From: Chris Wedgwood <cw@f00f.org>
Date: Wed, 13 Jul 2005 18:53:39 GMT
Subject: Re: [RFC PATCH] cogito --- don't overwrite metadata files in place (breaks CoW use)
Message-ID: <20050713185339.GA9260@taniwha.stupidest.org>
In-Reply-To: <pan.2005.07.13.07.03.26.398212@smurf.noris.de>

On Wed, Jul 13, 2005 at 09:03:26AM +0200, Matthias Urlichs wrote:

> You are ;-) the tree itsels is no symlinked, but HEAD points to
> refs/heads/<branch> by default.

Thanks for pointing that out.  I honestly never noticed that.

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 "$DEST" ] ; do
	    local NLINK=`readlink "$DEST"`

	    if [ ! -e "$NLINK" ] ; then
		# dangling link, just poke as-is
		echo "$1" > "$DEST"
		return $?
	    fi

	    # follow link
	    if [ -L "$NLINK" ] ; then
		count=$(("$count" + 1))
		if [ "$count" -gt 5 ] ; then
		    echo "Too many symlinks when resolving $2" 1>&2
		    return 1
		fi
		DEST="$NLINK"
	    fi
	done

	# end up with a regular file
	local TMPFILE=`mktemp "$DEST.tmp-XXXXXXX"`
	echo "$1" > "$TMPFILE"
	RET="$?"
	mv -f "$TMPFILE" "$DEST"
	return "$RET"
    }


Obvious changes from last time are:

  - mark things local

  - follow links, bailing out if it takes too long

  - if the link is dangling, just use as-is

  - when doing the 'replace' at the end use -f because it's quite
    possible someone will have done cp -Rl ~otheruser/tree here and mv
    *might* bitch if the UID is different?

  - return (some) errors (just because, it's not like cogito checks
    for these)