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From: Ivan Voras <ivoras@freebsd.org>
Date: Tue, 16 Nov 2010 01:33:53 +0100
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To: 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 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.

Without using intptr_t, if an application wants to hang a structure on
the cookie, it needs to maintain its own translation table
(index-to-pointer).