api/services: define the container metadata service

Working from feedback on the existing implementation, we have now
introduced a central metadata object to represent the lifecycle and pin
the resources required to implement what people today know as
containers. This includes the runtime specification and the root
filesystem snapshots. We also allow arbitrary labeling of the container.
Such provisions will bring the containerd definition of container closer
to what is expected by users.

The objects that encompass today's ContainerService, centered around the
runtime, will be known as tasks. These tasks take on the existing
lifecycle behavior of containerd's containers, which means that they are
deleted when they exit. Largely, there are no other changes except for
naming.

The `Container` object will operate purely as a metadata object. No
runtime state will be held on `Container`. It only informs the execution
service on what is required for creating tasks and the resources in use
by that container. The resources referenced by that container will be
deleted when the container is deleted, if not in use. In this sense,
users can create, list, label and delete containers in a similar way as
they do with docker today, without the complexity of runtime locks that
plagues current implementations.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

api/types/task/task.proto

@@ -0,0 +1,62 @@
+syntax = "proto3";
+
+package containerd.v1.types;
+
+import "gogoproto/gogo.proto";
+import "google/protobuf/any.proto";
+import "google/protobuf/timestamp.proto";
+
+enum Status {
+	option (gogoproto.goproto_enum_prefix) = false;
+	option (gogoproto.enum_customname) = "Status";
+
+	UNKNOWN = 0 [(gogoproto.enumvalue_customname) = "StatusUnknown"];
+	CREATED = 1 [(gogoproto.enumvalue_customname) = "StatusCreated"];
+	RUNNING = 2 [(gogoproto.enumvalue_customname) = "StatusRunning"];
+	STOPPED = 3 [(gogoproto.enumvalue_customname) = "StatusStopped"];
+	PAUSED = 4 [(gogoproto.enumvalue_customname) = "StatusPaused"];
+}
+
+message Task {
+	string id = 1; // TODO(stevvooe): For now, this is just the container id.
+	string container_id = 2;
+	uint32 pid = 3;
+	Status status = 4;
+	google.protobuf.Any spec = 5;
+}
+
+message Process {
+	uint32 pid = 1;
+	repeated string args = 2;
+	repeated string env = 3;
+	User user = 4;
+	string cwd = 5;
+	bool terminal = 6;
+	uint32 exit_status = 7;
+	Status status = 8;
+	google.protobuf.Any runtime_data = 9;
+}
+
+message User {
+	uint32 uid = 1;
+	uint32 gid = 2;
+	repeated uint32 additional_gids = 3;
+}
+
+message Event {
+	string id = 1;
+
+	enum EventType {
+		EXIT = 0;
+		OOM = 1;
+		CREATE = 2;
+		START = 3;
+		EXEC_ADDED = 4;
+		PAUSED = 5;
+	}
+
+	EventType type = 2;
+	uint32 pid = 3;
+	uint32 exit_status = 4;
+	google.protobuf.Timestamp exited_at = 5 [(gogoproto.stdtime) = true, (gogoproto.nullable) = false];
+}