Filesystem: Re-implemented Umount() and IsMounted() to work around AUFS

issues.

Umount() will now attempt to remove the mntpoint after umounting.
It will keep retrying for some time until the mntpoint is deleted.
Upstream-commit: 174f25909c525015cb84f1b82376091a1ac9c118
Component: engine

components/engine/filesystem.go

@@ -7,6 +7,7 @@ import (
 	"path/filepath"
 	"strings"
 	"syscall"
+	"time"
 )
 
 type Filesystem struct {
@@ -38,33 +39,57 @@ func (fs *Filesystem) Mount() error {
 		roBranches += fmt.Sprintf("%v=ro:", layer)
 	}
 	branches := fmt.Sprintf("br:%v:%v", rwBranch, roBranches)
-	return syscall.Mount("none", fs.RootFS, "aufs", 0, branches)
+	if err := syscall.Mount("none", fs.RootFS, "aufs", 0, branches); err != nil {
+		return err
+	}
+	if !fs.IsMounted() {
+		return errors.New("Mount failed")
+	}
+	return nil
 }
 
 func (fs *Filesystem) Umount() error {
 	if !fs.IsMounted() {
 		return errors.New("Umount: Filesystem not mounted")
 	}
-	return syscall.Unmount(fs.RootFS, 0)
+	if err := syscall.Unmount(fs.RootFS, 0); err != nil {
+		return err
+	}
+	if fs.IsMounted() {
+		return fmt.Errorf("Umount: Filesystem still mounted after calling umount(%v)", fs.RootFS)
+	}
+	for retries := 0; retries < 1000; retries++ {
+		err := os.Remove(fs.RootFS)
+		if err == nil {
+			// rm mntpoint succeeded
+			return nil
+		}
+		if os.IsNotExist(err) {
+			// mntpoint doesn't exist anymore. Success.
+			return nil
+		}
+		// fmt.Printf("(%v) Remove %v returned: %v\n", retries, fs.RootFS, err)
+		time.Sleep(10 * time.Millisecond)
+	}
+	return fmt.Errorf("Umount: Failed to umount %v", fs.RootFS)
 }
 
 func (fs *Filesystem) IsMounted() bool {
-	f, err := os.Open(fs.RootFS)
+	mntpoint, err := os.Stat(fs.RootFS)
 	if err != nil {
 		if os.IsNotExist(err) {
 			return false
 		}
 		panic(err)
 	}
-	list, err := f.Readdirnames(1)
-	f.Close()
+	parent, err := os.Stat(filepath.Join(fs.RootFS, ".."))
 	if err != nil {
-		return false
+		panic(err)
 	}
-	if len(list) > 0 {
-		return true
-	}
-	return false
+
+	mntpointSt := mntpoint.Sys().(*syscall.Stat_t)
+	parentSt := parent.Sys().(*syscall.Stat_t)
+	return mntpointSt.Dev != parentSt.Dev
 }
 
 type ChangeType int