Modify ShouldPass so that it checks the tags of a metric, if configured.

A plugin can have 'tagpass' and 'tagdrop' subsections:

[disk.tagpass]

And tagname = array lists of things to filter by:

fstype = [ "ext4", "xfs" ]
path = [ "/", /opt", "/home" ]

[disk.tagdrop]
path = [ "/" ]

config.go

@@ -43,6 +43,10 @@ type Config struct {
 func (c *Config) Plugins() map[string]*ast.Table {
 	return c.plugins
 }
+type TagFilter struct {
+	Name   string
+	Filter []string
+}
 
 // Outputs returns the configured outputs as a map of name -> output toml
 func (c *Config) Outputs() map[string]*ast.Table {
@@ -50,17 +54,21 @@ func (c *Config) Outputs() map[string]*ast.Table {
 }
 
 // ConfiguredPlugin containing a name, interval, and drop/pass prefix lists
+// Also lists the tags to filter
 type ConfiguredPlugin struct {
 	Name string
 
 	Drop []string
 	Pass []string
+	TagDrop []TagFilter
+
+	TagPass []TagFilter
 
 	Interval time.Duration
 }
 
 // ShouldPass returns true if the metric should pass, false if should drop
-func (cp *ConfiguredPlugin) ShouldPass(measurement string) bool {
+func (cp *ConfiguredPlugin) ShouldPass(measurement string, tags map[string]string) bool {
 	if cp.Pass != nil {
 		for _, pat := range cp.Pass {
 			if strings.HasPrefix(measurement, pat) {
@@ -81,16 +89,41 @@ func (cp *ConfiguredPlugin) ShouldPass(measurement string) bool {
 		return true
 	}
 
+	if cp.TagPass != nil {
+		for _, pat := range cp.TagPass {
+			if tagval, ok := tags[pat.Name]; ok {
+				for _, filter := range pat.Filter {
+					if filter == tagval {
 						return true
 					}
+				}
+			}
+		}
+		return false
+	}
+
+
+	if cp.TagDrop != nil {
+		for _, pat := range cp.TagDrop {
+			if tagval, ok := tags[pat.Name]; ok {
+				for _, filter := range pat.Filter {
+					if filter == tagval {
+						return false
+					}
+				}
+			}
+		}
+		return true
+	}
+
+	return nil
+}
 
 // ApplyOutput loads the toml config into the given interface
 func (c *Config) ApplyOutput(name string, v interface{}) error {
 	if c.outputs[name] != nil {
 		return toml.UnmarshalTable(c.outputs[name], v)
     }
-
-	return nil
 }
 
 // ApplyAgent loads the toml config into the given interface
@@ -147,9 +180,47 @@ func (c *Config) ApplyPlugin(name string, v interface{}) (*ConfiguredPlugin, err
 			}
 		}
 
+		if node, ok := tbl.Fields["tagpass"]; ok {
+			if subtbl, ok := node.(*ast.Table); ok {
+				for name, val := range subtbl.Fields {
+					if kv, ok := val.(*ast.KeyValue); ok {
+						tagfilter := &TagFilter{Name: name}
+						if ary, ok := kv.Value.(*ast.Array); ok {
+							for _, elem := range ary.Value {
+								if str, ok := elem.(*ast.String); ok {
+									tagfilter.Filter = append(tagfilter.Filter, str.Value)
+								}
+							}
+						}
+						cp.TagPass = append(cp.TagPass, *tagfilter)
+					}
+				}
+			}
+		}
+
+		if node, ok := tbl.Fields["tagdrop"]; ok {
+			if subtbl, ok := node.(*ast.Table); ok {
+				for name, val := range subtbl.Fields {
+					if kv, ok := val.(*ast.KeyValue); ok {
+						tagfilter := &TagFilter{Name: name}
+						if ary, ok := kv.Value.(*ast.Array); ok {
+							for _, elem := range ary.Value {
+								if str, ok := elem.(*ast.String); ok {
+									tagfilter.Filter = append(tagfilter.Filter, str.Value)
+								}
+							}
+						}
+						cp.TagDrop = append(cp.TagDrop, *tagfilter)
+					}
+				}
+			}
+		}
+
 		delete(tbl.Fields, "drop")
 		delete(tbl.Fields, "pass")
 		delete(tbl.Fields, "interval")
+		delete(tbl.Fields, "tagdrop")
+		delete(tbl.Fields, "tagpass")
 		return cp, toml.UnmarshalTable(tbl, v)
 	}
 
@@ -227,6 +298,20 @@ func LoadConfig(path string) (*Config, error) {
 	return c, nil
 }
 
+// ListTags returns a string of tags specified in the config,
+// line-protocol style
+func (c *Config) ListTags() string {
+	var tags []string
+
+	for k, v := range c.Tags {
+		tags = append(tags, fmt.Sprintf("%s=%s", k, v))
+	}
+
+	sort.Strings(tags)
+
+	return strings.Join(tags, " ")
+}
+
 type hasConfig interface {
 	BasicConfig() string
 }
@@ -281,6 +366,9 @@ database = "telegraf" # required.
 # Set the user agent for the POSTs (can be useful for log differentiation)
 # user_agent = "telegraf"
 
+# Tags can also be specified via a normal map, but only one form at a time:
+
+# [influxdb.tags]
 # tags = { "dc" = "us-east-1" }
 
 # Configuration for telegraf itself