[libvirt] virDomainGetMaxVcpus does not work as expected

[Claudio Bley]

Hi. Any opinions on this?

At Thu, 13 Feb 2014 14:50:08 +0100,
Claudio Bley wrote:
> 
> 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