fifo8: add fifo8_peek_buf() function

This is a wrapper function around fifo8_peekpop_buf() that allows the
caller to peek into the FIFO, including handling the case where there
is a wraparound of the internal FIFO buffer.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Octavian Purdila <tavip@google.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240828122258.928947-8-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

include/qemu/fifo8.h

@@ -76,6 +76,20 @@ uint8_t fifo8_pop(Fifo8 *fifo);
  */
 uint32_t fifo8_pop_buf(Fifo8 *fifo, uint8_t *dest, uint32_t destlen);
 
+/**
+ * fifo8_peek_buf:
+ * @fifo: FIFO to read from
+ * @dest: the buffer to write the data into (can be NULL)
+ * @destlen: size of @dest and maximum number of bytes to peek
+ *
+ * Peek a number of elements from the FIFO up to a maximum of @destlen.
+ * The peeked data is copied into the @dest buffer.
+ * Care is taken when the data wraps around in the ring buffer.
+ *
+ * Returns: number of bytes peeked.
+ */
+uint32_t fifo8_peek_buf(Fifo8 *fifo, uint8_t *dest, uint32_t destlen);
+
 /**
  * fifo8_pop_bufptr:
  * @fifo: FIFO to pop from

util/fifo8.c

@@ -140,6 +140,11 @@ uint32_t fifo8_pop_buf(Fifo8 *fifo, uint8_t *dest, uint32_t destlen)
     return fifo8_peekpop_buf(fifo, dest, destlen, true);
 }
 
+uint32_t fifo8_peek_buf(Fifo8 *fifo, uint8_t *dest, uint32_t destlen)
+{
+    return fifo8_peekpop_buf(fifo, dest, destlen, false);
+}
+
 void fifo8_drop(Fifo8 *fifo, uint32_t len)
 {
     len -= fifo8_pop_buf(fifo, NULL, len);