Constructing Red Hat Enterprise Linux v. 3
Countless external requests ask for either proprietary additions or hooks. In the open-source tradition, this is something we consistently have to refuse.
For Enterprise Linux v. 3, the initial set of requested features was about 500 items. Each of these was entered into our feature-tracking tool called Featurezilla, which actually is a derivative of the Bugzilla bug-tracking tool. Figure 1 shows several items in Featurezilla. To show that the jabs go both ways, one partner has a business manager whose name is Paul, name changed to protect the innocent. He manages a list as a text file, but back at his company, the list is referred to as Paulzilla.
We had countless tortuous internal meetings to prioritize and slog through the full set of 500 items. From that prioritized list, the engineering managers went off to try to get the list down to a manageable set that is humanly achievable by their team members. Ultimately, the list is negotiated down to something that vastly exceeds anything reasonably achievable by the development team. But, that's the Red Hat way, and it's only the beginning of the story.
To keep things interesting, in addition to having to develop to an aggressive schedule for Red Hat Enterprise Linux v. 3 development, a large amount of effort also is required to support the Enterprise Linux v. 2.1 maintenance stream. By the time Enterprise Linux v. 3 shipped, v. 2.1 had been out for 15 months. Because we provide a five-year life cycle for releases in the Enterprise Linux family, we simply cannot dump Enterprise Linux v. 2.1 support and maintenance work. The requirements demanded by our partners in the maintenance stream form an interesting paradox. When it comes to the objectives of the maintenance stream, it seems that all partners and high-profile customers speak out of both sides of their mouth. “Don't change anything! I'm using this release in production. Don't upset the apple cart”, is followed by “I really need this feature immediately. Hurry up and give it to me, but don't put anything else in.”
Ultimately, it all boils down to a careful case-by-case risk/benefit assessment. Internally, we review features and bug-fix proposals among the engineering ranks. It is well beyond my literary abilities to convey the strong-willed and passionate debates conducted over incorporating features or bug fixes that straddle the risk/benefit fence.
Some people have the mistaken impression that Red Hat simply pulls together a random collection of bits and pieces from the upstream Open Source community, slaps the Red Hat name on it and calls it a product. Truth be told, Red Hat engineers contribute a substantial percentage of upstream (for example, 2.4 and 2.6) kernel development. The productivity, breadth of knowledge and ability to be on top of a torrent of internal and external communication demonstrated by these kernel developers is stunning. They truly are world class and humbling to be among. But don't tell them that, lest it goes to their heads.
In addition to the sizable upstream enhancements that get pulled back into the Enterprise Linux kernel, a large set of enhancements is developed in-house to meet the product requirements. As an open-source company, all of the kernel enhancements are available to the community at large. The vast majority of these changes do end up being incorporated upstream.
The kernel in Enterprise Linux v. 3 primarily is based on the 2.4.21 kernel, but it has a huge number of features backported from the more recent 2.6 kernel. In recognition that the 2.6 kernel had not yet been stabilized, only key features deemed commercially ready were candidates for the backport into Enterprise Linux v. 3. Here's a little tip on how to really annoy a Red Hat kernel developer: say something like, “So, you guys just ship the stock 2.4.21 kernel; right?”
The most daunting challenges in constructing the Enterprise Linux v. 3 kernel were the requirements that support be provided for seven different architectures and that the kernels for these architectures all must be built from a common source tree. The seven architectures include: x86 (and Athlon), AMD64, Itanium 2, IBM mainframe (both s390 and s390x) and IBM's iSeries and pSeries PPC systems. Although each of these architectures is supported by the upstream kernels in varying degrees, the reality is many of these architectures are developed primarily in isolation. This inevitably leads to integration nightmares.
Another interesting twist to the story is Red Hat's kernel development team literally is spread all over the world. Out of necessity, this has led to virtually all interaction being done on-line. For example, we rarely have team meetings, as time-zone challenges get in the way. Sometimes this on-line communication goes to extremes; it's quite common to use IRC chat sessions to speak with someone sitting at the next desk. Yes, our mothers were right; we are a bunch of geeks.
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