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

From: Linus Torvalds <torvalds@osdl.org>
Date: Jul 13, 2005, 21:23 UTC
Message-ID: <Pine.LNX.4.58.0507131410430.17536@g5.osdl.org>
In-Reply-To: <20050713185339.GA9260@taniwha.stupidest.org>

On Wed, 13 Jul 2005, Chris Wedgwood wrote:

Show 11 quoted lines

> 
> How about the following?
> 
>     echo_to_file() {
> 	local DEST="$2"
> 	local count=1
> 	local RET
> 
> 	# follow symlinks until we run out or end up with something
> 	# dangling
> 	while [ -L "$DEST" ] ; do

If you really want to do something like this, then you should do it like this:

	update_head() {
		head="$GIT_DIR/HEAD"
		newvalue=$(git-rev-parse --verify "$1"^0) || exit
		if [ -L "$head" ]; then
			head=$(readlink "$head")
			case "$head" in
			refs/heads/*)
				head="$GIT_DIR"/"$head"
				;;
			*)
				exit 1
				;;
			esac
		fi
		echo $newvalue > "$head.lock" && rename "$head.lock" "$head"
	}

which is at least slightly simpler, and might even work thanks to that.

Your was buggy for several reasons:

 - following multiple links is _wrong_, since the next-level link could 
   actually be a symlink to another tree entirely (if somebody is crazy 
   enough to use "cp -Rl" to copy trees, then why not "cp -Rs"?)

   Ergo: you should only follow a symlink if it points to refs/heads, and 
   anything else would be a BUG.

 - you got relative links wrong.

Now, admittedly the above is totally untested too, so I'll probably have typos etc in there. But the basic point stands: don't go for complexity. Go for one _particular_ case.

		Linus