See also: last week's Kernel page.

Kernel development

The current stable kernel release is 2.2.11, though likely not for long. This release, it turns out, has a bug that causes a massive kernel memory leak in certain networking situations. In some cases, it can bring down a system in a hurry, resulting in grumpy users. Thus, Alan Cox has released a series of 2.2.12 pre-patches which contain the fix (by David Miller) and a lot of other stuff.

Perhaps the most controversial thing in 2.2.12pre is the inclusion of RAID 0.90. Serious RAID users have been waiting for this upgrade for a long time; now they can stop applying the patches separately. The update should also be welcome to Red Hat 6.0 users, since Red Hat slipped the newer RAID into their version of 2.2.5 for that distribution.

Others, however, are not so pleased. RAID 0.90 is a major and incompatible upgrade from the earlier versions. New utilities are required, the configuration file is different, and the format of the RAID arrays themselves is different. In theory the distributors should have been shipping the newer raidtools (which can work with the older implementation) for some time; some posts seem to indicate that not all distributions have done this, however. The configuration file change is not that hard to do, and the RAID array conversion happens pretty easily as well.

The real problem is this: once you have converted your RAID array to the new format, you are stuck with the new implementation. This, if 2.2.12 turns out not to work in a particular situation, moving back down to an older kernel becomes a hard and unpleasant task. That tends to scare people who are using the older RAID system, and understandably so.

Alan intends to push forward with the new RAID anyway, though he leaves the final decision to Linus. RAID 0.90 is a vastly improved implementation which certainly needs to get into the mainline, stable kernel at some point. 2.4 is still some months away, perhaps it is better to work in this code now.

Incompatible changes may happen again in 2.2.13, when the NFS patches are tentatively slated to be integrated. The new NFS code requires new versions of the NFS utilities which are not currently found in any of the distributions. There will likely be less complaining about this one, however. Any site which has been doing serious NFS service - especially in heterogeneous environments - has had to apply these patches anyway. The NFS update will give Linux a reasonable NFS server - for version 2 NFS, anyway.

Along these lines, knfsd 1.4.7 has been released by H.J. Lu. H.J. also notes that he has put the slides for his LinuxWorld NFS talk (which was interesting) on his FTP site as 'nfs.doc.tar.gz'. Details in his announcement.

Alex Buell has tracked down a strange 2.2 lockup problem that has been bothering him for some time. However, it is a difficult problem involving complex feline interactions; a patch may prove difficult to develop. Details in his note.

Use of up to 4GB of physical memory on IA-32 (x86) systems is now possible, thanks to a patch posted by Andrea Arcangeli of SuSE and Gerhard Wichert of Siemens. This patch, which applies to 2.3 kernels, allows the use of up to 4GB of memory as "anonymous" pages. Anonymous memory belongs to a process, but is not associated with a file on disk. Thus, you can malloc() huge arrays, but memory-mapping large files can not take advantage of the extra memory.

More information can be found in the announcement. The actual patch has been removed, because it is outdated at this point; a current version can be found on Andrea's FTP site. Linus has indicated that this patch will go into the 2.3 series, once he gets some changes he requested.

What's coming with 2.4 Joseph Pranevich has sent us the latest version of his Wonderful World of Linux 2.4 paper. Therein you'll find a detailed discussion of the changes to be found in the upcoming (year-end) stable kernel release.

Other patches and updates released this week include:

• The driver programming interface (DPI) version 0.1.0 has been released by David Olofson. DPI is an interface layer which is meant to help in the porting of drivers to the real-time Linux environment.

• Ulrich Windl released PPSkit 0.7.1, his patch for modern Network Time Protocol support and nanosecond timekeeping.

• Version 0.7 of the USB HOWTO has been released by Brad Hards.

Section Editor: Jon Corbet

For other kernel news, see: Kernelnotes Kernel traffic Kernel Newsflash

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