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Date: Tue, 16 Nov 2010 02:48:17 +0100
From: Luigi Rizzo <rizzo@iet.unipi.it>
To: Ivan Voras <ivoras@freebsd.org>
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Cc: svn-src-head@freebsd.org, Luigi Rizzo <luigi@freebsd.org>,
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Subject: Re: svn commit: r215178 - in head: lib/libc/sys sys/kern sys/sys
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On Tue, Nov 16, 2010 at 01:33:53AM +0100, Ivan Voras wrote:
> On 15 November 2010 18:10, Luigi Rizzo <rizzo@iet.unipi.it> wrote:
> 
> > 2. [generic] passing pointers between userland and kernel
> > requires remapping the pointer when going up or down.
> > As the mapping would be application specific, i don't
> > see much use in allowing room for a pointer without kernel code
> > to map userland <-> kernel pointers.
> 
> I'm not thinking of passing a *working* pointer into the kernel but
> used as a cookie, similar to how it's used in kqueue: the intention
> being the application can send and get a pointer which means something
> to the application, not something usable to the kernel.

oh, but then you are thinking of something completely different.
The SO_USER_COOKIE is never returned to the application; it is
only passed to another kernel subsystem, so it must be significant
there, not for the application.

cheers
luigi