RFD: Kernel release numbering

[Linus Torvalds]

This is an idea that has been brewing for some time: Andrew has mentioned
it a couple of times, I've talked to some people about it, and today Davem
sent a suggestion along similar lines to me for 2.6.12.

Namely that we could adopt the even/odd numbering scheme that we used to 
do on a minor number basis, and instead of dropping it entirely like we 
did, we could have just moved it to the release number, as an indication 
of what was the intent of the release.

The problem with major development trees like 2.4.x vs 2.5.x was that the 
release cycles were too long, and that people hated the back- and 
forward-porting. That said, it did serve a purpose - people kind of knew 
where they stood, even though we always ended up having to have big 
changes in the stable tree too, just to keep up with a changing landscape.

So the suggestion on the table would be to go back to even/odd, but do it 
at the "micro-level" of single releases, rather than make it a two- or 
three-year release cycle.

In this setup, all kernels would still be _stable_, in the sense that we
don't anticipate any real breakage (if we end up having to rip up so much
basic stuff that we have to break anything, we'd go back to the 2.7.x kind
of numbering scheme). So we should fear odd releases, but track them, to 
make sure that they are good (if you don't track them, and problems won't 
be fixed in the even version either)

But we'd basically have stricter concerns for an even release, and in
particular the plan would be that the diff files would alternate between
bigger ones (the 2.6.10->11 full diff was almost 5MB) and smaller ones (a
2.6.11->12 release would be a "stability only" thing, and hopefully the
diff file would be much smaller).

We'd still do the -rcX candidates as we go along in either case, so as a 
user you wouldn't even _need_ to know, but the numbering would be a rough 
guide to intentions. Ie I'd expect that distributions would always try to 
base their stuff off a 2.6.<even> release.

It seems like a sensible approach, and it's not like the 2.4.x vs 2.5.x
kind of even/odd thing didn't _work_, the problems really were an issue of
too big granularity making it hard for user and developers alike. So I see
this as a tweak of the "let's drop the notion althogether for now"  
decision, and just modify it to "even/odd is meaningful at all levels".

In other words, we'd have an increasing level of instability with an odd 
release number, depending on how long-term the instability is.

 - 2.6.<even>: even at all levels, aim for having had minimally intrusive 
   patches leading up to it (timeframe: a week or two)

with the odd numbers going like:

 - 2.6.<odd>: still a stable kernel, but accept bigger changes leading up 
   to it (timeframe: a month or two).
 - 2.<odd>.x: aim for big changes that may destabilize the kernel for 
   several releases (timeframe: a year or two)
 - <odd>.x.x: Linus went crazy, broke absolutely _everything_, and rewrote
   the kernel to be a microkernel using a special message-passing version 
   of Visual Basic. (timeframe: "we expect that he will be released from 
   the mental institution in a decade or two").

The reason I put a shorter timeframe on the "all-even" kernel is because I
don't want developers to be too itchy and sitting on stuff for too long if
they did something slightly bigger. In theory, the longer the better
there, but in practice this release numbering is still nothing but a hint
of the _intent_ of the developers - it's still not a guarantee of "we
fixed all bugs", and anybody who expects that (and tries to avoid all odd 
release entirely) is just setting himself up for not testing - and thus 
bugs.

Comments?

		Linus
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