linux-kernel - Re: A simple question of sys

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Message-ID: <20100920074838.GB5503@cr0.nay.redhat.com>
Date:	Mon, 20 Sep 2010 15:48:38 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Rofail Qu <rofail@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: A simple question of sys_

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.


>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.

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