Make a NaClDesc ctor for creating descs from NaClFileInfo.

src/public/nacl_file_info.h

+/*
+ * Copyright (c) 2013 The Native Client Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef NATIVE_CLIENT_SRC_PUBLIC_NACL_FILE_INFO_H_
+#define NATIVE_CLIENT_SRC_PUBLIC_NACL_FILE_INFO_H_
+
+#include "native_client/src/include/nacl_base.h"
+#include "native_client/src/include/portability.h"
+
+EXTERN_C_BEGIN
+
+struct NaClDesc;
+
+/*
+ * NaClFileToken is a single-use nonce that the NaCl process can use to query
+ * the browser process for trusted information about a file.  This helps
+ * establish that the file is known by the browser to be immutable and
+ * suitable for file-identity-based validation caching.
+ * lo == 0 && hi == 0 indicates the token is invalid and no additional
+ * information is available (see NaClFileTokenIsValid()).
+ */
+struct NaClFileToken {
+  uint64_t lo;
+  uint64_t hi;
+};
+
+static INLINE int NaClFileTokenIsValid(struct NaClFileToken *file_token) {
+  return !(file_token->lo == 0 && file_token->hi == 0);
+}
+
+struct NaClFileInfo {
+  /* desc is a posix file descriptor */
+  int32_t desc;
+  struct NaClFileToken file_token;
+};
+
+/*
+ * Creates a NaClDesc from the file descriptor/file handle and metadata
+ * in |info|, and associates that desc with the metadata.
+ */
+struct NaClDesc *NaClDescIoFromFileInfo(struct NaClFileInfo info,
+                                        int mode);
+
+
+EXTERN_C_END
+
+#endif /* NATIVE_CLIENT_SRC_PUBLIC_NACL_FILE_INFO_H_ */