3 files changed, 61 insertions, 18 deletions

diff --git a/pkg/sentry/fs/file.go b/pkg/sentry/fs/file.go
index f2683bbd2..6d93ef760 100644
--- a/pkg/sentry/fs/file.go
+++ b/pkg/sentry/fs/file.go
@@ -16,6 +16,7 @@ package fs
 
 import (
 	"math"
+	"sync"
 	"sync/atomic"
 
 	"gvisor.googlesource.com/gvisor/pkg/amutex"
@@ -72,9 +73,15 @@ type File struct {
 	// other files via the Dirent cache.
 	Dirent *Dirent
 
+	// flagsMu protects flags and async below.
+	flagsMu sync.Mutex `state:"nosave"`
+
 	// flags are the File's flags. Setting or getting flags is fully atomic
 	// and is not protected by mu (below).
-	flags atomic.Value `state:".(FileFlags)"`
+	flags FileFlags
+
+	// async handles O_ASYNC notifications.
+	async FileAsync
 
 	// mu is dual-purpose: first, to make read(2) and write(2) thread-safe
 	// in conformity with POSIX, and second, to cancel operations before they
@@ -99,8 +106,8 @@ func NewFile(ctx context.Context, dirent *Dirent, flags FileFlags, fops FileOper
 		UniqueID:       uniqueid.GlobalFromContext(ctx),
 		Dirent:         dirent,
 		FileOperations: fops,
+		flags:          flags,
 	}
-	f.flags.Store(flags)
 	f.mu.Init()
 	return f
 }
@@ -117,22 +124,40 @@ func (f *File) DecRef() {
 
 		// Release a reference on the Dirent.
 		f.Dirent.DecRef()
+
+		f.flagsMu.Lock()
+		if f.flags.Async && f.async != nil {
+			f.async.Unregister(f)
+		}
+		f.flagsMu.Unlock()
 	})
 }
 
 // Flags atomically loads the File's flags.
 func (f *File) Flags() FileFlags {
-	return f.flags.Load().(FileFlags)
+	f.flagsMu.Lock()
+	flags := f.flags
+	f.flagsMu.Unlock()
+	return flags
 }
 
 // SetFlags atomically changes the File's flags to the values contained
 // in newFlags. See SettableFileFlags for values that can be set.
 func (f *File) SetFlags(newFlags SettableFileFlags) {
-	flags := f.flags.Load().(FileFlags)
-	flags.Direct = newFlags.Direct
-	flags.NonBlocking = newFlags.NonBlocking
-	flags.Append = newFlags.Append
-	f.flags.Store(flags)
+	f.flagsMu.Lock()
+	f.flags.Direct = newFlags.Direct
+	f.flags.NonBlocking = newFlags.NonBlocking
+	f.flags.Append = newFlags.Append
+	if f.async != nil {
+		if newFlags.Async && !f.flags.Async {
+			f.async.Register(f)
+		}
+		if !newFlags.Async && f.flags.Async {
+			f.async.Unregister(f)
+		}
+	}
+	f.flags.Async = newFlags.Async
+	f.flagsMu.Unlock()
 }
 
 // Offset atomically loads the File's offset.
@@ -361,6 +386,27 @@ func (f *File) Msync(ctx context.Context, mr memmap.MappableRange) error {
 	return f.Fsync(ctx, int64(mr.Start), int64(mr.End-1), SyncData)
 }
 
+// A FileAsync sends signals to its owner when w is ready for IO.
+type FileAsync interface {
+	Register(w waiter.Waitable)
+	Unregister(w waiter.Waitable)
+}
+
+// Async gets the stored FileAsync or creates a new one with the supplied
+// function. If the supplied function is nil, no FileAsync is created and the
+// current value is returned.
+func (f *File) Async(newAsync func() FileAsync) FileAsync {
+	f.flagsMu.Lock()
+	defer f.flagsMu.Unlock()
+	if f.async == nil && newAsync != nil {
+		f.async = newAsync()
+		if f.flags.Async {
+			f.async.Register(f)
+		}
+	}
+	return f.async
+}
+
 // FileReader implements io.Reader and io.ReaderAt.
 type FileReader struct {
 	// Ctx is the context for the file reader.
diff --git a/pkg/sentry/fs/file_state.go b/pkg/sentry/fs/file_state.go
index 341cbda0b..3384737ab 100644
--- a/pkg/sentry/fs/file_state.go
+++ b/pkg/sentry/fs/file_state.go
@@ -18,13 +18,3 @@ package fs
 func (f *File) afterLoad() {
 	f.mu.Init()
 }
-
-// saveFlags is invoked by stateify.
-func (f *File) saveFlags() FileFlags {
-	return f.flags.Load().(FileFlags)
-}
-
-// loadFlags is invoked by stateify.
-func (f *File) loadFlags(flags FileFlags) {
-	f.flags.Store(flags)
-}
diff --git a/pkg/sentry/fs/flags.go b/pkg/sentry/fs/flags.go
index dfa6a3d62..7a8eefd02 100644
--- a/pkg/sentry/fs/flags.go
+++ b/pkg/sentry/fs/flags.go
@@ -42,6 +42,9 @@ type FileFlags struct {
 
 	// Directory indicates that this file must be a directory.
 	Directory bool
+
+	// Async indicates that this file sends signals on IO events.
+	Async bool
 }
 
 // SettableFileFlags is a subset of FileFlags above that can be changed
@@ -55,6 +58,9 @@ type SettableFileFlags struct {
 
 	// Append indicates this file is append only.
 	Append bool
+
+	// Async indicates that this file sends signals on IO events.
+	Async bool
 }
 
 // Settable returns the subset of f that are settable.
@@ -63,5 +69,6 @@ func (f FileFlags) Settable() SettableFileFlags {
 		Direct:      f.Direct,
 		NonBlocking: f.NonBlocking,
 		Append:      f.Append,
+		Async:       f.Async,
 	}
 }