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In-depth insights

Information from the Ottawa Linux Symposium (OLS) 2008 presentations

Thorsten Leemhuis

A range of background information around current and future developements in the Linux kernel have been made available in the PDF versions of the presentations recently given at the OLS. Users interested in the Linux kernel and its environment can, for example, find a good overview of the current development of the Wifi subsystem and details about several improvements to the ACPI subsystem currently in progress. Security-related issues, virtualisation, and regression and performance testing are also among the presented topics.

As in previous years, the organisers and presenters at the Ottawa Linux Symposium (OLS) 2008 held last week have made PDFs available with versions of the conference's presentations available for download. The documents don't just contain superficial PowerPoint or OpenOffice Impress presentations as is the custom at other conferences. Instead, the two PDF collections (1, 2) and the lecture-specific documents offer a vast amount of information interspersed with images, screen shots and diagrams on 550 tightly packed pages. As many of the kernel developers attend or present at the conference, many of the presentations deal with the background of current and future Linux kernel developments. There were also presentations about security-related aspects and userspace software.

Wifi support in the kernel: Retrospective, current status and outlook

Many users who run Linux on notebooks will probably be interested in the OLS presentation Tux on the Air: The State of Linux Wireless Networking". In this presentation, Red Hat employee and Wifi subsystem maintainer John W. Linville gives a good overview of the Linux kernel's current Wifi support options and offers some information about future developments.

Linville describes some background details and problems with the development of the MAC80211 Wifi stack. Many of the initial difficulties of this Wifi stack - which has been part of the main development branch since kernel version 2.6.22 - have been solved, says Linville, adding that the kernel now also contains a large number of Wifi drivers based on MAC80211. As a result, many users of the current kernels can start using their Wifi hardware with relatively little effort.

Additional Wifi drivers are still being developed. They include a MAC80211 variety of the tiacx driver suitable for old Wifi chips by Texas Instruments. However, legal issues surrounding the driver, developed by reverse engineering, currently prevent it from being integrated into the Linux kernel. If Texas Instruments cannot assist with the clarification of these issues, the Software Freedom Law Center (SFLC) may be called upon for help, said the text, referring to a similar case with the ath5k driver for Atheros hardware last year.

Still in an early stage of development is the as yet non-functional agnx driver for Airgo Wifi chips. It was programmed using documentation created by reverse engineering. However, there is now no developer to continue the reverse engineering process. The at76_usb and mrv8kng drivers for Atmel and Marvell Wifi chips, on the other hand, are in a better position. In the text of the presentation already written several weeks previously, Linville is optimistic that the two drivers can already be included in 2.6.27. However, the drivers are currently neither part of the main development branch nor of linux-next; therefore, the Wifi subsystem maintainer's hope may be unfounded and the drivers may only be incorporated in a future version of Linux.

The presentation also mentions a number of planned or pending improvements to the Wifi subsystem. It describes the cfg80211 configuration interface which is already partially supported by the kernel and is designed to replace the Wireless Extensions intermediary layer for configuring Wifi hardware. In addition, the Wifi stack and some drivers are soon to be fully compatible and co-operate with the HostAP software to provide a Wifi access point. According to the presentation the relevant code already exists in the kernel but is disabled.

However, Linville lists several other areas which are in need of improvement. Among them is the power management, which according to the presenter has a lot of room for improvement. For example, the connection to the access point is completely re-established from scratch every time a Linux system wakes up from standby (like ACPI S3/Suspend to RAM); while this usually works fine, it is not always reliable and causes delays when waking up the system, says Linville. He also notes that drivers and WLAN stack have so far not supported other power saving techniques offered by modern WLAN hardware.

At the end of the presentation, Linville mentions problems with WLAN firmware licensing and addresses the co-operation with the hardware vendors, criticising Broadcom for not contributing to the development of WLAN drivers and for not releasing any documentation like they did for their LAN hardware. On the other hand, Linville has praise for Ralink and Intel. He summarises that the situation around WLAN support has improved considerably recently. While WLAN support used to be a "ghetto" in Linux it is now no longer the operating system's greatest problem, he said.

Next: ACPI, power saving, virtualisation and performance...

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