git-etc

#!/bin/sh
# Track and restore system files and metadata in git. Use together with bmount.
#
# Usage example:
#
# # to backup
# $ git-etc init
# $ bmount insert /etc/apache2/sites-available /etc/apt
# $ git add . && git commit
#
# # to restore
# $ git clone <url> && git-etc init
# $ git-etc install
#
# TODO: add the functionality from rsconf that automatically detects changed or
# new configs (relative to dpkg's database) in /etc

# development directories, override on install
SCRIPT_HOME="$(dirname "$(readlink -f "$0")")"
DATADIR="$SCRIPT_HOME/share"

ERR_GIT_META_NOT_FOUND=36
ERR_PERL_LCHOWN_NOT_FOUND=37
ERR_GIT_DIFF_NON_EMPTY=38

set -o errexit

pre_test() {
	local h="$(git rev-parse --git-dir)/hooks"
	if ! grep -Rq "git meta" "$h"; then
		echo >&2 "not a git-etc-enabled git repo. run $0 init to fix this."
		exit $ERR_REPO_NOT_GITETC
	fi
}

git_install_hook() {
	local hdir="$1"
	local htype="$2"
	local hname="$3"
	local cleanmarker="## clean $hname ##"
	local hfile="$hdir/$htype"
	if [ -e "$hfile" ] && ! grep -qF "$cleanmarker" "$hfile"; then
		echo "git hook $htype already exists; please incorporate the following into it:"
		echo "-- $hfile"
		echo "#!/bin/sh"; cat
		echo "-- EOF"
	else
		{ echo "#!/bin/sh"; echo "$cleanmarker"; cat; } > "$hfile"
		chmod +x "$hfile"
	fi
}

git_install_meta_r_hook() {
	cat << EOF | git_install_hook "$@" git_meta_r_hook
if which git-meta >/dev/null; then
	git-etc meta-r "\$@"
fi
EOF
}

git_etc_meta_r() {
	SUBDIRECTORY_OK=1 . "$(git --exec-path)/git-sh-setup"
	cd_to_toplevel
	require_work_tree
	git meta -r
	# only store metadata for files tracked by bmount
	for host_bind in $(grep -o -P '(^|.*/).bmrc\s' ".gitmeta"); do
		tail -n+2 "$host_bind" | while read source; do
			source="$(echo -e "$source")"
			source="${source%/}"
			echo "$(dirname "$host_bind")/${source#/}"
		done
	done | sed -e 's|^\./\+||g' | sort -u | grep -vxF '.' | grep -F -f- ".gitmeta" > ".gitmeta.new" || true
	mv ".gitmeta.new" ".gitmeta"
	git add ".gitmeta"
	exit $?
}

git_install_meta_w_hook() {
	cat << EOF | git_install_hook "$@" git_meta_w_hook
if which git-meta >/dev/null; then
	git meta -w
fi
EOF
}

gitetc_init() {
	git init
	if ! which git-meta > /dev/null; then
		echo >&2 "you need to add git-meta to your path."
		exit $ERR_GIT_META_NOT_FOUND
	elif ! echo "use Lchown;" | perl; then
		echo >&2 "you need to install the Lchown perl module, also called liblchown-perl."
		exit $ERR_PERL_LCHOWN_NOT_FOUND
	fi
	local h="$(git rev-parse --git-dir)/hooks"
	git_install_meta_r_hook "$h" pre-commit
	git_install_meta_w_hook "$h" post-checkout
	git_install_meta_w_hook "$h" post-merge
	bmount init import
}

sudogit() {
	sudo git "$@"
	git reset # re-init index with user's own perms
}

gitetc_install() {
	if ! git diff --quiet; then
		echo >&2 "abort: git detected changes"
		git status
		exit $ERR_GIT_DIFF_NON_EMPTY
	fi
	sudo "$(which bmount)" -u . umountAll
	sudogit checkout -- .
	sudogit meta -w
	sudo "$(which bmount)" -u . mountAll
	test "$(bmount -u . status)" = "FULL"
	bmount list | while read pp; do
		pp="$(echo -e "$pp")" # bmount escapes special chars in list output
		local pp_rel="${pp#/}"
		if [ -d "$pp_rel" ]; then
			sudogit checkout -- "$pp_rel"
		else
			# git checkout tries to unlink, which doesn't work for bind-mounted files
			git cat-file -p "$(git rev-parse "HEAD:$pp_rel")" | sudo tee "$pp_rel" >/dev/null
		fi
	done
	sudogit meta -w
}

USAGE="Usage: $0 [-h] [init|install]"

while getopts r:h o; do
	case $o in
	h ) subcmd=help;;
	\? ) subcmd=?;;
	esac
done
shift `expr $OPTIND - 1`

subcmd="${subcmd:-$1}"
subcmd="${subcmd:-?}"

case $subcmd in
init)
	gitetc_init
	;;
install)
	pre_test
	gitetc_install
	;;
meta-r)
	git_etc_meta_r "$@"
	;;
help)
	cat <<EOF
$USAGE

subcommands (git repo):
init                set up this repo as a git-etc repo (add hooks, etc)
install             checkout files to / and set correct permissions.
EOF
	;;
*)
	echo >&2 "$USAGE"
	exit 2
	;;
esac