Synchronize virtfs rdwr state

virtfs/builder.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"strings"
+	"sync"
 )
 
 // BuildTree walks an FsNodeDecl spec and produces a *Tree.
@@ -257,31 +258,48 @@ func openLeaf(d *FsNodeDecl, uid, gid string, mode os.FileMode, name string) (Fi
 		isStreaming = true
 	case d.Rdwr != nil:
 		fn := d.Rdwr
+		var stateMu sync.Mutex
+		var writeMu sync.Mutex
 		var result []byte
-		var reqCtx context.Context
 		var reqCancel context.CancelFunc
 		blockFn = notBlocking
 		readFn = func() ([]byte, error) {
+			stateMu.Lock()
 			if result != nil {
-				return result, nil
+				out := make([]byte, len(result))
+				copy(out, result)
+				stateMu.Unlock()
+				return out, nil
 			}
+			stateMu.Unlock()
 			if d.Read != nil {
 				return d.Read()
 			}
 			return nil, nil
 		}
 		writeFn = func(data []byte) error {
-			reqCtx, reqCancel = context.WithCancel(context.Background())
+			writeMu.Lock()
-			r, err := fn(reqCtx, data)
+			defer writeMu.Unlock()
-			if err != nil {
+			ctx, cancel := context.WithCancel(context.Background())
-				return err
+			stateMu.Lock()
+			reqCancel = cancel
+			stateMu.Unlock()
+			r, err := fn(ctx, data)
+			stateMu.Lock()
+			reqCancel = nil
+			if err == nil {
+				result = append(result[:0], r...)
 			}
-			result = r
+			stateMu.Unlock()
-			return nil
+			cancel()
+			return err
 		}
 		closeFn := func() error {
-			if reqCancel != nil {
+			stateMu.Lock()
-				reqCancel()
+			cancel := reqCancel
+			stateMu.Unlock()
+			if cancel != nil {
+				cancel()
 			}
 			return nil
 		}