Re: [RFC PATCH] cogito --- don't overwrite metadata files in place (breaks CoW use)

From: Linus Torvalds <torvalds@osdl.org>
Date: Jul 13, 2005, 21:05 UTC
Message-ID: <Pine.LNX.4.58.0507131402210.17536@g5.osdl.org>
In-Reply-To: <20050713204458.GB11403@taniwha.stupidest.org>

On Wed, 13 Jul 2005, Chris Wedgwood wrote:

Show 12 quoted lines

> 
> The complexity I added was to deal with a situation where we have
> 
>   tree1/
> 	.git/HEAD -> refs/head/master
> 
> and I do "cp -Rl tree1 tree2" giving me:
> 
>   tree2/
> 	.git/HEAD -> refs/head/master
> 
>   and .git/refs/head/master is hardlinked between both trees.

AND THAT IS WRONG.

You shouldn't hardlink whole trees. Git will not guarantee that it breaks the links.

Right now, if you go a "git commit", and a number of other core git operations, it will use ">" to overwrite the HEAD. You're screwed.

Show 5 quoted lines

> > That is COW-safe, but the thing is, it's incredibly painful for many
> > other operations, and I won't guarantee that git in general is
> > always going to be COW-safe wrt all the git files.
> 
> What operations is this painful for?

Your script was tens of lines of code, and it was BUGGY.

And now you ask what it's painful for?

Guys, if you want to mess up code, the #1 rule is:
 - make complex code to handle insane situations

You're well on your way to do that.

Don't hardlink git trees. It's a bug to do so. It will eventually change the other git tree.

Hardlink git _object_ directories. That's a totally different thing.

		Linus