Adding an IPMI BMC device to KVM

[Corey Minyard <tcminyard@gmail.com>]

I've been working on adding an IPMI BMC as a virtual device under KVM.  I'm
doing this for two primary reasons, one to have a better test 
environment than
what I have now for testing IPMI issues, and second to be able to better
simulate a legacy environment for customers porting legacy software.

For those that don't know, IPMI is a system management interface.  Generally
systems with IPMI have a small microcontroller, called a BMC, that is 
always on
when the board is powered.  The BMC is capable of controlling power and 
reset
on the board, and it is hooked to sensors on the board (voltage, current,
temperature, the presence of things like DIMMS and power supplies, intrusion
detection, and a host of other things).  The main processor on a system can
communicate with the BMC over a device.  Often these systems also have a LAN
interface that lets you control the system remotely even when it's off.

In addition, IPMI provides access to FRU (Field Replaceable Unit) data that
describes the components of the system that can be replaced.  It also 
has data
records that describe the sensor, so it is possible to directly 
interpret the sensor
data and know what the sensor is measuring without outside data.

I've been struggling a bit with how to implement this.  There is a lot of
configuration information, and you need ways to simulate the sensors.  
This type
of interface is a little sensitive, since it has direct access to the 
reset and power
control of a system.

I was at first considering having the BMC be an external program that KVM
connected to over a chardev, with possibly a simulated LAN interface.  
This has
the advantage that the BMC can run even when KVM is down.  It could even
start up KVM for a "power up", though I'm not sure how valuable that 
would be.
Plus it could be used for other virtual machines.  However, that means 
there is
an interface to KVM over a chardev that could do nasty things, and even be a
possible intrusion point.  It also means there is a separate program to 
maintain.

You could also include the BMC inside of KVM and run it as a separate 
thread.
That way there doesn't have to be an insecure interface.  But the BMC 
will need
a lot of configuration data and this will add a bunch of code to KVM 
that's only
tangentially related to it.  And you would still need a way to simulate 
setting
sensors and such for testing things.

Either way, is this interesting for including into KVM?  Does anyone 
have any
opinions on the possible ways to implement this?

Thanks,

-corey