Add rootfs service

Add rootfs service to allow creation of rootfs from layer array

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

api/services/rootfs/rootfs.proto

@@ -0,0 +1,38 @@
+syntax = "proto3";
+
+package containerd.v1;
+
+import "gogoproto/gogo.proto";
+import "google/protobuf/empty.proto";
+import "github.com/docker/containerd/api/types/mount/mount.proto";
+import "github.com/docker/containerd/api/types/descriptor/descriptor.proto";
+
+service RootFS {
+	rpc Prepare(PrepareRequest) returns (PrepareResponse);
+
+	// TODO: Add method for initializing and retrieving mounts
+	//rpc InitMounts(InitRequest) returns (MountResponse);
+	//rpc Mounts(MountRequest) returns (MountResponse);
+}
+
+message PrepareRequest {
+	repeated containerd.v1.types.Descriptor layers = 1;
+}
+
+message PrepareResponse {
+	string chainid = 1 [(gogoproto.customtype) = "github.com/opencontainers/go-digest.Digest", (gogoproto.nullable) = false, (gogoproto.customname) = "ChainID"];
+}
+
+//message InitRequest {
+//	string name = 1;
+//	string chainID = 2;
+//	bool Readonly = 3;
+//}
+//
+//message MountRequest {
+//	string name = 1;
+//}
+//
+//message MountResponse {
+//	repeated containerd.v1.types.Mount mounts = 1;
+//}