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Date: Sat, 28 Oct 2006 09:29:06 -0700
From: Andrew Morton <akpm@osdl.org>
To: "Robert P. J. Day" <rpjday@mindspring.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: why "probe_kernel_address()", not "probe_user_address()"?
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On Sat, 28 Oct 2006 11:56:24 -0400 (EDT)
"Robert P. J. Day" <rpjday@mindspring.com> wrote:

> 
>   it seems odd that the purpose of the "probe_kernel_address()" macro
> is, in fact, to probe a *user* address (from linux/uaccess.h):
> 
> #define probe_kernel_address(addr, retval)              \
>         ({                                              \
>                 long ret;                               \
>                                                         \
>                 inc_preempt_count();                    \
>                 ret = __get_user(retval, addr);         \
>                 dec_preempt_count();                    \
>                 ret;                                    \
>         })
> 
>   given that that routine is referenced only 5 places in the entire
> source tree, wouldn't it be more meaningful to use a more appropriate
> name?
> 

You'll notice that all callers are indeed probing kernel addresses.  The
function _could_ be used for user addresses and could perhaps be called
probe_address().

One of the reasons this wrapper exists is to communicate that the
__get_user() it is in fact not being used to access user memory.