Torvalds releases Linux kernel 2.6.25

Linus Torvalds has released the latest version of the "stable" Linux kernel, version 2.6.25, which includes changes to Wi-Fi support, virtualisation, real-time scheduling and file systems.

The kernel, which was released approximately 10 weeks after its predecessor, includes broader Wi-Fi hardware support and the integration of more Wi-Fi drivers, according to Linux developers. Among the drivers integrated is Ath5k, which is compatible with chips by semiconductor system Wi-Fi developer Atheros.

On the virtualisation front, the KVM x86 emulator has been updated with more instructions and components, designed to improve performance and compatibility. Virtual prototyping platforms framework Virtio has also been updated, while paravirt_ops now works on the x86-64 architecture.

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Performance improvements were made to the Completely Fair Scheduler (CFS) real-time technology, which gets its first support for LatencyTop, a tool for helping track down latency problems.

The Ext4 file system also saw changes, and now uses checksums to ensure journal integrity. Ext4 is a journalling file system -- a file system type becoming popular because of its resistance to corruption in the event of a system crash or power failure.

The kernel includes the Smack (Simplified Mandatory Access Control Kernel) security framework, which is based on a set of mandatory access control rules and is designed for simplicity.

Developer improvements to Linux have been showing up as significant reliability gains in the enterprise over the past two years according to a recent Yankee Group survey, which found Linux distributions from Red Hat and Novell have increased reliability by an average of 75 percent since 2006.

However, Linux 2.6.25 implements a policy that could cause problems for some administrators: forbidding proprietary USB drivers access to certain core functionality. Developers warned two years ago this change was coming, but many USB drivers nevertheless remain proprietary. The 2.6.25 kernel includes changes that could cause problems for proprietary USB drivers that take the form of kernel modules.

Such drivers can no longer be compiled with unmodified Linux 2.6.25, due to the fact that the licence of an important API is only compatible with drivers that carry a GPLv2 or compatible licence.

Developers included this feature for a time in the development of kernel 2.6.16 in 2006, but it was removed before the kernel was finalised in order to give driver makers an opportunity to produce open-source drivers. However, many drivers remain proprietary.