Check Propagation properties of source mount point

Whether a shared/slave volume propagation will work or not also depends on
where source directory is mounted on and what are the propagation properties
of that mount point. For example, for shared volume mount to work, source
mount point should be shared. For slave volume mount to work, source mount
point should be either shared/slave.

This patch determines the mount point on which directory is mounted and
checks for desired minimum propagation properties of that mount point. It
errors out of configuration does not seem right.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

daemon/execdriver/native/create.go

@@ -293,6 +293,102 @@ func checkResetVolumePropagation(container *configs.Config) {
 	}
 }
 
+func getMountInfo(mountinfo []*mount.Info, dir string) *mount.Info {
+	for _, m := range mountinfo {
+		if m.Mountpoint == dir {
+			return m
+		}
+	}
+	return nil
+}
+
+// Get the source mount point of directory passed in as argument. Also return
+// optional fields.
+func getSourceMount(source string) (string, string, error) {
+	// Ensure any symlinks are resolved.
+	sourcePath, err := filepath.EvalSymlinks(source)
+	if err != nil {
+		return "", "", err
+	}
+
+	mountinfos, err := mount.GetMounts()
+	if err != nil {
+		return "", "", err
+	}
+
+	mountinfo := getMountInfo(mountinfos, sourcePath)
+	if mountinfo != nil {
+		return sourcePath, mountinfo.Optional, nil
+	}
+
+	path := sourcePath
+	for {
+		path = filepath.Dir(path)
+
+		mountinfo = getMountInfo(mountinfos, path)
+		if mountinfo != nil {
+			return path, mountinfo.Optional, nil
+		}
+
+		if path == "/" {
+			break
+		}
+	}
+
+	// If we are here, we did not find parent mount. Something is wrong.
+	return "", "", fmt.Errorf("Could not find source mount of %s", source)
+}
+
+// Ensure mount point on which path is mouted, is shared.
+func ensureShared(path string) error {
+	sharedMount := false
+
+	sourceMount, optionalOpts, err := getSourceMount(path)
+	if err != nil {
+		return err
+	}
+	// Make sure source mount point is shared.
+	optsSplit := strings.Split(optionalOpts, " ")
+	for _, opt := range optsSplit {
+		if strings.HasPrefix(opt, "shared:") {
+			sharedMount = true
+			break
+		}
+	}
+
+	if !sharedMount {
+		return fmt.Errorf("Path %s is mounted on %s but it is not a shared mount.", path, sourceMount)
+	}
+	return nil
+}
+
+// Ensure mount point on which path is mounted, is either shared or slave.
+func ensureSharedOrSlave(path string) error {
+	sharedMount := false
+	slaveMount := false
+
+	sourceMount, optionalOpts, err := getSourceMount(path)
+	if err != nil {
+		return err
+	}
+	// Make sure source mount point is shared.
+	optsSplit := strings.Split(optionalOpts, " ")
+	for _, opt := range optsSplit {
+		if strings.HasPrefix(opt, "shared:") {
+			sharedMount = true
+			break
+		} else if strings.HasPrefix(opt, "master:") {
+			slaveMount = true
+			break
+		}
+	}
+
+	if !sharedMount && !slaveMount {
+		return fmt.Errorf("Path %s is mounted on %s but it is not a shared or slave mount.", path, sourceMount)
+	}
+	return nil
+}
+
 func (d *Driver) setupMounts(container *configs.Config, c *execdriver.Command) error {
 	userMounts := make(map[string]struct{})
 	for _, m := range c.Mounts {
@@ -370,11 +466,17 @@ func (d *Driver) setupMounts(container *configs.Config, c *execdriver.Command) e
 
 		pFlag = mountPropagationMap[m.Propagation]
 		if pFlag == mount.SHARED || pFlag == mount.RSHARED {
+			if err := ensureShared(m.Source); err != nil {
+				return err
+			}
 			rootpg := container.RootPropagation
 			if rootpg != mount.SHARED && rootpg != mount.RSHARED {
 				execdriver.SetRootPropagation(container, mount.SHARED)
 			}
 		} else if pFlag == mount.SLAVE || pFlag == mount.RSLAVE {
+			if err := ensureSharedOrSlave(m.Source); err != nil {
+				return err
+			}
 			rootpg := container.RootPropagation
 			if rootpg != mount.SHARED && rootpg != mount.RSHARED && rootpg != mount.SLAVE && rootpg != mount.RSLAVE {
 				execdriver.SetRootPropagation(container, mount.RSLAVE)