The kernel column by Jon Masters # 81

John Masters is a Linux kernel hacker who has been working on Linux for almost 14 years, since he first attended university at the age of 13. Jon lives in Cambridge, Massachusetts, and works for a large enterprise Linux vendor. He publishes a daily Linux kernel mailing list summary at kernelpodcast.org and writes monthly columns for Linux User & Developer.

September saw the 2.6.31 release of the Linux kernel.

With it came the usual raft of new features: support for USB 3.0 (big thanks are due to Sarah Sharp and the Intel crowd for their work on that), CUSE (character devices in userspace), support for working with hardware performance counters, an in-kernel memory leak checker called Kmemleak (from the ever awesome Catalin Marinas) and many, many dozens of other features besides. You can see a list of these on the (community maintained) website at www.kernelnewbies.org/.

As mentioned, amongst the new features was support for character devices in userspace (CUSE). Just like FUSE allows file systems to be implemented as regular user programs that supply ‘file’ data to the kernel, CUSE allows character devices (such as sound cards) to be implemented in a similar fashion and using some of the same APIs as does FUSE. So while FUSE brought the ability to simply implement remote ssh or ftp file system mounts on your desktop, CUSE will eventually allow older sound subsystem APIs such as OSS to be implemented as simple wrappers in userspace.

Kmemleak was another great feature in the 2.6.31 kernel. It allows developers to receive an automated warning whenever the kernel seems to lose track of memory without properly cleaning it up. It fits in nicely with other efforts such as the ‘mudflap’ patches currently being worked on – these being intended to instead track unintended use of previously freed memory without allocation. Both these and other features should help track down more memory-related bugs before they bite – there was a minor memory corruption bug in fork code found just this past month, after being there for goodness knows how many years.