fs/splice: don't report a partialResult error if there is no data loss

PiperOrigin-RevId: 288642552

pkg/sentry/fs/file.go

@@ -555,6 +555,10 @@ type lockedWriter struct {
 	//
 	// This applies only to Write, not WriteAt.
 	Offset int64
+
+	// Err contains the first error encountered while copying. This is
+	// useful to determine whether Writer or Reader failed during io.Copy.
+	Err error
 }
 
 // Write implements io.Writer.Write.
@@ -590,5 +594,8 @@ func (w *lockedWriter) WriteAt(buf []byte, offset int64) (int, error) {
 			break
 		}
 	}
+	if w.Err == nil {
+		w.Err = err
+	}
 	return written, err
 }

pkg/sentry/fs/splice.go

@@ -167,6 +167,11 @@ func Splice(ctx context.Context, dst *File, src *File, opts SpliceOpts) (int64,
 		if !srcPipe && !opts.SrcOffset {
 			atomic.StoreInt64(&src.offset, src.offset+n)
 		}
+
+		// Don't report any errors if we have some progress without data loss.
+		if w.Err == nil {
+			err = nil
+		}
 	}
 
 	// Drop locks.

test/syscalls/linux/inotify.cc

@@ -1591,6 +1591,34 @@ TEST(Inotify, EpollNoDeadlock) {
   }
 }
 
+TEST(Inotify, SpliceEvent) {
+  int pipes[2];
+  ASSERT_THAT(pipe2(pipes, O_NONBLOCK), SyscallSucceeds());
+
+  const TempPath root = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir());
+  const FileDescriptor fd =
+      ASSERT_NO_ERRNO_AND_VALUE(InotifyInit1(IN_NONBLOCK));
+  const TempPath file1 = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFileWith(
+      root.path(), "some content", TempPath::kDefaultFileMode));
+
+  const FileDescriptor file1_fd =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(file1.path(), O_RDONLY));
+  const int watcher = ASSERT_NO_ERRNO_AND_VALUE(
+      InotifyAddWatch(fd.get(), file1.path(), IN_ALL_EVENTS));
+
+  char buf;
+  EXPECT_THAT(read(file1_fd.get(), &buf, 1), SyscallSucceeds());
+
+  EXPECT_THAT(splice(fd.get(), nullptr, pipes[1], nullptr,
+                     sizeof(struct inotify_event) + 1, SPLICE_F_NONBLOCK),
+              SyscallSucceedsWithValue(sizeof(struct inotify_event)));
+
+  const FileDescriptor read_fd(pipes[0]);
+  const std::vector<Event> events =
+      ASSERT_NO_ERRNO_AND_VALUE(DrainEvents(read_fd.get()));
+  ASSERT_THAT(events, Are({Event(IN_ACCESS, watcher)}));
+}
+
 }  // namespace
 }  // namespace testing
 }  // namespace gvisor