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Re: PATCH: Fix offset of mmap

To: James Simmons <jsimmons@transvirtual.com>
Subject: Re: PATCH: Fix offset of mmap
From: "H . J . Lu" <hjl@lucon.org>
Date: Fri, 14 Sep 2001 10:15:49 -0700
Cc: linux-mips@oss.sgi.com
In-reply-to: <Pine.LNX.4.10.10109141009260.20461-100000@transvirtual.com>; from jsimmons@transvirtual.com on Fri, Sep 14, 2001 at 10:10:58AM -0700
References: <20010914100700.A16047@lucon.org> <Pine.LNX.4.10.10109141009260.20461-100000@transvirtual.com>
Sender: owner-linux-mips@oss.sgi.com
User-agent: Mutt/1.2.5i
On Fri, Sep 14, 2001 at 10:10:58AM -0700, James Simmons wrote:
> 
> > We should check if offset of mmap is on the page boundary.
> 
> I believe this would break certain pieces of hardware. For example the
> mq200 framebuffer in the sigmarion is not paged aligned. You have to
> supply a offset to make it work.

How do you mmap a memory whose offset is not page aligned? The code
here is

return do_mmap2(addr, len, prot, flags, fd, offset >> PAGE_SHIFT);
                                            ^^^^^^^^^^^^^^^^^^^^

It is up to the user code to make sure everything is ok.


H.J.

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