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Subject: Re: Having problem with mmap system call!!!
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: root@chaos.analogic.com
Cc: "Srinivas G." <srinivasg@esntechnologies.co.in>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Date: Thu, 16 Sep 2004 14:31:36 +0100
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On Iau, 2004-09-16 at 15:07, Richard B. Johnson wrote:
>     if((vp = mmap((caddr_t) HINT, len, PROT, FLAGS, fd, addr)) == SHM_FAIL)
>     {
>         fprintf(stderr, "Can't access shared memory\n");
>         exit(EXIT_FAILURE);

SHM_FAIL is the wrong error check btw.

It is much better to do this in the driver than do nasty user mode hacks
using /dev/mem. When you do it kernel driver side you end up with a
cleaner mmap interface, a sensible permissions model and the hardware
device pages mapped directly and nicely into the app