Revert "blktap2: Use RING_COPY_REQUEST"

This reverts commit 19f6c522a6. It
did wrongly get associated with XSA-155, and was (rightfully) never
backported to any of the stable trees. See also
http://lists.xenproject.org/archives/html/xen-devel/2016-03/msg00571.html.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>

tools/blktap2/drivers/block-log.c

@@ -494,12 +494,11 @@ static int ctl_kick(struct tdlog_state* s, int fd)
   reqstart = s->bring.req_cons;
   reqend = s->sring->req_prod;
 
-  xen_mb();
   BDPRINTF("ctl: ring kicked (start = %u, end = %u)", reqstart, reqend);
 
   while (reqstart != reqend) {
     /* XXX actually submit these! */
-    RING_COPY_REQUEST(&s->bring, reqstart, &req);
+    memcpy(&req, RING_GET_REQUEST(&s->bring, reqstart), sizeof(req));
     BDPRINTF("ctl: read request %"PRIu64":%u", req.sector, req.count);
     s->bring.req_cons = ++reqstart;
 

tools/blktap2/drivers/tapdisk-vbd.c

@@ -1555,7 +1555,7 @@ tapdisk_vbd_pull_ring_requests(td_vbd_t *vbd)
 	int idx;
 	RING_IDX rp, rc;
 	td_ring_t *ring;
-	blkif_request_t req;
+	blkif_request_t *req;
 	td_vbd_request_t *vreq;
 
 	ring = &vbd->ring;
@@ -1566,16 +1566,16 @@ tapdisk_vbd_pull_ring_requests(td_vbd_t *vbd)
 	xen_rmb();
 
 	for (rc = ring->fe_ring.req_cons; rc != rp; rc++) {
-		RING_COPY_REQUEST(&ring->fe_ring, rc, &req);
+		req = RING_GET_REQUEST(&ring->fe_ring, rc);
 		++ring->fe_ring.req_cons;
 
-		idx  = req.id;
+		idx  = req->id;
 		vreq = &vbd->request_list[idx];
 
 		ASSERT(list_empty(&vreq->next));
 		ASSERT(vreq->secs_pending == 0);
 
-		memcpy(&vreq->req, &req, sizeof(blkif_request_t));
+		memcpy(&vreq->req, req, sizeof(blkif_request_t));
 		vbd->received++;
 		vreq->vbd = vbd;