[libvirt] XML support for arbitrary command line arguments

Harsh Bora harsh at linux.vnet.ibm.com
Tue Sep 14 05:33:04 UTC 2010


Hi Eric,
thanks for an early response.
I came across an interesting feature provided by VirtualBox and which is 
supported by QEMU as well (with 9p server in place) of sharing a folder 
on host with the guest. As the shared folder is on same physical 
machine, one need not necessarily use nfs/cifs to access the underlying 
storage and should be allowed to use more efficient means to access the 
same.

As QEMU provides support for accessing such shared directory with the 
help of 9p server, and therefore need to be passed additional 
commandline argument while starting, I wanted to test it using XML and 
libvirt.

Later, came the idea to my mind why not the VM management softwares 
(necessarily) have an option asking the user if he/she wants to share a 
folder on host with guest, and let it create an XML accordingly which 
will be passed to hypervisors and let the hypervisors decide how to do 
it efficiently.

I had discussed this with Matthias Bolte on #virt and he seems convinced 
to the idea as well.
So, if the idea looks good to everyone, we can have something like:

<shareddir fstype=local path='/folder/to/share' mount_tag='unique_tag' 
security_model='as_applicable'>

where    fstype = local filesystem
          path = path to export/share
          mount_tag = unique id which is visible in guest to mount this 
share
          security_model = passthrough/mapped/none

regards,
Harsh


On 09/13/2010 11:47 PM, Eric Blake wrote:
> On 09/13/2010 11:56 AM, Harsh Bora wrote:
>> Hi,
>> Is there a way by which I can pass arbitrary command line args to a
>> hypervisor (Qemu), and let the hypervisor decide what to do with it?
>>
>> I mean, is there a generic XML tag define which can be used to specify
>> 'n' number of command line args which are blindly passed to hypervisor
>> to process?
>
> Yes, as of libvirt 0.8.3.  It isn't yet well documented, but the list 
> has had several mails on the topic, such as:
> https://www.redhat.com/archives/libvir-list/2010-August/msg00589.html
>
> Meanwhile, what particular command line feature are you missing? 
> Ultimately, we would rather add direct libvirt XML support for all 
> qemu features, since that is more stable than using <qemu:commandline> 
> at your own risk, but without knowing what features people are trying 
> to add via <qemu:commandline>, we cannot prioritize which ones to 
> support directly in libvirt.
>




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