partitioning: fix race condition on loop device allocation

lib/functions/image/partitioning.sh

@@ -216,25 +216,9 @@ function prepare_partitions() {
 	flock -x $FD
 
 	declare -g LOOP
-	# replace losetup --find with own function and do 10 cycles
-	# losetup always return 1st free loop device and in parallel build,
-	# it often happens that same is found which resoults in:
-	# "failed to set up loop device: Device or resource busy"
-	# If we seek random way, chanches of allocating the same are significantly smaller.
-	FIND_LOOP_CYCLES=1
-	while : ; do
-		LOOP=$(find /dev/loop* | grep -Po "(\/dev\/loop\d|\/dev\/loop\d\d)$" | sort -R | head -1)
-		LOOP_COMPARE=$(losetup -l --noheadings --raw --output=NAME | grep $LOOP || true)
-		[[ -z $LOOP_COMPARE ]] && break
-		[[ $FIND_LOOP_CYCLES -gt 10 ]] && exit_with_error "Unable to find free loop device"
-		FIND_LOOP_CYCLES=$(( FIND_LOOP_CYCLES + 1 ))
-	done
-	display_alert "Allocated loop device" "LOOP=${LOOP} in cycle $FIND_LOOP_CYCLES"
-
-	CHECK_LOOP_FOR_SIZE="no" check_loop_device "$LOOP" # initially loop is zero sized, ignore it.
-
-        #--partscan is using to force the kernel for scaning partition table in preventing of partprobe errors
-	run_host_command_logged losetup --partscan "${LOOP}" "${SDCARD}".raw
+	#--partscan is using to force the kernel for scaning partition table in preventing of partprobe errors
+	LOOP=$(losetup --show --partscan --find "${SDCARD}".raw) || exit_with_error "Unable to find free loop device"
+	display_alert "Allocated loop device" "LOOP=${LOOP}"
 
 	# loop device was grabbed here, unlock
 	flock -u $FD