linux-kernel - Re: [03/17] is_vmalloc_addr(): Check if an address is within the vmalloc boundaries

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Message-Id: <167F960F-0A93-4263-8AE6-1B0CEBB2C9D1@cam.ac.uk>
Date:	Wed, 19 Sep 2007 09:44:09 +0100
From:	Anton Altaparmakov <aia21@....ac.uk>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Christoph Lameter <clameter@....com>,
	Christoph Hellwig <hch@....de>, Mel Gorman <mel@...net.ie>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Chinner <dgc@....com>, Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [03/17] is_vmalloc_addr(): Check if an address is within the vmalloc boundaries

On 19 Sep 2007, at 09:09, David Rientjes wrote:
> On Wed, 19 Sep 2007, Anton Altaparmakov wrote:
>>>> Index: linux-2.6/include/linux/mm.h
>>>> ===================================================================
>>>> --- linux-2.6.orig/include/linux/mm.h	2007-09-17 21:46:06.000000000
>>>> -0700
>>>> +++ linux-2.6/include/linux/mm.h	2007-09-17 23:56:54.000000000  
>>>> -0700
>>>> @@ -1158,6 +1158,14 @@ static inline unsigned long vma_pages(st
>>>> 	return (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
>>>> }
>>>>
>>>> +/* Determine if an address is within the vmalloc range */
>>>> +static inline int is_vmalloc_addr(const void *x)
>>>> +{
>>>> +	unsigned long addr = (unsigned long)x;
>>>> +
>>>> +	return addr >= VMALLOC_START && addr < VMALLOC_END;
>>>> +}
>>>
>>> This breaks on i386 because VMALLOC_END is defined in terms of  
>>> PKMAP_BASE
>>> in the CONFIG_HIGHMEM case.
>>
>> That is incorrect.  This works perfectly on i386 and on ALL  
>> architectures
>> supported by Linux.  A lot of places in the kernel already do this  
>> today
>> (mostly hand coded though, eg XFS and NTFS)...
>
> Hmm, really?
>
> After applying patches 1-3 in this series and compiling on my i386  
> with
> defconfig, I get this:
>
> In file included from include/linux/suspend.h:11,
>                  from arch/i386/kernel/asm-offsets.c:11:
> include/linux/mm.h: In function 'is_vmalloc_addr':
> include/linux/mm.h:1166: error: 'PKMAP_BASE' undeclared (first use  
> in this function)
> include/linux/mm.h:1166: error: (Each undeclared identifier is  
> reported only once
> include/linux/mm.h:1166: error: for each function it appears in.)
>
> so I don't know what you're talking about.

Just a compile failure not inherently broken!

Add:

#include <linux/highmem.h> to the top of linux/mm.h and it should  
compile just fine.

Although it may cause a problem as highmem.h also includes mm.h so a  
bit of trickery may be needed to get it to compile...

I suspect that is_vmalloc_addr() should not be in linux/mm.h at all  
and should be in linux/vmalloc.h instead and vmalloc.h should include  
linux/highmem.h.  That would be more sensible than sticking a vmalloc  
related function into linux/mm.h where it does not belong...

Best regards,

	Anton
-- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer, http://www.linux-ntfs.org/


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