# The 802.11 subsystems – for kernel developers

Explaining wireless 802.11 networking in the Linux kernel

2007-2009 Johannes Berg

This documentation is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License version 2 as published by the Free Software Foundation.

This documentation is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this documentation; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

For more details see the file COPYING in the source distribution of Linux.

These books attempt to give a description of the various subsystems that play a role in 802.11 wireless networking in Linux. Since these books are for kernel developers they attempts to document the structures and functions used in the kernel as well as giving a higher-level overview.

The reader is expected to be familiar with the 802.11 standard as published by the IEEE in 802.11-2007 (or possibly later versions). References to this standard will be given as "802.11-2007 8.1.5".

## Device registration

!Pinclude/net/cfg80211.h Device registration !Finclude/net/cfg80211.h ieee80211_band !Finclude/net/cfg80211.h ieee80211_channel_flags !Finclude/net/cfg80211.h ieee80211_channel !Finclude/net/cfg80211.h ieee80211_rate_flags !Finclude/net/cfg80211.h ieee80211_rate !Finclude/net/cfg80211.h ieee80211_sta_ht_cap !Finclude/net/cfg80211.h ieee80211_supported_band !Finclude/net/cfg80211.h cfg80211_signal_type !Finclude/net/cfg80211.h wiphy_params_flags !Finclude/net/cfg80211.h wiphy_flags !Finclude/net/cfg80211.h wiphy !Finclude/net/cfg80211.h wireless_dev !Finclude/net/cfg80211.h wiphy_new !Finclude/net/cfg80211.h wiphy_register !Finclude/net/cfg80211.h wiphy_unregister !Finclude/net/cfg80211.h wiphy_free !Finclude/net/cfg80211.h wiphy_name !Finclude/net/cfg80211.h wiphy_dev !Finclude/net/cfg80211.h wiphy_priv !Finclude/net/cfg80211.h priv_to_wiphy !Finclude/net/cfg80211.h set_wiphy_dev !Finclude/net/cfg80211.h wdev_priv !Finclude/net/cfg80211.h ieee80211_iface_limit !Finclude/net/cfg80211.h ieee80211_iface_combination !Finclude/net/cfg80211.h cfg80211_check_combinations

## Actions and configuration

!Pinclude/net/cfg80211.h Actions and configuration !Finclude/net/cfg80211.h cfg80211_ops !Finclude/net/cfg80211.h vif_params !Finclude/net/cfg80211.h key_params !Finclude/net/cfg80211.h survey_info_flags !Finclude/net/cfg80211.h survey_info !Finclude/net/cfg80211.h cfg80211_beacon_data !Finclude/net/cfg80211.h cfg80211_ap_settings !Finclude/net/cfg80211.h station_parameters !Finclude/net/cfg80211.h rate_info_flags !Finclude/net/cfg80211.h rate_info !Finclude/net/cfg80211.h station_info !Finclude/net/cfg80211.h monitor_flags !Finclude/net/cfg80211.h mpath_info_flags !Finclude/net/cfg80211.h mpath_info !Finclude/net/cfg80211.h bss_parameters !Finclude/net/cfg80211.h ieee80211_txq_params !Finclude/net/cfg80211.h cfg80211_crypto_settings !Finclude/net/cfg80211.h cfg80211_auth_request !Finclude/net/cfg80211.h cfg80211_assoc_request !Finclude/net/cfg80211.h cfg80211_deauth_request !Finclude/net/cfg80211.h cfg80211_disassoc_request !Finclude/net/cfg80211.h cfg80211_ibss_params !Finclude/net/cfg80211.h cfg80211_connect_params !Finclude/net/cfg80211.h cfg80211_pmksa !Finclude/net/cfg80211.h cfg80211_rx_mlme_mgmt !Finclude/net/cfg80211.h cfg80211_auth_timeout !Finclude/net/cfg80211.h cfg80211_rx_assoc_resp !Finclude/net/cfg80211.h cfg80211_assoc_timeout !Finclude/net/cfg80211.h cfg80211_tx_mlme_mgmt !Finclude/net/cfg80211.h cfg80211_ibss_joined !Finclude/net/cfg80211.h cfg80211_connect_result !Finclude/net/cfg80211.h cfg80211_roamed !Finclude/net/cfg80211.h cfg80211_disconnected !Finclude/net/cfg80211.h cfg80211_ready_on_channel !Finclude/net/cfg80211.h cfg80211_remain_on_channel_expired !Finclude/net/cfg80211.h cfg80211_new_sta !Finclude/net/cfg80211.h cfg80211_rx_mgmt !Finclude/net/cfg80211.h cfg80211_mgmt_tx_status !Finclude/net/cfg80211.h cfg80211_cqm_rssi_notify !Finclude/net/cfg80211.h cfg80211_cqm_pktloss_notify !Finclude/net/cfg80211.h cfg80211_michael_mic_failure

## Scanning and BSS list handling

!Pinclude/net/cfg80211.h Scanning and BSS list handling !Finclude/net/cfg80211.h cfg80211_ssid !Finclude/net/cfg80211.h cfg80211_scan_request !Finclude/net/cfg80211.h cfg80211_scan_done !Finclude/net/cfg80211.h cfg80211_bss !Finclude/net/cfg80211.h cfg80211_inform_bss_width_frame !Finclude/net/cfg80211.h cfg80211_inform_bss_width !Finclude/net/cfg80211.h cfg80211_unlink_bss !Finclude/net/cfg80211.h cfg80211_find_ie !Finclude/net/cfg80211.h ieee80211_bss_get_ie

## Utility functions

!Pinclude/net/cfg80211.h Utility functions !Finclude/net/cfg80211.h ieee80211_channel_to_frequency !Finclude/net/cfg80211.h ieee80211_frequency_to_channel !Finclude/net/cfg80211.h ieee80211_get_channel !Finclude/net/cfg80211.h ieee80211_get_response_rate !Finclude/net/cfg80211.h ieee80211_hdrlen !Finclude/net/cfg80211.h ieee80211_get_hdrlen_from_skb !Finclude/net/cfg80211.h ieee80211_radiotap_iterator

## Data path helpers

!Pinclude/net/cfg80211.h Data path helpers !Finclude/net/cfg80211.h ieee80211_data_to_8023 !Finclude/net/cfg80211.h ieee80211_data_from_8023 !Finclude/net/cfg80211.h ieee80211_amsdu_to_8023s !Finclude/net/cfg80211.h cfg80211_classify8021d

## Regulatory enforcement infrastructure

!Pinclude/net/cfg80211.h Regulatory enforcement infrastructure !Finclude/net/cfg80211.h regulatory_hint !Finclude/net/cfg80211.h wiphy_apply_custom_regulatory !Finclude/net/cfg80211.h freq_reg_info

## RFkill integration

!Pinclude/net/cfg80211.h RFkill integration !Finclude/net/cfg80211.h wiphy_rfkill_set_hw_state !Finclude/net/cfg80211.h wiphy_rfkill_start_polling !Finclude/net/cfg80211.h wiphy_rfkill_stop_polling

## Test mode

!Pinclude/net/cfg80211.h Test mode !Finclude/net/cfg80211.h cfg80211_testmode_alloc_reply_skb !Finclude/net/cfg80211.h cfg80211_testmode_reply !Finclude/net/cfg80211.h cfg80211_testmode_alloc_event_skb !Finclude/net/cfg80211.h cfg80211_testmode_event

## The basic mac80211 driver interface

You should read and understand the information contained within this part of the book while implementing a driver. In some chapters, advanced usage is noted, that may be skipped at first.

This part of the book only covers station and monitor mode functionality, additional information required to implement the other modes is covered in the second part of the book.

### Basic hardware handling

TBD

This chapter shall contain information on getting a hw struct allocated and registered with mac80211.

Since it is required to allocate rates/modes before registering a hw struct, this chapter shall also contain information on setting up the rate/mode structs.

Additionally, some discussion about the callbacks and the general programming model should be in here, including the definition of ieee80211_ops which will be referred to a lot.

Finally, a discussion of hardware capabilities should be done with references to other parts of the book.

!Finclude/net/mac80211.h ieee80211_hw !Finclude/net/mac80211.h ieee80211_hw_flags !Finclude/net/mac80211.h SET_IEEE80211_DEV !Finclude/net/mac80211.h SET_IEEE80211_PERM_ADDR !Finclude/net/mac80211.h ieee80211_ops !Finclude/net/mac80211.h ieee80211_alloc_hw !Finclude/net/mac80211.h ieee80211_register_hw !Finclude/net/mac80211.h ieee80211_unregister_hw !Finclude/net/mac80211.h ieee80211_free_hw

### PHY configuration

TBD

This chapter should describe PHY handling including start/stop callbacks and the various structures used.

!Finclude/net/mac80211.h ieee80211_conf !Finclude/net/mac80211.h ieee80211_conf_flags

### Virtual interfaces

TBD

This chapter should describe virtual interface basics that are relevant to the driver (VLANs, MGMT etc are not.) It should explain the use of the add_iface/remove_iface callbacks as well as the interface configuration callbacks.

Things related to AP mode should be discussed there.

Things related to supporting multiple interfaces should be in the appropriate chapter, a BIG FAT note should be here about this though and the recommendation to allow only a single interface in STA mode at first!

!Finclude/net/mac80211.h ieee80211_vif

### Receive and transmit processing

#### what should be here

TBD

This should describe the receive and transmit paths in mac80211/the drivers as well as transmit status handling.

#### Frame format

!Pinclude/net/mac80211.h Frame format

#### Packet alignment

!Pnet/mac80211/rx.c Packet alignment

#### Calling into mac80211 from interrupts

!Pinclude/net/mac80211.h Calling mac80211 from interrupts

#### functions/definitions

!Finclude/net/mac80211.h ieee80211_rx_status !Finclude/net/mac80211.h mac80211_rx_flags !Finclude/net/mac80211.h mac80211_tx_info_flags !Finclude/net/mac80211.h mac80211_tx_control_flags !Finclude/net/mac80211.h mac80211_rate_control_flags !Finclude/net/mac80211.h ieee80211_tx_rate !Finclude/net/mac80211.h ieee80211_tx_info !Finclude/net/mac80211.h ieee80211_tx_info_clear_status !Finclude/net/mac80211.h ieee80211_rx !Finclude/net/mac80211.h ieee80211_rx_ni !Finclude/net/mac80211.h ieee80211_rx_irqsafe !Finclude/net/mac80211.h ieee80211_tx_status !Finclude/net/mac80211.h ieee80211_tx_status_ni !Finclude/net/mac80211.h ieee80211_tx_status_irqsafe !Finclude/net/mac80211.h ieee80211_rts_get !Finclude/net/mac80211.h ieee80211_rts_duration !Finclude/net/mac80211.h ieee80211_ctstoself_get !Finclude/net/mac80211.h ieee80211_ctstoself_duration !Finclude/net/mac80211.h ieee80211_generic_frame_duration !Finclude/net/mac80211.h ieee80211_wake_queue !Finclude/net/mac80211.h ieee80211_stop_queue !Finclude/net/mac80211.h ieee80211_wake_queues !Finclude/net/mac80211.h ieee80211_stop_queues !Finclude/net/mac80211.h ieee80211_queue_stopped

### Frame filtering

!Pinclude/net/mac80211.h Frame filtering !Finclude/net/mac80211.h ieee80211_filter_flags

### The mac80211 workqueue

!Pinclude/net/mac80211.h mac80211 workqueue !Finclude/net/mac80211.h ieee80211_queue_work !Finclude/net/mac80211.h ieee80211_queue_delayed_work

## Advanced driver interface

Information contained within this part of the book is of interest only for advanced interaction of mac80211 with drivers to exploit more hardware capabilities and improve performance.

### LED support

Mac80211 supports various ways of blinking LEDs. Wherever possible, device LEDs should be exposed as LED class devices and hooked up to the appropriate trigger, which will then be triggered appropriately by mac80211.

!Finclude/net/mac80211.h ieee80211_get_tx_led_name !Finclude/net/mac80211.h ieee80211_get_rx_led_name !Finclude/net/mac80211.h ieee80211_get_assoc_led_name !Finclude/net/mac80211.h ieee80211_get_radio_led_name !Finclude/net/mac80211.h ieee80211_tpt_blink !Finclude/net/mac80211.h ieee80211_tpt_led_trigger_flags !Finclude/net/mac80211.h ieee80211_create_tpt_led_trigger

### Hardware crypto acceleration

!Pinclude/net/mac80211.h Hardware crypto acceleration !Finclude/net/mac80211.h set_key_cmd !Finclude/net/mac80211.h ieee80211_key_conf !Finclude/net/mac80211.h ieee80211_key_flags !Finclude/net/mac80211.h ieee80211_get_tkip_p1k !Finclude/net/mac80211.h ieee80211_get_tkip_p1k_iv !Finclude/net/mac80211.h ieee80211_get_tkip_p2k

### Powersave support

!Pinclude/net/mac80211.h Powersave support

### Beacon filter support

!Pinclude/net/mac80211.h Beacon filter support !Finclude/net/mac80211.h ieee80211_beacon_loss

### Multiple queues and QoS support

TBD

!Finclude/net/mac80211.h ieee80211_tx_queue_params

### Access point mode support

TBD

Some parts of the if_conf should be discussed here instead

Insert notes about VLAN interfaces with hw crypto here or in the hw crypto chapter.

#### support for powersaving clients

!Pinclude/net/mac80211.h AP support for powersaving clients !Finclude/net/mac80211.h ieee80211_get_buffered_bc !Finclude/net/mac80211.h ieee80211_beacon_get !Finclude/net/mac80211.h ieee80211_sta_eosp !Finclude/net/mac80211.h ieee80211_frame_release_type !Finclude/net/mac80211.h ieee80211_sta_ps_transition !Finclude/net/mac80211.h ieee80211_sta_ps_transition_ni !Finclude/net/mac80211.h ieee80211_sta_set_buffered !Finclude/net/mac80211.h ieee80211_sta_block_awake

### Supporting multiple virtual interfaces

TBD

Note: WDS with identical MAC address should almost always be OK

Insert notes about having multiple virtual interfaces with different MAC addresses here, note which configurations are supported by mac80211, add notes about supporting hw crypto with it.

!Finclude/net/mac80211.h ieee80211_iterate_active_interfaces !Finclude/net/mac80211.h ieee80211_iterate_active_interfaces_atomic

### Station handling

TODO

!Finclude/net/mac80211.h ieee80211_sta !Finclude/net/mac80211.h sta_notify_cmd !Finclude/net/mac80211.h ieee80211_find_sta !Finclude/net/mac80211.h ieee80211_find_sta_by_ifaddr

### Hardware scan offload

TBD

!Finclude/net/mac80211.h ieee80211_scan_completed

### Aggregation

#### TX A-MPDU aggregation

!Pnet/mac80211/agg-tx.c TX A-MPDU aggregation !Cnet/mac80211/agg-tx.c

#### RX A-MPDU aggregation

!Pnet/mac80211/agg-rx.c RX A-MPDU aggregation !Cnet/mac80211/agg-rx.c !Finclude/net/mac80211.h ieee80211_ampdu_mlme_action

### Spatial Multiplexing Powersave (SMPS)

!Pinclude/net/mac80211.h Spatial multiplexing power save !Finclude/net/mac80211.h ieee80211_request_smps !Finclude/net/mac80211.h ieee80211_smps_mode

## Rate control interface

TBD

This part of the book describes the rate control algorithm interface and how it relates to mac80211 and drivers.

### Rate Control API

TBD

!Finclude/net/mac80211.h ieee80211_start_tx_ba_session !Finclude/net/mac80211.h ieee80211_start_tx_ba_cb_irqsafe !Finclude/net/mac80211.h ieee80211_stop_tx_ba_session !Finclude/net/mac80211.h ieee80211_stop_tx_ba_cb_irqsafe !Finclude/net/mac80211.h ieee80211_rate_control_changed !Finclude/net/mac80211.h ieee80211_tx_rate_control !Finclude/net/mac80211.h rate_control_send_low

## Internals

TBD

This part of the book describes mac80211 internals.

### Key handling

#### Key handling basics

!Pnet/mac80211/key.c Key handling basics

#### MORE TBD

TBD

### Receive processing

TBD

### Transmit processing

TBD

### Station info handling

#### Programming information

!Fnet/mac80211/sta_info.h sta_info !Fnet/mac80211/sta_info.h ieee80211_sta_info_flags

#### STA information lifetime rules

!Pnet/mac80211/sta_info.c STA information lifetime rules

### Aggregation

!Fnet/mac80211/sta_info.h sta_ampdu_mlme !Fnet/mac80211/sta_info.h tid_ampdu_tx !Fnet/mac80211/sta_info.h tid_ampdu_rx

### Synchronisation

TBD

Locking, lots of RCU