[libvirt] [PATCH 2/5] s390: Report blank host model instead of "host"

[Jiri Denemark]

On Fri, Nov 04, 2016 at 11:00:29 -0400, Jason J. Herne wrote:
> On 11/03/2016 08:54 AM, Jiri Denemark wrote:
> > On Wed, Nov 02, 2016 at 16:34:32 -0400, Jason J. Herne wrote:
> >> From: "Collin L. Walling" <walling at linux.vnet.ibm.com>
> >>
> >> On s390 , the host's features are heavily influenced by not only the host
> >> hardware but also by hardware microcode level, host OS version, qemu
> >> version and kvm version. In this environment it does not make sense to
> >> attempt to report exact host details. Rather than use the generic "host"
> >> we leave this field blank.
> >>
> >> Signed-off-by: Collin L. Walling <walling at linux.vnet.ibm.com>
> >> Signed-off-by: Jason J. Herne <jjherne at linux.vnet.ibm.com>
> >> ---
> >>  src/cpu/cpu_s390.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/src/cpu/cpu_s390.c b/src/cpu/cpu_s390.c
> >> index 0f94084..c75eacb 100644
> >> --- a/src/cpu/cpu_s390.c
> >> +++ b/src/cpu/cpu_s390.c
> >> @@ -59,7 +59,7 @@ s390Decode(virCPUDefPtr cpu,
> >>      virCheckFlags(VIR_CONNECT_BASELINE_CPU_EXPAND_FEATURES, -1);
> >>
> >>      if (cpu->model == NULL &&
> >> -        VIR_STRDUP(cpu->model, "host") < 0)
> >> +        VIR_STRDUP(cpu->model, "") < 0)
> >>          return -1;
> >>
> >>      return 0;
> >
> > I think this function shouldn't do anything. Reporting "host" or even ""
> > as host CPU is pointless. If we cannot provide anything reasonable, we
> > should not report it at all.
> 
> I would agree. But virsh domcapabilities only indicates support for 
> host-model
> mode if we have something in cpu->hostModel.
> 
> virDomainCapsCPUFormat()
> ...
> if (cpu->hostModel) {
>          virBufferAddLit(buf, "supported='yes'>\n");
> 
> It also causes the guest to fail when trying to use host-model mode
> because virQEMUCapsInitHostCPUModel() skips setting qemuCaps->hostCPUModel
> if caps->host.cpu->model does not exist.

And that's what you need to change. As I wrote in my comments to patch
4/5, virQEMUCapsInitHostCPUModel() is the place where
qemuCaps->hostCPUModel should be initialized with the host CPU returned
by QEMU. If you do that, all the issues you mentioned will go away.

Jirka