[Libvir] RFC: A more convenient 'virsh create' command

Daniel P. Berrange berrange at redhat.com
Fri Aug 25 22:00:50 UTC 2006

On Fri, Aug 25, 2006 at 11:55:22PM +0200, Karel Zak wrote:
> On Fri, Aug 25, 2006 at 05:46:28PM +0100, Daniel P. Berrange wrote:
> > The current implementation of 'virsh create' takes an XML file as its only
> > parameter & creates a domain from this. This is great if you have a suitable
> > XML file already, but if you are just trying to automate some simple tasks
> > from the shell then the need to use XML is a little cumbersome. Thus I was
> > thinking perhaps we could have an alternate way to define a new VM (keep
> > the current XML based way too of course)
> > 
> > QEMU for example makes it very easy to launch a new VM:
> > 
> >    qemu -m 256 -hda /path/to/image.dsk -hdc /path/to/boot.iso 
> > 
> > Taking inspiration from this syntax we could allow:
> > 
> >    virsh start -m 256 -hda /path/to/image.dsk -hdc /path/to/boot.iso -name Foo
> > 
> > Internally, the 'start' command would simply transform these command
> > line args into the neccessary libvirt XML and then call the normal
> > create functions.
> > 
> > Another way would be have a 'genxml' command, which accepted these list
> > of devices / config properties & then printed out appropriate XMl. This
> > could be piped to the regular 'virsh create' command
> > 
> >   virsh genxml -m 256 -hda /path/to/image.dsk -hdc /path/to/boot.iso \
> >    -name Foo  | virsh create -
>   What use better command name instead "genxml"? For example "domgen".
>   (we have dominfo, domstate, ...). 
>   Same odd commad name is "dumpxml"...  XML of what? It should be
>   renamed to "domdump".

Well we can't break API - and there's a whole bunch of commands which
don't start with 'dom' prefix - pause, shutdown, create, resume, vcpuinfo,
setmem, setmaxmem, to name just a few - apart from nodeinfo & create
essentially every command performs some kinda of operation on a domain.
So I think needing to prefix all with 'dom' is a little overkill.

I agree that 'genxml' is a terrible name I suggest though - domgen is
nicer - or as below - just allow the args to be passed to regular create
command instead of an XML file path.

> > This isn't so critical for Xen, because people are already used to writing
> > config files before creating the domain, but when we get a QEMU backend
> > i think such a convenient method for defining new VMs will be neccessary
> > to encourage users to use virsh instead of manually calling 'qemu'. Even
> > for Xen users it would make shell script easier though :-)
>  I can imagine more commands like:
>      virsh> bufread /etc/xen/Foo.xml
>      virsh> bufedit Foo -hdc /path/file.img 
>      virsh> create --frombuf Foo
>  I think it could be nice for playful admins and developers. Or is
>  over engineering? ;-)

A little over-engineering - if we want to let people override contents of
an XML file - i'd just combine both into one, eg

    virsh create  -hda /path/file.img  /etc/xen/Foo.xml

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