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

[Anthony PERARD <anthony.perard@citrix.com>]

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.

> +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?

> +            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.

Also, that is where xl abort on migration.

> +            }
> +            break;
> +        case LIBXL_DOMAIN_TYPE_PV:
> +            rc = libxl__update_avail_vcpus_xenstore(gc, domid,
> +                                                    max_vcpus, map);
> +            break;
> +        default:
> +            abort();
> +        }
> +
> +        if (rc) {
> +            LOG(ERROR, "fail to update available cpu map for domain %d", domid);
> +            goto out;
> +        }
> +    }
> +
>      /* Memory limits:
>       *
>       * Currently there are three memory limits:



-- 
Anthony PERARD

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