linux-kernel - Re: Access MSR functions in userspace?

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Date:	Wed, 06 Feb 2008 16:48:14 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Hasan Rashid <hasan@...italpath.net>
CC:	"'Maxim Levitsky'" <maximlevitsky@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Access MSR functions in userspace?

Hasan Rashid wrote:
> Maxim, HPA,
> 
>  I loaded the module msr.o and when I try to use wrmsr or rdmsr from the msr
> tools I get rdmsr: open: No such device. It seems like device doesn't
> register upon module load. I have created the devices on the system using
> mknod. Meaning /dev/cpu/msr is there and I changed the appropriate path in
> the msr.c(module) and wrmsr.c (utlity) file. 
> 
> What would prompt this error message?
> 

/dev/cpu/msr is bogus.  It should be /dev/cpu/0/msr etc.

Sounds like your version of udev might be out of date, or you're using 
an old kernel which doesn't communicate /dev/cpu/* to udev properly.

Revert your hacks and, if you have to create the nodes manually, use the 
MAKEDEV script included with the msr-tools.

	-hpa
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