Category Archives: linux

There might be several reasons why the wireless drivers from your distro don’t fit the bill. You purchased a new wifi card which doesn’t have a driver in the kernel of your Linux system, or you would like to play with some cool new feature or just to make sure you have the latest and greatest, cutting edge 802.11 software.

Thanks to the work of the Linux wireless developers it is now possible to do that without upgrading your kernel. Using a compatibility layer you can compile and install the latest drivers and the 802.11 stack, and use it with your current kernel (that is, if you have a relatively recent kernel — if you have 2.6.24 or anything more recent, you’re good to go).

To use bleeding edge drivers, first make sure your kernel headers package is installed. Then fetch the necessary git trees:

mkdir compat-wireless && cd compat-wireless
git clone git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
git clone git://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/compat.git
git clone git://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/compat-wireless-2.6.git


The linux-next git tree contains the code for the next kernel release, and 802.11 updates are pulled into it on a regular basis. The compat and compat-wireless-2.6 trees implement the necessary compatibility layer, thus making it possible to use the wireless subsystem from linux-next with your kernel. You can also use your git trees to follow development, and keep your wireless drivers up to date: just pull from the remote repositories when you’d like to update. However, the linux-next repository is rebased on a regular basis, so you may want to check out the daily tag instead of pulling.

You can use the compat-wireless-2.6 directory to actually build the wireless subsystem:

cd compat-wireless-2.6


Specify where your newly fetched kernel tree and the compat tree are:

export GIT_TREE=`pwd`/../linux-next/
export GIT_COMPAT_TREE=`pwd`/../compat/


Then refresh compat-wireless-2.6 with the contents of your git trees:

./scripts/admin-refresh.sh


You can also select just a specific driver or group of drivers, e.g. if you only need the ath5k driver:

./scripts/driver-select ath5k


And that’s it, everything should be ready for the build.

make
sudo make install


Your newly built modules will go into the updates folder inside your kernel module directory. Reboot your box (or use the scripts supplied with compat-wireless-2.6 to reload any drivers).

Nowadays virtually all Linux distributions use NetworkManager to manage available network interfaces.  It makes interfaces connect automatically, for instance wireless network cards associate automatically to the access point with the strongest signal; ethernet cards can be set up via DHCP or configured with static parameters.

However, the strategy for keeping wireless interfaces connected involves scanning all available channels periodically — typically every two minutes.  For some wireless drivers, such as ath5k and ath9k this might take quite a few seconds, which means network traffic will stall for this period.  Even worse, while the problem is known, it is not possible to disable this feature or override the frequency of scans.  Background scanning is supposed to solve this issue, but the ath5k driver in Ubuntu Lucid does not support it yet.

Out of any other options, I decided to disable scanning in the source code and recompile NetworkManager.  It is quite trivial; as a first step, just fetch the source package:

% apt-get source network-manager

This will fetch and unpack the source tree of the network-manager package.

Update: you can install the build dependencies of network-manager via (thanks Andreas for the tip):

% apt-get build-dep network-manager

Save this patch, step into the network-manager folder, and apply the diff:

% curl -O http://nilvec.com/downloads/network-manager_disable-scan-if-connected.patch

% cd network-manager-0.8

% patch -p1 < ../network-manager_disable-scan-if-connected.patch

Update: to make sure Ubuntu won’t reinstall the original package you can bump the version of network-manager via (debchange is in the devscripts package):

% debchange -i

Just bump the version, or extend the version string with an extra part e.g. if you had 0.8-0ubuntu3, make it 0.8-0ubuntu3-disablescanning0.

% fakeroot dpkg-buildpackage

This patches and builds NetworkManager with scanning disabled while connected to an active access point.

% cd .. && sudo dpkg -i network-manager_0.8-0ubuntu3_i386.deb

There you go.  You should restart the network-manager service (or reboot your machine), and everything should work as supposed — no network stalls or lost packets due to wireless scans.