Re: [PATCH v2 2/3] libxl: update vcpus bitmap in retrieved guest config

[Wei Liu <wei.liu2@citrix.com>]

On Mon, Jun 13, 2016 at 06:39:36PM +0100, Anthony PERARD wrote:
> On Wed, Jun 08, 2016 at 03:28:45PM +0100, Wei Liu wrote:
> > ... because the available vcpu bitmap can change during domain life time
> > due to cpu hotplug and unplug.
> > 
> > For QEMU upstream, we interrogate QEMU for the number of vcpus. For
> > others, we look directly into xenstore for information.
> 
> I tried to migrate a guest, and libxl abort in
> libxl_retrieve_domain_configuration within the switch
> (device_model_version).
> 
> 
> > Reported-by: Jan Beulich <jbeulich@suse.com>
> > Signed-off-by: Wei Liu <wei.liu2@citrix.com>
> > ---
> >  tools/libxl/libxl.c | 87 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 87 insertions(+)
> > 
> > diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> > index 006b83f..02706ab 100644
> > --- a/tools/libxl/libxl.c
> > +++ b/tools/libxl/libxl.c
> > @@ -7222,6 +7222,53 @@ void libxl_mac_copy(libxl_ctx *ctx, libxl_mac *dst, libxl_mac *src)
> >          (*dst)[i] = (*src)[i];
> >  }
> >  
> > +static int libxl__update_avail_vcpus_qmp(libxl__gc *gc, uint32_t domid,
> > +                                         unsigned int max_vcpus,
> > +                                         libxl_bitmap *map)
> > +{
> > +    int rc;
> > +
> > +    /* For QEMU upstream we always need to return the number
> > +     * of cpus present to QEMU whether they are online or not;
> > +     * otherwise QEMU won't accept the saved state.
> > +     */
> > +    rc = libxl__qmp_query_cpus(gc, domid, map);
> > +    if (rc) {
> > +        LOG(ERROR, "fail to get number of cpus for domain %d", domid);
> > +        goto out;
> > +    }
> > +
> > +    rc = 0;
> 
> The value should already be 0 at this point.
> 

I would like to keep this as-is because this is an idiom that is safer
against further modification of this function.

> > +out:
> > +    return rc;
> > +}
> > +
> > +static int libxl__update_avail_vcpus_xenstore(libxl__gc *gc, uint32_t domid,
> > +                                              unsigned int max_vcpus,
> > +                                              libxl_bitmap *map)
> > +{
> > +    int rc;
> > +    unsigned int i;
> > +    const char *dompath;
> > +
> > +    dompath = libxl__xs_get_dompath(gc, domid);
> > +    if (!dompath) {
> > +        rc = ERROR_FAIL;
> > +        goto out;
> > +    }
> > +
> > +    for (i = 0; i < max_vcpus; i++) {
> > +        const char *path = GCSPRINTF("%s/cpu/%u/availability", dompath, i);
> > +        const char *content = libxl__xs_read(gc, XBT_NULL, path);
> > +        if (!strncmp(content, "online", strlen("online")))
> 
> I don't think strncmp is usefull here as one of the argument is a plain
> string. One could just use strcmp?
> 

Fine by me of course.

> > +            libxl_bitmap_set(map, i);
> > +    }
> > +
> > +    rc = 0;
> > +out:
> > +    return rc;
> > +}
> > +
> >  int libxl_retrieve_domain_configuration(libxl_ctx *ctx, uint32_t domid,
> >                                          libxl_domain_config *d_config)
> >  {
> > @@ -7270,6 +7317,46 @@ int libxl_retrieve_domain_configuration(libxl_ctx *ctx, uint32_t domid,
> >          libxl_dominfo_dispose(&info);
> >      }
> >  
> > +    /* VCPUs */
> > +    {
> > +        libxl_bitmap *map = &d_config->b_info.avail_vcpus;
> > +        unsigned int max_vcpus = d_config->b_info.max_vcpus;
> > +
> > +        libxl_bitmap_dispose(map);
> > +        libxl_bitmap_init(map);
> > +        libxl_bitmap_alloc(CTX, map, max_vcpus);
> > +        libxl_bitmap_set_none(map);
> > +
> > +        switch (d_config->b_info.type) {
> > +        case LIBXL_DOMAIN_TYPE_HVM:
> > +            switch (d_config->b_info.device_model_version) {
> > +            case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN:
> > +                rc = libxl__update_avail_vcpus_qmp(gc, domid,
> > +                                                   max_vcpus, map);
> > +                break;
> > +            case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL:
> > +            case LIBXL_DEVICE_MODEL_VERSION_NONE:
> > +                rc = libxl__update_avail_vcpus_xenstore(gc, domid,
> > +                                                        max_vcpus, map);
> > +                break;
> > +            default:
> > +            abort();
> 
> Missing indentation for abort.
> 

Will fix.

> Also, that is where xl abort on migration.
> 

Hmm...  This means the device model version is not valid (unknown?).

Can you paste in your guest config?

Wei.

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