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Re: kernel/975: mmap does not detect file changes.
The following reply was made to PR kernel/975; it has been noted by GNATS.
From: Artur Grabowski <email@example.com>
Cc: firstname.lastname@example.org, email@example.com
Subject: Re: kernel/975: mmap does not detect file changes.
Date: 16 Nov 1999 07:31:44 +0100
> >Number: 975
> >Category: kernel
> >Synopsis: mmap does not detect file changes.
> >Confidential: no
> >Severity: serious
> >Priority: medium
> >Responsible: bugs
> >State: open
> >Class: sw-bug
> >Submitter-Id: unknown
> >Arrival-Date: Mon Nov 15 15:10:01 MST 1999
> >Originator: Anders Arnholm
> >Release: OpenBSD 2.6
> System : OpenBSD 2.6
> Architecture: OpenBSD.i386
> Machine : i386
> The test program from cyrus imapd clamies that OpenBSD has no working
> mmap function. I have studies the problem a little and minimized the
> test program that finds teh error. The error seems to have to do with
> that after haing changed a file, mmaped to the process, following
> reads to the file handle does not find out that the file has been
> changed even if the the has been changed on disk.
> The error olny ocures if a page has been read from the first mmap and
> that mmap is still active when the second mmap occurs. (I have a small
> test program that does this).
Yes, this is known, it's an antique problem. I have looked a bit on the
unified buffer cache code written by Chuck Silvers for NetBSD that solves
this. As soon as I have some time left I'll give it another shot and maybe
help him to finish the code if it's not ready for prime-time.
This is a big project, so anyone with experience from the kernel and some
time should contact me if they want to help (besides correct mmap semantics,
this should give us a nice performance boost), because there is a lot of
small and big stuff that needs to be done here.