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    SubjectRe: [PATCH 0/2 v3] kvm: notify host when guest panicked
    On (Wed) 14 Mar 2012 [16:29:50], 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 start vm like this:
    > qemu ...\
    > -device virtio-serial \
    > -chardev socket,path=/tmp/foo,server,nowait,id=foo \
    > -device virtserialport,chardev=foo,name=port1 ...

    This is sufficient. On the host, you can open /tmp/foo using a custom
    program or nc (nc -U /tmp/foo). On the guest, you can just open
    /dev/virtio-ports/port1 and read/write into it.

    See the following links for more details.

    https://fedoraproject.org/wiki/Features/VirtioSerial#How_To_Test
    http://www.linux-kvm.org/page/Virtio-serial_API

    > You said that there are too many channels. Does it mean /tmp/foo is a channel?

    You can have several such -device virtserialport. The -device part
    describes what the guest will see. The -chardev part ties that to the
    host-side part of the channel.

    /tmp/foo is the host end-point for the channel, in the example above,
    and /dev/virtio-ports/port1 is the guest-side end-point.

    Amit


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