From 3b8a3a6aab881c9ff7ea561f9b2495d6ef3aa19a Mon Sep 17 00:00:00 2001
From: Michael Stapelberg <michael@stapelberg.de>
Date: Sat, 6 Dec 2014 23:10:57 +0100
Subject: [PATCH] export disk read/write stats

---
 varz/varz.go | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/varz/varz.go b/varz/varz.go
index 5eb6db1..081cb0e 100644
--- a/varz/varz.go
+++ b/varz/varz.go
@@ -2,11 +2,14 @@
 package varz
 
 import (
+	"bufio"
 	"flag"
 	"fmt"
 	"log"
 	"net/http"
+	"os"
 	"runtime"
+	"strings"
 	"sync"
 	"syscall"
 	"time"
@@ -21,6 +24,10 @@ var (
 	started = time.Now()
 )
 
+const (
+	bytesPerSector = 512
+)
+
 // A counter which is safe to use from multiple goroutines.
 type counter struct {
 	lock  sync.Mutex
@@ -55,6 +62,36 @@ func Varz(w http.ResponseWriter, r *http.Request) {
 			fmt.Fprintf(w, "available-bytes %d\n", stat.Bavail*uint64(stat.Bsize))
 		}
 	}
+
+	diskstats, err := os.Open("/proc/diskstats")
+	if err != nil {
+		return
+	}
+	defer diskstats.Close()
+
+	scanner := bufio.NewScanner(diskstats)
+	for scanner.Scan() {
+		// From http://sources.debian.net/src/linux/3.16.7-2/block/genhd.c/?hl=1141#L1141
+		// seq_printf(seqf, "%4d %7d %s %lu %lu %lu %u %lu %lu %lu %u %u %u %u\n",
+		var major, minor uint64
+		var device string
+		var reads, mergedreads, readsectors, readms uint64
+		var writes, mergedwrites, writtensectors, writems uint64
+		var inflight, ioticks, timeinqueue uint64
+		fmt.Sscanf(scanner.Text(), "%4d %7d %s %d %d %d %d %d %d %d %d %d %d %d",
+			&major, &minor, &device,
+			&reads, &mergedreads, &readsectors, &readms,
+			&writes, &mergedwrites, &writtensectors, &writems,
+			&inflight, &ioticks, &timeinqueue)
+		// Matches sda, xvda, …
+		if !strings.HasSuffix(device, "da") {
+			continue
+		}
+		fmt.Fprintf(w, "dev-reads.%s %d\n", device, reads)
+		fmt.Fprintf(w, "dev-bytes-read.%s %d\n", device, readsectors*bytesPerSector)
+		fmt.Fprintf(w, "dev-writes.%s %d\n", device, writes)
+		fmt.Fprintf(w, "dev-bytes-written.%s %d\n", device, writtensectors*bytesPerSector)
+	}
 }
 
 func Increment(key string) {
-- 
2.11.4.GIT