Re: writing to an mmap()'ed region requires read access?

[ Available lists | Index of freebsd-hackers | Month of Nov 1999 | Week of 30 Nov 1999 | Raw email | View thread | Wrap long lines | Reply | Tag ]
From
Matthew Dillon <dillon@apollo.backplane.com>
Date
30 Nov 1999 23:28:50
Subject
Re: writing to an mmap()'ed region requires read access?
Message-ID
199912010728.XAA29886@apollo.backplane.com

References to

[ Hide this part ]
:I was just playing with mmap() really for the first time, and I noticed
:something a bit odd. When you mmap() a file for writing, it also appears
:to require that you give it read permissions, else it dies on a signal 10.
:Any reason for this? (I'm using 3.3-STABLE (11/30/99) with the following
:program)
: -Brian

I've got a few hundred terrabytes of WOM to sell ya!

This is just a byproduct of the MMU implementation. Most MMU's do
not support write-only maps because most do not implement separate
read and write bits. You get a valid and a write-enable bit instead,
or you just get a valid bit and have to use the dirty bit to make the
page writable (no write-enable bit at all).

-Matt


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message



Elapsed time: 0.115 seconds