[libvirt] How to config my VM to use KVM with libvirt?

[Daniel P. Berrange]

On Tue, Jul 21, 2009 at 05:28:27PM -0400, Jim Paris wrote:
> Daniel P. Berrange wrote:
> > On Tue, Jul 21, 2009 at 09:46:17AM -0400, Jim Paris wrote:
> > > Speaking of this, I've noticed that
> > > 
> > > <domain type='qemu'>
> > >   <os>
> > >     <type arch='i686' machine='pc'>hvm</type>
> > >   </os>
> > > </domain>
> > > 
> > > runs WITH kvm on an x86_64 system.  Is that intended?
> > 
> > No, its not intended !
> ...
> > I'm actually wondering why we bother with #1 at all. If the
> > binary has '-no-kvm' and the domain is 'qemu', then it should
> > be used no matter what arch.
> 
> Agreed.  Below is a patch which should fix the oversight (lightly
> tested).
> 
> However, this is going to be a user-visible change and may cause
> people to complain that their existing 32-bit domains are unexpectedly
> running with -no-kvm.  Is that OK?  Technically it's a misconfiguration.

Counterpoint: people complaining that they requested 'qemu' and
got 'kvm' which they didn't want :-) As you say anyone relying on
this using KVM has mis-configured their VM.

> For the record, I think we've already broken this area once when
> 0.6.2 came out -- previous to that, even my 64-bit VMs had domain type
> "qemu", and libvirt ran my specified kvm binary without -no-kvm.

Yep, one or two people got tripped up by this, but its trivial
for them to fix it & we didn't get any large number of bug
reports.


> >From f7edd4c887512e4fc7c97b12a4f2409244af9eb3 Mon Sep 17 00:00:00 2001
> From: Jim Paris <jim at jtan.com>
> Date: Tue, 21 Jul 2009 17:07:51 -0400
> Subject: [PATCH] Always add -no-kvm and -no-kqemu, if available, for "qemu" domains.
> 
> If the qemu binary supports "-no-kvm" and/or "-no-kqemu", they should
> always be added for plain "qemu" domains.  Previously, we omitted them
> whenever the host and guest architectures implied that they would be
> disabled automatically, but that logic was flawed in some cases
> (such as i686 and x86_64).
> 
> Signed-off-by: Jim Paris <jim at jtan.com>
> ---
>  src/qemu_conf.c |   12 ++++--------
>  1 files changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/src/qemu_conf.c b/src/qemu_conf.c
> index 4043d70..f146598 100644
> --- a/src/qemu_conf.c
> +++ b/src/qemu_conf.c
> @@ -977,22 +977,18 @@ int qemudBuildCommandLine(virConnectPtr conn,
>      emulator = def->emulator;
>  
>      /* Need to explicitly disable KQEMU if
> -     * 1. Arch matches host arch
> -     * 2. Guest domain is 'qemu'
> -     * 3. The qemu binary has the -no-kqemu flag
> +     * 1. Guest domain is 'qemu'
> +     * 2. The qemu binary has the -no-kqemu flag
>       */
>      if ((qemuCmdFlags & QEMUD_CMD_FLAG_KQEMU) &&
> -        STREQ(ut.machine, def->os.arch) &&
>          def->virtType == VIR_DOMAIN_VIRT_QEMU)
>          disableKQEMU = 1;
>  
>      /* Need to explicitly disable KVM if
> -     * 1. Arch matches host arch
> -     * 2. Guest domain is 'qemu'
> -     * 3. The qemu binary has the -no-kvm flag
> +     * 1. Guest domain is 'qemu'
> +     * 2. The qemu binary has the -no-kvm flag
>       */
>      if ((qemuCmdFlags & QEMUD_CMD_FLAG_KVM) &&
> -        STREQ(ut.machine, def->os.arch) &&
>          def->virtType == VIR_DOMAIN_VIRT_QEMU)
>          disableKVM = 1;
>  

ACK, this looks fine.

Daniel
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