Path: utzoo!attcan!uunet!samsung!aplcen!haven!adm!smoke!gwyn
From: gwyn@smoke.BRL.MIL (Doug Gwyn)
Newsgroups: comp.unix.wizards
Subject: Re: mmap
Message-ID: <12097@smoke.BRL.MIL>
Date: 8 Feb 90 04:25:21 GMT
References: <12087@smoke.BRL.MIL> <22368@adm.BRL.MIL> <3399@paperboy.OSF.ORG>
Reply-To: gwyn@brl.arpa (Doug Gwyn)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 16

In article <3399@paperboy.OSF.ORG> lwa@osf.org (Larry Allen) writes:
>If you want to map "len" bytes using mmap, you ask to
>map "len" bytes.  If mmap is successful, it guarantees
>to return a pointer to an address a such that addresses
>a through a+len-1 are valid in your address space.

That doesn't mean they're safe to use!  They could overlay program
variables.  That is why I wanted a function to help determine page
alignment, so I could safely set up an array to use.

>In any case, I'm not sure what your point about non-Posix
>conformant systems is.  An application using mmap is not
>Posix conformant.

It is the implementation that is not POSIX conformant, due to
sticking PAGESIZE gratuitously in <unistd.h> (according to SVID3).