Re: [PATCH for-8.2 v2 1/2] qapi/migration: Deduplicate migration parameter field comments

[Peter Xu <peterx@redhat.com>]

On Sun, Aug 06, 2023 at 11:49:46AM -0400, Peter Xu wrote:
> > I think we have a tradeoff here.  If perpetuating the unclean and ugly
> > use of "" is what it takes to de-triplicate migration parameters, we may
> > decide to accept that.
> 
> I don't think it's a must.  As Dan raised, we can convert str -> StrOrNull
> for MigrationParameters. I assume it won't affect query-migrate-parameters
> anyway OTOH.
> 
> I assume it means there's nothing yet obvious that we overlooked on the
> whole idea.  Let me propose the formal patchset early next week.  It'll be
> mostly the patch I attached but just add those extra logics for StrOrNull,
> so the diffstat might be less attractive but hopefully still good enough to
> be accepted.

The new StrOrNull approach doesn't work with current migration object
properties.. as StrOrNull must be a pointer for @MigrationParameters not
static, and it stops working with offsetof():

../migration/options.c:218:5: error: cannot apply ‘offsetof’ to a non constant address
  218 |     DEFINE_PROP_STRING("tls-creds", MigrationState, parameters.tls_creds->u.s),
      |     ^~~~~~~~~~~~~~~~~~
../migration/options.c:219:5: error: cannot apply ‘offsetof’ to a non constant address
  219 |     DEFINE_PROP_STRING("tls-hostname", MigrationState, parameters.tls_hostname->u.s),
      |     ^~~~~~~~~~~~~~~~~~
../migration/options.c:220:5: error: cannot apply ‘offsetof’ to a non constant address
  220 |     DEFINE_PROP_STRING("tls-authz", MigrationState, parameters.tls_authz->u.s),
      |     ^~~~~~~~~~~~~~~~~~

Any easy way to fix this?  I.e., is there a way to declare StrOrNull (in
MigrationParameters of qapi/migration.json) to be statically allocated
rather than a pointer (just like default behavior of any uint* types)?

Thanks,

-- 
Peter Xu