Implement telegraf collecting stats on itself

closes #1348

internal/buffer/buffer.go

@@ -4,15 +4,17 @@ import (
 	"sync"
 
 	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/selfstat"
+)
+
+var (
+	MetricsWritten = selfstat.Register("agent", "metrics_written", map[string]string{})
+	MetricsDropped = selfstat.Register("agent", "metrics_dropped", map[string]string{})
 )
 
 // Buffer is an object for storing metrics in a circular buffer.
 type Buffer struct {
 	buf chan telegraf.Metric
-	// total dropped metrics
-	drops int
-	// total metrics added
-	total int
 
 	mu sync.Mutex
 }
@@ -36,25 +38,14 @@ func (b *Buffer) Len() int {
 	return len(b.buf)
 }
 
-// Drops returns the total number of dropped metrics that have occured in this
-// buffer since instantiation.
-func (b *Buffer) Drops() int {
-	return b.drops
-}
-
-// Total returns the total number of metrics that have been added to this buffer.
-func (b *Buffer) Total() int {
-	return b.total
-}
-
 // Add adds metrics to the buffer.
 func (b *Buffer) Add(metrics ...telegraf.Metric) {
 	for i, _ := range metrics {
-		b.total++
+		MetricsWritten.Incr(1)
 		select {
 		case b.buf <- metrics[i]:
 		default:
-			b.drops++
+			MetricsDropped.Incr(1)
 			<-b.buf
 			b.buf <- metrics[i]
 		}