[Libvir] what is virt-install doing differently?

[Daniel P. Berrange]

On Wed, Jan 31, 2007 at 03:09:48PM -0500, Aron Griffis wrote:
> You, Yongkang wrote:  [Thu Jan 25 2007, 10:26:33AM EST]
> > Thanks for the information. I have check /var/log/xen/xend.log.
> > Found something interesting. When using virt-install to install VTI
> > domain, it seemed didn't parse the right vcpu number to qemu-dm.
> > Please look at the following log:
> > 
> > 1. The spawning qemu log, when installation by virt-intall with vcpu=4:
> > ---------------------
> > [2007-01-25 23:14:13 xend 2817] INFO (image:418) spawning device models: /usr/lib/xen/bin/qemu-dm ['/usr/lib/xen/bin/qemu-dm', '-d', '9', '-m', '1024', '-boot', 'c', '-acpi', '-domain-name', 'test', '-net', 'nic,vlan=1,macaddr=00:16:3e:0a:d2:86,model=rtl8139', '-net', 'tap,vlan=1,bridge=xenbr0', '-vncunused', '-vnclisten', '127.0.0.1']
> > ~~~~~~~~~~~~
> > 
> > 2. The spawning qemu log, when use command "xm create":
> > ------------------------
> > [2007-01-25 17:13:13 xend 2817] INFO (image:418) spawning device models: /usr/lib/xen/bin/qemu-dm ['/usr/lib/xen/bin/qemu-dm', '-d', '7', '-m', '1024', '-boot', 'd', '-vcpus', '4', '-acpi', '-domain-name', 'ExampleVTIDomain', '-net', 'nic,vlan=1,macaddr=00:16:3e:31:42:c4,model=rtl8139', '-net', 'tap,vlan=1,bridge=xenbr0', '-vncviewer']
> > ~~~~~~~~~~~
> > 
> > There is "-vcpus 4" in the 2nd log. It means qemu would create up
> > a 4 vpucs VTI domain. 
> > 
> > For the situation 1, although qemu doesn't get any information about
> > "vcpu=4". But xen has already prepared 2 vcpus to qemu. Will it be
> > the problem? 
> 
> I'm looking through the code now to see if I can find where this is
> going awry, but while I'm looking, does this ring a bell for you?

Ok, I can see what's happening here. The SEXPR that we feed to XenD
when creating a guest with libvirt looks like this:

(vm
    (name XenGuest2)
    (memory 394)
    (maxmem 579)
    (vcpus 3)
    (uuid c7a5fdb2-cdaf-9455-926a-d65c16db1809)
    (image
        (hvm
            (kernel /usr/lib/xen/boot/hvmloader)
            (device_model /usr/lib/xen/bin/qemu-dm)
            (pae 1)
            (boot c)
            (vnc 1)
            (vncunused 1)
            (display :0.0)
            (xauthority /root/.xauthcmQHfd)
            (acpi 1)
            (apic 1)
            (vncpasswd 123456)
        )
    )
    (device (vbd (uname phy:/dev/HostVG/XenGuest2) (dev hda) (mode w)))
    (device (vif (bridge xenbr1) (mac 00:16:3E:66:92:9C) (type ioemu)))
)


But when you use 'xm create' it is ever so slightly different:

(vm
    (name XenGuest2)
    (memory 394)
    (maxmem 579)
    (vcpus 3)
    (uuid c7a5fdb2-cdaf-9455-926a-d65c16db1809)
    (image
        (hvm
            (kernel /usr/lib/xen/boot/hvmloader)
            (device_model /usr/lib/xen/bin/qemu-dm)
            (pae 1)
            (vcpus 3)
            (boot c)
            (vnc 1)
            (vncunused 1)
            (display :0.0)
            (xauthority /root/.xauthcmQHfd)
            (acpi 1)
            (apic 1)
            (vncpasswd 123456)
        )
    )
    (device (vbd (uname phy:/dev/HostVG/XenGuest2) (dev hda) (mode w)))
    (device (vif (bridge xenbr1) (mac 00:16:3E:66:92:9C) (type ioemu)))
)

Notice that the '(vcpus 3)' bit is duplicated twice in the SEXPR that
xm sends - once at top level and once within (image). It looks like
when creating HVM guests you need both set to get it to work correctly.
Frankly this is utterly insane - XenD should simply copy the top level
value for vcpus into the (image) block as needed.

Since we need compatability with all Xen 3.0.x series codebases, it looks 
like we'll need to do a tiny bit of magic in libvirt to also send the 
vcpus stuff twice for HVM. Urgh :-(

Regards,
Dan.
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