zfs-chroot: unmount everything under chroot mountpoint

Instead of manually tracking everything mounted under the chroot, check mounts and sort the list by the directory depth. Given directory depths of 10,9,8, assume that any directories at the same depth can be unmounted in any order.

Author: zdykstra

zfsbootmenu/bin/zfs-chroot

@@ -66,35 +66,25 @@ notices+=( "$(colorize white "*" ) $( colorize orange "${selected}" ) is mounted
 
 # Track submounts so we know how to clean up on exit
 trap cleanup HUP INT QUIT ABRT EXIT
-_mnt=( "${mountpoint}" )
 
 zdebug "mounted ${selected} to ${mountpoint}"
 
-mount -B /tmp "${mountpoint}/tmp" \
-  && _mnt=( "${mountpoint}/tmp" "${_mnt[@]}" )
-
-mount -t proc proc "${mountpoint}/proc" \
-  && _mnt=( "${mountpoint}/proc" "${_mnt[@]}" )
-
-mount -t sysfs sys "${mountpoint}/sys" \
-  && _mnt=( "${mountpoint}/sys" "${_mnt[@]}" )
-
-mount -B /dev "${mountpoint}/dev" \
-  && _mnt=( "${mountpoint}/dev" "${_mnt[@]}" )
+mount -B /tmp "${mountpoint}/tmp"
+mount -t proc proc "${mountpoint}/proc"
+mount -t sysfs sys "${mountpoint}/sys"
+mount -B /dev "${mountpoint}/dev"
 
 
 if mount_efivarfs "${efivarmode}" ; then
   efivarfs="${mountpoint}/sys/firmware/efi/efivars"
-  mount_efivarfs "${efivarmode}" "${efivarfs}" \
-    && _mnt=( "${efivarfs}" "${_mnt[@]}" )
+  mount_efivarfs "${efivarmode}" "${efivarfs}"
 
   notices+=( "\n$(colorize white "*" ) $( colorize orange "efivarfs" ) is mounted ${writemode}" )
 fi
 
 # Not all /dev filesystems have /dev/pts
 [ -d "${mountpoint}/dev/pts" ] \
-  && mount -t devpts pts "${mountpoint}/dev/pts" \
-  && _mnt=( "${mountpoint}/dev/pts" "${_mnt[@]}" )
+  && mount -t devpts pts "${mountpoint}/dev/pts"
 
 _SHELL=
 if [ -x "${mountpoint}/bin/bash" ] \
@@ -126,3 +116,20 @@ unset PROMPT_COMMAND
 if ! env "PS1=\[\033[0;33m\]${selected}\[\033[0m\] \w > " chroot ${mountpoint} ${_SHELL} ${chroot_extra} ; then
   zdebug "chroot ${selected}:${_SHELL} returned code $?"
 fi
+
+mounts=()
+
+mp_re="^${mountpoint}"
+
+# shellcheck disable=SC2034
+while read -r skip mp skip skip ; do
+  if [[ "${mp}" =~ ${mp_re} ]]; then
+    lines="${mp//[!\/]/}"
+    lines="${#lines}"
+    mounts+=( "${lines},${mp}" )
+  fi
+done < /proc/self/mounts
+
+while IFS=$'\n' read -r filesystem; do
+  _mnt+=( "${filesystem#*,}" )
+done <<<"$( printf '%s\n' "${mounts[@]}" | sort -n -k1 -r )"