Re: [PATCH v2 6/7] util/fifo8: Expose fifo8_pop_buf()

[Mark Cave-Ayland]

On 22/07/2024 17:07, Philippe Mathieu-Daudé wrote:

> Extract fifo8_pop_buf() from hw/scsi/esp.c and expose
> it as part of the <qemu/fifo8.h> API. This function takes
> care of non-contiguous (wrapped) FIFO buffer (which is an
> implementation detail).

I wonder if it is also worth updating the comment for fifo8_pop_bufptr() indicating 
that it returns a pointer to the internal buffer without checking for overflow, and 
that in general fifo8_pop_buf() is recommended instead? Otherwise:

Reviewed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>


ATB,

Mark.

> Suggested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
>   include/qemu/fifo8.h | 14 ++++++++++++++
>   hw/scsi/esp.c        | 36 +++---------------------------------
>   util/fifo8.c         | 29 +++++++++++++++++++++++++++++
>   3 files changed, 46 insertions(+), 33 deletions(-)
>
> diff --git a/include/qemu/fifo8.h b/include/qemu/fifo8.h
> index 686918a3a4..21c7a22937 100644
> --- a/include/qemu/fifo8.h
> +++ b/include/qemu/fifo8.h
> @@ -62,6 +62,20 @@ void fifo8_push_all(Fifo8 *fifo, const uint8_t *data, 
> uint32_t num);
>    */
>   uint8_t fifo8_pop(Fifo8 *fifo);
>   
> +/**
> + * fifo8_pop_buf:
> + * @fifo: FIFO to pop from
> + * @dest: the buffer to write the data into (can be NULL)
> + * @destlen: size of @dest and maximum number of bytes to pop
> + *
> + * Pop a number of elements from the FIFO up to a maximum of @destlen.
> + * The popped data is copied into the @dest buffer.
> + * Care is taken when the data wraps around in the ring buffer.
> + *
> + * Returns: number of bytes popped.
> + */
> +uint32_t fifo8_pop_buf(Fifo8 *fifo, uint8_t *dest, uint32_t destlen);
> +
>   /**
>    * fifo8_pop_constbuf:
>    * @fifo: FIFO to pop from
> diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
> index 64384f9b0e..cec847b54a 100644
> --- a/hw/scsi/esp.c
> +++ b/hw/scsi/esp.c
> @@ -197,39 +197,9 @@ static uint8_t esp_fifo_pop(ESPState *s)
>       return val;
>   }
>   
> -static uint32_t esp_fifo8_pop_buf(Fifo8 *fifo, uint8_t *dest, int maxlen)
> -{
> -    const uint8_t *buf;
> -    uint32_t n, n2;
> -    int len;
> -
> -    if (maxlen == 0) {
> -        return 0;
> -    }
> -
> -    len = maxlen;
> -    buf = fifo8_pop_constbuf(fifo, len, &n);
> -    if (dest) {
> -        memcpy(dest, buf, n);
> -    }
> -
> -    /* Add FIFO wraparound if needed */
> -    len -= n;
> -    len = MIN(len, fifo8_num_used(fifo));
> -    if (len) {
> -        buf = fifo8_pop_constbuf(fifo, len, &n2);
> -        if (dest) {
> -            memcpy(&dest[n], buf, n2);
> -        }
> -        n += n2;
> -    }
> -
> -    return n;
> -}
> -
>   static uint32_t esp_fifo_pop_buf(ESPState *s, uint8_t *dest, int maxlen)
>   {
> -    uint32_t len = esp_fifo8_pop_buf(&s->fifo, dest, maxlen);
> +    uint32_t len = fifo8_pop_buf(&s->fifo, dest, maxlen);
>   
>       esp_update_drq(s);
>       return len;
> @@ -335,7 +305,7 @@ static void do_command_phase(ESPState *s)
>       if (!cmdlen || !s->current_dev) {
>           return;
>       }
> -    esp_fifo8_pop_buf(&s->cmdfifo, buf, cmdlen);
> +    fifo8_pop_buf(&s->cmdfifo, buf, cmdlen);
>   
>       current_lun = scsi_device_find(&s->bus, 0, s->current_dev->id, s->lun);
>       if (!current_lun) {
> @@ -381,7 +351,7 @@ static void do_message_phase(ESPState *s)
>       /* Ignore extended messages for now */
>       if (s->cmdfifo_cdb_offset) {
>           int len = MIN(s->cmdfifo_cdb_offset, fifo8_num_used(&s->cmdfifo));
> -        esp_fifo8_pop_buf(&s->cmdfifo, NULL, len);
> +        fifo8_pop_buf(&s->cmdfifo, NULL, len);
>           s->cmdfifo_cdb_offset = 0;
>       }
>   }
> diff --git a/util/fifo8.c b/util/fifo8.c
> index 31f0d34c0c..6610b79182 100644
> --- a/util/fifo8.c
> +++ b/util/fifo8.c
> @@ -102,6 +102,35 @@ const uint8_t *fifo8_pop_constbuf(Fifo8 *fifo, uint32_t 
> max, uint32_t *numptr)
>       return fifo8_peekpop_buf(fifo, max, numptr, true);
>   }
>   
> +uint32_t fifo8_pop_buf(Fifo8 *fifo, uint8_t *dest, uint32_t destlen)
> +{
> +    const uint8_t *buf;
> +    uint32_t n1, n2 = 0;
> +    uint32_t len;
> +
> +    if (destlen == 0) {
> +        return 0;
> +    }
> +
> +    len = destlen;
> +    buf = fifo8_pop_constbuf(fifo, len, &n1);
> +    if (dest) {
> +        memcpy(dest, buf, n1);
> +    }
> +
> +    /* Add FIFO wraparound if needed */
> +    len -= n1;
> +    len = MIN(len, fifo8_num_used(fifo));
> +    if (len) {
> +        buf = fifo8_pop_constbuf(fifo, len, &n2);
> +        if (dest) {
> +            memcpy(&dest[n1], buf, n2);
> +        }
> +    }
> +
> +    return n1 + n2;
> +}
> +
>   bool fifo8_is_empty(Fifo8 *fifo)
>   {
>       return (fifo->num == 0);