How do we know that no one has ever used such configuration? The conversion
was meant to be bug-compatible.

Paolo

Il lun 16 ago 2021, 23:06 Eduardo Habkost <ehabkost@redhat.com> ha scritto:

> From: Yanan Wang <wangyanan55@huawei.com>
>
> In the SMP configuration, we should either provide a topology
> parameter with a reasonable value (greater than zero) or just
> omit it and QEMU will compute the missing value. Users should
> have never provided a configuration with parameters as zero
> (e.g. -smp 8,sockets=0) which should be treated as invalid.
>
> But commit 1e63fe68580 (machine: pass QAPI struct to mc->smp_parse)
> has added some doc which implied that 'anything=0' is valid and
> has the same semantics as omitting a parameter.
>
> To avoid meaningless configurations possibly introduced by users
> in the future and consequently a necessary deprecation process,
> fix the doc and also add the corresponding sanity check.
>
> Fixes: 1e63fe68580 (machine: pass QAPI struct to mc->smp_parse)
> Suggested-by: Andrew Jones <drjones@redhat.com>
> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
> Tested-by: Daniel P. Berrange <berrange@redhat.com>
> Reviewed-by: Andrew Jones <drjones@redhat.com>
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> Message-Id: <20210816024522.143124-2-wangyanan55@huawei.com>
> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> ---
>  hw/core/machine.c | 14 ++++++++++++++
>  qapi/machine.json |  6 +++---
>  qemu-options.hx   | 12 +++++++-----
>  3 files changed, 24 insertions(+), 8 deletions(-)
>
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 54e040587dd..a7e119469aa 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -832,6 +832,20 @@ static void machine_set_smp(Object *obj, Visitor *v,
> const char *name,
>          return;
>      }
>
> +    /*
> +     * A specified topology parameter must be greater than zero,
> +     * explicit configuration like "cpus=0" is not allowed.
> +     */
> +    if ((config->has_cpus && config->cpus == 0) ||
> +        (config->has_sockets && config->sockets == 0) ||
> +        (config->has_dies && config->dies == 0) ||
> +        (config->has_cores && config->cores == 0) ||
> +        (config->has_threads && config->threads == 0) ||
> +        (config->has_maxcpus && config->maxcpus == 0)) {
> +        error_setg(errp, "CPU topology parameters must be greater than
> zero");
> +        goto out_free;
> +    }
> +
>      mc->smp_parse(ms, config, errp);
>      if (*errp) {
>          goto out_free;
> diff --git a/qapi/machine.json b/qapi/machine.json
> index c3210ee1fb2..9272cb3cf8b 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -1288,8 +1288,8 @@
>  ##
>  # @SMPConfiguration:
>  #
> -# Schema for CPU topology configuration.  "0" or a missing value lets
> -# QEMU figure out a suitable value based on the ones that are provided.
> +# Schema for CPU topology configuration. A missing value lets QEMU
> +# figure out a suitable value based on the ones that are provided.
>  #
>  # @cpus: number of virtual CPUs in the virtual machine
>  #
> @@ -1297,7 +1297,7 @@
>  #
>  # @dies: number of dies per socket in the CPU topology
>  #
> -# @cores: number of cores per thread in the CPU topology
> +# @cores: number of cores per die in the CPU topology
>  #
>  # @threads: number of threads per core in the CPU topology
>  #
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 83aa59a920f..aee622f577d 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -227,11 +227,13 @@ SRST
>      of computing the CPU maximum count.
>
>      Either the initial CPU count, or at least one of the topology
> parameters
> -    must be specified. Values for any omitted parameters will be computed
> -    from those which are given. Historically preference was given to the
> -    coarsest topology parameters when computing missing values (ie sockets
> -    preferred over cores, which were preferred over threads), however,
> this
> -    behaviour is considered liable to change.
> +    must be specified. The specified parameters must be greater than zero,
> +    explicit configuration like "cpus=0" is not allowed. Values for any
> +    omitted parameters will be computed from those which are given.
> +    Historically preference was given to the coarsest topology parameters
> +    when computing missing values (ie sockets preferred over cores, which
> +    were preferred over threads), however, this behaviour is considered
> +    liable to change.
>  ERST
>
>  DEF("numa", HAS_ARG, QEMU_OPTION_numa,
> --
> 2.31.1
>
>