cephfs: add MountWithRoot to implement the root arg to ceph_mount

The existing Mount() method did not provide a way to access the root
path argument to ceph_mount. This new function allows the caller to
specify an alternate root dir for the mount.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

cephfs/cephfs.go

@@ -91,6 +91,17 @@ func (mount *MountInfo) Mount() error {
 	return getError(ret)
 }
 
+// MountWithRoot mounts the file system using the path provided for the root of
+// the mount. This establishes a connection capable of I/O.
+//
+// Implements:
+//  int ceph_mount(struct ceph_mount_info *cmount, const char *root);
+func (mount *MountInfo) MountWithRoot(root string) error {
+	croot := C.CString(root)
+	defer C.free(unsafe.Pointer(croot))
+	return getError(C.ceph_mount(mount.mount, croot))
+}
+
 // Unmount the file system.
 //
 // Implements:

cephfs/cephfs_test.go

@@ -276,3 +276,55 @@ func TestMdsCommandError(t *testing.T) {
 	assert.NotEqual(t, "", string(info))
 	assert.Contains(t, string(info), "unparseable JSON")
 }
+
+func TestMountWithRoot(t *testing.T) {
+	bMount := fsConnect(t)
+	defer func() {
+		assert.NoError(t, bMount.Unmount())
+		assert.NoError(t, bMount.Release())
+	}()
+
+	dir1 := "/test-mount-with-root"
+	err := bMount.MakeDir(dir1, 0755)
+	assert.NoError(t, err)
+	defer bMount.RemoveDir(dir1)
+
+	sub1 := "/i.was.here"
+	dir2 := dir1 + sub1
+	err = bMount.MakeDir(dir2, 0755)
+	assert.NoError(t, err)
+	defer bMount.RemoveDir(dir2)
+
+	t.Run("withRoot", func(t *testing.T) {
+		mount, err := CreateMount()
+		require.NoError(t, err)
+		require.NotNil(t, mount)
+		defer func() {
+			assert.NoError(t, mount.Unmount())
+			assert.NoError(t, mount.Release())
+		}()
+
+		err = mount.ReadDefaultConfigFile()
+		require.NoError(t, err)
+
+		err = mount.MountWithRoot(dir1)
+		assert.NoError(t, err)
+
+		err = mount.ChangeDir(sub1)
+		assert.NoError(t, err)
+	})
+	t.Run("badRoot", func(t *testing.T) {
+		mount, err := CreateMount()
+		require.NoError(t, err)
+		require.NotNil(t, mount)
+		defer func() {
+			assert.NoError(t, mount.Release())
+		}()
+
+		err = mount.ReadDefaultConfigFile()
+		require.NoError(t, err)
+
+		err = mount.MountWithRoot("/i-yam-what-i-yam")
+		assert.Error(t, err)
+	})
+}