add support for diskio name templates & udev tags

closes #1453
closes #1386
closes #1428

plugins/inputs/system/disk_linux.go

@@ -0,0 +1,66 @@
+package system
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+	"syscall"
+)
+
+type diskInfoCache struct {
+	stat   syscall.Stat_t
+	values map[string]string
+}
+
+var udevPath = "/run/udev/data"
+
+func (s *DiskIOStats) diskInfo(devName string) (map[string]string, error) {
+	fi, err := os.Stat("/dev/" + devName)
+	if err != nil {
+		return nil, err
+	}
+	stat, ok := fi.Sys().(*syscall.Stat_t)
+	if !ok {
+		return nil, nil
+	}
+
+	if s.infoCache == nil {
+		s.infoCache = map[string]diskInfoCache{}
+	}
+	ic, ok := s.infoCache[devName]
+	if ok {
+		return ic.values, nil
+	} else {
+		ic = diskInfoCache{
+			stat:   *stat,
+			values: map[string]string{},
+		}
+		s.infoCache[devName] = ic
+	}
+	di := ic.values
+
+	major := stat.Rdev >> 8 & 0xff
+	minor := stat.Rdev & 0xff
+
+	f, err := os.Open(fmt.Sprintf("%s/b%d:%d", udevPath, major, minor))
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	scnr := bufio.NewScanner(f)
+
+	for scnr.Scan() {
+		l := scnr.Text()
+		if len(l) < 4 || l[:2] != "E:" {
+			continue
+		}
+		kv := strings.SplitN(l[2:], "=", 2)
+		if len(kv) < 2 {
+			continue
+		}
+		di[kv[0]] = kv[1]
+	}
+
+	return di, nil
+}