[WasmFS] Implement fdatasync (#16675)

As an alias for `__wasi_fd_sync` (i.e. `fsync`). This flushes data more
conservatively than necessary, but it's not worth maintaining a separate code
path to avoid flushing file metadata right now.

Author: tlively

system/lib/wasmfs/syscalls.cpp

@@ -285,6 +285,11 @@ __wasi_errno_t __wasi_fd_sync(__wasi_fd_t fd) {
   return __WASI_ERRNO_SUCCESS;
 }
 
+int __syscall_fdatasync(int fd) {
+  // TODO: Optimize this to avoid unnecessarily flushing unnecessary metadata.
+  return __wasi_fd_sync(fd);
+}
+
 backend_t wasmfs_get_backend_by_fd(int fd) {
   auto openFile = wasmFS.getFileTable().locked().getEntry(fd);
   if (!openFile) {

tests/test_other.py

@@ -11616,6 +11616,11 @@ def test_unistd_create(self):
     self.set_setting('WASMFS')
     self.do_run_in_out_file_test('wasmfs/wasmfs_create.c')
 
+  def test_unistd_fdatasync(self):
+    # TODO: Remove this test in favor of unistd/misc.c
+    self.set_setting('WASMFS')
+    self.do_run_in_out_file_test('wasmfs/wasmfs_fdatasync.c')
+
   @also_with_wasmfs
   def test_unistd_seek(self):
     self.do_run_in_out_file_test('wasmfs/wasmfs_seek.c')

tests/wasmfs/wasmfs_fdatasync.c

@@ -0,0 +1,25 @@
+/*
+ * Copyright 2022 The Emscripten Authors.  All rights reserved.
+ * Emscripten is available under two separate licenses, the MIT license and the
+ * University of Illinois/NCSA Open Source License.  Both these licenses can be
+ * found in the LICENSE file.
+ */
+
+#include <assert.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+int main() {
+  int fd = creat("foo.txt", 0777);
+  assert(fd > 0);
+
+  int err = fdatasync(fd);
+  assert(err == 0);
+
+  close(fd);
+
+  printf("ok\n");
+}

tests/wasmfs/wasmfs_fdatasync.out

@@ -0,0 +1 @@
+ok