give all requests a struct reqtop

Dynamically creating it through Req_MakeTop() would further complicate
rollbacks.

The memory overhead is basically identical to embedding struct reqtop
into struct req, except that, for ESI, we have the (struct req).top
point to the top request's struct reqtop.

With this commit, tests/r02849.vtc and tests/r03003.vtc are failing as
excpected. While this may impose issues with git bisect, I still think
that this extra commit helps clarity.

bin/varnishd/cache/cache.h

@@ -537,7 +537,7 @@ struct req {
 	struct vcf		*vcf;
 };
 
-#define IS_TOPREQ(req) ((req)->top == NULL || (req)->top->topreq == (req))
+#define IS_TOPREQ(req) ((req)->top->topreq == (req))
 
 /*--------------------------------------------------------------------
  * Struct sess is a high memory-load structure because sessions typically

bin/varnishd/cache/cache_esi_deliver.c

@@ -139,6 +139,7 @@ ved_include(struct req *preq, const char *src, const char *host,
 
 	req->esi_level = preq->esi_level + 1;
 
+	memset(req->top, 0, sizeof *req->top);
 	req->top = preq->top;
 
 	HTTP_Setup(req->http, req->ws, req->vsl, SLT_ReqMethod);
@@ -264,16 +265,6 @@ ved_vdp_esi_init(struct req *req, void **priv)
 	*priv = ecx;
 	RFC2616_Weaken_Etag(req->resp);
 
-	if (IS_TOPREQ(req)) {
-		Req_MakeTop(req);
-		if (req->top == NULL) {
-			VSLb(req->vsl, SLT_Error,
-			    "(top)request workspace overflow");
-			Req_Fail(req, SC_OVERLOAD);
-			return (-1);
-		}
-	}
-
 	req->res_mode |= RES_ESI;
 	if (req->resp_len != 0)
 		req->resp_len = -1;

bin/varnishd/cache/cache_req.c

@@ -137,6 +137,11 @@ Req_New(const struct worker *wrk, struct sess *sp)
 	INIT_OBJ(req->htc, HTTP_CONN_MAGIC);
 	p = (void*)PRNDUP(p + sizeof(*req->htc));
 
+	req->top = (void*)p;
+	INIT_OBJ(req->top, REQTOP_MAGIC);
+	req->top->topreq = req;
+	p = (void*)PRNDUP(p + sizeof(*req->top));
+
 	assert(p < e);
 
 	WS_Init(req->ws, "req", p, e - p);
@@ -170,7 +175,6 @@ Req_Release(struct req *req)
 	CHECK_OBJ_NOTNULL(req, REQ_MAGIC);
 	MPL_AssertSane(req);
 	VSL_Flush(req->vsl, 0);
-	req->top = NULL;
 	MPL_Free(pp->mpl_req, req);
 }
 
@@ -189,7 +193,6 @@ Req_Rollback(struct req *req)
 	if (WS_Overflowed(req->ws))
 		req->wrk->stats->ws_client_overflow++;
 	WS_Reset(req->ws, req->ws_req);
-	req->top = NULL;
 }
 
 /*----------------------------------------------------------------------
@@ -235,7 +238,6 @@ Req_Cleanup(struct sess *sp, struct worker *wrk, struct req *req)
 	req->hash_ignore_busy = 0;
 	req->esi_level = 0;
 	req->is_hit = 0;
-	req->top = 0;
 
 	if (WS_Overflowed(req->ws))
 		wrk->stats->ws_client_overflow++;
@@ -254,20 +256,3 @@ Req_Fail(struct req *req, enum sess_close reason)
 	AN(req->transport->req_fail);
 	req->transport->req_fail(req, reason);
 }
-
-/*----------------------------------------------------------------------
- */
-
-void
-Req_MakeTop(struct req *req)
-{
-
-	CHECK_OBJ_ORNULL(req->top, REQTOP_MAGIC);
-	if (req->top != NULL)
-		return;
-	req->top = WS_Alloc(req->ws, sizeof *req->top);
-	if (req->top != NULL) {
-		INIT_OBJ(req->top, REQTOP_MAGIC);
-		req->top->topreq = req;
-	}
-}

bin/varnishd/cache/cache_varnishd.h

@@ -351,7 +351,6 @@ void Req_Rollback(struct req *req);
 void Req_Cleanup(struct sess *sp, struct worker *wrk, struct req *req);
 void Req_Fail(struct req *req, enum sess_close reason);
 void Req_AcctLogCharge(struct VSC_main_wrk *, struct req *);
-void Req_MakeTop(struct req *req);
 
 /* cache_req_body.c */
 int VRB_Ignore(struct req *);

bin/varnishd/cache/cache_vcl.c

@@ -101,11 +101,8 @@ VCL_Req2Ctx(struct vrt_ctx *ctx, struct req *req)
 	ctx->vcl = req->vcl;
 	ctx->vsl = req->vsl;
 	ctx->http_req = req->http;
-	CHECK_OBJ_ORNULL(req->top, REQTOP_MAGIC);
-	if (req->top != NULL)
-		ctx->http_req_top = req->top->topreq->http;
-	else
-		ctx->http_req_top = req->http;
+	CHECK_OBJ_NOTNULL(req->top, REQTOP_MAGIC);
+	ctx->http_req_top = req->top->topreq->http;
 	ctx->http_resp = req->resp;
 	ctx->req = req;
 	ctx->sp = req->sp;

bin/varnishd/cache/cache_vrt_vcl.c

@@ -428,7 +428,7 @@ vcl_call_method(struct worker *wrk, struct req *req, struct busyobj *bo,
 		CHECK_OBJ(req, REQ_MAGIC);
 		CHECK_OBJ_NOTNULL(req->sp, SESS_MAGIC);
 		CHECK_OBJ_NOTNULL(req->vcl, VCL_MAGIC);
-		CHECK_OBJ_ORNULL(req->top, REQTOP_MAGIC);
+		CHECK_OBJ_NOTNULL(req->top, REQTOP_MAGIC);
 		VCL_Req2Ctx(&ctx, req);
 	}
 	if (bo != NULL) {