[Libvir] Ruby bindings for libvirt

[Meng Kuan]

On 31 Aug 2007, at 1:56 AM, David Lutterkort wrote:

> On Thu, 2007-08-30 at 17:32 +0800, Meng Kuan wrote:
>>    [root at dell1 libvirt_ruby]# irb
>>    irb(main):001:0> require 'libvirt_ruby'
>>    => true
>>    irb(main):002:0> conn = Libvirt_ruby.virConnectOpenReadOnly("")
>>    => #<SWIG::TYPE_p__virConnect:0x2aaaaabc46c8>
>>    irb(main):003:0>  dom = Libvirt_ruby.virDomainLookupByID(conn, 0)
>>    => #<SWIG::TYPE_p__virDomain:0x2aaaaabb5df8>
>>    irb(main):004:0> ret = Libvirt_ruby.virDomainGetInfo(dom, info)
>>    NameError: undefined local variable or method `info' for  
>> main:Object
>>            from (irb):4
>>    irb(main):005:0>
>>
>> I am not sure how to create and pass in a ptr to a virDomainInfo
>> struct object into the virDomainGetInfo call within ruby.
>
> virDomainGetInfo uses the info structure to return the info. It's  
> going
> to be hard to replicate that 1-1 in Ruby; but you'd get a much better,
> more Ruby-ish API if you structure the various libvirt calls into a
> number of classes (Libvirt::Connection, Libvirt::Domain,
> Libvirt::DomainInfo etc.) so that your above code would look something
> like
>
>   conn = Libvirt::connectReadOnly("") # Returns a Libvirt::Connection
>   dom = conn.lookupDomainByID(0)      # Returns a Libvirt::Domain
>   info = dom.getInfo()                # Returns a Libvirt::DomainInfo
>

What I was missing was the "-autorename" argument when calling swig,  
i.e.

   swig -ruby -autorename libvirt.i

After compile and install of the resulting libvirt.so, here's what I  
can do in ruby:

   require 'libvirt'
   conn = Libvirt.vir_connect_open_read_only("")
   dom = Libvirt.vir_domain_lookup_by_id(conn, 0)
   info = Libvirt::VirDomainInfo.new
   Libvirt.vir_domain_get_info(dom, info)
   puts info.state   # => 1
   puts info.maxMem  # => 1047552

It's far from ruby-ish, but it works.


> I doubt that you can do that with Swig, but it's not terribly hard to
> write bindings by hand. Have a look at existing bindings, e.g. for
> rpm[1] or gamin[2].

I'll probably look into writing bindings by hand later on, but at  
this time due to my inexperience with C programming and lack of time,  
I am thinking of writing Ruby classes that wrap these C calls and use  
those Ruby classes instead.

Thanks for the pointers, David. Much appreciated.

cheers,
mengkuan