getParentMount: benefit from GetMounts filter

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/rootfs_linux.go

@@ -661,46 +661,26 @@ func mknodDevice(dest string, node *configs.Device) error {
 	return unix.Chown(dest, int(node.Uid), int(node.Gid))
 }
 
-func getMountInfo(mountinfo []*mountinfo.Info, dir string) *mountinfo.Info {
-	for _, m := range mountinfo {
-		if m.Mountpoint == dir {
-			return m
-		}
-	}
-	return nil
-}
-
 // Get the parent mount point of directory passed in as argument. Also return
 // optional fields.
 func getParentMount(rootfs string) (string, string, error) {
-	var path string
-
-	mountinfos, err := mountinfo.GetMounts(nil)
+	mi, err := mountinfo.GetMounts(mountinfo.ParentsFilter(rootfs))
 	if err != nil {
 		return "", "", err
 	}
-
-	mountinfo := getMountInfo(mountinfos, rootfs)
-	if mountinfo != nil {
-		return rootfs, mountinfo.Optional, nil
+	if len(mi) < 1 {
+		return "", "", fmt.Errorf("could not find parent mount of %s", rootfs)
 	}
 
-	path = rootfs
-	for {
-		path = filepath.Dir(path)
-
-		mountinfo = getMountInfo(mountinfos, path)
-		if mountinfo != nil {
-			return path, mountinfo.Optional, nil
-		}
-
-		if path == "/" {
-			break
+	// find the longest mount point
+	var idx, maxlen int
+	for i := range mi {
+		if len(mi[i].Mountpoint) > maxlen {
+			maxlen = len(mi[i].Mountpoint)
+			idx = i
 		}
 	}
-
-	// If we are here, we did not find parent mount. Something is wrong.
-	return "", "", fmt.Errorf("Could not find parent mount of %s", rootfs)
+	return mi[idx].Mountpoint, mi[idx].Optional, nil
 }
 
 // Make parent mount private if it was shared