[#1818] writecache: Increase error counter on background errors

Signed-off-by: Evgenii Stratonikov <evgeniy@morphbits.ru>

pkg/local_object_storage/writecache/options.go

@@ -52,6 +52,8 @@ type options struct {
 	maxBatchDelay time.Duration
 	// noSync is true iff FSTree allows unsynchronized writes.
 	noSync bool
+	// reportError is the function called when encountering disk errors in background workers.
+	reportError func(string, error)
 }
 
 // WithLogger sets logger.
@@ -142,3 +144,10 @@ func WithNoSync(noSync bool) Option {
 		o.noSync = noSync
 	}
 }
+
+// WithReportErrorFunc sets error reporting function.
+func WithReportErrorFunc(f func(string, error)) Option {
+	return func(o *options) {
+		o.reportError = f
+	}
+}