Add remap-uid-and-gid-for-lv

I've used this script to remap files' uids/gids of containers created
without a custom userns into their new range.  It's inferior to
`fuidshift` from the `lxc` project in that it doesn't handle ACLs and is
quite slow - probably because it calls a binary for every file.

By default, it runs in debug mode only printing the chown command
instead of executing it. You need to edit the file to use it.

It also only works with LVs (logical volumes from LVM), mounting them
automatically.

lxc/remap-uid-and-gid-for-lv

@@ -0,0 +1,71 @@
+#!/bin/sh
+# Remap all files uid/gid to a new range
+#
+# This is an inferior version of `fuidshift` from the `lxd-tools` Debian package, as it only handles uid/gid and
+# doesn't handle ACLs and thus journalctl's files and by that hinders updating systemd inside the container. It's also
+# quite slow.
+
+usage () {
+	echo "remap-uid-and-gid <container-name> [<target-lv>]"
+	printf "\nIf <target-lv> is not given it is computed from a default value with the given container name\n"
+	exit 1
+}
+
+CONTAINER_NAME="${1}"
+if [ "${CONTAINER_NAME}" = "" ]; then
+	usage
+fi
+
+TARGET_LV="${2}"
+if [ "${TARGET_LV}" = "" ]; then
+	GUESSED_LV="/dev/mapper/daffy--vg-lxc--${CONTAINER_NAME}"
+	if [ -e "${GUESSED_LV}" ]; then
+		TARGET_LV="${GUESSED_LV}"
+	fi
+fi
+if [ "${TARGET_LV}" = "" ]; then
+	usage
+fi
+
+if mount | grep -qF " on /mnt"; then
+	echo "Mountpoint /mnt is already in use."
+	exit 1
+fi
+
+mount "${TARGET_LV}" /mnt
+cd /mnt
+
+ROOT_USER_ID=$(get-lxc-idmap-config u $CONTAINER_NAME | cut -d ' ' -f 5)
+ROOT_GROUP_ID=$(get-lxc-idmap-config g $CONTAINER_NAME | cut -d ' ' -f 5)
+
+printf "uid: %s gid: %s\n" $ROOT_USER_ID $ROOT_GROUP_ID
+
+# We ignore links here, because they might not point to a valid location and would make our program fail. They are also
+# owned by whoever mounted the filesystem it seems, so don't need a chown.
+find . -xdev -not -type l -printf "%U %G %p\n" | \
+	while read F; do
+		U=$(echo $F | cut -d ' ' -f 1)
+		if [ ${U} -lt ${ROOT_USER_ID} ] || [ ${U} -gt $(( ${ROOT_USER_ID} + 65535 )) ]; then
+			NEW_U=$(( ${U} + ${ROOT_USER_ID} ))
+		else
+			NEW_U=${U}
+		fi
+
+		G=$(echo $F | cut -d ' ' -f 2)
+		if [ ${G} -lt ${ROOT_GROUP_ID} ] || [ ${G} -gt $(( ${ROOT_GROUP_ID} + 65535 )) ]; then
+			NEW_G=$(( ${G} + ${ROOT_GROUP_ID} ))
+		else
+			NEW_G=${G}
+		fi
+
+		if [ "${U}" = "${NEW_U}" ] && [ "${G}" = "${NEW_G}" ]; then
+			continue
+		fi
+
+		P=$(echo $F | cut -d ' ' -f 3-)
+		printf "chown %s:%s %s\n" ${NEW_U} ${NEW_G} "${P}"
+		# chown ${NEW_U}:${NEW_G} "${P}"
+	done
+
+cd /
+umount /mnt