Re: [XEN PATCH 1/8] libxl: Replace deprecated QMP command by "query-cpus-fast"

[Jason Andryuk <jandryuk@xxxxxxxxx>]

On Fri, Apr 23, 2021 at 12:16 PM Anthony PERARD
<anthony.perard@xxxxxxxxxx> wrote:
>
> We use the deprecated QMP command "query-cpus" which is removed in the
> QEMU 6.0 release. There's a replacement which is "query-cpus-fast",
> and have been available since QEMU 2.12 (April 2018).
>
> This patch try the new command first and when the command isn't
> available, it fall back to the deprecated one so libxl still works
> with older QEMU versions.
>
> Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> ---
>
> Notes:
>     This is v2 of '[XEN PATCH for-4.15] libxl: Replace deprecated QMP
>     command by "query-cpus-fast"' as the patch never made it into the
>     release.
>
>     changes:
>     - introduce a fallback for when the new command isn't available.
>
>  tools/libs/light/libxl_domain.c | 103 ++++++++++++++++++++++++++++++--
>  1 file changed, 98 insertions(+), 5 deletions(-)
>
> diff --git a/tools/libs/light/libxl_domain.c b/tools/libs/light/libxl_domain.c
> index 5d4ec9071160..8c003aa7cb04 100644
> --- a/tools/libs/light/libxl_domain.c
> +++ b/tools/libs/light/libxl_domain.c
> @@ -1740,6 +1740,35 @@ static int libxl__set_vcpuonline_xenstore(libxl__gc 
> *gc, uint32_t domid,
>      return rc;
>  }
>
> +static int qmp_parse_query_cpus_fast(libxl__gc *gc,
> +                                     libxl_domid domid,
> +                                     const libxl__json_object *response,
> +                                     libxl_bitmap *const map)
> +{
> +    int i;
> +    const libxl__json_object *cpu;
> +
> +    libxl_bitmap_set_none(map);
> +    /* Parse response to QMP command "query-cpus-fast":
> +     * [ { 'cpu-index': 'int',...} ]
> +     */
> +    for (i = 0; (cpu = libxl__json_array_get(response, i)); i++) {
> +        unsigned int cpu_index;
> +        const libxl__json_object *o;
> +
> +        o = libxl__json_map_get("cpu-index", cpu, JSON_INTEGER);

Looks like qmp_parse_query_cpus_fast and qmp_parse_query_cpus just
differ by the key string.  So you could pass it in as an argument -
maybe with qmp_parse_query_cpus_fast and qmp_parse_query_cpus as
wrappers around a common implementation?

But if you prefer this separate function, it's fine.

Reviewed-by: Jason Andryuk <jandryuk@xxxxxxxxx>