error handling for non-loaded module

code/leak.c

@@ -9,9 +9,10 @@
 
 #include "pipe_utils.c"
 
+#define LKM_DEVICE "/dev/lkm"
+
 // where does this come from?
 #define OBJS_PER_SLAB 42
-
 #define PIPE_BUFFER   (OBJS_PER_SLAB * 10)
 
 int pipes[PIPE_BUFFER][2];
@@ -20,9 +21,15 @@ int
 main(void)
 {
 	printf("main: start\n");
-	FILE *device = fopen("/dev/lkm", "r+");
+	FILE *device = fopen(LKM_DEVICE, "r+");
 
 	printf("main: fopen: %p\n", device);
+	if (!device) {
+		printf(
+		    "main: fopen: Error opening %s. Make sure the kernel module is loaded\n",
+		    LKM_DEVICE);
+		exit(1);
+	}
 
 	printf("main: draining lower page free lists: %u objects\n",
 	    PIPE_BUFFER);