[Build] fix file_data_loader.cpp build issues for windows

extension/data_loader/file_data_loader.cpp

@@ -6,6 +6,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+#include <executorch/extension/data_loader/pread.h>
 #include <executorch/extension/data_loader/file_data_loader.h>
 
 #include <algorithm>
@@ -17,7 +18,6 @@
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
-#include <unistd.h>
 
 #include <executorch/runtime/core/error.h>
 #include <executorch/runtime/core/result.h>
@@ -69,8 +69,10 @@ FileDataLoader::~FileDataLoader() {
   // file_name_ can be nullptr if this instance was moved from, but freeing a
   // null pointer is safe.
   std::free(const_cast<char*>(file_name_));
-  // fd_ can be -1 if this instance was moved from, but closing a negative fd is
-  // safe (though it will return an error).
+  // fd_ can be -1 if this instance was moved from.
+  if (fd_ == -1) {
+    return;
+  }
   ::close(fd_);
 }
 

extension/data_loader/pread.h

@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// This file ensures that a pread-compatible function is defined in the global namespace for windows and posix environments.
+
+#pragma once
+
+#ifndef _WIN32
+#include <unistd.h>
+#else
+#include <executorch/runtime/platform/compiler.h> // For ssize_t.
+#include <io.h>
+
+#include <windows.h>
+// To avoid conflicts with std::numeric_limits<int32_t>::max() in
+// file_data_loader.cpp.
+#undef max
+
+inline ssize_t pread(int fd, void* buf, size_t nbytes, size_t offset) {
+  OVERLAPPED overlapped; /* The offset for ReadFile. */
+  memset(&overlapped, 0, sizeof(overlapped));
+  overlapped.Offset = offset;
+  overlapped.OffsetHigh = offset >> 32;
+
+  BOOL result; /* The result of ReadFile. */
+  DWORD bytes_read; /* The number of bytes read. */
+  HANDLE file = (HANDLE)_get_osfhandle(fd);
+
+  result = ReadFile(file, buf, nbytes, &bytes_read, &overlapped);
+  DWORD error = GetLastError();
+  if (!result) {
+    if (error == ERROR_IO_PENDING) {
+      result = GetOverlappedResult(file, &overlapped, &bytes_read, TRUE);
+      if (!result) {
+        error = GetLastError();
+      }
+    }
+  }
+  if (!result) {
+    // Translate error into errno.
+    switch (error) {
+      case ERROR_HANDLE_EOF:
+        errno = 0;
+        break;
+      default:
+        errno = EIO;
+        break;
+    }
+    return -1;
+  }
+  return bytes_read;
+}
+
+#endif

extension/data_loader/targets.bzl

@@ -40,6 +40,7 @@ def define_common_targets():
     runtime.cxx_library(
         name = "file_data_loader",
         srcs = ["file_data_loader.cpp"],
+        headers = ["pread.h"],
         exported_headers = ["file_data_loader.h"],
         visibility = [
             "//executorch/test/...",