Add a notify method for directors and implement it for VBE

Pondering solutions for varnishcache#4183 it became apparent that we currently have no way
for core code to notify directors of changes, in particular changes of the
admin_health. I looked into re-using the healthy callback, but it is unsuitable
because VRT_Healthy() does not even call it for an "auto" admin_health.

So the cleanest option is another director callback, which is cheap and also
helps us maintain clean layering.

bin/varnishd/cache/cache_backend.c

@@ -675,6 +675,21 @@ vbe_healthy(VRT_CTX, VCL_BACKEND d, VCL_TIME *t)
 	return (!bp->sick);
 }
 
+static VCL_VOID v_matchproto_(vdi_notify_f)
+vbe_notify(VCL_BACKEND d)
+{
+	const struct vdi_ahealth *ah;
+	struct backend *bp;
+
+	CHECK_OBJ_NOTNULL(d, DIRECTOR_MAGIC);
+	CAST_OBJ_NOTNULL(bp, d->priv, BACKEND_MAGIC);
+	CHECK_OBJ_NOTNULL(d->vdir, VCLDIR_MAGIC);
+	ah = d->vdir->admin_health;
+
+	// sick == 0 for _noprobe
+	if (ah == VDI_AH_SICK || (ah == VDI_AH_AUTO && bp->sick))
+		VBE_connwait_signal_all(bp);
+}
 
 /*--------------------------------------------------------------------
  */
@@ -690,7 +705,8 @@ static const struct vdi_methods vbe_methods[1] = {{
 	.destroy =		vbe_destroy,
 	.panic =		vbe_panic,
 	.list =			vbe_list,
-	.healthy =		vbe_healthy
+	.healthy =		vbe_healthy,
+	.notify =		vbe_notify
 }};
 
 static const struct vdi_methods vbe_methods_noprobe[1] = {{
@@ -703,7 +719,8 @@ static const struct vdi_methods vbe_methods_noprobe[1] = {{
 	.event =		vbe_dir_event,
 	.destroy =		vbe_destroy,
 	.panic =		vbe_panic,
-	.list =			vbe_list
+	.list =			vbe_list,
+	.notify =		vbe_notify
 }};
 
 /*--------------------------------------------------------------------

bin/varnishd/cache/cache_director.c

@@ -265,6 +265,22 @@ VRT_SetChanged(VCL_BACKEND d, VCL_TIME changed)
 		d->vdir->health_changed = changed;
 }
 
+/*--------------------------------------------------------------------
+ * Notify of change (admin_health for now) outside backend
+ */
+
+VCL_VOID
+VRT_Notify(VCL_BACKEND d)
+{
+
+	CHECK_OBJ_NOTNULL(d, DIRECTOR_MAGIC);
+	CHECK_OBJ_NOTNULL(d->vdir, VCLDIR_MAGIC);
+	CHECK_OBJ_NOTNULL(d->vdir->methods, VDI_METHODS_MAGIC);
+	if (d->vdir->methods->notify == NULL)
+		return;
+	d->vdir->methods->notify(d);
+}
+
 /* Send Event ----------------------------------------------------------
  */
 

include/vrt.h

@@ -46,7 +46,7 @@
 #  error "include vdef.h before vrt.h"
 #endif
 
-#define VRT_MAJOR_VERSION	20U
+#define VRT_MAJOR_VERSION	21U
 
 #define VRT_MINOR_VERSION	0U
 
@@ -58,6 +58,9 @@
  * binary/load-time compatible, increment MAJOR version
  *
  * NEXT (2024-03-15)
+ * 21.0
+ *	notify callback added to struct vdi_methods
+ *	VRT_Notify() added
  * 20.0 (2024-09-13)
  *	struct vrt_backend.backend_wait_timeout added
  *	struct vrt_backend.backend_wait_limit  added
@@ -737,6 +740,7 @@ typedef void vdi_release_f(VCL_BACKEND);
 typedef void vdi_destroy_f(VCL_BACKEND);
 typedef void vdi_panic_f(VCL_BACKEND, struct vsb *);
 typedef void vdi_list_f(VRT_CTX, VCL_BACKEND, struct vsb *, int, int);
+typedef void vdi_notify_f(VCL_BACKEND);
 
 struct vdi_methods {
 	unsigned			magic;
@@ -755,6 +759,9 @@ struct vdi_methods {
 	vdi_destroy_f			*destroy;
 	vdi_panic_f			*panic;
 	vdi_list_f			*list;
+	// when something changes outside the backend's control
+	// (for now, admin health)
+	vdi_notify_f			*notify;
 };
 
 struct director {
@@ -767,6 +774,7 @@ struct director {
 };
 
 VCL_BOOL VRT_Healthy(VRT_CTX, VCL_BACKEND, VCL_TIME *);
+VCL_VOID VRT_Notify(VCL_BACKEND);
 VCL_VOID VRT_SetChanged(VCL_BACKEND, VCL_TIME);
 VCL_BACKEND VRT_AddDirector(VRT_CTX, const struct vdi_methods *,
     void *, const char *, ...) v_printflike_(4, 5);