> Date: Thu, 26 Oct 95 17:50:18 EDT
> From: davide@PIPER.NECTAR.CS.CMU.EDU

> >Number:         1697
> >Category:       bin
> >Synopsis:       vi uses mmap() instead of read(); can corrupt remote files

> >Description:
> 	vi seems to use mmap() instead of read() on files being edited.  This
> 	is bad because mmap() of a file from a remote file system (in this case
> 	AFS 3.0 1.6, but also NFS) is not consistent.  That is, while metadata
> 	such as modification time and length are obtained correctly from the
> 	filesystem, the data pages in memory objects are NOT updated when the
> 	remote file changes.  I have just repeated this with two NetBSD/i386
> 	laptops (-current) running NFS but not AFS, so it is NOT an AFS problem.

> >Fix:
> 	Either (1) get vi to stop using mmap() or (2) get mmap() to do the
> 	right thing.  Since this problem can result in file corruption (if
> 	you don't notice the wrong part you will write it out and it will
> 	become the "correct" file contents, which actually happened to me),
> 	I think this is severe.

This is really a problem with the VM system, of course.

I've been thinking about a better design for the VM code,
but it would take quite a while to implement...

Gordon Ross