lxc: Move remap-uid-and-gid-for-lv to fuidshift

Instead of my custom-baked implementation, that doesn't support
file system ACLs and is quite slow, we switch to `fuidshift` from the
`lxd-tools` Debian package.

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

@@ -1,9 +1,8 @@
 #!/bin/sh
-# Remap all files uid/gid to a new range
+# Remap all files uid/gid to a new range using fuidshift
+#
+# This is a wrapper around `fuidshift` from `lxd-tools` Debian package for my use-case of LVM based root disks.
 #
-# 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>]"
@@ -11,8 +10,13 @@ usage () {
 	exit 1
 }
 
+if [ "$(which fuidshift)" = "" ]; then
+	echo "fuidshift binary not found. Please install lxd-tools package."
+	exit 1
+fi
+
 CONTAINER_NAME="${1}"
-if [ "${CONTAINER_NAME}" = "" ]; then
+if [ "${CONTAINER_NAME}" = "" ] || [ "${CONTAINER_NAME}" = "--help" ] || [ "${CONTAINER_NAME}" = "-h" ]; then
 	usage
 fi
 
@@ -33,51 +37,13 @@ if mount | grep -qF " on /mnt"; then
 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 $ROOT_GROUP_ID
-
-# We ignore links here, because they might not point to a valid location and would make our program fail. They are also
-# owned by whoever mounted the filesystem it seems, so don't need a chown.
-# Funny enough, the above statement is not true. I see symlinks in the container that are not owned by a valid user
-# inside the container ...
-# chown
-#       -h, --no-dereference
-#              affect  symbolic links instead of any referenced file (useful only on systems
-#              that can change the ownership of a symlink)
-#
-#       --from=CURRENT_OWNER:CURRENT_GROUP
-#              change the owner and/or group of each file only if its current  owner  and/or
-#              group  match  those  specified  here.  Either may be omitted, in which case a
-#              match is not required for the omitted attribute
-#
-find . -xdev -printf "%U %G %p\n" | \
-	while read F; do
-		U=$(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
+# we get e.g. lxc.idmap = u 0 1000000 65535 and want u:0:1000000:65535
+USER_NAMESPACE=$(get-lxc-idmap-config u $CONTAINER_NAME | sed -r -e 's/.*= (.*)/\1/' -e 's/ /:/g')
+GROUP_NAMESPACE=$(get-lxc-idmap-config g $CONTAINER_NAME | sed -r -e 's/.*= (.*)/\1/' -e 's/ /:/g')
 
-		P=$(echo $F | cut -d ' ' -f 3-)
-		printf "chown --no-dereference %s:%s %s\n" ${NEW_U} ${NEW_G} "${P}"
-		# chown --no-dereference ${NEW_U}:${NEW_G} "${P}"
-	done
+printf "fuidshift %s %s %s\n" /mnt $USER_NAMESPACE $GROUP_NAMESPACE
+# fuidshift /mnt $USER_NAMESPACE $GROUP_NAMESPACE
 
 cd /
 umount /mnt