Re: [Qemu-devel] Adding an IPMI BMC device to KVM

[Avi Kivity <avi@redhat.com>]

On 05/07/2012 05:30 PM, Anthony Liguori wrote:
> On 05/06/2012 09:39 AM, Avi Kivity wrote:
>> On 05/06/2012 05:35 PM, Anthony Liguori wrote:
>>> On 05/06/2012 08:11 AM, Avi Kivity wrote:
>>> libvirt is essentially the BMC for a virtual guest.  I would suggest
>>> looking at implementing an IPMI interface to libvirt and exposing it
>>> to the guest through a USB RNDIS device.
>>>
>>
>> That's the first option.  One unanswered question is what to do when the
>> guest is down?  Someone should listen for IPMI events, but we can't make
>> it libvirt unconditionally, since many instances of libvirt are active
>> at any one time.
>>
>> Note the IPMI external interface needs to be migrated, like any other.
>
> For all intents and purposes, the BMC/RSA is a separate physical
> machine.  

That's true for any other card on a machine.

> If you really wanted to model it, you would launch two instances of
> QEMU.  The BMC instance would have a virtual NIC and would share a USB
> bus with the slave QEMU instance (probably via USBoIP).  The USB bus
> is how the BMC exposes IPMI to the guest (via a USB rndis adapter),
> remote media, etc.  I believe some BMC's also expose IPMI over i2c but
> that's pretty low bandwidth.

That is one way to do it.  Figure out the interactions between two
different parts in a machine, define an interface for them to
communicate, and split them into two processes.  We don't usually do
that; I believe your motivation is that the two have different power
domains (but then so do NICs with wake-on-LAN support).

> At any rate, you would have some sort of virtual hardware device that
> essentially spoke QMP to the slave instance.  You could just do
> virtio-serial and call it a day actually.

Sorry I lost you.  Which is the master and which is the slave?

> It really boils down to what you are trying to do.  If you want to
> just get some piece of software working that expects to do IPMI, the
> easiest thing to do is run IPMI in the host and use a USB rndis
> interface to interact with it.

That would be most strange.  A remote client connecting to the IPMI
interface would control the power level of the host, not the guest.

> I don't think there's a tremendous amount of value in QEMU making
> itself look like an IBM IMM or whatever HP/Dell's equivalent is.  As I
> said, these stacks are hugely complicated and there are better ways of
> doing out of band management (like talk to libvirt directly).

I have to agree here.

-- 
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