kfifo: provide kfifo_is_empty_spinlocked()

Provide two spinlocked versions of kfifo_is_empty() to be used with
spinlocked variants of kfifo_in() and kfifo_out().
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Stefani Seibold <stefani@seibold.net>

include/linux/kfifo.h

@@ -246,6 +246,37 @@ __kfifo_int_must_check_helper(int val)
 	__tmpq->kfifo.in == __tmpq->kfifo.out; \
 })
 
+/**
+ * kfifo_is_empty_spinlocked - returns true if the fifo is empty using
+ * a spinlock for locking
+ * @fifo: address of the fifo to be used
+ * @lock: spinlock to be used for locking
+ */
+#define kfifo_is_empty_spinlocked(fifo, lock) \
+({ \
+	unsigned long __flags; \
+	bool __ret; \
+	spin_lock_irqsave(lock, __flags); \
+	__ret = kfifo_is_empty(fifo); \
+	spin_unlock_irqrestore(lock, __flags); \
+	__ret; \
+})
+
+/**
+ * kfifo_is_empty_spinlocked_noirqsave  - returns true if the fifo is empty
+ * using a spinlock for locking, doesn't disable interrupts
+ * @fifo: address of the fifo to be used
+ * @lock: spinlock to be used for locking
+ */
+#define kfifo_is_empty_spinlocked_noirqsave(fifo, lock) \
+({ \
+	bool __ret; \
+	spin_lock(lock); \
+	__ret = kfifo_is_empty(fifo); \
+	spin_unlock(lock); \
+	__ret; \
+})
+
 /**
  * kfifo_is_full - returns true if the fifo is full
  * @fifo: address of the fifo to be used