* Improve teardown_mountpoint to recursively find all submounts and

unmount them, instead of working from a hard-coded list.  This makes
  the code resilient against other submounts being added later, including
  downstream.
* Also nuke the sleep / udevadm settle calls in the process, which should
  never be required and slow down the builds.

debian/changelog

@@ -1,3 +1,14 @@
+livecd-rootfs (2.456) UNRELEASED; urgency=medium
+
+  * Improve teardown_mountpoint to recursively find all submounts and
+    unmount them, instead of working from a hard-coded list.  This makes
+    the code resilient against other submounts being added later, including
+    downstream.
+  * Also nuke the sleep / udevadm settle calls in the process, which should
+    never be required and slow down the builds.
+
+ -- Steve Langasek <steve.langasek@ubuntu.com>  Wed, 13 Sep 2017 13:38:58 -0700
+
 livecd-rootfs (2.455) artful; urgency=medium
 
   * Restore the call to 'umount -R $mountpoint' from umount_partition,

live-build/functions

@@ -95,14 +95,13 @@ teardown_mountpoint() {
     # Reverse the operations from setup_mountpoint
     local mountpoint="$1"
 
-    umount "$mountpoint/var/cache/apt"
-    umount "$mountpoint/var/lib/apt"
-    umount "$mountpoint/tmp"
-    umount "$mountpoint/sys"
-    umount "$mountpoint/proc"
-    umount -R "$mountpoint/dev"
-    udevadm settle
-    sleep 3
+    # ensure we have exactly one trailing slash, and escape all slashes for awk
+    mountpoint_match=$(echo "$mountpoint" | sed -e's,/$,,; s,/,\\/,g;')'\/'
+    # sort -r ensures that deeper mountpoints are unmounted first
+    for submount in $(awk </proc/self/mounts "\$2 ~ /$mountpoint_match/ \
+                      { print \$2 }" | LC_ALL=C sort -r); do
+        umount $submount
+    done
     mv resolv.conf.tmp "$mountpoint/etc/resolv.conf"
 }