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 either a Unix file descriptor or a Windows file handle. */
+  int32_t desc;

[jvoung (off chromium), 2014/05/16 18:02:05]

btw, Nick do you remember what the original intention of the "or" is?

(a) Is the "or" in the sense that this should be a NaClHandle (if so, then
should this be changed to NaClHandle which is also declared under src/public/)?

(b) Or is the "or" in the sense that this could be a union. Either a posix fd
(so on windows would need to convert w/ _open_osfhandle) or a NaClHandle?  The
code in chrome's trusted plugin seems to assume it's a posix fd... So, if we
want to be more strict and make this a NaClHandle, then the trusted plugin code
will need to be changed. With the factory method below NaClDescIoFromFileInfo,
I've been assuming case (a).

[Mark Seaborn, 2014/05/16 18:23:29]

If this field contains a Windows handle, I think it's fine to leave this as
int32_t on Windows, for two reasons:

While Windows' HANDLE is a typedef for void*, Windows does use an int type to
represent handles in some cases, in particular _open_osfhandle().  Handles are
really just ints.  It's simpler for NaCl to just use int32_t here.

While NaClHandle is declared in src/public/imc_types.h, this is an IMCism.  IMC
is deprecated and will eventually go away, so it's good for the
validator-caching code to not depend on its typedefs.

[jvoung (off chromium), 2014/05/16 20:58:43]

Okay, on further inspection, it looks like all the users in NaCl and Chrome have
treated this as a posix file descriptor. It was only the validation_cache.h's
ResolveFileToken() method that expected a file desc or file handle.

I've changed the comment here to reflect that it's a posix file descriptor, and
changed the ctor.

+  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_ */