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From: John Alvord <jalvo@mbay.net>
To: Luis Miguel Correia Henriques <umiguel@alunos.deis.isec.pt>
Cc: <linux-kernel@vger.kernel.org>
Subject: Re: copy to user
Date: Tue, 20 Nov 2001 13:28:29 -0800
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On Tue, 20 Nov 2001 20:54:42 +0000 (WET), Luis Miguel Correia
Henriques <umiguel@alunos.deis.isec.pt> wrote:

>The reason that I need it to spend CPU time is that I'm developing a fault
>injector. The purpose of a fault injection tool is, as you could imagine,
>to test some critical systems and it's capacity to recover from fails. The
>reason for changing the code of a process is that process must be delayed
>but without leaving the CPU - everything must look like nothing wrong is
>happening, except for other processes that are waiting for something from
>the delayed process...
>
>Maybe I should have explained this before... sorry.
>
>I suppose now you can understand why SIGSTOP won't work. Hope you can help
>me :)
>
>About using udelay... this soluction seemed fine to me at first but if I
>hang the CPU with udelay the scheduler will no be doing it's job (isn't
>it?). This would give me even more intrusiveness (another requirement: the
>less intrusiveness as possible).
>
>Isn't there any doubt that copy_to_user can handle my problem? When I use
>it to change CS, this function returns the correct number of bytes (and no
>error) but, when I try to read... the old data is still there. I suppose
>there is a page/segment protection against writing to CS, isn't it?

Maybe the kernel logic could lock the relevent page so it couldn't be
paged out...

john alvord
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