In-Reply-To: <op.thi3x1mvnwjy9v@titan>
References: <op.thi3x1mvnwjy9v@titan>
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From: Kyle Moffett <mrmacman_g4@mac.com>
Subject: Re: copy_from_user / copy_to_user with no swap space
Date: Mon, 16 Oct 2006 15:39:16 -0400
To: mfbaustx <mfbaustx@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
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On Oct 16, 2006, at 15:19:03, mfbaustx wrote:
> So you're absolutely obligated to DO the copy at the time the  
> kernel is executing on behalf of that process.  Once your process/ 
> thread is context swapped, you've lost the [correct] information on  
> the address mapping.

Yes, this is correct.

> So, IF you MUST copy_from/to_user when in the context of the  
> process, AND IF you have no virtual memory/swapping, THEN must it  
> not be true that you can ALWAYS dereferences your user space pointers?

I'm not sure I entirely understand what you're asking here; perhaps  
you could rephrase or explain what you're trying to do?  From what I  
can pick up from your description; you may be missing that program  
text pages and memory-mapped files may be "swapped-out" even  
*without* a swap device.  As an example, when I first start /bin/bash  
(ignoring readahead for the moment), very little of the binary and  
shared libraries are actually in memory (the rest is left on disk).   
When I use data or call a function that hasn't been loaded from disk  
yet, a major fault occurs, the kernel loads data from the bash  
executable file or a shared library, and then maps it into the  
process address space.

Cheers,
Kyle Moffett

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