libbrillo: Add MountNamespaceInterface and UnownedMountNamespace

Add the interface class MountNamespaceInterface and the
UnownedMountNamespace class which only has one method to return the
namespace path.

Only one process should have the ability to create MountNamespace at a
given path. However more than one processes need to enter this namespace.
Thus the path of the namespace is needed by multiple independent
packages. The interface class is created for this need.

BUG=chromium:1052197
TEST=FEATURES=test emerge-betty libbrillo

Change-Id: I9892da25c5ff9614bc3574e9f7e589fa059f81c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2160141
Tested-by: Betul Soysal <betuls@google.com>
Commit-Queue: Betul Soysal <betuls@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Cr-Mirrored-From: https://chromium.googlesource.com/chromiumos/platform2
Cr-Mirrored-Commit: f8c0d1f43c844ac26f655d3724780c1022fbb4be

1 files changed, 30 insertions, 3 deletions

diff --git a/brillo/namespaces/mount_namespace.h b/brillo/namespaces/mount_namespace.h
index 76ed07b..bfadff0 100644
--- a/brillo/namespaces/mount_namespace.h
+++ b/brillo/namespaces/mount_namespace.h
@@ -13,7 +13,34 @@
 
 namespace brillo {
 
-class BRILLO_EXPORT MountNamespace {
+class BRILLO_EXPORT MountNamespaceInterface {
+  // An interface declaring the basic functionality of a mount namespace bound
+  // to a specific path. This basic functionality consists of reporting the
+  // namespace path.
+ public:
+  virtual ~MountNamespaceInterface() = default;
+
+  virtual const base::FilePath& path() const = 0;
+};
+
+class BRILLO_EXPORT UnownedMountNamespace : public MountNamespaceInterface {
+  // A class to store and retrieve the path of a persistent namespace. This
+  // class doesn't create nor destroy the namespace.
+ public:
+  explicit UnownedMountNamespace(const base::FilePath& ns_path)
+      : ns_path_(ns_path) {}
+
+  ~UnownedMountNamespace() override;
+
+  const base::FilePath& path() const override { return ns_path_; }
+
+ private:
+  base::FilePath ns_path_;
+
+  DISALLOW_COPY_AND_ASSIGN(UnownedMountNamespace);
+};
+
+class BRILLO_EXPORT MountNamespace : public MountNamespaceInterface {
   // A class to create a persistent mount namespace bound to a specific path.
   // A new mount namespace is unshared from the mount namespace of the calling
   // process when Create() is called; the namespace of the calling process
@@ -24,11 +51,11 @@ class BRILLO_EXPORT MountNamespace {
   // destroyed when the object goes out of scope.
  public:
   MountNamespace(const base::FilePath& ns_path, Platform* platform);
-  ~MountNamespace();
+  ~MountNamespace() override;
 
   bool Create();
   bool Destroy();
-  const base::FilePath& path() const { return ns_path_; }
+  const base::FilePath& path() const override { return ns_path_; }
 
  private:
   base::FilePath ns_path_;