[#373] fstree: Add metrics

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/local_object_storage/blobstor/fstree/metrics.go

@@ -0,0 +1,26 @@
+package fstree
+
+import "time"
+
+type Metrics interface {
+	SetMode(readOnly bool)
+	Close()
+
+	Iterate(d time.Duration, success bool)
+	Delete(d time.Duration, success bool)
+	Exists(d time.Duration, success bool)
+	Put(d time.Duration, size int, success bool)
+	Get(d time.Duration, size int, success bool)
+	GetRange(d time.Duration, size int, success bool)
+}
+
+type noopMetrics struct{}
+
+func (m *noopMetrics) SetMode(bool)                      {}
+func (m *noopMetrics) Close()                            {}
+func (m *noopMetrics) Iterate(time.Duration, bool)       {}
+func (m *noopMetrics) Delete(time.Duration, bool)        {}
+func (m *noopMetrics) Exists(time.Duration, bool)        {}
+func (m *noopMetrics) Put(time.Duration, int, bool)      {}
+func (m *noopMetrics) Get(time.Duration, int, bool)      {}
+func (m *noopMetrics) GetRange(time.Duration, int, bool) {}