On 05/07/2012 10:11 AM, Avi Kivity wrote:
On 05/07/2012 05:55 PM, Anthony Liguori wrote:
For all intents and purposes, the BMC/RSA is a separate physical
machine.
That's true for any other card on a machine.
It has a separate power source for all intents and purposes. If you
think of it in QOM terms, what connects the nodes together ultimately
is the "Vcc" pin that travels across all devices. The RTC is a little
special because it has a battery backed CMOS/clock but it's also
handled specially.
And we fail to emulate it correctly as well, wrt. alarms.
The BMC does not share Vcc. It's no different than a separate
physical box. It just shares a couple buses.
It controls the main power place, reset line, can read VGA and emulate
keyboard, seems pretty well integrated.
Emulating the keyboard is done through USB. How the VGA thing works
is very vendor dependent. The VGA snooping can happen as part of the
display path (essentially connected via a VGA cable) or it can be a
side-band using a special graphics adapter. I think QEMU VNC
emulation is a pretty good analogy actually.
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).
The power still comes from the PCI bus.
Maybe. But it's on when the rest of the machine is off. So Vcc is not
shared.
That's all plumbed through the PCI bus FWIW.
Think of something like a blade center. Each individual blade does
not have it's own BMC. There's a single common BMC that provides an
IPMI interface for all blades. Yet each blade still sees an IPMI
interface via a USB rndis device.
You can rip out the memory, PCI devices, etc. from a box while the
Power is in and the BMC will be unaffected.
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?
The BMC is the master, system being controlled is the slave.
Ah okay. It also has to read the VGA output (say via vnc) and supply
keyboard input (via sendkey).
Right, QMP + VNC is a pretty accurate analogy.
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.
IPMI with a custom backend is what I mean. That's what I mean by an
IPMI -> libvirt bridge. You could build a libvirt client that exposes
an IPMI interface and when you issue IPMI commands, it translate it to
libvirt operations.
This can run as a normal process on the host and then network it to
the guest via an emulated USB rndis device. Existing software on the
guest shouldn't be able to tell the difference as long as it doesn't
try to use I2C to talk to the BMC.
I still like the single process solution, it is more in line with the
rest of qemu and handles live migration better.
Two QEMU processes could be migrated in unison if you really wanted to
support that...
With qemu-system-mips/sh4 you could probably even run the real BMC
software stack if you were so inclined :-)
But even better would
be not to do this at all, and satisfy the remote management requirements
using the existing tools.
Right.
Regards,
Anthony Liguori