kfifo: add explicit error checking in all the examples

Provide a check in all the kfifo examples to validate the correct
execution of each testcase.

Signed-off-by: Andrea Righi <arighi@develer.com>
Acked-by: Stefani Seibold <stefani@seibold.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/samples/kfifo/bytestream-example.c b/samples/kfifo/bytestream-example.c
index a94e694..178061e 100644
--- a/samples/kfifo/bytestream-example.c
+++ b/samples/kfifo/bytestream-example.c
@@ -44,7 +44,7 @@
 static DECLARE_KFIFO(test, unsigned char, FIFO_SIZE);
 #endif
 
-static unsigned char expected_result[FIFO_SIZE] = {
+static const unsigned char expected_result[FIFO_SIZE] = {
 	 3,  4,  5,  6,  7,  8,  9,  0,
 	 1, 20, 21, 22, 23, 24, 25, 26,
 	27, 28, 29, 30, 31, 32, 33, 34,
@@ -90,9 +90,14 @@
 
 	printk(KERN_INFO "queue len: %u\n", kfifo_len(&test));
 
+	/* show the first value without removing from the fifo */
+	if (kfifo_peek(&test, &i))
+		printk(KERN_INFO "%d\n", i);
+
 	/* check the correctness of all values in the fifo */
 	j = 0;
 	while (kfifo_get(&test, &i)) {
+		printk(KERN_INFO "item = %d\n", i);
 		if (i != expected_result[j++]) {
 			printk(KERN_WARNING "value mismatch: test failed\n");
 			return -EIO;