Constructing Red Hat Enterprise Linux v. 3
Many people have little understanding of the behind-the-scenes efforts required to construct an enterprise Linux distribution. The fact that this process largely can be taken for granted is actually a compliment. This article offers a glimpse into the methodology we used to deliver Red Hat Enterprise Linux v. 3 (Enterprise Linux v. 3). As you will see, we faced numerous challenges along the way. Then again, if it would have been easy, it wouldn't have been so much fun.
Throughout this article, the focus is on how the release was put together. This article primarily discusses the development of the kernel used in Enterprise Linux v. 3. The kernel is only a fraction of an overall distribution, the portion that controls the underlying hardware and system resources. The challenges faced by the other teams, with projects such as compiler tools, the installer, hundreds of application packages, documentation and testing, are equally daunting. Each of these items was developed by gifted individuals.
Allow me to start by noting that we here at Red Hat have established strong relationships with our key partners in the industry. Although partners' anonymity is guarded here, I'm sure they can identify where they fit in to this story and recognize that it's all in good humor.
High customer expectations have been set by the proprietary UNIX operating systems, and customers planning to migrate from UNIX to Linux do not want to adopt technology that cannot deliver the same level of robustness, quality, support and compatibility. Business users demand stability and reliability. In some cases this means bleeding-edge technology is not appropriate for inclusion in a product. Users also want the ability to run across a wide range of architectures and hardware components, thereby realizing the Linux goals of avoiding proprietary vendor lock-in. Support needs to be in the form of ongoing maintenance for several years, including security and bug fixes, as well as incremental hardware support and valuable, but not destabilizing, feature enhancements.
The ball gets rolling on a new release by identifying the targeted feature set. Next to strong opinions, the second most plentiful commodity at Red Hat is feature requests. They come from all directions, such as insatiable independent hardware/software vendors, demanding customers, both large and small, and Red Hat's worldwide sales and service support organizations. Additionally, as many ideas are generated within Red Hat engineering, ranging from performance and usability enhancements to marketing proposals on how to organize the product set.
Obviously, we don't have infinite developer resources, so the major challenge is to choose the best of these ideas. Another key feature acceptance criteria is conformance with upstream Linux direction, which is necessary for compatibility and to remain true to the spirit of the kernel.org tree governed by Linus Torvalds and containing contributions from around the world.
Here's a few examples of the challenging scenarios we face in requirements gathering:
We ask each of our partners to submit a reasonably sized top-ten list. One partner's requirements came in the form of a binder that was two inches thick. This became affectionately known as the bible. My first exposure to the bible came when it was heaved onto my desk with a resounding thud. When I saw that, I swear that my heart went thud, too.
The more mathematically inclined partners do internalize the concept of a top-ten list. However, most ended up using a tactic that those of you familiar with TCP/IP networking should recognize—the sliding window protocol. The way it works is as soon as any of your features have been accepted, those pop off the top of the stack, freeing up space for features 11, 12 and 13 to all of a sudden become cataclysmic issues.
The following is a representative example feature list from a hardware vendor:
Support more than 32GB of memory on x86.
Support more than eight CPUs.
Support for our new XYZ100 series computers. (This is a thinly veiled multiple feature request; behind it is a series of required device drivers, PCI IDs and installer hooks.)
Updated I/O adapter driver. (This ultimately turns into differences of opinions regarding to which newer version this refers).
Integrated support for the vendor's proprietary baseboard management software. (A perennial list item, which consistently gets rejected to the amazement of the requester.)
Compiler optimizations to match the latest chipsets.
USB support for our CD-ROM drive. (Needed because the drive is brain-dead and doesn't conform to the spec—of course that subtlety is absent in the initial feature request.)
Support for more than 128 disks.
Then, there's typically the following implied requirements:
All of these feature requests apply to multiple architectures, including x86, AMD64 and Itanium 2.
Oh, by the way, we also want this feature backported to the prior Enterprise Linux v. 2.1 release.
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