fifo8: introduce fifo8_peek() function

This allows uses to peek the byte at the current head of the FIFO.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Octavian Purdila <tavip@google.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240828122258.928947-9-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

include/qemu/fifo8.h

@@ -62,6 +62,17 @@ void fifo8_push_all(Fifo8 *fifo, const uint8_t *data, uint32_t num);
  */
 uint8_t fifo8_pop(Fifo8 *fifo);
 
+/**
+ * fifo8_peek:
+ * @fifo: fifo to peek from
+ *
+ * Peek the data byte at the current head of the FIFO. Clients are responsible
+ * for checking for emptyness using fifo8_is_empty().
+ *
+ * Returns: The peeked data byte.
+ */
+uint8_t fifo8_peek(Fifo8 *fifo);
+
 /**
  * fifo8_pop_buf:
  * @fifo: FIFO to pop from

util/fifo8.c

@@ -71,6 +71,12 @@ uint8_t fifo8_pop(Fifo8 *fifo)
     return ret;
 }
 
+uint8_t fifo8_peek(Fifo8 *fifo)
+{
+    assert(fifo->num > 0);
+    return fifo->data[fifo->head];
+}
+
 static const uint8_t *fifo8_peekpop_bufptr(Fifo8 *fifo, uint32_t max,
                                            uint32_t skip, uint32_t *numptr,
                                            bool do_pop)