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7.4 Linux Bluetooth Support

As with many emerging technologies, there are competing
implementations of Linux Bluetooth support. The main two
implementations are
Affix and
BlueZ. Affix
was originally developed by Nokia and is now hosted as an open source
project at
SourceForge
(http://affix.sourceforge.net).
BlueZ is also hosted at SourceForge is (http://bluez.sourceforge.net) and the
official Bluetooth stack of the Linux kernel.

Although Affix is a mature and functional project, BlueZ receives
more testing and has more widespread adoption. For this reason, this
chapter focuses on the uses of the BlueZ Linux Bluetooth stack and
libraries.

This section includes all the information that you need to install
and configure Bluetooth support from scratch. It is possible that
your Linux distribution already contains preconfigured Bluetooth
support, which will save you effort. However, the installation
instructions provide useful background information for
troubleshooting.

7.4.1 Distributions

As Bluetooth is a relative newcomer to Linux, BlueZ support across
commercial distributions varies. Generally speaking, if the kernel
shipping with your distribution is older than 2.4.22, it is a good
idea to upgrade it. Users of
"bleeding-edge" distributions such
as Debian Unstable and Gentoo should find that Bluetooth is
adequately supported.

7.4.2 Configuring the Kernel

Bluetooth support under
Linux requires a recent kernel. If your
kernel is Version 2.4.22 or better, or a 2.6 series kernel, then
you're all set. Otherwise, you must upgrade your
kernel. Alternatively, if you do not wish to upgrade, and have kernel
2.4.18 or better compiled from source, you can apply the patches from
the "kernel patches" area of the
BlueZ web site (http://bluez.sourceforge.net). Regardless,
it's worth checking out the patches, because there
are often improvements available that have not yet been merged into
the main Linux kernel source.

cd /usr/src/linux 
gzip -dc  ..  /patch-2.4.22-mh1.gz | patch -p1 

find . -name '*rej'

Chapter 2 explains how to configure and compile
a kernel. Table 7-3 and Table 7-4 show the options that must be set in your
kernel configuration to enable Bluetooth support. You can either
configure Bluetooth support to be compiled into the kernel or to be
loadable on-demand in the form of modules. Many Linux distributions
choose to ship with modules, so we proceed on the assumption that you
will use modules. This removes the need to recompile your kernel if
you acquire a different type of Bluetooth device.

Figure 7-3 and Figure 7-4 show
the Bluetooth configuration options from the 2.4.24 kernel.

Figure 7-3. Configuring Bluetooth support in the Linux kernel

Figure 7-4. Configuring Bluetooth hardware support in the Linux kernel

You should not enable the Bluetooth device support in the USB drivers section of your kernel configuration (CONFIG_USB_BLUETOOTH). This is a vestigial driver from very early Bluetooth work and will prevent the BlueZ Bluetooth stack from operating. If you are using a distribution's precompiled kernel, this corresponds to the bluetooth kernel module, and you should prevent it from being loaded. This can be done either by ensuring the BlueZ hci_usb module is loaded instead of the USB Bluetooth module or by disabling the module by adding its name to hotplug's configuration list (/etc/hotplug/blacklist).

Once your kernel is compiled and you have rebooted, you must
configure Linux so it knows how to load the appropriate Bluetooth
protocol modules. Most modern distributions come with
/etc/modules.conf already set up for Bluetooth
use, but you may be missing the required configuration.

To verify this, ensure that the contents of Example 7-1 are present in
/etc/modules.conf. If you need to change this
file, run depmod -a to ensure automatic loading of
modules by the kernel. You must be the root user to perform this
operation.

Example 7-1. Module configuration for BlueZ

# BlueZ modules
alias net-pf-31 bluez
alias bt-proto-0 l2cap
alias bt-proto-2 sco
alias bt-proto-3 rfcomm
alias bt-proto-4 bnep
alias tty-ldisc-15 hci_uart
alias char-major-10-250 hci_vhci

Linux distributions may vary in the way they manage the /etc/modules.conf file. Debian GNU/Linux, for example, requires you put the contents of Example 7-1 in a separate file in /etc/modutils and run /sbin/update-modules; however, if you use the pre-packaged Debian BlueZ utilities, this file is already provided for you.

7.4.3 Supporting Subsystems

Depending on your hardware configuration, you must ensure you are
running some extra supporting software to initialize your Bluetooth
device.

7.4.3.1 PCMCIA

If your Bluetooth adapter is a PC card or a CF card, you must have
kernel support for PCMCIA and the
PCMCIA card services software installed.
This software is responsible for initializing your adapter when it is
plugged in and loading the required drivers into the kernel.

BlueZ requires PCMCIA card services to be Version 3.2.2 or higher. If
your Linux distribution has an older version, you can update it from
http://pcmcia-cs.sourceforge.net.
See Chapter 2 for complete instructions on
compiling pcmcia-cs from source.

7.4.3.2 Hotplug

The Linux hotplug
subsystem enables you to plug in a device and have it immediately
ready to use. It is similar in function to the card manager from
PCMCIA card services, except it is generalized to include USB,
Firewire (IEEE 1394), and network devices. The 2.6 series of Linux
kernels adds hotplug capability to even more subsystems, such as SCSI
and input devices.

When hotplug detects a new device, it loads the necessary driver
modules into the kernel, and it runs any scripts the user has
configured. In the case of BlueZ, hotplug is required for certain
Bluetooth devices that require firmware downloaded to them, such as
the USB dongles based on the Broadcom chipset.

Hotplug ships with most Linux distributions. Version 2002_08_26 or
later is required. If you need to install it separately, download it
from http://linux-hotplug.sourceforge.net/.