[#1608] object: Add IO tag adjustment layer

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

internal/qos/tags.go

@@ -0,0 +1,39 @@
+package qos
+
+import "fmt"
+
+type IOTag string
+
+const (
+	IOTagClient     IOTag = "client"
+	IOTagInternal   IOTag = "internal"
+	IOTagBackground IOTag = "background"
+	IOTagWritecache IOTag = "writecache"
+	IOTagPolicer    IOTag = "policer"
+	IOTagCritical   IOTag = "critical"
+
+	ioTagUnknown IOTag = ""
+)
+
+func FromRawString(s string) (IOTag, error) {
+	switch s {
+	case string(IOTagCritical):
+		return IOTagCritical, nil
+	case string(IOTagClient):
+		return IOTagClient, nil
+	case string(IOTagInternal):
+		return IOTagInternal, nil
+	case string(IOTagBackground):
+		return IOTagBackground, nil
+	case string(IOTagWritecache):
+		return IOTagWritecache, nil
+	case string(IOTagPolicer):
+		return IOTagPolicer, nil
+	default:
+		return ioTagUnknown, fmt.Errorf("unknown tag %s", s)
+	}
+}
+
+func (t IOTag) String() string {
+	return string(t)
+}