From: Linus Torvalds <torvalds@linux-foundation.org>
Newsgroups: fa.linux.kernel
Subject: Re: Linux 2.6.29
Date: Fri, 27 Mar 2009 16:05:26 UTC
Message-ID: <fa.eRXdWbD9yff31vp4h4qsT3zFFuE@ifi.uio.no>

On Fri, 27 Mar 2009, Mike Galbraith wrote:
> >
> > If you're using the kernel-of-they-day, you're probably using git, and
> > CONFIG_LOCALVERSION_AUTO=y should be mandatory.
>
> I sure hope it never becomes mandatory, I despise that thing.  I don't
> even do -rc tags.  .nn is .nn until baked and nn.1 appears.

If you're a git user that changes kernels frequently, then enabling
CONFIG_LOCALVERSION_AUTO is _really_ convenient when you learn to use it.

This is quite common for me:

	gitk v$(uname -r)..

and it works exactly due to CONFIG_LOCALVERSION_AUTO (and because git is
rather good at figuring out version numbers). It's a great way to say
"ok, what is in my git tree that I'm not actually running right now".

Another case where CONFIG_LOCALVERSION_AUTO is very useful is when you're
noticing some new broken behavior, but it took you a while to notice.
You've rebooted several times since, but you know it worked last Tuesday.
What do you do?

The thing to do is

	grep "Linux version" /var/log/messages*

and figure out what the good version was, and then do

	git bisect start
	git bisect good ..that-version..
	git bisect bad v$(uname -r)

and off you go. This is _very_ convenient if you are working with some
"random git kernel of the day" like I am (and like hopefully others are
too, in order to get test coverage).

> (would be nice if baked were immediately handed to stable .nn.0 instead
> of being in limbo for a bit, but I don't drive the cart, just tag along
> behind [w. shovel];)

Note that the "v2.6.29[-rcX" part is totally _useless_ in many cases,
because if you're working past merges, and especially if you end up doing
bisection, it is very possible that the main Makefile says "2.6.28-rc2",
but the code you're working on wasn't actually _merged_ until after
2.6.29.

In other words, the main Makefile version is totally useless in non-linear
development, and is meaningful _only_ at specific release times. In
between releases, it's essentially a random thing, since non-linear
development means that versioning simply fundamentally isn't some simple
monotonic numbering. And this is exactly when CONFIG_LOCALVERSION_AUTO is
a huge deal.

(It's even more so if you end up looking at "next" or merging other
peoples trees. If you only ever track my kernel, and you only ever
fast-forward - no bisection, no nothing - then the release numbering looks
"simple", and things like LOCALVERSION looks just like noise).

			Linus