Add Event controls

Add Event controls and implement "stream" commands.

PiperOrigin-RevId: 390691702

2 files changed, 67 insertions, 0 deletions

diff --git a/pkg/sentry/control/BUILD b/pkg/sentry/control/BUILD
index fa3fe47c1..a4934a565 100644
--- a/pkg/sentry/control/BUILD
+++ b/pkg/sentry/control/BUILD
@@ -6,6 +6,7 @@ go_library(
     name = "control",
     srcs = [
         "control.go",
+        "events.go",
         "fs.go",
         "lifecycle.go",
         "logging.go",
@@ -20,6 +21,7 @@ go_library(
     deps = [
         "//pkg/abi/linux",
         "//pkg/context",
+        "//pkg/eventchannel",
         "//pkg/fd",
         "//pkg/log",
         "//pkg/sentry/fdimport",
diff --git a/pkg/sentry/control/events.go b/pkg/sentry/control/events.go
new file mode 100644
index 000000000..92e437ae7
--- /dev/null
+++ b/pkg/sentry/control/events.go
@@ -0,0 +1,65 @@
+// Copyright 2021 The gVisor 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 control
+
+import (
+	"errors"
+	"fmt"
+
+	"gvisor.dev/gvisor/pkg/eventchannel"
+	"gvisor.dev/gvisor/pkg/urpc"
+)
+
+// EventsOpts are the arguments for eventchannel-related commands.
+type EventsOpts struct {
+	urpc.FilePayload
+}
+
+// Events is the control server state for eventchannel-related commands.
+type Events struct {
+	emitter eventchannel.Emitter
+}
+
+// AttachDebugEmitter receives a connected unix domain socket FD from the client
+// and establishes it as a new emitter for the sentry eventchannel. Any existing
+// emitters are replaced on a subsequent attach.
+func (e *Events) AttachDebugEmitter(o *EventsOpts, _ *struct{}) error {
+	if len(o.FilePayload.Files) < 1 {
+		return errors.New("no output writer provided")
+	}
+
+	sock, err := o.ReleaseFD(0)
+	if err != nil {
+		return err
+	}
+	sockFD := sock.Release()
+
+	// SocketEmitter takes ownership of sockFD.
+	emitter, err := eventchannel.SocketEmitter(sockFD)
+	if err != nil {
+		return fmt.Errorf("failed to create SocketEmitter for FD %d: %v", sockFD, err)
+	}
+
+	// If there is already a debug emitter, close the old one.
+	if e.emitter != nil {
+		e.emitter.Close()
+	}
+
+	e.emitter = eventchannel.DebugEmitterFrom(emitter)
+
+	// Register the new stream destination.
+	eventchannel.AddEmitter(e.emitter)
+	return nil
+}