kfifo: add kfifo_initialized

Simple inline that checks if kfifo_init() has been executed on a fifo.

This is useful for walking all per CPU fifos, when some of them might not
have been brought up yet.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Stefani Seibold <stefani@seibold.net>
Cc: Roland Dreier <rdreier@cisco.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Andy Walls <awalls@radix.net>
Cc: Vikram Dhillon <dhillonv10@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/kfifo.h

@@ -116,6 +116,16 @@ extern __must_check unsigned int kfifo_out(struct kfifo *fifo,
 extern __must_check unsigned int kfifo_out_peek(struct kfifo *fifo,
 				void *to, unsigned int len, unsigned offset);
 
+/**
+ * kfifo_initialized - Check if kfifo is initialized.
+ * @fifo: fifo to check
+ * Return %true if FIFO is initialized, otherwise %false.
+ * Assumes the fifo was 0 before.
+ */
+static inline bool kfifo_initialized(struct kfifo *fifo)
+{
+	return fifo->buffer != 0;
+}
 
 /**
  * kfifo_reset - removes the entire FIFO contents