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

To: Sheng Yang <sheng@xxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 3/7] xen/hvm: Xen PV extension of HVM initialization
From: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Date: Tue, 2 Mar 2010 09:22:15 +0000
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, "Yaozu \(Eddie\) Dong" <eddie.dong@xxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, Jeremy Fitzhardinge <Jeremy.Fitzhardinge@xxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>
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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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