4 files changed, 93 insertions, 58 deletions

diff --git a/pkg/sentry/kernel/aio.go b/pkg/sentry/kernel/aio.go
new file mode 100644
index 000000000..0ac78c0b8
--- /dev/null
+++ b/pkg/sentry/kernel/aio.go
@@ -0,0 +1,81 @@
+// Copyright 2020 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 kernel
+
+import (
+	"time"
+
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/log"
+)
+
+// AIOCallback is an function that does asynchronous I/O on behalf of a task.
+type AIOCallback func(context.Context)
+
+// QueueAIO queues an AIOCallback which will be run asynchronously.
+func (t *Task) QueueAIO(cb AIOCallback) {
+	ctx := taskAsyncContext{t: t}
+	wg := &t.TaskSet().aioGoroutines
+	wg.Add(1)
+	go func() {
+		cb(ctx)
+		wg.Done()
+	}()
+}
+
+type taskAsyncContext struct {
+	context.NoopSleeper
+	t *Task
+}
+
+// Debugf implements log.Logger.Debugf.
+func (ctx taskAsyncContext) Debugf(format string, v ...interface{}) {
+	ctx.t.Debugf(format, v...)
+}
+
+// Infof implements log.Logger.Infof.
+func (ctx taskAsyncContext) Infof(format string, v ...interface{}) {
+	ctx.t.Infof(format, v...)
+}
+
+// Warningf implements log.Logger.Warningf.
+func (ctx taskAsyncContext) Warningf(format string, v ...interface{}) {
+	ctx.t.Warningf(format, v...)
+}
+
+// IsLogging implements log.Logger.IsLogging.
+func (ctx taskAsyncContext) IsLogging(level log.Level) bool {
+	return ctx.t.IsLogging(level)
+}
+
+// Deadline implements context.Context.Deadline.
+func (ctx taskAsyncContext) Deadline() (time.Time, bool) {
+	return ctx.t.Deadline()
+}
+
+// Done implements context.Context.Done.
+func (ctx taskAsyncContext) Done() <-chan struct{} {
+	return ctx.t.Done()
+}
+
+// Err implements context.Context.Err.
+func (ctx taskAsyncContext) Err() error {
+	return ctx.t.Err()
+}
+
+// Value implements context.Context.Value.
+func (ctx taskAsyncContext) Value(key interface{}) interface{} {
+	return ctx.t.Value(key)
+}
diff --git a/pkg/sentry/kernel/context.go b/pkg/sentry/kernel/context.go
index 0c40bf315..dd5f0f5fa 100644
--- a/pkg/sentry/kernel/context.go
+++ b/pkg/sentry/kernel/context.go
@@ -18,7 +18,6 @@ import (
 	"time"
 
 	"gvisor.dev/gvisor/pkg/context"
-	"gvisor.dev/gvisor/pkg/log"
 )
 
 // contextID is the kernel package's type for context.Context.Value keys.
@@ -113,55 +112,3 @@ func (*Task) Done() <-chan struct{} {
 func (*Task) Err() error {
 	return nil
 }
-
-// AsyncContext returns a context.Context that may be used by goroutines that
-// do work on behalf of t and therefore share its contextual values, but are
-// not t's task goroutine (e.g. asynchronous I/O).
-func (t *Task) AsyncContext() context.Context {
-	return taskAsyncContext{t: t}
-}
-
-type taskAsyncContext struct {
-	context.NoopSleeper
-	t *Task
-}
-
-// Debugf implements log.Logger.Debugf.
-func (ctx taskAsyncContext) Debugf(format string, v ...interface{}) {
-	ctx.t.Debugf(format, v...)
-}
-
-// Infof implements log.Logger.Infof.
-func (ctx taskAsyncContext) Infof(format string, v ...interface{}) {
-	ctx.t.Infof(format, v...)
-}
-
-// Warningf implements log.Logger.Warningf.
-func (ctx taskAsyncContext) Warningf(format string, v ...interface{}) {
-	ctx.t.Warningf(format, v...)
-}
-
-// IsLogging implements log.Logger.IsLogging.
-func (ctx taskAsyncContext) IsLogging(level log.Level) bool {
-	return ctx.t.IsLogging(level)
-}
-
-// Deadline implements context.Context.Deadline.
-func (ctx taskAsyncContext) Deadline() (time.Time, bool) {
-	return ctx.t.Deadline()
-}
-
-// Done implements context.Context.Done.
-func (ctx taskAsyncContext) Done() <-chan struct{} {
-	return ctx.t.Done()
-}
-
-// Err implements context.Context.Err.
-func (ctx taskAsyncContext) Err() error {
-	return ctx.t.Err()
-}
-
-// Value implements context.Context.Value.
-func (ctx taskAsyncContext) Value(key interface{}) interface{} {
-	return ctx.t.Value(key)
-}
diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index 52491da7a..554a42e05 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -452,9 +452,7 @@ func (k *Kernel) SaveTo(w io.Writer) error {
 		return err
 	}
 
-	// Ensure that all pending asynchronous work is complete:
-	//   - inode and mount release
-	//   - asynchronuous IO
+	// Ensure that all inode and mount release operations have completed.
 	fs.AsyncBarrier()
 
 	// Once all fs work has completed (flushed references have all been released),
@@ -1249,13 +1247,15 @@ func (k *Kernel) Kill(es ExitStatus) {
 }
 
 // Pause requests that all tasks in k temporarily stop executing, and blocks
-// until all tasks in k have stopped. Multiple calls to Pause nest and require
-// an equal number of calls to Unpause to resume execution.
+// until all tasks and asynchronous I/O operations in k have stopped. Multiple
+// calls to Pause nest and require an equal number of calls to Unpause to
+// resume execution.
 func (k *Kernel) Pause() {
 	k.extMu.Lock()
 	k.tasks.BeginExternalStop()
 	k.extMu.Unlock()
 	k.tasks.runningGoroutines.Wait()
+	k.tasks.aioGoroutines.Wait()
 }
 
 // Unpause ends the effect of a previous call to Pause. If Unpause is called
diff --git a/pkg/sentry/kernel/threads.go b/pkg/sentry/kernel/threads.go
index bf2dabb6e..872e1a82d 100644
--- a/pkg/sentry/kernel/threads.go
+++ b/pkg/sentry/kernel/threads.go
@@ -87,6 +87,13 @@ type TaskSet struct {
 	// at time of save (but note that this is not necessarily the same thing as
 	// sync.WaitGroup's zero value).
 	runningGoroutines sync.WaitGroup `state:"nosave"`
+
+	// aioGoroutines is the number of goroutines running async I/O
+	// callbacks.
+	//
+	// aioGoroutines is not saved but is required to be zero at the time of
+	// save.
+	aioGoroutines sync.WaitGroup `state:"nosave"`
 }
 
 // newTaskSet returns a new, empty TaskSet.