Improve FUSE async/noreply call logic

This change adds bookkeeping variables for the
FUSE request. With them, old insecure confusing
code we used to process async requests is replaced
by new clear compiling ones. Future code can take
advantage of them to have better control of each
requests.

1 files changed, 12 insertions, 19 deletions

diff --git a/pkg/sentry/fsimpl/fuse/dev.go b/pkg/sentry/fsimpl/fuse/dev.go
index 6022593d6..e7296c189 100644
--- a/pkg/sentry/fsimpl/fuse/dev.go
+++ b/pkg/sentry/fsimpl/fuse/dev.go
@@ -367,22 +367,20 @@ func (fd *DeviceFD) Seek(ctx context.Context, offset int64, whence int32) (int64
 
 // sendResponse sends a response to the waiting task (if any).
 func (fd *DeviceFD) sendResponse(ctx context.Context, fut *futureResponse) error {
-	// See if the running task need to perform some action before returning.
-	// Since we just finished writing the future, we can be sure that
-	// getResponse generates a populated response.
-	if err := fd.noReceiverAction(ctx, fut.getResponse()); err != nil {
-		return err
-	}
+	// Signal the task waiting on a response if any.
+	defer close(fut.ch)
 
 	// Signal that the queue is no longer full.
 	select {
 	case fd.fullQueueCh <- struct{}{}:
 	default:
 	}
-	fd.numActiveRequests -= 1
+	fd.numActiveRequests--
+
+	if fut.async {
+		return fd.asyncCallBack(ctx, fut.getResponse())
+	}
 
-	// Signal the task waiting on a response.
-	close(fut.ch)
 	return nil
 }
 
@@ -404,23 +402,18 @@ func (fd *DeviceFD) sendError(ctx context.Context, errno int32, req *Request) er
 	delete(fd.completions, respHdr.Unique)
 
 	fut.hdr = &respHdr
-	if err := fd.sendResponse(ctx, fut); err != nil {
-		return err
-	}
-
-	return nil
+	return fd.sendResponse(ctx, fut)
 }
 
-// noReceiverAction has the calling kernel.Task do some action if its known that no
-// receiver is going to be waiting on the future channel. This is to be used by:
-// FUSE_INIT.
-func (fd *DeviceFD) noReceiverAction(ctx context.Context, r *Response) error {
+// asyncCallBack executes pre-defined callback function for async requests.
+// Currently used by: FUSE_INIT.
+func (fd *DeviceFD) asyncCallBack(ctx context.Context, r *Response) error {
 	switch r.opcode {
 	case linux.FUSE_INIT:
 		creds := auth.CredentialsFromContext(ctx)
 		rootUserNs := kernel.KernelFromContext(ctx).RootUserNamespace()
 		return fd.fs.conn.InitRecv(r, creds.HasCapabilityIn(linux.CAP_SYS_ADMIN, rootUserNs))
-		// TODO(gvisor.dev/issue/3247): support async read: correctly process the response using information from r.options.
+		// TODO(gvisor.dev/issue/3247): support async read: correctly process the response.
 	}
 
 	return nil