Re: Question on GIT usage.

From: Linus Torvalds <torvalds@osdl.org>
Date: Oct 29, 2005, 02:06 UTC
Message-ID: <Pine.LNX.4.64.0510281847220.3348@g5.osdl.org>
In-Reply-To: <4362C700.6020901@candelatech.com>

On Fri, 28 Oct 2005, Ben Greear wrote:

Show 5 quoted lines

> 
> I have a kernel GIT tree to hold my developing patches...
> 
> I need to build this kernel for 4-5 different processors (c3, p2, p4, p4-smp,
> etc).

Sounds like you just want to use a separate build directory for the kernel, which you can do quite independently of git (of course, not too many people use it, so the separate-object-directory Kbuild infrastructure has bugs every once in a while..)

The way it _should_ work is that you can do something like this:

	.. have a clean source-tree in ~/src/linux ..

	# set up the build tree
	cd
	mkdir build-tree
	cd ~/src/linux
	make O=~/build-tree oldconfig

	# go there and build it
	cd ~/build-tree
	make

and now you can have a build-tree for each of your different architectures.

Now, you _can_ certainly do the very same thing with just multiple git repositories, and pull between them. That has its own set of advantages too: you can have slight differences between the trees. Of course, if you know you don't want any differences between the trees, that's not an advantage, that's a disadvantage.

You can also have just one single real git repository, and then have that one checked out multiple times. Use GIT_OBJECT_DIRECTORY to share the core objects, and then you can have ten different git trees without duplicating all your objects and pack-files.

> Is there any clever way to have this one git repository keep these
> other source trees in sync so that I can do incremental builds?

If you really want them 100%, the separate build trees is the best option.

That said, a lot of _other_ projects don't do separate build trees that well (and as mentioned, sometimes it breaks for the kernel too), and git certainly could be set up to be a "poor mans separate build tree".

Right now the easiest way to do that is to just have separate repositories (and share at least _some_ objects by just using "git clone -l -s" to clone them), but it could be hacked to be more geared explicitly towards that..

		Linus