Re: [Qemu-devel] [PATCH v2 07/11] migration: check global params for validity

[Eduardo Habkost <ehabkost@redhat.com>]

On Tue, Jul 18, 2017 at 09:56:06AM +0800, Peter Xu wrote:
> On Mon, Jul 17, 2017 at 03:25:05PM -0300, Eduardo Habkost wrote:
> > On Mon, Jul 17, 2017 at 04:26:07PM +0800, Peter Xu wrote:
> > > Adding validity check for the migration parameters passed in via global
> > > properties.
> > > 
> > > Signed-off-by: Peter Xu <peterx@redhat.com>
> > > ---
> > >  migration/migration.c | 34 ++++++++++++++++++++++++++++++++++
> > >  1 file changed, 34 insertions(+)
> > > 
> > > diff --git a/migration/migration.c b/migration/migration.c
> > > index 8c65054..5a7f22c 100644
> > > --- a/migration/migration.c
> > > +++ b/migration/migration.c
> > > @@ -2109,6 +2109,39 @@ static void migration_instance_init(Object *obj)
> > >      ms->parameters.tls_hostname = g_strdup("");
> > >  }
> > >  
> > > +static void migration_instance_post_init(Object *obj)
> > > +{
> > > +    MigrationState *ms = (MigrationState *)obj;
> > > +    Error *err = NULL;
> > > +    MigrationParameters params = {
> > > +        .has_compress_level = true,
> > > +        .compress_level = ms->parameters.compress_level,
> > > +        .has_compress_threads = true,
> > > +        .compress_threads = ms->parameters.compress_threads,
> > > +        .has_decompress_threads = true,
> > > +        .decompress_threads = ms->parameters.decompress_threads,
> > > +        .has_cpu_throttle_initial = true,
> > > +        .cpu_throttle_initial = ms->parameters.cpu_throttle_initial,
> > > +        .has_cpu_throttle_increment = true,
> > > +        .cpu_throttle_increment = ms->parameters.cpu_throttle_increment,
> > > +        .has_max_bandwidth = true,
> > > +        .max_bandwidth = ms->parameters.max_bandwidth,
> > > +        .has_downtime_limit = true,
> > > +        .downtime_limit = ms->parameters.downtime_limit,
> > > +        .has_x_checkpoint_delay = true,
> > > +        .x_checkpoint_delay = ms->parameters.x_checkpoint_delay,
> > > +        .has_block_incremental = true,
> > > +        .block_incremental = ms->parameters.block_incremental,
> > > +    };
> > > +
> > > +    /* We have applied all the migration properties... */
> > > +
> > > +    if (!migrate_params_check(&params, &err)) {
> > 
> > Why not just:
> >   if (!migrate_params_check(&ms->parameters, &err))
> > ?
> > 
> > If the ms->parameters.has_* fields are not set to true anywhere,
> > we can set them to true in instance_init.
> 
> Sure.
> 
> > 
> > (This would also also us to use QAPI_CLONE in
> > qmp_query_migrate_parameters() instead of manually copying each
> > field.
> > 
> > 
> > > +        error_report_err(err);
> > > +        exit(1);
> > > +    }
> > > +}
> > 
> > On real devices, this is normally done on realize (which has
> > proper error reporting).  We never realize the TYPE_MIGRATION
> > object because it's not a real device, though.
> 
> Hmm...
> 
> > 
> > Doing error checks on post_init feels fragile, as the only way
> > errors can be handled is triggering exit(1) in the middle of an
> > object_new() call.
> > 
> > As we have only one place where the TYPE_MIGRATION object is
> > created, I suggest calling migrate_params_check() inside
> > migration_object_init().
> 
> ... How about I just provide a realize() for it? Then I can drop the
> QOM patch 4, also, I can keep the checks along with the object itself.

qdev does lots of other stuff at realize time (e.g. it adds the
device to the device tree), and I don't think we want to trigger
that.

-- 
Eduardo