Ubuntu Manpage: IEEE80211 — 802.11 network layer

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NAME

     IEEE80211 — 802.11 network layer

SYNOPSIS

     #include <net80211/ieee80211_var.h>

     void
     ieee80211_ifattach(struct ieee80211com *ic, const uint8_t macaddr[IEEE80211_ADDR_LEN]);

     void
     ieee80211_ifdetach(struct ieee80211com *ic);

DESCRIPTION

IEEE 802.11 device drivers are written to use the infrastructure provided by the IEEE80211
software layer. This software provides a support framework for drivers that includes ifnet
cloning, state management, and a user management API by which applications interact with
802.11 devices. Most drivers depend on the IEEE80211 layer for protocol services but
devices that off-load functionality may bypass the layer to connect directly to the device
(e.g. the ndis(4) emulation support does this).

A IEEE80211 device driver implements 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. This enables construction of interesting applications such as
an AP vap and one or more WDS vaps or multiple AP vaps, each with a different security
model. The IEEE80211 layer virtualizes most 802.11 state and coordinates vap state changes
including scheduling multiple vaps. State that is not virtualized includes the current
channel and WME/WMM parameters. Protocol processing is typically handled entirely in the
IEEE80211 layer with drivers responsible purely for moving data between the host and device.
Similarly, IEEE80211 handles most ioctl(2) requests without entering the driver; instead
drivers are notified of state changes that require their involvement.

The virtual radio interface defined by the IEEE80211 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.

DATA STRUCTURES

     The virtual radio architecture splits state between a single per-device ieee80211com
     structure and one or more ieee80211vap structures.  Drivers are expected to setup various
     shared state in these structures at device attach and during vap creation but otherwise
     should treat them as read-only.  The ieee80211com structure is allocated by the IEEE80211
     layer as adjunct data to a device's ifnet; it is accessed through the if_l2com structure
     member.  The ieee80211vap structure is allocated by the driver in the “vap create” method
     and should be extended with any driver-private state.  This technique of giving the driver
     control to allocate data structures is used for other IEEE80211 data structures and should
     be exploited to maintain driver-private state together with public IEEE80211 state.

     The other main data structures are the station, or node, table that tracks peers in the
     local BSS, and the channel table that defines the current set of available radio channels.
     Both tables are bound to the ieee80211com structure and shared by all vaps.  Long-lasting
     references to a node are counted to guard against premature reclamation.  In particular
     every packet sent/received holds a node reference (either explicitly for transmit or
     implicitly on receive).

     The ieee80211com and ieee80211vap structures also hold a collection of method pointers that
     drivers fill-in and/or override to take control of certain operations.  These methods are
     the primary way drivers are bound to the IEEE80211 layer and are described below.

DRIVER ATTACH/DETACH

Drivers attach to the IEEE80211 layer with the ieee80211_ifattach() function. The driver is
expected to allocate and setup any device-private data structures before passing control.
The ieee80211com structure must be pre-initialized with state required to setup the
IEEE80211 layer:

ic_ifp Backpointer to the physical device's ifnet.

ic_caps Device/driver capabilities; see below for a complete description.

ic_channels Table of channels the device is capable of operating on. This is initially
provided by the driver but may be changed through calls that change the
regulatory state.

ic_nchan Number of entries in ic_channels.

On return from ieee80211_ifattach() the driver is expected to override default callback
functions in the ieee80211com structure to register it's private routines. Methods marked
with a “*” must be provided by the driver.

ic_vap_create*
Create a vap instance of the specified type (operating mode). Any fixed BSSID
and/or MAC address is provided. Drivers that support multi-bssid operation may
honor the requested BSSID or assign their own.

ic_vap_delete*
Destroy a vap instance created with ic_vap_create.

ic_getradiocaps
Return the list of calibrated channels for the radio. The default method
returns the current list of channels (space permitting).

ic_setregdomain
Process a request to change regulatory state. The routine may reject a request
or constrain changes (e.g. reduce transmit power caps). The default method
accepts all proposed changes.

ic_send_mgmt
Send an 802.11 management frame. The default method fabricates the frame using
IEEE80211 state and passes it to the driver through the ic_raw_xmit method.

ic_raw_xmit Transmit a raw 802.11 frame. The default method drops the frame and generates
a message on the console.

ic_updateslot
Update hardware state after an 802.11 IFS slot time change. There is no
default method; the pointer may be NULL in which case it will not be used.

ic_update_mcast
Update hardware for a change in the multicast packet filter. The default
method prints a console message.

ic_update_promisc
Update hardware for a change in the promiscuous mode setting. The default
method prints a console message.

ic_newassoc Update driver/device state for association to a new AP (in station mode) or
when a new station associates (e.g. in AP mode). There is no default method;
the pointer may be NULL in which case it will not be used.

ic_node_alloc
Allocate and initialize a ieee80211_node structure. This method cannot sleep.
The default method allocates zero'd memory using malloc(9). Drivers should
override this method to allocate extended storage for their own needs. Memory
allocated by the driver must be tagged with M_80211_NODE to balance the memory
allocation statistics.

ic_node_free
Reclaim storage of a node allocated by ic_node_alloc. Drivers are expected to
interpose their own method to cleanup private state but must call through this
method to allow IEEE80211 to reclaim it's private state.

ic_node_cleanup
Cleanup state in a ieee80211_node created by ic_node_alloc. This operation is
distinguished from ic_node_free in that it may be called long before the node
is actually reclaimed to cleanup adjunct state. This can happen, for example,
when a node must not be reclaimed due to references held by packets in the
transmit queue. Drivers typically interpose ic_node_cleanup instead of
ic_node_free.

ic_node_age Age, and potentially reclaim, resources associated with a node. The default
method ages frames on the power-save queue (in AP mode) and pending frames in
the receive reorder queues (for stations using A-MPDU).

ic_node_drain
Reclaim all optional resources associated with a node. This call is used to
free up resources when they are in short supply.

ic_node_getrssi
Return the Receive Signal Strength Indication (RSSI) in .5 dBm units for the
specified node. This interface returns a subset of the information returned by
ic_node_getsignal. The default method calculates a filtered average over the
last ten samples passed in to ieee80211_input(9) or ieee80211_input_all(9).

ic_node_getsignal
Return the RSSI and noise floor (in .5 dBm units) for a station. The default
method calculates RSSI as described above; the noise floor returned is the last
value supplied to ieee80211_input(9) or ieee80211_input_all(9).

ic_node_getmimoinfo
Return MIMO radio state for a station in support of the IEEE80211_IOC_STA_INFO
ioctl request. The default method returns nothing.

ic_scan_start*
Prepare driver/hardware state for scanning. This callback is done in a
sleepable context.

ic_scan_end*
Restore driver/hardware state after scanning completes. This callback is done
in a sleepable context.

ic_set_channel*
Set the current radio channel using ic_curchan. This callback is done in a
sleepable context.

ic_scan_curchan
Start scanning on a channel. This method is called immediately after each
channel change and must initiate the work to scan a channel and schedule a
timer to advance to the next channel in the scan list. This callback is done
in a sleepable context. The default method handles active scan work (e.g.
sending ProbeRequest frames), and schedules a call to ieee80211_scan_next(9)
according to the maximum dwell time for the channel. Drivers that off-load
scan work to firmware typically use this method to trigger per-channel scan
activity.

ic_scan_mindwell
Handle reaching the minimum dwell time on a channel when scanning. This event
is triggered when one or more stations have been found on a channel and the
minimum dwell time has been reached. This callback is done in a sleepable
context. The default method signals the scan machinery to advance to the next
channel as soon as possible. Drivers can use this method to preempt further
work (e.g. if scanning is handled by firmware) or ignore the request to force
maximum dwell time on a channel.

ic_recv_action
Process a received Action frame. The default method points to
ieee80211_recv_action(9) which provides a mechanism for setting up handlers for
each Action frame class.

ic_send_action
Transmit an Action frame. The default method points to
ieee80211_send_action(9) which provides a mechanism for setting up handlers for
each Action frame class.

ic_ampdu_enable
Check if transmit A-MPDU should be enabled for the specified station and AC.
The default method checks a per-AC traffic rate against a per-vap threshold to
decide if A-MPDU should be enabled. This method also rate-limits ADDBA
requests so that requests are not made too frequently when a receiver has
limited resources.

ic_addba_request
Request A-MPDU transmit aggregation. The default method sets up local state
and issues an ADDBA Request Action frame. Drivers may interpose this method if
they need to setup private state for handling transmit A-MPDU.

ic_addb_response
Process a received ADDBA Response Action frame and setup resources as needed
for doing transmit A-MPDU.

ic_addb_stop
Shutdown an A-MPDU transmit stream for the specified station and AC. The
default method reclaims local state after sending a DelBA Action frame.

ic_bar_response
Process a response to a transmitted BAR control frame.

ic_ampdu_rx_start
Prepare to receive A-MPDU data from the specified station for the TID.

ic_ampdu_rx_stop
Terminate receipt of A-MPDU data from the specified station for the TID.

Once the IEEE80211 layer is attached to a driver there are two more steps typically done to
complete the work:

1. Setup “radiotap support” for capturing raw 802.11 packets that pass through the device.
This is done with a call to ieee80211_radiotap_attach(9).

2. Do any final device setup like enabling interrupts.

State is torn down and reclaimed with a call to ieee80211_ifdetach(). Note this call may
result in multiple callbacks into the driver so it should be done before any critical driver
state is reclaimed. On return from ieee80211_ifdetach() all associated vaps and ifnet
structures are reclaimed or inaccessible to user applications so it is safe to teardown
driver state without worry about being re-entered. The driver is responsible for calling
if_free(9) on the ifnet it allocated for the physical device.

DRIVER CAPABILITIES

Driver/device capabilities are specified using several sets of flags in the ieee80211com
structure. General capabilities are specified by ic_caps. Hardware cryptographic
capabilities are specified by ic_cryptocaps. 802.11n capabilities, if any, are specified by
ic_htcaps. The IEEE80211 layer propagates a subset of these capabilities to each vap
through the equivalent fields: iv_caps, iv_cryptocaps, and iv_htcaps. The following general
capabilities are defined:

IEEE80211_C_STA Device is capable of operating in station (aka Infrastructure) mode.

IEEE80211_C_8023ENCAP Device requires 802.3-encapsulated frames be passed for transmit. By
default IEEE80211 will encapsulate all outbound frames as 802.11
frames (without a PLCP header).

IEEE80211_C_FF Device supports Atheros Fast-Frames.

IEEE80211_C_TURBOP Device supports Atheros Dynamic Turbo mode.

IEEE80211_C_IBSS Device is capable of operating in adhoc/IBSS mode.

IEEE80211_C_PMGT Device supports dynamic power-management (aka power save) in station
mode.

IEEE80211_C_HOSTAP Device is capable of operating as an Access Point in Infrastructure
mode.

IEEE80211_C_AHDEMO Device is capable of operating in Adhoc Demo mode. In this mode the
device is used purely to send/receive raw 802.11 frames.

IEEE80211_C_SWRETRY Device supports software retry of transmitted frames.

IEEE80211_C_TXPMGT Device support dynamic transmit power changes on transmitted frames;
also known as Transmit Power Control (TPC).

IEEE80211_C_SHSLOT Device supports short slot time operation (for 802.11g).

IEEE80211_C_SHPREAMBLE
Device supports short preamble operation (for 802.11g).

IEEE80211_C_MONITOR Device is capable of operating in monitor mode.

IEEE80211_C_DFS Device supports radar detection and/or DFS. DFS protocol support can
be handled by IEEE80211 but the device must be capable of detecting
radar events.

IEEE80211_C_MBSS Device is capable of operating in MeshBSS (MBSS) mode (as defined by
802.11s Draft 3.0).

IEEE80211_C_WPA1 Device supports WPA1 operation.

IEEE80211_C_WPA2 Device supports WPA2/802.11i operation.

IEEE80211_C_BURST Device supports frame bursting.

IEEE80211_C_WME Device supports WME/WMM operation (at the moment this is mostly
support for sending and receiving QoS frames with EDCF).

IEEE80211_C_WDS Device supports transmit/receive of 4-address frames.

IEEE80211_C_BGSCAN Device supports background scanning.

IEEE80211_C_TXFRAG Device supports transmit of fragmented 802.11 frames.

IEEE80211_C_TDMA Device is capable of operating in TDMA mode.

The follow general crypto capabilities are defined. In general IEEE80211 will fall-back to
software support when a device is not capable of hardware acceleration of a cipher. This
can be done on a per-key basis. IEEE80211 can also handle software Michael calculation
combined with hardware AES acceleration.

IEEE80211_CRYPTO_WEP Device supports hardware WEP cipher.

IEEE80211_CRYPTO_TKIP Device supports hardware TKIP cipher.

IEEE80211_CRYPTO_AES_OCB
Device supports hardware AES-OCB cipher.

IEEE80211_CRYPTO_AES_CCM
Device supports hardware AES-CCM cipher.

IEEE80211_CRYPTO_TKIPMIC
Device supports hardware Michael for use with TKIP.

IEEE80211_CRYPTO_CKIP Devices supports hardware CKIP cipher.

The follow general 802.11n capabilities are defined. The first capabilities are defined
exactly as they appear in the 802.11n specification. Capabilities beginning with
IEEE80211_HTC_AMPDU are used solely by the IEEE80211 layer.

IEEE80211_HTCAP_CHWIDTH40
Device supports 20/40 channel width operation.

IEEE80211_HTCAP_SMPS_DYNAMIC
Device supports dynamic SM power save operation.

IEEE80211_HTCAP_SMPS_ENA
Device supports static SM power save operation.

IEEE80211_HTCAP_GREENFIELD
Device supports Greenfield preamble.

IEEE80211_HTCAP_SHORTGI20
Device supports Short Guard Interval on 20MHz channels.

IEEE80211_HTCAP_SHORTGI40
Device supports Short Guard Interval on 40MHz channels.

IEEE80211_HTCAP_TXSTBC
Device supports Space Time Block Convolution (STBC) for transmit.

IEEE80211_HTCAP_RXSTBC_1STREAM
Device supports 1 spatial stream for STBC receive.

IEEE80211_HTCAP_RXSTBC_2STREAM
Device supports 1-2 spatial streams for STBC receive.

IEEE80211_HTCAP_RXSTBC_3STREAM
Device supports 1-3 spatial streams for STBC receive.

IEEE80211_HTCAP_MAXAMSDU_7935
Device supports A-MSDU frames up to 7935 octets.

IEEE80211_HTCAP_MAXAMSDU_3839
Device supports A-MSDU frames up to 3839 octets.

IEEE80211_HTCAP_DSSSCCK40
Device supports use of DSSS/CCK on 40MHz channels.

IEEE80211_HTCAP_PSMP Device supports PSMP.

IEEE80211_HTCAP_40INTOLERANT
Device is intolerant of 40MHz wide channel use.

IEEE80211_HTCAP_LSIGTXOPPROT
Device supports L-SIG TXOP protection.

IEEE80211_HTC_AMPDU Device supports A-MPDU aggregation. Note that any 802.11n compliant
device must support A-MPDU receive so this implicitly means support
for transmit of A-MPDU frames.

IEEE80211_HTC_AMSDU Device supports A-MSDU aggregation. Note that any 802.11n compliant
device must support A-MSDU receive so this implicitly means support
for transmit of A-MSDU frames.

IEEE80211_HTC_HT Device supports High Throughput (HT) operation. This capability must
be set to enable 802.11n functionality in IEEE80211.

IEEE80211_HTC_SMPS Device supports MIMO Power Save operation.