Add sysfs spec

_samples/blkinfo.go

@@ -2,13 +2,28 @@ package main
 
 import (
 	"fmt"
+	"os"
+	"strings"
 
 	blkinfo "github.com/blp1526/go-blkinfo"
 	"gopkg.in/yaml.v2"
 )
 
 func main() {
-	bi, err := blkinfo.New("/dev/sda1")
+	args := os.Args
+	if len(args) != 2 {
+		desc := []string{
+			"USAGE:",
+			"  go run _samples/blkinfo.go [device]",
+			"EXAMPLE:",
+			"  go run _samples/blkinfo.go /dev/sda1",
+		}
+		fmt.Println(strings.Join(desc, "\n"))
+		os.Exit(0)
+	}
+
+	path := args[1]
+	bi, err := blkinfo.New(path)
 	if err != nil {
 		panic(err)
 	}

blkinfo.go

@@ -150,6 +150,9 @@ func mountpoint(mtab string, realPath string) (string, error) {
 }
 
 func majorMinor(realPath string) (string, error) {
+	// https://github.com/torvalds/linux/blob/d13937116f1e82bf508a6325111b322c30c85eb9/fs/block_dev.c#L1229-L1242
+	// /sys/block/dm-0/slaves/sda --> /sys/block/sda
+	// /sys/block/sda/holders/dm-0 --> /sys/block/dm-0
 	baseName := filepath.Base(realPath)
 	sysBlockPath := filepath.Join("/", "sys", "block")
 	fileInfos, err := ioutil.ReadDir(sysBlockPath)