Stories by Jonathan Corbet

Kernel space: udev rules, but whose?

Once upon a time, a Linux distribution would be installed with a /dev directory fully populated with device files. Most of them represented hardware which would never be present on the installed system, but they needed to be there just in case. Toward the end of this era, it was not uncommon to find systems with around 20,000 special files in /dev, and the number continued to grow. This scheme was unwieldy at best, and the growing number of hotpluggable devices (and devices in general) threatened to make the whole structure collapse under its own weight. Something, clearly, needed to be done.

Making power policy just work

The kernel can't know if you want those low-priority processes to use all the CPU power on the system, or if you want them to pile up on one CPU and save power on the rest. Developers debate the best way to set the system's power rules.

Kernel space: The Tru64 Advanced Filesystem

On June 23, HP announced that it was releasing the source for the "Tru64 Advanced Filesystem" (or AdvFS) under version 2 of the GPL. This is, clearly, a large release of code from HP. What is a bit less clear is what the value of this release will be for Linux. In the end, that value is likely to be significant, but it will be probably realized in relatively indirect and difficult-to-measure ways.

Kernel space: drivers that don't make the kernel scene

Arjan van de Ven's kernel oops report always makes for interesting reading; it is a quick summary of what is making the most kernels crash over the past week. It thus points to where some of the most urgent bugs are to be found. Sometimes, though, this report can raise larger issues as well. Consider the June 16 report, which notes that quite a few kernel crashes were the result of a not-quite-ready wireless update shipped by Fedora. Ingo Molnar was quick to jump on this report with a process-related complaint:

Kernel space: Interview with Andrew Morton

Andrew Morton is well-known in the kernel community for doing a wide variety of different tasks: maintaining the -mm tree for patches that may be on their way to the mainline, reviewing lots of patches, giving presentations about working with the community, and, in general, handling lots of important and visible kernel development chores. Things are changing in the way he does things, though, so we asked him a few questions by email. He responded at length about the -mm tree and how that is changing with the advent of linux-next, kernel quality, and what folks can do to help make the kernel better.

Kernel space: The big kernel lock strikes again

The AIM benchmark attempts to measure system throughput by running a large number of tasks (perhaps thousands of them), each of which is exercising some part of the kernel. Yanmin Zhang reported that his AIM results got about 40% worse under the 2.6.26-rc1 kernel. He took the trouble to bisect the problem; the guilty patch turned out to be the generic semaphores code. Reverting that patch made the performance regression go away - at the cost of restoring over 7,000 lines of old, unlamented code. The thought of bringing back the previous semaphore implementation was enough to inspire a few people to look more deeply at the problem.

Kernel space: Time to slow down?

All communities develop rituals over time. One of the enduring linux-kernel rituals is the regular heated discussion on development processes and kernel quality. To an outside observer, these events can give the impression that the whole enterprise is about to come crashing down. But the reality is a lot like the New Year celebrations the author was privileged enough to see in Beijing: vast amounts of smoke and noise, but everybody gets back to work as usual the next day.

Ksplice: kernel patches without reboots

The kernel developers are generally quite good about responding to security problems. Once a vulnerability in the kernel has been found, a patch comes out in short order; system administrators can then apply the patch (or get a patched kernel from their distributor), reboot the system, and get on with life knowing that the vulnerability has been fixed. It is a system which works pretty well.

A better ext4 filesystem for Linux

Linux's ext4 filesystem, the successor to ext3, may well be the filesystem many of us are using a few years from now. Things have been relatively quiet on that front - at least, outside of the relevant mailing lists - but the ext4 developers have not been idle. Some of their work has now come to the surface with Ted Ts'o's posting of the ext4 merge plans for 2.6.25.

Kernel space: a better btrfs

Chris Mason has recently released Btrfs v0.10, which contains a number of interesting new features. In general, Btrfs has come a long way since LWN first wrote about it last June. Btrfs may, in some years, be the filesystem most of us are using - at least, for those of us who will still be using rotating storage then. So it bears watching.

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