Re: [Qemu-devel] [PATCH 0/2 v3] kvm: notify host when guest panicked

[Avi Kivity]

On 03/14/2012 11:53 AM, Wen Congyang wrote:
> At 03/14/2012 05:24 PM, Avi Kivity Wrote:
> > On 03/14/2012 10:29 AM, Wen Congyang wrote:
> >> At 03/13/2012 06:47 PM, Avi Kivity Wrote:
> >>> On 03/13/2012 11:18 AM, Daniel P. Berrange wrote:
> >>>> On Mon, Mar 12, 2012 at 12:33:33PM +0200, Avi Kivity wrote:
> >>>>> On 03/12/2012 11:04 AM, Wen Congyang wrote:
> >>>>>> Do you have any other comments about this patch?
> >>>>>>
> >>>>>
> >>>>> Not really, but I'm not 100% convinced the patch is worthwhile.  It's
> >>>>> likely to only be used by Linux, which has kexec facilities, and you can
> >>>>> put talk to management via virtio-serial and describe the crash in more
> >>>>> details than a simple hypercall.
> >>>>
> >>>> As mentioned before, I don't think virtio-serial is a good fit for this.
> >>>> We want something that is simple & guaranteed always available. Using
> >>>> virtio-serial requires significant setup work on both the host and guest.
> >>>
> >>> So what?  It needs to be done anyway for the guest agent.
> >>>
> >>>> Many management application won't know to make a vioserial device 
> >>>> available
> >>>> to all guests they create. 
> >>>
> >>> Then they won't know to deal with the panic event either.
> >>>
> >>>> Most administrators won't even configure kexec,
> >>>> let alone virtio serial on top of it. 
> >>>
> >>> It should be done by the OS vendor, not the individual admin.
> >>>
> >>>> The hypercall requires zero host
> >>>> side config, and zero guest side config, which IMHO is what we need for
> >>>> this feature.
> >>>
> >>> If it was this one feature, yes.  But we keep getting more and more
> >>> features like that and we bloat the hypervisor.  There's a reason we
> >>> have a host-to-guest channel, we should use it.
> >>>
> >>
> >> I donot know how to use virtio-serial.
> > 
> > I don't either, copying Amit.
> > 
> >> I start vm like this:
> >> qemu ...\
> >>    -device virtio-serial \
> >>   -chardev socket,path=/tmp/foo,server,nowait,id=foo \
> >>   -device virtserialport,chardev=foo,name=port1 ...
> >>
> >> You said that there are too many channels. Does it mean /tmp/foo is a 
> >> channel?
> > 
> > Probably.
>
> Hmm, if we use virtio-serial, the guest kernel writes something into the 
> channel when
> the os is panicked. Is it right?

Right.

> If so, is this channel visible to guest userspace? If the channle is visible 
> to guest
> userspace, the program running in userspace may write the same message to the 
> channel.
>

Surely there's some kind of access control on channels.

-- 
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