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

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Mon, Jun 13, 2016 at 07:21:53PM +0100, Wei Liu wrote:
> 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@xxxxxxxx>
> > > Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> > > ---
> > >  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?

With all commented line removed:

builder = 'hvm'
memory = 500
vcpus = 2
maxvcpus = 6
name = "arch"
vif = [ 'type=ioemu,mac=00:16:3e:XX:XX:XX' ]
disk = [
'phy:/dev/vg42/guest_arch64,hda,w',
 'file:/root/vm/iso/archlinux-2014.04.01-dual.iso,hdc:cdrom,r',
]
device_model_args_hvm = [
]
usbdevice='tablet'
boot="cd"
serial='pty'
sdl = 0
vnc = 1
vnclisten = '0.0.0.0'
vncunused = 1
spice=0
uuid = "XXXX"


-- 
Anthony PERARD

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