linux-kernel - Re: Question on IS

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Message-ID: <46BAC093.1000503@zytor.com>
Date:	Thu, 09 Aug 2007 00:21:55 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	jidong xiao <jidong.xiao@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Question on IS_ERR

jidong xiao wrote:
> On 8/9/07, H. Peter Anvin <hpa@...or.com> wrote:
>> No.  There is no requirement that the pointer is page-aligned.  The last
>> page of the address space is (in the Linux kernel) invalid by
>> definition, so there are in effect three kinds of pointers in the Linux
>> kernel: valid pointers, NULL, and ERR_PTR()s.
>>
>>        -hpa
>>
> 
> Regarding "The last page of the address space is invalid by definition",
> I am wondering why do we define the last page as invalid.
> The reason for defining this is just because we want to take use of
> the error number handling?
> 

Pretty much.

	-hpa
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