From mboxrd@z Thu Jan  1 00:00:00 1970
From: Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps
Date: Fri, 23 Apr 2010 14:46:07 +0200
Message-ID: <201004231446.07880.arnd@arndb.de>
References: <20100420195349.dab60b1d.yoshikawa.takuya@oss.ntt.co.jp> <201004231427.30725.arnd@arndb.de> <4BD195B7.3070409@redhat.com>
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Cc: Alexander Graf <agraf@suse.de>,
	Fernando Luis =?utf-8?q?V=C3=A1zquez_Cao?=
	<fernando@oss.ntt.co.jp>,
	Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>,
	mtosatti@redhat.com, kvm@vger.kernel.org, kvm-ia64@vger.kernel.org,
	kvm-ppc@vger.kernel.org
To: Avi Kivity <avi@redhat.com>
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On Friday 23 April 2010, Avi Kivity wrote:
> On 04/23/2010 03:27 PM, Arnd Bergmann wrote:
> >
> >> Using a 64-bit integer avoids the problem (though perhaps not sufficient
> >> for s390, Arnd?)
> >>      
> > When there is only a __u64 for the address, it will work on s390 as well,
> > gcc is smart enough to clear the upper bit on a cast from long to pointer.
> >    
> 
> Ah, much more convenient than compat_ioctl.  I assume it part of the 
> ABI, not a gccism?

I don't think it's part of the ABI, but it's required to guarantee
that code like this works:

int compare_pointer(void *a, void *b)
{
	unsigned long ai = (unsigned long)a, bi = (unsigned long)b;

	return ai == bi; /* true if a and b point to the same object */
}

We certainly rely on this already.

	Arnd