How to get actual disk size from libvirt-python (3 questions!)

I've been working with virt-manager and am now moving into some custom code using python and libvirt.

I have noticed that some of my VMs show "unknown" in regard to the disk "Storage size".

Using virsh gives me what roughly appear to be correct results:

virsh # domblkinfo 10 vda
Capacity:       32212254720
Allocation:     31936634880
Physical:       31935758336

... "Capacity" I assume is the maximum of the defined drive. However in this case, the actual defined size, (using qemu-img) the guest OS sees as 25GB (total) - which is what was requested.

virsh domblkinfo shows 30G (if those numbers are bytes)

The host OS says the current qcow2 file size is 17GB. (which makes sense as it is a COW disk).

However...

I can't seem to find a way to do this using libvirt-python. Has anyone done this?
The documentation seems to be a bit murky as to what those numbers actually mean - suggesting that they are block size. Seem to be bytes to me.
Where did the extra 5Gb come from?

Thanks in advance!

Solution

in short, you should first extract info about disks path from domain XML, and the pass it to blockInfo() method, so the full script will look like the following:

import libvirt
from xml.dom import minidom

conn = libvirt.open('qemu:///system')
domainIDs = conn.listAllDomains(0)

print("\tNAME\tSTATE\tCPUs\tMEM\tDISK\tUSED")
for domain in domainIDs:
        raw_xml = domain.XMLDesc(0)
        state, maxmem, mem2, cpus, cput = domain.info()
        name = domain.name()
        mem   = domain.maxMemory()/1024**2
        xml = minidom.parseString(raw_xml)
        diskTypes = xml.getElementsByTagName('disk')
        for diskType in diskTypes:
                if diskType.getAttribute('device') == 'disk':
                        diskNodes = diskType.childNodes
                        for diskNode in diskNodes:
                                if diskNode.nodeName == 'source':
                                        for attr in diskNode.attributes.keys():
                                                if diskNode.attributes[attr].name == 'file':
                                                        blkinf = domain.blockInfo(diskNode.attributes[attr].value)
                if   state == 1: vmstate = "running"
                elif state == 5: vmstate = "stopped"
                disksize = round(blkinf[0]/1024**3)
                diskused = round(blkinf[1]/1024**3)
        print(name+"\t"+vmstate+"\t"+str(cpus)+"\t"+str(mem)+"G"+"\t"+str(disksize)+"G\t"+str(diskused)+"G")

conn.close()

the result should be like following:

        NAME    STATE   CPUs    MEM     DISK    USED
cos6-copy       stopped 2       1.0G    64G     2G
centos6.i386    running 2       1.0G    64G     2G