linux-kernel - Re: A simple question of sys

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Message-ID: <AANLkTim2NWLE4vhPL-P8JLS3bu9f=V8GqwF0xhE7S87m@mail.gmail.com>
Date:	Mon, 20 Sep 2010 16:28:36 +0800
From:	Rofail Qu <rofail@...il.com>
To:	Américo Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: A simple question of sys_

2010/9/20 Américo Wang <xiyou.wangcong@...il.com>:
> On Fri, Sep 17, 2010 at 02:58:30PM +0800, Rofail Qu wrote:
>>How to use macro IS_ERR() ?
>>
>>It defines as,
>>...
>>#define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO)
>>static inline long __must_check IS_ERR(const void *ptr)
>>{
>>       return IS_ERR_VALUE((unsigned long)ptr);
>>}
>>...
>>so when pass x as a pointer and x>=-MAX_ERRNO (including NULL or any
>>valid address),
>>IS_ERR() will return true!
>
> NULL is not an error pointer, you missed the cast to unsigned long.
Ahh, yeah. A stupid mistake i have.
Thanks.
>
>
>>IS_ERR(x) seems to use on judge if "x" is a valid error number, right?
>>
>
> Strictly speaking, it checks if 'x' is an error pointer.
Then what is the range of a valid pointer?
At least less than (unsigned long)-MAX_ERRNO from this case.
>
>
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