ieee80211_ifattach (9)

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Copyright (c) 2009 Sam Leffler, Errno Consulting
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(The comments found at the beginning of the groff file "man9/ieee80211_ifattach.9freebsd".)

NAME

IEEE80211 - 802.11 network layer

SYNOPSIS

In net80211/ieee80211_var.h Ft void Fn ieee80211_ifattach struct ieee80211com *ic const uint8_t macaddr[IEEE80211_ADDR_LEN] Ft void Fn ieee80211_ifdetach struct ieee80211com *ic

DESCRIPTION

IEEE 802.11 device drivers are written to use the infrastructure provided by the ifconfig 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 ifconfig 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 ifconfig 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 ifconfig 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 ifconfig layer with drivers responsible purely for moving data between the host and device. Similarly, ifconfig 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 ifconfig 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 Vt ieee80211com structure and one or more Vt 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 Vt ieee80211com structure is allocated by the ifconfig layer as adjunct data to a device's Vt ifnet ; it is accessed through the Vt if_l2com structure member. The Vt 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 ifconfig data structures and should be exploited to maintain driver-private state together with public ifconfig 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 Vt 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 Vt ieee80211com and Vt 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 ifconfig layer and are described below.

DRIVER ATTACH/DETACH

Drivers attach to the ifconfig layer with the Fn ieee80211_ifattach function. The driver is expected to allocate and setup any device-private data structures before passing control. The Vt ieee80211com structure must be pre-initialized with state required to setup the ifconfig 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 Fn ieee80211_ifattach the driver is expected to override default callback functions in the Vt 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 ifconfig 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 Vt 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 ifconfig to reclaim it's private state.

ic_node_cleanup

Cleanup state in a Vt 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_input9 or ieee80211_input_all9.

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_input9 or ieee80211_input_all9.

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 Vt 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_next9 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_action9 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_action9 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 ifconfig 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_attach9.
2. Do any final device setup like enabling interrupts.

State is torn down and reclaimed with a call to Fn 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 Fn 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_free9 on the ifnet it allocated for the physical device.

DRIVER CAPABILITIES

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

Device supports MIMO Power Save operation.

IEEE80211_HTC_RIFS

Device supports Reduced Inter Frame Spacing (RIFS).

SEE ALSO

ioctl(2), ndis(4), ieee80211_amrr9, ieee80211_beacon9, ieee80211_bmiss9, ieee80211_crypto9, ieee80211_ddb9, ieee80211_input9, ieee80211_node9, ieee80211_output9, ieee80211_proto9, ieee80211_radiotap9, ieee80211_regdomain9, ieee80211_scan9, ieee80211_vap9, ifnet(9), malloc(9)