Introduce VSC stat cache_hitmiss, to count hits on hit-for-miss.

bin/varnishd/cache/cache_hash.c

@@ -440,6 +440,7 @@ HSH_Lookup(struct req *req, struct objcore **ocp, struct objcore **bocp,
 				wrk->stats->cache_hitpass++;
 				oc = NULL;
 			} else if (oc->flags & OC_F_PASS) {
+				wrk->stats->cache_hitmiss++;
 				oc = NULL;
 				*bocp = hsh_insert_busyobj(wrk, oh);
 			} else {
@@ -462,7 +463,7 @@ HSH_Lookup(struct req *req, struct objcore **ocp, struct objcore **bocp,
 	}
 
 	if (exp_oc != NULL && exp_oc->flags & OC_F_PASS) {
-		wrk->stats->cache_hitpass++;
+		wrk->stats->cache_hitmiss++;
 		exp_oc = NULL;
 		busy_found = 0;
 	}

bin/varnishtest/tests/c00014.vtc

@@ -44,4 +44,5 @@ client c2 {
 client c1 -wait
 
 varnish v1 -expect cache_hitpass == 0
+varnish v1 -expect cache_hitmiss == 1
 varnish v1 -expect cache_miss == 2

bin/varnishtest/tests/c00081.vtc

@@ -47,3 +47,4 @@ client c1 {
 
 varnish v1 -expect MAIN.cache_hitpass == 1
 varnish v1 -expect MAIN.cache_miss == 2
+varnish v1 -expect MAIN.cache_hitmiss == 0

bin/varnishtest/tests/r00425.vtc

@@ -30,4 +30,5 @@ client c1 {
 } -run
 
 varnish v1 -expect cache_hitpass == 0
+varnish v1 -expect cache_hitmiss == 2
 varnish v1 -expect cache_miss == 3

include/tbl/vsc_f_main.h

@@ -99,6 +99,15 @@ VSC_FF(cache_hitpass,		uint64_t, 1, 'c', 'i', info,
 	" decision is being used."
 )
 
+VSC_FF(cache_hitmiss,		uint64_t, 1, 'c', 'i', info,
+    "Cache hits for miss.",
+	"Count of hits for miss."
+	" A cache hit for miss indicates that Varnish is going to"
+	" proceed as for a cache miss without request coalescing, and"
+	" this decision has been cached. This counts how many times the"
+	" cached decision is being used."
+)
+
 VSC_FF(cache_miss,		uint64_t, 1, 'c', 'i', info,
     "Cache misses",
 	"Count of misses."