Add get-lxc-idmap-config script

This script handles uid/gid ranges for creating unprivileged containers as root.

lxc/get-lxc-idmap-config

@@ -0,0 +1,80 @@
+#!/bin/sh
+# Manage uid/gid maps for containers
+#
+# This script manages uids/gids assigned to certain containers or groups of containers. It uses /etc/subuid and
+# /etc/subgid by default to save the information. All the ranges are owned by root as we don't want to support creation
+# of containers by unprivileged users, but rather want to create unprivileged containers as root user.
+
+USER_ID=0
+FIRST_ID=1000000
+DEFAULT_COUNT=65536
+FILENAME="/etc/sub_____id"
+
+get_filename () (
+	TYPE="${1}"
+	echo "${FILENAME}" | sed "s/_____/${TYPE}/"
+)
+
+find_range () (
+	TYPE="${1}"
+	NAME="${2}"
+	FILENAME="$(get_filename ${TYPE})"
+
+	grep -A 1 "^# ${NAME}$" "${FILENAME}" -A 1 | tail -n 1
+)
+
+get_last_range () (
+	TYPE="${1}"
+	grep "^${USER_ID}:" "$(get_filename ${TYPE})" | tail -n 1
+)
+
+get_new_range () (
+	TYPE="${1}"
+	LAST_RANGE=$(get_last_range "${TYPE}")
+	if [ "${LAST_RANGE}" = "" ]; then
+		NEW_ID=$FIRST_ID;
+	else
+		LAST_ID=$(echo "${LAST_RANGE}" | cut -d : -f 2)
+		LAST_COUNT=$(echo "${LAST_RANGE}" | cut -d : -f 3)
+		NEW_ID=$(( $LAST_ID + $LAST_COUNT ))
+	fi
+	echo "${USER_ID}:${NEW_ID}:${DEFAULT_COUNT}"
+)
+
+append_range () (
+	TYPE="${1}"
+	FILENAME="$(get_filename ${TYPE})"
+	NAME="${2}"
+	RANGE="${3}"
+	printf "# ${NAME}\n${RANGE}\n" >> "${FILENAME}"
+)
+
+usage () {
+	echo "usage: get-lxc-idmap-config <u|g> <container-group-name>"
+	exit 1
+}
+
+
+TYPE="${1}"
+if [ "${TYPE}" = "" || "${TYPE}" == "--help" || "${TYPE}" == "-h" ]; then
+	usage
+fi
+
+NAME="${2}"
+if [ "${NAME}" = "" ]; then
+	usage
+fi
+
+RANGE=$(find_range "${TYPE}" "${NAME}")
+
+if [ "${RANGE}" = "" ]; then
+	RANGE=$(get_new_range "${TYPE}")
+	if [ "${RANGE}" = "" ]; then
+		exit 1
+	fi
+	append_range "${TYPE}" "${NAME}" "${RANGE}"
+fi
+
+RANGE_START=$(echo ${RANGE} | cut -d : -f 2)
+RANGE_COUNT=$(echo ${RANGE} | cut -d : -f 3)
+printf "lxc.idmap = %s 0 %s %s\n" "${TYPE}" "${RANGE_START}" "$(( ${RANGE_COUNT} - 1))"