show uploaded filename in SQLFORM.grid

[rajjm...@gmail.com]

db.define_table('Files',
    Field("filename", "upload",default=None, uploadfolder=os.path.join(request.folder, 'uploads')))

grid = SQLFORM.smartgrid(db.Files)


Displays:
List id, and file.

Id    Filename   
1    file

How to show the uploaded filename instead file?