Re: [libvirt] [RFC] Unify KVM kernel-space and user-space code into a single project

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')

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

Daniel