Create swap file only if absent

Signed-off-by: Guillaume Rose <guillaume.rose@docker.com>

pkg/swap/swap.sh

@@ -115,7 +115,13 @@ done
 ### Required? exit 1
 ### Else? exit 0
 
+if [ "$ENCRYPT" == "true" ]; then
+	SWAPDEV=/dev/mapper/swapfile
+else
+	SWAPDEV=$path
+fi
 
+if [ ! -f $path ] || ! [ $(stat -c "%s" $path) == $(disksize_to_count 1 $size) ]; then
 	## Allocate the file
 	dd if=/dev/zero of=$path bs=1024 count=$(disksize_to_count 1024 $size)
 	chmod 0600 $path
@@ -127,11 +133,9 @@ if [ "$ENCRYPT" == "true" ]; then
 		#losetup ${loop} ${path}
 
 		cryptsetup open --type plain --key-file /dev/urandom --key-size=256 --cipher=aes-cbc-essiv:sha256 --offset=0  ${path} swapfile
-	SWAPDEV=/dev/mapper/swapfile
-else
-	SWAPDEV=$path
 	fi
 
-## mkswap and swapon the device
 	/sbin/mkswap $SWAPDEV
+fi
+
 /sbin/swapon $SWAPDEV