fellow_cache: Add a counter for object errors after the initial read

src/VSC_fellow.vsc

@@ -67,6 +67,18 @@
 	Number of times a disk object (vampireobject) was accessed and
 	a get operation was already in progress
 
+.. varnish_vsc:: c_mem_obj_fail
+	:type:	counter
+	:level:	info
+	:oneliner:	A memory object failed
+
+	Number of times a failed memory object is encountered. This is
+	most likely because some IO failed after the intial creation
+	of the in memory object. This could be a disk write error or a
+	read error of segments or segment lists.
+
+	Details are logged as ``SLT_Error`` to *vsl(7)*.
+
 .. varnish_vsc:: c_mem_obj_free
 	:type:	counter
 	:level:	info

src/fellow_storage.c

@@ -660,11 +660,14 @@ sfedsk_objslim(struct worker *wrk, struct objcore *dskoc)
 /* handle fellow_cache_res for iterators */
 static int
 stvfe_fcr_handle_iter(struct worker *wrk, struct objcore *oc,
-    const struct stevedore *stv, struct fellow_cache_res fcr)
+    const struct stevedore *stv, const struct stvfe *stvfe,
+    struct fellow_cache_res fcr)
 {
 	if (fcr.status == fcr_ok)
 		return (fcr.r.integer);
 
+	stvfe->stats->c_mem_obj_fail++;
+
 	VSLb(wrk->vsl, SLT_Error, "%s %s %s: %s",
 	    stv->name, stv->ident,
 	    fellow_cache_res_s[fcr.status],
@@ -830,7 +833,7 @@ sfemem_iterator(struct worker *wrk, struct objcore *oc,
 		VC4013_INIT(wrk, oc);
 		fcr = fellow_cache_obj_iter(stvfe->fc, fco, priv, func, final);
 		VC4013_FINI();
-		return (stvfe_fcr_handle_iter(wrk, oc, stv, fcr));
+		return (stvfe_fcr_handle_iter(wrk, oc, stv, stvfe, fcr));
 	}
 
 	INIT_OBJ(&fs, FELLOW_STREAM_MAGIC);
@@ -855,7 +858,7 @@ sfemem_iterator(struct worker *wrk, struct objcore *oc,
 
 	fcr = fellow_cache_obj_iter(stvfe->fc, fco,
 	    &fs, fellow_stream_f, final);
-	ret = stvfe_fcr_handle_iter(wrk, oc, stv, fcr);
+	ret = stvfe_fcr_handle_iter(wrk, oc, stv, stvfe, fcr);
 
   out:
 	HSH_DerefBoc(wrk, oc);
@@ -880,7 +883,7 @@ sfedsk_iterator(struct worker *wrk, struct objcore *dskoc,
 	fcr = fellow_cache_obj_iter(stvfe->fc, fcoc.fco, priv, func, final);
 	VC4013_FINI();
 	fcoc_fini(stvfe->fc, &fcoc);
-	return (stvfe_fcr_handle_iter(wrk, dskoc, stv, fcr));
+	return (stvfe_fcr_handle_iter(wrk, dskoc, stv, stvfe, fcr));
 }
 
 static inline struct fellow_busy *