Daniel P. Berrange wrote:
On Fri, Apr 09, 2010 at 03:53:37PM +0100, Antoine Martin wrote:
Daniel P. Berrange wrote:
On Fri, Apr 09, 2010 at 03:31:37PM +0100, Antoine Martin wrote:
[snip]
* not everything is exposed via libvirt: virsh can retrieve vncdisplay but libvirt (or at least the python bindings) does not. How come? This happens to be one thing I need for writing a libvirt backend for my virtual desktop software. The 'virsh vncdisplay' command is simply fetching the XML doc for the guest and then extracting the VNC port using a xpath expression
/domain/devices/graphics[@type='vnc']/@port
So for python you'd want to just get an XML handling module and do similar. Yes, I saw that in the virsh code. Shouldn't this be part of the libvirt api proper?? Isn't it supposed to shield us from dealing with files and XML? It isn't scalable to add APIs for extracting each possible piece of info from the XML. All languages have APIs for extracting data from XML using XPath (or DOM). Thus it is better to leave that flexibility to the apps rather than hardcoding APIs for it in libvirt. The XML schemas/docs are a formal part of the libvit API, so we're not trying to sheild that from apps.
I was thinking of something like: domain.get_attribute("vncdisplay")
Because it's a shame to have to use virsh as a wrapper (or XML file parsing) and re-do all the work that was done to get to the domain object when all your really want is just an attribute..
You can already do that very simply in python using lxml
from lxml import etree tree = etree.parse(domain.XMLDesc()) r = tree.xpath('/domain/devices/graphics[@type='vnc']/@port') Thanks for that!
So adding an API for this is only saving at best 2 lines of code, and is much less flexible in what it can do Understood. Could this code be wrapped libvirt side with something like: domain.xpath('/domain/devices/graphics[@type='vnc']/@port') So that libvirt consumers dont need an explicit dependency on XML libraries?
Just another question that came to mind: how do I get notified when something happens to a domain? IE: how can I fire a script whenever a domain is created/added/stopped? Thanks Antoine
Daniel