linux-kernel - Re: Question on IS

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Message-ID: <4104961b0708082331h4f868113g9a9e76905883619b@mail.gmail.com>
Date:	Thu, 9 Aug 2007 14:31:35 +0800
From:	"jidong xiao" <jidong.xiao@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Question on IS_ERR

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?

Regards
Jason
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