Re: [RFC PATCH 0/6] xen/abi: On wide bitfields inside primitive types

["Alejandro Vallejo" <alejandro.vallejo@cloud.com>]

On Tue Oct 29, 2024 at 6:16 PM GMT, Alejandro Vallejo wrote:
> Non-boolean bitfields in the hypercall ABI make it fairly inconvenient to
> create bindings for any language because (a) they are always ad-hoc and are
> subject to restrictions regular fields are not (b) require boilerplate that
> regular fields do not and (c) might not even be part of the core language,
> forcing avoidable external libraries into any sort of generic library.
>
> This patch (it's a series merely to split roughly by maintainer) is one such
> case that I happened to spot while playing around. It's the grant_version
> field, buried under an otherwise empty grant_opts.
>
> The invariant I'd like to (slowly) introduce and discuss is that fields may
> have bitflags (e.g: a packed array of booleans indexed by some enumerated
> type), but not be mixed with wider fields in the same primitive type. This
> ensures any field containing an integer of any kind can be referred by pointer
> and treated the same way as any other with regards to sizeof() and the like.
>
> I'd like to have a certain consensus about this general point before going
> establishing this restriction in the IDL system I'm working on.
>
> My preference would be to fold everything into a single patch if we decide to
> follow through with this particular case. As I said before, the split is
> artificial for review.
>
> Alejandro Vallejo (6):
>   xen/domctl: Refine grant_opts into grant_version
>   tools: Rename grant_opts to grant_version
>   tools/ocaml: Rename grant_opts to grant_version
>   xen/arm: Rename grant_opts to grant_version
>   xen/x86: Rename grant_opts to grant_version
>   xen/common: Rename grant_opts to grant_version
>
>  tools/helpers/init-xenstore-domain.c             |  2 +-
>  tools/libs/light/libxl_create.c                  |  2 +-
>  tools/ocaml/libs/xc/xenctrl_stubs.c              |  3 +--
>  tools/python/xen/lowlevel/xc/xc.c                |  2 +-
>  tools/tests/paging-mempool/test-paging-mempool.c |  2 +-
>  tools/tests/resource/test-resource.c             |  6 +++---
>  tools/tests/tsx/test-tsx.c                       |  4 ++--
>  xen/arch/arm/dom0less-build.c                    |  4 ++--
>  xen/arch/arm/domain_build.c                      |  2 +-
>  xen/arch/x86/setup.c                             |  2 +-
>  xen/common/domain.c                              |  6 +++---
>  xen/common/grant_table.c                         |  3 +--
>  xen/include/public/domctl.h                      | 15 +++++++++++----
>  xen/include/xen/grant_table.h                    |  4 ++--
>  14 files changed, 31 insertions(+), 26 deletions(-)

Bah. I sent it too early. The new field in patches 2-6 ought to be
max_grant_version. Regardless, the general point still holds, I hope.

Cheers,
Alejandro