util/fifo8: Introduce fifo8_peek_buf()
To be able to peek at FIFO content without popping it,
introduce the fifo8_peek_buf() method by factoring
common content from fifo8_pop_buf().
Reviewed-by: Francisco Iglesias <frasse.iglesias@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20231109192814.95977-3-philmd@linaro.org>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
diff --git a/include/qemu/fifo8.h b/include/qemu/fifo8.h
index d0d02bc..c6295c6 100644
--- a/include/qemu/fifo8.h
+++ b/include/qemu/fifo8.h
@@ -94,6 +94,33 @@
const uint8_t *fifo8_pop_buf(Fifo8 *fifo, uint32_t max, uint32_t *numptr);
/**
+ * fifo8_peek_buf: read upto max bytes from the fifo
+ * @fifo: FIFO to read from
+ * @max: maximum number of bytes to peek
+ * @numptr: pointer filled with number of bytes returned (can be NULL)
+ *
+ * Peek into a number of elements from the FIFO up to a maximum of max.
+ * The buffer containing the data peeked into is returned. This buffer points
+ * directly into the FIFO backing store. Since data is invalidated once any
+ * of the fifo8_* APIs are called on the FIFO, it is the caller responsibility
+ * to access it before doing further API calls.
+ *
+ * The function may return fewer bytes than requested when the data wraps
+ * around in the ring buffer; in this case only a contiguous part of the data
+ * is returned.
+ *
+ * The number of valid bytes returned is populated in *numptr; will always
+ * return at least 1 byte. max must not be 0 or greater than the number of
+ * bytes in the FIFO.
+ *
+ * Clients are responsible for checking the availability of requested data
+ * using fifo8_num_used().
+ *
+ * Returns: A pointer to peekable data.
+ */
+const uint8_t *fifo8_peek_buf(Fifo8 *fifo, uint32_t max, uint32_t *numptr);
+
+/**
* fifo8_reset:
* @fifo: FIFO to reset
*
diff --git a/util/fifo8.c b/util/fifo8.c
index 2eeed56..4e01b53 100644
--- a/util/fifo8.c
+++ b/util/fifo8.c
@@ -66,7 +66,8 @@
return ret;
}
-const uint8_t *fifo8_pop_buf(Fifo8 *fifo, uint32_t max, uint32_t *numptr)
+static const uint8_t *fifo8_peekpop_buf(Fifo8 *fifo, uint32_t max,
+ uint32_t *numptr, bool do_pop)
{
uint8_t *ret;
uint32_t num;
@@ -74,15 +75,28 @@
assert(max > 0 && max <= fifo->num);
num = MIN(fifo->capacity - fifo->head, max);
ret = &fifo->data[fifo->head];
- fifo->head += num;
- fifo->head %= fifo->capacity;
- fifo->num -= num;
+
+ if (do_pop) {
+ fifo->head += num;
+ fifo->head %= fifo->capacity;
+ fifo->num -= num;
+ }
if (numptr) {
*numptr = num;
}
return ret;
}
+const uint8_t *fifo8_peek_buf(Fifo8 *fifo, uint32_t max, uint32_t *numptr)
+{
+ return fifo8_peekpop_buf(fifo, max, numptr, false);
+}
+
+const uint8_t *fifo8_pop_buf(Fifo8 *fifo, uint32_t max, uint32_t *numptr)
+{
+ return fifo8_peekpop_buf(fifo, max, numptr, true);
+}
+
void fifo8_reset(Fifo8 *fifo)
{
fifo->num = 0;
