Retry losetup -d for up to 10 seconds.

When partition tables are added to loopback devices, this can set off a
chain of udev hooks that may still be holding the loopback open. Failing
to detach loopback devices was the reason we were seeing leaked tmpfs
volumes.

Fixes bug #1178091

Change-Id: I836d6e2bbce824951dd4786e3ef28273ea18ee73

bin/disk-image-create

@@ -112,7 +112,7 @@ mv $TMP_BUILD_DIR/mnt $TMP_BUILD_DIR/built
 _NEEDED_SIZE=$(sudo du --block-size=800 -x -s ${TMP_BUILD_DIR}/built | awk ' { print $1 } ')
 truncate -s${_NEEDED_SIZE}K $TMP_IMAGE_PATH
 LOOPDEV=$(sudo losetup --show -f $TMP_IMAGE_PATH)
-export EXTRA_UNMOUNT="sudo losetup -d $LOOPDEV"
+export EXTRA_UNMOUNT="detach_loopback $LOOPDEV"
 export IMAGE_BLOCK_DEVICE=$LOOPDEV
 eval_run_d block-device "IMAGE_BLOCK_DEVICE="
 OPTS=""

lib/common-functions

@@ -1,3 +1,4 @@
+# vim: syntax=sh ts=4 sts=4 sw=2:et
 # Copyright 2012 Hewlett-Packard Development Company, L.P.
 # All Rights Reserved.
 #
@@ -159,3 +160,16 @@ function run_d() {
     check_break after-$1 bash
 }
 
+function detach_loopback() {
+    local loopdev=$1
+    # loopback dev may be tied up a bit by udev events triggered by partition events
+    for try in $(seq 10 -1 1) ; do
+        if sudo losetup -d $loopdev ; then
+            return 0
+        fi
+        echo $loopdev may be busy, sleeping up to $try more seconds...
+        sleep 1
+    done
+    echo Gave up trying to detach $loopdev
+    return 1
+}