3 files changed, 214 insertions, 0 deletions
diff --git a/pkg/sentry/platform/interrupt/BUILD b/pkg/sentry/platform/interrupt/BUILD
new file mode 100644
index 000000000..33dde2a31
--- /dev/null
+++ b/pkg/sentry/platform/interrupt/BUILD
@@ -0,0 +1,19 @@
+package(licenses = ["notice"])  # Apache 2.0
+
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
+
+go_library(
+    name = "interrupt",
+    srcs = [
+        "interrupt.go",
+    ],
+    importpath = "gvisor.googlesource.com/gvisor/pkg/sentry/platform/interrupt",
+    visibility = ["//pkg/sentry:internal"],
+)
+
+go_test(
+    name = "interrupt_test",
+    size = "small",
+    srcs = ["interrupt_test.go"],
+    embed = [":interrupt"],
+)
diff --git a/pkg/sentry/platform/interrupt/interrupt.go b/pkg/sentry/platform/interrupt/interrupt.go
new file mode 100644
index 000000000..ca4f42087
--- /dev/null
+++ b/pkg/sentry/platform/interrupt/interrupt.go
@@ -0,0 +1,96 @@
+// Copyright 2018 Google Inc.
+//
+// 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 interrupt provides an interrupt helper.
+package interrupt
+
+import (
+	"fmt"
+	"sync"
+)
+
+// Receiver receives interrupt notifications from a Forwarder.
+type Receiver interface {
+	// NotifyInterrupt is called when the Receiver receives an interrupt.
+	NotifyInterrupt()
+}
+
+// Forwarder is a helper for delivering delayed signal interruptions.
+//
+// This helps platform implementations with Interrupt semantics.
+type Forwarder struct {
+	// mu protects the below.
+	mu sync.Mutex
+
+	// dst is the function to be called when NotifyInterrupt() is called. If
+	// dst is nil, pending will be set instead, causing the next call to
+	// Enable() to return false.
+	dst     Receiver
+	pending bool
+}
+
+// Enable attempts to enable interrupt forwarding to r. If f has already
+// received an interrupt, Enable does nothing and returns false. Otherwise,
+// future calls to f.NotifyInterrupt() cause r.NotifyInterrupt() to be called,
+// and Enable returns true.
+//
+// Usage:
+//
+// if !f.Enable(r) {
+//     // There was an interrupt.
+//     return
+// }
+// defer f.Disable()
+//
+// Preconditions: r must not be nil. f must not already be forwarding
+// interrupts to a Receiver.
+func (f *Forwarder) Enable(r Receiver) bool {
+	if r == nil {
+		panic("nil Receiver")
+	}
+	f.mu.Lock()
+	if f.dst != nil {
+		f.mu.Unlock()
+		panic(fmt.Sprintf("already forwarding interrupts to %+v", f.dst))
+	}
+	if f.pending {
+		f.pending = false
+		f.mu.Unlock()
+		return false
+	}
+	f.dst = r
+	f.mu.Unlock()
+	return true
+}
+
+// Disable stops interrupt forwarding. If interrupt forwarding is already
+// disabled, Disable is a no-op.
+func (f *Forwarder) Disable() {
+	f.mu.Lock()
+	f.dst = nil
+	f.mu.Unlock()
+}
+
+// NotifyInterrupt implements Receiver.NotifyInterrupt. If interrupt forwarding
+// is enabled, the configured Receiver will be notified. Otherwise the
+// interrupt will be delivered to the next call to Enable.
+func (f *Forwarder) NotifyInterrupt() {
+	f.mu.Lock()
+	if f.dst != nil {
+		f.dst.NotifyInterrupt()
+	} else {
+		f.pending = true
+	}
+	f.mu.Unlock()
+}
diff --git a/pkg/sentry/platform/interrupt/interrupt_test.go b/pkg/sentry/platform/interrupt/interrupt_test.go
new file mode 100644
index 000000000..7c49eeea6
--- /dev/null
+++ b/pkg/sentry/platform/interrupt/interrupt_test.go
@@ -0,0 +1,99 @@
+// Copyright 2018 Google Inc.
+//
+// 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 interrupt
+
+import (
+	"testing"
+)
+
+type countingReceiver struct {
+	interrupts int
+}
+
+// NotifyInterrupt implements Receiver.NotifyInterrupt.
+func (r *countingReceiver) NotifyInterrupt() {
+	r.interrupts++
+}
+
+func TestSingleInterruptBeforeEnable(t *testing.T) {
+	var (
+		f Forwarder
+		r countingReceiver
+	)
+	f.NotifyInterrupt()
+	// The interrupt should cause the first Enable to fail.
+	if f.Enable(&r) {
+		f.Disable()
+		t.Fatalf("Enable: got true, wanted false")
+	}
+	// The failing Enable "acknowledges" the interrupt, allowing future Enables
+	// to succeed.
+	if !f.Enable(&r) {
+		t.Fatalf("Enable: got false, wanted true")
+	}
+	f.Disable()
+}
+
+func TestMultipleInterruptsBeforeEnable(t *testing.T) {
+	var (
+		f Forwarder
+		r countingReceiver
+	)
+	f.NotifyInterrupt()
+	f.NotifyInterrupt()
+	// The interrupts should cause the first Enable to fail.
+	if f.Enable(&r) {
+		f.Disable()
+		t.Fatalf("Enable: got true, wanted false")
+	}
+	// Interrupts are deduplicated while the Forwarder is disabled, so the
+	// failing Enable "acknowledges" all interrupts, allowing future Enables to
+	// succeed.
+	if !f.Enable(&r) {
+		t.Fatalf("Enable: got false, wanted true")
+	}
+	f.Disable()
+}
+
+func TestSingleInterruptAfterEnable(t *testing.T) {
+	var (
+		f Forwarder
+		r countingReceiver
+	)
+	if !f.Enable(&r) {
+		t.Fatalf("Enable: got false, wanted true")
+	}
+	defer f.Disable()
+	f.NotifyInterrupt()
+	if r.interrupts != 1 {
+		t.Errorf("interrupts: got %d, wanted 1", r.interrupts)
+	}
+}
+
+func TestMultipleInterruptsAfterEnable(t *testing.T) {
+	var (
+		f Forwarder
+		r countingReceiver
+	)
+	if !f.Enable(&r) {
+		t.Fatalf("Enable: got false, wanted true")
+	}
+	defer f.Disable()
+	f.NotifyInterrupt()
+	f.NotifyInterrupt()
+	if r.interrupts != 2 {
+		t.Errorf("interrupts: got %d, wanted 2", r.interrupts)
+	}
+}