Re: [Xen-devel] [PATCH] ring/macro: Add a new macro to detect whether there is an overflow in requests and response.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.01.13 at 18:32, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:
> We want to be able to exit if the difference between the request
> produced (what the frontend tells us) and the requests consumed
> (what we have so far processed) is greater than the ring size.
> 
> If so, we should terminate the loop as the request produced
> is not trusted and it means it is bogus.
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
>  xen/include/public/io/ring.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/xen/include/public/io/ring.h b/xen/include/public/io/ring.h
> index 38b7051..219ab63 100644
> --- a/xen/include/public/io/ring.h
> +++ b/xen/include/public/io/ring.h
> @@ -234,6 +234,12 @@ typedef struct __name##_back_ring __name##_back_ring_t
>  #define RING_REQUEST_CONS_OVERFLOW(_r, _cons)                           \
>      (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
>  
> +/* Loop termination condition: Is the difference between request produced
> + * and request consumed greater than the ring size. If so, terminate the
> + * loop. */
> +#define RING_REQUEST_PROD_OVERFLOW(_r, _cons, _prod)                     \
> +    (((_prod) - (_prod)) > RING_SIZE(_r))

Clearly one of the two _prod-s ought to be _cons?

Jan

> +
>  #define RING_PUSH_REQUESTS(_r) do {                                     \
>      xen_wmb(); /* back sees requests /before/ updated producer index */ \
>      (_r)->sring->req_prod = (_r)->req_prod_pvt;                         \
> -- 
> 1.8.0.2
> 
> 
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