[libvirt] virDomainGetMaxVcpus does not work as expected

[Claudio Bley]

Hi.

When calling virDomainGetMaxVcpus
(http://libvirt.org/html/libvirt-libvirt.html#virDomainGetMaxVcpus) on
an inactive domain, I receive this error:

scala> res2.getMaxVcpus()
libvirt: Domain Config error : Requested operation is not valid: domain is not running
org.libvirt.LibvirtException: Requested operation is not valid: domain is not running
        at org.libvirt.ErrorHandler.processError(ErrorHandler.java:31)
        at org.libvirt.ErrorHandler.processError(ErrorHandler.java:46)
        at org.libvirt.Domain.getMaxVcpus(Domain.java:571)
        at .<init>(<console>:13)
...

(this is from Java, but that doesn't matter)

The docs say:

> If the guest is inactive, this is basically the same as
> virConnectGetMaxVcpus(). If the guest is running this will reflect
> the maximum number of virtual CPUs the guest was booted with.

But, apparently, all the driver implementations for
virDomainGetMaxVcpus forward to
<driver>DomainGetVcpusFlags(.., VIR_DOMAIN_AFFECT_LIVE | VIR_DOMAIN_VCPU_MAXIMUM).
_______________________________,~~~~~~~~~~~~~~~~~~~~~~


$ git grep --show-function 'GetVcpusFlags.*AFFECT_LIVE'
src/esx/esx_driver.c=esxDomainGetMaxVcpus(virDomainPtr domain)
src/esx/esx_driver.c:    return esxDomainGetVcpusFlags(domain, (VIR_DOMAIN_AFFECT_LIVE |
src/openvz/openvz_driver.c=static int openvzDomainGetMaxVcpus(virDomainPtr dom)
src/openvz/openvz_driver.c:    return openvzDomainGetVcpusFlags(dom, (VIR_DOMAIN_AFFECT_LIVE |
src/qemu/qemu_driver.c=qemuDomainGetMaxVcpus(virDomainPtr dom)
src/qemu/qemu_driver.c:    return qemuDomainGetVcpusFlags(dom, (VIR_DOMAIN_AFFECT_LIVE |
src/test/test_driver.c=testDomainGetMaxVcpus(virDomainPtr domain)
src/test/test_driver.c:    return testDomainGetVcpusFlags(domain, (VIR_DOMAIN_AFFECT_LIVE |
src/vbox/vbox_tmpl.c=vboxDomainGetMaxVcpus(virDomainPtr dom)
src/vbox/vbox_tmpl.c:    return vboxDomainGetVcpusFlags(dom, (VIR_DOMAIN_AFFECT_LIVE |


AFAICS, this was introduced with

commit 50c51f13e2af04afac46e181c4ed62581545a488
Author: Eric Blake <eblake at redhat.com>
Date:   Mon Sep 27 16:37:53 2010 -0600

    vcpu: make old API trivially wrap to new API


Whereas the function's contract was documented earlier by

commit b412cfadb502c76df095c2c4548c27abf7c4873f
Author: Daniel Veillard <veillard at redhat.com>
Date:   Thu Mar 8 08:31:07 2007 +0000


To be honest, I'm not sure whether this worked as described at some
time in the past _at all_.

How to fix this? Change the documentation or the flag?

Claudio