From a63c57093b610e8707653fb2320f48e2ad5acbc2 Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Wed, 12 Jun 2013 10:07:20 +0200 Subject: [PATCH] io/ring.h: new macro to detect whether there are too many requests on the ring Backends may need to protect themselves against an insane number of produced requests stored by a frontend, in case they iterate over requests until reaching the req_prod value. There can't be more requests on the ring than the difference between produced requests and produced (but possibly not yet published) responses. This is a more strict alternative to a patch previously posted by Konrad Rzeszutek Wilk . Signed-off-by: Jan Beulich Acked-by: Keir Fraser --- xen/include/public/io/ring.h | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/xen/include/public/io/ring.h b/xen/include/public/io/ring.h index d9884f5a0f..bdfb998cec 100644 --- a/xen/include/public/io/ring.h +++ b/xen/include/public/io/ring.h @@ -234,6 +234,10 @@ typedef struct __name##_back_ring __name##_back_ring_t #define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \ (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r)) +/* Ill-behaved frontend determination: Can there be this many requests? */ +#define RING_REQUEST_PROD_OVERFLOW(_r, _prod) \ + (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r)) + #define RING_PUSH_REQUESTS(_r) do { \ xen_wmb(); /* back sees requests /before/ updated producer index */ \ (_r)->sring->req_prod = (_r)->req_prod_pvt; \ -- 2.30.2