From mboxrd@z Thu Jan  1 00:00:00 1970
From: prasadjoshi124@gmail.com (Prasad Joshi)
Date: Sun, 3 Apr 2011 23:47:41 +0100
Subject: i/o opening error for PCI access
In-Reply-To: <BANLkTikPRMOXm9BrZfpBcek_NiZe+fYwXQ@mail.gmail.com>
References: <BANLkTikPRMOXm9BrZfpBcek_NiZe+fYwXQ@mail.gmail.com>
Message-ID: <BANLkTikwP8h0ny9pkBpXZQ51K74-H_t1Yw@mail.gmail.com>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

On Sun, Apr 3, 2011 at 6:11 PM, Sengottuvelan S
<sengottuvelan.s@gmail.com> wrote:
> Hi All,
>
> I am trying to access /dev/mem in my user process. I could not access
> because not a privileged access. I tried to use iopl(3) call in linux 2.6,

I am not sure, but after reading the manpage, it looks like iopl will
give access to the IO ports not the files.

> but i am getting unresolved symbol for this.? Is any other way to get access
> in user process. I am not sure how to solve this. Can you someone throw some
> light on this.
>
> ?? if(iopl(3)){
> ??????? fprintf(stderr, "Cannot get I/O permissions (being root helps)");
> ??????? return -1;
> ??? }
> ? if ((fd = open("/dev/mem", O_RDWR | O_SYNC)) < 0) {
> ??????? fprintf(stderr, "Failed to open /dev/mem");
> ??????? return -1;
> ??? }

If you look at the file permission, you will notice only root has
permission to write the /dev/mem

$ ls -l /dev/mem
crw-r----- 1 root kmem 1, 1 2011-04-03 08:42 /dev/mem

Opening it for read/write will surely fail.

Thanks and Regards,
Prasad

>
> --
> Regards,
> S. Sengottuvelan.
>
> --
> Regards,
> S. Sengottuvelan.
>
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