linux-kernel - RE: return negative number for unsigned long function in kernel

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Message-ID: <314BE1148B8C8D468A05944FDF577583069B0222@MRE02.enterprise.com>
Date:	Wed, 7 Mar 2007 08:31:09 -0500
From:	"Chen, Dongliang" <Chen.D@...-t.com>
To:	"H. Peter Anvin" <hpa@...or.com>, "Andreas Schwab" <schwab@...e.de>
Cc:	<linux-kernel@...r.kernel.org>
Subject: RE: return negative number for unsigned long function in kernel

Peter & Andreas,

Thank you very much for your help. 

I understood that the kernel error numbers are limited. The largest
error number for i386 (kernel 2.6) is 131 so far.  Assume that the
virtual address returned from do_mmap_pgoff will never exceed (unsigned
long)(-1000L), which is in the address range one page below the maximum
virtual address, then IS_ERR_VALUE() should work.

Dongliang Chen

Staff Engineer
EMS Technologies, Inc - Defense & Space Systems
660 Engineering Dr 
Norcross, GA 30092
Tel: 770-263-9200 x 4379

-----Original Message-----
From: H. Peter Anvin [mailto:hpa@...or.com] 
Sent: Tuesday, March 06, 2007 7:39 PM
To: Chen, Dongliang
Cc: linux-kernel@...r.kernel.org
Subject: Re: return negative number for unsigned long function in kernel

H. Peter Anvin wrote:
>If you want to test for errorness, you could use the macro 
>IS_ERR_VALUE().  Unfortunately the macro isn't all that safe, in that
it 
>will give you the wrong answer if it's ever used on something that 
>*isn't* an unsigned long.

-----Original Message-----
From: Andreas Schwab [mailto:schwab@...e.de] 
Sent: Tuesday, March 06, 2007 2:06 PM
To: Chen, Dongliang
Cc: linux-kernel@...r.kernel.org
Subject: Re: return negative number for unsigned long function in kernel

Andreas Schwab wrote:
>The return value is directly passed to user space (it's the guts of the
>mmap syscall).  The glibc wrapper transforms it appropriately so that
errno >is set and -1 is returned if there is an error.

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