linux-kernel - Re: mmaping a kernel buffer to user space

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Message-ID: <653402b90610311144y790c62e7ve1cd00389d42b9b5@mail.gmail.com>
Date:	Tue, 31 Oct 2006 19:44:19 +0000
From:	"Miguel Ojeda" <maxextreme@...il.com>
To:	"Jiri Slaby" <jirislaby@...il.com>
Cc:	"Guillermo Marcus" <marcus@...uni-mannheim.de>,
	linux-kernel@...r.kernel.org
Subject: Re: mmaping a kernel buffer to user space

On 10/31/06, Jiri Slaby <jirislaby@...il.com> wrote:
> Guillermo Marcus wrote:
> > Hi Jiri,
> >
> > The fact that it does not works with RAM is well documented in LDD3,
> > pages 430++. It says (and I tested) that remap_xxx_range does not work
> > in this case. They suggest a method using nopage, similar to the one I
> > implement.
>
> Could somebody confirm, that this still holds?
>

Hum, I also tried it some days ago and it didn't work for me, so I
read LDD3 and I found such explanation about such limitation of
remap_pfn_range(). I heard then that changed in 2.6.15 because of the
new flag; so I have had the same situation.

If it is possible to remap a kernel buffer to userspace with
remap_pfn_range, how should be done the right way?

> > I do not see why remap_xxx_range has the limitation, but it is there.
> > The question is then: can the limitation be removed, or can we implement
> > a new function that maps RAM all at once without the need for a nopage
> > implementation?
> >
> > In any case, here is the code.
>
> Hmm, interesting. I used remap_pfn_range for this purpose today and it worked (I
> double-checked this). I should probably do the rework :(.
>
> regards,
>
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