On Tue, 22 Jun 1999 16:25:32 +0930 (CST) 
 blymn@baea.com.au (Brett Lymn) wrote:

 > Like we do now :-)

What are you talking about?  Take a look at vfs_vnops.c:vn_writechk().
That is called from vn_open().

Considering that you must open a file for writing before you can mmap
it with PROT_WRITE, that is closed off, too.

        -- Jason R. Thorpe <thorpej@nas.nasa.gov>