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Date: Sun, 22 Jul 2012 13:39:57 +0200
From: Sasha Levin <levinsasha928@gmail.com>
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Subject: Re: [Qemu-devel] [PATCH v7.5] kvm: notify host when the guest is
 panicked
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To: Wen Congyang <wency@cn.fujitsu.com>
Cc: Gleb Natapov <gleb@redhat.com>, kvm list <kvm@vger.kernel.org>, Jan Kiszka <jan.kiszka@siemens.com>, qemu-devel <qemu-devel@nongnu.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Avi Kivity <avi@redhat.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

On 07/21/2012 10:44 AM, Wen Congyang wrote:
> We can know the guest is panicked when the guest runs on xen.
> But we do not have such feature on kvm.
> 
> Another purpose of this feature is: management app(for example:
> libvirt) can do auto dump when the guest is panicked. If management
> app does not do auto dump, the guest's user can do dump by hand if
> he sees the guest is panicked.
> 
> We have three solutions to implement this feature:
> 1. use vmcall
> 2. use I/O port
> 3. use virtio-serial.
> 
> We have decided to avoid touching hypervisor. The reason why I choose
> choose the I/O port is:
> 1. it is easier to implememt
> 2. it does not depend any virtual device
> 3. it can work when starting the kernel

Was the option of implementing a virtio-watchdog driver considered?

You're basically re-implementing a watchdog, a guest-host interface and a set of protocols for guest-host communications.

Why can't we re-use everything we have now, push a virtio watchdog driver into drivers/watchdog/, and gain a more complete solution to detecting hangs inside the guest.