linux-kernel - Re: [PATCH 00/16] mm: prepare for converting vm->vm

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Date:	Fri, 30 Mar 2012 03:19:45 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	akpm@...ux-foundation.org, khlebnikov@...nvz.org,
	minchan@...nel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	hughd@...gle.com, benh@...nel.crashing.org, linux@....linux.org.uk
Subject: Re: [PATCH 00/16] mm: prepare for converting vm->vm_flags to 64-bit

On Fri, Mar 23, 2012 at 12:19:36PM -0400, KOSAKI Motohiro wrote:
> On 3/22/2012 5:28 PM, Al Viro wrote:
> > On Thu, Mar 22, 2012 at 02:26:47PM -0700, Andrew Morton wrote:
> >> It would be nice to find some way of triggering compiler warnings or
> >> sparse warnings if someone mixes a 32-bit type with a vm_flags_t.  Any
> >> thoughts on this?
> >>
> >> (Maybe that's what __nocast does, but Documentation/sparse.txt doesn't
> >> describe it)
> > 
> > Use __bitwise for that - check how gfp_t is handled.
> 
> Hmm..
> 
> If now we activate __bitwise, really plenty driver start create lots warnings.
> Does it make sense?

Huh?  Why would they?  Just adjust definitions of VM_... to include
force-cast to vm_flags_t and we should be OK...

> In fact, x86-32 keep 32bit vma_t forever. thus all x86 specific driver don't
> need any change. Moreover many ancient drivers has no maintainer and I can't
> expect such driver will be fixed even though a warning occur.

What warning?  If something does manual vma->vm_flags = 0xwhatever, then yes,
we do want it dealt with.  If it's vma->vm_flags |= VM_something, there should
be no warnings at all...
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