Hi,
Following up from Tim's "Support pure Xen as a hypervisor" proposal last
month[1] I'd like to start working on this and maybe even make a little bit of
progress while I'm at CCC in Denver.
Helpfully James Bulpin managed to get CS + libvirt + xen to start an instance
in a simple configuration. Although the patches[2] are not intended to be
production-ready :) they help highlight some of the areas we need to change.
Some of the areas are:
1. hypervisor detection
Where we currently look for KVM specifically ("lsmod | grep kvm") we could
switch to either detecting any Linux hypervisor (by reading
/sys/hypervisor/type) and assuming if a hypervisor is present then we can use
libvirt on it (is this a fair assumption?) Or we could white-list “kvm” or
“xen”. Or we could query libvirt directly (perhaps via 'virsh capabilities'?)
2. fiddling with the domain.xml
When starting a domain via libvirt the XML configuration has
hypervisor-specific stuff in it. Some of this is easy to change like:
<domain type='kvm'>
obviously becomes
<domain type='xen'>
and
<emulator>/usr/libexec/qemu-kvm</emulator>
should probably be
<emulator>/some/other/path/qemu-dm</emulator>
Some is a bit more invasive (to the VM) such as the virtual hardware type
should be switched from "virtio" to "xen" (and the block device in Linux will
change from /dev/vd* to /dev/xvd*) and we'll have to either implement or work
around the lack of
<channel type='unix'> ...
-- I presume this is a control channel into the system VM. Perhaps we could
implement this in libvirt/libxl using vchan?
3. system VMs?
It would be very convenient if the system VM images could work on both xen and
KVM. This is probably doable as long as we don't bake in virtual hardware
specific information (such as /dev/vda) in the image. We could use the qcow2
format in both cases. What do you think?
… and I’m sure there’s more.
Anyway, feedback would be welcome. If anyone else in Denver wants to chat, then
come grab me later!
Cheers,
Dave Scott
[1]
http://mail-archives.apache.org/mod_mbox/cloudstack-users/201403.mbox/%3ccajgxtbnbmqtq81ralgh2kma7v5wjyzkr3xnyasmkc_br+uk...@mail.gmail.com%3e
[2] https://github.com/jamesbulpin/cloudstack/commits/jamesb_xen_exploratory
