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Date: Tue, 30 Oct 2012 23:12:56 -0200
From: Marcelo Tosatti <mtosatti@redhat.com>
Message-ID: <20121031011256.GC12325@amt.cnet>
References: <0a2274eccf1b1dd420f16359f7e1de74fa2f9fbe.1351131144.git.hutao@cn.fujitsu.com>
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Subject: Re: [Qemu-devel] [PATCH v11] kvm: notify host when the guest is
	panicked
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To: Hu Tao <hutao@cn.fujitsu.com>
Cc: Andrew Jones <drjones@redhat.com>, 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>, Blue Swirl <blauwirbel@gmail.com>, Avi Kivity <avi@redhat.com>, Luiz Capitulino <lcapitulino@redhat.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Sasha Levin <levinsasha928@gmail.com>

On Thu, Oct 25, 2012 at 11:42:32AM +0800, Hu Tao 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

It has been asked earlier why a simple virtio device is not usable
for this (with no response IIRC).

Also, there is no high level documentation: purpose of the interface,
how a management application should use it, etc.