Date: Tue, 30 Nov 1999 23:28:44 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: "Brian J. McGovern" <mcgovern@spoon.beta.com> Cc: hackers@FreeBSD.ORG Subject: Re: writing to an mmap()'ed region requires read access? Message-ID: <199912010728.XAA29886@apollo.backplane.com> References: <199912010444.XAA17911@spoon.beta.com>
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: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
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