Re: [Xen-devel] [PATCH] libxl: avoid bringing up vcpus already online

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Mon, Nov 17, 2014 at 10:29:19AM +0000, Ian Campbell wrote:
> On Mon, 2014-11-17 at 09:41 +0000, Wei Liu wrote:
> > On Mon, Nov 17, 2014 at 05:28:58PM +0800, Chao Peng wrote:
> > > Avoid sending duplicated qmp commands and eliminate the confusing error
> > > messages like "Unable to add CPU: 0, it already exists".
> > > 
> > > Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> > > ---
> > >  tools/libxl/libxl.c |    2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> > > index f7961f6..d040e5c 100644
> > > --- a/tools/libxl/libxl.c
> > > +++ b/tools/libxl/libxl.c
> > > @@ -5450,7 +5450,7 @@ static int libxl__set_vcpuonline_qmp(libxl__gc *gc, 
> > > uint32_t domid,
> > >          LOGE(ERROR, "getting domain info list");
> > >          return ERROR_FAIL;
> > >      }
> > > -    for (i = 0; i <= info.vcpu_max_id; i++) {
> > > +    for (i = info.vcpu_online; i <= info.vcpu_max_id; i++) {
> > 
> > I don't think this is right. You're making an assumption that vcpu 0 to
> > vcpu "info.vcpu_online" are online, which might not be true in hotplug /
> > hot-unplug scenario.
> 
> Indeed. Adding Anthony for his input.

It's probably not a good "fix" to avoid the error message. As Wei said,
vcpu 0 to vcpu ${info.vcpu_online} might not all be online.

At the time I've written this function, there were no way to query QEMU
to know which CPU are online. So the only way was to send the QMP
command anyway and get an error back. Unfortunately, the error that QEMU
send back is not suppose to be parsed (as it's only for human to read
and might change in the futur) and libxl_qmp is not ready to handle this
kind of error in a better way, so it just print them.

-- 
Anthony PERARD

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