EnableSendfile and $r->sendfile

[Dave Viner <suppressed>]

I'm trying to understand the full effect of the EnableSendfile  
directive.  If I set the directive to 'Off', what happens when I  
invoke $r->sendfile($myfile) ??

My hope is that the $r->sendfile will simply use mechanism other than  
sendfile() to read/send the given file (maybe allocate a buffer, read  
in file to buffer, send buffer, repeat until file is eof()... or  
something similar).  But I've looked in the source, but I can't seem  
to convince myself that this will actually happen.

Thanks
dave viner