native: support for FreeBSD

Signed-off-by: Samuel Karp <me@samuelkarp.com>

snapshots/native/native.go

@@ -328,11 +328,8 @@ func (o *snapshotter) mounts(s storage.Snapshot) []mount.Mount {
 	return []mount.Mount{
 		{
 			Source:  source,
-			Type:   "bind",
-			Options: []string{
-				roFlag,
-				"rbind",
-			},
+			Type:    mountType,
+			Options: append(defaultMountOptions, roFlag),
 		},
 	}
 }

snapshots/native/native_default.go

@@ -0,0 +1,23 @@
+// +build !freebsd
+
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package native
+
+const mountType = "bind"
+
+var defaultMountOptions = []string{"rbind"}

snapshots/native/native_freebsd.go

@@ -0,0 +1,23 @@
+// +build freebsd
+
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package native
+
+const mountType = "nullfs"
+
+var defaultMountOptions = []string{}