[Libvir] Dom0 and entitlement

Richard W.M. Jones rjones at redhat.com
Mon Jan 21 11:48:56 UTC 2008

Katti, Vadiraj (STSD-Openview) wrote:
> Hi,
>  I've some questions related to xen. Can anybody help me regarding the 
> following questions.

These sound more like Xen questions, but anyway ...

> 1. Is dom0 a logical system(like any other vm's that are configured on 
> it) ? If yes, then all xm commands should be applicable to it (ex : 
> vcpu-set) .

In Xen, dom0 is "just" one of the normal guests that runs on top of the 
hypervisor.  However it has special / privileged treatment and is 
essential to the system.

XenSource have discussed scenarios where there are multiple dom0's, but 
I don't know if this has ever been implemented.

> 2. /proc on dom0 reflects the physical or logical utilization.

If I understand the question, then /proc on dom0 reflects the state of 
the dom0 guest, not the underlying system.  libvirt gives you methods to 
access status of the whole system (but only from dom0 because it 
requires some privileged calls).

> 3. Is there any entitelment concept in xen for cpu and memory? What is 
> cpu weight used for and how is set.
> 4. virt-manager shows physical or logical utilization (cpu, memory)

virt-manager uses libvirt, so it shows the state of the whole machine.

> 5. How do i get the IP address of each of the guests from dom0 ?

You can't.  Guests can send out packets with any source IP they like, 
and its up to DHCP / manual configuration / firewall rules to enforce 
(or not) local policy.  A guest may have several network interfaces or 
none at all.

> 6. What are the interfaces in domU to tell me that its a guest (or dom0) 
> and also the type of virtualization ( eg. XEN/ VMWARE etc  )

A guest can discover that it is running under virtualization very easily 
(even a fullvirt guest).  Probably the best place to start is to use 
something like HAL (http://www.freedesktop.org/wiki/Software/hal) to 
examine the hardware available.  You'll see that emulated processors and 
devices have QEMU-related names under Xen and KVM, since both Xen and 
KVM use QEMU to emulate devices.

For example, on a fullvirt guest running under KVM:

   $ hal-device
   4: udi = '/org/freedesktop/Hal/devices/storage_serial_QM00001'
     info.product = 'QEMU HARDDISK'  (string)

   5: udi = '/org/freedesktop/Hal/devices/storage_serial_QM00003'
     info.product = 'QEMU CD-ROM'  (string)

   $ grep QEMU /proc/cpuinfo
   model name     : QEMU Virtual CPU version 0.9.0

The presence of an RTL-8139 network card and Cirrus Logic GD 5446 
graphics card is a bit of a giveaway too.  These are the standard 
devices that QEMU emulates, but under Xen paravirt you'll have 
Xen/paravirt-specific devices.

A Xen dom0 specifically will have a file '/proc/xen/privcmd'.

There are so many different types of virtualization, and degrees of 
virtualization, no one to my knowledge has written an exhaustive set of 
tests for this.


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