linux-kernel - Re: [patch 21/26] Xen-paravirt_ops: Use the hvc console infrastructure for Xen console

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Date:	Fri, 16 Mar 2007 09:54:51 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Andi Kleen <ak@....de>, Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, virtualization@...ts.osdl.org,
	xen-devel@...ts.xensource.com, Chris Wright <chrisw@...s-sol.org>,
	Zachary Amsden <zach@...are.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [patch 21/26] Xen-paravirt_ops: Use the hvc console infrastructure for Xen console


* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Implement a Xen back-end for hvc console.

> +	cons = intf->out_cons;
> +	prod = intf->out_prod;
> +	mb();
> +	BUG_ON((prod - cons) > sizeof(intf->out));
> +
> +	while ((sent < len) && ((prod - cons) < sizeof(intf->out)))
> +		intf->out[MASK_XENCONS_IDX(prod++, intf->out)] = data[sent++];
> +
> +	wmb();
> +	intf->out_prod = prod;

> +	prod = intf->in_prod;
> +	mb();
> +	BUG_ON((prod - cons) > sizeof(intf->in));

such mb()'s are typically a sign of "i have no clear idea what SMP 
serialization rules apply here, but something is needed because 
otherwise it breaks" ?

	Ingo
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