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

[Peter Crosthwaite]

On Fri, Jan 31, 2014 at 8:02 AM, Beniamino Galvani <address@hidden> wrote:
> 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.
>

In an ideal world its two patches. Although its totally not worth a
respin if Peter is happy to take as-is.

> Signed-off-by: Beniamino Galvani <address@hidden>

Reviewed-by: Peter Crosthwaite <address@hidden>

> ---
>  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
>
>