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Re: [Xen-devel] [PATCH 2/6] xen/hvm kexec: unregister shutdown+sysrq wat

To: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 2/6] xen/hvm kexec: unregister shutdown+sysrq watches during reboot
From: Olaf Hering <olaf@xxxxxxxxx>
Date: Thu, 28 Jul 2011 13:02:19 +0200
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>
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On Thu, Jul 28, Ian Campbell wrote:

> Getting into the kdump kernel is a kexec like operation though and
> shares many of the code paths, doesn't it?

The big difference is that kdump is entered in an unreliable state,
while kexec is a controlled reboot.

> > > If this requires changes outside the kernel (e.g. state reset helpers
> > > in hypervisor or tools) - so be it.
> > 
> > Are you suggesting that there have to be ways for a domU to query the
> > state of its registered watches and shut them all down during very early
> > boot?
> Perhaps the xenstore protocol could be enhanced with a mechanism to
> clear all existing watches? A kernel could call that at start of day.

I wonder why xenstore knows that sysrq and shutdown nodes are busy,
while the device, backend and state files can be watched twice.


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