From: Linus Torvalds <email@example.com>
Subject: Re: Linux 2.6.29
Date: Fri, 27 Mar 2009 16:05:26 UTC
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
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).