Polish and add-ons; the latest updates in Linux 2.6.26

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WiFi ahoy! Part four

Information source: source code administration Many of the links in this article and in the [anchorlink attachment] brief description of interesting but less important changes[/anchorlink] appended to it, point to some related commit or other in the web front end of the Linux source code that Linus Torvald administers using Git. A great deal of additional information can be found there dealing with individual changes and their backgrounds. The patches used in various commits can be found in the web front end under the commitdiff link and the accompanying comments and documentation changes often make them a good source of additional information, even for interested non-programmers. On the lower part of the displayed page, the Git web front end shows a list of files that have been changed in connection with the corresponding commit. To the right of the file names are links that can be used to display the changes to the individual files separately. This makes it possible to view individual changes to the documentation, for instance, or to the Kconfig files that are responsible for the kernel configuration.

Following the integration of the MAC80211 WiFi stack into version 2.6.22 and the numerous drivers based on it in 2.6.24 and 2.6.25, there have once again been a number of improvements to both the infrastructure and the drivers for wireless hardware. The rudimentary support for high speed wireless data transfer according to the IEEE 802.11n draft standard, first integrated into 2.6.25, has been honed even further -- the kernel hackers have activated the fast transfer mode in the iwl4965 Iwlwifi driver.

The WiFi LED found on many notebooks now works correctly with both Iwlwifi drivers â a small detail, but not be underestimated. Kernel developers have done a significant overhaul of the still relatively new cfg80211 wireless configuration interface. This is laying the groundwork for the replacement in the long run of Wireless Extensions, currently used for wireless configuration.

Thanks to the work of the Open80211s project and driver developers, the WiFi stack along with the zd1211rw and b43 drivers can now also handle mesh networks according to draft 2.0 of the IEEE draft standard 802.11s â until now, only the WiFi driver for OLPC notebooks was able to cope with mesh. For the first time, the b43 driver for Broadcom wireless chips supports PCMCIA hardware, as well as QoS (Quality of Service). The older bcm43xx Broadcom driver had to make way for the b43 and b43legacy drivers; the IEEE80211-softmac wireless stack suffered the same fate.

The infrastructure for IBSS (Independent Basic Service Set), used in ad hoc networks has been optimised in a number of ways and now supports IBSS merging. There have also been numerous improvements to the wireless infrastructure when operated as an access point â this is still a work in progress, as what has been done so far is only of real interest to developers and users who like to experiment with additional components and patches. This group may also be interested to read a PDF called "The mac80211 subsystem for kernel developers", recently published by kernel hacker Johannes Berg.

Infrastructure improvements for everyone

Once again, there was a whole range of small improvements to the still quite new Completely Fair Scheduler (CFS). The changes make diverse improvements to the scheduler responsible for handling CPU resource allocation to processes and tasks. People that use desktop systems are unlikely to notice this, since the optimisations can only really be noticed in more complex configurations â among these are environments that depend on realtime characteristics.

Kernel hackers have extended the UDF file system in 2.6.26 to support UDF version 2.50, which is often used on Blu-ray discs. Numerous patches (1,2, 3) further extend the CIFS code to support Microsoft's Distributed File System (DFS). In future, when mounting a share for a Windows or Samba server, CIFS will follow the DFS entries for the actual shares, which are often maintained from other servers â until now, these had to be added directly by hand or other client software had to be used. Also in future, the kernel will react differently when file attributes in CIFS file systems are changed, as long as the server is not using UNIX extensions or Cifsacl -- a special mount parameter allows the legacy behavior to be reactivated.

Well-versed users and kernel developers can now use the KGDB kernel debugger when troubleshooting x86 systems (core, x86 support, documentation, kernel parameters). Torvalds â originally a staunch opponent of integrating a debugger into the kernel â finally integrated KGDB into 2.6.26 without any (public) grumbling after leaving it out of 2.6.25. Kernel hackers took the time between the two releases to make a number of changes that addressed points of controversy in the code and the design of the debugger. These changes, along with others made previously, significantly rebuilt and streamlined the LinSysSoft Technologies maintained debugger -- kernel developers often refer to it as KGDB light, and it still lacks some functions, such as KGDB over ethernet.

Kernel developers have integrated the code supporting Active State Power Management (ASPM), already briefly introduced into the main development line in 2.6.25, in a new revamped form. This allows 2.6.26 to run on less power than its predecessor on modern notebooks â since the kernel hackers expect a few hitches with ASPM, the PCI express power management technology has been deactivated in the standard configuration for the time being.

More: Virtualization technology expanded and updates under the hood

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