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xen-devel
Re: [Xen-devel] Re: [PATCH 12/13] Unplug emulated disks and nics
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To: |
Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx> |
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Subject: |
Re: [Xen-devel] Re: [PATCH 12/13] Unplug emulated disks and nics |
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From: |
Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> |
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Date: |
Fri, 9 Jul 2010 11:54:24 +0100 |
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Cc: |
"jeremy@xxxxxxxx" <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "stefano@xxxxxxxxxxxxxx" <stefano@xxxxxxxxxxxxxx>, "ddutile@xxxxxxxxxx" <ddutile@xxxxxxxxxx>, "sheng@xxxxxxxxxxxxxxx" <sheng@xxxxxxxxxxxxxxx> |
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Fri, 09 Jul 2010 03:55:24 -0700 |
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<alpine.DEB.2.00.1006211456360.18470@kaball-desktop> <1277136847-13266-12-git-send-email-stefano@xxxxxxxxxxxxxx> <4C2CEF56.4050008@xxxxxxxxxx> <alpine.DEB.2.00.1007051255310.29110@kaball-desktop> <4C34DD1B.3010601@xxxxxxxxxx> <alpine.DEB.2.00.1007081246440.21432@kaball-desktop> <4C362DC3.7000101@xxxxxxxxxx> <1278624583.12109.15.camel@xxxxxxxxxxxxxxxxxxxxx> <4C364A3F.8020900@xxxxxxxxxx> <1278662546.28432.602.camel@xxxxxxxxxxxxxxxxxxxxxx> |
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Alpine 2.00 (DEB 1167 2008-08-23) |
On Fri, 9 Jul 2010, Ian Campbell wrote:
> >
> > > Any guest which uses xvda in its configuration file today will be using
> > > emulated devices but I think that with Stefano's patch and your proposed
> > > change in default on a Xen system without support for unplug will start
> > > using PV devices without unplugging the emulated ones first.
> > >
> > Well, Stefano requires the admin to add unplug switch to kernel cmd line,
>
> In the case where the host platform does not support the unplug protocol
> this is correct and requiring explicit admin action to allow the PV
> frontends to activate is the only safe option WRT the users data.
>
> However if the host platform does support the unplug protocol then this
> is incorrect. In that case the default (in the absence of the command
> line option) is to automatically unplug any device for which a PV driver
> is available and so no command line option will be required in the
> common case. (see xen_unplug_emulated_devices() under the comment "Set
> the default value of xen_emul_unplug depending on...")
>
that's right: on host platforms supporting unplug no command line options
are required; on the other hand if the host platform does not support
unplug then xen_emul_unplug=ignore is required to use PV drivers anyway.
> > so I don't see the harm in defaulting to unplug...
>
> As I described in my previous mail this is unsafe on host platforms
> which do not support unplug. As I describe above it is unnecessary on
> host platforms which do support unplug
>
yep, keep in mind the copy and paste example.
If you are happy about the patch, I'll include it in my next version.
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