Add per-disk IO performance monitoring

disks_test.go

@@ -2,6 +2,8 @@ package main
 
 import (
 	"encoding/json"
+	"os"
+	"path/filepath"
 	"testing"
 )
 
@@ -17,6 +19,22 @@ func TestIsPhysicalDiskName(t *testing.T) {
 	}
 }
 
+func TestReadDiskIOStats(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "diskstats")
+	data := "   8       0 sda 100 2 300 40 50 3 700 80 4 90 120 0 0 0 0 0 0\n   7       0 loop0 999 0 999 0 999 0 999 0 0 0 0\n"
+	if err := os.WriteFile(path, []byte(data), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	stats := readDiskIOStats(path)
+	disk, ok := stats["sda"]
+	if !ok || disk.reads != 100 || disk.readSectors != 300 || disk.writes != 50 || disk.writeSectors != 700 || disk.inFlight != 4 || disk.ioMS != 90 || disk.weightedMS != 120 {
+		t.Fatalf("unexpected stats: %+v", disk)
+	}
+	if _, exists := stats["loop0"]; exists {
+		t.Fatal("virtual device must be ignored")
+	}
+}
+
 func TestSumFilesystemUsage(t *testing.T) {
 	device := lsblkDevice{Children: []lsblkDevice{
 		{FSUsed: json.RawMessage(`100`), FSAvail: json.RawMessage(`300`)},