Support creating temporary files for sync file operations.

base/file_util_proxy.h

Index: base/file_util_proxy.h
diff --git a/base/file_util_proxy.h b/base/file_util_proxy.h
index e0b04cb220abd5259c031bef189b5d88ce49930f..72cb0b6231e42464d500dccda6dc74991150c6bd 100644
--- a/base/file_util_proxy.h
+++ b/base/file_util_proxy.h
@@ -64,9 +64,18 @@ class BASE_API FileUtilProxy {
                            CreateOrOpenCallback* callback);
 
   // Creates a temporary file for writing.  The path and an open file handle
-  // are returned.  It is invalid to pass NULL for the callback.
+  // are returned.  It is invalid to pass NULL for the callback.  The file
+  // flags should at least set base::PLATFORM_FILE_TEMPORARY and
+  // base::PLATFORM_FILE_WRITE and some flag related to the temporary file
+  // creation.  A typical example would be:
+  //   base::PLATFORM_FILE_CREATE_ALWAYS |

[darin (slow to review), 2011/06/04 21:06:01]

i think having to specify PLATFORM_FILE_TEMPORARY makes the API redundant.  the
method name is CreateTemporary after all!

how about we rename file_flags to additional_file_flags (or
optional_file_flags), and then we document that CREATE_ALWAYS, WRITE, and
TEMPORARY bits comprise the default file flags.  this way the callers can pass 0
if they don't need to specify anything special.

so i would expect to see CreateTemporary(loop, 0, callback) in many cases or
CreateTemporary(loop, PLATFORM_FILE_ASYNC, callback) in cases where we want to
open the file for async IO.

finally, it occurs to me that fixing this method to make it possible to not set
PLATFORM_FILE_ASYNC doesn't really fix the original issue you were trying to
solve.  the problem you had was that the Write method cannot handle a
PlatformFile that was opened with PLATFORM_FILE_ASYNC.  maybe we should look
into modifying the Write function to support that mode as well?

[Sam Kerner (Chrome), 2011/06/06 22:19:27]

I looked in to doing this a while ago, and I think I added a TODO around the
Write method.  If you want to do this, I can point you to the docs and show you
a unit test that can exercise it.

+  //   base::PLATFORM_FILE_WRITE |
+  //   base::PLATFORM_FILE_TEMPORARY
+  // for synchronous writes.  Add base::PLATFORM_FILE_ASYNC to support
+  // asynchronous file operations for net::FileStream.
   static bool CreateTemporary(
       scoped_refptr<MessageLoopProxy> message_loop_proxy,
+      int file_flags,
       CreateTemporaryCallback* callback);
 
   // Close the given file handle.