Storage Access Framework and native code

Question

I want to develop an App that uses the Storage Access Framework but processes the provided files with JNI native code.

Via the Storage Access Framework I get a Uri after a call to startActivityForResult() with a Intent.ACTION_OPEN_DOCUMENT intent. From this I can get an InputStream, ParcelFileDescriptor or similar.

Is there a way to get from this something (like for example a FILE) that I can pass on to my native code so that it can directly read from/write to the file provided by the content provider?

Background:

The C part of the JNI interface (which I didn't write but can modify/extend) can load two kinds of data

1. files specified by a file name const char *filename that can be opened with open()
2. data in a buffer jbyteArray array containing the bytes that make up the "file"

and can write to

1. a file path const char *filename that can be opened with fopen()

Currently, when opening a file with Intent.ACTION_OPEN_DOCUMENT the Uri uri obtained in onActivityResult() is converted to an input stream with getContentResolver().openInputStream(uri) and then read into a byte[] buffer which is passed to the native code. Once the native code is done, it saves the result to a temporary file whose path is passed back to the Java side. The Java code then reads the temporary file and puts its content into a FileOutputStream obtained from the uri.

This is obviously horribly inefficient and ugly.