cephfs admin: add a SubVolumeGroupPath function

The SubVolumeGroupPath function maps the subvolumegroup to a path from
the root of the cephfs, and works like `ceph fs subvolumegroup getpath
...`.

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

cephfs/admin/subvolumegroup.go

@@ -77,3 +77,18 @@ func (fsa *FSAdmin) RemoveSubVolumeGroup(volume, name string) error {
 	})
 	return checkEmptyResponseExpected(r, s, err)
 }
+
+// SubVolumeGroupPath returns the path to the subvolume from the root of the
+// file system.
+//
+// Similar To:
+//  ceph fs subvolumegroup getpath <volume> <group_name>
+func (fsa *FSAdmin) SubVolumeGroupPath(volume, name string) (string, error) {
+	m := map[string]string{
+		"prefix":     "fs subvolumegroup getpath",
+		"vol_name":   volume,
+		"group_name": name,
+		// ceph doesn't respond in json for this cmd (even if you ask)
+	}
+	return extractPathResponse(fsa.marshalMgrCommand(m))
+}

cephfs/admin/subvolumegroup_test.go

@@ -87,3 +87,26 @@ func TestRemoveSubVolumeGroup(t *testing.T) {
 	nowCount := len(lsvg)
 	assert.Equal(t, beforeCount, nowCount)
 }
+
+func TestSubVolumeGroupPath(t *testing.T) {
+	fsa := getFSAdmin(t)
+	volume := "cephfs"
+	group := "grewp"
+
+	err := fsa.CreateSubVolumeGroup(volume, group, nil)
+	assert.NoError(t, err)
+	defer func() {
+		err := fsa.RemoveSubVolumeGroup(volume, group)
+		assert.NoError(t, err)
+	}()
+
+	path, err := fsa.SubVolumeGroupPath(volume, group)
+	assert.NoError(t, err)
+	assert.Contains(t, path, "/volumes/"+group)
+	assert.NotContains(t, path, "\n")
+
+	// invalid group name
+	path, err = fsa.SubVolumeGroupPath(volume, "oops")
+	assert.Error(t, err)
+	assert.Equal(t, "", path)
+}