Torvalds Releases Kernel 2.6.25: GPL Only Restriction Imposed

Apr 18, 2008

Linus Torvalds has released the new 2.6.25 kernel just slightly behind schedule. Besides improvements to the CFS scheduler and a plethora of new drivers, the kernel also introduces a political aspect: it debars non-GPLd USB drivers.

Linus Torvalds actually wanted to release version 2.6.25 last weekend, but the large number of patches caused Torvalds and the developer team to wait another couple of days before going for the release, and to introduce an intermediate pre-release. The final release is now here and it considerably boost the range of supported hardware. Many lines of code introduced various improvements for the fairly recent Mac80211 WLAN stack including the new "Ath5k " driver for Atheros WLAN chips, as a successor to the Madwifi driver. The new driver is dual licensed under the GPL and the ISC license, a simplified BSD license, compared to Madwifi which never made the kernel due to proprietary components. "rtl8180" now supports the RTL8180 and RTL8185 WLAN chips by Realtek. Support for chips that support the fast Draft N standard has been introduced and no longer has an experimental tag.

Another fairly recent kernel component has been reworked, the Completely Fair Scheduler, which has been optimized for realtime environments. The SMACK security framework is completely new. It promises improved handling compared to SELinux. A patch that allowed the kernel to use a differentiated system description table (DSDT) in the initial ramdisk has been removed. This re-introduces the kernel's reliance on the DSDT information in the computer BIOS which are often erroneous.

A political dimension has been added in the form of a controversial change to USB support. Developer Kroah-Hartman pushed through his change outlawing proprietary USB drivers. This has been implemented in the form of the USB kernel driver "EXPORT_SYMBOL_GPL" flag which has to exist to export required interfaces. This means that drivers will need to be GPLd or released under a compatible license to make the grade. The kernel had a similar patch previously, but it was removed in favor of better hardware support.

The enhanced "ext4" filesystem is not yet suitable for production use and is included in the kernel mainly for test and development purposes. Among other features it includes large file and large filesystem support, along with journal checksums that log changes to the filesystem and thus allow data to be restored after a crash. Progress has been made with respect to the x86 and x86_64 branch merges. New drivers have also been introduced for the network and audio subsystems..

The changelog has an extensive list of changes. As usual, the new kernel is available either as a patch, or as a complete source code package from the kernel.org site.

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