osbuilder: fix loop devices manipulation in image-builder.sh

Improve image-builder.sh to avoid the sporadic failures observed during
the CI builds of images. Also, some cosmetic changes to indentation.

Fixes: #172

Signed-off-by: Marco Vedovati <mvedovati@suse.com>

image-builder/image_builder.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # Copyright (c) 2017 Intel Corporation
 #
@@ -63,13 +63,15 @@ do
 		h)	usage ;;
 		o)	IMAGE="${OPTARG}" ;;
 		r)	ROOT_FREE_SPACE="${OPTARG}" ;;
-		s)	IMG_SIZE=${OPTARG}
+		s)	{
+		IMG_SIZE=${OPTARG}
 		if [ ${IMG_SIZE} -le 0 ]; then
 			die "Image size has to be greater than 0 MB."
 		fi
 		if [ ${IMG_SIZE} -gt ${MAX_IMG_SIZE_MB} ]; then
 			die "Image size should not be greater than ${MAX_IMG_SIZE_MB} MB."
 		fi
+		 }
 		 ;;
 		f)	FS_TYPE="${OPTARG}" ;;
 	esac
@@ -159,16 +161,42 @@ calculate_img_size()
 
 }
 
-# Cleanup
-cleanup()
+unmount()
 {
 	sync
 	umount -l ${MOUNT_DIR}
 	rmdir ${MOUNT_DIR}
-    fsck -D -y "${DEVICE}p1"
-    losetup -d "${DEVICE}"
 }
 
+detach()
+{
+	losetup -d "${DEVICE}"
+
+	# From `man losetup` about -d option:
+	# Note that since Linux v3.7 kernel uses "lazy device destruction".
+	# The detach operation does not return EBUSY  error  anymore  if
+	# device is actively used by system, but it is marked by autoclear
+	# flag and destroyed later
+	info "Waiting for ${DEVICE} to detach"
+
+	local i=0
+	local max_tries=5
+	while [[ "$i" < "$max_tries" ]]; do
+		sleep 1
+		# If either the 'p1' partition has disappeared or partprobe failed, then
+		# the loop device should be correctly detached
+		if ! [ -b "${DEVICE}p1" ] || ! partprobe -s ${DEVICE}; then
+			break
+		fi
+		((i+=1))
+		echo -n "."
+	done
+
+	[[ "$i" == "$max_tries" ]] && die "Cannot detach ${DEVICE}"
+	info "detached"
+}
+
+
 create_rootfs_disk()
 {
 	ATTEMPT_NUM=$(($ATTEMPT_NUM+1))
@@ -199,12 +227,22 @@ create_rootfs_disk()
 	DEVICE=$(losetup -P -f --show "${IMAGE}")
 
 	#Refresh partition table
-    partprobe "${DEVICE}"
+	partprobe -s "${DEVICE}"
+	# Poll for the block device p1
+	local i=0
+	local max_tries=5
+	while [[ "$i" < "$max_tries" ]]; do
+		[ -b "${DEVICE}p1" ] && break
+		((i+=1))
+		echo -n "."
+		sleep 1
+	done
+	[[ "$i" == "$max_tries" ]] && die "File ${DEVICE}p1 is not a block device"
 
 	MOUNT_DIR=$(mktemp -d osbuilder-mount-dir.XXXX)
-    info "Formating Image using ext4 format"
+	info "Formatting Image using ext4 filesystem"
 	mkfs.ext4 -q -F -b "${BLOCK_SIZE}" "${DEVICE}p1"
-    OK "Image formated"
+	OK "Image formatted"
 
 	info "Mounting root partition"
 	mount "${DEVICE}p1" "${MOUNT_DIR}"
@@ -222,10 +260,11 @@ create_rootfs_disk()
 	if [ $ROOTFS_SIZE -gt $AVAIL_DISK ]; then
 		# Increase the size but remain aligned to 128
 		MEM_BOUNDARY=$(($MEM_BOUNDARY+128))
-        rm -f ${IMAGE}
 		OLD_IMG_SIZE=${IMG_SIZE}
 		unset IMG_SIZE
-        cleanup
+		unmount
+		detach
+		rm -f ${IMAGE}
 		create_rootfs_disk
 	fi
 }
@@ -237,6 +276,9 @@ info "Copying content from rootfs to root partition"
 cp -a "${ROOTFS}"/* ${MOUNT_DIR}
 OK "rootfs copied"
 
-cleanup
+unmount
+# Optimize
+fsck.ext4 -D -y "${DEVICE}p1"
+detach
 
 info "Image created. Virtual size: ${IMG_SIZE}MB."