[Qemu-devel] [PATCH v5 1/4] util/fifo8: implement push/pop of multiple bytes

[Beniamino Galvani <b.galvani@gmail.com>]

The patch adds functions fifo8_push_all() and fifo8_pop_buf() which
can be used respectively to push the content of a memory buffer to the
fifo and to pop multiple bytes obtaining a pointer to the fifo backing
buffer.

In addition, it implements fifo8_num_free() and fifo8_num_used() which
allow to check if a multi-byte operation can be performed.

Signed-off-by: Beniamino Galvani <b.galvani@gmail.com>
---
 include/qemu/fifo8.h |   61 ++++++++++++++++++++++++++++++++++++++++++++++++++
 util/fifo8.c         |   46 +++++++++++++++++++++++++++++++++++++
 2 files changed, 107 insertions(+)

diff --git a/include/qemu/fifo8.h b/include/qemu/fifo8.h
index d318f71..8820780 100644
--- a/include/qemu/fifo8.h
+++ b/include/qemu/fifo8.h
@@ -44,6 +44,19 @@ void fifo8_destroy(Fifo8 *fifo);
 void fifo8_push(Fifo8 *fifo, uint8_t data);
 
 /**
+ * fifo8_push_all:
+ * @fifo: FIFO to push to
+ * @data: data to push
+ * @size: number of bytes to push
+ *
+ * Push a byte array to the FIFO. Behaviour is undefined if the FIFO is full.
+ * Clients are responsible for checking the space left in the FIFO using
+ * fifo8_num_free().
+ */
+
+void fifo8_push_all(Fifo8 *fifo, const uint8_t *data, uint32_t num);
+
+/**
  * fifo8_pop:
  * @fifo: fifo to pop from
  *
@@ -56,6 +69,32 @@ void fifo8_push(Fifo8 *fifo, uint8_t data);
 uint8_t fifo8_pop(Fifo8 *fifo);
 
 /**
+ * fifo8_pop_buf:
+ * @fifo: FIFO to pop from
+ * @max: maximum number of bytes to pop
+ * @num: actual number of returned bytes
+ *
+ * Pop a number of elements from the FIFO up to a maximum of max. The buffer
+ * containing the popped data is returned. This buffer points directly into
+ * the FIFO backing store and data is invalidated once any of the fifo8_* APIs
+ * are called on the FIFO.
+ *
+ * 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 *num; 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 popped data.
+ */
+const uint8_t *fifo8_pop_buf(Fifo8 *fifo, uint32_t max, uint32_t *num);
+
+/**
  * fifo8_reset:
  * @fifo: FIFO to reset
  *
@@ -86,6 +125,28 @@ bool fifo8_is_empty(Fifo8 *fifo);
 
 bool fifo8_is_full(Fifo8 *fifo);
 
+/**
+ * fifo8_num_free:
+ * @fifo: FIFO to check
+ *
+ * Return the number of free bytes in the FIFO.
+ *
+ * Returns: Number of free bytes.
+ */
+
+uint32_t fifo8_num_free(Fifo8 *fifo);
+
+/**
+ * fifo8_num_used:
+ * @fifo: FIFO to check
+ *
+ * Return the number of used bytes in the FIFO.
+ *
+ * Returns: Number of used bytes.
+ */
+
+uint32_t fifo8_num_used(Fifo8 *fifo);
+
 extern const VMStateDescription vmstate_fifo8;
 
 #define VMSTATE_FIFO8(_field, _state) {                              \
diff --git a/util/fifo8.c b/util/fifo8.c
index 013e903..a7503c2 100644
--- a/util/fifo8.c
+++ b/util/fifo8.c
@@ -37,6 +37,27 @@ void fifo8_push(Fifo8 *fifo, uint8_t data)
     fifo->num++;
 }
 
+void fifo8_push_all(Fifo8 *fifo, const uint8_t *data, uint32_t num)
+{
+    uint32_t start, avail;
+
+    if (fifo->num + num > fifo->capacity) {
+        abort();
+    }
+
+    start = (fifo->head + fifo->num) % fifo->capacity;
+
+    if (start + num <= fifo->capacity) {
+        memcpy(&fifo->data[start], data, num);
+    } else {
+        avail = fifo->capacity - start;
+        memcpy(&fifo->data[start], data, avail);
+        memcpy(&fifo->data[0], &data[avail], num - avail);
+    }
+
+    fifo->num += num;
+}
+
 uint8_t fifo8_pop(Fifo8 *fifo)
 {
     uint8_t ret;
@@ -50,6 +71,21 @@ uint8_t fifo8_pop(Fifo8 *fifo)
     return ret;
 }
 
+const uint8_t *fifo8_pop_buf(Fifo8 *fifo, uint32_t max, uint32_t *num)
+{
+    uint8_t *ret;
+
+    if (max == 0 || max > fifo->num) {
+        abort();
+    }
+    *num = MIN(fifo->capacity - fifo->head, max);
+    ret = &fifo->data[fifo->head];
+    fifo->head += *num;
+    fifo->head %= fifo->capacity;
+    fifo->num -= *num;
+    return ret;
+}
+
 void fifo8_reset(Fifo8 *fifo)
 {
     fifo->num = 0;
@@ -65,6 +101,16 @@ bool fifo8_is_full(Fifo8 *fifo)
     return (fifo->num == fifo->capacity);
 }
 
+uint32_t fifo8_num_free(Fifo8 *fifo)
+{
+    return fifo->capacity - fifo->num;
+}
+
+uint32_t fifo8_num_used(Fifo8 *fifo)
+{
+    return fifo->num;
+}
+
 const VMStateDescription vmstate_fifo8 = {
     .name = "Fifo8",
     .version_id = 1,
-- 
1.7.10.4