before stopping the hardware timers).

SEE ALSO

     ieee80211(9), ifnet(9), malloc(9)