linux-kernel - Re: [PATCH LINUX v5] xen: event channel arrays are xen_ulong

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Date:	Thu, 7 Mar 2013 07:17:42 +0000
From:	Ian Campbell <ian.campbell@...rix.com>
To:	Will Deacon <will.deacon@....com>
CC:	Rob Herring <robherring2@...il.com>,
	"xen-devel@...tsxen.org" <xen-devel@...ts.xen.org>,
	"Keir (Xen.org)" <keir@....org>,
	"Stefano Stabellini" <Stefano.Stabellini@...citrix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"Tim (Xen.org)" <tim@....org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jan Beulich <JBeulich@...e.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Nicolas Pitre <nico@...xnic.net>
Subject: Re: [PATCH LINUX v5] xen: event channel arrays are xen_ulong_t and
 not unsigned long

On Thu, 2013-03-07 at 03:17 +0000, Will Deacon wrote:
> > I looked and couldn't see an existing 64 bit xchg, was I looking in the
> > wrong place? Ah, wait, I see atomic64_xchg now. But that needs an
> > atomic64_t while I have a xen_ulong_t (which == 64 bits on ARM). This is
> > a kernel<->hypervisor ABI so I can't just change it to an atomic64_t. I
> > suppose I could cast (see below, untested) but that seems rather icky.
> 
> You can play some container_of tricks, like we do in cmpxchg64 to get this
> right. Alternatively, we could look at an xchg8 implementation which some
> other architectures have (although they seem to be 64-bit machines).

I went with the container of trick + appropriate Kconfig depends and
sent a patch out a couple of seconds ago.

Thanks for your help/advice!

Ian.

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