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Re: [libvirt] [PATCH 1/5] lib: Add API for specific vCPU hot(un)plug



On Wed, Feb 22, 2017 at 01:34:54PM +0100, Peter Krempa wrote:
> On Wed, Feb 22, 2017 at 12:16:51 +0000, Daniel Berrange wrote:
> > On Fri, Feb 10, 2017 at 06:10:18PM +0100, Peter Krempa wrote:
> > > Similarly to domainSetGuestVcpus this commit adds API which allows to
> > > modify state of individual vcpus rather than just setting the count.
> > > 
> > > This allows to enable CPUs in specific guest NUMA nodes to achieve any
> > > necessary configuration.
> > > ---
> > >  include/libvirt/libvirt-domain.h |  5 +++++
> > >  src/driver-hypervisor.h          |  7 ++++++
> > >  src/libvirt-domain.c             | 48 ++++++++++++++++++++++++++++++++++++++++
> > >  src/libvirt_public.syms          |  5 +++++
> > >  src/remote/remote_driver.c       |  1 +
> > >  src/remote/remote_protocol.x     | 16 +++++++++++++-
> > >  src/remote_protocol-structs      |  7 ++++++
> > >  7 files changed, 88 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/include/libvirt/libvirt-domain.h b/include/libvirt/libvirt-domain.h
> > > index e303140a2..c0f715d66 100644
> > > --- a/include/libvirt/libvirt-domain.h
> > > +++ b/include/libvirt/libvirt-domain.h
> > > @@ -4528,4 +4528,9 @@ int virDomainSetGuestVcpus(virDomainPtr domain,
> > >                             int state,
> > >                             unsigned int flags);
> > > 
> > > +int virDomainSetVcpu(virDomainPtr domain,
> > > +                     const char *vcpumap,
> > > +                     int state,
> > > +                     unsigned int flags);
> > 
> > In adding support for this to perl/go bindings I see that this is using
> > a different style to the existing APIs. With the exception of the
> > virDomainSetGuestVcpus() API, everything else dealing with CPU maps
> > uses an 'unsigned char *cpu' & 'int maplen' pair to store the data as
> > a bitmap. I think we should change this API to also use the bitmap
> > rather than the textual format as it gives consistency with other
> > APIs, particularly when mapping into other languages.  For example
> > in Go, the bitmaps get turned into a boolean array, so it is a very
> > natural representation to manipulate - the textual format is rather
> > inconvenient in this respect.
> 
> I modelled this API after the qemuDomainSetGuestVcpus and
> qemuDomainGetGuestVcpusParams which already uses the string
> representation rather the harder-to-use bitmap one, since they are in
> for a while we can't change those.

Yep, we can't change those, but we can't avoid spreading the inconsistency
further, as all the other  methods relating to CPUs aginst virDomain use
a bitmap

Regards,
Daniel
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