Cleanup unmount_dir function

Cleanup this function to work with a symlinked directory.  Document
it's behaviour more exactly, and add a simple unit-test for it (not
run by default, due to doing things like mounting and unmounting
system dirs on a live system, which doesn't seem safe for CI.  But it
is useful for developers ensuring sanity).

Change-Id: I335316019ef948758392b03e91f9869102a472b9

lib/common-functions

@@ -281,12 +281,26 @@ function mount_proc_dev_sys () {
     sudo mount -t sysfs none $TMP_MOUNT_PATH/sys
 }
 
-function unmount_dir () {
-    local pattern="$1" mnts=""
-    if [ -n "$pattern" ] && awk '{print $2}' < /proc/mounts | grep "^$pattern"; then
-        mnts=`awk '{print $2}' < /proc/mounts | grep "^$pattern" | sort -r`
-    fi
-    if [ -n "$mnts" ]; then
-        sudo umount -fl $mnts || true
+# Recursively unmount directories under a given directory DIR
+# usage:
+#  unmount_dir DIR
+function unmount_dir {
+    local dir="$1"
+    local real_dir
+    local mnts
+
+    if [ ! -d $dir ]; then
+        echo "*** $dir is not a directory"
+        return 1
     fi
+
+    # get rid of any symlink elements in the incoming path, because
+    # /proc/mounts is the real path
+    real_dir=$(readlink -e $dir)
+
+    mnts=$(awk '{print $2}' < /proc/mounts | grep "^$real_dir" | sort -r)
+    for m in $mnts; do
+        echo "Unmount $m"
+        sudo umount -fl $m || true
+    done
 }

tests/dib_functions_test.sh

@@ -0,0 +1,50 @@
+#!/bin/bash
+
+# unit testing for some of the common-functions
+#
+# This is fairly invasive and *may* leave behind mounts, etc, that
+# need a human in the loop.  Thus it's mostly useful for developers
+# during testing, but not so great for CI
+
+source ../lib/common-functions
+
+#
+# Directory mounting and unmounting
+#
+
+# make mount points
+TMP_DIR=$(mktemp -d)
+cd $TMP_DIR
+mkdir mnt
+mkdir mnt/proc mnt/dev mnt/dev/pts mnt/sysfs mnt/sys
+
+# for extra complexity, simulate the path being behind a symlink
+ln -s mnt mnt-symlink
+TMP_MOUNT_PATH=$TMP_DIR/mnt-symlink
+
+# mount devices
+mount_proc_dev_sys
+
+if [ $(grep "$TMP_DIR" /proc/mounts | wc -l) -ne 4 ]; then
+    echo "*** FAILED to mount all directories"
+    # we might be in an unclean state here, but something is broken...
+    # we don't want to delete mounted system directories
+    return 1
+else
+    echo "*** PASS : mounted all directories"
+fi
+
+# umount devices
+unmount_dir $TMP_MOUNT_PATH
+
+if [ $(grep "$TMP_DIR" /proc/mounts | wc -l) -ne 0 ]; then
+    echo "*** FAILED due to mounts being left behind"
+    return 1
+else
+    echo "*** PASS all directories unmounted"
+fi
+
+# cleanup
+rm -rf $TMP_DIR
+
+### TODO more tests here