Re: [PATCH 09/21] migration: Extract code to mark all parameters as present

[Peter Xu <peterx@redhat.com>]

On Mon, Jun 02, 2025 at 10:37:58PM -0300, Fabiano Rosas wrote:
> MigrationParameters needs to have all of its has_* fields marked as
> true when used as the return of query_migrate_parameters because the
> corresponding QMP command has all of its members non-optional by
> design, despite them being marked as optional in migration.json.
> 
> Extract this code into a function and make it assert if any field is
> missing. With this we ensure future changes will not inadvertently
> leave any parameters missing.
> 
> Also assert that s->parameters _does not_ have any of its has_* fields
> set. This structure is internal to the migration code and it should
> not rely on the QAPI-generate has_* fields. We might want to store
> migration parameters differently in the future.
> 
> Signed-off-by: Fabiano Rosas <farosas@suse.de>
> ---
>  migration/options.c | 74 ++++++++++++++++++++++++++++-----------------
>  1 file changed, 46 insertions(+), 28 deletions(-)
> 
> diff --git a/migration/options.c b/migration/options.c
> index e2e3ab717f..dd62e726cb 100644
> --- a/migration/options.c
> +++ b/migration/options.c
> @@ -936,6 +936,40 @@ static void tls_option_set_str(StrOrNull **dstp, StrOrNull *src)
>      }
>  }
>  
> +static void migrate_mark_all_params_present(MigrationParameters *p)
> +{
> +    int len, n_str_args = 3; /* tls-creds, tls-hostname, tls-authz */

Could you remind me why we don't set has_*=true for these three?

> +    bool *has_fields[] = {
> +        &p->has_throttle_trigger_threshold, &p->has_cpu_throttle_initial,
> +        &p->has_cpu_throttle_increment, &p->has_cpu_throttle_tailslow,
> +        &p->has_max_bandwidth, &p->has_avail_switchover_bandwidth,
> +        &p->has_downtime_limit, &p->has_x_checkpoint_delay,
> +        &p->has_multifd_channels, &p->has_multifd_compression,
> +        &p->has_multifd_zlib_level, &p->has_multifd_qatzip_level,
> +        &p->has_multifd_zstd_level, &p->has_xbzrle_cache_size,
> +        &p->has_max_postcopy_bandwidth, &p->has_max_cpu_throttle,
> +        &p->has_announce_initial, &p->has_announce_max, &p->has_announce_rounds,
> +        &p->has_announce_step, &p->has_block_bitmap_mapping,
> +        &p->has_x_vcpu_dirty_limit_period, &p->has_vcpu_dirty_limit,
> +        &p->has_mode, &p->has_zero_page_detection, &p->has_direct_io,
> +    };
> +
> +    /*
> +     * The has_* fields of MigrationParameters are used by QAPI to
> +     * inform whether an optional struct member is present. Keep this
> +     * decoupled from the internal usage (not QAPI) by leaving the
> +     * has_* fields of s->parameters unused.
> +     */
> +    assert(p != &(migrate_get_current())->parameters);

This is OK, I'm not sure whether we're over-cautious though.. but..

> +
> +    len = ARRAY_SIZE(has_fields);
> +    assert(len + n_str_args == MIGRATION_PARAMETER__MAX);

.. I definitely like this assert.

> +
> +    for (int i = 0; i < len; i++) {
> +        *has_fields[i] = true;
> +    }
> +}
> +
>  MigrationParameters *qmp_query_migrate_parameters(Error **errp)
>  {
>      MigrationParameters *params;
> @@ -943,68 +977,52 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
>  
>      /* TODO use QAPI_CLONE() instead of duplicating it inline */
>      params = g_malloc0(sizeof(*params));
> -    params->has_throttle_trigger_threshold = true;
> +
>      params->throttle_trigger_threshold = s->parameters.throttle_trigger_threshold;
> -    params->has_cpu_throttle_initial = true;
>      params->cpu_throttle_initial = s->parameters.cpu_throttle_initial;
> -    params->has_cpu_throttle_increment = true;
>      params->cpu_throttle_increment = s->parameters.cpu_throttle_increment;
> -    params->has_cpu_throttle_tailslow = true;
>      params->cpu_throttle_tailslow = s->parameters.cpu_throttle_tailslow;
>  
>      tls_option_set_str(&params->tls_creds, s->parameters.tls_creds);
>      tls_option_set_str(&params->tls_hostname, s->parameters.tls_hostname);
>      tls_option_set_str(&params->tls_authz, s->parameters.tls_authz);
>  
> -    params->has_max_bandwidth = true;
>      params->max_bandwidth = s->parameters.max_bandwidth;
> -    params->has_avail_switchover_bandwidth = true;
>      params->avail_switchover_bandwidth = s->parameters.avail_switchover_bandwidth;
> -    params->has_downtime_limit = true;
>      params->downtime_limit = s->parameters.downtime_limit;
> -    params->has_x_checkpoint_delay = true;
>      params->x_checkpoint_delay = s->parameters.x_checkpoint_delay;
> -    params->has_multifd_channels = true;
>      params->multifd_channels = s->parameters.multifd_channels;
> -    params->has_multifd_compression = true;
>      params->multifd_compression = s->parameters.multifd_compression;
> -    params->has_multifd_zlib_level = true;
>      params->multifd_zlib_level = s->parameters.multifd_zlib_level;
> -    params->has_multifd_qatzip_level = true;
>      params->multifd_qatzip_level = s->parameters.multifd_qatzip_level;
> -    params->has_multifd_zstd_level = true;
>      params->multifd_zstd_level = s->parameters.multifd_zstd_level;
> -    params->has_xbzrle_cache_size = true;
>      params->xbzrle_cache_size = s->parameters.xbzrle_cache_size;
> -    params->has_max_postcopy_bandwidth = true;
>      params->max_postcopy_bandwidth = s->parameters.max_postcopy_bandwidth;
> -    params->has_max_cpu_throttle = true;
>      params->max_cpu_throttle = s->parameters.max_cpu_throttle;
> -    params->has_announce_initial = true;
>      params->announce_initial = s->parameters.announce_initial;
> -    params->has_announce_max = true;
>      params->announce_max = s->parameters.announce_max;
> -    params->has_announce_rounds = true;
>      params->announce_rounds = s->parameters.announce_rounds;
> -    params->has_announce_step = true;
>      params->announce_step = s->parameters.announce_step;
> -
> -    params->has_block_bitmap_mapping = true;
>      params->block_bitmap_mapping =
>          QAPI_CLONE(BitmapMigrationNodeAliasList,
>                     s->parameters.block_bitmap_mapping);
> -
> -    params->has_x_vcpu_dirty_limit_period = true;
>      params->x_vcpu_dirty_limit_period = s->parameters.x_vcpu_dirty_limit_period;
> -    params->has_vcpu_dirty_limit = true;
>      params->vcpu_dirty_limit = s->parameters.vcpu_dirty_limit;
> -    params->has_mode = true;
>      params->mode = s->parameters.mode;
> -    params->has_zero_page_detection = true;
>      params->zero_page_detection = s->parameters.zero_page_detection;
> -    params->has_direct_io = true;
>      params->direct_io = s->parameters.direct_io;
>  
> +    /*
> +     * query-migrate-parameters expects all members of
> +     * MigrationParameters to be present, but we cannot mark them
> +     * non-optional in QAPI because the structure is also used for
> +     * migrate-set-parameters, which needs the optionality. Force all
> +     * parameters to be seen as present now. Note that this depends on
> +     * some form of default being set for every member of
> +     * MigrationParameters, currently done during qdev init using
> +     * migration_properties defined in this file.
> +     */
> +    migrate_mark_all_params_present(params);
>      return params;
>  }
>  
> -- 
> 2.35.3
> 

-- 
Peter Xu