kfifo API type safety

This patch enhances the type safety for the kfifo API.  It is now safe
to put const data into a non const FIFO and the API will now generate a
compiler warning when reading from the fifo where the destination
address is pointing to a const variable.

As a side effect the kfifo_put() does now expect the value of an element
instead a pointer to the element.  This was suggested Russell King.  It
make the handling of the kfifo_put easier since there is no need to
create a helper variable for getting the address of a pointer or to pass
integers of different sizes.

IMHO the API break is okay, since there are currently only six users of
kfifo_put().

The code is also cleaner by kicking out the "if (0)" expressions.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Stefani Seibold <stefani@seibold.net>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

samples/kfifo/bytestream-example.c

@@ -64,7 +64,7 @@ static int __init testfunc(void)
 
 	/* put values into the fifo */
 	for (i = 0; i != 10; i++)
-		kfifo_put(&test, &i);
+		kfifo_put(&test, i);
 
 	/* show the number of used elements */
 	printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test));
@@ -85,7 +85,7 @@ static int __init testfunc(void)
 	kfifo_skip(&test);
 
 	/* put values into the fifo until is full */
-	for (i = 20; kfifo_put(&test, &i); i++)
+	for (i = 20; kfifo_put(&test, i); i++)
 		;
 
 	printk(KERN_INFO "queue len: %u\n", kfifo_len(&test));

samples/kfifo/dma-example.c

@@ -39,7 +39,7 @@ static int __init example_init(void)
 	kfifo_in(&fifo, "test", 4);
 
 	for (i = 0; i != 9; i++)
-		kfifo_put(&fifo, &i);
+		kfifo_put(&fifo, i);
 
 	/* kick away first byte */
 	kfifo_skip(&fifo);

samples/kfifo/inttype-example.c

@@ -61,7 +61,7 @@ static int __init testfunc(void)
 
 	/* put values into the fifo */
 	for (i = 0; i != 10; i++)
-		kfifo_put(&test, &i);
+		kfifo_put(&test, i);
 
 	/* show the number of used elements */
 	printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test));
@@ -78,7 +78,7 @@ static int __init testfunc(void)
 	kfifo_skip(&test);
 
 	/* put values into the fifo until is full */
-	for (i = 20; kfifo_put(&test, &i); i++)
+	for (i = 20; kfifo_put(&test, i); i++)
 		;
 
 	printk(KERN_INFO "queue len: %u\n", kfifo_len(&test));