[libvirt] Writing a new driver for libvirt

[Orr, David-P64407]

Thanks for the response.  I will look that the functions that you have
pointed out for the other drivers here and see how they would be
implemented for ours.  Based on your description I think we would use a
stateless driver, since there are external tools and configurations
available.

To answer your question, it is actually a version of VMware Workstation
with a Hypervisor added to it.  This is for our TVE product here at
General Dynamics; here is a link to the product description:

http://www.gdc4s.com/content/detail.cfm?item=35a995b0-b3b7-4097-9324-2c5
0008b3a75

Another question, how mature is the CIM interface of libvirt.  I have
not had much time to look at it yet, but we would be using it for remote
management.

David Orr
General Dynamics
Software Engineer
David.Orr at gdc4s.com

|-----Original Message-----
|From: Daniel P. Berrange [mailto:berrange at redhat.com]
|Sent: Wednesday, August 27, 2008 10:03 AM
|To: Orr, David-P64407
|Cc: libvir-list at redhat.com
|Subject: Re: [libvirt] Writing a new driver for libvirt
|
|On Wed, Aug 27, 2008 at 09:47:40AM -0700, Orr, David-P64407 wrote:
|> Hey all,
|>
|> I am new to libvirt and have been asked to look at the possibility of
|> writing a libvirt driver for a hypervisor we are using.  I am
wondering
|> if someone can give me the basics on what is involved in
accomplishing
|> this task, what are the basics of writing a new driver?  I have
looked
|> at the documentation posted and been poking around the code and just
|> wanted to ask someone to point me in the right direction.
|
|There are essentially two types of libvirt driver styles. First one I
|call 'stateless', where libvirt doesn't maintain any persistent info
|itself, and just talks to the hypervisor / external tools to implement
|every API. The second style is 'stateful', where libvirt directly
manages
|everything, including persistence of the domain configuration info.
|
|Examples of stateless drivers are  Xen, and OpenVZ.
|
|Examples of stateful drivers are QEMU, LXC
|
|As for choosing which style to use, it depends on the hypervisor in
|question.
|If your hypervisor has ability to storage persistent configuration
data,
|and
|make that available to libvirt, then stateless is the best approac
because
|it provides interoperability with existing tools for that hypervisor.
|
|As for actually implementing things, you can take an incremental
approach,
|adding impls for individual methods as you go. The 'struct _virDriver'
|in src/driver.h file lists all the  APIs you need for a complete impl
|of libvirt on a hypervisor, but you certainly don't need to have all of
|them to get something useful working.
|
|I'd recommend starting with Probe, Open, Close, NumOfDomains,
ListDomains
|and DomainGetInfo. That should be enough to get 'virsh list' working.
|
|Then, add  NumOfDefinedDomains and ListDefinedDomain. That will get the
|virsh list --inactive  command working
|
|Then add  NodeGetInfo and GetCapabilities, which lets 'virsh nodeinfo'
|and 'virsh capabilities' to work.
|
|Then add  DomainDumpXML  to allow a domain config to be queried via
|virsh dumpxml
|
|And then add
DomainCreateLinux/DomainCreate/DomainDefine/DomainUndefine
|to allow new domains to be created, started, and deleted.
|
|At this point you'll have a pretty good impl working. Anything else
beyond
|this point is just a nice bonus.
|
|For parsing XML file, the 'src/domain_conf.h' file APIs should be used.
|There are other useful APIs for internal use in util.h, capabilities.h,
|buf.h, and memory.h.
|
|Also look at the HACKING file for general guidelines.
|
|Finally, ask questions on this list for anything you don't understand.
|The task of writing new hypervisor drivers is not at all documented
|but there are lots of people who can advise you....
|
|
|Out of interest..... what hypervisor are you using ?
|
|Regards,
|Daniel
|--
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