linux-kernel - Re: [Xen-devel] [PATCH 3/7] xen/hvm: Xen PV extension of HVM initialization

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Message-ID: <1267521735.11737.23107.camel@zakaz.uk.xensource.com>
Date:	Tue, 2 Mar 2010 09:22:15 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Sheng Yang <sheng@...ux.intel.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Keir Fraser <Keir.Fraser@...citrix.com>,
	Jeremy Fitzhardinge <Jeremy.Fitzhardinge@...rix.com>,
	Ian Pratt <Ian.Pratt@...citrix.com>,
	xen-devel <xen-devel@...ts.xensource.com>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"Yaozu (Eddie) Dong" <eddie.dong@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 3/7] xen/hvm: Xen PV extension of  HVM
 initialization

On Tue, 2010-03-02 at 01:38 +0000, Sheng Yang wrote:
> 
> A annoy thing in pv drivers is that it would test if the domain type
> is _NOT_ XEN_NATIVE. So set the domain to XEN_HVM_DOMAIN would result
> in PV driver initialization then probably panic. 

What _actually_ panics?

Registration of the frontend devices should be completely harmless
(apart from a little wasted RAM) unless a xenbus driver manages to come
up and enumerate the xen bus and cause the ->probe function run.

You should be gating the xenbus startup on the availability of PV
functionality not the individual driver registrations. This keeps the
test in a single easy to maintain place.

Compare with pci_register_driver and all of the callers of that function
-- not a single one of them has an "is_pci_available" test anywhere.

Ian.

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