Make VMODs actually fail warm-ups

The implementation is similar to the load/discard dance when a load
fails. New VGC functions are introduced iff the VCL has at least one
VMOD handling events.

The generated code looks like this:

	static unsigned vgc_inistep;
	static unsigned vgc_warmupstep;

	...

	static int
	VGC_Load(VRT_CTX)
	{
		...
	}

	static int
	VGC_Discard(VRT_CTX)
	{
		...
	}

	static int
	VGC_Warmup(VRT_CTX, enum vcl_event_e ev)
	{

		vgc_warmupstep = 0;

		/* 4 */
		if (Vmod_debug_Func._event(ctx, &vmod_priv_debug, ev))
			return (1);
		vgc_warmupstep = 4;

		return (0);
	}

	static int
	VGC_Use(VRT_CTX, enum vcl_event_e ev)
	{

		/* 4 */
		if (Vmod_debug_Func._event(ctx, &vmod_priv_debug, ev))
			return (1);

		return (0);
	}

	static int
	VGC_Cooldown(VRT_CTX, enum vcl_event_e ev)
	{
		int retval = 0;

		/* 4 */
		if (vgc_warmupstep >= 4 &&
		    Vmod_debug_Func._event(ctx, &vmod_priv_debug, ev) != 0)
			retval = 1;

		return (retval);
	}

	static int
	VGC_Event(VRT_CTX, enum vcl_event_e ev)
	{
		if (ev == VCL_EVENT_LOAD)
			return(VGC_Load(ctx));
		if (ev == VCL_EVENT_WARM)
			return(VGC_Warmup(ctx, ev));
		if (ev == VCL_EVENT_USE)
			return(VGC_Use(ctx, ev));
		if (ev == VCL_EVENT_COLD)
			return(VGC_Cooldown(ctx, ev));
		if (ev == VCL_EVENT_DISCARD)
			return(VGC_Discard(ctx));

		return (1);
	}

However, if there are no VMODs handling events, no new functions shall
be generated, leading to code looking like this:

	static unsigned vgc_inistep;
	static unsigned vgc_warmupstep;

	...

	static int
	VGC_Load(VRT_CTX)
	{
		...
	}

	static int
	VGC_Discard(VRT_CTX)
	{
		...
	}

	static int
	VGC_Event(VRT_CTX, enum vcl_event_e ev)
	{
		if (ev == VCL_EVENT_LOAD)
			return(VGC_Load(ctx));
		if (ev == VCL_EVENT_DISCARD)
			return(VGC_Discard(ctx));

		(void)vgc_warmupstep;
		return (0);
	}

doc/sphinx/reference/vmod.rst

@@ -383,6 +383,13 @@ first with a ``VCL_EVENT_WARM`` event. Unless a user decides that a given VCL
 should always be warm, an inactive VMOD will eventually become cold and should
 manage resources accordingly.
 
+An event function must return zero upon success. It is only possible to fail
+an initialization with the ``VCL_EVENT_LOAD`` or ``VCL_EVENT_WARM`` events.
+Should such a failure happen, a ``VCL_EVENT_DISCARD`` or ``VCL_EVENT_COLD``
+event will be sent to the VMODs that succeeded to put them back in a cold
+state. The VMOD that failed will not receive this event, and therefore must
+not be left half-initialized should a failure occur.
+
 If your VMOD is running an asynchronous background job you can hold a reference
 to the VCL to prevent it from going cold too soon and get the same guarantees
 as backends with ongoing requests for instance. For that, you must acquire the

lib/libvcc/vcc_compile.c

@@ -325,20 +325,22 @@ EmitCoordinates(const struct vcc *tl, struct vsb *vsb)
 /*--------------------------------------------------------------------
  * Init/Fini/Event
  *
- * We call Fini-s in the opposite order of init-s.
- * Other events are called in same order as init-s, no matter which
- * event it might be.
+ * We call DISCARD and COLD events in the opposite order of LOAD and
+ * WARM.
  */
 
 static void
 EmitInitFini(const struct vcc *tl)
 {
 	struct inifin *p;
+	unsigned has_event = 0;
 
-	Fh(tl, 0, "\nstatic unsigned vgc_inistep;\n");
+	Fh(tl, 0, "\n");
+	Fh(tl, 0, "static unsigned vgc_inistep;\n");
+	Fh(tl, 0, "static unsigned vgc_warmupstep;\n");
 
 	/*
-	 * INIT
+	 * LOAD
 	 */
 	Fc(tl, 0, "\nstatic int\nVGC_Load(VRT_CTX)\n{\n\n");
 	Fc(tl, 0, "\tvgc_inistep = 0;\n\n");
@@ -349,6 +351,10 @@ EmitInitFini(const struct vcc *tl)
 			Fc(tl, 0, "\t/* %u */\n%s\n", p->n, VSB_data(p->ini));
 		Fc(tl, 0, "\tvgc_inistep = %u;\n\n", p->n);
 		VSB_delete(p->ini);
+
+		AZ(VSB_finish(p->event));
+		if (VSB_len(p->event))
+			has_event = 1;
 	}
 
 	Fc(tl, 0, "\t(void)VGC_function_vcl_init(ctx);\n");
@@ -356,7 +362,7 @@ EmitInitFini(const struct vcc *tl)
 	Fc(tl, 0, "}\n");
 
 	/*
-	 * FINI
+	 * DISCARD
 	 */
 	Fc(tl, 0, "\nstatic int\nVGC_Discard(VRT_CTX)\n{\n\n");
 
@@ -375,6 +381,66 @@ EmitInitFini(const struct vcc *tl)
 	Fc(tl, 0, "\treturn(0);\n");
 	Fc(tl, 0, "}\n");
 
+	if (has_event) {
+		/*
+		 * WARM
+		 */
+		Fc(tl, 0, "\nstatic int\n");
+		Fc(tl, 0, "VGC_Warmup(VRT_CTX, enum vcl_event_e ev)\n{\n\n");
+
+		Fc(tl, 0, "\tvgc_warmupstep = 0;\n\n");
+		VTAILQ_FOREACH(p, &tl->inifin, list) {
+			assert(p->n > 0);
+			if (VSB_len(p->event)) {
+				Fc(tl, 0, "\t/* %u */\n", p->n);
+				Fc(tl, 0, "\tif (%s)\n", VSB_data(p->event));
+				Fc(tl, 0, "\t\treturn (1);\n");
+				Fc(tl, 0, "\tvgc_warmupstep = %u;\n\n", p->n);
+			}
+		}
+
+		Fc(tl, 0, "\treturn (0);\n");
+		Fc(tl, 0, "}\n");
+
+		/*
+		 * USE (deprecated)
+		 */
+		Fc(tl, 0, "\nstatic int\n");
+		Fc(tl, 0, "VGC_Use(VRT_CTX, enum vcl_event_e ev)\n{\n\n");
+
+		VTAILQ_FOREACH(p, &tl->inifin, list) {
+			assert(p->n > 0);
+			if (VSB_len(p->event)) {
+				Fc(tl, 0, "\t/* %u */\n", p->n);
+				Fc(tl, 0, "\tif (%s)\n", VSB_data(p->event));
+				Fc(tl, 0, "\t\treturn (1);\n\n");
+			}
+		}
+
+		Fc(tl, 0, "\treturn (0);\n");
+		Fc(tl, 0, "}\n");
+
+		/*
+		 * COLD
+		 */
+		Fc(tl, 0, "\nstatic int\n");
+		Fc(tl, 0, "VGC_Cooldown(VRT_CTX, enum vcl_event_e ev)\n{\n");
+		Fc(tl, 0, "\tint retval = 0;\n\n");
+
+		VTAILQ_FOREACH_REVERSE(p, &tl->inifin, inifinhead, list) {
+			if (VSB_len(p->event)) {
+				Fc(tl, 0, "\t/* %u */\n", p->n);
+				Fc(tl, 0, "\tif (vgc_warmupstep >= %u &&\n", p->n);
+				Fc(tl, 0, "\t    %s != 0)\n", VSB_data(p->event));
+				Fc(tl, 0, "\t\tretval = 1;\n\n");
+			}
+			VSB_delete(p->event);
+		}
+
+		Fc(tl, 0, "\treturn (retval);\n");
+		Fc(tl, 0, "}\n");
+	}
+
 	/*
 	 * EVENTS
 	 */
@@ -383,16 +449,20 @@ EmitInitFini(const struct vcc *tl)
 	Fc(tl, 0, "{\n");
 	Fc(tl, 0, "\tif (ev == VCL_EVENT_LOAD)\n");
 	Fc(tl, 0, "\t\treturn(VGC_Load(ctx));\n");
+	if (has_event) {
+		Fc(tl, 0, "\tif (ev == VCL_EVENT_WARM)\n");
+		Fc(tl, 0, "\t\treturn(VGC_Warmup(ctx, ev));\n");
+		Fc(tl, 0, "\tif (ev == VCL_EVENT_USE)\n");
+		Fc(tl, 0, "\t\treturn(VGC_Use(ctx, ev));\n");
+		Fc(tl, 0, "\tif (ev == VCL_EVENT_COLD)\n");
+		Fc(tl, 0, "\t\treturn(VGC_Cooldown(ctx, ev));\n");
+	}
 	Fc(tl, 0, "\tif (ev == VCL_EVENT_DISCARD)\n");
 	Fc(tl, 0, "\t\treturn(VGC_Discard(ctx));\n");
 	Fc(tl, 0, "\n");
-	VTAILQ_FOREACH(p, &tl->inifin, list) {
-		AZ(VSB_finish(p->event));
-		if (VSB_len(p->event))
-			Fc(tl, 0, "\t/* %u */\n%s\n", p->n, VSB_data(p->event));
-		VSB_delete(p->event);
-	}
-	Fc(tl, 0, "\treturn (0);\n");
+	if (!has_event)
+		Fc(tl, 0, "\t(void)vgc_warmupstep;\n");
+	Fc(tl, 0, "\treturn (%d);\n", has_event ? 1 : 0);
 	Fc(tl, 0, "}\n");
 }
 

lib/libvcc/vcc_vmod.c

@@ -228,8 +228,7 @@ vcc_ParseImport(struct vcc *tl)
 			VSB_printf(ifp->fin,
 			    "\t\t(void)%s(ctx, &vmod_priv_%.*s,\n"
 			    "\t\t    VCL_EVENT_DISCARD);\n", p, PF(mod));
-			VSB_printf(ifp->event,
-			    "\t(void)%s(ctx, &vmod_priv_%.*s, ev);\n",
+			VSB_printf(ifp->event, "\t%s(ctx, &vmod_priv_%.*s, ev)",
 			    p, PF(mod));
 		} else {
 			sym = VCC_AddSymbolStr(tl, p, SYM_FUNC);