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Re: [Xen-devel] Race condition in /etc/xen/scripts/block

To: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Race condition in /etc/xen/scripts/block
From: Bastian de Groot <degroot@xxxxxxxxxxxxx>
Date: Fri, 16 Jul 2010 13:28:39 +0200
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Hi James, 

thank you for your fast reply. The VMs are not PV domains, so the problem 
seems to be pretty much the same as yours. I would be very glad if you could 
publish the patch, so that I can test if it works for me.

Thanks again,

Am Freitag 16 Juli 2010 12:07:29 schrieben Sie:
> > Hello,
> >
> > I am trying to figure out the behavior of the hook-script for block
> devices
> > (/etc/xen/scripts/block).
> >
> > Here is the problem:
> > I want to start a VM. It shall boot from a dm-device, which is setup
> by a
> > script executed in the script /etc/xen/scripts/block. The dm-device
> doesn't
> > exist when "xm start " is executed .
> >
> > When I place the setup script at the top of the block-script,
> everything
> > works fine (http://pastebin.com/UYYbGupC). But when the script is
> placed in
> > the phy case branch of the block-script, the VM won't start
> > (http://pastebin.com/iPdJ65AH).
> >
> > Whether the VM starts or not, also depends on the runtime of the setup
> script.
> > When the script is executed fast, it is much more likely that the VM
> starts.
> > So, is there a way to setup a device in the hook-script?
> >
> > My configuration: Xen 3.4 on a 2.6.32 Kernel
> >
> > I would appreciate your help on that very much,
> > Bastian
> I've seen a similar thing when using drbd. When you run 'xm start' the
> drbd device is 'secondary' and one of the things the block setup script
> does is make it 'primary' which means it can be opened/accessed.
> Unfortunately most of the time qemu-dm has already tried to open it and
> failed by then.
> In that case I solved it by having qemu-dm try to open in a loop with a
> sleep each time. Not the most elegant solution but it works.
> I don't think the same problem exists with PV domains so if you are
> using a PV DomU then I've probably not been much help...
> James

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