Add an event for directors going sick

Pondering solutions for varnishcache#4183 it became apparent that we need a way to notify
directors of changes to the admin_health without crossing the VDI/VBE layering.

Besides adding another director callback, one option is to add an event to the
existing event facility, which so far was only used for VCL-related events. We
now add VDI_EVENT_SICK as a director-specific event, which is cheap and also
helps us maintain clean layering.

bin/varnishd/cache/cache_backend.c

@@ -561,6 +561,11 @@ vbe_dir_event(const struct director *d, enum vcl_event_e ev)
 		VRT_VSC_Hide(bp->vsc_seg);
 	} else if (ev == VCL_EVENT_DISCARD) {
 		VRT_DelDirector(&bp->director);
+	} else if (ev == VDI_EVENT_SICK) {
+		const struct vdi_ahealth *ah = d->vdir->admin_health;
+
+		if (ah == VDI_AH_SICK || (ah == VDI_AH_AUTO && bp->sick))
+			VBE_connwait_signal_all(bp);
 	}
 }
 
@@ -661,7 +666,6 @@ vbe_healthy(VRT_CTX, VCL_BACKEND d, VCL_TIME *t)
 	return (!bp->sick);
 }
 
-
 /*--------------------------------------------------------------------
  */
 

include/vrt.h

@@ -48,7 +48,7 @@
 
 #define VRT_MAJOR_VERSION	20U
 
-#define VRT_MINOR_VERSION	0U
+#define VRT_MINOR_VERSION	1U
 
 /***********************************************************************
  * Major and minor VRT API versions.
@@ -57,6 +57,8 @@
  * Whenever something is deleted or changed in a way which is not
  * binary/load-time compatible, increment MAJOR version
  *
+ * 20.1 (2024-11-08)
+ *	VDI_EVENT_SICK added to enum vcl_event_e
  * 20.0 (2024-09-13)
  *	struct vrt_backend.backend_wait_timeout added
  *	struct vrt_backend.backend_wait_limit  added
@@ -493,14 +495,16 @@ struct vmod_data {
 };
 
 /***********************************************************************
- * VCL events sent to VMODs
+ * VCL events sent to VMODs and directors
  */
 
 enum vcl_event_e {
 	VCL_EVENT_LOAD,
 	VCL_EVENT_WARM,
 	VCL_EVENT_COLD,
 	VCL_EVENT_DISCARD,
+	// Only for directors
+	VDI_EVENT_SICK,
 };
 
 typedef int vmod_event_f(VRT_CTX, struct vmod_priv *, enum vcl_event_e);