Ignore rootfs, use blkid to find partition type if sfdisk doesn't rep…

…ort.

Should fix CentOS 7, but untested.

Fixes #6

fs.go

@@ -113,6 +113,10 @@ func statFS(mnt string) (fs fsStat, err error) {
 		if len(f) < 3 {
 			continue
 		}
+		if f[0] == "rootfs" {
+			// See https://github.com/google/embiggen-disk/issues/6
+			continue
+		}
 		if f[1] == mnt {
 			fs.mnt = mnt
 			fs.dev = f[0]

lvm.go

@@ -19,6 +19,7 @@ package main
 import (
 	"bufio"
 	"bytes"
+	"errors"
 	"fmt"
 	"os/exec"
 	"strconv"
@@ -41,10 +42,7 @@ func (r lvResizer) state() (s lvState, err error) {
 	//   /dev/debvg/root:debvg:3:1:-1:1:8434778112:1029636:-1:0:-1:254:0
 	outb, err := exec.Command("lvdisplay", "-c", s.dev).Output()
 	if err != nil {
-		if ee, ok := err.(*exec.ExitError); ok && len(ee.Stderr) > 0 {
-			err = fmt.Errorf("%v; stderr: %s", err, ee.Stderr)
-		}
-		return s, fmt.Errorf("running lvdisplay -c %s: %v", s.dev, err)
+		return s, fmt.Errorf("running lvdisplay -c %s: %v", s.dev, execErrDetail(err))
 	}
 	f := strings.Split(strings.TrimSpace(string(outb)), ":")
 	if len(f) < 13 {
@@ -66,10 +64,7 @@ func (r lvResizer) DepResizer() (Resizer, error) {
 
 	out, err := exec.Command("pvdisplay", "-c").Output()
 	if err != nil {
-		if ee, ok := err.(*exec.ExitError); ok && len(ee.Stderr) > 0 {
-			err = fmt.Errorf("%v; stderr: %s", err, ee.Stderr)
-		}
-		return nil, fmt.Errorf("running pvdisplay -c: %v", err)
+		return nil, fmt.Errorf("running pvdisplay -c: %v", execErrDetail(err))
 	}
 	bs := bufio.NewScanner(bytes.NewReader(out))
 	for bs.Scan() {
@@ -124,8 +119,7 @@ func (r pvResizer) State() (string, error) {
 	dev := string(r)
 	out, err := exec.Command("pvdisplay", "-c", dev).Output()
 	if err != nil {
-		// TODO: factor out ExitError.Stderr handling above & use here.
-		return "", err
+		return "", errors.New(execErrDetail(err))
 	}
 	f := strings.Split(strings.TrimSpace(string(out)), ":")
 	if len(f) < 3 {

part.go

@@ -77,6 +77,23 @@ func (p partitionResizer) Resize() error {
 	case "dos":
 	case "gpt":
 		isGPT = true
+	case "":
+		// Old version of sfdisk? See https://github.com/google/embiggen-disk/issues/6
+		// Use blkid to figure out what it is.
+		// But only trust the value "dos", because if it's gpt and sfdisk
+		// is old and doesn't support gpt, we don't want to use that old sfdisk
+		// to manipulate the gpt tables.
+		out, err := exec.Command("blkid", "-o", "export", diskDev).Output()
+		if err != nil {
+			return fmt.Errorf("error running blkid: %v", execErrDetail(err))
+		}
+		m := regexp.MustCompile(`(?m)^PTTYPE=(.+)\n`).FindSubmatch(out)
+		if m == nil {
+			return fmt.Errorf("`blkid -o export %s` lacked PTTYPE line, got: %s", diskDev, out)
+		}
+		if got := string(m[1]); got != "dos" {
+			return fmt.Errorf("Old sfdisk and `blkid -o export %s` reports unexpected PTTYPE=%s", got)
+		}
 	default:
 		// It might work, but fail as a precaution. Untested.
 		return fmt.Errorf("unsupported partition table type %q on %s", t, diskDev)

util.go

@@ -0,0 +1,29 @@
+/*
+Copyright 2018 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package main
+
+import (
+	"fmt"
+	"os/exec"
+)
+
+func execErrDetail(err error) string {
+	if ee, ok := err.(*exec.ExitError); ok && len(ee.Stderr) > 0 {
+		return fmt.Sprintf("%v; stderr: %s", err, ee.Stderr)
+	}
+	return err.Error()
+}