1. Basic Expectations
2. Basic Diagram of Component Interaction
3. Understanding what each part does

1. hostapd Configuration
2. ath9k notes

Changelog

• 2009-02-13: Site now hosted at Linode. Johannes Berg pointed out some clarifications. Updated Versions.
• 2009-02-05: Updated Versions. No patching should be required again
• 2009-01-30: Updated Text. Changes/Proofreading by Tony Vroon
• 2009-01-29: Updated Versions. iw patch no longer needed. compat-wireless handles the net_device_ops now.
• 2009-01-28: Updated Versions. Upstream broke using 2.6.28 due to the addition of net_device_ops (I think, I had to revert some commits to make it work), so I added notes on how to get past that. Added temporary patches for latest libnl. They are NOT ready for upstream. For upstream, all references to nl_handle need to be renamed to nl_sock and the patch needs to have those two terms reversed. I'll be doing this tonight. Also, hostapd needed a change for the regulatory code setting with the new stuff. It looks like it was erroring out if the reg domain was already what you were trying to change it to.
• 2008-12-30: Updated libnl version to reflect the last 'good' version. Updated iw to reflect the removal of defconfig/.config
• 2008-12-22: Updated versions. No patching necessary now. All patches have been merged upstream.
• 2008-12-12 #2: Patch merged upstream for iw.
• 2008-12-12: Updated versions. Patches have been updated to work towards how hostapd handles the different versions.
• 2008-12-09: Updated versions. Hostapd no longer requires patch for new libnl
• 2008-12-08: Initial split into stable/git

Warnings/Preface

This document is written targeting those who are looking to jump onto the bleeding edge of linux wireless development. Odds are good that at least one of the packages listed, in the state you grab it, is broken. In fact, they all might be broken when you jump onto it. Once a kernel is released with master mode available by default, and stable releases of all of these packages are available, I'll release a new version of this document that uses stable releases of these packages and outlines all the necessary steps to a stable router.

Basic expectations:

1. Linux Kernel 2.6.27 or later with wireless extensions enabled
   The compat-wireless patchset is not maintained for kernels older then 2.6.27, making older kernels impractical targets
2. Comfortable using the command line
3. Not afraid to break the system we're configuring
4. Basic developmental tools available (gcc, autoconf, git)
5. The account being used to do this has sudo abilities
6. You have a good system backup, and a working restore procedure

Basic Diagram of Component Interaction

[Wireless Card]
      |
[Linux Kernel ]
  |    |
[udev][libnl]-[iw]       
   |  /   \       
 [crda]    \     
    |       \     
[ Wireless ] |
[Regulatory] |
[ Database ] |
             |
             |
        [ hostapd ]

Understanding what each part does

Wireless Card: Should be self explanitory... handles sending/receiving wireless packets

Linux Kernel: The linux kernel contains the driver for the wireless card, the mac80211 subsystem which handles packet generation and scheduling, and the nl80211 subsystem, which handles configuring the wireless interfaces for userspace

libnl: libnl is the transport layer used to communicate with the kernel via netlink

udev: udev is the facility the kernel uses to pass events/calls to crda

iw: iw is a userspace utility that we can use to test that libnl is working correctly, as well as create additional virtual wireless interfaces on the wireless card

crda: crda is a userspace program that the kernel queries (through udev) to find what channels/frequencies are usable, and at what powers. This moves the information out of static tables maintained in kernel to userspace, which allows them to be updated without reloading drivers/rebooting

Wireless Regulatory Database: database of allowable frequencies and transmit power levels used by crda

hostapd: This is the daemon that handles generation of beacons and other wireless packets, as wel as wpa-psk, wpa2, etc encryptions.

Successes/Failures/Questions/Concerns to: wireless@erley.org

Get Code

# you'll want to change this if you're doing this somewhere other than /usr/src
cd /usr/src

# Get the wireless-testing tree (this will take a while) 
git clone git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless-testing.git

# Get compat-wireless
git clone git://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/compat-wireless-2.6.git

# Get wireless regdb
git clone git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless-regdb.git

# Get crda
git clone git://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/crda.git

# Get libnl (optional)
git clone git://git.kernel.org/pub/scm/libs/netlink/libnl.git

# Get Hostapd, wpa-supplicant, etc...
git clone git://w1.fi/srv/git/hostap.git

# Get iw 
git clone http://git.sipsolutions.net/iw.git

Build libnl & install it

# You only need to do this if your distro doesn't ship a relatively recent version
# of libnl.  Most distros are shipping libnl-1.1 or later, which will work for
# what we need.
cd libnl

# This is going to install libnl into /usr.
# you may need to point this elsewhere for your system.
autoconf
./configure --prefix=/usr
make && sudo make install
cd ..

Build crda & install it (and install the wireless regdb)

cd wireless-regdb

# First we need to create the location for the wireless regulatory
# database
mkdir -p /usr/lib/crda

# Now we copy the regulatory db over.  Note, no need to 'make' here as
# the wireless regdb shipped by git is already signed and setup as needed
cp regulatory.bin /usr/lib/crda/

cd ..

# Now we build crda
cd crda

# I HIGHLY recommend installing this as it configures udev for using crda
# automatically.
make && sudo make install

cd ..

Build iw & install it

cd iw

# You can leave out the 'sudo make install' if you don't want
# to install iw or overwrite your system iw.
make && sudo make install

cd ..

Build hostapd & install it

cd hostap/hostapd

# Copy the default config to .config for use during this build
cp defconfig .config

# Edit .config
vi .config 

#  you need to uncomment these lines, at a minimum, and make sure
#  CONFIG_LIBNL_LOC points to wherever you installed libnl to in
#  step 3.
# 
#  CONFIG_DRIVER_NL80211=y
#  LIBNL=/usr
#  CFLAGS += -I$(LIBNL)/include
#  LIBS += -L$(LIBNL)/lib
#
#    and add
#
#  CONFIG_LIBNL20=y
#
#  If it dies with: 
#      error: 'struct hostapd_config' has no member named 'ieee80211n'
#
#  uncomment
#
#  CONFIG_IEEE80211N=y
# 

# You can leave out the 'sudo make install' if you don't want 
# to install hostapd or overwrite your system hostapd.
make && sudo make install

cd ../..

Build compat-wireless & install it

cd compat-wireless-2.6
export GIT_TREE=../wireless-testing
scripts/admin-update.sh
make && sudo make install

Notes & Addendums

1. hostapd Configuration

   Configuring hostapd to use the nl80211 driver is as easy as:

   interface=wlan0 # Replace this with your wireless interface
     driver=nl80211

2. ath9k notes

   802.11n support can be configured in the appropriate section of hostapd.conf, here's the config I'm currently using for my ath9k device, listed as: Atheros AR5416 MAC/BB Rev:2 AR2133 RF Rev:81

   ieee80211n=1
     ht_capab=[HT40-][SHORT-GI-40][DSSS_CCK-40]

   the ht_capab shown here is based on a combination of voodoo and the output of iw list, and may or may not be accurate as I don't yet have any other 802.11n devices to test with