linux-kernel - Re: [Qemu-devel] [PATCH v8] kvm: notify host when the guest is panicked

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Date:	Mon, 13 Aug 2012 13:48:39 -0600
From:	Eric Blake <eblake@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Wen Congyang <wency@...fujitsu.com>,
	Gleb Natapov <gleb@...hat.com>, kvm list <kvm@...r.kernel.org>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	qemu-devel <qemu-devel@...gnu.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Avi Kivity <avi@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [Qemu-devel] [PATCH v8] kvm: notify host when the guest is panicked

On 08/13/2012 12:21 PM, Marcelo Tosatti wrote:
> On Wed, Aug 08, 2012 at 10:43:01AM +0800, 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
> 
> How about searching for the "Kernel panic - not syncing" string 
> in the guests serial output? Say libvirtd could take an action upon
> that?
> 
> Advantages:
> - It works for all architectures.
> - It does not depend on any virtual device.

But it _does_ depend on a serial console, and furthermore requires
libvirt to tee the serial console (right now, libvirt can treat the
console as an opaque pass-through to the end user, but if you expect
libvirt to parse the serial console for a particular string, you've lost
some efficiency).

> - It works as early as serial console output does (panics before
> that should be rare).
> - It allows you to see why the guest panicked.

I think your arguments for a serial console have already been made and
refuted in earlier versions of this patch series, which is WHY this
series is still applicable.

-- 
Eric Blake   eblake@...hat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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