linux-kernel - Re: [patch 07/18] v4l: nopage

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Date:	Sun, 9 Dec 2007 09:10:58 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	npiggin@...e.de, mchehab@...radead.org,
	v4l-dvb-maintainer@...uxtv.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>, Andy Whitcroft <apw@...dowen.org>
Subject: Re: [patch 07/18] v4l: nopage

On Fri, 7 Dec 2007 16:31:42 -0800 Andrew Morton wrote:

> On Wed, 05 Dec 2007 18:15:54 +1100
> npiggin@...e.de wrote:
> 
> > +static int
> > +videobuf_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> >  {
> >  	struct page *page;
> >  
> > -	dprintk(3,"nopage: fault @ %08lx [vma %08lx-%08lx]\n",
> > -		vaddr,vma->vm_start,vma->vm_end);
> > -	if (vaddr > vma->vm_end)
> > -		return NOPAGE_SIGBUS;
> > +	dprintk(3,"fault: fault @ %08lx [vma %08lx-%08lx]\n",
> > +		(unsigned long)vmf->virtual_address,vma->vm_start,vma->vm_end);
> >  	page = alloc_page(GFP_USER | __GFP_DMA32);
> >  	if (!page)
> > -		return NOPAGE_OOM;
> > +		return VM_FAULT_OOM;
> >  	clear_user_page(page_address(page), vaddr, page);
> 
> This didn't compile on sparc64 because `vaddr' is undefined.
> 
> 
> Let us see why:
> 
> #define clear_user_page(page, vaddr, pg)	clear_page(page)
> #define copy_user_page(to, from, vaddr, pg)	copy_page(to, from)
> 
> #define __alloc_zeroed_user_highpage(movableflags, vma, vaddr) \
> 	alloc_page_vma(GFP_HIGHUSER | __GFP_ZERO | movableflags, vma, vaddr)
> 
> root cause: lack of argument checking on x86 due to stupid macros.

Hm, I would have said that the root cause was that Nick removed the
vaddr parameter from the function parameters:

-static struct page*
-videobuf_vm_nopage(struct vm_area_struct *vma, unsigned long vaddr,
-		   int *type)
+static int
+videobuf_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 {

Should the function now produce 'vaddr' internally?


> Could someone *please* start a little project of extirpating this utter
> brain damage?  Convert those macros to typechecked static inlines on x86
> (at least) so this sort of thing (which happens again and again and again)
> is lessened?

Yep, unless someone else is already doing so...

> macros are such miserable things.  I wonder if we could get checkpatch to
> help out here?  


---
~Randy
Features and documentation: http://lwn.net/Articles/260136/
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